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41 results

inode.c

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    Theodore Ts'o authored
    This function really counts the free clusters reported in the block
    group descriptors, so rename it to reduce confusion.
    
    Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
    5dee5437
    History
    inode.c 135.99 KiB
    /*
     *  linux/fs/ext4/inode.c
     *
     * Copyright (C) 1992, 1993, 1994, 1995
     * Remy Card (card@masi.ibp.fr)
     * Laboratoire MASI - Institut Blaise Pascal
     * Universite Pierre et Marie Curie (Paris VI)
     *
     *  from
     *
     *  linux/fs/minix/inode.c
     *
     *  Copyright (C) 1991, 1992  Linus Torvalds
     *
     *  64-bit file support on 64-bit platforms by Jakub Jelinek
     *	(jj@sunsite.ms.mff.cuni.cz)
     *
     *  Assorted race fixes, rewrite of ext4_get_block() by Al Viro, 2000
     */
    
    #include <linux/module.h>
    #include <linux/fs.h>
    #include <linux/time.h>
    #include <linux/jbd2.h>
    #include <linux/highuid.h>
    #include <linux/pagemap.h>
    #include <linux/quotaops.h>
    #include <linux/string.h>
    #include <linux/buffer_head.h>
    #include <linux/writeback.h>
    #include <linux/pagevec.h>
    #include <linux/mpage.h>
    #include <linux/namei.h>
    #include <linux/uio.h>
    #include <linux/bio.h>
    #include <linux/workqueue.h>
    #include <linux/kernel.h>
    #include <linux/printk.h>
    #include <linux/slab.h>
    #include <linux/ratelimit.h>
    
    #include "ext4_jbd2.h"
    #include "xattr.h"
    #include "acl.h"
    #include "ext4_extents.h"
    #include "truncate.h"
    
    #include <trace/events/ext4.h>
    
    #define MPAGE_DA_EXTENT_TAIL 0x01
    
    static inline int ext4_begin_ordered_truncate(struct inode *inode,
    					      loff_t new_size)
    {
    	trace_ext4_begin_ordered_truncate(inode, new_size);
    	/*
    	 * If jinode is zero, then we never opened the file for
    	 * writing, so there's no need to call
    	 * jbd2_journal_begin_ordered_truncate() since there's no
    	 * outstanding writes we need to flush.
    	 */
    	if (!EXT4_I(inode)->jinode)
    		return 0;
    	return jbd2_journal_begin_ordered_truncate(EXT4_JOURNAL(inode),
    						   EXT4_I(inode)->jinode,
    						   new_size);
    }
    
    static void ext4_invalidatepage(struct page *page, unsigned long offset);
    static int noalloc_get_block_write(struct inode *inode, sector_t iblock,
    				   struct buffer_head *bh_result, int create);
    static int ext4_set_bh_endio(struct buffer_head *bh, struct inode *inode);
    static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate);
    static int __ext4_journalled_writepage(struct page *page, unsigned int len);
    static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh);
    
    /*
     * Test whether an inode is a fast symlink.
     */
    static int ext4_inode_is_fast_symlink(struct inode *inode)
    {
    	int ea_blocks = EXT4_I(inode)->i_file_acl ?
    		(inode->i_sb->s_blocksize >> 9) : 0;
    
    	return (S_ISLNK(inode->i_mode) && inode->i_blocks - ea_blocks == 0);
    }
    
    /*
     * Restart the transaction associated with *handle.  This does a commit,
     * so before we call here everything must be consistently dirtied against
     * this transaction.
     */
    int ext4_truncate_restart_trans(handle_t *handle, struct inode *inode,
    				 int nblocks)
    {
    	int ret;
    
    	/*
    	 * Drop i_data_sem to avoid deadlock with ext4_map_blocks.  At this
    	 * moment, get_block can be called only for blocks inside i_size since
    	 * page cache has been already dropped and writes are blocked by
    	 * i_mutex. So we can safely drop the i_data_sem here.
    	 */
    	BUG_ON(EXT4_JOURNAL(inode) == NULL);
    	jbd_debug(2, "restarting handle %p\n", handle);
    	up_write(&EXT4_I(inode)->i_data_sem);
    	ret = ext4_journal_restart(handle, nblocks);
    	down_write(&EXT4_I(inode)->i_data_sem);
    	ext4_discard_preallocations(inode);
    
    	return ret;
    }
    
    /*
     * Called at the last iput() if i_nlink is zero.
     */
    void ext4_evict_inode(struct inode *inode)
    {
    	handle_t *handle;
    	int err;
    
    	trace_ext4_evict_inode(inode);
    
    	ext4_ioend_wait(inode);
    
    	if (inode->i_nlink) {
    		/*
    		 * When journalling data dirty buffers are tracked only in the
    		 * journal. So although mm thinks everything is clean and
    		 * ready for reaping the inode might still have some pages to
    		 * write in the running transaction or waiting to be
    		 * checkpointed. Thus calling jbd2_journal_invalidatepage()
    		 * (via truncate_inode_pages()) to discard these buffers can
    		 * cause data loss. Also even if we did not discard these
    		 * buffers, we would have no way to find them after the inode
    		 * is reaped and thus user could see stale data if he tries to
    		 * read them before the transaction is checkpointed. So be
    		 * careful and force everything to disk here... We use
    		 * ei->i_datasync_tid to store the newest transaction
    		 * containing inode's data.
    		 *
    		 * Note that directories do not have this problem because they
    		 * don't use page cache.
    		 */
    		if (ext4_should_journal_data(inode) &&
    		    (S_ISLNK(inode->i_mode) || S_ISREG(inode->i_mode))) {
    			journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
    			tid_t commit_tid = EXT4_I(inode)->i_datasync_tid;
    
    			jbd2_log_start_commit(journal, commit_tid);
    			jbd2_log_wait_commit(journal, commit_tid);
    			filemap_write_and_wait(&inode->i_data);
    		}
    		truncate_inode_pages(&inode->i_data, 0);
    		goto no_delete;
    	}
    
    	if (!is_bad_inode(inode))
    		dquot_initialize(inode);
    
    	if (ext4_should_order_data(inode))
    		ext4_begin_ordered_truncate(inode, 0);
    	truncate_inode_pages(&inode->i_data, 0);
    
    	if (is_bad_inode(inode))
    		goto no_delete;
    
    	handle = ext4_journal_start(inode, ext4_blocks_for_truncate(inode)+3);
    	if (IS_ERR(handle)) {
    		ext4_std_error(inode->i_sb, PTR_ERR(handle));
    		/*
    		 * If we're going to skip the normal cleanup, we still need to
    		 * make sure that the in-core orphan linked list is properly
    		 * cleaned up.
    		 */
    		ext4_orphan_del(NULL, inode);
    		goto no_delete;
    	}
    
    	if (IS_SYNC(inode))
    		ext4_handle_sync(handle);
    	inode->i_size = 0;
    	err = ext4_mark_inode_dirty(handle, inode);
    	if (err) {
    		ext4_warning(inode->i_sb,
    			     "couldn't mark inode dirty (err %d)", err);
    		goto stop_handle;
    	}
    	if (inode->i_blocks)
    		ext4_truncate(inode);
    
    	/*
    	 * ext4_ext_truncate() doesn't reserve any slop when it
    	 * restarts journal transactions; therefore there may not be
    	 * enough credits left in the handle to remove the inode from
    	 * the orphan list and set the dtime field.
    	 */
    	if (!ext4_handle_has_enough_credits(handle, 3)) {
    		err = ext4_journal_extend(handle, 3);
    		if (err > 0)
    			err = ext4_journal_restart(handle, 3);
    		if (err != 0) {
    			ext4_warning(inode->i_sb,
    				     "couldn't extend journal (err %d)", err);
    		stop_handle:
    			ext4_journal_stop(handle);
    			ext4_orphan_del(NULL, inode);
    			goto no_delete;
    		}
    	}
    
    	/*
    	 * Kill off the orphan record which ext4_truncate created.
    	 * AKPM: I think this can be inside the above `if'.
    	 * Note that ext4_orphan_del() has to be able to cope with the
    	 * deletion of a non-existent orphan - this is because we don't
    	 * know if ext4_truncate() actually created an orphan record.
    	 * (Well, we could do this if we need to, but heck - it works)
    	 */
    	ext4_orphan_del(handle, inode);
    	EXT4_I(inode)->i_dtime	= get_seconds();
    
    	/*
    	 * One subtle ordering requirement: if anything has gone wrong
    	 * (transaction abort, IO errors, whatever), then we can still
    	 * do these next steps (the fs will already have been marked as
    	 * having errors), but we can't free the inode if the mark_dirty
    	 * fails.
    	 */
    	if (ext4_mark_inode_dirty(handle, inode))
    		/* If that failed, just do the required in-core inode clear. */
    		ext4_clear_inode(inode);
    	else
    		ext4_free_inode(handle, inode);
    	ext4_journal_stop(handle);
    	return;
    no_delete:
    	ext4_clear_inode(inode);	/* We must guarantee clearing of inode... */
    }
    
    #ifdef CONFIG_QUOTA
    qsize_t *ext4_get_reserved_space(struct inode *inode)
    {
    	return &EXT4_I(inode)->i_reserved_quota;
    }
    #endif
    
    /*
     * Calculate the number of metadata blocks need to reserve
     * to allocate a block located at @lblock
     */
    static int ext4_calc_metadata_amount(struct inode *inode, ext4_lblk_t lblock)
    {
    	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
    		return ext4_ext_calc_metadata_amount(inode, lblock);
    
    	return ext4_ind_calc_metadata_amount(inode, lblock);
    }
    
    /*
     * Called with i_data_sem down, which is important since we can call
     * ext4_discard_preallocations() from here.
     */
    void ext4_da_update_reserve_space(struct inode *inode,
    					int used, int quota_claim)
    {
    	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    	struct ext4_inode_info *ei = EXT4_I(inode);
    
    	spin_lock(&ei->i_block_reservation_lock);
    	trace_ext4_da_update_reserve_space(inode, used);
    	if (unlikely(used > ei->i_reserved_data_blocks)) {
    		ext4_msg(inode->i_sb, KERN_NOTICE, "%s: ino %lu, used %d "
    			 "with only %d reserved data blocks\n",
    			 __func__, inode->i_ino, used,
    			 ei->i_reserved_data_blocks);
    		WARN_ON(1);
    		used = ei->i_reserved_data_blocks;
    	}
    
    	/* Update per-inode reservations */
    	ei->i_reserved_data_blocks -= used;
    	ei->i_reserved_meta_blocks -= ei->i_allocated_meta_blocks;
    	percpu_counter_sub(&sbi->s_dirtyclusters_counter,
    			   used + ei->i_allocated_meta_blocks);
    	ei->i_allocated_meta_blocks = 0;
    
    	if (ei->i_reserved_data_blocks == 0) {
    		/*
    		 * We can release all of the reserved metadata blocks
    		 * only when we have written all of the delayed
    		 * allocation blocks.
    		 */
    		percpu_counter_sub(&sbi->s_dirtyclusters_counter,
    				   ei->i_reserved_meta_blocks);
    		ei->i_reserved_meta_blocks = 0;
    		ei->i_da_metadata_calc_len = 0;
    	}
    	spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
    
    	/* Update quota subsystem for data blocks */
    	if (quota_claim)
    		dquot_claim_block(inode, EXT4_C2B(sbi, used));
    	else {
    		/*
    		 * We did fallocate with an offset that is already delayed
    		 * allocated. So on delayed allocated writeback we should
    		 * not re-claim the quota for fallocated blocks.
    		 */
    		dquot_release_reservation_block(inode, EXT4_C2B(sbi, used));
    	}
    
    	/*
    	 * If we have done all the pending block allocations and if
    	 * there aren't any writers on the inode, we can discard the
    	 * inode's preallocations.
    	 */
    	if ((ei->i_reserved_data_blocks == 0) &&
    	    (atomic_read(&inode->i_writecount) == 0))
    		ext4_discard_preallocations(inode);
    }
    
    static int __check_block_validity(struct inode *inode, const char *func,
    				unsigned int line,
    				struct ext4_map_blocks *map)
    {
    	if (!ext4_data_block_valid(EXT4_SB(inode->i_sb), map->m_pblk,
    				   map->m_len)) {
    		ext4_error_inode(inode, func, line, map->m_pblk,
    				 "lblock %lu mapped to illegal pblock "
    				 "(length %d)", (unsigned long) map->m_lblk,
    				 map->m_len);
    		return -EIO;
    	}
    	return 0;
    }
    
    #define check_block_validity(inode, map)	\
    	__check_block_validity((inode), __func__, __LINE__, (map))
    
    /*
     * Return the number of contiguous dirty pages in a given inode
     * starting at page frame idx.
     */
    static pgoff_t ext4_num_dirty_pages(struct inode *inode, pgoff_t idx,
    				    unsigned int max_pages)
    {
    	struct address_space *mapping = inode->i_mapping;
    	pgoff_t	index;
    	struct pagevec pvec;
    	pgoff_t num = 0;
    	int i, nr_pages, done = 0;
    
    	if (max_pages == 0)
    		return 0;
    	pagevec_init(&pvec, 0);
    	while (!done) {
    		index = idx;
    		nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
    					      PAGECACHE_TAG_DIRTY,
    					      (pgoff_t)PAGEVEC_SIZE);
    		if (nr_pages == 0)
    			break;
    		for (i = 0; i < nr_pages; i++) {
    			struct page *page = pvec.pages[i];
    			struct buffer_head *bh, *head;
    
    			lock_page(page);
    			if (unlikely(page->mapping != mapping) ||
    			    !PageDirty(page) ||
    			    PageWriteback(page) ||
    			    page->index != idx) {
    				done = 1;
    				unlock_page(page);
    				break;
    			}
    			if (page_has_buffers(page)) {
    				bh = head = page_buffers(page);
    				do {
    					if (!buffer_delay(bh) &&
    					    !buffer_unwritten(bh))
    						done = 1;
    					bh = bh->b_this_page;
    				} while (!done && (bh != head));
    			}
    			unlock_page(page);
    			if (done)
    				break;
    			idx++;
    			num++;
    			if (num >= max_pages) {
    				done = 1;
    				break;
    			}
    		}
    		pagevec_release(&pvec);
    	}
    	return num;
    }
    
    /*
     * The ext4_map_blocks() function tries to look up the requested blocks,
     * and returns if the blocks are already mapped.
     *
     * Otherwise it takes the write lock of the i_data_sem and allocate blocks
     * and store the allocated blocks in the result buffer head and mark it
     * mapped.
     *
     * If file type is extents based, it will call ext4_ext_map_blocks(),
     * Otherwise, call with ext4_ind_map_blocks() to handle indirect mapping
     * based files
     *
     * On success, it returns the number of blocks being mapped or allocate.
     * if create==0 and the blocks are pre-allocated and uninitialized block,
     * the result buffer head is unmapped. If the create ==1, it will make sure
     * the buffer head is mapped.
     *
     * It returns 0 if plain look up failed (blocks have not been allocated), in
     * that casem, buffer head is unmapped
     *
     * It returns the error in case of allocation failure.
     */
    int ext4_map_blocks(handle_t *handle, struct inode *inode,
    		    struct ext4_map_blocks *map, int flags)
    {
    	int retval;
    
    	map->m_flags = 0;
    	ext_debug("ext4_map_blocks(): inode %lu, flag %d, max_blocks %u,"
    		  "logical block %lu\n", inode->i_ino, flags, map->m_len,
    		  (unsigned long) map->m_lblk);
    	/*
    	 * Try to see if we can get the block without requesting a new
    	 * file system block.
    	 */
    	down_read((&EXT4_I(inode)->i_data_sem));
    	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
    		retval = ext4_ext_map_blocks(handle, inode, map, 0);
    	} else {
    		retval = ext4_ind_map_blocks(handle, inode, map, 0);
    	}
    	up_read((&EXT4_I(inode)->i_data_sem));
    
    	if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
    		int ret = check_block_validity(inode, map);
    		if (ret != 0)
    			return ret;
    	}
    
    	/* If it is only a block(s) look up */
    	if ((flags & EXT4_GET_BLOCKS_CREATE) == 0)
    		return retval;
    
    	/*
    	 * Returns if the blocks have already allocated
    	 *
    	 * Note that if blocks have been preallocated
    	 * ext4_ext_get_block() returns th create = 0
    	 * with buffer head unmapped.
    	 */
    	if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED)
    		return retval;
    
    	/*
    	 * When we call get_blocks without the create flag, the
    	 * BH_Unwritten flag could have gotten set if the blocks
    	 * requested were part of a uninitialized extent.  We need to
    	 * clear this flag now that we are committed to convert all or
    	 * part of the uninitialized extent to be an initialized
    	 * extent.  This is because we need to avoid the combination
    	 * of BH_Unwritten and BH_Mapped flags being simultaneously
    	 * set on the buffer_head.
    	 */
    	map->m_flags &= ~EXT4_MAP_UNWRITTEN;
    
    	/*
    	 * New blocks allocate and/or writing to uninitialized extent
    	 * will possibly result in updating i_data, so we take
    	 * the write lock of i_data_sem, and call get_blocks()
    	 * with create == 1 flag.
    	 */
    	down_write((&EXT4_I(inode)->i_data_sem));
    
    	/*
    	 * if the caller is from delayed allocation writeout path
    	 * we have already reserved fs blocks for allocation
    	 * let the underlying get_block() function know to
    	 * avoid double accounting
    	 */
    	if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
    		ext4_set_inode_state(inode, EXT4_STATE_DELALLOC_RESERVED);
    	/*
    	 * We need to check for EXT4 here because migrate
    	 * could have changed the inode type in between
    	 */
    	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
    		retval = ext4_ext_map_blocks(handle, inode, map, flags);
    	} else {
    		retval = ext4_ind_map_blocks(handle, inode, map, flags);
    
    		if (retval > 0 && map->m_flags & EXT4_MAP_NEW) {
    			/*
    			 * We allocated new blocks which will result in
    			 * i_data's format changing.  Force the migrate
    			 * to fail by clearing migrate flags
    			 */
    			ext4_clear_inode_state(inode, EXT4_STATE_EXT_MIGRATE);
    		}
    
    		/*
    		 * Update reserved blocks/metadata blocks after successful
    		 * block allocation which had been deferred till now. We don't
    		 * support fallocate for non extent files. So we can update
    		 * reserve space here.
    		 */
    		if ((retval > 0) &&
    			(flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE))
    			ext4_da_update_reserve_space(inode, retval, 1);
    	}
    	if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
    		ext4_clear_inode_state(inode, EXT4_STATE_DELALLOC_RESERVED);
    
    	up_write((&EXT4_I(inode)->i_data_sem));
    	if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
    		int ret = check_block_validity(inode, map);
    		if (ret != 0)
    			return ret;
    	}
    	return retval;
    }
    
    /* Maximum number of blocks we map for direct IO at once. */
    #define DIO_MAX_BLOCKS 4096
    
    static int _ext4_get_block(struct inode *inode, sector_t iblock,
    			   struct buffer_head *bh, int flags)
    {
    	handle_t *handle = ext4_journal_current_handle();
    	struct ext4_map_blocks map;
    	int ret = 0, started = 0;
    	int dio_credits;
    
    	map.m_lblk = iblock;
    	map.m_len = bh->b_size >> inode->i_blkbits;
    
    	if (flags && !handle) {
    		/* Direct IO write... */
    		if (map.m_len > DIO_MAX_BLOCKS)
    			map.m_len = DIO_MAX_BLOCKS;
    		dio_credits = ext4_chunk_trans_blocks(inode, map.m_len);
    		handle = ext4_journal_start(inode, dio_credits);
    		if (IS_ERR(handle)) {
    			ret = PTR_ERR(handle);
    			return ret;
    		}
    		started = 1;
    	}
    
    	ret = ext4_map_blocks(handle, inode, &map, flags);
    	if (ret > 0) {
    		map_bh(bh, inode->i_sb, map.m_pblk);
    		bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;
    		bh->b_size = inode->i_sb->s_blocksize * map.m_len;
    		ret = 0;
    	}
    	if (started)
    		ext4_journal_stop(handle);
    	return ret;
    }
    
    int ext4_get_block(struct inode *inode, sector_t iblock,
    		   struct buffer_head *bh, int create)
    {
    	return _ext4_get_block(inode, iblock, bh,
    			       create ? EXT4_GET_BLOCKS_CREATE : 0);
    }
    
    /*
     * `handle' can be NULL if create is zero
     */
    struct buffer_head *ext4_getblk(handle_t *handle, struct inode *inode,
    				ext4_lblk_t block, int create, int *errp)
    {
    	struct ext4_map_blocks map;
    	struct buffer_head *bh;
    	int fatal = 0, err;
    
