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32 results

shmem.c

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  • shmem.c 112.19 KiB
    /*
     * Resizable virtual memory filesystem for Linux.
     *
     * Copyright (C) 2000 Linus Torvalds.
     *		 2000 Transmeta Corp.
     *		 2000-2001 Christoph Rohland
     *		 2000-2001 SAP AG
     *		 2002 Red Hat Inc.
     * Copyright (C) 2002-2011 Hugh Dickins.
     * Copyright (C) 2011 Google Inc.
     * Copyright (C) 2002-2005 VERITAS Software Corporation.
     * Copyright (C) 2004 Andi Kleen, SuSE Labs
     *
     * Extended attribute support for tmpfs:
     * Copyright (c) 2004, Luke Kenneth Casson Leighton <lkcl@lkcl.net>
     * Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
     *
     * tiny-shmem:
     * Copyright (c) 2004, 2008 Matt Mackall <mpm@selenic.com>
     *
     * This file is released under the GPL.
     */
    
    #include <linux/fs.h>
    #include <linux/init.h>
    #include <linux/vfs.h>
    #include <linux/mount.h>
    #include <linux/ramfs.h>
    #include <linux/pagemap.h>
    #include <linux/file.h>
    #include <linux/mm.h>
    #include <linux/sched/signal.h>
    #include <linux/export.h>
    #include <linux/swap.h>
    #include <linux/uio.h>
    #include <linux/khugepaged.h>
    #include <linux/hugetlb.h>
    
    #include <asm/tlbflush.h> /* for arch/microblaze update_mmu_cache() */
    
    static struct vfsmount *shm_mnt;
    
    #ifdef CONFIG_SHMEM
    /*
     * This virtual memory filesystem is heavily based on the ramfs. It
     * extends ramfs by the ability to use swap and honor resource limits
     * which makes it a completely usable filesystem.
     */
    
    #include <linux/xattr.h>
    #include <linux/exportfs.h>
    #include <linux/posix_acl.h>
    #include <linux/posix_acl_xattr.h>
    #include <linux/mman.h>
    #include <linux/string.h>
    #include <linux/slab.h>
    #include <linux/backing-dev.h>
    #include <linux/shmem_fs.h>
    #include <linux/writeback.h>
    #include <linux/blkdev.h>
    #include <linux/pagevec.h>
    #include <linux/percpu_counter.h>
    #include <linux/falloc.h>
    #include <linux/splice.h>
    #include <linux/security.h>
    #include <linux/swapops.h>
    #include <linux/mempolicy.h>
    #include <linux/namei.h>
    #include <linux/ctype.h>
    #include <linux/migrate.h>
    #include <linux/highmem.h>
    #include <linux/seq_file.h>
    #include <linux/magic.h>
    #include <linux/syscalls.h>
    #include <linux/fcntl.h>
    #include <uapi/linux/memfd.h>
    #include <linux/userfaultfd_k.h>
    #include <linux/rmap.h>
    #include <linux/uuid.h>
    
    #include <linux/uaccess.h>
    #include <asm/pgtable.h>
    
    #include "internal.h"
    
    #define BLOCKS_PER_PAGE  (PAGE_SIZE/512)
    #define VM_ACCT(size)    (PAGE_ALIGN(size) >> PAGE_SHIFT)
    
    /* Pretend that each entry is of this size in directory's i_size */
    #define BOGO_DIRENT_SIZE 20
    
    /* Symlink up to this size is kmalloc'ed instead of using a swappable page */
    #define SHORT_SYMLINK_LEN 128
    
    /*
     * shmem_fallocate communicates with shmem_fault or shmem_writepage via
     * inode->i_private (with i_mutex making sure that it has only one user at
     * a time): we would prefer not to enlarge the shmem inode just for that.
     */
    struct shmem_falloc {
    	wait_queue_head_t *waitq; /* faults into hole wait for punch to end */
    	pgoff_t start;		/* start of range currently being fallocated */
    	pgoff_t next;		/* the next page offset to be fallocated */
    	pgoff_t nr_falloced;	/* how many new pages have been fallocated */
    	pgoff_t nr_unswapped;	/* how often writepage refused to swap out */
    };
    
    #ifdef CONFIG_TMPFS
    static unsigned long shmem_default_max_blocks(void)
    {
    	return totalram_pages / 2;
    }
    
    static unsigned long shmem_default_max_inodes(void)
    {
    	return min(totalram_pages - totalhigh_pages, totalram_pages / 2);
    }
    #endif
    
    static bool shmem_should_replace_page(struct page *page, gfp_t gfp);
    static int shmem_replace_page(struct page **pagep, gfp_t gfp,
    				struct shmem_inode_info *info, pgoff_t index);
    static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
    		struct page **pagep, enum sgp_type sgp,
    		gfp_t gfp, struct vm_area_struct *vma,
    		struct vm_fault *vmf, int *fault_type);
    
    int shmem_getpage(struct inode *inode, pgoff_t index,
    		struct page **pagep, enum sgp_type sgp)
    {
    	return shmem_getpage_gfp(inode, index, pagep, sgp,
    		mapping_gfp_mask(inode->i_mapping), NULL, NULL, NULL);
    }
    
    static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
    {
    	return sb->s_fs_info;
    }
    
    /*
     * shmem_file_setup pre-accounts the whole fixed size of a VM object,
     * for shared memory and for shared anonymous (/dev/zero) mappings
     * (unless MAP_NORESERVE and sysctl_overcommit_memory <= 1),
     * consistent with the pre-accounting of private mappings ...
     */
    static inline int shmem_acct_size(unsigned long flags, loff_t size)
    {
    	return (flags & VM_NORESERVE) ?
    		0 : security_vm_enough_memory_mm(current->mm, VM_ACCT(size));
    }
    
    static inline void shmem_unacct_size(unsigned long flags, loff_t size)
    {
    	if (!(flags & VM_NORESERVE))
    		vm_unacct_memory(VM_ACCT(size));
    }
    
    static inline int shmem_reacct_size(unsigned long flags,
    		loff_t oldsize, loff_t newsize)
    {
    	if (!(flags & VM_NORESERVE)) {
    		if (VM_ACCT(newsize) > VM_ACCT(oldsize))
    			return security_vm_enough_memory_mm(current->mm,
    					VM_ACCT(newsize) - VM_ACCT(oldsize));
    		else if (VM_ACCT(newsize) < VM_ACCT(oldsize))
    			vm_unacct_memory(VM_ACCT(oldsize) - VM_ACCT(newsize));
    	}
    	return 0;
    }
    
    /*
     * ... whereas tmpfs objects are accounted incrementally as
     * pages are allocated, in order to allow large sparse files.
     * shmem_getpage reports shmem_acct_block failure as -ENOSPC not -ENOMEM,
     * so that a failure on a sparse tmpfs mapping will give SIGBUS not OOM.
     */
    static inline int shmem_acct_block(unsigned long flags, long pages)
    {
    	if (!(flags & VM_NORESERVE))
    		return 0;
    
    	return security_vm_enough_memory_mm(current->mm,
    			pages * VM_ACCT(PAGE_SIZE));
    }
    
    static inline void shmem_unacct_blocks(unsigned long flags, long pages)
    {
    	if (flags & VM_NORESERVE)
    		vm_unacct_memory(pages * VM_ACCT(PAGE_SIZE));
    }
    
    static inline bool shmem_inode_acct_block(struct inode *inode, long pages)
    {
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
    
    	if (shmem_acct_block(info->flags, pages))
    		return false;
    
    	if (sbinfo->max_blocks) {
    		if (percpu_counter_compare(&sbinfo->used_blocks,
    					   sbinfo->max_blocks - pages) > 0)
    			goto unacct;
    		percpu_counter_add(&sbinfo->used_blocks, pages);
    	}
    
    	return true;
    
    unacct:
    	shmem_unacct_blocks(info->flags, pages);
    	return false;
    }
    
    static inline void shmem_inode_unacct_blocks(struct inode *inode, long pages)
    {
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
    
    	if (sbinfo->max_blocks)
    		percpu_counter_sub(&sbinfo->used_blocks, pages);
    	shmem_unacct_blocks(info->flags, pages);
    }
    
    static const struct super_operations shmem_ops;
    static const struct address_space_operations shmem_aops;
    static const struct file_operations shmem_file_operations;
    static const struct inode_operations shmem_inode_operations;
    static const struct inode_operations shmem_dir_inode_operations;
    static const struct inode_operations shmem_special_inode_operations;
    static const struct vm_operations_struct shmem_vm_ops;
    static struct file_system_type shmem_fs_type;
    
    bool vma_is_shmem(struct vm_area_struct *vma)
    {
    	return vma->vm_ops == &shmem_vm_ops;
    }
    
    static LIST_HEAD(shmem_swaplist);
    static DEFINE_MUTEX(shmem_swaplist_mutex);
    
    static int shmem_reserve_inode(struct super_block *sb)
    {
    	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
    	if (sbinfo->max_inodes) {
    		spin_lock(&sbinfo->stat_lock);
    		if (!sbinfo->free_inodes) {
    			spin_unlock(&sbinfo->stat_lock);
    			return -ENOSPC;
    		}
    		sbinfo->free_inodes--;
    		spin_unlock(&sbinfo->stat_lock);
    	}
    	return 0;
    }
    
    static void shmem_free_inode(struct super_block *sb)
    {
    	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
    	if (sbinfo->max_inodes) {
    		spin_lock(&sbinfo->stat_lock);
    		sbinfo->free_inodes++;
    		spin_unlock(&sbinfo->stat_lock);
    	}
    }
    
    /**
     * shmem_recalc_inode - recalculate the block usage of an inode
     * @inode: inode to recalc
     *
     * We have to calculate the free blocks since the mm can drop
     * undirtied hole pages behind our back.
     *
     * But normally   info->alloced == inode->i_mapping->nrpages + info->swapped
     * So mm freed is info->alloced - (inode->i_mapping->nrpages + info->swapped)
     *
     * It has to be called with the spinlock held.
     */
    static void shmem_recalc_inode(struct inode *inode)
    {
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	long freed;
    
    	freed = info->alloced - info->swapped - inode->i_mapping->nrpages;
    	if (freed > 0) {
    		info->alloced -= freed;
    		inode->i_blocks -= freed * BLOCKS_PER_PAGE;
    		shmem_inode_unacct_blocks(inode, freed);
    	}
    }
    
    bool shmem_charge(struct inode *inode, long pages)
    {
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	unsigned long flags;
    
    	if (!shmem_inode_acct_block(inode, pages))
    		return false;
    
    	spin_lock_irqsave(&info->lock, flags);
    	info->alloced += pages;
    	inode->i_blocks += pages * BLOCKS_PER_PAGE;
    	shmem_recalc_inode(inode);
    	spin_unlock_irqrestore(&info->lock, flags);
    	inode->i_mapping->nrpages += pages;
    
    	return true;
    }
    
    void shmem_uncharge(struct inode *inode, long pages)
    {
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	unsigned long flags;
    
    	spin_lock_irqsave(&info->lock, flags);
    	info->alloced -= pages;
    	inode->i_blocks -= pages * BLOCKS_PER_PAGE;
    	shmem_recalc_inode(inode);
    	spin_unlock_irqrestore(&info->lock, flags);
    
    	shmem_inode_unacct_blocks(inode, pages);
    }
    
    /*
     * Replace item expected in radix tree by a new item, while holding tree lock.
     */
    static int shmem_radix_tree_replace(struct address_space *mapping,
    			pgoff_t index, void *expected, void *replacement)
    {
    	struct radix_tree_node *node;
    	void __rcu **pslot;
    	void *item;
    
    	VM_BUG_ON(!expected);
    	VM_BUG_ON(!replacement);
    	item = __radix_tree_lookup(&mapping->i_pages, index, &node, &pslot);
    	if (!item)
    		return -ENOENT;
    	if (item != expected)
    		return -ENOENT;
    	__radix_tree_replace(&mapping->i_pages, node, pslot,
    			     replacement, NULL);
    	return 0;
    }
    
    /*
     * Sometimes, before we decide whether to proceed or to fail, we must check
     * that an entry was not already brought back from swap by a racing thread.
     *
     * Checking page is not enough: by the time a SwapCache page is locked, it
     * might be reused, and again be SwapCache, using the same swap as before.
     */
    static bool shmem_confirm_swap(struct address_space *mapping,
    			       pgoff_t index, swp_entry_t swap)
    {
    	void *item;
    
    	rcu_read_lock();
    	item = radix_tree_lookup(&mapping->i_pages, index);
    	rcu_read_unlock();
    	return item == swp_to_radix_entry(swap);
    }
    
    /*
     * Definitions for "huge tmpfs": tmpfs mounted with the huge= option
     *
     * SHMEM_HUGE_NEVER:
     *	disables huge pages for the mount;
     * SHMEM_HUGE_ALWAYS:
     *	enables huge pages for the mount;
     * SHMEM_HUGE_WITHIN_SIZE:
     *	only allocate huge pages if the page will be fully within i_size,
     *	also respect fadvise()/madvise() hints;
     * SHMEM_HUGE_ADVISE:
     *	only allocate huge pages if requested with fadvise()/madvise();
     */
    
    #define SHMEM_HUGE_NEVER	0
    #define SHMEM_HUGE_ALWAYS	1
    #define SHMEM_HUGE_WITHIN_SIZE	2
    #define SHMEM_HUGE_ADVISE	3
    
    /*
     * Special values.
     * Only can be set via /sys/kernel/mm/transparent_hugepage/shmem_enabled:
     *
     * SHMEM_HUGE_DENY:
     *	disables huge on shm_mnt and all mounts, for emergency use;
     * SHMEM_HUGE_FORCE:
     *	enables huge on shm_mnt and all mounts, w/o needing option, for testing;
     *
     */
    #define SHMEM_HUGE_DENY		(-1)
    #define SHMEM_HUGE_FORCE	(-2)
    
    #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
    /* ifdef here to avoid bloating shmem.o when not necessary */
    
    static int shmem_huge __read_mostly;
    
    #if defined(CONFIG_SYSFS) || defined(CONFIG_TMPFS)
    static int shmem_parse_huge(const char *str)
    {
    	if (!strcmp(str, "never"))
    		return SHMEM_HUGE_NEVER;
    	if (!strcmp(str, "always"))
    		return SHMEM_HUGE_ALWAYS;
    	if (!strcmp(str, "within_size"))
    		return SHMEM_HUGE_WITHIN_SIZE;
    	if (!strcmp(str, "advise"))
    		return SHMEM_HUGE_ADVISE;
    	if (!strcmp(str, "deny"))
    		return SHMEM_HUGE_DENY;
    	if (!strcmp(str, "force"))
    		return SHMEM_HUGE_FORCE;
    	return -EINVAL;
    }
    
    static const char *shmem_format_huge(int huge)
    {
    	switch (huge) {
    	case SHMEM_HUGE_NEVER:
    		return "never";
    	case SHMEM_HUGE_ALWAYS:
    		return "always";
    	case SHMEM_HUGE_WITHIN_SIZE:
    		return "within_size";
    	case SHMEM_HUGE_ADVISE:
    		return "advise";
    	case SHMEM_HUGE_DENY:
    		return "deny";
    	case SHMEM_HUGE_FORCE:
    		return "force";
    	default:
    		VM_BUG_ON(1);
    		return "bad_val";
    	}
    }
    #endif
    
    static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
    		struct shrink_control *sc, unsigned long nr_to_split)
    {
    	LIST_HEAD(list), *pos, *next;
    	LIST_HEAD(to_remove);
    	struct inode *inode;
    	struct shmem_inode_info *info;
    	struct page *page;
    	unsigned long batch = sc ? sc->nr_to_scan : 128;
    	int removed = 0, split = 0;
    
    	if (list_empty(&sbinfo->shrinklist))
    		return SHRINK_STOP;
    
    	spin_lock(&sbinfo->shrinklist_lock);
    	list_for_each_safe(pos, next, &sbinfo->shrinklist) {
    		info = list_entry(pos, struct shmem_inode_info, shrinklist);
    
    		/* pin the inode */
    		inode = igrab(&info->vfs_inode);
    
    		/* inode is about to be evicted */
    		if (!inode) {
    			list_del_init(&info->shrinklist);
    			removed++;
    			goto next;
    		}
    
    		/* Check if there's anything to gain */
    		if (round_up(inode->i_size, PAGE_SIZE) ==
    				round_up(inode->i_size, HPAGE_PMD_SIZE)) {
    			list_move(&info->shrinklist, &to_remove);
    			removed++;
    			goto next;
    		}
    
    		list_move(&info->shrinklist, &list);
    next:
    		if (!--batch)
    			break;
    	}
    	spin_unlock(&sbinfo->shrinklist_lock);
    
    	list_for_each_safe(pos, next, &to_remove) {
    		info = list_entry(pos, struct shmem_inode_info, shrinklist);
    		inode = &info->vfs_inode;
    		list_del_init(&info->shrinklist);
    		iput(inode);
    	}
    
    	list_for_each_safe(pos, next, &list) {
    		int ret;
    
    		info = list_entry(pos, struct shmem_inode_info, shrinklist);
    		inode = &info->vfs_inode;
    
    		if (nr_to_split && split >= nr_to_split)
    			goto leave;
    
    		page = find_get_page(inode->i_mapping,
    				(inode->i_size & HPAGE_PMD_MASK) >> PAGE_SHIFT);
    		if (!page)
    			goto drop;
    
    		/* No huge page at the end of the file: nothing to split */
    		if (!PageTransHuge(page)) {
    			put_page(page);
    			goto drop;
    		}
    
    		/*
    		 * Leave the inode on the list if we failed to lock
    		 * the page at this time.
    		 *
    		 * Waiting for the lock may lead to deadlock in the
    		 * reclaim path.
    		 */
    		if (!trylock_page(page)) {
    			put_page(page);
    			goto leave;
    		}
    
    		ret = split_huge_page(page);
    		unlock_page(page);
    		put_page(page);
    