    	J_ASSERT(handle != NULL || create == 0);
    
    	map.m_lblk = block;
    	map.m_len = 1;
    	err = ext4_map_blocks(handle, inode, &map,
    			      create ? EXT4_GET_BLOCKS_CREATE : 0);
    
    	if (err < 0)
    		*errp = err;
    	if (err <= 0)
    		return NULL;
    	*errp = 0;
    
    	bh = sb_getblk(inode->i_sb, map.m_pblk);
    	if (!bh) {
    		*errp = -EIO;
    		return NULL;
    	}
    	if (map.m_flags & EXT4_MAP_NEW) {
    		J_ASSERT(create != 0);
    		J_ASSERT(handle != NULL);
    
    		/*
    		 * Now that we do not always journal data, we should
    		 * keep in mind whether this should always journal the
    		 * new buffer as metadata.  For now, regular file
    		 * writes use ext4_get_block instead, so it's not a
    		 * problem.
    		 */
    		lock_buffer(bh);
    		BUFFER_TRACE(bh, "call get_create_access");
    		fatal = ext4_journal_get_create_access(handle, bh);
    		if (!fatal && !buffer_uptodate(bh)) {
    			memset(bh->b_data, 0, inode->i_sb->s_blocksize);
    			set_buffer_uptodate(bh);
    		}
    		unlock_buffer(bh);
    		BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
    		err = ext4_handle_dirty_metadata(handle, inode, bh);
    		if (!fatal)
    			fatal = err;
    	} else {
    		BUFFER_TRACE(bh, "not a new buffer");
    	}
    	if (fatal) {
    		*errp = fatal;
    		brelse(bh);
    		bh = NULL;
    	}
    	return bh;
    }
    
    struct buffer_head *ext4_bread(handle_t *handle, struct inode *inode,
    			       ext4_lblk_t block, int create, int *err)
    {
    	struct buffer_head *bh;
    
    	bh = ext4_getblk(handle, inode, block, create, err);
    	if (!bh)
    		return bh;
    	if (buffer_uptodate(bh))
    		return bh;
    	ll_rw_block(READ_META, 1, &bh);
    	wait_on_buffer(bh);
    	if (buffer_uptodate(bh))
    		return bh;
    	put_bh(bh);
    	*err = -EIO;
    	return NULL;
    }
    
    static int walk_page_buffers(handle_t *handle,
    			     struct buffer_head *head,
    			     unsigned from,
    			     unsigned to,
    			     int *partial,
    			     int (*fn)(handle_t *handle,
    				       struct buffer_head *bh))
    {
    	struct buffer_head *bh;
    	unsigned block_start, block_end;
    	unsigned blocksize = head->b_size;
    	int err, ret = 0;
    	struct buffer_head *next;
    
    	for (bh = head, block_start = 0;
    	     ret == 0 && (bh != head || !block_start);
    	     block_start = block_end, bh = next) {
    		next = bh->b_this_page;
    		block_end = block_start + blocksize;
    		if (block_end <= from || block_start >= to) {
    			if (partial && !buffer_uptodate(bh))
    				*partial = 1;
    			continue;
    		}
    		err = (*fn)(handle, bh);
    		if (!ret)
    			ret = err;
    	}
    	return ret;
    }
    
    /*
     * To preserve ordering, it is essential that the hole instantiation and
     * the data write be encapsulated in a single transaction.  We cannot
     * close off a transaction and start a new one between the ext4_get_block()
     * and the commit_write().  So doing the jbd2_journal_start at the start of
     * prepare_write() is the right place.
     *
     * Also, this function can nest inside ext4_writepage() ->
     * block_write_full_page(). In that case, we *know* that ext4_writepage()
     * has generated enough buffer credits to do the whole page.  So we won't
     * block on the journal in that case, which is good, because the caller may
     * be PF_MEMALLOC.
     *
     * By accident, ext4 can be reentered when a transaction is open via
     * quota file writes.  If we were to commit the transaction while thus
     * reentered, there can be a deadlock - we would be holding a quota
     * lock, and the commit would never complete if another thread had a
     * transaction open and was blocking on the quota lock - a ranking
     * violation.
     *
     * So what we do is to rely on the fact that jbd2_journal_stop/journal_start
     * will _not_ run commit under these circumstances because handle->h_ref
     * is elevated.  We'll still have enough credits for the tiny quotafile
     * write.
     */
    static int do_journal_get_write_access(handle_t *handle,
    				       struct buffer_head *bh)
    {
    	int dirty = buffer_dirty(bh);
    	int ret;
    
    	if (!buffer_mapped(bh) || buffer_freed(bh))
    		return 0;
    	/*
    	 * __block_write_begin() could have dirtied some buffers. Clean
    	 * the dirty bit as jbd2_journal_get_write_access() could complain
    	 * otherwise about fs integrity issues. Setting of the dirty bit
    	 * by __block_write_begin() isn't a real problem here as we clear
    	 * the bit before releasing a page lock and thus writeback cannot
    	 * ever write the buffer.
    	 */
    	if (dirty)
    		clear_buffer_dirty(bh);
    	ret = ext4_journal_get_write_access(handle, bh);
    	if (!ret && dirty)
    		ret = ext4_handle_dirty_metadata(handle, NULL, bh);
    	return ret;
    }
    
    static int ext4_get_block_write(struct inode *inode, sector_t iblock,
    		   struct buffer_head *bh_result, int create);
    static int ext4_write_begin(struct file *file, struct address_space *mapping,
    			    loff_t pos, unsigned len, unsigned flags,
    			    struct page **pagep, void **fsdata)
    {
    	struct inode *inode = mapping->host;
    	int ret, needed_blocks;
    	handle_t *handle;
    	int retries = 0;
    	struct page *page;
    	pgoff_t index;
    	unsigned from, to;
    
    	trace_ext4_write_begin(inode, pos, len, flags);
    	/*
    	 * Reserve one block more for addition to orphan list in case
    	 * we allocate blocks but write fails for some reason
    	 */
    	needed_blocks = ext4_writepage_trans_blocks(inode) + 1;
    	index = pos >> PAGE_CACHE_SHIFT;
    	from = pos & (PAGE_CACHE_SIZE - 1);
    	to = from + len;
    
    retry:
    	handle = ext4_journal_start(inode, needed_blocks);
    	if (IS_ERR(handle)) {
    		ret = PTR_ERR(handle);
    		goto out;
    	}
    
    	/* We cannot recurse into the filesystem as the transaction is already
    	 * started */
    	flags |= AOP_FLAG_NOFS;
    
    	page = grab_cache_page_write_begin(mapping, index, flags);
    	if (!page) {
    		ext4_journal_stop(handle);
    		ret = -ENOMEM;
    		goto out;
    	}
    	*pagep = page;
    
    	if (ext4_should_dioread_nolock(inode))
    		ret = __block_write_begin(page, pos, len, ext4_get_block_write);
    	else
    		ret = __block_write_begin(page, pos, len, ext4_get_block);
    
    	if (!ret && ext4_should_journal_data(inode)) {
    		ret = walk_page_buffers(handle, page_buffers(page),
    				from, to, NULL, do_journal_get_write_access);
    	}
    
    	if (ret) {
    		unlock_page(page);
    		page_cache_release(page);
    		/*
    		 * __block_write_begin may have instantiated a few blocks
    		 * outside i_size.  Trim these off again. Don't need
    		 * i_size_read because we hold i_mutex.
    		 *
    		 * Add inode to orphan list in case we crash before
    		 * truncate finishes
    		 */
    		if (pos + len > inode->i_size && ext4_can_truncate(inode))
    			ext4_orphan_add(handle, inode);
    
    		ext4_journal_stop(handle);
    		if (pos + len > inode->i_size) {
    			ext4_truncate_failed_write(inode);
    			/*
    			 * If truncate failed early the inode might
    			 * still be on the orphan list; we need to
    			 * make sure the inode is removed from the
    			 * orphan list in that case.
    			 */
    			if (inode->i_nlink)
    				ext4_orphan_del(NULL, inode);
    		}
    	}
    
    	if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
    		goto retry;
    out:
    	return ret;
    }
    
    /* For write_end() in data=journal mode */
    static int write_end_fn(handle_t *handle, struct buffer_head *bh)
    {
    	if (!buffer_mapped(bh) || buffer_freed(bh))
    		return 0;
    	set_buffer_uptodate(bh);
    	return ext4_handle_dirty_metadata(handle, NULL, bh);
    }
    
    static int ext4_generic_write_end(struct file *file,
    				  struct address_space *mapping,
    				  loff_t pos, unsigned len, unsigned copied,
    				  struct page *page, void *fsdata)
    {
    	int i_size_changed = 0;
    	struct inode *inode = mapping->host;
    	handle_t *handle = ext4_journal_current_handle();
    
    	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
    
    	/*
    	 * No need to use i_size_read() here, the i_size
    	 * cannot change under us because we hold i_mutex.
    	 *
    	 * But it's important to update i_size while still holding page lock:
    	 * page writeout could otherwise come in and zero beyond i_size.
    	 */
    	if (pos + copied > inode->i_size) {
    		i_size_write(inode, pos + copied);
    		i_size_changed = 1;
    	}
    
    	if (pos + copied >  EXT4_I(inode)->i_disksize) {
    		/* We need to mark inode dirty even if
    		 * new_i_size is less that inode->i_size
    		 * bu greater than i_disksize.(hint delalloc)
    		 */
    		ext4_update_i_disksize(inode, (pos + copied));
    		i_size_changed = 1;
    	}
    	unlock_page(page);
    	page_cache_release(page);
    
    	/*
    	 * Don't mark the inode dirty under page lock. First, it unnecessarily
    	 * makes the holding time of page lock longer. Second, it forces lock
    	 * ordering of page lock and transaction start for journaling
    	 * filesystems.
    	 */
    	if (i_size_changed)
    		ext4_mark_inode_dirty(handle, inode);
    
    	return copied;
    }
    
    /*
     * We need to pick up the new inode size which generic_commit_write gave us
     * `file' can be NULL - eg, when called from page_symlink().
     *
     * ext4 never places buffers on inode->i_mapping->private_list.  metadata
     * buffers are managed internally.
     */
    static int ext4_ordered_write_end(struct file *file,
    				  struct address_space *mapping,
    				  loff_t pos, unsigned len, unsigned copied,
    				  struct page *page, void *fsdata)
    {
    	handle_t *handle = ext4_journal_current_handle();
    	struct inode *inode = mapping->host;
    	int ret = 0, ret2;
    
    	trace_ext4_ordered_write_end(inode, pos, len, copied);
    	ret = ext4_jbd2_file_inode(handle, inode);
    
    	if (ret == 0) {
    		ret2 = ext4_generic_write_end(file, mapping, pos, len, copied,
    							page, fsdata);
    		copied = ret2;
    		if (pos + len > inode->i_size && ext4_can_truncate(inode))
    			/* if we have allocated more blocks and copied
    			 * less. We will have blocks allocated outside
    			 * inode->i_size. So truncate them
    			 */
    			ext4_orphan_add(handle, inode);
    		if (ret2 < 0)
    			ret = ret2;
    	}
    	ret2 = ext4_journal_stop(handle);
    	if (!ret)
    		ret = ret2;
    
    	if (pos + len > inode->i_size) {
    		ext4_truncate_failed_write(inode);
    		/*
    		 * If truncate failed early the inode might still be
    		 * on the orphan list; we need to make sure the inode
    		 * is removed from the orphan list in that case.
    		 */
    		if (inode->i_nlink)
    			ext4_orphan_del(NULL, inode);
    	}
    
    
    	return ret ? ret : copied;
    }
    
    static int ext4_writeback_write_end(struct file *file,
    				    struct address_space *mapping,
    				    loff_t pos, unsigned len, unsigned copied,
    				    struct page *page, void *fsdata)
    {
    	handle_t *handle = ext4_journal_current_handle();
    	struct inode *inode = mapping->host;
    	int ret = 0, ret2;
    
    	trace_ext4_writeback_write_end(inode, pos, len, copied);
    	ret2 = ext4_generic_write_end(file, mapping, pos, len, copied,
    							page, fsdata);
    	copied = ret2;
    	if (pos + len > inode->i_size && ext4_can_truncate(inode))
    		/* if we have allocated more blocks and copied
    		 * less. We will have blocks allocated outside
    		 * inode->i_size. So truncate them
    		 */
    		ext4_orphan_add(handle, inode);
    
    	if (ret2 < 0)
    		ret = ret2;
    
    	ret2 = ext4_journal_stop(handle);
    	if (!ret)
    		ret = ret2;
    
    	if (pos + len > inode->i_size) {
    		ext4_truncate_failed_write(inode);
    		/*
    		 * If truncate failed early the inode might still be
    		 * on the orphan list; we need to make sure the inode
    		 * is removed from the orphan list in that case.
    		 */
    		if (inode->i_nlink)
    			ext4_orphan_del(NULL, inode);
    	}
    
    	return ret ? ret : copied;
    }
    
    static int ext4_journalled_write_end(struct file *file,
    				     struct address_space *mapping,
    				     loff_t pos, unsigned len, unsigned copied,
    				     struct page *page, void *fsdata)
    {
    	handle_t *handle = ext4_journal_current_handle();
    	struct inode *inode = mapping->host;
    	int ret = 0, ret2;
    	int partial = 0;
    	unsigned from, to;
    	loff_t new_i_size;
    
    	trace_ext4_journalled_write_end(inode, pos, len, copied);
    	from = pos & (PAGE_CACHE_SIZE - 1);
    	to = from + len;
    
    	BUG_ON(!ext4_handle_valid(handle));
    
    	if (copied < len) {
    		if (!PageUptodate(page))
    			copied = 0;
    		page_zero_new_buffers(page, from+copied, to);
    	}
    
    	ret = walk_page_buffers(handle, page_buffers(page), from,
    				to, &partial, write_end_fn);
    	if (!partial)
    		SetPageUptodate(page);
    	new_i_size = pos + copied;
    	if (new_i_size > inode->i_size)
    		i_size_write(inode, pos+copied);
    	ext4_set_inode_state(inode, EXT4_STATE_JDATA);
    	EXT4_I(inode)->i_datasync_tid = handle->h_transaction->t_tid;
    	if (new_i_size > EXT4_I(inode)->i_disksize) {
    		ext4_update_i_disksize(inode, new_i_size);
    		ret2 = ext4_mark_inode_dirty(handle, inode);
    		if (!ret)
    			ret = ret2;
    	}
    
    	unlock_page(page);
    	page_cache_release(page);
    	if (pos + len > inode->i_size && ext4_can_truncate(inode))
    		/* if we have allocated more blocks and copied
    		 * less. We will have blocks allocated outside
    		 * inode->i_size. So truncate them
    		 */
    		ext4_orphan_add(handle, inode);
    
    	ret2 = ext4_journal_stop(handle);
    	if (!ret)
    		ret = ret2;
    	if (pos + len > inode->i_size) {
    		ext4_truncate_failed_write(inode);
    		/*
    		 * If truncate failed early the inode might still be
    		 * on the orphan list; we need to make sure the inode
    		 * is removed from the orphan list in that case.
    		 */
    		if (inode->i_nlink)
    			ext4_orphan_del(NULL, inode);
    	}
    
    	return ret ? ret : copied;
    }
    
    /*
     * Reserve a single cluster located at lblock
     */
    int ext4_da_reserve_space(struct inode *inode, ext4_lblk_t lblock)
    {
    	int retries = 0;
    	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    	struct ext4_inode_info *ei = EXT4_I(inode);
    	unsigned int md_needed;
    	int ret;
    
    	/*
    	 * recalculate the amount of metadata blocks to reserve
    	 * in order to allocate nrblocks
    	 * worse case is one extent per block
    	 */
    repeat:
    	spin_lock(&ei->i_block_reservation_lock);
    	md_needed = EXT4_NUM_B2C(sbi,
    				 ext4_calc_metadata_amount(inode, lblock));
    	trace_ext4_da_reserve_space(inode, md_needed);
    	spin_unlock(&ei->i_block_reservation_lock);
    
    	/*
    	 * We will charge metadata quota at writeout time; this saves
    	 * us from metadata over-estimation, though we may go over by
    	 * a small amount in the end.  Here we just reserve for data.
    	 */
    	ret = dquot_reserve_block(inode, EXT4_C2B(sbi, 1));
    	if (ret)
    		return ret;
    	/*
    	 * We do still charge estimated metadata to the sb though;
    	 * we cannot afford to run out of free blocks.
    	 */
    	if (ext4_claim_free_blocks(sbi, md_needed + 1, 0)) {
    		dquot_release_reservation_block(inode, EXT4_C2B(sbi, 1));
    		if (ext4_should_retry_alloc(inode->i_sb, &retries)) {
    			yield();
    			goto repeat;
    		}
    		return -ENOSPC;
    	}
    	spin_lock(&ei->i_block_reservation_lock);
    	ei->i_reserved_data_blocks++;
    	ei->i_reserved_meta_blocks += md_needed;
    	spin_unlock(&ei->i_block_reservation_lock);
    
    	return 0;       /* success */
    }
    
    static void ext4_da_release_space(struct inode *inode, int to_free)
    {
    	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    	struct ext4_inode_info *ei = EXT4_I(inode);
    
    	if (!to_free)
    		return;		/* Nothing to release, exit */
    
    	spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
    
    	trace_ext4_da_release_space(inode, to_free);
    	if (unlikely(to_free > ei->i_reserved_data_blocks)) {
    		/*
    		 * if there aren't enough reserved blocks, then the
    		 * counter is messed up somewhere.  Since this
    		 * function is called from invalidate page, it's
    		 * harmless to return without any action.
    		 */
    		ext4_msg(inode->i_sb, KERN_NOTICE, "ext4_da_release_space: "
    			 "ino %lu, to_free %d with only %d reserved "
    			 "data blocks\n", inode->i_ino, to_free,
    			 ei->i_reserved_data_blocks);
    		WARN_ON(1);
    		to_free = ei->i_reserved_data_blocks;
    	}
    	ei->i_reserved_data_blocks -= to_free;
    
    	if (ei->i_reserved_data_blocks == 0) {
    		/*
    		 * We can release all of the reserved metadata blocks
    		 * only when we have written all of the delayed
    		 * allocation blocks.
    		 * Note that in case of bigalloc, i_reserved_meta_blocks,
    		 * i_reserved_data_blocks, etc. refer to number of clusters.
    		 */
    		percpu_counter_sub(&sbi->s_dirtyclusters_counter,
    				   ei->i_reserved_meta_blocks);
    		ei->i_reserved_meta_blocks = 0;
    		ei->i_da_metadata_calc_len = 0;
    	}
    
    	/* update fs dirty data blocks counter */
    	percpu_counter_sub(&sbi->s_dirtyclusters_counter, to_free);
    
    	spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
    
    	dquot_release_reservation_block(inode, EXT4_C2B(sbi, to_free));
    }
    
    static void ext4_da_page_release_reservation(struct page *page,
    					     unsigned long offset)
    {
    	int to_release = 0;
    	struct buffer_head *head, *bh;
    	unsigned int curr_off = 0;
    	struct inode *inode = page->mapping->host;
    	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    	int num_clusters;
    
    	head = page_buffers(page);
    	bh = head;
    	do {
    		unsigned int next_off = curr_off + bh->b_size;
    
    		if ((offset <= curr_off) && (buffer_delay(bh))) {
    			to_release++;
    			clear_buffer_delay(bh);
    		}
    		curr_off = next_off;
    	} while ((bh = bh->b_this_page) != head);
    
    	/* If we have released all the blocks belonging to a cluster, then we
    	 * need to release the reserved space for that cluster. */
    	num_clusters = EXT4_NUM_B2C(sbi, to_release);
    	while (num_clusters > 0) {
    		ext4_fsblk_t lblk;
    		lblk = (page->index << (PAGE_CACHE_SHIFT - inode->i_blkbits)) +
    			((num_clusters - 1) << sbi->s_cluster_bits);
    		if (sbi->s_cluster_ratio == 1 ||
    		    !ext4_find_delalloc_cluster(inode, lblk, 1))
    			ext4_da_release_space(inode, 1);
    
    		num_clusters--;
    	}
    }
    
    /*
     * Delayed allocation stuff
     */
    
    /*
     * mpage_da_submit_io - walks through extent of pages and try to write
     * them with writepage() call back
     *
     * @mpd->inode: inode
     * @mpd->first_page: first page of the extent
     * @mpd->next_page: page after the last page of the extent
     *
     * By the time mpage_da_submit_io() is called we expect all blocks
     * to be allocated. this may be wrong if allocation failed.
     *
     * As pages are already locked by write_cache_pages(), we can't use it
     */
    static int mpage_da_submit_io(struct mpage_da_data *mpd,
    			      struct ext4_map_blocks *map)
    {
    	struct pagevec pvec;
    	unsigned long index, end;
    	int ret = 0, err, nr_pages, i;
    	struct inode *inode = mpd->inode;
    	struct address_space *mapping = inode->i_mapping;
    	loff_t size = i_size_read(inode);
    	unsigned int len, block_start;
    	struct buffer_head *bh, *page_bufs = NULL;
    	int journal_data = ext4_should_journal_data(inode);
    	sector_t pblock = 0, cur_logical = 0;
    	struct ext4_io_submit io_submit;
    
    	BUG_ON(mpd->next_page <= mpd->first_page);
    	memset(&io_submit, 0, sizeof(io_submit));
    	/*
    	 * We need to start from the first_page to the next_page - 1
    	 * to make sure we also write the mapped dirty buffer_heads.
    	 * If we look at mpd->b_blocknr we would only be looking
    	 * at the currently mapped buffer_heads.
    	 */
    	index = mpd->first_page;
    	end = mpd->next_page - 1;
    
    	pagevec_init(&pvec, 0);
    	while (index <= end) {
    		nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
    		if (nr_pages == 0)
    			break;
    		for (i = 0; i < nr_pages; i++) {
    			int commit_write = 0, skip_page = 0;
    			struct page *page = pvec.pages[i];
    
    			index = page->index;
    			if (index > end)
    				break;
    
    			if (index == size >> PAGE_CACHE_SHIFT)
    				len = size & ~PAGE_CACHE_MASK;
    			else
    				len = PAGE_CACHE_SIZE;
    			if (map) {
    				cur_logical = index << (PAGE_CACHE_SHIFT -
    							inode->i_blkbits);
    				pblock = map->m_pblk + (cur_logical -
    							map->m_lblk);
    			}
    			index++;
    
    			BUG_ON(!PageLocked(page));
    			BUG_ON(PageWriteback(page));
    
    			/*
    			 * If the page does not have buffers (for
    			 * whatever reason), try to create them using
    			 * __block_write_begin.  If this fails,
    			 * skip the page and move on.
    			 */
    			if (!page_has_buffers(page)) {
    				if (__block_write_begin(page, 0, len,
    						noalloc_get_block_write)) {
    				skip_page:
    					unlock_page(page);
    					continue;
    				}
    				commit_write = 1;
    			}
    
    			bh = page_bufs = page_buffers(page);
    			block_start = 0;
    			do {
    				if (!bh)
    					goto skip_page;
    				if (map && (cur_logical >= map->m_lblk) &&
    				    (cur_logical <= (map->m_lblk +
    						     (map->m_len - 1)))) {
    					if (buffer_delay(bh)) {
    						clear_buffer_delay(bh);
    						bh->b_blocknr = pblock;
    					}
    					if (buffer_unwritten(bh) ||
    					    buffer_mapped(bh))
    						BUG_ON(bh->b_blocknr != pblock);
    					if (map->m_flags & EXT4_MAP_UNINIT)
    						set_buffer_uninit(bh);
    					clear_buffer_unwritten(bh);
    				}
    
    				/* skip page if block allocation undone */
    				if (buffer_delay(bh) || buffer_unwritten(bh))
    					skip_page = 1;
    				bh = bh->b_this_page;
    				block_start += bh->b_size;
    				cur_logical++;
    				pblock++;
    			} while (bh != page_bufs);
    
    			if (skip_page)
    				goto skip_page;
    
    			if (commit_write)
    				/* mark the buffer_heads as dirty & uptodate */
    				block_commit_write(page, 0, len);
    
    			clear_page_dirty_for_io(page);
    			/*
    			 * Delalloc doesn't support data journalling,
    			 * but eventually maybe we'll lift this
    			 * restriction.
    			 */
    			if (unlikely(journal_data && PageChecked(page)))
    				err = __ext4_journalled_writepage(page, len);
    			else if (test_opt(inode->i_sb, MBLK_IO_SUBMIT))
    				err = ext4_bio_write_page(&io_submit, page,
    							  len, mpd->wbc);
    			else if (buffer_uninit(page_bufs)) {
    				ext4_set_bh_endio(page_bufs, inode);
    				err = block_write_full_page_endio(page,
    					noalloc_get_block_write,
    					mpd->wbc, ext4_end_io_buffer_write);
    			} else
    				err = block_write_full_page(page,
    					noalloc_get_block_write, mpd->wbc);
    
    			if (!err)
    				mpd->pages_written++;
    			/*
    			 * In error case, we have to continue because
    			 * remaining pages are still locked
    			 */
    			if (ret == 0)
    				ret = err;
    		}
    		pagevec_release(&pvec);
    	}
    	ext4_io_submit(&io_submit);
    	return ret;
    }
    
    static void ext4_da_block_invalidatepages(struct mpage_da_data *mpd)
    {
    	int nr_pages, i;
    	pgoff_t index, end;
    	struct pagevec pvec;
    	struct inode *inode = mpd->inode;
    	struct address_space *mapping = inode->i_mapping;
    
    	index = mpd->first_page;
    	end   = mpd->next_page - 1;
    	while (index <= end) {
    		nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
    		if (nr_pages == 0)
    			break;
    		for (i = 0; i < nr_pages; i++) {
    			struct page *page = pvec.pages[i];
    			if (page->index > end)
    				break;
    			BUG_ON(!PageLocked(page));
    			BUG_ON(PageWriteback(page));
    			block_invalidatepage(page, 0);
    			ClearPageUptodate(page);
    			unlock_page(page);
    		}
    		index = pvec.pages[nr_pages - 1]->index + 1;
    		pagevec_release(&pvec);
    	}
    	return;
    }
    
    static void ext4_print_free_blocks(struct inode *inode)
    {
    	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    	printk(KERN_CRIT "Total free blocks count %lld\n",
    	       EXT4_C2B(EXT4_SB(inode->i_sb),
    			ext4_count_free_clusters(inode->i_sb)));
    	printk(KERN_CRIT "Free/Dirty block details\n");
    	printk(KERN_CRIT "free_blocks=%lld\n",
    	       (long long) EXT4_C2B(EXT4_SB(inode->i_sb),
    		percpu_counter_sum(&sbi->s_freeclusters_counter)));
    	printk(KERN_CRIT "dirty_blocks=%lld\n",
    	       (long long) EXT4_C2B(EXT4_SB(inode->i_sb),
    		percpu_counter_sum(&sbi->s_dirtyclusters_counter)));
    	printk(KERN_CRIT "Block reservation details\n");
    	printk(KERN_CRIT "i_reserved_data_blocks=%u\n",
    	       EXT4_I(inode)->i_reserved_data_blocks);
    	printk(KERN_CRIT "i_reserved_meta_blocks=%u\n",
    	       EXT4_I(inode)->i_reserved_meta_blocks);
    	return;
    }
    
    /*
     * mpage_da_map_and_submit - go through given space, map them
     *       if necessary, and then submit them for I/O
     *
     * @mpd - bh describing space
     *
     * The function skips space we know is already mapped to disk blocks.
     *
     */
    static void mpage_da_map_and_submit(struct mpage_da_data *mpd)
    {
    	int err, blks, get_blocks_flags;
    	struct ext4_map_blocks map, *mapp = NULL;
    	sector_t next = mpd->b_blocknr;
    	unsigned max_blocks = mpd->b_size >> mpd->inode->i_blkbits;
    	loff_t disksize = EXT4_I(mpd->inode)->i_disksize;
    	handle_t *handle = NULL;
    
    	/*
    	 * If the blocks are mapped already, or we couldn't accumulate
    	 * any blocks, then proceed immediately to the submission stage.
    	 */
    	if ((mpd->b_size == 0) ||
    	    ((mpd->b_state  & (1 << BH_Mapped)) &&
    	     !(mpd->b_state & (1 << BH_Delay)) &&
    	     !(mpd->b_state & (1 << BH_Unwritten))))
    		goto submit_io;
    
    	handle = ext4_journal_current_handle();
    	BUG_ON(!handle);
    
    	/*
    	 * Call ext4_map_blocks() to allocate any delayed allocation
    	 * blocks, or to convert an uninitialized extent to be
    	 * initialized (in the case where we have written into
    	 * one or more preallocated blocks).
    	 *
    	 * We pass in the magic EXT4_GET_BLOCKS_DELALLOC_RESERVE to
    	 * indicate that we are on the delayed allocation path.  This
    	 * affects functions in many different parts of the allocation
    	 * call path.  This flag exists primarily because we don't
    	 * want to change *many* call functions, so ext4_map_blocks()
    	 * will set the EXT4_STATE_DELALLOC_RESERVED flag once the
    	 * inode's allocation semaphore is taken.
    	 *
    	 * If the blocks in questions were delalloc blocks, set
    	 * EXT4_GET_BLOCKS_DELALLOC_RESERVE so the delalloc accounting
    	 * variables are updated after the blocks have been allocated.
    	 */
    	map.m_lblk = next;
    	map.m_len = max_blocks;
    	get_blocks_flags = EXT4_GET_BLOCKS_CREATE;
    	if (ext4_should_dioread_nolock(mpd->inode))
    		get_blocks_flags |= EXT4_GET_BLOCKS_IO_CREATE_EXT;
    	if (mpd->b_state & (1 << BH_Delay))
    		get_blocks_flags |= EXT4_GET_BLOCKS_DELALLOC_RESERVE;
    
    	blks = ext4_map_blocks(handle, mpd->inode, &map, get_blocks_flags);
    	if (blks < 0) {
    		struct super_block *sb = mpd->inode->i_sb;
    
    		err = blks;
    		/*
    		 * If get block returns EAGAIN or ENOSPC and there
    		 * appears to be free blocks we will just let
    		 * mpage_da_submit_io() unlock all of the pages.
    		 */
    		if (err == -EAGAIN)
    			goto submit_io;
    
    		if (err == -ENOSPC && ext4_count_free_clusters(sb)) {
    			mpd->retval = err;
    			goto submit_io;
    		}
    
    		/*
    		 * get block failure will cause us to loop in
    		 * writepages, because a_ops->writepage won't be able
    		 * to make progress. The page will be redirtied by
    		 * writepage and writepages will again try to write
    		 * the same.
    		 */
    		if (!(EXT4_SB(sb)->s_mount_flags & EXT4_MF_FS_ABORTED)) {
    			ext4_msg(sb, KERN_CRIT,
    				 "delayed block allocation failed for inode %lu "
    				 "at logical offset %llu with max blocks %zd "
    				 "with error %d", mpd->inode->i_ino,
    				 (unsigned long long) next,
    				 mpd->b_size >> mpd->inode->i_blkbits, err);
    			ext4_msg(sb, KERN_CRIT,
    				"This should not happen!! Data will be lost\n");
    			if (err == -ENOSPC)
    				ext4_print_free_blocks(mpd->inode);
    		}
    		/* invalidate all the pages */
    		ext4_da_block_invalidatepages(mpd);
    
    		/* Mark this page range as having been completed */
    		mpd->io_done = 1;
    		return;
    	}
    	BUG_ON(blks == 0);
    
    	mapp = &map;
    	if (map.m_flags & EXT4_MAP_NEW) {
    		struct block_device *bdev = mpd->inode->i_sb->s_bdev;
    		int i;
    
    		for (i = 0; i < map.m_len; i++)
    			unmap_underlying_metadata(bdev, map.m_pblk + i);
    
    		if (ext4_should_order_data(mpd->inode)) {
    			err = ext4_jbd2_file_inode(handle, mpd->inode);
    			if (err)
    				/* Only if the journal is aborted */
    				return;
    		}
    	}
    
    	/*
    	 * Update on-disk size along with block allocation.
    	 */
    	disksize = ((loff_t) next + blks) << mpd->inode->i_blkbits;
    	if (disksize > i_size_read(mpd->inode))
    		disksize = i_size_read(mpd->inode);
    	if (disksize > EXT4_I(mpd->inode)->i_disksize) {
    		ext4_update_i_disksize(mpd->inode, disksize);
    		err = ext4_mark_inode_dirty(handle, mpd->inode);
    		if (err)
    			ext4_error(mpd->inode->i_sb,
    				   "Failed to mark inode %lu dirty",
    				   mpd->inode->i_ino);
    	}
    
    submit_io:
    	mpage_da_submit_io(mpd, mapp);
    	mpd->io_done = 1;
    }
    
    #define BH_FLAGS ((1 << BH_Uptodate) | (1 << BH_Mapped) | \
    		(1 << BH_Delay) | (1 << BH_Unwritten))
    
    /*
     * mpage_add_bh_to_extent - try to add one more block to extent of blocks
     *
     * @mpd->lbh - extent of blocks
     * @logical - logical number of the block in the file
     * @bh - bh of the block (used to access block's state)
     *
     * the function is used to collect contig. blocks in same state
     */
    static void mpage_add_bh_to_extent(struct mpage_da_data *mpd,
    				   sector_t logical, size_t b_size,
    				   unsigned long b_state)
    {
    	sector_t next;
    	int nrblocks = mpd->b_size >> mpd->inode->i_blkbits;
    
    	/*
    	 * XXX Don't go larger than mballoc is willing to allocate
    	 * This is a stopgap solution.  We eventually need to fold
    	 * mpage_da_submit_io() into this function and then call
    	 * ext4_map_blocks() multiple times in a loop
    	 */
    	if (nrblocks >= 8*1024*1024/mpd->inode->i_sb->s_blocksize)
    		goto flush_it;
    
    	/* check if thereserved journal credits might overflow */
    	if (!(ext4_test_inode_flag(mpd->inode, EXT4_INODE_EXTENTS))) {
    		if (nrblocks >= EXT4_MAX_TRANS_DATA) {
    			/*
    			 * With non-extent format we are limited by the journal
    			 * credit available.  Total credit needed to insert
    			 * nrblocks contiguous blocks is dependent on the
    			 * nrblocks.  So limit nrblocks.
    			 */
    			goto flush_it;
    		} else if ((nrblocks + (b_size >> mpd->inode->i_blkbits)) >
    				EXT4_MAX_TRANS_DATA) {
    			/*
    			 * Adding the new buffer_head would make it cross the
    			 * allowed limit for which we have journal credit
    			 * reserved. So limit the new bh->b_size
    			 */
    			b_size = (EXT4_MAX_TRANS_DATA - nrblocks) <<
    						mpd->inode->i_blkbits;
    			/* we will do mpage_da_submit_io in the next loop */
    		}
    	}
    	/*
    	 * First block in the extent
    	 */
    	if (mpd->b_size == 0) {
    		mpd->b_blocknr = logical;
    		mpd->b_size = b_size;
    		mpd->b_state = b_state & BH_FLAGS;
    		return;
    	}
    
    	next = mpd->b_blocknr + nrblocks;
    	/*
    	 * Can we merge the block to our big extent?
    	 */
    	if (logical == next && (b_state & BH_FLAGS) == mpd->b_state) {
    		mpd->b_size += b_size;
    		return;
    	}
    
    flush_it:
    	/*
    	 * We couldn't merge the block to our extent, so we
    	 * need to flush current  extent and start new one
    	 */
    	mpage_da_map_and_submit(mpd);
    	return;
    }
    
    static int ext4_bh_delay_or_unwritten(handle_t *handle, struct buffer_head *bh)
    {
    	return (buffer_delay(bh) || buffer_unwritten(bh)) && buffer_dirty(bh);
    }
    
    /*
     * This is a special get_blocks_t callback which is used by
     * ext4_da_write_begin().  It will either return mapped block or
     * reserve space for a single block.
     *
     * For delayed buffer_head we have BH_Mapped, BH_New, BH_Delay set.
     * We also have b_blocknr = -1 and b_bdev initialized properly
     *
     * For unwritten buffer_head we have BH_Mapped, BH_New, BH_Unwritten set.
     * We also have b_blocknr = physicalblock mapping unwritten extent and b_bdev
     * initialized properly.
     */
    static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
    				  struct buffer_head *bh, int create)
    {
    	struct ext4_map_blocks map;
    	int ret = 0;
    	sector_t invalid_block = ~((sector_t) 0xffff);
    
    	if (invalid_block < ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es))
    		invalid_block = ~0;
    
    	BUG_ON(create == 0);
    	BUG_ON(bh->b_size != inode->i_sb->s_blocksize);
    
    	map.m_lblk = iblock;
    	map.m_len = 1;
    
    	/*
    	 * first, we need to know whether the block is allocated already
    	 * preallocated blocks are unmapped but should treated
    	 * the same as allocated blocks.
    	 */
    	ret = ext4_map_blocks(NULL, inode, &map, 0);
    	if (ret < 0)
    		return ret;
    	if (ret == 0) {
    		if (buffer_delay(bh))
    			return 0; /* Not sure this could or should happen */
    		/*
    		 * XXX: __block_write_begin() unmaps passed block, is it OK?
    		 */
    		/* If the block was allocated from previously allocated cluster,
    		 * then we dont need to reserve it again. */
    		if (!(map.m_flags & EXT4_MAP_FROM_CLUSTER)) {
    			ret = ext4_da_reserve_space(inode, iblock);
    			if (ret)
    				/* not enough space to reserve */
    				return ret;
    		}
    
    		map_bh(bh, inode->i_sb, invalid_block);
    		set_buffer_new(bh);
    		set_buffer_delay(bh);
    		return 0;
    	}
    
    	map_bh(bh, inode->i_sb, map.m_pblk);
    	bh->b_state = (bh->b_state & ~EXT4_MAP_FLAGS) | map.m_flags;
    
    	if (buffer_unwritten(bh)) {
    		/* A delayed write to unwritten bh should be marked
    		 * new and mapped.  Mapped ensures that we don't do
    		 * get_block multiple times when we write to the same
    		 * offset and new ensures that we do proper zero out
    		 * for partial write.
    		 */
    		set_buffer_new(bh);
    		set_buffer_mapped(bh);
    	}
    	return 0;
    }
    
    /*
     * This function is used as a standard get_block_t calback function
     * when there is no desire to allocate any blocks.  It is used as a
     * callback function for block_write_begin() and block_write_full_page().
     * These functions should only try to map a single block at a time.
     *
     * Since this function doesn't do block allocations even if the caller
     * requests it by passing in create=1, it is critically important that
     * any caller checks to make sure that any buffer heads are returned
     * by this function are either all already mapped or marked for
     * delayed allocation before calling  block_write_full_page().  Otherwise,
     * b_blocknr could be left unitialized, and the page write functions will
     * be taken by surprise.
     */
    static int noalloc_get_block_write(struct inode *inode, sector_t iblock,
    				   struct buffer_head *bh_result, int create)
    {
    	BUG_ON(bh_result->b_size != inode->i_sb->s_blocksize);
    	return _ext4_get_block(inode, iblock, bh_result, 0);
    }
    
    static int bget_one(handle_t *handle, struct buffer_head *bh)
    {
    	get_bh(bh);
    	return 0;
    }
    
    static int bput_one(handle_t *handle, struct buffer_head *bh)
    {
    	put_bh(bh);
    	return 0;
    }
    
    static int __ext4_journalled_writepage(struct page *page,
    				       unsigned int len)
    {
    	struct address_space *mapping = page->mapping;
    	struct inode *inode = mapping->host;
    	struct buffer_head *page_bufs;
    	handle_t *handle = NULL;
    	int ret = 0;
    	int err;
    
    	ClearPageChecked(page);
    	page_bufs = page_buffers(page);
    	BUG_ON(!page_bufs);
    	walk_page_buffers(handle, page_bufs, 0, len, NULL, bget_one);
    	/* As soon as we unlock the page, it can go away, but we have
    	 * references to buffers so we are safe */
    	unlock_page(page);
    
    	handle = ext4_journal_start(inode, ext4_writepage_trans_blocks(inode));
    	if (IS_ERR(handle)) {
    		ret = PTR_ERR(handle);
    		goto out;
    	}
    
    	BUG_ON(!ext4_handle_valid(handle));
    
    	ret = walk_page_buffers(handle, page_bufs, 0, len, NULL,
    				do_journal_get_write_access);
    
    	err = walk_page_buffers(handle, page_bufs, 0, len, NULL,
    				write_end_fn);
    	if (ret == 0)
    		ret = err;
    	EXT4_I(inode)->i_datasync_tid = handle->h_transaction->t_tid;
    	err = ext4_journal_stop(handle);
    	if (!ret)
    		ret = err;
    
    	walk_page_buffers(handle, page_bufs, 0, len, NULL, bput_one);
    	ext4_set_inode_state(inode, EXT4_STATE_JDATA);
    out:
    	return ret;
    }
    
    static int ext4_set_bh_endio(struct buffer_head *bh, struct inode *inode);
    static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate);
    