    		/* If split failed leave the inode on the list */
    		if (ret)
    			goto leave;
    
    		split++;
    drop:
    		list_del_init(&info->shrinklist);
    		removed++;
    leave:
    		iput(inode);
    	}
    
    	spin_lock(&sbinfo->shrinklist_lock);
    	list_splice_tail(&list, &sbinfo->shrinklist);
    	sbinfo->shrinklist_len -= removed;
    	spin_unlock(&sbinfo->shrinklist_lock);
    
    	return split;
    }
    
    static long shmem_unused_huge_scan(struct super_block *sb,
    		struct shrink_control *sc)
    {
    	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
    
    	if (!READ_ONCE(sbinfo->shrinklist_len))
    		return SHRINK_STOP;
    
    	return shmem_unused_huge_shrink(sbinfo, sc, 0);
    }
    
    static long shmem_unused_huge_count(struct super_block *sb,
    		struct shrink_control *sc)
    {
    	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
    	return READ_ONCE(sbinfo->shrinklist_len);
    }
    #else /* !CONFIG_TRANSPARENT_HUGE_PAGECACHE */
    
    #define shmem_huge SHMEM_HUGE_DENY
    
    static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
    		struct shrink_control *sc, unsigned long nr_to_split)
    {
    	return 0;
    }
    #endif /* CONFIG_TRANSPARENT_HUGE_PAGECACHE */
    
    /*
     * Like add_to_page_cache_locked, but error if expected item has gone.
     */
    static int shmem_add_to_page_cache(struct page *page,
    				   struct address_space *mapping,
    				   pgoff_t index, void *expected)
    {
    	int error, nr = hpage_nr_pages(page);
    
    	VM_BUG_ON_PAGE(PageTail(page), page);
    	VM_BUG_ON_PAGE(index != round_down(index, nr), page);
    	VM_BUG_ON_PAGE(!PageLocked(page), page);
    	VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
    	VM_BUG_ON(expected && PageTransHuge(page));
    
    	page_ref_add(page, nr);
    	page->mapping = mapping;
    	page->index = index;
    
    	xa_lock_irq(&mapping->i_pages);
    	if (PageTransHuge(page)) {
    		void __rcu **results;
    		pgoff_t idx;
    		int i;
    
    		error = 0;
    		if (radix_tree_gang_lookup_slot(&mapping->i_pages,
    					&results, &idx, index, 1) &&
    				idx < index + HPAGE_PMD_NR) {
    			error = -EEXIST;
    		}
    
    		if (!error) {
    			for (i = 0; i < HPAGE_PMD_NR; i++) {
    				error = radix_tree_insert(&mapping->i_pages,
    						index + i, page + i);
    				VM_BUG_ON(error);
    			}
    			count_vm_event(THP_FILE_ALLOC);
    		}
    	} else if (!expected) {
    		error = radix_tree_insert(&mapping->i_pages, index, page);
    	} else {
    		error = shmem_radix_tree_replace(mapping, index, expected,
    								 page);
    	}
    
    	if (!error) {
    		mapping->nrpages += nr;
    		if (PageTransHuge(page))
    			__inc_node_page_state(page, NR_SHMEM_THPS);
    		__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
    		__mod_node_page_state(page_pgdat(page), NR_SHMEM, nr);
    		xa_unlock_irq(&mapping->i_pages);
    	} else {
    		page->mapping = NULL;
    		xa_unlock_irq(&mapping->i_pages);
    		page_ref_sub(page, nr);
    	}
    	return error;
    }
    
    /*
     * Like delete_from_page_cache, but substitutes swap for page.
     */
    static void shmem_delete_from_page_cache(struct page *page, void *radswap)
    {
    	struct address_space *mapping = page->mapping;
    	int error;
    
    	VM_BUG_ON_PAGE(PageCompound(page), page);
    
    	xa_lock_irq(&mapping->i_pages);
    	error = shmem_radix_tree_replace(mapping, page->index, page, radswap);
    	page->mapping = NULL;
    	mapping->nrpages--;
    	__dec_node_page_state(page, NR_FILE_PAGES);
    	__dec_node_page_state(page, NR_SHMEM);
    	xa_unlock_irq(&mapping->i_pages);
    	put_page(page);
    	BUG_ON(error);
    }
    
    /*
     * Remove swap entry from radix tree, free the swap and its page cache.
     */
    static int shmem_free_swap(struct address_space *mapping,
    			   pgoff_t index, void *radswap)
    {
    	void *old;
    
    	xa_lock_irq(&mapping->i_pages);
    	old = radix_tree_delete_item(&mapping->i_pages, index, radswap);
    	xa_unlock_irq(&mapping->i_pages);
    	if (old != radswap)
    		return -ENOENT;
    	free_swap_and_cache(radix_to_swp_entry(radswap));
    	return 0;
    }
    
    /*
     * Determine (in bytes) how many of the shmem object's pages mapped by the
     * given offsets are swapped out.
     *
     * This is safe to call without i_mutex or the i_pages lock thanks to RCU,
     * as long as the inode doesn't go away and racy results are not a problem.
     */
    unsigned long shmem_partial_swap_usage(struct address_space *mapping,
    						pgoff_t start, pgoff_t end)
    {
    	struct radix_tree_iter iter;
    	void __rcu **slot;
    	struct page *page;
    	unsigned long swapped = 0;
    
    	rcu_read_lock();
    
    	radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start) {
    		if (iter.index >= end)
    			break;
    
    		page = radix_tree_deref_slot(slot);
    
    		if (radix_tree_deref_retry(page)) {
    			slot = radix_tree_iter_retry(&iter);
    			continue;
    		}
    
    		if (radix_tree_exceptional_entry(page))
    			swapped++;
    
    		if (need_resched()) {
    			slot = radix_tree_iter_resume(slot, &iter);
    			cond_resched_rcu();
    		}
    	}
    
    	rcu_read_unlock();
    
    	return swapped << PAGE_SHIFT;
    }
    
    /*
     * Determine (in bytes) how many of the shmem object's pages mapped by the
     * given vma is swapped out.
     *
     * This is safe to call without i_mutex or the i_pages lock thanks to RCU,
     * as long as the inode doesn't go away and racy results are not a problem.
     */
    unsigned long shmem_swap_usage(struct vm_area_struct *vma)
    {
    	struct inode *inode = file_inode(vma->vm_file);
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	struct address_space *mapping = inode->i_mapping;
    	unsigned long swapped;
    
    	/* Be careful as we don't hold info->lock */
    	swapped = READ_ONCE(info->swapped);
    
    	/*
    	 * The easier cases are when the shmem object has nothing in swap, or
    	 * the vma maps it whole. Then we can simply use the stats that we
    	 * already track.
    	 */
    	if (!swapped)
    		return 0;
    
    	if (!vma->vm_pgoff && vma->vm_end - vma->vm_start >= inode->i_size)
    		return swapped << PAGE_SHIFT;
    
    	/* Here comes the more involved part */
    	return shmem_partial_swap_usage(mapping,
    			linear_page_index(vma, vma->vm_start),
    			linear_page_index(vma, vma->vm_end));
    }
    
    /*
     * SysV IPC SHM_UNLOCK restore Unevictable pages to their evictable lists.
     */
    void shmem_unlock_mapping(struct address_space *mapping)
    {
    	struct pagevec pvec;
    	pgoff_t indices[PAGEVEC_SIZE];
    	pgoff_t index = 0;
    
    	pagevec_init(&pvec);
    	/*
    	 * Minor point, but we might as well stop if someone else SHM_LOCKs it.
    	 */
    	while (!mapping_unevictable(mapping)) {
    		/*
    		 * Avoid pagevec_lookup(): find_get_pages() returns 0 as if it
    		 * has finished, if it hits a row of PAGEVEC_SIZE swap entries.
    		 */
    		pvec.nr = find_get_entries(mapping, index,
    					   PAGEVEC_SIZE, pvec.pages, indices);
    		if (!pvec.nr)
    			break;
    		index = indices[pvec.nr - 1] + 1;
    		pagevec_remove_exceptionals(&pvec);
    		check_move_unevictable_pages(pvec.pages, pvec.nr);
    		pagevec_release(&pvec);
    		cond_resched();
    	}
    }
    
    /*
     * Remove range of pages and swap entries from radix tree, and free them.
     * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
     */
    static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
    								 bool unfalloc)
    {
    	struct address_space *mapping = inode->i_mapping;
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	pgoff_t start = (lstart + PAGE_SIZE - 1) >> PAGE_SHIFT;
    	pgoff_t end = (lend + 1) >> PAGE_SHIFT;
    	unsigned int partial_start = lstart & (PAGE_SIZE - 1);
    	unsigned int partial_end = (lend + 1) & (PAGE_SIZE - 1);
    	struct pagevec pvec;
    	pgoff_t indices[PAGEVEC_SIZE];
    	long nr_swaps_freed = 0;
    	pgoff_t index;
    	int i;
    
    	if (lend == -1)
    		end = -1;	/* unsigned, so actually very big */
    
    	pagevec_init(&pvec);
    	index = start;
    	while (index < end) {
    		pvec.nr = find_get_entries(mapping, index,
    			min(end - index, (pgoff_t)PAGEVEC_SIZE),
    			pvec.pages, indices);
    		if (!pvec.nr)
    			break;
    		for (i = 0; i < pagevec_count(&pvec); i++) {
    			struct page *page = pvec.pages[i];
    
    			index = indices[i];
    			if (index >= end)
    				break;
    
    			if (radix_tree_exceptional_entry(page)) {
    				if (unfalloc)
    					continue;
    				nr_swaps_freed += !shmem_free_swap(mapping,
    								index, page);
    				continue;
    			}
    
    			VM_BUG_ON_PAGE(page_to_pgoff(page) != index, page);
    
    			if (!trylock_page(page))
    				continue;
    
    			if (PageTransTail(page)) {
    				/* Middle of THP: zero out the page */
    				clear_highpage(page);
    				unlock_page(page);
    				continue;
    			} else if (PageTransHuge(page)) {
    				if (index == round_down(end, HPAGE_PMD_NR)) {
    					/*
    					 * Range ends in the middle of THP:
    					 * zero out the page
    					 */
    					clear_highpage(page);
    					unlock_page(page);
    					continue;
    				}
    				index += HPAGE_PMD_NR - 1;
    				i += HPAGE_PMD_NR - 1;
    			}
    
    			if (!unfalloc || !PageUptodate(page)) {
    				VM_BUG_ON_PAGE(PageTail(page), page);
    				if (page_mapping(page) == mapping) {
    					VM_BUG_ON_PAGE(PageWriteback(page), page);
    					truncate_inode_page(mapping, page);
    				}
    			}
    			unlock_page(page);
    		}
    		pagevec_remove_exceptionals(&pvec);
    		pagevec_release(&pvec);
    		cond_resched();
    		index++;
    	}
    
    	if (partial_start) {
    		struct page *page = NULL;
    		shmem_getpage(inode, start - 1, &page, SGP_READ);
    		if (page) {
    			unsigned int top = PAGE_SIZE;
    			if (start > end) {
    				top = partial_end;
    				partial_end = 0;
    			}
    			zero_user_segment(page, partial_start, top);
    			set_page_dirty(page);
    			unlock_page(page);
    			put_page(page);
    		}
    	}
    	if (partial_end) {
    		struct page *page = NULL;
    		shmem_getpage(inode, end, &page, SGP_READ);
    		if (page) {
    			zero_user_segment(page, 0, partial_end);
    			set_page_dirty(page);
    			unlock_page(page);
    			put_page(page);
    		}
    	}
    	if (start >= end)
    		return;
    
    	index = start;
    	while (index < end) {
    		cond_resched();
    
    		pvec.nr = find_get_entries(mapping, index,
    				min(end - index, (pgoff_t)PAGEVEC_SIZE),
    				pvec.pages, indices);
    		if (!pvec.nr) {
    			/* If all gone or hole-punch or unfalloc, we're done */
    			if (index == start || end != -1)
    				break;
    			/* But if truncating, restart to make sure all gone */
    			index = start;
    			continue;
    		}
    		for (i = 0; i < pagevec_count(&pvec); i++) {
    			struct page *page = pvec.pages[i];
    
    			index = indices[i];
    			if (index >= end)
    				break;
    
    			if (radix_tree_exceptional_entry(page)) {
    				if (unfalloc)
    					continue;
    				if (shmem_free_swap(mapping, index, page)) {
    					/* Swap was replaced by page: retry */
    					index--;
    					break;
    				}
    				nr_swaps_freed++;
    				continue;
    			}
    
    			lock_page(page);
    
    			if (PageTransTail(page)) {
    				/* Middle of THP: zero out the page */
    				clear_highpage(page);
    				unlock_page(page);
    				/*
    				 * Partial thp truncate due 'start' in middle
    				 * of THP: don't need to look on these pages
    				 * again on !pvec.nr restart.
    				 */
    				if (index != round_down(end, HPAGE_PMD_NR))
    					start++;
    				continue;
    			} else if (PageTransHuge(page)) {
    				if (index == round_down(end, HPAGE_PMD_NR)) {
    					/*
    					 * Range ends in the middle of THP:
    					 * zero out the page
    					 */
    					clear_highpage(page);
    					unlock_page(page);
    					continue;
    				}
    				index += HPAGE_PMD_NR - 1;
    				i += HPAGE_PMD_NR - 1;
    			}
    
    			if (!unfalloc || !PageUptodate(page)) {
    				VM_BUG_ON_PAGE(PageTail(page), page);
    				if (page_mapping(page) == mapping) {
    					VM_BUG_ON_PAGE(PageWriteback(page), page);
    					truncate_inode_page(mapping, page);
    				} else {
    					/* Page was replaced by swap: retry */
    					unlock_page(page);
    					index--;
    					break;
    				}
    			}
    			unlock_page(page);
    		}
    		pagevec_remove_exceptionals(&pvec);
    		pagevec_release(&pvec);
    		index++;
    	}
    
    	spin_lock_irq(&info->lock);
    	info->swapped -= nr_swaps_freed;
    	shmem_recalc_inode(inode);
    	spin_unlock_irq(&info->lock);
    }
    
    void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
    {
    	shmem_undo_range(inode, lstart, lend, false);
    	inode->i_ctime = inode->i_mtime = current_time(inode);
    }
    EXPORT_SYMBOL_GPL(shmem_truncate_range);
    
    static int shmem_getattr(const struct path *path, struct kstat *stat,
    			 u32 request_mask, unsigned int query_flags)
    {
    	struct inode *inode = path->dentry->d_inode;
    	struct shmem_inode_info *info = SHMEM_I(inode);
    
    	if (info->alloced - info->swapped != inode->i_mapping->nrpages) {
    		spin_lock_irq(&info->lock);
    		shmem_recalc_inode(inode);
    		spin_unlock_irq(&info->lock);
    	}
    	generic_fillattr(inode, stat);
    	return 0;
    }
    
    static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
    {
    	struct inode *inode = d_inode(dentry);
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
    	int error;
    
    	error = setattr_prepare(dentry, attr);
    	if (error)
    		return error;
    
    	if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) {
    		loff_t oldsize = inode->i_size;
    		loff_t newsize = attr->ia_size;
    
    		/* protected by i_mutex */
    		if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) ||
    		    (newsize > oldsize && (info->seals & F_SEAL_GROW)))
    			return -EPERM;
    
    		if (newsize != oldsize) {
    			error = shmem_reacct_size(SHMEM_I(inode)->flags,
    					oldsize, newsize);
    			if (error)
    				return error;
    			i_size_write(inode, newsize);
    			inode->i_ctime = inode->i_mtime = current_time(inode);
    		}
    		if (newsize <= oldsize) {
    			loff_t holebegin = round_up(newsize, PAGE_SIZE);
    			if (oldsize > holebegin)
    				unmap_mapping_range(inode->i_mapping,
    							holebegin, 0, 1);
    			if (info->alloced)
    				shmem_truncate_range(inode,
    							newsize, (loff_t)-1);
    			/* unmap again to remove racily COWed private pages */
    			if (oldsize > holebegin)
    				unmap_mapping_range(inode->i_mapping,
    							holebegin, 0, 1);
    
    			/*
    			 * Part of the huge page can be beyond i_size: subject
    			 * to shrink under memory pressure.
    			 */
    			if (IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE)) {
    				spin_lock(&sbinfo->shrinklist_lock);
    				/*
    				 * _careful to defend against unlocked access to
    				 * ->shrink_list in shmem_unused_huge_shrink()
    				 */
    				if (list_empty_careful(&info->shrinklist)) {
    					list_add_tail(&info->shrinklist,
    							&sbinfo->shrinklist);
    					sbinfo->shrinklist_len++;
    				}
    				spin_unlock(&sbinfo->shrinklist_lock);
    			}
    		}
    	}
    
    	setattr_copy(inode, attr);
    	if (attr->ia_valid & ATTR_MODE)
    		error = posix_acl_chmod(inode, inode->i_mode);
    	return error;
    }
    
    static void shmem_evict_inode(struct inode *inode)
    {
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
    
    	if (inode->i_mapping->a_ops == &shmem_aops) {
    		shmem_unacct_size(info->flags, inode->i_size);
    		inode->i_size = 0;
    		shmem_truncate_range(inode, 0, (loff_t)-1);
    		if (!list_empty(&info->shrinklist)) {
    			spin_lock(&sbinfo->shrinklist_lock);
    			if (!list_empty(&info->shrinklist)) {
    				list_del_init(&info->shrinklist);
    				sbinfo->shrinklist_len--;
    			}
    			spin_unlock(&sbinfo->shrinklist_lock);
    		}
    		if (!list_empty(&info->swaplist)) {
    			mutex_lock(&shmem_swaplist_mutex);
    			list_del_init(&info->swaplist);
    			mutex_unlock(&shmem_swaplist_mutex);
    		}
    	}
    
    	simple_xattrs_free(&info->xattrs);
    	WARN_ON(inode->i_blocks);
    	shmem_free_inode(inode->i_sb);
    	clear_inode(inode);
    }
    
    static unsigned long find_swap_entry(struct radix_tree_root *root, void *item)
    {
    	struct radix_tree_iter iter;
    	void __rcu **slot;
    	unsigned long found = -1;
    	unsigned int checked = 0;
    
    	rcu_read_lock();
    	radix_tree_for_each_slot(slot, root, &iter, 0) {
    		void *entry = radix_tree_deref_slot(slot);
    
    		if (radix_tree_deref_retry(entry)) {
    			slot = radix_tree_iter_retry(&iter);
    			continue;
    		}
    		if (entry == item) {
    			found = iter.index;
    			break;
    		}
    		checked++;
    		if ((checked % 4096) != 0)
    			continue;
    		slot = radix_tree_iter_resume(slot, &iter);
    		cond_resched_rcu();
    	}
    
    	rcu_read_unlock();
    	return found;
    }
    
    /*
     * If swap found in inode, free it and move page from swapcache to filecache.
     */
    static int shmem_unuse_inode(struct shmem_inode_info *info,
    			     swp_entry_t swap, struct page **pagep)
    {
    	struct address_space *mapping = info->vfs_inode.i_mapping;
    	void *radswap;
    	pgoff_t index;
    	gfp_t gfp;
    	int error = 0;
    
    	radswap = swp_to_radix_entry(swap);
    	index = find_swap_entry(&mapping->i_pages, radswap);
    	if (index == -1)
    		return -EAGAIN;	/* tell shmem_unuse we found nothing */
    