    /*
     * Note that we don't need to start a transaction unless we're journaling data
     * because we should have holes filled from ext4_page_mkwrite(). We even don't
     * need to file the inode to the transaction's list in ordered mode because if
     * we are writing back data added by write(), the inode is already there and if
     * we are writing back data modified via mmap(), no one guarantees in which
     * transaction the data will hit the disk. In case we are journaling data, we
     * cannot start transaction directly because transaction start ranks above page
     * lock so we have to do some magic.
     *
     * This function can get called via...
     *   - ext4_da_writepages after taking page lock (have journal handle)
     *   - journal_submit_inode_data_buffers (no journal handle)
     *   - shrink_page_list via pdflush (no journal handle)
     *   - grab_page_cache when doing write_begin (have journal handle)
     *
     * We don't do any block allocation in this function. If we have page with
     * multiple blocks we need to write those buffer_heads that are mapped. This
     * is important for mmaped based write. So if we do with blocksize 1K
     * truncate(f, 1024);
     * a = mmap(f, 0, 4096);
     * a[0] = 'a';
     * truncate(f, 4096);
     * we have in the page first buffer_head mapped via page_mkwrite call back
     * but other bufer_heads would be unmapped but dirty(dirty done via the
     * do_wp_page). So writepage should write the first block. If we modify
     * the mmap area beyond 1024 we will again get a page_fault and the
     * page_mkwrite callback will do the block allocation and mark the
     * buffer_heads mapped.
     *
     * We redirty the page if we have any buffer_heads that is either delay or
     * unwritten in the page.
     *
     * We can get recursively called as show below.
     *
     *	ext4_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->
     *		ext4_writepage()
     *
     * But since we don't do any block allocation we should not deadlock.
     * Page also have the dirty flag cleared so we don't get recurive page_lock.
     */
    static int ext4_writepage(struct page *page,
    			  struct writeback_control *wbc)
    {
    	int ret = 0, commit_write = 0;
    	loff_t size;
    	unsigned int len;
    	struct buffer_head *page_bufs = NULL;
    	struct inode *inode = page->mapping->host;
    
    	trace_ext4_writepage(page);
    	size = i_size_read(inode);
    	if (page->index == size >> PAGE_CACHE_SHIFT)
    		len = size & ~PAGE_CACHE_MASK;
    	else
    		len = PAGE_CACHE_SIZE;
    
    	/*
    	 * If the page does not have buffers (for whatever reason),
    	 * try to create them using __block_write_begin.  If this
    	 * fails, redirty the page and move on.
    	 */
    	if (!page_has_buffers(page)) {
    		if (__block_write_begin(page, 0, len,
    					noalloc_get_block_write)) {
    		redirty_page:
    			redirty_page_for_writepage(wbc, page);
    			unlock_page(page);
    			return 0;
    		}
    		commit_write = 1;
    	}
    	page_bufs = page_buffers(page);
    	if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
    			      ext4_bh_delay_or_unwritten)) {
    		/*
    		 * We don't want to do block allocation, so redirty
    		 * the page and return.  We may reach here when we do
    		 * a journal commit via journal_submit_inode_data_buffers.
    		 * We can also reach here via shrink_page_list
    		 */
    		goto redirty_page;
    	}
    	if (commit_write)
    		/* now mark the buffer_heads as dirty and uptodate */
    		block_commit_write(page, 0, len);
    
    	if (PageChecked(page) && ext4_should_journal_data(inode))
    		/*
    		 * It's mmapped pagecache.  Add buffers and journal it.  There
    		 * doesn't seem much point in redirtying the page here.
    		 */
    		return __ext4_journalled_writepage(page, len);
    
    	if (buffer_uninit(page_bufs)) {
    		ext4_set_bh_endio(page_bufs, inode);
    		ret = block_write_full_page_endio(page, noalloc_get_block_write,
    					    wbc, ext4_end_io_buffer_write);
    	} else
    		ret = block_write_full_page(page, noalloc_get_block_write,
    					    wbc);
    
    	return ret;
    }
    
    /*
     * This is called via ext4_da_writepages() to
     * calculate the total number of credits to reserve to fit
     * a single extent allocation into a single transaction,
     * ext4_da_writpeages() will loop calling this before
     * the block allocation.
     */
    
    static int ext4_da_writepages_trans_blocks(struct inode *inode)
    {
    	int max_blocks = EXT4_I(inode)->i_reserved_data_blocks;
    
    	/*
    	 * With non-extent format the journal credit needed to
    	 * insert nrblocks contiguous block is dependent on
    	 * number of contiguous block. So we will limit
    	 * number of contiguous block to a sane value
    	 */
    	if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) &&
    	    (max_blocks > EXT4_MAX_TRANS_DATA))
    		max_blocks = EXT4_MAX_TRANS_DATA;
    
    	return ext4_chunk_trans_blocks(inode, max_blocks);
    }
    
    /*
     * write_cache_pages_da - walk the list of dirty pages of the given
     * address space and accumulate pages that need writing, and call
     * mpage_da_map_and_submit to map a single contiguous memory region
     * and then write them.
     */
    static int write_cache_pages_da(struct address_space *mapping,
    				struct writeback_control *wbc,
    				struct mpage_da_data *mpd,
    				pgoff_t *done_index)
    {
    	struct buffer_head	*bh, *head;
    	struct inode		*inode = mapping->host;
    	struct pagevec		pvec;
    	unsigned int		nr_pages;
    	sector_t		logical;
    	pgoff_t			index, end;
    	long			nr_to_write = wbc->nr_to_write;
    	int			i, tag, ret = 0;
    
    	memset(mpd, 0, sizeof(struct mpage_da_data));
    	mpd->wbc = wbc;
    	mpd->inode = inode;
    	pagevec_init(&pvec, 0);
    	index = wbc->range_start >> PAGE_CACHE_SHIFT;
    	end = wbc->range_end >> PAGE_CACHE_SHIFT;
    
    	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
    		tag = PAGECACHE_TAG_TOWRITE;
    	else
    		tag = PAGECACHE_TAG_DIRTY;
    
    	*done_index = index;
    	while (index <= end) {
    		nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
    			      min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
    		if (nr_pages == 0)
    			return 0;
    
    		for (i = 0; i < nr_pages; i++) {
    			struct page *page = pvec.pages[i];
    
    			/*
    			 * At this point, the page may be truncated or
    			 * invalidated (changing page->mapping to NULL), or
    			 * even swizzled back from swapper_space to tmpfs file
    			 * mapping. However, page->index will not change
    			 * because we have a reference on the page.
    			 */
    			if (page->index > end)
    				goto out;
    
    			*done_index = page->index + 1;
    
    			/*
    			 * If we can't merge this page, and we have
    			 * accumulated an contiguous region, write it
    			 */
    			if ((mpd->next_page != page->index) &&
    			    (mpd->next_page != mpd->first_page)) {
    				mpage_da_map_and_submit(mpd);
    				goto ret_extent_tail;
    			}
    
    			lock_page(page);
    
    			/*
    			 * If the page is no longer dirty, or its
    			 * mapping no longer corresponds to inode we
    			 * are writing (which means it has been
    			 * truncated or invalidated), or the page is
    			 * already under writeback and we are not
    			 * doing a data integrity writeback, skip the page
    			 */
    			if (!PageDirty(page) ||
    			    (PageWriteback(page) &&
    			     (wbc->sync_mode == WB_SYNC_NONE)) ||
    			    unlikely(page->mapping != mapping)) {
    				unlock_page(page);
    				continue;
    			}
    
    			wait_on_page_writeback(page);
    			BUG_ON(PageWriteback(page));
    
    			if (mpd->next_page != page->index)
    				mpd->first_page = page->index;
    			mpd->next_page = page->index + 1;
    			logical = (sector_t) page->index <<
    				(PAGE_CACHE_SHIFT - inode->i_blkbits);
    
    			if (!page_has_buffers(page)) {
    				mpage_add_bh_to_extent(mpd, logical,
    						       PAGE_CACHE_SIZE,
    						       (1 << BH_Dirty) | (1 << BH_Uptodate));
    				if (mpd->io_done)
    					goto ret_extent_tail;
    			} else {
    				/*
    				 * Page with regular buffer heads,
    				 * just add all dirty ones
    				 */
    				head = page_buffers(page);
    				bh = head;
    				do {
    					BUG_ON(buffer_locked(bh));
    					/*
    					 * We need to try to allocate
    					 * unmapped blocks in the same page.
    					 * Otherwise we won't make progress
    					 * with the page in ext4_writepage
    					 */
    					if (ext4_bh_delay_or_unwritten(NULL, bh)) {
    						mpage_add_bh_to_extent(mpd, logical,
    								       bh->b_size,
    								       bh->b_state);
    						if (mpd->io_done)
    							goto ret_extent_tail;
    					} else if (buffer_dirty(bh) && (buffer_mapped(bh))) {
    						/*
    						 * mapped dirty buffer. We need
    						 * to update the b_state
    						 * because we look at b_state
    						 * in mpage_da_map_blocks.  We
    						 * don't update b_size because
    						 * if we find an unmapped
    						 * buffer_head later we need to
    						 * use the b_state flag of that
    						 * buffer_head.
    						 */
    						if (mpd->b_size == 0)
    							mpd->b_state = bh->b_state & BH_FLAGS;
    					}
    					logical++;
    				} while ((bh = bh->b_this_page) != head);
    			}
    
    			if (nr_to_write > 0) {
    				nr_to_write--;
    				if (nr_to_write == 0 &&
    				    wbc->sync_mode == WB_SYNC_NONE)
    					/*
    					 * We stop writing back only if we are
    					 * not doing integrity sync. In case of
    					 * integrity sync we have to keep going
    					 * because someone may be concurrently
    					 * dirtying pages, and we might have
    					 * synced a lot of newly appeared dirty
    					 * pages, but have not synced all of the
    					 * old dirty pages.
    					 */
    					goto out;
    			}
    		}
    		pagevec_release(&pvec);
    		cond_resched();
    	}
    	return 0;
    ret_extent_tail:
    	ret = MPAGE_DA_EXTENT_TAIL;
    out:
    	pagevec_release(&pvec);
    	cond_resched();
    	return ret;
    }
    
    
    static int ext4_da_writepages(struct address_space *mapping,
    			      struct writeback_control *wbc)
    {
    	pgoff_t	index;
    	int range_whole = 0;
    	handle_t *handle = NULL;
    	struct mpage_da_data mpd;
    	struct inode *inode = mapping->host;
    	int pages_written = 0;
    	unsigned int max_pages;
    	int range_cyclic, cycled = 1, io_done = 0;
    	int needed_blocks, ret = 0;
    	long desired_nr_to_write, nr_to_writebump = 0;
    	loff_t range_start = wbc->range_start;
    	struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
    	pgoff_t done_index = 0;
    	pgoff_t end;
    
    	trace_ext4_da_writepages(inode, wbc);
    
    	/*
    	 * No pages to write? This is mainly a kludge to avoid starting
    	 * a transaction for special inodes like journal inode on last iput()
    	 * because that could violate lock ordering on umount
    	 */
    	if (!mapping->nrpages || !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
    		return 0;
    
    	/*
    	 * If the filesystem has aborted, it is read-only, so return
    	 * right away instead of dumping stack traces later on that
    	 * will obscure the real source of the problem.  We test
    	 * EXT4_MF_FS_ABORTED instead of sb->s_flag's MS_RDONLY because
    	 * the latter could be true if the filesystem is mounted
    	 * read-only, and in that case, ext4_da_writepages should
    	 * *never* be called, so if that ever happens, we would want
    	 * the stack trace.
    	 */
    	if (unlikely(sbi->s_mount_flags & EXT4_MF_FS_ABORTED))
    		return -EROFS;
    
    	if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
    		range_whole = 1;
    
    	range_cyclic = wbc->range_cyclic;
    	if (wbc->range_cyclic) {
    		index = mapping->writeback_index;
    		if (index)
    			cycled = 0;
    		wbc->range_start = index << PAGE_CACHE_SHIFT;
    		wbc->range_end  = LLONG_MAX;
    		wbc->range_cyclic = 0;
    		end = -1;
    	} else {
    		index = wbc->range_start >> PAGE_CACHE_SHIFT;
    		end = wbc->range_end >> PAGE_CACHE_SHIFT;
    	}
    
    	/*
    	 * This works around two forms of stupidity.  The first is in
    	 * the writeback code, which caps the maximum number of pages
    	 * written to be 1024 pages.  This is wrong on multiple
    	 * levels; different architectues have a different page size,
    	 * which changes the maximum amount of data which gets
    	 * written.  Secondly, 4 megabytes is way too small.  XFS
    	 * forces this value to be 16 megabytes by multiplying
    	 * nr_to_write parameter by four, and then relies on its
    	 * allocator to allocate larger extents to make them
    	 * contiguous.  Unfortunately this brings us to the second
    	 * stupidity, which is that ext4's mballoc code only allocates
    	 * at most 2048 blocks.  So we force contiguous writes up to
    	 * the number of dirty blocks in the inode, or
    	 * sbi->max_writeback_mb_bump whichever is smaller.
    	 */
    	max_pages = sbi->s_max_writeback_mb_bump << (20 - PAGE_CACHE_SHIFT);
    	if (!range_cyclic && range_whole) {
    		if (wbc->nr_to_write == LONG_MAX)
    			desired_nr_to_write = wbc->nr_to_write;
    		else
    			desired_nr_to_write = wbc->nr_to_write * 8;
    	} else
    		desired_nr_to_write = ext4_num_dirty_pages(inode, index,
    							   max_pages);
    	if (desired_nr_to_write > max_pages)
    		desired_nr_to_write = max_pages;
    
    	if (wbc->nr_to_write < desired_nr_to_write) {
    		nr_to_writebump = desired_nr_to_write - wbc->nr_to_write;
    		wbc->nr_to_write = desired_nr_to_write;
    	}
    
    retry:
    	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
    		tag_pages_for_writeback(mapping, index, end);
    
    	while (!ret && wbc->nr_to_write > 0) {
    
    		/*
    		 * we  insert one extent at a time. So we need
    		 * credit needed for single extent allocation.
    		 * journalled mode is currently not supported
    		 * by delalloc
    		 */
    		BUG_ON(ext4_should_journal_data(inode));
    		needed_blocks = ext4_da_writepages_trans_blocks(inode);
    
    		/* start a new transaction*/
    		handle = ext4_journal_start(inode, needed_blocks);
    		if (IS_ERR(handle)) {
    			ret = PTR_ERR(handle);
    			ext4_msg(inode->i_sb, KERN_CRIT, "%s: jbd2_start: "
    			       "%ld pages, ino %lu; err %d", __func__,
    				wbc->nr_to_write, inode->i_ino, ret);
    			goto out_writepages;
    		}
    
    		/*
    		 * Now call write_cache_pages_da() to find the next
    		 * contiguous region of logical blocks that need
    		 * blocks to be allocated by ext4 and submit them.
    		 */
    		ret = write_cache_pages_da(mapping, wbc, &mpd, &done_index);
    		/*
    		 * If we have a contiguous extent of pages and we
    		 * haven't done the I/O yet, map the blocks and submit
    		 * them for I/O.
    		 */
    		if (!mpd.io_done && mpd.next_page != mpd.first_page) {
    			mpage_da_map_and_submit(&mpd);
    			ret = MPAGE_DA_EXTENT_TAIL;
    		}
    		trace_ext4_da_write_pages(inode, &mpd);
    		wbc->nr_to_write -= mpd.pages_written;
    
    		ext4_journal_stop(handle);
    
    		if ((mpd.retval == -ENOSPC) && sbi->s_journal) {
    			/* commit the transaction which would
    			 * free blocks released in the transaction
    			 * and try again
    			 */
    			jbd2_journal_force_commit_nested(sbi->s_journal);
    			ret = 0;
    		} else if (ret == MPAGE_DA_EXTENT_TAIL) {
    			/*
    			 * got one extent now try with
    			 * rest of the pages
    			 */
    			pages_written += mpd.pages_written;
    			ret = 0;
    			io_done = 1;
    		} else if (wbc->nr_to_write)
    			/*
    			 * There is no more writeout needed
    			 * or we requested for a noblocking writeout
    			 * and we found the device congested
    			 */
    			break;
    	}
    	if (!io_done && !cycled) {
    		cycled = 1;
    		index = 0;
    		wbc->range_start = index << PAGE_CACHE_SHIFT;
    		wbc->range_end  = mapping->writeback_index - 1;
    		goto retry;
    	}
    
    	/* Update index */
    	wbc->range_cyclic = range_cyclic;
    	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
    		/*
    		 * set the writeback_index so that range_cyclic
    		 * mode will write it back later
    		 */
    		mapping->writeback_index = done_index;
    
    out_writepages:
    	wbc->nr_to_write -= nr_to_writebump;
    	wbc->range_start = range_start;
    	trace_ext4_da_writepages_result(inode, wbc, ret, pages_written);
    	return ret;
    }
    
    #define FALL_BACK_TO_NONDELALLOC 1
    static int ext4_nonda_switch(struct super_block *sb)
    {
    	s64 free_blocks, dirty_blocks;
    	struct ext4_sb_info *sbi = EXT4_SB(sb);
    
    	/*
    	 * switch to non delalloc mode if we are running low
    	 * on free block. The free block accounting via percpu
    	 * counters can get slightly wrong with percpu_counter_batch getting
    	 * accumulated on each CPU without updating global counters
    	 * Delalloc need an accurate free block accounting. So switch
    	 * to non delalloc when we are near to error range.
    	 */
    	free_blocks  = EXT4_C2B(sbi,
    		percpu_counter_read_positive(&sbi->s_freeclusters_counter));
    	dirty_blocks = percpu_counter_read_positive(&sbi->s_dirtyclusters_counter);
    	if (2 * free_blocks < 3 * dirty_blocks ||
    		free_blocks < (dirty_blocks + EXT4_FREEBLOCKS_WATERMARK)) {
    		/*
    		 * free block count is less than 150% of dirty blocks
    		 * or free blocks is less than watermark
    		 */
    		return 1;
    	}
    	/*
    	 * Even if we don't switch but are nearing capacity,
    	 * start pushing delalloc when 1/2 of free blocks are dirty.
    	 */
    	if (free_blocks < 2 * dirty_blocks)
    		writeback_inodes_sb_if_idle(sb);
    
    	return 0;
    }
    
    static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
    			       loff_t pos, unsigned len, unsigned flags,
    			       struct page **pagep, void **fsdata)
    {
    	int ret, retries = 0;
    	struct page *page;
    	pgoff_t index;
    	struct inode *inode = mapping->host;
    	handle_t *handle;
    	loff_t page_len;
    
    	index = pos >> PAGE_CACHE_SHIFT;
    
    	if (ext4_nonda_switch(inode->i_sb)) {
    		*fsdata = (void *)FALL_BACK_TO_NONDELALLOC;
    		return ext4_write_begin(file, mapping, pos,
    					len, flags, pagep, fsdata);
    	}
    	*fsdata = (void *)0;
    	trace_ext4_da_write_begin(inode, pos, len, flags);
    retry:
    	/*
    	 * With delayed allocation, we don't log the i_disksize update
    	 * if there is delayed block allocation. But we still need
    	 * to journalling the i_disksize update if writes to the end
    	 * of file which has an already mapped buffer.
    	 */
    	handle = ext4_journal_start(inode, 1);
    	if (IS_ERR(handle)) {
    		ret = PTR_ERR(handle);
    		goto out;
    	}
    	/* We cannot recurse into the filesystem as the transaction is already
    	 * started */
    	flags |= AOP_FLAG_NOFS;
    
    	page = grab_cache_page_write_begin(mapping, index, flags);
    	if (!page) {
    		ext4_journal_stop(handle);
    		ret = -ENOMEM;
    		goto out;
    	}
    	*pagep = page;
    
    	ret = __block_write_begin(page, pos, len, ext4_da_get_block_prep);
    	if (ret < 0) {
    		unlock_page(page);
    		ext4_journal_stop(handle);
    		page_cache_release(page);
    		/*
    		 * block_write_begin may have instantiated a few blocks
    		 * outside i_size.  Trim these off again. Don't need
    		 * i_size_read because we hold i_mutex.
    		 */
    		if (pos + len > inode->i_size)
    			ext4_truncate_failed_write(inode);
    	} else {
    		page_len = pos & (PAGE_CACHE_SIZE - 1);
    		if (page_len > 0) {
    			ret = ext4_discard_partial_page_buffers_no_lock(handle,
    				inode, page, pos - page_len, page_len,
    				EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED);
    		}
    	}
    
    	if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
    		goto retry;
    out:
    	return ret;
    }
    
    /*
     * Check if we should update i_disksize
     * when write to the end of file but not require block allocation
     */
    static int ext4_da_should_update_i_disksize(struct page *page,
    					    unsigned long offset)
    {
    	struct buffer_head *bh;
    	struct inode *inode = page->mapping->host;
    	unsigned int idx;
    	int i;
    
    	bh = page_buffers(page);
    	idx = offset >> inode->i_blkbits;
    
    	for (i = 0; i < idx; i++)
    		bh = bh->b_this_page;
    
    	if (!buffer_mapped(bh) || (buffer_delay(bh)) || buffer_unwritten(bh))
    		return 0;
    	return 1;
    }
    
    static int ext4_da_write_end(struct file *file,
    			     struct address_space *mapping,
    			     loff_t pos, unsigned len, unsigned copied,
    			     struct page *page, void *fsdata)
    {
    	struct inode *inode = mapping->host;
    	int ret = 0, ret2;
    	handle_t *handle = ext4_journal_current_handle();
    	loff_t new_i_size;
    	unsigned long start, end;
    	int write_mode = (int)(unsigned long)fsdata;
    	loff_t page_len;
    
    	if (write_mode == FALL_BACK_TO_NONDELALLOC) {
    		if (ext4_should_order_data(inode)) {
    			return ext4_ordered_write_end(file, mapping, pos,
    					len, copied, page, fsdata);
    		} else if (ext4_should_writeback_data(inode)) {
    			return ext4_writeback_write_end(file, mapping, pos,
    					len, copied, page, fsdata);
    		} else {
    			BUG();
    		}
    	}
    
    	trace_ext4_da_write_end(inode, pos, len, copied);
    	start = pos & (PAGE_CACHE_SIZE - 1);
    	end = start + copied - 1;
    
    	/*
    	 * generic_write_end() will run mark_inode_dirty() if i_size
    	 * changes.  So let's piggyback the i_disksize mark_inode_dirty
    	 * into that.
    	 */
    
    	new_i_size = pos + copied;
    	if (new_i_size > EXT4_I(inode)->i_disksize) {
    		if (ext4_da_should_update_i_disksize(page, end)) {
    			down_write(&EXT4_I(inode)->i_data_sem);
    			if (new_i_size > EXT4_I(inode)->i_disksize) {
    				/*
    				 * Updating i_disksize when extending file
    				 * without needing block allocation
    				 */
    				if (ext4_should_order_data(inode))
    					ret = ext4_jbd2_file_inode(handle,
    								   inode);
    
    				EXT4_I(inode)->i_disksize = new_i_size;
    			}
    			up_write(&EXT4_I(inode)->i_data_sem);
    			/* We need to mark inode dirty even if
    			 * new_i_size is less that inode->i_size
    			 * bu greater than i_disksize.(hint delalloc)
    			 */
    			ext4_mark_inode_dirty(handle, inode);
    		}
    	}
    	ret2 = generic_write_end(file, mapping, pos, len, copied,
    							page, fsdata);
    
    	page_len = PAGE_CACHE_SIZE -
    			((pos + copied - 1) & (PAGE_CACHE_SIZE - 1));
    
    	if (page_len > 0) {
    		ret = ext4_discard_partial_page_buffers_no_lock(handle,
    			inode, page, pos + copied - 1, page_len,
    			EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED);
    	}
    
    	copied = ret2;
    	if (ret2 < 0)
    		ret = ret2;
    	ret2 = ext4_journal_stop(handle);
    	if (!ret)
    		ret = ret2;
    
    	return ret ? ret : copied;
    }
    
    static void ext4_da_invalidatepage(struct page *page, unsigned long offset)
    {
    	/*
    	 * Drop reserved blocks
    	 */
    	BUG_ON(!PageLocked(page));
    	if (!page_has_buffers(page))
    		goto out;
    
    	ext4_da_page_release_reservation(page, offset);
    
    out:
    	ext4_invalidatepage(page, offset);
    
    	return;
    }
    
    /*
     * Force all delayed allocation blocks to be allocated for a given inode.
     */
    int ext4_alloc_da_blocks(struct inode *inode)
    {
    	trace_ext4_alloc_da_blocks(inode);
    
    	if (!EXT4_I(inode)->i_reserved_data_blocks &&
    	    !EXT4_I(inode)->i_reserved_meta_blocks)
    		return 0;
    
    	/*
    	 * We do something simple for now.  The filemap_flush() will
    	 * also start triggering a write of the data blocks, which is
    	 * not strictly speaking necessary (and for users of
    	 * laptop_mode, not even desirable).  However, to do otherwise
    	 * would require replicating code paths in:
    	 *
    	 * ext4_da_writepages() ->
    	 *    write_cache_pages() ---> (via passed in callback function)
    	 *        __mpage_da_writepage() -->
    	 *           mpage_add_bh_to_extent()
    	 *           mpage_da_map_blocks()
    	 *
    	 * The problem is that write_cache_pages(), located in
    	 * mm/page-writeback.c, marks pages clean in preparation for
    	 * doing I/O, which is not desirable if we're not planning on
    	 * doing I/O at all.
    	 *
    	 * We could call write_cache_pages(), and then redirty all of
    	 * the pages by calling redirty_page_for_writepage() but that
    	 * would be ugly in the extreme.  So instead we would need to
    	 * replicate parts of the code in the above functions,
    	 * simplifying them because we wouldn't actually intend to
    	 * write out the pages, but rather only collect contiguous
    	 * logical block extents, call the multi-block allocator, and
    	 * then update the buffer heads with the block allocations.
    	 *
    	 * For now, though, we'll cheat by calling filemap_flush(),
    	 * which will map the blocks, and start the I/O, but not
    	 * actually wait for the I/O to complete.
    	 */
    	return filemap_flush(inode->i_mapping);
    }
    
    /*
     * bmap() is special.  It gets used by applications such as lilo and by
     * the swapper to find the on-disk block of a specific piece of data.
     *
     * Naturally, this is dangerous if the block concerned is still in the
     * journal.  If somebody makes a swapfile on an ext4 data-journaling
     * filesystem and enables swap, then they may get a nasty shock when the
     * data getting swapped to that swapfile suddenly gets overwritten by
     * the original zero's written out previously to the journal and
     * awaiting writeback in the kernel's buffer cache.
     *
     * So, if we see any bmap calls here on a modified, data-journaled file,
     * take extra steps to flush any blocks which might be in the cache.
     */
    static sector_t ext4_bmap(struct address_space *mapping, sector_t block)
    {
    	struct inode *inode = mapping->host;
    	journal_t *journal;
    	int err;
    
    	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
    			test_opt(inode->i_sb, DELALLOC)) {
    		/*
    		 * With delalloc we want to sync the file
    		 * so that we can make sure we allocate
    		 * blocks for file
    		 */
    		filemap_write_and_wait(mapping);
    	}
    
    	if (EXT4_JOURNAL(inode) &&
    	    ext4_test_inode_state(inode, EXT4_STATE_JDATA)) {
    		/*
    		 * This is a REALLY heavyweight approach, but the use of
    		 * bmap on dirty files is expected to be extremely rare:
    		 * only if we run lilo or swapon on a freshly made file
    		 * do we expect this to happen.
    		 *
    		 * (bmap requires CAP_SYS_RAWIO so this does not
    		 * represent an unprivileged user DOS attack --- we'd be
    		 * in trouble if mortal users could trigger this path at
    		 * will.)
    		 *
    		 * NB. EXT4_STATE_JDATA is not set on files other than
    		 * regular files.  If somebody wants to bmap a directory
    		 * or symlink and gets confused because the buffer
    		 * hasn't yet been flushed to disk, they deserve
    		 * everything they get.
    		 */
    
    		ext4_clear_inode_state(inode, EXT4_STATE_JDATA);
    		journal = EXT4_JOURNAL(inode);
    		jbd2_journal_lock_updates(journal);
    		err = jbd2_journal_flush(journal);
    		jbd2_journal_unlock_updates(journal);
    
    		if (err)
    			return 0;
    	}
    
    	return generic_block_bmap(mapping, block, ext4_get_block);
    }
    
    static int ext4_readpage(struct file *file, struct page *page)
    {
    	trace_ext4_readpage(page);
    	return mpage_readpage(page, ext4_get_block);
    }
    
    static int
    ext4_readpages(struct file *file, struct address_space *mapping,
    		struct list_head *pages, unsigned nr_pages)
    {
    	return mpage_readpages(mapping, pages, nr_pages, ext4_get_block);
    }
    
    static void ext4_invalidatepage_free_endio(struct page *page, unsigned long offset)
    {
    	struct buffer_head *head, *bh;
    	unsigned int curr_off = 0;
    
    	if (!page_has_buffers(page))
    		return;
    	head = bh = page_buffers(page);
    	do {
    		if (offset <= curr_off && test_clear_buffer_uninit(bh)
    					&& bh->b_private) {
    			ext4_free_io_end(bh->b_private);
    			bh->b_private = NULL;
    			bh->b_end_io = NULL;
    		}
    		curr_off = curr_off + bh->b_size;
    		bh = bh->b_this_page;
    	} while (bh != head);
    }
    
    static void ext4_invalidatepage(struct page *page, unsigned long offset)
    {
    	journal_t *journal = EXT4_JOURNAL(page->mapping->host);
    
    	trace_ext4_invalidatepage(page, offset);
    
    	/*
    	 * free any io_end structure allocated for buffers to be discarded
    	 */
    	if (ext4_should_dioread_nolock(page->mapping->host))
    		ext4_invalidatepage_free_endio(page, offset);
    	/*
    	 * If it's a full truncate we just forget about the pending dirtying
    	 */
    	if (offset == 0)
    		ClearPageChecked(page);
    
    	if (journal)
    		jbd2_journal_invalidatepage(journal, page, offset);
    	else
    		block_invalidatepage(page, offset);
    }
    
    static int ext4_releasepage(struct page *page, gfp_t wait)
    {
    	journal_t *journal = EXT4_JOURNAL(page->mapping->host);
    
    	trace_ext4_releasepage(page);
    
    	WARN_ON(PageChecked(page));
    	if (!page_has_buffers(page))
    		return 0;
    	if (journal)
    		return jbd2_journal_try_to_free_buffers(journal, page, wait);
    	else
    		return try_to_free_buffers(page);
    }
    
    /*
     * ext4_get_block used when preparing for a DIO write or buffer write.
     * We allocate an uinitialized extent if blocks haven't been allocated.
     * The extent will be converted to initialized after the IO is complete.
     */
    static int ext4_get_block_write(struct inode *inode, sector_t iblock,
    		   struct buffer_head *bh_result, int create)
    {
    	ext4_debug("ext4_get_block_write: inode %lu, create flag %d\n",
    		   inode->i_ino, create);
    	return _ext4_get_block(inode, iblock, bh_result,
    			       EXT4_GET_BLOCKS_IO_CREATE_EXT);
    }
    
    static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
    			    ssize_t size, void *private, int ret,
    			    bool is_async)
    {
    	struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode;
            ext4_io_end_t *io_end = iocb->private;
    	struct workqueue_struct *wq;
    	unsigned long flags;
    	struct ext4_inode_info *ei;
    
    	/* if not async direct IO or dio with 0 bytes write, just return */
    	if (!io_end || !size)
    		goto out;
    
    	ext_debug("ext4_end_io_dio(): io_end 0x%p"
    		  "for inode %lu, iocb 0x%p, offset %llu, size %llu\n",
     		  iocb->private, io_end->inode->i_ino, iocb, offset,
    		  size);
    
    	/* if not aio dio with unwritten extents, just free io and return */
    	if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
    		ext4_free_io_end(io_end);
    		iocb->private = NULL;
    out:
    		if (is_async)
    			aio_complete(iocb, ret, 0);
    		inode_dio_done(inode);
    		return;
    	}
    
    	io_end->offset = offset;
    	io_end->size = size;
    	if (is_async) {
    		io_end->iocb = iocb;
    		io_end->result = ret;
    	}
    	wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
    
    	/* Add the io_end to per-inode completed aio dio list*/
    	ei = EXT4_I(io_end->inode);
    	spin_lock_irqsave(&ei->i_completed_io_lock, flags);
    	list_add_tail(&io_end->list, &ei->i_completed_io_list);
    	spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
    
    	/* queue the work to convert unwritten extents to written */
    	queue_work(wq, &io_end->work);
    	iocb->private = NULL;
    
    	/* XXX: probably should move into the real I/O completion handler */
    	inode_dio_done(inode);
    }
    
    static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate)
    {
    	ext4_io_end_t *io_end = bh->b_private;
    	struct workqueue_struct *wq;
    	struct inode *inode;
    	unsigned long flags;
    
    	if (!test_clear_buffer_uninit(bh) || !io_end)
    		goto out;
    
    	if (!(io_end->inode->i_sb->s_flags & MS_ACTIVE)) {
    		printk("sb umounted, discard end_io request for inode %lu\n",
    			io_end->inode->i_ino);
    		ext4_free_io_end(io_end);
    		goto out;
    	}
    
    	/*
    	 * It may be over-defensive here to check EXT4_IO_END_UNWRITTEN now,
    	 * but being more careful is always safe for the future change.
    	 */
    	inode = io_end->inode;
    	if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
    		io_end->flag |= EXT4_IO_END_UNWRITTEN;
    		atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
    	}
    
    	/* Add the io_end to per-inode completed io list*/
    	spin_lock_irqsave(&EXT4_I(inode)->i_completed_io_lock, flags);
    	list_add_tail(&io_end->list, &EXT4_I(inode)->i_completed_io_list);
    	spin_unlock_irqrestore(&EXT4_I(inode)->i_completed_io_lock, flags);
    
    	wq = EXT4_SB(inode->i_sb)->dio_unwritten_wq;
    	/* queue the work to convert unwritten extents to written */
    	queue_work(wq, &io_end->work);
    out:
    	bh->b_private = NULL;
    	bh->b_end_io = NULL;
    	clear_buffer_uninit(bh);
    	end_buffer_async_write(bh, uptodate);
    }
    
    static int ext4_set_bh_endio(struct buffer_head *bh, struct inode *inode)
    {
    	ext4_io_end_t *io_end;
    	struct page *page = bh->b_page;
    	loff_t offset = (sector_t)page->index << PAGE_CACHE_SHIFT;
    	size_t size = bh->b_size;
    
    retry:
    	io_end = ext4_init_io_end(inode, GFP_ATOMIC);
    	if (!io_end) {
    		pr_warn_ratelimited("%s: allocation fail\n", __func__);
    		schedule();
    		goto retry;
    	}
    	io_end->offset = offset;
    	io_end->size = size;
    	/*
    	 * We need to hold a reference to the page to make sure it
    	 * doesn't get evicted before ext4_end_io_work() has a chance
    	 * to convert the extent from written to unwritten.
    	 */
    	io_end->page = page;
    	get_page(io_end->page);
    
    	bh->b_private = io_end;
    	bh->b_end_io = ext4_end_io_buffer_write;
    	return 0;
    }
    
    /*
     * For ext4 extent files, ext4 will do direct-io write to holes,
     * preallocated extents, and those write extend the file, no need to
     * fall back to buffered IO.
     *
     * For holes, we fallocate those blocks, mark them as uninitialized
     * If those blocks were preallocated, we mark sure they are splited, but
     * still keep the range to write as uninitialized.
     *
     * The unwrritten extents will be converted to written when DIO is completed.
     * For async direct IO, since the IO may still pending when return, we
     * set up an end_io call back function, which will do the conversion
     * when async direct IO completed.
     *
     * If the O_DIRECT write will extend the file then add this inode to the
     * orphan list.  So recovery will truncate it back to the original size
     * if the machine crashes during the write.
     *
     */
    static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
    			      const struct iovec *iov, loff_t offset,
    			      unsigned long nr_segs)
    {
    	struct file *file = iocb->ki_filp;
    	struct inode *inode = file->f_mapping->host;
    	ssize_t ret;
    	size_t count = iov_length(iov, nr_segs);
    
    	loff_t final_size = offset + count;
    	if (rw == WRITE && final_size <= inode->i_size) {
    		/*
     		 * We could direct write to holes and fallocate.
    		 *
     		 * Allocated blocks to fill the hole are marked as uninitialized
     		 * to prevent parallel buffered read to expose the stale data
     		 * before DIO complete the data IO.
    		 *
     		 * As to previously fallocated extents, ext4 get_block
     		 * will just simply mark the buffer mapped but still
     		 * keep the extents uninitialized.
     		 *
    		 * for non AIO case, we will convert those unwritten extents
    		 * to written after return back from blockdev_direct_IO.
    		 *
    		 * for async DIO, the conversion needs to be defered when
    		 * the IO is completed. The ext4 end_io callback function
    		 * will be called to take care of the conversion work.
    		 * Here for async case, we allocate an io_end structure to
    		 * hook to the iocb.
     		 */
    		iocb->private = NULL;
    		EXT4_I(inode)->cur_aio_dio = NULL;
    		if (!is_sync_kiocb(iocb)) {
    			iocb->private = ext4_init_io_end(inode, GFP_NOFS);
    			if (!iocb->private)
    				return -ENOMEM;
    			/*
    			 * we save the io structure for current async
    			 * direct IO, so that later ext4_map_blocks()
    			 * could flag the io structure whether there
    			 * is a unwritten extents needs to be converted
    			 * when IO is completed.
    			 */
    			EXT4_I(inode)->cur_aio_dio = iocb->private;
    		}
    
    		ret = __blockdev_direct_IO(rw, iocb, inode,
    					 inode->i_sb->s_bdev, iov,
    					 offset, nr_segs,
    					 ext4_get_block_write,
    					 ext4_end_io_dio,
    					 NULL,
    					 DIO_LOCKING | DIO_SKIP_HOLES);
    		if (iocb->private)
    			EXT4_I(inode)->cur_aio_dio = NULL;
    		/*
    		 * The io_end structure takes a reference to the inode,
    		 * that structure needs to be destroyed and the
    		 * reference to the inode need to be dropped, when IO is
    		 * complete, even with 0 byte write, or failed.
    		 *
    		 * In the successful AIO DIO case, the io_end structure will be
    		 * desctroyed and the reference to the inode will be dropped
    		 * after the end_io call back function is called.
    		 *
    		 * In the case there is 0 byte write, or error case, since
    		 * VFS direct IO won't invoke the end_io call back function,
    		 * we need to free the end_io structure here.
    		 */
    		if (ret != -EIOCBQUEUED && ret <= 0 && iocb->private) {
    			ext4_free_io_end(iocb->private);
    			iocb->private = NULL;
    		} else if (ret > 0 && ext4_test_inode_state(inode,
    						EXT4_STATE_DIO_UNWRITTEN)) {
    			int err;
    			/*
    			 * for non AIO case, since the IO is already
    			 * completed, we could do the conversion right here
    			 */
    			err = ext4_convert_unwritten_extents(inode,
    							     offset, ret);
    			if (err < 0)
    				ret = err;
    			ext4_clear_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
    		}
    		return ret;
    	}
    
    	/* for write the the end of file case, we fall back to old way */
    	return ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs);
    }
    
    static ssize_t ext4_direct_IO(int rw, struct kiocb *iocb,
    			      const struct iovec *iov, loff_t offset,
    			      unsigned long nr_segs)
    {
    	struct file *file = iocb->ki_filp;
    	struct inode *inode = file->f_mapping->host;
    	ssize_t ret;
    
    	/*
    	 * If we are doing data journalling we don't support O_DIRECT
    	 */
    	if (ext4_should_journal_data(inode))
    		return 0;
    
    	trace_ext4_direct_IO_enter(inode, offset, iov_length(iov, nr_segs), rw);
    	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
    		ret = ext4_ext_direct_IO(rw, iocb, iov, offset, nr_segs);
    	else
    		ret = ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs);
    	trace_ext4_direct_IO_exit(inode, offset,
    				iov_length(iov, nr_segs), rw, ret);
    	return ret;
    }
    
    /*
     * Pages can be marked dirty completely asynchronously from ext4's journalling
     * activity.  By filemap_sync_pte(), try_to_unmap_one(), etc.  We cannot do
     * much here because ->set_page_dirty is called under VFS locks.  The page is
     * not necessarily locked.
     *
     * We cannot just dirty the page and leave attached buffers clean, because the
     * buffers' dirty state is "definitive".  We cannot just set the buffers dirty
     * or jbddirty because all the journalling code will explode.
     *
     * So what we do is to mark the page "pending dirty" and next time writepage
     * is called, propagate that into the buffers appropriately.
     */
    static int ext4_journalled_set_page_dirty(struct page *page)
    {
    	SetPageChecked(page);
    	return __set_page_dirty_nobuffers(page);
    }
    
    static const struct address_space_operations ext4_ordered_aops = {
    	.readpage		= ext4_readpage,
    	.readpages		= ext4_readpages,
    	.writepage		= ext4_writepage,
    	.write_begin		= ext4_write_begin,
    	.write_end		= ext4_ordered_write_end,
    	.bmap			= ext4_bmap,
    	.invalidatepage		= ext4_invalidatepage,
    	.releasepage		= ext4_releasepage,
    	.direct_IO		= ext4_direct_IO,
    	.migratepage		= buffer_migrate_page,
    	.is_partially_uptodate  = block_is_partially_uptodate,
    	.error_remove_page	= generic_error_remove_page,
    };
    
    static const struct address_space_operations ext4_writeback_aops = {
    	.readpage		= ext4_readpage,
    	.readpages		= ext4_readpages,
    	.writepage		= ext4_writepage,
    	.write_begin		= ext4_write_begin,
    	.write_end		= ext4_writeback_write_end,
    	.bmap			= ext4_bmap,
    	.invalidatepage		= ext4_invalidatepage,
    	.releasepage		= ext4_releasepage,
    	.direct_IO		= ext4_direct_IO,
    	.migratepage		= buffer_migrate_page,
    	.is_partially_uptodate  = block_is_partially_uptodate,
    	.error_remove_page	= generic_error_remove_page,
    };
    
    static const struct address_space_operations ext4_journalled_aops = {
    	.readpage		= ext4_readpage,
    	.readpages		= ext4_readpages,
    	.writepage		= ext4_writepage,
    	.write_begin		= ext4_write_begin,
    	.write_end		= ext4_journalled_write_end,
    	.set_page_dirty		= ext4_journalled_set_page_dirty,
    	.bmap			= ext4_bmap,
    	.invalidatepage		= ext4_invalidatepage,
    	.releasepage		= ext4_releasepage,
    	.direct_IO		= ext4_direct_IO,
    	.is_partially_uptodate  = block_is_partially_uptodate,
    	.error_remove_page	= generic_error_remove_page,
    };
    
    static const struct address_space_operations ext4_da_aops = {
    	.readpage		= ext4_readpage,
    	.readpages		= ext4_readpages,
    	.writepage		= ext4_writepage,
    	.writepages		= ext4_da_writepages,
    	.write_begin		= ext4_da_write_begin,
    	.write_end		= ext4_da_write_end,
    	.bmap			= ext4_bmap,
    	.invalidatepage		= ext4_da_invalidatepage,
    	.releasepage		= ext4_releasepage,
    	.direct_IO		= ext4_direct_IO,
    	.migratepage		= buffer_migrate_page,
    	.is_partially_uptodate  = block_is_partially_uptodate,
    	.error_remove_page	= generic_error_remove_page,
    };
    
    void ext4_set_aops(struct inode *inode)
    {
    	if (ext4_should_order_data(inode) &&
    		test_opt(inode->i_sb, DELALLOC))
    		inode->i_mapping->a_ops = &ext4_da_aops;
    	else if (ext4_should_order_data(inode))
    		inode->i_mapping->a_ops = &ext4_ordered_aops;
    	else if (ext4_should_writeback_data(inode) &&
    		 test_opt(inode->i_sb, DELALLOC))
    		inode->i_mapping->a_ops = &ext4_da_aops;
    	else if (ext4_should_writeback_data(inode))
    		inode->i_mapping->a_ops = &ext4_writeback_aops;
    	else
    		inode->i_mapping->a_ops = &ext4_journalled_aops;
    }
    