    	/*
    	 * Move _head_ to start search for next from here.
    	 * But be careful: shmem_evict_inode checks list_empty without taking
    	 * mutex, and there's an instant in list_move_tail when info->swaplist
    	 * would appear empty, if it were the only one on shmem_swaplist.
    	 */
    	if (shmem_swaplist.next != &info->swaplist)
    		list_move_tail(&shmem_swaplist, &info->swaplist);
    
    	gfp = mapping_gfp_mask(mapping);
    	if (shmem_should_replace_page(*pagep, gfp)) {
    		mutex_unlock(&shmem_swaplist_mutex);
    		error = shmem_replace_page(pagep, gfp, info, index);
    		mutex_lock(&shmem_swaplist_mutex);
    		/*
    		 * We needed to drop mutex to make that restrictive page
    		 * allocation, but the inode might have been freed while we
    		 * dropped it: although a racing shmem_evict_inode() cannot
    		 * complete without emptying the radix_tree, our page lock
    		 * on this swapcache page is not enough to prevent that -
    		 * free_swap_and_cache() of our swap entry will only
    		 * trylock_page(), removing swap from radix_tree whatever.
    		 *
    		 * We must not proceed to shmem_add_to_page_cache() if the
    		 * inode has been freed, but of course we cannot rely on
    		 * inode or mapping or info to check that.  However, we can
    		 * safely check if our swap entry is still in use (and here
    		 * it can't have got reused for another page): if it's still
    		 * in use, then the inode cannot have been freed yet, and we
    		 * can safely proceed (if it's no longer in use, that tells
    		 * nothing about the inode, but we don't need to unuse swap).
    		 */
    		if (!page_swapcount(*pagep))
    			error = -ENOENT;
    	}
    
    	/*
    	 * We rely on shmem_swaplist_mutex, not only to protect the swaplist,
    	 * but also to hold up shmem_evict_inode(): so inode cannot be freed
    	 * beneath us (pagelock doesn't help until the page is in pagecache).
    	 */
    	if (!error)
    		error = shmem_add_to_page_cache(*pagep, mapping, index,
    						radswap);
    	if (error != -ENOMEM) {
    		/*
    		 * Truncation and eviction use free_swap_and_cache(), which
    		 * only does trylock page: if we raced, best clean up here.
    		 */
    		delete_from_swap_cache(*pagep);
    		set_page_dirty(*pagep);
    		if (!error) {
    			spin_lock_irq(&info->lock);
    			info->swapped--;
    			spin_unlock_irq(&info->lock);
    			swap_free(swap);
    		}
    	}
    	return error;
    }
    
    /*
     * Search through swapped inodes to find and replace swap by page.
     */
    int shmem_unuse(swp_entry_t swap, struct page *page)
    {
    	struct list_head *this, *next;
    	struct shmem_inode_info *info;
    	struct mem_cgroup *memcg;
    	int error = 0;
    
    	/*
    	 * There's a faint possibility that swap page was replaced before
    	 * caller locked it: caller will come back later with the right page.
    	 */
    	if (unlikely(!PageSwapCache(page) || page_private(page) != swap.val))
    		goto out;
    
    	/*
    	 * Charge page using GFP_KERNEL while we can wait, before taking
    	 * the shmem_swaplist_mutex which might hold up shmem_writepage().
    	 * Charged back to the user (not to caller) when swap account is used.
    	 */
    	error = mem_cgroup_try_charge(page, current->mm, GFP_KERNEL, &memcg,
    			false);
    	if (error)
    		goto out;
    	/* No radix_tree_preload: swap entry keeps a place for page in tree */
    	error = -EAGAIN;
    
    	mutex_lock(&shmem_swaplist_mutex);
    	list_for_each_safe(this, next, &shmem_swaplist) {
    		info = list_entry(this, struct shmem_inode_info, swaplist);
    		if (info->swapped)
    			error = shmem_unuse_inode(info, swap, &page);
    		else
    			list_del_init(&info->swaplist);
    		cond_resched();
    		if (error != -EAGAIN)
    			break;
    		/* found nothing in this: move on to search the next */
    	}
    	mutex_unlock(&shmem_swaplist_mutex);
    
    	if (error) {
    		if (error != -ENOMEM)
    			error = 0;
    		mem_cgroup_cancel_charge(page, memcg, false);
    	} else
    		mem_cgroup_commit_charge(page, memcg, true, false);
    out:
    	unlock_page(page);
    	put_page(page);
    	return error;
    }
    
    /*
     * Move the page from the page cache to the swap cache.
     */
    static int shmem_writepage(struct page *page, struct writeback_control *wbc)
    {
    	struct shmem_inode_info *info;
    	struct address_space *mapping;
    	struct inode *inode;
    	swp_entry_t swap;
    	pgoff_t index;
    
    	VM_BUG_ON_PAGE(PageCompound(page), page);
    	BUG_ON(!PageLocked(page));
    	mapping = page->mapping;
    	index = page->index;
    	inode = mapping->host;
    	info = SHMEM_I(inode);
    	if (info->flags & VM_LOCKED)
    		goto redirty;
    	if (!total_swap_pages)
    		goto redirty;
    
    	/*
    	 * Our capabilities prevent regular writeback or sync from ever calling
    	 * shmem_writepage; but a stacking filesystem might use ->writepage of
    	 * its underlying filesystem, in which case tmpfs should write out to
    	 * swap only in response to memory pressure, and not for the writeback
    	 * threads or sync.
    	 */
    	if (!wbc->for_reclaim) {
    		WARN_ON_ONCE(1);	/* Still happens? Tell us about it! */
    		goto redirty;
    	}
    
    	/*
    	 * This is somewhat ridiculous, but without plumbing a SWAP_MAP_FALLOC
    	 * value into swapfile.c, the only way we can correctly account for a
    	 * fallocated page arriving here is now to initialize it and write it.
    	 *
    	 * That's okay for a page already fallocated earlier, but if we have
    	 * not yet completed the fallocation, then (a) we want to keep track
    	 * of this page in case we have to undo it, and (b) it may not be a
    	 * good idea to continue anyway, once we're pushing into swap.  So
    	 * reactivate the page, and let shmem_fallocate() quit when too many.
    	 */
    	if (!PageUptodate(page)) {
    		if (inode->i_private) {
    			struct shmem_falloc *shmem_falloc;
    			spin_lock(&inode->i_lock);
    			shmem_falloc = inode->i_private;
    			if (shmem_falloc &&
    			    !shmem_falloc->waitq &&
    			    index >= shmem_falloc->start &&
    			    index < shmem_falloc->next)
    				shmem_falloc->nr_unswapped++;
    			else
    				shmem_falloc = NULL;
    			spin_unlock(&inode->i_lock);
    			if (shmem_falloc)
    				goto redirty;
    		}
    		clear_highpage(page);
    		flush_dcache_page(page);
    		SetPageUptodate(page);
    	}
    
    	swap = get_swap_page(page);
    	if (!swap.val)
    		goto redirty;
    
    	/*
    	 * Add inode to shmem_unuse()'s list of swapped-out inodes,
    	 * if it's not already there.  Do it now before the page is
    	 * moved to swap cache, when its pagelock no longer protects
    	 * the inode from eviction.  But don't unlock the mutex until
    	 * we've incremented swapped, because shmem_unuse_inode() will
    	 * prune a !swapped inode from the swaplist under this mutex.
    	 */
    	mutex_lock(&shmem_swaplist_mutex);
    	if (list_empty(&info->swaplist))
    		list_add_tail(&info->swaplist, &shmem_swaplist);
    
    	if (add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {
    		spin_lock_irq(&info->lock);
    		shmem_recalc_inode(inode);
    		info->swapped++;
    		spin_unlock_irq(&info->lock);
    
    		swap_shmem_alloc(swap);
    		shmem_delete_from_page_cache(page, swp_to_radix_entry(swap));
    
    		mutex_unlock(&shmem_swaplist_mutex);
    		BUG_ON(page_mapped(page));
    		swap_writepage(page, wbc);
    		return 0;
    	}
    
    	mutex_unlock(&shmem_swaplist_mutex);
    	put_swap_page(page, swap);
    redirty:
    	set_page_dirty(page);
    	if (wbc->for_reclaim)
    		return AOP_WRITEPAGE_ACTIVATE;	/* Return with page locked */
    	unlock_page(page);
    	return 0;
    }
    
    #if defined(CONFIG_NUMA) && defined(CONFIG_TMPFS)
    static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
    {
    	char buffer[64];
    
    	if (!mpol || mpol->mode == MPOL_DEFAULT)
    		return;		/* show nothing */
    
    	mpol_to_str(buffer, sizeof(buffer), mpol);
    
    	seq_printf(seq, ",mpol=%s", buffer);
    }
    
    static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
    {
    	struct mempolicy *mpol = NULL;
    	if (sbinfo->mpol) {
    		spin_lock(&sbinfo->stat_lock);	/* prevent replace/use races */
    		mpol = sbinfo->mpol;
    		mpol_get(mpol);
    		spin_unlock(&sbinfo->stat_lock);
    	}
    	return mpol;
    }
    #else /* !CONFIG_NUMA || !CONFIG_TMPFS */
    static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
    {
    }
    static inline struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
    {
    	return NULL;
    }
    #endif /* CONFIG_NUMA && CONFIG_TMPFS */
    #ifndef CONFIG_NUMA
    #define vm_policy vm_private_data
    #endif
    
    static void shmem_pseudo_vma_init(struct vm_area_struct *vma,
    		struct shmem_inode_info *info, pgoff_t index)
    {
    	/* Create a pseudo vma that just contains the policy */
    	vma->vm_start = 0;
    	/* Bias interleave by inode number to distribute better across nodes */
    	vma->vm_pgoff = index + info->vfs_inode.i_ino;
    	vma->vm_ops = NULL;
    	vma->vm_policy = mpol_shared_policy_lookup(&info->policy, index);
    }
    
    static void shmem_pseudo_vma_destroy(struct vm_area_struct *vma)
    {
    	/* Drop reference taken by mpol_shared_policy_lookup() */
    	mpol_cond_put(vma->vm_policy);
    }
    
    static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
    			struct shmem_inode_info *info, pgoff_t index)
    {
    	struct vm_area_struct pvma;
    	struct page *page;
    	struct vm_fault vmf;
    
    	shmem_pseudo_vma_init(&pvma, info, index);
    	vmf.vma = &pvma;
    	vmf.address = 0;
    	page = swap_cluster_readahead(swap, gfp, &vmf);
    	shmem_pseudo_vma_destroy(&pvma);
    
    	return page;
    }
    
    static struct page *shmem_alloc_hugepage(gfp_t gfp,
    		struct shmem_inode_info *info, pgoff_t index)
    {
    	struct vm_area_struct pvma;
    	struct inode *inode = &info->vfs_inode;
    	struct address_space *mapping = inode->i_mapping;
    	pgoff_t idx, hindex;
    	void __rcu **results;
    	struct page *page;
    
    	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
    		return NULL;
    
    	hindex = round_down(index, HPAGE_PMD_NR);
    	rcu_read_lock();
    	if (radix_tree_gang_lookup_slot(&mapping->i_pages, &results, &idx,
    				hindex, 1) && idx < hindex + HPAGE_PMD_NR) {
    		rcu_read_unlock();
    		return NULL;
    	}
    	rcu_read_unlock();
    
    	shmem_pseudo_vma_init(&pvma, info, hindex);
    	page = alloc_pages_vma(gfp | __GFP_COMP | __GFP_NORETRY | __GFP_NOWARN,
    			HPAGE_PMD_ORDER, &pvma, 0, numa_node_id(), true);
    	shmem_pseudo_vma_destroy(&pvma);
    	if (page)
    		prep_transhuge_page(page);
    	return page;
    }
    
    static struct page *shmem_alloc_page(gfp_t gfp,
    			struct shmem_inode_info *info, pgoff_t index)
    {
    	struct vm_area_struct pvma;
    	struct page *page;
    
    	shmem_pseudo_vma_init(&pvma, info, index);
    	page = alloc_page_vma(gfp, &pvma, 0);
    	shmem_pseudo_vma_destroy(&pvma);
    
    	return page;
    }
    
    static struct page *shmem_alloc_and_acct_page(gfp_t gfp,
    		struct inode *inode,
    		pgoff_t index, bool huge)
    {
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	struct page *page;
    	int nr;
    	int err = -ENOSPC;
    
    	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
    		huge = false;
    	nr = huge ? HPAGE_PMD_NR : 1;
    
    	if (!shmem_inode_acct_block(inode, nr))
    		goto failed;
    
    	if (huge)
    		page = shmem_alloc_hugepage(gfp, info, index);
    	else
    		page = shmem_alloc_page(gfp, info, index);
    	if (page) {
    		__SetPageLocked(page);
    		__SetPageSwapBacked(page);
    		return page;
    	}
    
    	err = -ENOMEM;
    	shmem_inode_unacct_blocks(inode, nr);
    failed:
    	return ERR_PTR(err);
    }
    
    /*
     * When a page is moved from swapcache to shmem filecache (either by the
     * usual swapin of shmem_getpage_gfp(), or by the less common swapoff of
     * shmem_unuse_inode()), it may have been read in earlier from swap, in
     * ignorance of the mapping it belongs to.  If that mapping has special
     * constraints (like the gma500 GEM driver, which requires RAM below 4GB),
     * we may need to copy to a suitable page before moving to filecache.
     *
     * In a future release, this may well be extended to respect cpuset and
     * NUMA mempolicy, and applied also to anonymous pages in do_swap_page();
     * but for now it is a simple matter of zone.
     */
    static bool shmem_should_replace_page(struct page *page, gfp_t gfp)
    {
    	return page_zonenum(page) > gfp_zone(gfp);
    }
    
    static int shmem_replace_page(struct page **pagep, gfp_t gfp,
    				struct shmem_inode_info *info, pgoff_t index)
    {
    	struct page *oldpage, *newpage;
    	struct address_space *swap_mapping;
    	pgoff_t swap_index;
    	int error;
    
    	oldpage = *pagep;
    	swap_index = page_private(oldpage);
    	swap_mapping = page_mapping(oldpage);
    
    	/*
    	 * We have arrived here because our zones are constrained, so don't
    	 * limit chance of success by further cpuset and node constraints.
    	 */
    	gfp &= ~GFP_CONSTRAINT_MASK;
    	newpage = shmem_alloc_page(gfp, info, index);
    	if (!newpage)
    		return -ENOMEM;
    
    	get_page(newpage);
    	copy_highpage(newpage, oldpage);
    	flush_dcache_page(newpage);
    
    	__SetPageLocked(newpage);
    	__SetPageSwapBacked(newpage);
    	SetPageUptodate(newpage);
    	set_page_private(newpage, swap_index);
    	SetPageSwapCache(newpage);
    
    	/*
    	 * Our caller will very soon move newpage out of swapcache, but it's
    	 * a nice clean interface for us to replace oldpage by newpage there.
    	 */
    	xa_lock_irq(&swap_mapping->i_pages);
    	error = shmem_radix_tree_replace(swap_mapping, swap_index, oldpage,
    								   newpage);
    	if (!error) {
    		__inc_node_page_state(newpage, NR_FILE_PAGES);
    		__dec_node_page_state(oldpage, NR_FILE_PAGES);
    	}
    	xa_unlock_irq(&swap_mapping->i_pages);
    
    	if (unlikely(error)) {
    		/*
    		 * Is this possible?  I think not, now that our callers check
    		 * both PageSwapCache and page_private after getting page lock;
    		 * but be defensive.  Reverse old to newpage for clear and free.
    		 */
    		oldpage = newpage;
    	} else {
    		mem_cgroup_migrate(oldpage, newpage);
    		lru_cache_add_anon(newpage);
    		*pagep = newpage;
    	}
    
    	ClearPageSwapCache(oldpage);
    	set_page_private(oldpage, 0);
    
    	unlock_page(oldpage);
    	put_page(oldpage);
    	put_page(oldpage);
    	return error;
    }
    
    /*
     * shmem_getpage_gfp - find page in cache, or get from swap, or allocate
     *
     * If we allocate a new one we do not mark it dirty. That's up to the
     * vm. If we swap it in we mark it dirty since we also free the swap
     * entry since a page cannot live in both the swap and page cache.
     *
     * fault_mm and fault_type are only supplied by shmem_fault:
     * otherwise they are NULL.
     */
    static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
    	struct page **pagep, enum sgp_type sgp, gfp_t gfp,
    	struct vm_area_struct *vma, struct vm_fault *vmf, int *fault_type)
    {
    	struct address_space *mapping = inode->i_mapping;
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	struct shmem_sb_info *sbinfo;
    	struct mm_struct *charge_mm;
    	struct mem_cgroup *memcg;
    	struct page *page;
    	swp_entry_t swap;
    	enum sgp_type sgp_huge = sgp;
    	pgoff_t hindex = index;
    	int error;
    	int once = 0;
    	int alloced = 0;
    
    	if (index > (MAX_LFS_FILESIZE >> PAGE_SHIFT))
    		return -EFBIG;
    	if (sgp == SGP_NOHUGE || sgp == SGP_HUGE)
    		sgp = SGP_CACHE;
    repeat:
    	swap.val = 0;
    	page = find_lock_entry(mapping, index);
    	if (radix_tree_exceptional_entry(page)) {
    		swap = radix_to_swp_entry(page);
    		page = NULL;
    	}
    
    	if (sgp <= SGP_CACHE &&
    	    ((loff_t)index << PAGE_SHIFT) >= i_size_read(inode)) {
    		error = -EINVAL;
    		goto unlock;
    	}
    
    	if (page && sgp == SGP_WRITE)
    		mark_page_accessed(page);
    
    	/* fallocated page? */
    	if (page && !PageUptodate(page)) {
    		if (sgp != SGP_READ)
    			goto clear;
    		unlock_page(page);
    		put_page(page);
    		page = NULL;
    	}
    	if (page || (sgp == SGP_READ && !swap.val)) {
    		*pagep = page;
    		return 0;
    	}
    
    	/*
    	 * Fast cache lookup did not find it:
    	 * bring it back from swap or allocate.
    	 */
    	sbinfo = SHMEM_SB(inode->i_sb);
    	charge_mm = vma ? vma->vm_mm : current->mm;
    
    	if (swap.val) {
    		/* Look it up and read it in.. */
    		page = lookup_swap_cache(swap, NULL, 0);
    		if (!page) {
    			/* Or update major stats only when swapin succeeds?? */
    			if (fault_type) {
    				*fault_type |= VM_FAULT_MAJOR;
    				count_vm_event(PGMAJFAULT);
    				count_memcg_event_mm(charge_mm, PGMAJFAULT);
    			}
    			/* Here we actually start the io */
    			page = shmem_swapin(swap, gfp, info, index);
    			if (!page) {
    				error = -ENOMEM;
    				goto failed;
    			}
    		}
    
    		/* We have to do this with page locked to prevent races */
    		lock_page(page);
    		if (!PageSwapCache(page) || page_private(page) != swap.val ||
    		    !shmem_confirm_swap(mapping, index, swap)) {
    			error = -EEXIST;	/* try again */
    			goto unlock;
    		}
    		if (!PageUptodate(page)) {
    			error = -EIO;
    			goto failed;
    		}
    		wait_on_page_writeback(page);
    
    		if (shmem_should_replace_page(page, gfp)) {
    			error = shmem_replace_page(&page, gfp, info, index);
    			if (error)
    				goto failed;
    		}
    
    		error = mem_cgroup_try_charge(page, charge_mm, gfp, &memcg,
    				false);
    		if (!error) {
    			error = shmem_add_to_page_cache(page, mapping, index,
    						swp_to_radix_entry(swap));
    			/*
    			 * We already confirmed swap under page lock, and make
    			 * no memory allocation here, so usually no possibility
    			 * of error; but free_swap_and_cache() only trylocks a
    			 * page, so it is just possible that the entry has been
    			 * truncated or holepunched since swap was confirmed.
    			 * shmem_undo_range() will have done some of the
    			 * unaccounting, now delete_from_swap_cache() will do
    			 * the rest.
    			 * Reset swap.val? No, leave it so "failed" goes back to
    			 * "repeat": reading a hole and writing should succeed.
    			 */
    			if (error) {
    				mem_cgroup_cancel_charge(page, memcg, false);
    				delete_from_swap_cache(page);
    			}
    		}
    		if (error)
    			goto failed;
    
    		mem_cgroup_commit_charge(page, memcg, true, false);
    
    		spin_lock_irq(&info->lock);
    		info->swapped--;
    		shmem_recalc_inode(inode);
    		spin_unlock_irq(&info->lock);
    
    		if (sgp == SGP_WRITE)
    			mark_page_accessed(page);
    
    		delete_from_swap_cache(page);
    		set_page_dirty(page);
    		swap_free(swap);
    
    	} else {
    		if (vma && userfaultfd_missing(vma)) {
    			*fault_type = handle_userfault(vmf, VM_UFFD_MISSING);
    			return 0;
    		}
    
    		/* shmem_symlink() */
    		if (mapping->a_ops != &shmem_aops)
    			goto alloc_nohuge;
    		if (shmem_huge == SHMEM_HUGE_DENY || sgp_huge == SGP_NOHUGE)
    			goto alloc_nohuge;
    		if (shmem_huge == SHMEM_HUGE_FORCE)
    			goto alloc_huge;
    		switch (sbinfo->huge) {
    			loff_t i_size;
    			pgoff_t off;
    		case SHMEM_HUGE_NEVER:
    			goto alloc_nohuge;
    		case SHMEM_HUGE_WITHIN_SIZE:
    			off = round_up(index, HPAGE_PMD_NR);
    			i_size = round_up(i_size_read(inode), PAGE_SIZE);
    			if (i_size >= HPAGE_PMD_SIZE &&
    					i_size >> PAGE_SHIFT >= off)
    				goto alloc_huge;
    			/* fallthrough */
    		case SHMEM_HUGE_ADVISE:
    			if (sgp_huge == SGP_HUGE)
    				goto alloc_huge;
    			/* TODO: implement fadvise() hints */
    			goto alloc_nohuge;
    		}
    
    alloc_huge:
    		page = shmem_alloc_and_acct_page(gfp, inode, index, true);
    		if (IS_ERR(page)) {
    alloc_nohuge:		page = shmem_alloc_and_acct_page(gfp, inode,
    					index, false);
    		}
    		if (IS_ERR(page)) {
    			int retry = 5;
    			error = PTR_ERR(page);
    			page = NULL;
    			if (error != -ENOSPC)
    				goto failed;
    			/*
    			 * Try to reclaim some spece by splitting a huge page
    			 * beyond i_size on the filesystem.
    			 */
    			while (retry--) {
    				int ret;
    				ret = shmem_unused_huge_shrink(sbinfo, NULL, 1);
    				if (ret == SHRINK_STOP)
    					break;
    				if (ret)
    					goto alloc_nohuge;
    			}
    			goto failed;
    		}
    
    		if (PageTransHuge(page))
    			hindex = round_down(index, HPAGE_PMD_NR);
    		else
    			hindex = index;
    
    		if (sgp == SGP_WRITE)
    			__SetPageReferenced(page);
    
    		error = mem_cgroup_try_charge(page, charge_mm, gfp, &memcg,
    				PageTransHuge(page));
    		if (error)
    			goto unacct;
    		error = radix_tree_maybe_preload_order(gfp & GFP_RECLAIM_MASK,
    				compound_order(page));
    		if (!error) {
    			error = shmem_add_to_page_cache(page, mapping, hindex,
    							NULL);
    			radix_tree_preload_end();
    		}
    		if (error) {
    			mem_cgroup_cancel_charge(page, memcg,
    					PageTransHuge(page));
    			goto unacct;
    		}
    		mem_cgroup_commit_charge(page, memcg, false,
    				PageTransHuge(page));
    		lru_cache_add_anon(page);
    
    		spin_lock_irq(&info->lock);
    		info->alloced += 1 << compound_order(page);
    		inode->i_blocks += BLOCKS_PER_PAGE << compound_order(page);
    		shmem_recalc_inode(inode);
    		spin_unlock_irq(&info->lock);
    		alloced = true;
    
    		if (PageTransHuge(page) &&
    				DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE) <
    				hindex + HPAGE_PMD_NR - 1) {
    			/*
    			 * Part of the huge page is beyond i_size: subject
    			 * to shrink under memory pressure.
    			 */
    			spin_lock(&sbinfo->shrinklist_lock);
    			/*
    			 * _careful to defend against unlocked access to
    			 * ->shrink_list in shmem_unused_huge_shrink()
    			 */
    			if (list_empty_careful(&info->shrinklist)) {
    				list_add_tail(&info->shrinklist,
    						&sbinfo->shrinklist);
    				sbinfo->shrinklist_len++;
    			}
    			spin_unlock(&sbinfo->shrinklist_lock);
    		}
    
    		/*
    		 * Let SGP_FALLOC use the SGP_WRITE optimization on a new page.
    		 */
    		if (sgp == SGP_FALLOC)
    			sgp = SGP_WRITE;
    clear:
    		/*
    		 * Let SGP_WRITE caller clear ends if write does not fill page;
    		 * but SGP_FALLOC on a page fallocated earlier must initialize
    		 * it now, lest undo on failure cancel our earlier guarantee.
    		 */
    		if (sgp != SGP_WRITE && !PageUptodate(page)) {
    			struct page *head = compound_head(page);
    			int i;
    
    			for (i = 0; i < (1 << compound_order(head)); i++) {
    				clear_highpage(head + i);
    				flush_dcache_page(head + i);
    			}
    			SetPageUptodate(head);
    		}
    	}
    
    	/* Perhaps the file has been truncated since we checked */
    	if (sgp <= SGP_CACHE &&
    	    ((loff_t)index << PAGE_SHIFT) >= i_size_read(inode)) {
    		if (alloced) {
    			ClearPageDirty(page);
    			delete_from_page_cache(page);
    			spin_lock_irq(&info->lock);
    			shmem_recalc_inode(inode);
    			spin_unlock_irq(&info->lock);
    		}
    		error = -EINVAL;
    		goto unlock;
    	}
    	*pagep = page + index - hindex;
    	return 0;
    
    	/*
    	 * Error recovery.
    	 */
    unacct:
    	shmem_inode_unacct_blocks(inode, 1 << compound_order(page));
    
    	if (PageTransHuge(page)) {
    		unlock_page(page);
    		put_page(page);
    		goto alloc_nohuge;
    	}
    failed:
    	if (swap.val && !shmem_confirm_swap(mapping, index, swap))
    		error = -EEXIST;
    unlock:
    	if (page) {
    		unlock_page(page);
    		put_page(page);
    	}
    	if (error == -ENOSPC && !once++) {
    		spin_lock_irq(&info->lock);
    		shmem_recalc_inode(inode);
    		spin_unlock_irq(&info->lock);
    		goto repeat;
    	}
    	if (error == -EEXIST)	/* from above or from radix_tree_insert */
    		goto repeat;
    	return error;
    }
    
    /*
     * This is like autoremove_wake_function, but it removes the wait queue
     * entry unconditionally - even if something else had already woken the
     * target.
     */
    static int synchronous_wake_function(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
    {
    	int ret = default_wake_function(wait, mode, sync, key);
    	list_del_init(&wait->entry);
    	return ret;
    }
    
    static int shmem_fault(struct vm_fault *vmf)
    {
    	struct vm_area_struct *vma = vmf->vma;
    	struct inode *inode = file_inode(vma->vm_file);
    	gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
    	enum sgp_type sgp;
    	int error;
    	int ret = VM_FAULT_LOCKED;
    
    	/*
    	 * Trinity finds that probing a hole which tmpfs is punching can
    	 * prevent the hole-punch from ever completing: which in turn
    	 * locks writers out with its hold on i_mutex.  So refrain from
    	 * faulting pages into the hole while it's being punched.  Although
    	 * shmem_undo_range() does remove the additions, it may be unable to
    	 * keep up, as each new page needs its own unmap_mapping_range() call,
    	 * and the i_mmap tree grows ever slower to scan if new vmas are added.
    	 *
    	 * It does not matter if we sometimes reach this check just before the
    	 * hole-punch begins, so that one fault then races with the punch:
    	 * we just need to make racing faults a rare case.
    	 *
    	 * The implementation below would be much simpler if we just used a
    	 * standard mutex or completion: but we cannot take i_mutex in fault,
    	 * and bloating every shmem inode for this unlikely case would be sad.
    	 */
    	if (unlikely(inode->i_private)) {
    		struct shmem_falloc *shmem_falloc;
    
    		spin_lock(&inode->i_lock);
    		shmem_falloc = inode->i_private;
    		if (shmem_falloc &&
    		    shmem_falloc->waitq &&
    		    vmf->pgoff >= shmem_falloc->start &&
    		    vmf->pgoff < shmem_falloc->next) {
    			wait_queue_head_t *shmem_falloc_waitq;
    			DEFINE_WAIT_FUNC(shmem_fault_wait, synchronous_wake_function);
    
    			ret = VM_FAULT_NOPAGE;
    			if ((vmf->flags & FAULT_FLAG_ALLOW_RETRY) &&
    			   !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
    				/* It's polite to up mmap_sem if we can */
    				up_read(&vma->vm_mm->mmap_sem);
    				ret = VM_FAULT_RETRY;
    			}
    
    			shmem_falloc_waitq = shmem_falloc->waitq;
    			prepare_to_wait(shmem_falloc_waitq, &shmem_fault_wait,
    					TASK_UNINTERRUPTIBLE);
    			spin_unlock(&inode->i_lock);
    			schedule();
    
    			/*
    			 * shmem_falloc_waitq points into the shmem_fallocate()
    			 * stack of the hole-punching task: shmem_falloc_waitq
    			 * is usually invalid by the time we reach here, but
    			 * finish_wait() does not dereference it in that case;
    			 * though i_lock needed lest racing with wake_up_all().
    			 */
    			spin_lock(&inode->i_lock);
    			finish_wait(shmem_falloc_waitq, &shmem_fault_wait);
    			spin_unlock(&inode->i_lock);
    			return ret;
    		}
    		spin_unlock(&inode->i_lock);
    	}
    
    	sgp = SGP_CACHE;
    
    	if ((vma->vm_flags & VM_NOHUGEPAGE) ||
    	    test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
    		sgp = SGP_NOHUGE;
    	else if (vma->vm_flags & VM_HUGEPAGE)
    		sgp = SGP_HUGE;
    
    	error = shmem_getpage_gfp(inode, vmf->pgoff, &vmf->page, sgp,
    				  gfp, vma, vmf, &ret);
    	if (error)
    		return ((error == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS);
    	return ret;
    }
    
    unsigned long shmem_get_unmapped_area(struct file *file,
    				      unsigned long uaddr, unsigned long len,
    				      unsigned long pgoff, unsigned long flags)
    {
    	unsigned long (*get_area)(struct file *,
    		unsigned long, unsigned long, unsigned long, unsigned long);
    	unsigned long addr;
    	unsigned long offset;
    	unsigned long inflated_len;
    	unsigned long inflated_addr;
    	unsigned long inflated_offset;
    
    	if (len > TASK_SIZE)
    		return -ENOMEM;
    
    	get_area = current->mm->get_unmapped_area;
    	addr = get_area(file, uaddr, len, pgoff, flags);
    
    	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
    		return addr;
    	if (IS_ERR_VALUE(addr))
    		return addr;
    	if (addr & ~PAGE_MASK)
    		return addr;
    	if (addr > TASK_SIZE - len)
    		return addr;
    
    	if (shmem_huge == SHMEM_HUGE_DENY)
    		return addr;
    	if (len < HPAGE_PMD_SIZE)
    		return addr;
    	if (flags & MAP_FIXED)
    		return addr;
    	/*
    	 * Our priority is to support MAP_SHARED mapped hugely;
    	 * and support MAP_PRIVATE mapped hugely too, until it is COWed.
    	 * But if caller specified an address hint, respect that as before.
    	 */
    	if (uaddr)
    		return addr;
    
    	if (shmem_huge != SHMEM_HUGE_FORCE) {
    		struct super_block *sb;
    
    		if (file) {
    			VM_BUG_ON(file->f_op != &shmem_file_operations);
    			sb = file_inode(file)->i_sb;
    		} else {
    			/*
    			 * Called directly from mm/mmap.c, or drivers/char/mem.c
    			 * for "/dev/zero", to create a shared anonymous object.
    			 */
    			if (IS_ERR(shm_mnt))
    				return addr;
    			sb = shm_mnt->mnt_sb;
    		}
    		if (SHMEM_SB(sb)->huge == SHMEM_HUGE_NEVER)
    			return addr;
    	}
    
    	offset = (pgoff << PAGE_SHIFT) & (HPAGE_PMD_SIZE-1);
    	if (offset && offset + len < 2 * HPAGE_PMD_SIZE)
    		return addr;
    	if ((addr & (HPAGE_PMD_SIZE-1)) == offset)
    		return addr;
    
    	inflated_len = len + HPAGE_PMD_SIZE - PAGE_SIZE;
    	if (inflated_len > TASK_SIZE)
    		return addr;
    	if (inflated_len < len)
    		return addr;
    
    	inflated_addr = get_area(NULL, 0, inflated_len, 0, flags);
    	if (IS_ERR_VALUE(inflated_addr))
    		return addr;
    	if (inflated_addr & ~PAGE_MASK)
    		return addr;
    
    	inflated_offset = inflated_addr & (HPAGE_PMD_SIZE-1);
    	inflated_addr += offset - inflated_offset;
    	if (inflated_offset > offset)
    		inflated_addr += HPAGE_PMD_SIZE;
    
    	if (inflated_addr > TASK_SIZE - len)
    		return addr;
    	return inflated_addr;
    }
    