    
    /*
     * ext4_discard_partial_page_buffers()
     * Wrapper function for ext4_discard_partial_page_buffers_no_lock.
     * This function finds and locks the page containing the offset
     * "from" and passes it to ext4_discard_partial_page_buffers_no_lock.
     * Calling functions that already have the page locked should call
     * ext4_discard_partial_page_buffers_no_lock directly.
     */
    int ext4_discard_partial_page_buffers(handle_t *handle,
    		struct address_space *mapping, loff_t from,
    		loff_t length, int flags)
    {
    	struct inode *inode = mapping->host;
    	struct page *page;
    	int err = 0;
    
    	page = find_or_create_page(mapping, from >> PAGE_CACHE_SHIFT,
    				   mapping_gfp_mask(mapping) & ~__GFP_FS);
    	if (!page)
    		return -EINVAL;
    
    	err = ext4_discard_partial_page_buffers_no_lock(handle, inode, page,
    		from, length, flags);
    
    	unlock_page(page);
    	page_cache_release(page);
    	return err;
    }
    
    /*
     * ext4_discard_partial_page_buffers_no_lock()
     * Zeros a page range of length 'length' starting from offset 'from'.
     * Buffer heads that correspond to the block aligned regions of the
     * zeroed range will be unmapped.  Unblock aligned regions
     * will have the corresponding buffer head mapped if needed so that
     * that region of the page can be updated with the partial zero out.
     *
     * This function assumes that the page has already been  locked.  The
     * The range to be discarded must be contained with in the given page.
     * If the specified range exceeds the end of the page it will be shortened
     * to the end of the page that corresponds to 'from'.  This function is
     * appropriate for updating a page and it buffer heads to be unmapped and
     * zeroed for blocks that have been either released, or are going to be
     * released.
     *
     * handle: The journal handle
     * inode:  The files inode
     * page:   A locked page that contains the offset "from"
     * from:   The starting byte offset (from the begining of the file)
     *         to begin discarding
     * len:    The length of bytes to discard
     * flags:  Optional flags that may be used:
     *
     *         EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED
     *         Only zero the regions of the page whose buffer heads
     *         have already been unmapped.  This flag is appropriate
     *         for updateing the contents of a page whose blocks may
     *         have already been released, and we only want to zero
     *         out the regions that correspond to those released blocks.
     *
     * Returns zero on sucess or negative on failure.
     */
    int ext4_discard_partial_page_buffers_no_lock(handle_t *handle,
    		struct inode *inode, struct page *page, loff_t from,
    		loff_t length, int flags)
    {
    	ext4_fsblk_t index = from >> PAGE_CACHE_SHIFT;
    	unsigned int offset = from & (PAGE_CACHE_SIZE-1);
    	unsigned int blocksize, max, pos;
    	unsigned int end_of_block, range_to_discard;
    	ext4_lblk_t iblock;
    	struct buffer_head *bh;
    	int err = 0;
    
    	blocksize = inode->i_sb->s_blocksize;
    	max = PAGE_CACHE_SIZE - offset;
    
    	if (index != page->index)
    		return -EINVAL;
    
    	/*
    	 * correct length if it does not fall between
    	 * 'from' and the end of the page
    	 */
    	if (length > max || length < 0)
    		length = max;
    
    	iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);
    
    	if (!page_has_buffers(page)) {
    		/*
    		 * If the range to be discarded covers a partial block
    		 * we need to get the page buffers.  This is because
    		 * partial blocks cannot be released and the page needs
    		 * to be updated with the contents of the block before
    		 * we write the zeros on top of it.
    		 */
    		if (!(from & (blocksize - 1)) ||
    		    !((from + length) & (blocksize - 1))) {
    			create_empty_buffers(page, blocksize, 0);
    		} else {
    			/*
    			 * If there are no partial blocks,
    			 * there is nothing to update,
    			 * so we can return now
    			 */
    			return 0;
    		}
    	}
    
    	/* Find the buffer that contains "offset" */
    	bh = page_buffers(page);
    	pos = blocksize;
    	while (offset >= pos) {
    		bh = bh->b_this_page;
    		iblock++;
    		pos += blocksize;
    	}
    
    	pos = offset;
    	while (pos < offset + length) {
    		err = 0;
    
    		/* The length of space left to zero and unmap */
    		range_to_discard = offset + length - pos;
    
    		/* The length of space until the end of the block */
    		end_of_block = blocksize - (pos & (blocksize-1));
    
    		/*
    		 * Do not unmap or zero past end of block
    		 * for this buffer head
    		 */
    		if (range_to_discard > end_of_block)
    			range_to_discard = end_of_block;
    
    
    		/*
    		 * Skip this buffer head if we are only zeroing unampped
    		 * regions of the page
    		 */
    		if (flags & EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED &&
    			buffer_mapped(bh))
    				goto next;
    
    		/* If the range is block aligned, unmap */
    		if (range_to_discard == blocksize) {
    			clear_buffer_dirty(bh);
    			bh->b_bdev = NULL;
    			clear_buffer_mapped(bh);
    			clear_buffer_req(bh);
    			clear_buffer_new(bh);
    			clear_buffer_delay(bh);
    			clear_buffer_unwritten(bh);
    			clear_buffer_uptodate(bh);
    			zero_user(page, pos, range_to_discard);
    			BUFFER_TRACE(bh, "Buffer discarded");
    			goto next;
    		}
    
    		/*
    		 * If this block is not completely contained in the range
    		 * to be discarded, then it is not going to be released. Because
    		 * we need to keep this block, we need to make sure this part
    		 * of the page is uptodate before we modify it by writeing
    		 * partial zeros on it.
    		 */
    		if (!buffer_mapped(bh)) {
    			/*
    			 * Buffer head must be mapped before we can read
    			 * from the block
    			 */
    			BUFFER_TRACE(bh, "unmapped");
    			ext4_get_block(inode, iblock, bh, 0);
    			/* unmapped? It's a hole - nothing to do */
    			if (!buffer_mapped(bh)) {
    				BUFFER_TRACE(bh, "still unmapped");
    				goto next;
    			}
    		}
    
    		/* Ok, it's mapped. Make sure it's up-to-date */
    		if (PageUptodate(page))
    			set_buffer_uptodate(bh);
    
    		if (!buffer_uptodate(bh)) {
    			err = -EIO;
    			ll_rw_block(READ, 1, &bh);
    			wait_on_buffer(bh);
    			/* Uhhuh. Read error. Complain and punt.*/
    			if (!buffer_uptodate(bh))
    				goto next;
    		}
    
    		if (ext4_should_journal_data(inode)) {
    			BUFFER_TRACE(bh, "get write access");
    			err = ext4_journal_get_write_access(handle, bh);
    			if (err)
    				goto next;
    		}
    
    		zero_user(page, pos, range_to_discard);
    
    		err = 0;
    		if (ext4_should_journal_data(inode)) {
    			err = ext4_handle_dirty_metadata(handle, inode, bh);
    		} else
    			mark_buffer_dirty(bh);
    
    		BUFFER_TRACE(bh, "Partial buffer zeroed");
    next:
    		bh = bh->b_this_page;
    		iblock++;
    		pos += range_to_discard;
    	}
    
    	return err;
    }
    
    /*
     * ext4_block_truncate_page() zeroes out a mapping from file offset `from'
     * up to the end of the block which corresponds to `from'.
     * This required during truncate. We need to physically zero the tail end
     * of that block so it doesn't yield old data if the file is later grown.
     */
    int ext4_block_truncate_page(handle_t *handle,
    		struct address_space *mapping, loff_t from)
    {
    	unsigned offset = from & (PAGE_CACHE_SIZE-1);
    	unsigned length;
    	unsigned blocksize;
    	struct inode *inode = mapping->host;
    
    	blocksize = inode->i_sb->s_blocksize;
    	length = blocksize - (offset & (blocksize - 1));
    
    	return ext4_block_zero_page_range(handle, mapping, from, length);
    }
    
    /*
     * ext4_block_zero_page_range() zeros out a mapping of length 'length'
     * starting from file offset 'from'.  The range to be zero'd must
     * be contained with in one block.  If the specified range exceeds
     * the end of the block it will be shortened to end of the block
     * that cooresponds to 'from'
     */
    int ext4_block_zero_page_range(handle_t *handle,
    		struct address_space *mapping, loff_t from, loff_t length)
    {
    	ext4_fsblk_t index = from >> PAGE_CACHE_SHIFT;
    	unsigned offset = from & (PAGE_CACHE_SIZE-1);
    	unsigned blocksize, max, pos;
    	ext4_lblk_t iblock;
    	struct inode *inode = mapping->host;
    	struct buffer_head *bh;
    	struct page *page;
    	int err = 0;
    
    	page = find_or_create_page(mapping, from >> PAGE_CACHE_SHIFT,
    				   mapping_gfp_mask(mapping) & ~__GFP_FS);
    	if (!page)
    		return -EINVAL;
    
    	blocksize = inode->i_sb->s_blocksize;
    	max = blocksize - (offset & (blocksize - 1));
    
    	/*
    	 * correct length if it does not fall between
    	 * 'from' and the end of the block
    	 */
    	if (length > max || length < 0)
    		length = max;
    
    	iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);
    
    	if (!page_has_buffers(page))
    		create_empty_buffers(page, blocksize, 0);
    
    	/* Find the buffer that contains "offset" */
    	bh = page_buffers(page);
    	pos = blocksize;
    	while (offset >= pos) {
    		bh = bh->b_this_page;
    		iblock++;
    		pos += blocksize;
    	}
    
    	err = 0;
    	if (buffer_freed(bh)) {
    		BUFFER_TRACE(bh, "freed: skip");
    		goto unlock;
    	}
    
    	if (!buffer_mapped(bh)) {
    		BUFFER_TRACE(bh, "unmapped");
    		ext4_get_block(inode, iblock, bh, 0);
    		/* unmapped? It's a hole - nothing to do */
    		if (!buffer_mapped(bh)) {
    			BUFFER_TRACE(bh, "still unmapped");
    			goto unlock;
    		}
    	}
    
    	/* Ok, it's mapped. Make sure it's up-to-date */
    	if (PageUptodate(page))
    		set_buffer_uptodate(bh);
    
    	if (!buffer_uptodate(bh)) {
    		err = -EIO;
    		ll_rw_block(READ, 1, &bh);
    		wait_on_buffer(bh);
    		/* Uhhuh. Read error. Complain and punt. */
    		if (!buffer_uptodate(bh))
    			goto unlock;
    	}
    
    	if (ext4_should_journal_data(inode)) {
    		BUFFER_TRACE(bh, "get write access");
    		err = ext4_journal_get_write_access(handle, bh);
    		if (err)
    			goto unlock;
    	}
    
    	zero_user(page, offset, length);
    
    	BUFFER_TRACE(bh, "zeroed end of block");
    
    	err = 0;
    	if (ext4_should_journal_data(inode)) {
    		err = ext4_handle_dirty_metadata(handle, inode, bh);
    	} else
    		mark_buffer_dirty(bh);
    
    unlock:
    	unlock_page(page);
    	page_cache_release(page);
    	return err;
    }
    
    int ext4_can_truncate(struct inode *inode)
    {
    	if (S_ISREG(inode->i_mode))
    		return 1;
    	if (S_ISDIR(inode->i_mode))
    		return 1;
    	if (S_ISLNK(inode->i_mode))
    		return !ext4_inode_is_fast_symlink(inode);
    	return 0;
    }
    
    /*
     * ext4_punch_hole: punches a hole in a file by releaseing the blocks
     * associated with the given offset and length
     *
     * @inode:  File inode
     * @offset: The offset where the hole will begin
     * @len:    The length of the hole
     *
     * Returns: 0 on sucess or negative on failure
     */
    
    int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
    {
    	struct inode *inode = file->f_path.dentry->d_inode;
    	if (!S_ISREG(inode->i_mode))
    		return -ENOTSUPP;
    
    	if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
    		/* TODO: Add support for non extent hole punching */
    		return -ENOTSUPP;
    	}
    
    	if (EXT4_SB(inode->i_sb)->s_cluster_ratio > 1) {
    		/* TODO: Add support for bigalloc file systems */
    		return -ENOTSUPP;
    	}
    
    	return ext4_ext_punch_hole(file, offset, length);
    }
    
    /*
     * ext4_truncate()
     *
     * We block out ext4_get_block() block instantiations across the entire
     * transaction, and VFS/VM ensures that ext4_truncate() cannot run
     * simultaneously on behalf of the same inode.
     *
     * As we work through the truncate and commmit bits of it to the journal there
     * is one core, guiding principle: the file's tree must always be consistent on
     * disk.  We must be able to restart the truncate after a crash.
     *
     * The file's tree may be transiently inconsistent in memory (although it
     * probably isn't), but whenever we close off and commit a journal transaction,
     * the contents of (the filesystem + the journal) must be consistent and
     * restartable.  It's pretty simple, really: bottom up, right to left (although
     * left-to-right works OK too).
     *
     * Note that at recovery time, journal replay occurs *before* the restart of
     * truncate against the orphan inode list.
     *
     * The committed inode has the new, desired i_size (which is the same as
     * i_disksize in this case).  After a crash, ext4_orphan_cleanup() will see
     * that this inode's truncate did not complete and it will again call
     * ext4_truncate() to have another go.  So there will be instantiated blocks
     * to the right of the truncation point in a crashed ext4 filesystem.  But
     * that's fine - as long as they are linked from the inode, the post-crash
     * ext4_truncate() run will find them and release them.
     */
    void ext4_truncate(struct inode *inode)
    {
    	trace_ext4_truncate_enter(inode);
    
    	if (!ext4_can_truncate(inode))
    		return;
    
    	ext4_clear_inode_flag(inode, EXT4_INODE_EOFBLOCKS);
    
    	if (inode->i_size == 0 && !test_opt(inode->i_sb, NO_AUTO_DA_ALLOC))
    		ext4_set_inode_state(inode, EXT4_STATE_DA_ALLOC_CLOSE);
    
    	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
    		ext4_ext_truncate(inode);
    	else
    		ext4_ind_truncate(inode);
    
    	trace_ext4_truncate_exit(inode);
    }
    
    /*
     * ext4_get_inode_loc returns with an extra refcount against the inode's
     * underlying buffer_head on success. If 'in_mem' is true, we have all
     * data in memory that is needed to recreate the on-disk version of this
     * inode.
     */
    static int __ext4_get_inode_loc(struct inode *inode,
    				struct ext4_iloc *iloc, int in_mem)
    {
    	struct ext4_group_desc	*gdp;
    	struct buffer_head	*bh;
    	struct super_block	*sb = inode->i_sb;
    	ext4_fsblk_t		block;
    	int			inodes_per_block, inode_offset;
    
    	iloc->bh = NULL;
    	if (!ext4_valid_inum(sb, inode->i_ino))
    		return -EIO;
    
    	iloc->block_group = (inode->i_ino - 1) / EXT4_INODES_PER_GROUP(sb);
    	gdp = ext4_get_group_desc(sb, iloc->block_group, NULL);
    	if (!gdp)
    		return -EIO;
    
    	/*
    	 * Figure out the offset within the block group inode table
    	 */
    	inodes_per_block = EXT4_SB(sb)->s_inodes_per_block;
    	inode_offset = ((inode->i_ino - 1) %
    			EXT4_INODES_PER_GROUP(sb));
    	block = ext4_inode_table(sb, gdp) + (inode_offset / inodes_per_block);
    	iloc->offset = (inode_offset % inodes_per_block) * EXT4_INODE_SIZE(sb);
    
    	bh = sb_getblk(sb, block);
    	if (!bh) {
    		EXT4_ERROR_INODE_BLOCK(inode, block,
    				       "unable to read itable block");
    		return -EIO;
    	}
    	if (!buffer_uptodate(bh)) {
    		lock_buffer(bh);
    
    		/*
    		 * If the buffer has the write error flag, we have failed
    		 * to write out another inode in the same block.  In this
    		 * case, we don't have to read the block because we may
    		 * read the old inode data successfully.
    		 */
    		if (buffer_write_io_error(bh) && !buffer_uptodate(bh))
    			set_buffer_uptodate(bh);
    
    		if (buffer_uptodate(bh)) {
    			/* someone brought it uptodate while we waited */
    			unlock_buffer(bh);
    			goto has_buffer;
    		}
    
    		/*
    		 * If we have all information of the inode in memory and this
    		 * is the only valid inode in the block, we need not read the
    		 * block.
    		 */
    		if (in_mem) {
    			struct buffer_head *bitmap_bh;
    			int i, start;
    
    			start = inode_offset & ~(inodes_per_block - 1);
    
    			/* Is the inode bitmap in cache? */
    			bitmap_bh = sb_getblk(sb, ext4_inode_bitmap(sb, gdp));
    			if (!bitmap_bh)
    				goto make_io;
    
    			/*
    			 * If the inode bitmap isn't in cache then the
    			 * optimisation may end up performing two reads instead
    			 * of one, so skip it.
    			 */
    			if (!buffer_uptodate(bitmap_bh)) {
    				brelse(bitmap_bh);
    				goto make_io;
    			}
    			for (i = start; i < start + inodes_per_block; i++) {
    				if (i == inode_offset)
    					continue;
    				if (ext4_test_bit(i, bitmap_bh->b_data))
    					break;
    			}
    			brelse(bitmap_bh);
    			if (i == start + inodes_per_block) {
    				/* all other inodes are free, so skip I/O */
    				memset(bh->b_data, 0, bh->b_size);
    				set_buffer_uptodate(bh);
    				unlock_buffer(bh);
    				goto has_buffer;
    			}
    		}
    
    make_io:
    		/*
    		 * If we need to do any I/O, try to pre-readahead extra
    		 * blocks from the inode table.
    		 */
    		if (EXT4_SB(sb)->s_inode_readahead_blks) {
    			ext4_fsblk_t b, end, table;
    			unsigned num;
    
    			table = ext4_inode_table(sb, gdp);
    			/* s_inode_readahead_blks is always a power of 2 */
    			b = block & ~(EXT4_SB(sb)->s_inode_readahead_blks-1);
    			if (table > b)
    				b = table;
    			end = b + EXT4_SB(sb)->s_inode_readahead_blks;
    			num = EXT4_INODES_PER_GROUP(sb);
    			if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
    				       EXT4_FEATURE_RO_COMPAT_GDT_CSUM))
    				num -= ext4_itable_unused_count(sb, gdp);
    			table += num / inodes_per_block;
    			if (end > table)
    				end = table;
    			while (b <= end)
    				sb_breadahead(sb, b++);
    		}
    
    		/*
    		 * There are other valid inodes in the buffer, this inode
    		 * has in-inode xattrs, or we don't have this inode in memory.
    		 * Read the block from disk.
    		 */
    		trace_ext4_load_inode(inode);
    		get_bh(bh);
    		bh->b_end_io = end_buffer_read_sync;
    		submit_bh(READ_META, bh);
    		wait_on_buffer(bh);
    		if (!buffer_uptodate(bh)) {
    			EXT4_ERROR_INODE_BLOCK(inode, block,
    					       "unable to read itable block");
    			brelse(bh);
    			return -EIO;
    		}
    	}
    has_buffer:
    	iloc->bh = bh;
    	return 0;
    }
    
    int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc)
    {
    	/* We have all inode data except xattrs in memory here. */
    	return __ext4_get_inode_loc(inode, iloc,
    		!ext4_test_inode_state(inode, EXT4_STATE_XATTR));
    }
    
    void ext4_set_inode_flags(struct inode *inode)
    {
    	unsigned int flags = EXT4_I(inode)->i_flags;
    
    	inode->i_flags &= ~(S_SYNC|S_APPEND|S_IMMUTABLE|S_NOATIME|S_DIRSYNC);
    	if (flags & EXT4_SYNC_FL)
    		inode->i_flags |= S_SYNC;
    	if (flags & EXT4_APPEND_FL)
    		inode->i_flags |= S_APPEND;
    	if (flags & EXT4_IMMUTABLE_FL)
    		inode->i_flags |= S_IMMUTABLE;
    	if (flags & EXT4_NOATIME_FL)
    		inode->i_flags |= S_NOATIME;
    	if (flags & EXT4_DIRSYNC_FL)
    		inode->i_flags |= S_DIRSYNC;
    }
    