    #ifdef CONFIG_NUMA
    static int shmem_set_policy(struct vm_area_struct *vma, struct mempolicy *mpol)
    {
    	struct inode *inode = file_inode(vma->vm_file);
    	return mpol_set_shared_policy(&SHMEM_I(inode)->policy, vma, mpol);
    }
    
    static struct mempolicy *shmem_get_policy(struct vm_area_struct *vma,
    					  unsigned long addr)
    {
    	struct inode *inode = file_inode(vma->vm_file);
    	pgoff_t index;
    
    	index = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
    	return mpol_shared_policy_lookup(&SHMEM_I(inode)->policy, index);
    }
    #endif
    
    int shmem_lock(struct file *file, int lock, struct user_struct *user)
    {
    	struct inode *inode = file_inode(file);
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	int retval = -ENOMEM;
    
    	spin_lock_irq(&info->lock);
    	if (lock && !(info->flags & VM_LOCKED)) {
    		if (!user_shm_lock(inode->i_size, user))
    			goto out_nomem;
    		info->flags |= VM_LOCKED;
    		mapping_set_unevictable(file->f_mapping);
    	}
    	if (!lock && (info->flags & VM_LOCKED) && user) {
    		user_shm_unlock(inode->i_size, user);
    		info->flags &= ~VM_LOCKED;
    		mapping_clear_unevictable(file->f_mapping);
    	}
    	retval = 0;
    
    out_nomem:
    	spin_unlock_irq(&info->lock);
    	return retval;
    }
    
    static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
    {
    	file_accessed(file);
    	vma->vm_ops = &shmem_vm_ops;
    	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE) &&
    			((vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK) <
    			(vma->vm_end & HPAGE_PMD_MASK)) {
    		khugepaged_enter(vma, vma->vm_flags);
    	}
    	return 0;
    }
    
    static struct inode *shmem_get_inode(struct super_block *sb, const struct inode *dir,
    				     umode_t mode, dev_t dev, unsigned long flags)
    {
    	struct inode *inode;
    	struct shmem_inode_info *info;
    	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
    
    	if (shmem_reserve_inode(sb))
    		return NULL;
    
    	inode = new_inode(sb);
    	if (inode) {
    		inode->i_ino = get_next_ino();
    		inode_init_owner(inode, dir, mode);
    		inode->i_blocks = 0;
    		inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
    		inode->i_generation = get_seconds();
    		info = SHMEM_I(inode);
    		memset(info, 0, (char *)inode - (char *)info);
    		spin_lock_init(&info->lock);
    		info->seals = F_SEAL_SEAL;
    		info->flags = flags & VM_NORESERVE;
    		INIT_LIST_HEAD(&info->shrinklist);
    		INIT_LIST_HEAD(&info->swaplist);
    		simple_xattrs_init(&info->xattrs);
    		cache_no_acl(inode);
    
    		switch (mode & S_IFMT) {
    		default:
    			inode->i_op = &shmem_special_inode_operations;
    			init_special_inode(inode, mode, dev);
    			break;
    		case S_IFREG:
    			inode->i_mapping->a_ops = &shmem_aops;
    			inode->i_op = &shmem_inode_operations;
    			inode->i_fop = &shmem_file_operations;
    			mpol_shared_policy_init(&info->policy,
    						 shmem_get_sbmpol(sbinfo));
    			break;
    		case S_IFDIR:
    			inc_nlink(inode);
    			/* Some things misbehave if size == 0 on a directory */
    			inode->i_size = 2 * BOGO_DIRENT_SIZE;
    			inode->i_op = &shmem_dir_inode_operations;
    			inode->i_fop = &simple_dir_operations;
    			break;
    		case S_IFLNK:
    			/*
    			 * Must not load anything in the rbtree,
    			 * mpol_free_shared_policy will not be called.
    			 */
    			mpol_shared_policy_init(&info->policy, NULL);
    			break;
    		}
    	} else
    		shmem_free_inode(sb);
    	return inode;
    }
    
    bool shmem_mapping(struct address_space *mapping)
    {
    	return mapping->a_ops == &shmem_aops;
    }
    
    static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
    				  pmd_t *dst_pmd,
    				  struct vm_area_struct *dst_vma,
    				  unsigned long dst_addr,
    				  unsigned long src_addr,
    				  bool zeropage,
    				  struct page **pagep)
    {
    	struct inode *inode = file_inode(dst_vma->vm_file);
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	struct address_space *mapping = inode->i_mapping;
    	gfp_t gfp = mapping_gfp_mask(mapping);
    	pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
    	struct mem_cgroup *memcg;
    	spinlock_t *ptl;
    	void *page_kaddr;
    	struct page *page;
    	pte_t _dst_pte, *dst_pte;
    	int ret;
    
    	ret = -ENOMEM;
    	if (!shmem_inode_acct_block(inode, 1))
    		goto out;
    
    	if (!*pagep) {
    		page = shmem_alloc_page(gfp, info, pgoff);
    		if (!page)
    			goto out_unacct_blocks;
    
    		if (!zeropage) {	/* mcopy_atomic */
    			page_kaddr = kmap_atomic(page);
    			ret = copy_from_user(page_kaddr,
    					     (const void __user *)src_addr,
    					     PAGE_SIZE);
    			kunmap_atomic(page_kaddr);
    
    			/* fallback to copy_from_user outside mmap_sem */
    			if (unlikely(ret)) {
    				*pagep = page;
    				shmem_inode_unacct_blocks(inode, 1);
    				/* don't free the page */
    				return -EFAULT;
    			}
    		} else {		/* mfill_zeropage_atomic */
    			clear_highpage(page);
    		}
    	} else {
    		page = *pagep;
    		*pagep = NULL;
    	}
    
    	VM_BUG_ON(PageLocked(page) || PageSwapBacked(page));
    	__SetPageLocked(page);
    	__SetPageSwapBacked(page);
    	__SetPageUptodate(page);
    
    	ret = mem_cgroup_try_charge(page, dst_mm, gfp, &memcg, false);
    	if (ret)
    		goto out_release;
    
    	ret = radix_tree_maybe_preload(gfp & GFP_RECLAIM_MASK);
    	if (!ret) {
    		ret = shmem_add_to_page_cache(page, mapping, pgoff, NULL);
    		radix_tree_preload_end();
    	}
    	if (ret)
    		goto out_release_uncharge;
    
    	mem_cgroup_commit_charge(page, memcg, false, false);
    
    	_dst_pte = mk_pte(page, dst_vma->vm_page_prot);
    	if (dst_vma->vm_flags & VM_WRITE)
    		_dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));
    
    	ret = -EEXIST;
    	dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
    	if (!pte_none(*dst_pte))
    		goto out_release_uncharge_unlock;
    
    	lru_cache_add_anon(page);
    
    	spin_lock(&info->lock);
    	info->alloced++;
    	inode->i_blocks += BLOCKS_PER_PAGE;
    	shmem_recalc_inode(inode);
    	spin_unlock(&info->lock);
    
    	inc_mm_counter(dst_mm, mm_counter_file(page));
    	page_add_file_rmap(page, false);
    	set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
    
    	/* No need to invalidate - it was non-present before */
    	update_mmu_cache(dst_vma, dst_addr, dst_pte);
    	unlock_page(page);
    	pte_unmap_unlock(dst_pte, ptl);
    	ret = 0;
    out:
    	return ret;
    out_release_uncharge_unlock:
    	pte_unmap_unlock(dst_pte, ptl);
    out_release_uncharge:
    	mem_cgroup_cancel_charge(page, memcg, false);
    out_release:
    	unlock_page(page);
    	put_page(page);
    out_unacct_blocks:
    	shmem_inode_unacct_blocks(inode, 1);
    	goto out;
    }
    
    int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm,
    			   pmd_t *dst_pmd,
    			   struct vm_area_struct *dst_vma,
    			   unsigned long dst_addr,
    			   unsigned long src_addr,
    			   struct page **pagep)
    {
    	return shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
    				      dst_addr, src_addr, false, pagep);
    }
    
    int shmem_mfill_zeropage_pte(struct mm_struct *dst_mm,
    			     pmd_t *dst_pmd,
    			     struct vm_area_struct *dst_vma,
    			     unsigned long dst_addr)
    {
    	struct page *page = NULL;
    
    	return shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
    				      dst_addr, 0, true, &page);
    }
    
    #ifdef CONFIG_TMPFS
    static const struct inode_operations shmem_symlink_inode_operations;
    static const struct inode_operations shmem_short_symlink_operations;
    
    #ifdef CONFIG_TMPFS_XATTR
    static int shmem_initxattrs(struct inode *, const struct xattr *, void *);
    #else
    #define shmem_initxattrs NULL
    #endif
    
    static int
    shmem_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;
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	pgoff_t index = pos >> PAGE_SHIFT;
    
    	/* i_mutex is held by caller */
    	if (unlikely(info->seals & (F_SEAL_WRITE | F_SEAL_GROW))) {
    		if (info->seals & F_SEAL_WRITE)
    			return -EPERM;
    		if ((info->seals & F_SEAL_GROW) && pos + len > inode->i_size)
    			return -EPERM;
    	}
    
    	return shmem_getpage(inode, index, pagep, SGP_WRITE);
    }
    
    static int
    shmem_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;
    
    	if (pos + copied > inode->i_size)
    		i_size_write(inode, pos + copied);
    
    	if (!PageUptodate(page)) {
    		struct page *head = compound_head(page);
    		if (PageTransCompound(page)) {
    			int i;
    
    			for (i = 0; i < HPAGE_PMD_NR; i++) {
    				if (head + i == page)
    					continue;
    				clear_highpage(head + i);
    				flush_dcache_page(head + i);
    			}
    		}
    		if (copied < PAGE_SIZE) {
    			unsigned from = pos & (PAGE_SIZE - 1);
    			zero_user_segments(page, 0, from,
    					from + copied, PAGE_SIZE);
    		}
    		SetPageUptodate(head);
    	}
    	set_page_dirty(page);
    	unlock_page(page);
    	put_page(page);
    
    	return copied;
    }
    
    static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
    {
    	struct file *file = iocb->ki_filp;
    	struct inode *inode = file_inode(file);
    	struct address_space *mapping = inode->i_mapping;
    	pgoff_t index;
    	unsigned long offset;
    	enum sgp_type sgp = SGP_READ;
    	int error = 0;
    	ssize_t retval = 0;
    	loff_t *ppos = &iocb->ki_pos;
    
    	/*
    	 * Might this read be for a stacking filesystem?  Then when reading
    	 * holes of a sparse file, we actually need to allocate those pages,
    	 * and even mark them dirty, so it cannot exceed the max_blocks limit.
    	 */
    	if (!iter_is_iovec(to))
    		sgp = SGP_CACHE;
    
    	index = *ppos >> PAGE_SHIFT;
    	offset = *ppos & ~PAGE_MASK;
    
    	for (;;) {
    		struct page *page = NULL;
    		pgoff_t end_index;
    		unsigned long nr, ret;
    		loff_t i_size = i_size_read(inode);
    
    		end_index = i_size >> PAGE_SHIFT;
    		if (index > end_index)
    			break;
    		if (index == end_index) {
    			nr = i_size & ~PAGE_MASK;
    			if (nr <= offset)
    				break;
    		}
    
    		error = shmem_getpage(inode, index, &page, sgp);
    		if (error) {
    			if (error == -EINVAL)
    				error = 0;
    			break;
    		}
    		if (page) {
    			if (sgp == SGP_CACHE)
    				set_page_dirty(page);
    			unlock_page(page);
    		}
    
    		/*
    		 * We must evaluate after, since reads (unlike writes)
    		 * are called without i_mutex protection against truncate
    		 */
    		nr = PAGE_SIZE;
    		i_size = i_size_read(inode);
    		end_index = i_size >> PAGE_SHIFT;
    		if (index == end_index) {
    			nr = i_size & ~PAGE_MASK;
    			if (nr <= offset) {
    				if (page)
    					put_page(page);
    				break;
    			}
    		}
    		nr -= offset;
    
    		if (page) {
    			/*
    			 * If users can be writing to this page using arbitrary
    			 * virtual addresses, take care about potential aliasing
    			 * before reading the page on the kernel side.
    			 */
    			if (mapping_writably_mapped(mapping))
    				flush_dcache_page(page);
    			/*
    			 * Mark the page accessed if we read the beginning.
    			 */
    			if (!offset)
    				mark_page_accessed(page);
    		} else {
    			page = ZERO_PAGE(0);
    			get_page(page);
    		}
    
    		/*
    		 * Ok, we have the page, and it's up-to-date, so
    		 * now we can copy it to user space...
    		 */
    		ret = copy_page_to_iter(page, offset, nr, to);
    		retval += ret;
    		offset += ret;
    		index += offset >> PAGE_SHIFT;
    		offset &= ~PAGE_MASK;
    
    		put_page(page);
    		if (!iov_iter_count(to))
    			break;
    		if (ret < nr) {
    			error = -EFAULT;
    			break;
    		}
    		cond_resched();
    	}
    
    	*ppos = ((loff_t) index << PAGE_SHIFT) + offset;
    	file_accessed(file);
    	return retval ? retval : error;
    }
    
    /*
     * llseek SEEK_DATA or SEEK_HOLE through the radix_tree.
     */
    static pgoff_t shmem_seek_hole_data(struct address_space *mapping,
    				    pgoff_t index, pgoff_t end, int whence)
    {
    	struct page *page;
    	struct pagevec pvec;
    	pgoff_t indices[PAGEVEC_SIZE];
    	bool done = false;
    	int i;
    
    	pagevec_init(&pvec);
    	pvec.nr = 1;		/* start small: we may be there already */
    	while (!done) {
    		pvec.nr = find_get_entries(mapping, index,
    					pvec.nr, pvec.pages, indices);
    		if (!pvec.nr) {
    			if (whence == SEEK_DATA)
    				index = end;
    			break;
    		}
    		for (i = 0; i < pvec.nr; i++, index++) {
    			if (index < indices[i]) {
    				if (whence == SEEK_HOLE) {
    					done = true;
    					break;
    				}
    				index = indices[i];
    			}
    			page = pvec.pages[i];
    			if (page && !radix_tree_exceptional_entry(page)) {
    				if (!PageUptodate(page))
    					page = NULL;
    			}
    			if (index >= end ||
    			    (page && whence == SEEK_DATA) ||
    			    (!page && whence == SEEK_HOLE)) {
    				done = true;
    				break;
    			}
    		}
    		pagevec_remove_exceptionals(&pvec);
    		pagevec_release(&pvec);
    		pvec.nr = PAGEVEC_SIZE;
    		cond_resched();
    	}
    	return index;
    }
    
    static loff_t shmem_file_llseek(struct file *file, loff_t offset, int whence)
    {
    	struct address_space *mapping = file->f_mapping;
    	struct inode *inode = mapping->host;
    	pgoff_t start, end;
    	loff_t new_offset;
    
    	if (whence != SEEK_DATA && whence != SEEK_HOLE)
    		return generic_file_llseek_size(file, offset, whence,
    					MAX_LFS_FILESIZE, i_size_read(inode));
    	inode_lock(inode);
    	/* We're holding i_mutex so we can access i_size directly */
    
    	if (offset < 0)
    		offset = -EINVAL;
    	else if (offset >= inode->i_size)
    		offset = -ENXIO;
    	else {
    		start = offset >> PAGE_SHIFT;
    		end = (inode->i_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
    		new_offset = shmem_seek_hole_data(mapping, start, end, whence);
    		new_offset <<= PAGE_SHIFT;
    		if (new_offset > offset) {
    			if (new_offset < inode->i_size)
    				offset = new_offset;
    			else if (whence == SEEK_DATA)
    				offset = -ENXIO;
    			else
    				offset = inode->i_size;
    		}
    	}
    
    	if (offset >= 0)
    		offset = vfs_setpos(file, offset, MAX_LFS_FILESIZE);
    	inode_unlock(inode);
    	return offset;
    }
    
    /*
     * We need a tag: a new tag would expand every radix_tree_node by 8 bytes,
     * so reuse a tag which we firmly believe is never set or cleared on tmpfs
     * or hugetlbfs because they are memory only filesystems.
     */
    #define MEMFD_TAG_PINNED        PAGECACHE_TAG_TOWRITE
    #define LAST_SCAN               4       /* about 150ms max */
    
    static void memfd_tag_pins(struct address_space *mapping)
    {
    	struct radix_tree_iter iter;
    	void __rcu **slot;
    	pgoff_t start;
    	struct page *page;
    
    	lru_add_drain();
    	start = 0;
    	rcu_read_lock();
    
    	radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start) {
    		page = radix_tree_deref_slot(slot);
    		if (!page || radix_tree_exception(page)) {
    			if (radix_tree_deref_retry(page)) {
    				slot = radix_tree_iter_retry(&iter);
    				continue;
    			}
    		} else if (page_count(page) - page_mapcount(page) > 1) {
    			xa_lock_irq(&mapping->i_pages);
    			radix_tree_tag_set(&mapping->i_pages, iter.index,
    					   MEMFD_TAG_PINNED);
    			xa_unlock_irq(&mapping->i_pages);
    		}
    
    		if (need_resched()) {
    			slot = radix_tree_iter_resume(slot, &iter);
    			cond_resched_rcu();
    		}
    	}
    	rcu_read_unlock();
    }
    
    /*
     * Setting SEAL_WRITE requires us to verify there's no pending writer. However,
     * via get_user_pages(), drivers might have some pending I/O without any active
     * user-space mappings (eg., direct-IO, AIO). Therefore, we look at all pages
     * and see whether it has an elevated ref-count. If so, we tag them and wait for
     * them to be dropped.
     * The caller must guarantee that no new user will acquire writable references
     * to those pages to avoid races.
     */
    static int memfd_wait_for_pins(struct address_space *mapping)
    {
    	struct radix_tree_iter iter;
    	void __rcu **slot;
    	pgoff_t start;
    	struct page *page;
    	int error, scan;
    
    	memfd_tag_pins(mapping);
    
    	error = 0;
    	for (scan = 0; scan <= LAST_SCAN; scan++) {
    		if (!radix_tree_tagged(&mapping->i_pages, MEMFD_TAG_PINNED))
    			break;
    
    		if (!scan)
    			lru_add_drain_all();
    		else if (schedule_timeout_killable((HZ << scan) / 200))
    			scan = LAST_SCAN;
    
    		start = 0;
    		rcu_read_lock();
    		radix_tree_for_each_tagged(slot, &mapping->i_pages, &iter,
    					   start, MEMFD_TAG_PINNED) {
    
    			page = radix_tree_deref_slot(slot);
    			if (radix_tree_exception(page)) {
    				if (radix_tree_deref_retry(page)) {
    					slot = radix_tree_iter_retry(&iter);
    					continue;
    				}
    
    				page = NULL;
    			}
    
    			if (page &&
    			    page_count(page) - page_mapcount(page) != 1) {
    				if (scan < LAST_SCAN)
    					goto continue_resched;
    
    				/*
    				 * On the last scan, we clean up all those tags
    				 * we inserted; but make a note that we still
    				 * found pages pinned.
    				 */
    				error = -EBUSY;
    			}
    
    			xa_lock_irq(&mapping->i_pages);
    			radix_tree_tag_clear(&mapping->i_pages,
    					     iter.index, MEMFD_TAG_PINNED);
    			xa_unlock_irq(&mapping->i_pages);
    continue_resched:
    			if (need_resched()) {
    				slot = radix_tree_iter_resume(slot, &iter);
    				cond_resched_rcu();
    			}
    		}
    		rcu_read_unlock();
    	}
    
    	return error;
    }
    
    static unsigned int *memfd_file_seals_ptr(struct file *file)
    {
    	if (shmem_file(file))
    		return &SHMEM_I(file_inode(file))->seals;
    
    #ifdef CONFIG_HUGETLBFS
    	if (is_file_hugepages(file))
    		return &HUGETLBFS_I(file_inode(file))->seals;
    #endif
    
    	return NULL;
    }
    
    #define F_ALL_SEALS (F_SEAL_SEAL | \
    		     F_SEAL_SHRINK | \
    		     F_SEAL_GROW | \
    		     F_SEAL_WRITE)
    
    static int memfd_add_seals(struct file *file, unsigned int seals)
    {
    	struct inode *inode = file_inode(file);
    	unsigned int *file_seals;
    	int error;
    
    	/*
    	 * SEALING
    	 * Sealing allows multiple parties to share a tmpfs or hugetlbfs file
    	 * but restrict access to a specific subset of file operations. Seals
    	 * can only be added, but never removed. This way, mutually untrusted
    	 * parties can share common memory regions with a well-defined policy.
    	 * A malicious peer can thus never perform unwanted operations on a
    	 * shared object.
    	 *
    	 * Seals are only supported on special tmpfs or hugetlbfs files and
    	 * always affect the whole underlying inode. Once a seal is set, it
    	 * may prevent some kinds of access to the file. Currently, the
    	 * following seals are defined:
    	 *   SEAL_SEAL: Prevent further seals from being set on this file
    	 *   SEAL_SHRINK: Prevent the file from shrinking
    	 *   SEAL_GROW: Prevent the file from growing
    	 *   SEAL_WRITE: Prevent write access to the file
    	 *
    	 * As we don't require any trust relationship between two parties, we
    	 * must prevent seals from being removed. Therefore, sealing a file
    	 * only adds a given set of seals to the file, it never touches
    	 * existing seals. Furthermore, the "setting seals"-operation can be
    	 * sealed itself, which basically prevents any further seal from being
    	 * added.
    	 *
    	 * Semantics of sealing are only defined on volatile files. Only
    	 * anonymous tmpfs and hugetlbfs files support sealing. More
    	 * importantly, seals are never written to disk. Therefore, there's
    	 * no plan to support it on other file types.
    	 */
    
    	if (!(file->f_mode & FMODE_WRITE))
    		return -EPERM;
    	if (seals & ~(unsigned int)F_ALL_SEALS)
    		return -EINVAL;
    
    	inode_lock(inode);
    
    	file_seals = memfd_file_seals_ptr(file);
    	if (!file_seals) {
    		error = -EINVAL;
    		goto unlock;
    	}
    
    	if (*file_seals & F_SEAL_SEAL) {
    		error = -EPERM;
    		goto unlock;
    	}
    
    	if ((seals & F_SEAL_WRITE) && !(*file_seals & F_SEAL_WRITE)) {
    		error = mapping_deny_writable(file->f_mapping);
    		if (error)
    			goto unlock;
    
    		error = memfd_wait_for_pins(file->f_mapping);
    		if (error) {
    			mapping_allow_writable(file->f_mapping);
    			goto unlock;
    		}
    	}
    
    	*file_seals |= seals;
    	error = 0;
    
    unlock:
    	inode_unlock(inode);
    	return error;
    }
    
    static int memfd_get_seals(struct file *file)
    {
    	unsigned int *seals = memfd_file_seals_ptr(file);
    
    	return seals ? *seals : -EINVAL;
    }
    
    long memfd_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
    {
    	long error;
    
    	switch (cmd) {
    	case F_ADD_SEALS:
    		/* disallow upper 32bit */
    		if (arg > UINT_MAX)
    			return -EINVAL;
    
    		error = memfd_add_seals(file, arg);
    		break;
    	case F_GET_SEALS:
    		error = memfd_get_seals(file);
    		break;
    	default:
    		error = -EINVAL;
    		break;
    	}
    
    	return error;
    }
    
    static long shmem_fallocate(struct file *file, int mode, loff_t offset,
    							 loff_t len)
    {
    	struct inode *inode = file_inode(file);
    	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	struct shmem_falloc shmem_falloc;
    	pgoff_t start, index, end;
    	int error;
    
    	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
    		return -EOPNOTSUPP;
    
    	inode_lock(inode);
    
    	if (mode & FALLOC_FL_PUNCH_HOLE) {
    		struct address_space *mapping = file->f_mapping;
    		loff_t unmap_start = round_up(offset, PAGE_SIZE);
    		loff_t unmap_end = round_down(offset + len, PAGE_SIZE) - 1;
    		DECLARE_WAIT_QUEUE_HEAD_ONSTACK(shmem_falloc_waitq);
    
    		/* protected by i_mutex */
    		if (info->seals & F_SEAL_WRITE) {
    			error = -EPERM;
    			goto out;
    		}
    
    		shmem_falloc.waitq = &shmem_falloc_waitq;
    		shmem_falloc.start = unmap_start >> PAGE_SHIFT;
    		shmem_falloc.next = (unmap_end + 1) >> PAGE_SHIFT;
    		spin_lock(&inode->i_lock);
    		inode->i_private = &shmem_falloc;
    		spin_unlock(&inode->i_lock);
    
    		if ((u64)unmap_end > (u64)unmap_start)
    			unmap_mapping_range(mapping, unmap_start,
    					    1 + unmap_end - unmap_start, 0);
    		shmem_truncate_range(inode, offset, offset + len - 1);
    		/* No need to unmap again: hole-punching leaves COWed pages */
    
    		spin_lock(&inode->i_lock);
    		inode->i_private = NULL;
    		wake_up_all(&shmem_falloc_waitq);
    		WARN_ON_ONCE(!list_empty(&shmem_falloc_waitq.head));
    		spin_unlock(&inode->i_lock);
    		error = 0;
    		goto out;
    	}
    
    	/* We need to check rlimit even when FALLOC_FL_KEEP_SIZE */
    	error = inode_newsize_ok(inode, offset + len);
    	if (error)
    		goto out;
    
    	if ((info->seals & F_SEAL_GROW) && offset + len > inode->i_size) {
    		error = -EPERM;
    		goto out;
    	}
    
    	start = offset >> PAGE_SHIFT;
    	end = (offset + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
    	/* Try to avoid a swapstorm if len is impossible to satisfy */
    	if (sbinfo->max_blocks && end - start > sbinfo->max_blocks) {
    		error = -ENOSPC;
    		goto out;
    	}
    
    	shmem_falloc.waitq = NULL;
    	shmem_falloc.start = start;
    	shmem_falloc.next  = start;
    	shmem_falloc.nr_falloced = 0;
    	shmem_falloc.nr_unswapped = 0;
    	spin_lock(&inode->i_lock);
    	inode->i_private = &shmem_falloc;
    	spin_unlock(&inode->i_lock);
    
    	for (index = start; index < end; index++) {
    		struct page *page;
    
    		/*
    		 * Good, the fallocate(2) manpage permits EINTR: we may have
    		 * been interrupted because we are using up too much memory.
    		 */
    		if (signal_pending(current))
    			error = -EINTR;
    		else if (shmem_falloc.nr_unswapped > shmem_falloc.nr_falloced)
    			error = -ENOMEM;
    		else
    			error = shmem_getpage(inode, index, &page, SGP_FALLOC);
    		if (error) {
    			/* Remove the !PageUptodate pages we added */
    			if (index > start) {
    				shmem_undo_range(inode,
    				    (loff_t)start << PAGE_SHIFT,
    				    ((loff_t)index << PAGE_SHIFT) - 1, true);
    			}
    			goto undone;
    		}
    
    		/*
    		 * Inform shmem_writepage() how far we have reached.
    		 * No need for lock or barrier: we have the page lock.
    		 */
    		shmem_falloc.next++;
    		if (!PageUptodate(page))
    			shmem_falloc.nr_falloced++;
    
    		/*
    		 * If !PageUptodate, leave it that way so that freeable pages
    		 * can be recognized if we need to rollback on error later.
    		 * But set_page_dirty so that memory pressure will swap rather
    		 * than free the pages we are allocating (and SGP_CACHE pages
    		 * might still be clean: we now need to mark those dirty too).
    		 */
    		set_page_dirty(page);
    		unlock_page(page);
    		put_page(page);
    		cond_resched();
    	}
    
    	if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)
    		i_size_write(inode, offset + len);
    	inode->i_ctime = current_time(inode);
    undone:
    	spin_lock(&inode->i_lock);
    	inode->i_private = NULL;
    	spin_unlock(&inode->i_lock);
    out:
    	inode_unlock(inode);
    	return error;
    }
    
    static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
    {
    	struct shmem_sb_info *sbinfo = SHMEM_SB(dentry->d_sb);
    
    	buf->f_type = TMPFS_MAGIC;
    	buf->f_bsize = PAGE_SIZE;
    	buf->f_namelen = NAME_MAX;
    	if (sbinfo->max_blocks) {
    		buf->f_blocks = sbinfo->max_blocks;
    		buf->f_bavail =
    		buf->f_bfree  = sbinfo->max_blocks -
    				percpu_counter_sum(&sbinfo->used_blocks);
    	}
    	if (sbinfo->max_inodes) {
    		buf->f_files = sbinfo->max_inodes;
    		buf->f_ffree = sbinfo->free_inodes;
    	}
    	/* else leave those fields 0 like simple_statfs */
    	return 0;
    }
    
    /*
     * File creation. Allocate an inode, and we're done..
     */
    static int
    shmem_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
    {
    	struct inode *inode;
    	int error = -ENOSPC;
    
    	inode = shmem_get_inode(dir->i_sb, dir, mode, dev, VM_NORESERVE);
    	if (inode) {
    		error = simple_acl_create(dir, inode);
    		if (error)
    			goto out_iput;
    		error = security_inode_init_security(inode, dir,
    						     &dentry->d_name,
    						     shmem_initxattrs, NULL);
    		if (error && error != -EOPNOTSUPP)
    			goto out_iput;
    
    		error = 0;
    		dir->i_size += BOGO_DIRENT_SIZE;
    		dir->i_ctime = dir->i_mtime = current_time(dir);
    		d_instantiate(dentry, inode);
    		dget(dentry); /* Extra count - pin the dentry in core */
    	}
    	return error;
    out_iput:
    	iput(inode);
    	return error;
    }
    
    static int
    shmem_tmpfile(struct inode *dir, struct dentry *dentry, umode_t mode)
    {
    	struct inode *inode;
    	int error = -ENOSPC;
    
    	inode = shmem_get_inode(dir->i_sb, dir, mode, 0, VM_NORESERVE);
    	if (inode) {
    		error = security_inode_init_security(inode, dir,
    						     NULL,
    						     shmem_initxattrs, NULL);
    		if (error && error != -EOPNOTSUPP)
    			goto out_iput;
    		error = simple_acl_create(dir, inode);
    		if (error)
    			goto out_iput;
    		d_tmpfile(dentry, inode);
    	}
    	return error;
    out_iput:
    	iput(inode);
    	return error;
    }
    
    static int shmem_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
    {
    	int error;
    
    	if ((error = shmem_mknod(dir, dentry, mode | S_IFDIR, 0)))
    		return error;
    	inc_nlink(dir);
    	return 0;
    }
    
    static int shmem_create(struct inode *dir, struct dentry *dentry, umode_t mode,
    		bool excl)
    {
    	return shmem_mknod(dir, dentry, mode | S_IFREG, 0);
    }
    
    /*
     * Link a file..
     */
    static int shmem_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
    {
    	struct inode *inode = d_inode(old_dentry);
    	int ret;
    
    	/*
    	 * No ordinary (disk based) filesystem counts links as inodes;
    	 * but each new link needs a new dentry, pinning lowmem, and
    	 * tmpfs dentries cannot be pruned until they are unlinked.
    	 */
    	ret = shmem_reserve_inode(inode->i_sb);
    	if (ret)
    		goto out;
    
    	dir->i_size += BOGO_DIRENT_SIZE;
    	inode->i_ctime = dir->i_ctime = dir->i_mtime = current_time(inode);
    	inc_nlink(inode);
    	ihold(inode);	/* New dentry reference */
    	dget(dentry);		/* Extra pinning count for the created dentry */
    	d_instantiate(dentry, inode);
    out:
    	return ret;
    }
    
    static int shmem_unlink(struct inode *dir, struct dentry *dentry)
    {
    	struct inode *inode = d_inode(dentry);
    
    	if (inode->i_nlink > 1 && !S_ISDIR(inode->i_mode))
    		shmem_free_inode(inode->i_sb);
    
    	dir->i_size -= BOGO_DIRENT_SIZE;
    	inode->i_ctime = dir->i_ctime = dir->i_mtime = current_time(inode);
    	drop_nlink(inode);
    	dput(dentry);	/* Undo the count from "create" - this does all the work */
    	return 0;
    }
    
    static int shmem_rmdir(struct inode *dir, struct dentry *dentry)
    {
    	if (!simple_empty(dentry))
    		return -ENOTEMPTY;
    
    	drop_nlink(d_inode(dentry));
    	drop_nlink(dir);
    	return shmem_unlink(dir, dentry);
    }
    
    static int shmem_exchange(struct inode *old_dir, struct dentry *old_dentry, struct inode *new_dir, struct dentry *new_dentry)
    {
    	bool old_is_dir = d_is_dir(old_dentry);
    	bool new_is_dir = d_is_dir(new_dentry);
    
    	if (old_dir != new_dir && old_is_dir != new_is_dir) {
    		if (old_is_dir) {
    			drop_nlink(old_dir);
    			inc_nlink(new_dir);
    		} else {
    			drop_nlink(new_dir);
    			inc_nlink(old_dir);
    		}
    	}
    	old_dir->i_ctime = old_dir->i_mtime =
    	new_dir->i_ctime = new_dir->i_mtime =
    	d_inode(old_dentry)->i_ctime =
    	d_inode(new_dentry)->i_ctime = current_time(old_dir);
    
    	return 0;
    }
    
    static int shmem_whiteout(struct inode *old_dir, struct dentry *old_dentry)
    {
    	struct dentry *whiteout;
    	int error;
    
    	whiteout = d_alloc(old_dentry->d_parent, &old_dentry->d_name);
    	if (!whiteout)
    		return -ENOMEM;
    
    	error = shmem_mknod(old_dir, whiteout,
    			    S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV);
    	dput(whiteout);
    	if (error)
    		return error;
    
    	/*
    	 * Cheat and hash the whiteout while the old dentry is still in
    	 * place, instead of playing games with FS_RENAME_DOES_D_MOVE.
    	 *
    	 * d_lookup() will consistently find one of them at this point,
    	 * not sure which one, but that isn't even important.
    	 */
    	d_rehash(whiteout);
    	return 0;
    }
    
    /*
     * The VFS layer already does all the dentry stuff for rename,
     * we just have to decrement the usage count for the target if
     * it exists so that the VFS layer correctly free's it when it
     * gets overwritten.
     */
    static int shmem_rename2(struct inode *old_dir, struct dentry *old_dentry, struct inode *new_dir, struct dentry *new_dentry, unsigned int flags)
    {
    	struct inode *inode = d_inode(old_dentry);
    	int they_are_dirs = S_ISDIR(inode->i_mode);
    
    	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE | RENAME_WHITEOUT))
    		return -EINVAL;
    
    	if (flags & RENAME_EXCHANGE)
    		return shmem_exchange(old_dir, old_dentry, new_dir, new_dentry);
    
    	if (!simple_empty(new_dentry))
    		return -ENOTEMPTY;
    
    	if (flags & RENAME_WHITEOUT) {
    		int error;
    
    		error = shmem_whiteout(old_dir, old_dentry);
    		if (error)
    			return error;
    	}
    
    	if (d_really_is_positive(new_dentry)) {
    		(void) shmem_unlink(new_dir, new_dentry);
    		if (they_are_dirs) {
    			drop_nlink(d_inode(new_dentry));
    			drop_nlink(old_dir);
    		}
    	} else if (they_are_dirs) {
    		drop_nlink(old_dir);
    		inc_nlink(new_dir);
    	}
    
    	old_dir->i_size -= BOGO_DIRENT_SIZE;
    	new_dir->i_size += BOGO_DIRENT_SIZE;
    	old_dir->i_ctime = old_dir->i_mtime =
    	new_dir->i_ctime = new_dir->i_mtime =
    	inode->i_ctime = current_time(old_dir);
    	return 0;
    }
    
    static int shmem_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
    {
    	int error;
    	int len;
    	struct inode *inode;
    	struct page *page;
    
    	len = strlen(symname) + 1;
    	if (len > PAGE_SIZE)
    		return -ENAMETOOLONG;
    
    	inode = shmem_get_inode(dir->i_sb, dir, S_IFLNK|S_IRWXUGO, 0, VM_NORESERVE);
    	if (!inode)
    		return -ENOSPC;
    
    	error = security_inode_init_security(inode, dir, &dentry->d_name,
    					     shmem_initxattrs, NULL);
    	if (error) {
    		if (error != -EOPNOTSUPP) {
    			iput(inode);
    			return error;
    		}
    		error = 0;
    	}
    
    	inode->i_size = len-1;
    	if (len <= SHORT_SYMLINK_LEN) {
    		inode->i_link = kmemdup(symname, len, GFP_KERNEL);
    		if (!inode->i_link) {
    			iput(inode);
    			return -ENOMEM;
    		}
    		inode->i_op = &shmem_short_symlink_operations;
    	} else {
    		inode_nohighmem(inode);
    		error = shmem_getpage(inode, 0, &page, SGP_WRITE);
    		if (error) {
    			iput(inode);
    			return error;
    		}
    		inode->i_mapping->a_ops = &shmem_aops;
    		inode->i_op = &shmem_symlink_inode_operations;
    		memcpy(page_address(page), symname, len);
    		SetPageUptodate(page);
    		set_page_dirty(page);
    		unlock_page(page);
    		put_page(page);
    	}
    	dir->i_size += BOGO_DIRENT_SIZE;
    	dir->i_ctime = dir->i_mtime = current_time(dir);
    	d_instantiate(dentry, inode);
    	dget(dentry);
    	return 0;
    }
    
    static void shmem_put_link(void *arg)
    {
    	mark_page_accessed(arg);
    	put_page(arg);
    }
    
    static const char *shmem_get_link(struct dentry *dentry,
    				  struct inode *inode,
    				  struct delayed_call *done)
    {
    	struct page *page = NULL;
    	int error;
    	if (!dentry) {
    		page = find_get_page(inode->i_mapping, 0);
    		if (!page)
    			return ERR_PTR(-ECHILD);
    		if (!PageUptodate(page)) {
    			put_page(page);
    			return ERR_PTR(-ECHILD);
    		}
    	} else {
    		error = shmem_getpage(inode, 0, &page, SGP_READ);
    		if (error)
    			return ERR_PTR(error);
    		unlock_page(page);
    	}
    	set_delayed_call(done, shmem_put_link, page);
    	return page_address(page);
    }
    
    #ifdef CONFIG_TMPFS_XATTR
    /*
     * Superblocks without xattr inode operations may get some security.* xattr
     * support from the LSM "for free". As soon as we have any other xattrs
     * like ACLs, we also need to implement the security.* handlers at
     * filesystem level, though.
     */
    