    /* Propagate flags from i_flags to EXT4_I(inode)->i_flags */
    void ext4_get_inode_flags(struct ext4_inode_info *ei)
    {
    	unsigned int vfs_fl;
    	unsigned long old_fl, new_fl;
    
    	do {
    		vfs_fl = ei->vfs_inode.i_flags;
    		old_fl = ei->i_flags;
    		new_fl = old_fl & ~(EXT4_SYNC_FL|EXT4_APPEND_FL|
    				EXT4_IMMUTABLE_FL|EXT4_NOATIME_FL|
    				EXT4_DIRSYNC_FL);
    		if (vfs_fl & S_SYNC)
    			new_fl |= EXT4_SYNC_FL;
    		if (vfs_fl & S_APPEND)
    			new_fl |= EXT4_APPEND_FL;
    		if (vfs_fl & S_IMMUTABLE)
    			new_fl |= EXT4_IMMUTABLE_FL;
    		if (vfs_fl & S_NOATIME)
    			new_fl |= EXT4_NOATIME_FL;
    		if (vfs_fl & S_DIRSYNC)
    			new_fl |= EXT4_DIRSYNC_FL;
    	} while (cmpxchg(&ei->i_flags, old_fl, new_fl) != old_fl);
    }
    
    static blkcnt_t ext4_inode_blocks(struct ext4_inode *raw_inode,
    				  struct ext4_inode_info *ei)
    {
    	blkcnt_t i_blocks ;
    	struct inode *inode = &(ei->vfs_inode);
    	struct super_block *sb = inode->i_sb;
    
    	if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
    				EXT4_FEATURE_RO_COMPAT_HUGE_FILE)) {
    		/* we are using combined 48 bit field */
    		i_blocks = ((u64)le16_to_cpu(raw_inode->i_blocks_high)) << 32 |
    					le32_to_cpu(raw_inode->i_blocks_lo);
    		if (ext4_test_inode_flag(inode, EXT4_INODE_HUGE_FILE)) {
    			/* i_blocks represent file system block size */
    			return i_blocks  << (inode->i_blkbits - 9);
    		} else {
    			return i_blocks;
    		}
    	} else {
    		return le32_to_cpu(raw_inode->i_blocks_lo);
    	}
    }
    
    struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
    {
    	struct ext4_iloc iloc;
    	struct ext4_inode *raw_inode;
    	struct ext4_inode_info *ei;
    	struct inode *inode;
    	journal_t *journal = EXT4_SB(sb)->s_journal;
    	long ret;
    	int block;
    
    	inode = iget_locked(sb, ino);
    	if (!inode)
    		return ERR_PTR(-ENOMEM);
    	if (!(inode->i_state & I_NEW))
    		return inode;
    
    	ei = EXT4_I(inode);
    	iloc.bh = NULL;
    
    	ret = __ext4_get_inode_loc(inode, &iloc, 0);
    	if (ret < 0)
    		goto bad_inode;
    	raw_inode = ext4_raw_inode(&iloc);
    	inode->i_mode = le16_to_cpu(raw_inode->i_mode);
    	inode->i_uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low);
    	inode->i_gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);
    	if (!(test_opt(inode->i_sb, NO_UID32))) {
    		inode->i_uid |= le16_to_cpu(raw_inode->i_uid_high) << 16;
    		inode->i_gid |= le16_to_cpu(raw_inode->i_gid_high) << 16;
    	}
    	inode->i_nlink = le16_to_cpu(raw_inode->i_links_count);
    
    	ext4_clear_state_flags(ei);	/* Only relevant on 32-bit archs */
    	ei->i_dir_start_lookup = 0;
    	ei->i_dtime = le32_to_cpu(raw_inode->i_dtime);
    	/* We now have enough fields to check if the inode was active or not.
    	 * This is needed because nfsd might try to access dead inodes
    	 * the test is that same one that e2fsck uses
    	 * NeilBrown 1999oct15
    	 */
    	if (inode->i_nlink == 0) {
    		if (inode->i_mode == 0 ||
    		    !(EXT4_SB(inode->i_sb)->s_mount_state & EXT4_ORPHAN_FS)) {
    			/* this inode is deleted */
    			ret = -ESTALE;
    			goto bad_inode;
    		}
    		/* The only unlinked inodes we let through here have
    		 * valid i_mode and are being read by the orphan
    		 * recovery code: that's fine, we're about to complete
    		 * the process of deleting those. */
    	}
    	ei->i_flags = le32_to_cpu(raw_inode->i_flags);
    	inode->i_blocks = ext4_inode_blocks(raw_inode, ei);
    	ei->i_file_acl = le32_to_cpu(raw_inode->i_file_acl_lo);
    	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_64BIT))
    		ei->i_file_acl |=
    			((__u64)le16_to_cpu(raw_inode->i_file_acl_high)) << 32;
    	inode->i_size = ext4_isize(raw_inode);
    	ei->i_disksize = inode->i_size;
    #ifdef CONFIG_QUOTA
    	ei->i_reserved_quota = 0;
    #endif
    	inode->i_generation = le32_to_cpu(raw_inode->i_generation);
    	ei->i_block_group = iloc.block_group;
    	ei->i_last_alloc_group = ~0;
    	/*
    	 * NOTE! The in-memory inode i_data array is in little-endian order
    	 * even on big-endian machines: we do NOT byteswap the block numbers!
    	 */
    	for (block = 0; block < EXT4_N_BLOCKS; block++)
    		ei->i_data[block] = raw_inode->i_block[block];
    	INIT_LIST_HEAD(&ei->i_orphan);
    
    	/*
    	 * Set transaction id's of transactions that have to be committed
    	 * to finish f[data]sync. We set them to currently running transaction
    	 * as we cannot be sure that the inode or some of its metadata isn't
    	 * part of the transaction - the inode could have been reclaimed and
    	 * now it is reread from disk.
    	 */
    	if (journal) {
    		transaction_t *transaction;
    		tid_t tid;
    
    		read_lock(&journal->j_state_lock);
    		if (journal->j_running_transaction)
    			transaction = journal->j_running_transaction;
    		else
    			transaction = journal->j_committing_transaction;
    		if (transaction)
    			tid = transaction->t_tid;
    		else
    			tid = journal->j_commit_sequence;
    		read_unlock(&journal->j_state_lock);
    		ei->i_sync_tid = tid;
    		ei->i_datasync_tid = tid;
    	}
    
    	if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
    		ei->i_extra_isize = le16_to_cpu(raw_inode->i_extra_isize);
    		if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize >
    		    EXT4_INODE_SIZE(inode->i_sb)) {
    			ret = -EIO;
    			goto bad_inode;
    		}
    		if (ei->i_extra_isize == 0) {
    			/* The extra space is currently unused. Use it. */
    			ei->i_extra_isize = sizeof(struct ext4_inode) -
    					    EXT4_GOOD_OLD_INODE_SIZE;
    		} else {
    			__le32 *magic = (void *)raw_inode +
    					EXT4_GOOD_OLD_INODE_SIZE +
    					ei->i_extra_isize;
    			if (*magic == cpu_to_le32(EXT4_XATTR_MAGIC))
    				ext4_set_inode_state(inode, EXT4_STATE_XATTR);
    		}
    	} else
    		ei->i_extra_isize = 0;
    
    	EXT4_INODE_GET_XTIME(i_ctime, inode, raw_inode);
    	EXT4_INODE_GET_XTIME(i_mtime, inode, raw_inode);
    	EXT4_INODE_GET_XTIME(i_atime, inode, raw_inode);
    	EXT4_EINODE_GET_XTIME(i_crtime, ei, raw_inode);
    
    	inode->i_version = le32_to_cpu(raw_inode->i_disk_version);
    	if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
    		if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
    			inode->i_version |=
    			(__u64)(le32_to_cpu(raw_inode->i_version_hi)) << 32;
    	}
    
    	ret = 0;
    	if (ei->i_file_acl &&
    	    !ext4_data_block_valid(EXT4_SB(sb), ei->i_file_acl, 1)) {
    		EXT4_ERROR_INODE(inode, "bad extended attribute block %llu",
    				 ei->i_file_acl);
    		ret = -EIO;
    		goto bad_inode;
    	} else if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
    		if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
    		    (S_ISLNK(inode->i_mode) &&
    		     !ext4_inode_is_fast_symlink(inode)))
    			/* Validate extent which is part of inode */
    			ret = ext4_ext_check_inode(inode);
    	} else if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
    		   (S_ISLNK(inode->i_mode) &&
    		    !ext4_inode_is_fast_symlink(inode))) {
    		/* Validate block references which are part of inode */
    		ret = ext4_ind_check_inode(inode);
    	}
    	if (ret)
    		goto bad_inode;
    
    	if (S_ISREG(inode->i_mode)) {
    		inode->i_op = &ext4_file_inode_operations;
    		inode->i_fop = &ext4_file_operations;
    		ext4_set_aops(inode);
    	} else if (S_ISDIR(inode->i_mode)) {
    		inode->i_op = &ext4_dir_inode_operations;
    		inode->i_fop = &ext4_dir_operations;
    	} else if (S_ISLNK(inode->i_mode)) {
    		if (ext4_inode_is_fast_symlink(inode)) {
    			inode->i_op = &ext4_fast_symlink_inode_operations;
    			nd_terminate_link(ei->i_data, inode->i_size,
    				sizeof(ei->i_data) - 1);
    		} else {
    			inode->i_op = &ext4_symlink_inode_operations;
    			ext4_set_aops(inode);
    		}
    	} else if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode) ||
    	      S_ISFIFO(inode->i_mode) || S_ISSOCK(inode->i_mode)) {
    		inode->i_op = &ext4_special_inode_operations;
    		if (raw_inode->i_block[0])
    			init_special_inode(inode, inode->i_mode,
    			   old_decode_dev(le32_to_cpu(raw_inode->i_block[0])));
    		else
    			init_special_inode(inode, inode->i_mode,
    			   new_decode_dev(le32_to_cpu(raw_inode->i_block[1])));
    	} else {
    		ret = -EIO;
    		EXT4_ERROR_INODE(inode, "bogus i_mode (%o)", inode->i_mode);
    		goto bad_inode;
    	}
    	brelse(iloc.bh);
    	ext4_set_inode_flags(inode);
    	unlock_new_inode(inode);
    	return inode;
    
    bad_inode:
    	brelse(iloc.bh);
    	iget_failed(inode);
    	return ERR_PTR(ret);
    }
    
    static int ext4_inode_blocks_set(handle_t *handle,
    				struct ext4_inode *raw_inode,
    				struct ext4_inode_info *ei)
    {
    	struct inode *inode = &(ei->vfs_inode);
    	u64 i_blocks = inode->i_blocks;
    	struct super_block *sb = inode->i_sb;
    
    	if (i_blocks <= ~0U) {
    		/*
    		 * i_blocks can be represnted in a 32 bit variable
    		 * as multiple of 512 bytes
    		 */
    		raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
    		raw_inode->i_blocks_high = 0;
    		ext4_clear_inode_flag(inode, EXT4_INODE_HUGE_FILE);
    		return 0;
    	}
    	if (!EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_HUGE_FILE))
    		return -EFBIG;
    
    	if (i_blocks <= 0xffffffffffffULL) {
    		/*
    		 * i_blocks can be represented in a 48 bit variable
    		 * as multiple of 512 bytes
    		 */
    		raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
    		raw_inode->i_blocks_high = cpu_to_le16(i_blocks >> 32);
    		ext4_clear_inode_flag(inode, EXT4_INODE_HUGE_FILE);
    	} else {
    		ext4_set_inode_flag(inode, EXT4_INODE_HUGE_FILE);
    		/* i_block is stored in file system block size */
    		i_blocks = i_blocks >> (inode->i_blkbits - 9);
    		raw_inode->i_blocks_lo   = cpu_to_le32(i_blocks);
    		raw_inode->i_blocks_high = cpu_to_le16(i_blocks >> 32);
    	}
    	return 0;
    }
    
    /*
     * Post the struct inode info into an on-disk inode location in the
     * buffer-cache.  This gobbles the caller's reference to the
     * buffer_head in the inode location struct.
     *
     * The caller must have write access to iloc->bh.
     */
    static int ext4_do_update_inode(handle_t *handle,
    				struct inode *inode,
    				struct ext4_iloc *iloc)
    {
    	struct ext4_inode *raw_inode = ext4_raw_inode(iloc);
    	struct ext4_inode_info *ei = EXT4_I(inode);
    	struct buffer_head *bh = iloc->bh;
    	int err = 0, rc, block;
    
    	/* For fields not not tracking in the in-memory inode,
    	 * initialise them to zero for new inodes. */
    	if (ext4_test_inode_state(inode, EXT4_STATE_NEW))
    		memset(raw_inode, 0, EXT4_SB(inode->i_sb)->s_inode_size);
    
    	ext4_get_inode_flags(ei);
    	raw_inode->i_mode = cpu_to_le16(inode->i_mode);
    	if (!(test_opt(inode->i_sb, NO_UID32))) {
    		raw_inode->i_uid_low = cpu_to_le16(low_16_bits(inode->i_uid));
    		raw_inode->i_gid_low = cpu_to_le16(low_16_bits(inode->i_gid));
    /*
     * Fix up interoperability with old kernels. Otherwise, old inodes get
     * re-used with the upper 16 bits of the uid/gid intact
     */
    		if (!ei->i_dtime) {
    			raw_inode->i_uid_high =
    				cpu_to_le16(high_16_bits(inode->i_uid));
    			raw_inode->i_gid_high =
    				cpu_to_le16(high_16_bits(inode->i_gid));
    		} else {
    			raw_inode->i_uid_high = 0;
    			raw_inode->i_gid_high = 0;
    		}
    	} else {
    		raw_inode->i_uid_low =
    			cpu_to_le16(fs_high2lowuid(inode->i_uid));
    		raw_inode->i_gid_low =
    			cpu_to_le16(fs_high2lowgid(inode->i_gid));
    		raw_inode->i_uid_high = 0;
    		raw_inode->i_gid_high = 0;
    	}
    	raw_inode->i_links_count = cpu_to_le16(inode->i_nlink);
    
    	EXT4_INODE_SET_XTIME(i_ctime, inode, raw_inode);
    	EXT4_INODE_SET_XTIME(i_mtime, inode, raw_inode);
    	EXT4_INODE_SET_XTIME(i_atime, inode, raw_inode);
    	EXT4_EINODE_SET_XTIME(i_crtime, ei, raw_inode);
    
    	if (ext4_inode_blocks_set(handle, raw_inode, ei))
    		goto out_brelse;
    	raw_inode->i_dtime = cpu_to_le32(ei->i_dtime);
    	raw_inode->i_flags = cpu_to_le32(ei->i_flags & 0xFFFFFFFF);
    	if (EXT4_SB(inode->i_sb)->s_es->s_creator_os !=
    	    cpu_to_le32(EXT4_OS_HURD))
    		raw_inode->i_file_acl_high =
    			cpu_to_le16(ei->i_file_acl >> 32);
    	raw_inode->i_file_acl_lo = cpu_to_le32(ei->i_file_acl);
    	ext4_isize_set(raw_inode, ei->i_disksize);
    	if (ei->i_disksize > 0x7fffffffULL) {
    		struct super_block *sb = inode->i_sb;
    		if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
    				EXT4_FEATURE_RO_COMPAT_LARGE_FILE) ||
    				EXT4_SB(sb)->s_es->s_rev_level ==
    				cpu_to_le32(EXT4_GOOD_OLD_REV)) {
    			/* If this is the first large file
    			 * created, add a flag to the superblock.
    			 */
    			err = ext4_journal_get_write_access(handle,
    					EXT4_SB(sb)->s_sbh);
    			if (err)
    				goto out_brelse;
    			ext4_update_dynamic_rev(sb);
    			EXT4_SET_RO_COMPAT_FEATURE(sb,
    					EXT4_FEATURE_RO_COMPAT_LARGE_FILE);
    			sb->s_dirt = 1;
    			ext4_handle_sync(handle);
    			err = ext4_handle_dirty_metadata(handle, NULL,
    					EXT4_SB(sb)->s_sbh);
    		}
    	}
    	raw_inode->i_generation = cpu_to_le32(inode->i_generation);
    	if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode)) {
    		if (old_valid_dev(inode->i_rdev)) {
    			raw_inode->i_block[0] =
    				cpu_to_le32(old_encode_dev(inode->i_rdev));
    			raw_inode->i_block[1] = 0;
    		} else {
    			raw_inode->i_block[0] = 0;
    			raw_inode->i_block[1] =
    				cpu_to_le32(new_encode_dev(inode->i_rdev));
    			raw_inode->i_block[2] = 0;
    		}
    	} else
    		for (block = 0; block < EXT4_N_BLOCKS; block++)
    			raw_inode->i_block[block] = ei->i_data[block];
    
    	raw_inode->i_disk_version = cpu_to_le32(inode->i_version);
    	if (ei->i_extra_isize) {
    		if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
    			raw_inode->i_version_hi =
    			cpu_to_le32(inode->i_version >> 32);
    		raw_inode->i_extra_isize = cpu_to_le16(ei->i_extra_isize);
    	}
    
    	BUFFER_TRACE(bh, "call ext4_handle_dirty_metadata");
    	rc = ext4_handle_dirty_metadata(handle, NULL, bh);
    	if (!err)
    		err = rc;
    	ext4_clear_inode_state(inode, EXT4_STATE_NEW);
    
    	ext4_update_inode_fsync_trans(handle, inode, 0);
    out_brelse:
    	brelse(bh);
    	ext4_std_error(inode->i_sb, err);
    	return err;
    }
    
    /*
     * ext4_write_inode()
     *
     * We are called from a few places:
     *
     * - Within generic_file_write() for O_SYNC files.
     *   Here, there will be no transaction running. We wait for any running
     *   trasnaction to commit.
     *
     * - Within sys_sync(), kupdate and such.
     *   We wait on commit, if tol to.
     *
     * - Within prune_icache() (PF_MEMALLOC == true)
     *   Here we simply return.  We can't afford to block kswapd on the
     *   journal commit.
     *
     * In all cases it is actually safe for us to return without doing anything,
     * because the inode has been copied into a raw inode buffer in
     * ext4_mark_inode_dirty().  This is a correctness thing for O_SYNC and for
     * knfsd.
     *
     * Note that we are absolutely dependent upon all inode dirtiers doing the
     * right thing: they *must* call mark_inode_dirty() after dirtying info in
     * which we are interested.
     *
     * It would be a bug for them to not do this.  The code:
     *
     *	mark_inode_dirty(inode)
     *	stuff();
     *	inode->i_size = expr;
     *
     * is in error because a kswapd-driven write_inode() could occur while
     * `stuff()' is running, and the new i_size will be lost.  Plus the inode
     * will no longer be on the superblock's dirty inode list.
     */
    int ext4_write_inode(struct inode *inode, struct writeback_control *wbc)
    {
    	int err;
    
    	if (current->flags & PF_MEMALLOC)
    		return 0;
    
    	if (EXT4_SB(inode->i_sb)->s_journal) {
    		if (ext4_journal_current_handle()) {
    			jbd_debug(1, "called recursively, non-PF_MEMALLOC!\n");
    			dump_stack();
    			return -EIO;
    		}
    
    		if (wbc->sync_mode != WB_SYNC_ALL)
    			return 0;
    
    		err = ext4_force_commit(inode->i_sb);
    	} else {
    		struct ext4_iloc iloc;
    
    		err = __ext4_get_inode_loc(inode, &iloc, 0);
    		if (err)
    			return err;
    		if (wbc->sync_mode == WB_SYNC_ALL)
    			sync_dirty_buffer(iloc.bh);
    		if (buffer_req(iloc.bh) && !buffer_uptodate(iloc.bh)) {
    			EXT4_ERROR_INODE_BLOCK(inode, iloc.bh->b_blocknr,
    					 "IO error syncing inode");
    			err = -EIO;
    		}
    		brelse(iloc.bh);
    	}
    	return err;
    }
    
    /*
     * ext4_setattr()
     *
     * Called from notify_change.
     *
     * We want to trap VFS attempts to truncate the file as soon as
     * possible.  In particular, we want to make sure that when the VFS
     * shrinks i_size, we put the inode on the orphan list and modify
     * i_disksize immediately, so that during the subsequent flushing of
     * dirty pages and freeing of disk blocks, we can guarantee that any
     * commit will leave the blocks being flushed in an unused state on
     * disk.  (On recovery, the inode will get truncated and the blocks will
     * be freed, so we have a strong guarantee that no future commit will
     * leave these blocks visible to the user.)
     *
     * Another thing we have to assure is that if we are in ordered mode
     * and inode is still attached to the committing transaction, we must
     * we start writeout of all the dirty pages which are being truncated.
     * This way we are sure that all the data written in the previous
     * transaction are already on disk (truncate waits for pages under
     * writeback).
     *
     * Called with inode->i_mutex down.
     */
    int ext4_setattr(struct dentry *dentry, struct iattr *attr)
    {
    	struct inode *inode = dentry->d_inode;
    	int error, rc = 0;
    	int orphan = 0;
    	const unsigned int ia_valid = attr->ia_valid;
    
    	error = inode_change_ok(inode, attr);
    	if (error)
    		return error;
    
    	if (is_quota_modification(inode, attr))
    		dquot_initialize(inode);
    	if ((ia_valid & ATTR_UID && attr->ia_uid != inode->i_uid) ||
    		(ia_valid & ATTR_GID && attr->ia_gid != inode->i_gid)) {
    		handle_t *handle;
    
    		/* (user+group)*(old+new) structure, inode write (sb,
    		 * inode block, ? - but truncate inode update has it) */
    		handle = ext4_journal_start(inode, (EXT4_MAXQUOTAS_INIT_BLOCKS(inode->i_sb)+
    					EXT4_MAXQUOTAS_DEL_BLOCKS(inode->i_sb))+3);
    		if (IS_ERR(handle)) {
    			error = PTR_ERR(handle);
    			goto err_out;
    		}
    		error = dquot_transfer(inode, attr);
    		if (error) {
    			ext4_journal_stop(handle);
    			return error;
    		}
    		/* Update corresponding info in inode so that everything is in
    		 * one transaction */
    		if (attr->ia_valid & ATTR_UID)
    			inode->i_uid = attr->ia_uid;
    		if (attr->ia_valid & ATTR_GID)
    			inode->i_gid = attr->ia_gid;
    		error = ext4_mark_inode_dirty(handle, inode);
    		ext4_journal_stop(handle);
    	}
    
    	if (attr->ia_valid & ATTR_SIZE) {
    		inode_dio_wait(inode);
    
    		if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
    			struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    
    			if (attr->ia_size > sbi->s_bitmap_maxbytes)
    				return -EFBIG;
    		}
    	}
    
    	if (S_ISREG(inode->i_mode) &&
    	    attr->ia_valid & ATTR_SIZE &&
    	    (attr->ia_size < inode->i_size)) {
    		handle_t *handle;
    
    		handle = ext4_journal_start(inode, 3);
    		if (IS_ERR(handle)) {
    			error = PTR_ERR(handle);
    			goto err_out;
    		}
    		if (ext4_handle_valid(handle)) {
    			error = ext4_orphan_add(handle, inode);
    			orphan = 1;
    		}
    		EXT4_I(inode)->i_disksize = attr->ia_size;
    		rc = ext4_mark_inode_dirty(handle, inode);
    		if (!error)
    			error = rc;
    		ext4_journal_stop(handle);
    
    		if (ext4_should_order_data(inode)) {
    			error = ext4_begin_ordered_truncate(inode,
    							    attr->ia_size);
    			if (error) {
    				/* Do as much error cleanup as possible */
    				handle = ext4_journal_start(inode, 3);
    				if (IS_ERR(handle)) {
    					ext4_orphan_del(NULL, inode);
    					goto err_out;
    				}
    				ext4_orphan_del(handle, inode);
    				orphan = 0;
    				ext4_journal_stop(handle);
    				goto err_out;
    			}
    		}
    	}
    
    	if (attr->ia_valid & ATTR_SIZE) {
    		if (attr->ia_size != i_size_read(inode)) {
    			truncate_setsize(inode, attr->ia_size);
    			ext4_truncate(inode);
    		} else if (ext4_test_inode_flag(inode, EXT4_INODE_EOFBLOCKS))
    			ext4_truncate(inode);
    	}
    
    	if (!rc) {
    		setattr_copy(inode, attr);
    		mark_inode_dirty(inode);
    	}
    
    	/*
    	 * If the call to ext4_truncate failed to get a transaction handle at
    	 * all, we need to clean up the in-core orphan list manually.
    	 */
    	if (orphan && inode->i_nlink)
    		ext4_orphan_del(NULL, inode);
    
    	if (!rc && (ia_valid & ATTR_MODE))
    		rc = ext4_acl_chmod(inode);
    
    err_out:
    	ext4_std_error(inode->i_sb, error);
    	if (!error)
    		error = rc;
    	return error;
    }
    
    int ext4_getattr(struct vfsmount *mnt, struct dentry *dentry,
    		 struct kstat *stat)
    {
    	struct inode *inode;
    	unsigned long delalloc_blocks;
    
    	inode = dentry->d_inode;
    	generic_fillattr(inode, stat);
    
    	/*
    	 * We can't update i_blocks if the block allocation is delayed
    	 * otherwise in the case of system crash before the real block
    	 * allocation is done, we will have i_blocks inconsistent with
    	 * on-disk file blocks.
    	 * We always keep i_blocks updated together with real
    	 * allocation. But to not confuse with user, stat
    	 * will return the blocks that include the delayed allocation
    	 * blocks for this file.
    	 */
    	delalloc_blocks = EXT4_I(inode)->i_reserved_data_blocks;
    
    	stat->blocks += (delalloc_blocks << inode->i_sb->s_blocksize_bits)>>9;
    	return 0;
    }
    
    static int ext4_index_trans_blocks(struct inode *inode, int nrblocks, int chunk)
    {
    	if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
    		return ext4_ind_trans_blocks(inode, nrblocks, chunk);
    	return ext4_ext_index_trans_blocks(inode, nrblocks, chunk);
    }
    
    /*
     * Account for index blocks, block groups bitmaps and block group
     * descriptor blocks if modify datablocks and index blocks
     * worse case, the indexs blocks spread over different block groups
     *
     * If datablocks are discontiguous, they are possible to spread over
     * different block groups too. If they are contiuguous, with flexbg,
     * they could still across block group boundary.
     *
     * Also account for superblock, inode, quota and xattr blocks
     */
    static int ext4_meta_trans_blocks(struct inode *inode, int nrblocks, int chunk)
    {
    	ext4_group_t groups, ngroups = ext4_get_groups_count(inode->i_sb);
    	int gdpblocks;
    	int idxblocks;
    	int ret = 0;
    
    	/*
    	 * How many index blocks need to touch to modify nrblocks?
    	 * The "Chunk" flag indicating whether the nrblocks is
    	 * physically contiguous on disk
    	 *
    	 * For Direct IO and fallocate, they calls get_block to allocate
    	 * one single extent at a time, so they could set the "Chunk" flag
    	 */
    	idxblocks = ext4_index_trans_blocks(inode, nrblocks, chunk);
    
    	ret = idxblocks;
    
    	/*
    	 * Now let's see how many group bitmaps and group descriptors need
    	 * to account
    	 */
    	groups = idxblocks;
    	if (chunk)
    		groups += 1;
    	else
    		groups += nrblocks;
    
    	gdpblocks = groups;
    	if (groups > ngroups)
    		groups = ngroups;
    	if (groups > EXT4_SB(inode->i_sb)->s_gdb_count)
    		gdpblocks = EXT4_SB(inode->i_sb)->s_gdb_count;
    
    	/* bitmaps and block group descriptor blocks */
    	ret += groups + gdpblocks;
    
    	/* Blocks for super block, inode, quota and xattr blocks */
    	ret += EXT4_META_TRANS_BLOCKS(inode->i_sb);
    
    	return ret;
    }
    
    /*
     * Calculate the total number of credits to reserve to fit
     * the modification of a single pages into a single transaction,
     * which may include multiple chunks of block allocations.
     *
     * This could be called via ext4_write_begin()
     *
     * We need to consider the worse case, when
     * one new block per extent.
     */
    int ext4_writepage_trans_blocks(struct inode *inode)
    {
    	int bpp = ext4_journal_blocks_per_page(inode);
    	int ret;
    
    	ret = ext4_meta_trans_blocks(inode, bpp, 0);
    
    	/* Account for data blocks for journalled mode */
    	if (ext4_should_journal_data(inode))
    		ret += bpp;
    	return ret;
    }
    
    /*
     * Calculate the journal credits for a chunk of data modification.
     *
     * This is called from DIO, fallocate or whoever calling
     * ext4_map_blocks() to map/allocate a chunk of contiguous disk blocks.
     *
     * journal buffers for data blocks are not included here, as DIO
     * and fallocate do no need to journal data buffers.
     */
    int ext4_chunk_trans_blocks(struct inode *inode, int nrblocks)
    {
    	return ext4_meta_trans_blocks(inode, nrblocks, 1);
    }
    
    /*
     * The caller must have previously called ext4_reserve_inode_write().
     * Give this, we know that the caller already has write access to iloc->bh.
     */
    int ext4_mark_iloc_dirty(handle_t *handle,
    			 struct inode *inode, struct ext4_iloc *iloc)
    {
    	int err = 0;
    
    	if (test_opt(inode->i_sb, I_VERSION))
    		inode_inc_iversion(inode);
    
    	/* the do_update_inode consumes one bh->b_count */
    	get_bh(iloc->bh);
    
    	/* ext4_do_update_inode() does jbd2_journal_dirty_metadata */
    	err = ext4_do_update_inode(handle, inode, iloc);
    	put_bh(iloc->bh);
    	return err;
    }
    
    /*
     * On success, We end up with an outstanding reference count against
     * iloc->bh.  This _must_ be cleaned up later.
     */
    
    int
    ext4_reserve_inode_write(handle_t *handle, struct inode *inode,
    			 struct ext4_iloc *iloc)
    {
    	int err;
    
    	err = ext4_get_inode_loc(inode, iloc);
    	if (!err) {
    		BUFFER_TRACE(iloc->bh, "get_write_access");
    		err = ext4_journal_get_write_access(handle, iloc->bh);
    		if (err) {
    			brelse(iloc->bh);
    			iloc->bh = NULL;
    		}
    	}
    	ext4_std_error(inode->i_sb, err);
    	return err;
    }
    
    /*
     * Expand an inode by new_extra_isize bytes.
     * Returns 0 on success or negative error number on failure.
     */
    static int ext4_expand_extra_isize(struct inode *inode,
    				   unsigned int new_extra_isize,
    				   struct ext4_iloc iloc,
    				   handle_t *handle)
    {
    	struct ext4_inode *raw_inode;
    	struct ext4_xattr_ibody_header *header;
    
    	if (EXT4_I(inode)->i_extra_isize >= new_extra_isize)
    		return 0;
    
    	raw_inode = ext4_raw_inode(&iloc);
    
    	header = IHDR(inode, raw_inode);
    
    	/* No extended attributes present */
    	if (!ext4_test_inode_state(inode, EXT4_STATE_XATTR) ||
    	    header->h_magic != cpu_to_le32(EXT4_XATTR_MAGIC)) {
    		memset((void *)raw_inode + EXT4_GOOD_OLD_INODE_SIZE, 0,
    			new_extra_isize);
    		EXT4_I(inode)->i_extra_isize = new_extra_isize;
    		return 0;
    	}
    
    	/* try to expand with EAs present */
    	return ext4_expand_extra_isize_ea(inode, new_extra_isize,
    					  raw_inode, handle);
    }
    
    /*
     * What we do here is to mark the in-core inode as clean with respect to inode
     * dirtiness (it may still be data-dirty).
     * This means that the in-core inode may be reaped by prune_icache
     * without having to perform any I/O.  This is a very good thing,
     * because *any* task may call prune_icache - even ones which
     * have a transaction open against a different journal.
     *
     * Is this cheating?  Not really.  Sure, we haven't written the
     * inode out, but prune_icache isn't a user-visible syncing function.
     * Whenever the user wants stuff synced (sys_sync, sys_msync, sys_fsync)
     * we start and wait on commits.
     *
     * Is this efficient/effective?  Well, we're being nice to the system
     * by cleaning up our inodes proactively so they can be reaped
     * without I/O.  But we are potentially leaving up to five seconds'
     * worth of inodes floating about which prune_icache wants us to
     * write out.  One way to fix that would be to get prune_icache()
     * to do a write_super() to free up some memory.  It has the desired
     * effect.
     */
    int ext4_mark_inode_dirty(handle_t *handle, struct inode *inode)
    {
    	struct ext4_iloc iloc;
    	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
    	static unsigned int mnt_count;
    	int err, ret;
    
    	might_sleep();
    	trace_ext4_mark_inode_dirty(inode, _RET_IP_);
    	err = ext4_reserve_inode_write(handle, inode, &iloc);
    	if (ext4_handle_valid(handle) &&
    	    EXT4_I(inode)->i_extra_isize < sbi->s_want_extra_isize &&
    	    !ext4_test_inode_state(inode, EXT4_STATE_NO_EXPAND)) {
    		/*
    		 * We need extra buffer credits since we may write into EA block
    		 * with this same handle. If journal_extend fails, then it will
    		 * only result in a minor loss of functionality for that inode.
    		 * If this is felt to be critical, then e2fsck should be run to
    		 * force a large enough s_min_extra_isize.
    		 */
    		if ((jbd2_journal_extend(handle,
    			     EXT4_DATA_TRANS_BLOCKS(inode->i_sb))) == 0) {
    			ret = ext4_expand_extra_isize(inode,
    						      sbi->s_want_extra_isize,
    						      iloc, handle);
    			if (ret) {
    				ext4_set_inode_state(inode,
    						     EXT4_STATE_NO_EXPAND);
    				if (mnt_count !=
    					le16_to_cpu(sbi->s_es->s_mnt_count)) {
    					ext4_warning(inode->i_sb,
    					"Unable to expand inode %lu. Delete"
    					" some EAs or run e2fsck.",
    					inode->i_ino);
    					mnt_count =
    					  le16_to_cpu(sbi->s_es->s_mnt_count);
    				}
    			}
    		}
    	}
    	if (!err)
    		err = ext4_mark_iloc_dirty(handle, inode, &iloc);
    	return err;
    }
    
    /*
     * ext4_dirty_inode() is called from __mark_inode_dirty()
     *
     * We're really interested in the case where a file is being extended.
     * i_size has been changed by generic_commit_write() and we thus need
     * to include the updated inode in the current transaction.
     *
     * Also, dquot_alloc_block() will always dirty the inode when blocks
     * are allocated to the file.
     *
     * If the inode is marked synchronous, we don't honour that here - doing
     * so would cause a commit on atime updates, which we don't bother doing.
     * We handle synchronous inodes at the highest possible level.
     */
    void ext4_dirty_inode(struct inode *inode, int flags)
    {
    	handle_t *handle;
    
    	handle = ext4_journal_start(inode, 2);
    	if (IS_ERR(handle))
    		goto out;
    
    	ext4_mark_inode_dirty(handle, inode);
    
    	ext4_journal_stop(handle);
    out:
    	return;
    }
    
    #if 0
    /*
     * Bind an inode's backing buffer_head into this transaction, to prevent
     * it from being flushed to disk early.  Unlike
     * ext4_reserve_inode_write, this leaves behind no bh reference and
     * returns no iloc structure, so the caller needs to repeat the iloc
     * lookup to mark the inode dirty later.
     */
    static int ext4_pin_inode(handle_t *handle, struct inode *inode)
    {
    	struct ext4_iloc iloc;
    
    	int err = 0;
    	if (handle) {
    		err = ext4_get_inode_loc(inode, &iloc);
    		if (!err) {
    			BUFFER_TRACE(iloc.bh, "get_write_access");
    			err = jbd2_journal_get_write_access(handle, iloc.bh);
    			if (!err)
    				err = ext4_handle_dirty_metadata(handle,
    								 NULL,
    								 iloc.bh);
    			brelse(iloc.bh);
    		}
    	}
    	ext4_std_error(inode->i_sb, err);
    	return err;
    }
    #endif
    
    int ext4_change_inode_journal_flag(struct inode *inode, int val)
    {
    	journal_t *journal;
    	handle_t *handle;
    	int err;
    
    	/*
    	 * We have to be very careful here: changing a data block's
    	 * journaling status dynamically is dangerous.  If we write a
    	 * data block to the journal, change the status and then delete
    	 * that block, we risk forgetting to revoke the old log record
    	 * from the journal and so a subsequent replay can corrupt data.
    	 * So, first we make sure that the journal is empty and that
    	 * nobody is changing anything.
    	 */
    
    	journal = EXT4_JOURNAL(inode);
    	if (!journal)
    		return 0;
    	if (is_journal_aborted(journal))
    		return -EROFS;
    
    	jbd2_journal_lock_updates(journal);
    	jbd2_journal_flush(journal);
    
    	/*
    	 * OK, there are no updates running now, and all cached data is
    	 * synced to disk.  We are now in a completely consistent state
    	 * which doesn't have anything in the journal, and we know that
    	 * no filesystem updates are running, so it is safe to modify
    	 * the inode's in-core data-journaling state flag now.
    	 */
    
    	if (val)
    		ext4_set_inode_flag(inode, EXT4_INODE_JOURNAL_DATA);
    	else
    		ext4_clear_inode_flag(inode, EXT4_INODE_JOURNAL_DATA);
    	ext4_set_aops(inode);
    
    	jbd2_journal_unlock_updates(journal);
    
    	/* Finally we can mark the inode as dirty. */
    
    	handle = ext4_journal_start(inode, 1);
    	if (IS_ERR(handle))
    		return PTR_ERR(handle);
    
    	err = ext4_mark_inode_dirty(handle, inode);
    	ext4_handle_sync(handle);
    	ext4_journal_stop(handle);
    	ext4_std_error(inode->i_sb, err);
    
    	return err;
    }
    
    static int ext4_bh_unmapped(handle_t *handle, struct buffer_head *bh)
    {
    	return !buffer_mapped(bh);
    }
    
    int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
    {
    	struct page *page = vmf->page;
    	loff_t size;
    	unsigned long len;
    	int ret;
    	struct file *file = vma->vm_file;
    	struct inode *inode = file->f_path.dentry->d_inode;
    	struct address_space *mapping = inode->i_mapping;
    	handle_t *handle;
    	get_block_t *get_block;
    	int retries = 0;
    
    	/*
    	 * This check is racy but catches the common case. We rely on
    	 * __block_page_mkwrite() to do a reliable check.
    	 */
    	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
    	/* Delalloc case is easy... */
    	if (test_opt(inode->i_sb, DELALLOC) &&
    	    !ext4_should_journal_data(inode) &&
    	    !ext4_nonda_switch(inode->i_sb)) {
    		do {
    			ret = __block_page_mkwrite(vma, vmf,
    						   ext4_da_get_block_prep);
    		} while (ret == -ENOSPC &&
    		       ext4_should_retry_alloc(inode->i_sb, &retries));
    		goto out_ret;
    	}
    
    	lock_page(page);
    	size = i_size_read(inode);
    	/* Page got truncated from under us? */
    	if (page->mapping != mapping || page_offset(page) > size) {
    		unlock_page(page);
    		ret = VM_FAULT_NOPAGE;
    		goto out;
    	}
    
    	if (page->index == size >> PAGE_CACHE_SHIFT)
    		len = size & ~PAGE_CACHE_MASK;
    	else
    		len = PAGE_CACHE_SIZE;
    	/*
    	 * Return if we have all the buffers mapped. This avoids the need to do
    	 * journal_start/journal_stop which can block and take a long time
    	 */
    	if (page_has_buffers(page)) {
    		if (!walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
    					ext4_bh_unmapped)) {
    			/* Wait so that we don't change page under IO */
    			wait_on_page_writeback(page);
    			ret = VM_FAULT_LOCKED;
    			goto out;
    		}
    	}
    	unlock_page(page);
    	/* OK, we need to fill the hole... */
    	if (ext4_should_dioread_nolock(inode))
    		get_block = ext4_get_block_write;
    	else
    		get_block = ext4_get_block;
    retry_alloc:
    	handle = ext4_journal_start(inode, ext4_writepage_trans_blocks(inode));
    	if (IS_ERR(handle)) {
    		ret = VM_FAULT_SIGBUS;
    		goto out;
    	}
    	ret = __block_page_mkwrite(vma, vmf, get_block);
    	if (!ret && ext4_should_journal_data(inode)) {
    		if (walk_page_buffers(handle, page_buffers(page), 0,
    			  PAGE_CACHE_SIZE, NULL, do_journal_get_write_access)) {
    			unlock_page(page);
    			ret = VM_FAULT_SIGBUS;
    			goto out;
    		}
    		ext4_set_inode_state(inode, EXT4_STATE_JDATA);
    	}
    	ext4_journal_stop(handle);
    	if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
    		goto retry_alloc;
    out_ret:
    	ret = block_page_mkwrite_return(ret);
    out:
    	return ret;
    }