    /*
     * Callback for security_inode_init_security() for acquiring xattrs.
     */
    static int shmem_initxattrs(struct inode *inode,
    			    const struct xattr *xattr_array,
    			    void *fs_info)
    {
    	struct shmem_inode_info *info = SHMEM_I(inode);
    	const struct xattr *xattr;
    	struct simple_xattr *new_xattr;
    	size_t len;
    
    	for (xattr = xattr_array; xattr->name != NULL; xattr++) {
    		new_xattr = simple_xattr_alloc(xattr->value, xattr->value_len);
    		if (!new_xattr)
    			return -ENOMEM;
    
    		len = strlen(xattr->name) + 1;
    		new_xattr->name = kmalloc(XATTR_SECURITY_PREFIX_LEN + len,
    					  GFP_KERNEL);
    		if (!new_xattr->name) {
    			kfree(new_xattr);
    			return -ENOMEM;
    		}
    
    		memcpy(new_xattr->name, XATTR_SECURITY_PREFIX,
    		       XATTR_SECURITY_PREFIX_LEN);
    		memcpy(new_xattr->name + XATTR_SECURITY_PREFIX_LEN,
    		       xattr->name, len);
    
    		simple_xattr_list_add(&info->xattrs, new_xattr);
    	}
    
    	return 0;
    }
    
    static int shmem_xattr_handler_get(const struct xattr_handler *handler,
    				   struct dentry *unused, struct inode *inode,
    				   const char *name, void *buffer, size_t size)
    {
    	struct shmem_inode_info *info = SHMEM_I(inode);
    
    	name = xattr_full_name(handler, name);
    	return simple_xattr_get(&info->xattrs, name, buffer, size);
    }
    
    static int shmem_xattr_handler_set(const struct xattr_handler *handler,
    				   struct dentry *unused, struct inode *inode,
    				   const char *name, const void *value,
    				   size_t size, int flags)
    {
    	struct shmem_inode_info *info = SHMEM_I(inode);
    
    	name = xattr_full_name(handler, name);
    	return simple_xattr_set(&info->xattrs, name, value, size, flags);
    }
    
    static const struct xattr_handler shmem_security_xattr_handler = {
    	.prefix = XATTR_SECURITY_PREFIX,
    	.get = shmem_xattr_handler_get,
    	.set = shmem_xattr_handler_set,
    };
    
    static const struct xattr_handler shmem_trusted_xattr_handler = {
    	.prefix = XATTR_TRUSTED_PREFIX,
    	.get = shmem_xattr_handler_get,
    	.set = shmem_xattr_handler_set,
    };
    
    static const struct xattr_handler *shmem_xattr_handlers[] = {
    #ifdef CONFIG_TMPFS_POSIX_ACL
    	&posix_acl_access_xattr_handler,
    	&posix_acl_default_xattr_handler,
    #endif
    	&shmem_security_xattr_handler,
    	&shmem_trusted_xattr_handler,
    	NULL
    };
    
    static ssize_t shmem_listxattr(struct dentry *dentry, char *buffer, size_t size)
    {
    	struct shmem_inode_info *info = SHMEM_I(d_inode(dentry));
    	return simple_xattr_list(d_inode(dentry), &info->xattrs, buffer, size);
    }
    #endif /* CONFIG_TMPFS_XATTR */
    
    static const struct inode_operations shmem_short_symlink_operations = {
    	.get_link	= simple_get_link,
    #ifdef CONFIG_TMPFS_XATTR
    	.listxattr	= shmem_listxattr,
    #endif
    };
    
    static const struct inode_operations shmem_symlink_inode_operations = {
    	.get_link	= shmem_get_link,
    #ifdef CONFIG_TMPFS_XATTR
    	.listxattr	= shmem_listxattr,
    #endif
    };
    
    static struct dentry *shmem_get_parent(struct dentry *child)
    {
    	return ERR_PTR(-ESTALE);
    }
    
    static int shmem_match(struct inode *ino, void *vfh)
    {
    	__u32 *fh = vfh;
    	__u64 inum = fh[2];
    	inum = (inum << 32) | fh[1];
    	return ino->i_ino == inum && fh[0] == ino->i_generation;
    }
    
    static struct dentry *shmem_fh_to_dentry(struct super_block *sb,
    		struct fid *fid, int fh_len, int fh_type)
    {
    	struct inode *inode;
    	struct dentry *dentry = NULL;
    	u64 inum;
    
    	if (fh_len < 3)
    		return NULL;
    
    	inum = fid->raw[2];
    	inum = (inum << 32) | fid->raw[1];
    
    	inode = ilookup5(sb, (unsigned long)(inum + fid->raw[0]),
    			shmem_match, fid->raw);
    	if (inode) {
    		dentry = d_find_alias(inode);
    		iput(inode);
    	}
    
    	return dentry;
    }
    
    static int shmem_encode_fh(struct inode *inode, __u32 *fh, int *len,
    				struct inode *parent)
    {
    	if (*len < 3) {
    		*len = 3;
    		return FILEID_INVALID;
    	}
    
    	if (inode_unhashed(inode)) {
    		/* Unfortunately insert_inode_hash is not idempotent,
    		 * so as we hash inodes here rather than at creation
    		 * time, we need a lock to ensure we only try
    		 * to do it once
    		 */
    		static DEFINE_SPINLOCK(lock);
    		spin_lock(&lock);
    		if (inode_unhashed(inode))
    			__insert_inode_hash(inode,
    					    inode->i_ino + inode->i_generation);
    		spin_unlock(&lock);
    	}
    
    	fh[0] = inode->i_generation;
    	fh[1] = inode->i_ino;
    	fh[2] = ((__u64)inode->i_ino) >> 32;
    
    	*len = 3;
    	return 1;
    }
    
    static const struct export_operations shmem_export_ops = {
    	.get_parent     = shmem_get_parent,
    	.encode_fh      = shmem_encode_fh,
    	.fh_to_dentry	= shmem_fh_to_dentry,
    };
    
    static int shmem_parse_options(char *options, struct shmem_sb_info *sbinfo,
    			       bool remount)
    {
    	char *this_char, *value, *rest;
    	struct mempolicy *mpol = NULL;
    	uid_t uid;
    	gid_t gid;
    
    	while (options != NULL) {
    		this_char = options;
    		for (;;) {
    			/*
    			 * NUL-terminate this option: unfortunately,
    			 * mount options form a comma-separated list,
    			 * but mpol's nodelist may also contain commas.
    			 */
    			options = strchr(options, ',');
    			if (options == NULL)
    				break;
    			options++;
    			if (!isdigit(*options)) {
    				options[-1] = '\0';
    				break;
    			}
    		}
    		if (!*this_char)
    			continue;
    		if ((value = strchr(this_char,'=')) != NULL) {
    			*value++ = 0;
    		} else {
    			pr_err("tmpfs: No value for mount option '%s'\n",
    			       this_char);
    			goto error;
    		}
    
    		if (!strcmp(this_char,"size")) {
    			unsigned long long size;
    			size = memparse(value,&rest);
    			if (*rest == '%') {
    				size <<= PAGE_SHIFT;
    				size *= totalram_pages;
    				do_div(size, 100);
    				rest++;
    			}
    			if (*rest)
    				goto bad_val;
    			sbinfo->max_blocks =
    				DIV_ROUND_UP(size, PAGE_SIZE);
    		} else if (!strcmp(this_char,"nr_blocks")) {
    			sbinfo->max_blocks = memparse(value, &rest);
    			if (*rest)
    				goto bad_val;
    		} else if (!strcmp(this_char,"nr_inodes")) {
    			sbinfo->max_inodes = memparse(value, &rest);
    			if (*rest)
    				goto bad_val;
    		} else if (!strcmp(this_char,"mode")) {
    			if (remount)
    				continue;
    			sbinfo->mode = simple_strtoul(value, &rest, 8) & 07777;
    			if (*rest)
    				goto bad_val;
    		} else if (!strcmp(this_char,"uid")) {
    			if (remount)
    				continue;
    			uid = simple_strtoul(value, &rest, 0);
    			if (*rest)
    				goto bad_val;
    			sbinfo->uid = make_kuid(current_user_ns(), uid);
    			if (!uid_valid(sbinfo->uid))
    				goto bad_val;
    		} else if (!strcmp(this_char,"gid")) {
    			if (remount)
    				continue;
    			gid = simple_strtoul(value, &rest, 0);
    			if (*rest)
    				goto bad_val;
    			sbinfo->gid = make_kgid(current_user_ns(), gid);
    			if (!gid_valid(sbinfo->gid))
    				goto bad_val;
    #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
    		} else if (!strcmp(this_char, "huge")) {
    			int huge;
    			huge = shmem_parse_huge(value);
    			if (huge < 0)
    				goto bad_val;
    			if (!has_transparent_hugepage() &&
    					huge != SHMEM_HUGE_NEVER)
    				goto bad_val;
    			sbinfo->huge = huge;
    #endif
    #ifdef CONFIG_NUMA
    		} else if (!strcmp(this_char,"mpol")) {
    			mpol_put(mpol);
    			mpol = NULL;
    			if (mpol_parse_str(value, &mpol))
    				goto bad_val;
    #endif
    		} else {
    			pr_err("tmpfs: Bad mount option %s\n", this_char);
    			goto error;
    		}
    	}
    	sbinfo->mpol = mpol;
    	return 0;
    
    bad_val:
    	pr_err("tmpfs: Bad value '%s' for mount option '%s'\n",
    	       value, this_char);
    error:
    	mpol_put(mpol);
    	return 1;
    
    }
    
    static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
    {
    	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
    	struct shmem_sb_info config = *sbinfo;
    	unsigned long inodes;
    	int error = -EINVAL;
    
    	config.mpol = NULL;
    	if (shmem_parse_options(data, &config, true))
    		return error;
    
    	spin_lock(&sbinfo->stat_lock);
    	inodes = sbinfo->max_inodes - sbinfo->free_inodes;
    	if (percpu_counter_compare(&sbinfo->used_blocks, config.max_blocks) > 0)
    		goto out;
    	if (config.max_inodes < inodes)
    		goto out;
    	/*
    	 * Those tests disallow limited->unlimited while any are in use;
    	 * but we must separately disallow unlimited->limited, because
    	 * in that case we have no record of how much is already in use.
    	 */
    	if (config.max_blocks && !sbinfo->max_blocks)
    		goto out;
    	if (config.max_inodes && !sbinfo->max_inodes)
    		goto out;
    
    	error = 0;
    	sbinfo->huge = config.huge;
    	sbinfo->max_blocks  = config.max_blocks;
    	sbinfo->max_inodes  = config.max_inodes;
    	sbinfo->free_inodes = config.max_inodes - inodes;
    
    	/*
    	 * Preserve previous mempolicy unless mpol remount option was specified.
    	 */
    	if (config.mpol) {
    		mpol_put(sbinfo->mpol);
    		sbinfo->mpol = config.mpol;	/* transfers initial ref */
    	}
    out:
    	spin_unlock(&sbinfo->stat_lock);
    	return error;
    }
    
    static int shmem_show_options(struct seq_file *seq, struct dentry *root)
    {
    	struct shmem_sb_info *sbinfo = SHMEM_SB(root->d_sb);
    
    	if (sbinfo->max_blocks != shmem_default_max_blocks())
    		seq_printf(seq, ",size=%luk",
    			sbinfo->max_blocks << (PAGE_SHIFT - 10));
    	if (sbinfo->max_inodes != shmem_default_max_inodes())
    		seq_printf(seq, ",nr_inodes=%lu", sbinfo->max_inodes);
    	if (sbinfo->mode != (S_IRWXUGO | S_ISVTX))
    		seq_printf(seq, ",mode=%03ho", sbinfo->mode);
    	if (!uid_eq(sbinfo->uid, GLOBAL_ROOT_UID))
    		seq_printf(seq, ",uid=%u",
    				from_kuid_munged(&init_user_ns, sbinfo->uid));
    	if (!gid_eq(sbinfo->gid, GLOBAL_ROOT_GID))
    		seq_printf(seq, ",gid=%u",
    				from_kgid_munged(&init_user_ns, sbinfo->gid));
    #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
    	/* Rightly or wrongly, show huge mount option unmasked by shmem_huge */
    	if (sbinfo->huge)
    		seq_printf(seq, ",huge=%s", shmem_format_huge(sbinfo->huge));
    #endif
    	shmem_show_mpol(seq, sbinfo->mpol);
    	return 0;
    }
    
    #define MFD_NAME_PREFIX "memfd:"
    #define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1)
    #define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN)
    
    #define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB)
    
    SYSCALL_DEFINE2(memfd_create,
    		const char __user *, uname,
    		unsigned int, flags)
    {
    	unsigned int *file_seals;
    	struct file *file;
    	int fd, error;
    	char *name;
    	long len;
    
    	if (!(flags & MFD_HUGETLB)) {
    		if (flags & ~(unsigned int)MFD_ALL_FLAGS)
    			return -EINVAL;
    	} else {
    		/* Allow huge page size encoding in flags. */
    		if (flags & ~(unsigned int)(MFD_ALL_FLAGS |
    				(MFD_HUGE_MASK << MFD_HUGE_SHIFT)))
    			return -EINVAL;
    	}
    
    	/* length includes terminating zero */
    	len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
    	if (len <= 0)
    		return -EFAULT;
    	if (len > MFD_NAME_MAX_LEN + 1)
    		return -EINVAL;
    
    	name = kmalloc(len + MFD_NAME_PREFIX_LEN, GFP_KERNEL);
    	if (!name)
    		return -ENOMEM;
    
    	strcpy(name, MFD_NAME_PREFIX);
    	if (copy_from_user(&name[MFD_NAME_PREFIX_LEN], uname, len)) {
    		error = -EFAULT;
    		goto err_name;
    	}
    
    	/* terminating-zero may have changed after strnlen_user() returned */
    	if (name[len + MFD_NAME_PREFIX_LEN - 1]) {
    		error = -EFAULT;
    		goto err_name;
    	}
    
    	fd = get_unused_fd_flags((flags & MFD_CLOEXEC) ? O_CLOEXEC : 0);
    	if (fd < 0) {
    		error = fd;
    		goto err_name;
    	}
    
    	if (flags & MFD_HUGETLB) {
    		struct user_struct *user = NULL;
    
    		file = hugetlb_file_setup(name, 0, VM_NORESERVE, &user,
    					HUGETLB_ANONHUGE_INODE,
    					(flags >> MFD_HUGE_SHIFT) &
    					MFD_HUGE_MASK);
    	} else
    		file = shmem_file_setup(name, 0, VM_NORESERVE);
    	if (IS_ERR(file)) {
    		error = PTR_ERR(file);
    		goto err_fd;
    	}
    	file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
    	file->f_flags |= O_RDWR | O_LARGEFILE;
    
    	if (flags & MFD_ALLOW_SEALING) {
    		file_seals = memfd_file_seals_ptr(file);
    		*file_seals &= ~F_SEAL_SEAL;
    	}
    
    	fd_install(fd, file);
    	kfree(name);
    	return fd;
    
    err_fd:
    	put_unused_fd(fd);
    err_name:
    	kfree(name);
    	return error;
    }
    
    #endif /* CONFIG_TMPFS */
    
    static void shmem_put_super(struct super_block *sb)
    {
    	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
    
    	percpu_counter_destroy(&sbinfo->used_blocks);
    	mpol_put(sbinfo->mpol);
    	kfree(sbinfo);
    	sb->s_fs_info = NULL;
    }
    
    int shmem_fill_super(struct super_block *sb, void *data, int silent)
    {
    	struct inode *inode;
    	struct shmem_sb_info *sbinfo;
    	int err = -ENOMEM;
    
    	/* Round up to L1_CACHE_BYTES to resist false sharing */
    	sbinfo = kzalloc(max((int)sizeof(struct shmem_sb_info),
    				L1_CACHE_BYTES), GFP_KERNEL);
    	if (!sbinfo)
    		return -ENOMEM;
    
    	sbinfo->mode = S_IRWXUGO | S_ISVTX;
    	sbinfo->uid = current_fsuid();
    	sbinfo->gid = current_fsgid();
    	sb->s_fs_info = sbinfo;
    
    #ifdef CONFIG_TMPFS
    	/*
    	 * Per default we only allow half of the physical ram per
    	 * tmpfs instance, limiting inodes to one per page of lowmem;
    	 * but the internal instance is left unlimited.
    	 */
    	if (!(sb->s_flags & SB_KERNMOUNT)) {
    		sbinfo->max_blocks = shmem_default_max_blocks();
    		sbinfo->max_inodes = shmem_default_max_inodes();
    		if (shmem_parse_options(data, sbinfo, false)) {
    			err = -EINVAL;
    			goto failed;
    		}
    	} else {
    		sb->s_flags |= SB_NOUSER;
    	}
    	sb->s_export_op = &shmem_export_ops;
    	sb->s_flags |= SB_NOSEC;
    #else
    	sb->s_flags |= SB_NOUSER;
    #endif
    
    	spin_lock_init(&sbinfo->stat_lock);
    	if (percpu_counter_init(&sbinfo->used_blocks, 0, GFP_KERNEL))
    		goto failed;
    	sbinfo->free_inodes = sbinfo->max_inodes;
    	spin_lock_init(&sbinfo->shrinklist_lock);
    	INIT_LIST_HEAD(&sbinfo->shrinklist);
    
    	sb->s_maxbytes = MAX_LFS_FILESIZE;
    	sb->s_blocksize = PAGE_SIZE;
    	sb->s_blocksize_bits = PAGE_SHIFT;
    	sb->s_magic = TMPFS_MAGIC;
    	sb->s_op = &shmem_ops;
    	sb->s_time_gran = 1;
    #ifdef CONFIG_TMPFS_XATTR
    	sb->s_xattr = shmem_xattr_handlers;
    #endif
    #ifdef CONFIG_TMPFS_POSIX_ACL
    	sb->s_flags |= SB_POSIXACL;
    #endif
    	uuid_gen(&sb->s_uuid);
    
    	inode = shmem_get_inode(sb, NULL, S_IFDIR | sbinfo->mode, 0, VM_NORESERVE);
    	if (!inode)
    		goto failed;
    	inode->i_uid = sbinfo->uid;
    	inode->i_gid = sbinfo->gid;
    	sb->s_root = d_make_root(inode);
    	if (!sb->s_root)
    		goto failed;
    	return 0;
    
    failed:
    	shmem_put_super(sb);
    	return err;
    }
    
    static struct kmem_cache *shmem_inode_cachep;
    
    static struct inode *shmem_alloc_inode(struct super_block *sb)
    {
    	struct shmem_inode_info *info;
    	info = kmem_cache_alloc(shmem_inode_cachep, GFP_KERNEL);
    	if (!info)
    		return NULL;
    	return &info->vfs_inode;
    }
    
    static void shmem_destroy_callback(struct rcu_head *head)
    {
    	struct inode *inode = container_of(head, struct inode, i_rcu);
    	if (S_ISLNK(inode->i_mode))
    		kfree(inode->i_link);
    	kmem_cache_free(shmem_inode_cachep, SHMEM_I(inode));
    }
    
    static void shmem_destroy_inode(struct inode *inode)
    {
    	if (S_ISREG(inode->i_mode))
    		mpol_free_shared_policy(&SHMEM_I(inode)->policy);
    	call_rcu(&inode->i_rcu, shmem_destroy_callback);
    }
    
    static void shmem_init_inode(void *foo)
    {
    	struct shmem_inode_info *info = foo;
    	inode_init_once(&info->vfs_inode);
    }
    
    static void shmem_init_inodecache(void)
    {
    	shmem_inode_cachep = kmem_cache_create("shmem_inode_cache",
    				sizeof(struct shmem_inode_info),
    				0, SLAB_PANIC|SLAB_ACCOUNT, shmem_init_inode);
    }
    
    static void shmem_destroy_inodecache(void)
    {
    	kmem_cache_destroy(shmem_inode_cachep);
    }
    
    static const struct address_space_operations shmem_aops = {
    	.writepage	= shmem_writepage,
    	.set_page_dirty	= __set_page_dirty_no_writeback,
    #ifdef CONFIG_TMPFS
    	.write_begin	= shmem_write_begin,
    	.write_end	= shmem_write_end,
    #endif
    #ifdef CONFIG_MIGRATION
    	.migratepage	= migrate_page,
    #endif
    	.error_remove_page = generic_error_remove_page,
    };
    
    static const struct file_operations shmem_file_operations = {
    	.mmap		= shmem_mmap,
    	.get_unmapped_area = shmem_get_unmapped_area,
    #ifdef CONFIG_TMPFS
    	.llseek		= shmem_file_llseek,
    	.read_iter	= shmem_file_read_iter,
    	.write_iter	= generic_file_write_iter,
    	.fsync		= noop_fsync,
    	.splice_read	= generic_file_splice_read,
    	.splice_write	= iter_file_splice_write,
    	.fallocate	= shmem_fallocate,
    #endif
    };
    
    static const struct inode_operations shmem_inode_operations = {
    	.getattr	= shmem_getattr,
    	.setattr	= shmem_setattr,
    #ifdef CONFIG_TMPFS_XATTR
    	.listxattr	= shmem_listxattr,
    	.set_acl	= simple_set_acl,
    #endif
    };
    
    static const struct inode_operations shmem_dir_inode_operations = {
    #ifdef CONFIG_TMPFS
    	.create		= shmem_create,
    	.lookup		= simple_lookup,
    	.link		= shmem_link,
    	.unlink		= shmem_unlink,
    	.symlink	= shmem_symlink,
    	.mkdir		= shmem_mkdir,
    	.rmdir		= shmem_rmdir,
    	.mknod		= shmem_mknod,
    	.rename		= shmem_rename2,
    	.tmpfile	= shmem_tmpfile,
    #endif
    #ifdef CONFIG_TMPFS_XATTR
    	.listxattr	= shmem_listxattr,
    #endif
    #ifdef CONFIG_TMPFS_POSIX_ACL
    	.setattr	= shmem_setattr,
    	.set_acl	= simple_set_acl,
    #endif
    };
    
    static const struct inode_operations shmem_special_inode_operations = {
    #ifdef CONFIG_TMPFS_XATTR
    	.listxattr	= shmem_listxattr,
    #endif
    #ifdef CONFIG_TMPFS_POSIX_ACL
    	.setattr	= shmem_setattr,
    	.set_acl	= simple_set_acl,
    #endif
    };
    
    static const struct super_operations shmem_ops = {
    	.alloc_inode	= shmem_alloc_inode,
    	.destroy_inode	= shmem_destroy_inode,
    #ifdef CONFIG_TMPFS
    	.statfs		= shmem_statfs,
    	.remount_fs	= shmem_remount_fs,
    	.show_options	= shmem_show_options,
    #endif
    	.evict_inode	= shmem_evict_inode,
    	.drop_inode	= generic_delete_inode,
    	.put_super	= shmem_put_super,
    #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
    	.nr_cached_objects	= shmem_unused_huge_count,
    	.free_cached_objects	= shmem_unused_huge_scan,
    #endif
    };
    
    static const struct vm_operations_struct shmem_vm_ops = {
    	.fault		= shmem_fault,
    	.map_pages	= filemap_map_pages,
    #ifdef CONFIG_NUMA
    	.set_policy     = shmem_set_policy,
    	.get_policy     = shmem_get_policy,
    #endif
    };
    
    static struct dentry *shmem_mount(struct file_system_type *fs_type,
    	int flags, const char *dev_name, void *data)
    {
    	return mount_nodev(fs_type, flags, data, shmem_fill_super);
    }
    
    static struct file_system_type shmem_fs_type = {
    	.owner		= THIS_MODULE,
    	.name		= "tmpfs",
    	.mount		= shmem_mount,
    	.kill_sb	= kill_litter_super,
    	.fs_flags	= FS_USERNS_MOUNT,
    };
    
    int __init shmem_init(void)
    {
    	int error;
    
    	/* If rootfs called this, don't re-init */
    	if (shmem_inode_cachep)
    		return 0;
    
    	shmem_init_inodecache();
    
    	error = register_filesystem(&shmem_fs_type);
    	if (error) {
    		pr_err("Could not register tmpfs\n");
    		goto out2;
    	}
    
    	shm_mnt = kern_mount(&shmem_fs_type);
    	if (IS_ERR(shm_mnt)) {
    		error = PTR_ERR(shm_mnt);
    		pr_err("Could not kern_mount tmpfs\n");
    		goto out1;
    	}
    
    #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
    	if (has_transparent_hugepage() && shmem_huge > SHMEM_HUGE_DENY)
    		SHMEM_SB(shm_mnt->mnt_sb)->huge = shmem_huge;
    	else
    		shmem_huge = 0; /* just in case it was patched */
    #endif
    	return 0;
    
    out1:
    	unregister_filesystem(&shmem_fs_type);
    out2:
    	shmem_destroy_inodecache();
    	shm_mnt = ERR_PTR(error);
    	return error;
    }
    
    #if defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE) && defined(CONFIG_SYSFS)
    static ssize_t shmem_enabled_show(struct kobject *kobj,
    		struct kobj_attribute *attr, char *buf)
    {
    	int values[] = {
    		SHMEM_HUGE_ALWAYS,
    		SHMEM_HUGE_WITHIN_SIZE,
    		SHMEM_HUGE_ADVISE,
    		SHMEM_HUGE_NEVER,
    		SHMEM_HUGE_DENY,
    		SHMEM_HUGE_FORCE,
    	};
    	int i, count;
    
    	for (i = 0, count = 0; i < ARRAY_SIZE(values); i++) {
    		const char *fmt = shmem_huge == values[i] ? "[%s] " : "%s ";
    
    		count += sprintf(buf + count, fmt,
    				shmem_format_huge(values[i]));
    	}
    	buf[count - 1] = '\n';
    	return count;
    }
    
    static ssize_t shmem_enabled_store(struct kobject *kobj,
    		struct kobj_attribute *attr, const char *buf, size_t count)
    {
    	char tmp[16];
    	int huge;
    
    	if (count + 1 > sizeof(tmp))
    		return -EINVAL;
    	memcpy(tmp, buf, count);
    	tmp[count] = '\0';
    	if (count && tmp[count - 1] == '\n')
    		tmp[count - 1] = '\0';
    
    	huge = shmem_parse_huge(tmp);
    	if (huge == -EINVAL)
    		return -EINVAL;
    	if (!has_transparent_hugepage() &&
    			huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY)
    		return -EINVAL;
    
    	shmem_huge = huge;
    	if (shmem_huge > SHMEM_HUGE_DENY)
    		SHMEM_SB(shm_mnt->mnt_sb)->huge = shmem_huge;
    	return count;
    }
    
    struct kobj_attribute shmem_enabled_attr =
    	__ATTR(shmem_enabled, 0644, shmem_enabled_show, shmem_enabled_store);
    #endif /* CONFIG_TRANSPARENT_HUGE_PAGECACHE && CONFIG_SYSFS */
    
    #ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
    bool shmem_huge_enabled(struct vm_area_struct *vma)
    {
    	struct inode *inode = file_inode(vma->vm_file);
    	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
    	loff_t i_size;
    	pgoff_t off;
    
    	if (shmem_huge == SHMEM_HUGE_FORCE)
    		return true;
    	if (shmem_huge == SHMEM_HUGE_DENY)
    		return false;
    	switch (sbinfo->huge) {
    		case SHMEM_HUGE_NEVER:
    			return false;
    		case SHMEM_HUGE_ALWAYS:
    			return true;
    		case SHMEM_HUGE_WITHIN_SIZE:
    			off = round_up(vma->vm_pgoff, HPAGE_PMD_NR);
    			i_size = round_up(i_size_read(inode), PAGE_SIZE);
    			if (i_size >= HPAGE_PMD_SIZE &&
    					i_size >> PAGE_SHIFT >= off)
    				return true;
    			/* fall through */
    		case SHMEM_HUGE_ADVISE:
    			/* TODO: implement fadvise() hints */
    			return (vma->vm_flags & VM_HUGEPAGE);
    		default:
    			VM_BUG_ON(1);
    			return false;
    	}
    }
    #endif /* CONFIG_TRANSPARENT_HUGE_PAGECACHE */
    
    #else /* !CONFIG_SHMEM */
    
    /*
     * tiny-shmem: simple shmemfs and tmpfs using ramfs code
     *
     * This is intended for small system where the benefits of the full
     * shmem code (swap-backed and resource-limited) are outweighed by
     * their complexity. On systems without swap this code should be
     * effectively equivalent, but much lighter weight.
     */
    
    static struct file_system_type shmem_fs_type = {
    	.name		= "tmpfs",
    	.mount		= ramfs_mount,
    	.kill_sb	= kill_litter_super,
    	.fs_flags	= FS_USERNS_MOUNT,
    };
    
    int __init shmem_init(void)
    {
    	BUG_ON(register_filesystem(&shmem_fs_type) != 0);
    
    	shm_mnt = kern_mount(&shmem_fs_type);
    	BUG_ON(IS_ERR(shm_mnt));
    
    	return 0;
    }
    
    int shmem_unuse(swp_entry_t swap, struct page *page)
    {
    	return 0;
    }
    
    int shmem_lock(struct file *file, int lock, struct user_struct *user)
    {
    	return 0;
    }
    
    void shmem_unlock_mapping(struct address_space *mapping)
    {
    }
    
    #ifdef CONFIG_MMU
    unsigned long shmem_get_unmapped_area(struct file *file,
    				      unsigned long addr, unsigned long len,
    				      unsigned long pgoff, unsigned long flags)
    {
    	return current->mm->get_unmapped_area(file, addr, len, pgoff, flags);
    }
    #endif
    
    void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
    {
    	truncate_inode_pages_range(inode->i_mapping, lstart, lend);
    }
    EXPORT_SYMBOL_GPL(shmem_truncate_range);
    
    #define shmem_vm_ops				generic_file_vm_ops
    #define shmem_file_operations			ramfs_file_operations
    #define shmem_get_inode(sb, dir, mode, dev, flags)	ramfs_get_inode(sb, dir, mode, dev)
    #define shmem_acct_size(flags, size)		0
    #define shmem_unacct_size(flags, size)		do {} while (0)
    
    #endif /* CONFIG_SHMEM */
    
    /* common code */
    
    static const struct dentry_operations anon_ops = {
    	.d_dname = simple_dname
    };
    
    static struct file *__shmem_file_setup(struct vfsmount *mnt, const char *name, loff_t size,
    				       unsigned long flags, unsigned int i_flags)
    {
    	struct file *res;
    	struct inode *inode;
    	struct path path;
    	struct super_block *sb;
    	struct qstr this;
    
    	if (IS_ERR(mnt))
    		return ERR_CAST(mnt);
    
    	if (size < 0 || size > MAX_LFS_FILESIZE)
    		return ERR_PTR(-EINVAL);
    
    	if (shmem_acct_size(flags, size))
    		return ERR_PTR(-ENOMEM);
    
    	res = ERR_PTR(-ENOMEM);
    	this.name = name;
    	this.len = strlen(name);
    	this.hash = 0; /* will go */
    	sb = mnt->mnt_sb;
    	path.mnt = mntget(mnt);
    	path.dentry = d_alloc_pseudo(sb, &this);
    	if (!path.dentry)
    		goto put_memory;
    	d_set_d_op(path.dentry, &anon_ops);
    
    	res = ERR_PTR(-ENOSPC);
    	inode = shmem_get_inode(sb, NULL, S_IFREG | S_IRWXUGO, 0, flags);
    	if (!inode)
    		goto put_memory;
    
    	inode->i_flags |= i_flags;
    	d_instantiate(path.dentry, inode);
    	inode->i_size = size;
    	clear_nlink(inode);	/* It is unlinked */
    	res = ERR_PTR(ramfs_nommu_expand_for_mapping(inode, size));
    	if (IS_ERR(res))
    		goto put_path;
    
    	res = alloc_file(&path, FMODE_WRITE | FMODE_READ,
    		  &shmem_file_operations);
    	if (IS_ERR(res))
    		goto put_path;
    
    	return res;
    
    put_memory:
    	shmem_unacct_size(flags, size);
    put_path:
    	path_put(&path);
    	return res;
    }
    
    /**
     * shmem_kernel_file_setup - get an unlinked file living in tmpfs which must be
     * 	kernel internal.  There will be NO LSM permission checks against the
     * 	underlying inode.  So users of this interface must do LSM checks at a
     *	higher layer.  The users are the big_key and shm implementations.  LSM
     *	checks are provided at the key or shm level rather than the inode.
     * @name: name for dentry (to be seen in /proc/<pid>/maps
     * @size: size to be set for the file
     * @flags: VM_NORESERVE suppresses pre-accounting of the entire object size
     */
    struct file *shmem_kernel_file_setup(const char *name, loff_t size, unsigned long flags)
    {
    	return __shmem_file_setup(shm_mnt, name, size, flags, S_PRIVATE);
    }
    
    /**
     * shmem_file_setup - get an unlinked file living in tmpfs
     * @name: name for dentry (to be seen in /proc/<pid>/maps
     * @size: size to be set for the file
     * @flags: VM_NORESERVE suppresses pre-accounting of the entire object size
     */
    struct file *shmem_file_setup(const char *name, loff_t size, unsigned long flags)
    {
    	return __shmem_file_setup(shm_mnt, name, size, flags, 0);
    }
    EXPORT_SYMBOL_GPL(shmem_file_setup);
    
    /**
     * shmem_file_setup_with_mnt - get an unlinked file living in tmpfs
     * @mnt: the tmpfs mount where the file will be created
     * @name: name for dentry (to be seen in /proc/<pid>/maps
     * @size: size to be set for the file
     * @flags: VM_NORESERVE suppresses pre-accounting of the entire object size
     */
    struct file *shmem_file_setup_with_mnt(struct vfsmount *mnt, const char *name,
    				       loff_t size, unsigned long flags)
    {
    	return __shmem_file_setup(mnt, name, size, flags, 0);
    }
    EXPORT_SYMBOL_GPL(shmem_file_setup_with_mnt);
    
    /**
     * shmem_zero_setup - setup a shared anonymous mapping
     * @vma: the vma to be mmapped is prepared by do_mmap_pgoff
     */
    int shmem_zero_setup(struct vm_area_struct *vma)
    {
    	struct file *file;
    	loff_t size = vma->vm_end - vma->vm_start;
    
    	/*
    	 * Cloning a new file under mmap_sem leads to a lock ordering conflict
    	 * between XFS directory reading and selinux: since this file is only
    	 * accessible to the user through its mapping, use S_PRIVATE flag to
    	 * bypass file security, in the same way as shmem_kernel_file_setup().
    	 */
    	file = shmem_kernel_file_setup("dev/zero", size, vma->vm_flags);
    	if (IS_ERR(file))
    		return PTR_ERR(file);
    
    	if (vma->vm_file)
    		fput(vma->vm_file);
    	vma->vm_file = file;
    	vma->vm_ops = &shmem_vm_ops;
    
    	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE) &&
    			((vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK) <
    			(vma->vm_end & HPAGE_PMD_MASK)) {
    		khugepaged_enter(vma, vma->vm_flags);
    	}
    
    	return 0;
    }
    
    /**
     * shmem_read_mapping_page_gfp - read into page cache, using specified page allocation flags.
     * @mapping:	the page's address_space
     * @index:	the page index
     * @gfp:	the page allocator flags to use if allocating
     *
     * This behaves as a tmpfs "read_cache_page_gfp(mapping, index, gfp)",
     * with any new page allocations done using the specified allocation flags.
     * But read_cache_page_gfp() uses the ->readpage() method: which does not
     * suit tmpfs, since it may have pages in swapcache, and needs to find those
     * for itself; although drivers/gpu/drm i915 and ttm rely upon this support.
     *
     * i915_gem_object_get_pages_gtt() mixes __GFP_NORETRY | __GFP_NOWARN in
     * with the mapping_gfp_mask(), to avoid OOMing the machine unnecessarily.
     */
    struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
    					 pgoff_t index, gfp_t gfp)
    {
    #ifdef CONFIG_SHMEM
    	struct inode *inode = mapping->host;
    	struct page *page;
    	int error;
    
    	BUG_ON(mapping->a_ops != &shmem_aops);
    	error = shmem_getpage_gfp(inode, index, &page, SGP_CACHE,
    				  gfp, NULL, NULL, NULL);
    	if (error)
    		page = ERR_PTR(error);
    	else
    		unlock_page(page);
    	return page;
    #else
    	/*
    	 * The tiny !SHMEM case uses ramfs without swap
    	 */
    	return read_cache_page_gfp(mapping, index, gfp);
    #endif
    }
    EXPORT_SYMBOL_GPL(shmem_read_mapping_page_gfp);