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32 results

buffered-io.c

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  • cache.c 11.62 KiB
    /*
     * Squashfs - a compressed read only filesystem for Linux
     *
     * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
     * Phillip Lougher <phillip@squashfs.org.uk>
     *
     * This program is free software; you can redistribute it and/or
     * modify it under the terms of the GNU General Public License
     * as published by the Free Software Foundation; either version 2,
     * or (at your option) any later version.
     *
     * This program is distributed in the hope that it will be useful,
     * but WITHOUT ANY WARRANTY; without even the implied warranty of
     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     * GNU General Public License for more details.
     *
     * You should have received a copy of the GNU General Public License
     * along with this program; if not, write to the Free Software
     * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
     *
     * cache.c
     */
    
    /*
     * Blocks in Squashfs are compressed.  To avoid repeatedly decompressing
     * recently accessed data Squashfs uses two small metadata and fragment caches.
     *
     * This file implements a generic cache implementation used for both caches,
     * plus functions layered ontop of the generic cache implementation to
     * access the metadata and fragment caches.
     *
     * To avoid out of memory and fragmentation issues with vmalloc the cache
     * uses sequences of kmalloced PAGE_CACHE_SIZE buffers.
     *
     * It should be noted that the cache is not used for file datablocks, these
     * are decompressed and cached in the page-cache in the normal way.  The
     * cache is only used to temporarily cache fragment and metadata blocks
     * which have been read as as a result of a metadata (i.e. inode or
     * directory) or fragment access.  Because metadata and fragments are packed
     * together into blocks (to gain greater compression) the read of a particular
     * piece of metadata or fragment will retrieve other metadata/fragments which
     * have been packed with it, these because of locality-of-reference may be read
     * in the near future. Temporarily caching them ensures they are available for
     * near future access without requiring an additional read and decompress.
     */
    
    #include <linux/fs.h>
    #include <linux/vfs.h>
    #include <linux/slab.h>
    #include <linux/vmalloc.h>
    #include <linux/sched.h>
    #include <linux/spinlock.h>
    #include <linux/wait.h>
    #include <linux/pagemap.h>
    
    #include "squashfs_fs.h"
    #include "squashfs_fs_sb.h"
    #include "squashfs.h"
    #include "page_actor.h"
    
    /*
     * Look-up block in cache, and increment usage count.  If not in cache, read
     * and decompress it from disk.
     */
    struct squashfs_cache_entry *squashfs_cache_get(struct super_block *sb,
    	struct squashfs_cache *cache, u64 block, int length)
    {
    	int i, n;
    	struct squashfs_cache_entry *entry;
    
    	spin_lock(&cache->lock);
    
    	while (1) {
    		for (i = cache->curr_blk, n = 0; n < cache->entries; n++) {
    			if (cache->entry[i].block == block) {
    				cache->curr_blk = i;
    				break;
    			}
    			i = (i + 1) % cache->entries;
    		}
    
    		if (n == cache->entries) {
    			/*
    			 * Block not in cache, if all cache entries are used
    			 * go to sleep waiting for one to become available.
    			 */
    			if (cache->unused == 0) {
    				cache->num_waiters++;
    				spin_unlock(&cache->lock);
    				wait_event(cache->wait_queue, cache->unused);
    				spin_lock(&cache->lock);
    				cache->num_waiters--;
    				continue;
    			}
    
    			/*
    			 * At least one unused cache entry.  A simple
    			 * round-robin strategy is used to choose the entry to
    			 * be evicted from the cache.
    			 */
    			i = cache->next_blk;
    			for (n = 0; n < cache->entries; n++) {
    				if (cache->entry[i].refcount == 0)
    					break;
    				i = (i + 1) % cache->entries;
    			}
    
    			cache->next_blk = (i + 1) % cache->entries;
    			entry = &cache->entry[i];
    
    			/*
    			 * Initialise chosen cache entry, and fill it in from
    			 * disk.
    			 */
    			cache->unused--;
    			entry->block = block;
    			entry->refcount = 1;
    			entry->pending = 1;
    			entry->num_waiters = 0;
    			entry->error = 0;
    			spin_unlock(&cache->lock);
    
    			entry->length = squashfs_read_data(sb, block, length,
    				&entry->next_index, entry->actor);
    
    			spin_lock(&cache->lock);
    
    			if (entry->length < 0)
    				entry->error = entry->length;
    
    			entry->pending = 0;
    
    			/*
    			 * While filling this entry one or more other processes
    			 * have looked it up in the cache, and have slept
    			 * waiting for it to become available.
    			 */
    			if (entry->num_waiters) {
    				spin_unlock(&cache->lock);
    				wake_up_all(&entry->wait_queue);
    			} else
    				spin_unlock(&cache->lock);
    
    			goto out;
    		}
    
    		/*
    		 * Block already in cache.  Increment refcount so it doesn't
    		 * get reused until we're finished with it, if it was
    		 * previously unused there's one less cache entry available
    		 * for reuse.
    		 */
    		entry = &cache->entry[i];
    		if (entry->refcount == 0)
    			cache->unused--;
    		entry->refcount++;
    
    		/*
    		 * If the entry is currently being filled in by another process
    		 * go to sleep waiting for it to become available.
    		 */
    		if (entry->pending) {
    			entry->num_waiters++;
    			spin_unlock(&cache->lock);
    			wait_event(entry->wait_queue, !entry->pending);
    		} else
    			spin_unlock(&cache->lock);
    
    		goto out;
    	}
    
    out:
    	TRACE("Got %s %d, start block %lld, refcount %d, error %d\n",
    		cache->name, i, entry->block, entry->refcount, entry->error);
    
    	if (entry->error)
    		ERROR("Unable to read %s cache entry [%llx]\n", cache->name,
    							block);
    	return entry;
    }
    
    
    /*
     * Release cache entry, once usage count is zero it can be reused.
     */
    void squashfs_cache_put(struct squashfs_cache_entry *entry)
    {
    	struct squashfs_cache *cache = entry->cache;
    
    	spin_lock(&cache->lock);
    	entry->refcount--;
    	if (entry->refcount == 0) {
    		cache->unused++;
    		/*
    		 * If there's any processes waiting for a block to become
    		 * available, wake one up.
    		 */
    		if (cache->num_waiters) {
    			spin_unlock(&cache->lock);
    			wake_up(&cache->wait_queue);
    			return;
    		}
    	}
    	spin_unlock(&cache->lock);
    }
    
    /*
     * Delete cache reclaiming all kmalloced buffers.
     */
    void squashfs_cache_delete(struct squashfs_cache *cache)
    {
    	int i, j;
    
    	if (cache == NULL)
    		return;
    
    	for (i = 0; i < cache->entries; i++) {
    		if (cache->entry[i].data) {
    			for (j = 0; j < cache->pages; j++)
    				kfree(cache->entry[i].data[j]);
    			kfree(cache->entry[i].data);
    		}
    		kfree(cache->entry[i].actor);
    	}
    
    	kfree(cache->entry);
    	kfree(cache);
    }
    
    
    /*
     * Initialise cache allocating the specified number of entries, each of
     * size block_size.  To avoid vmalloc fragmentation issues each entry
     * is allocated as a sequence of kmalloced PAGE_CACHE_SIZE buffers.
     */
    struct squashfs_cache *squashfs_cache_init(char *name, int entries,
    	int block_size)
    {
    	int i, j;
    	struct squashfs_cache *cache = kzalloc(sizeof(*cache), GFP_KERNEL);
    
    	if (cache == NULL) {
    		ERROR("Failed to allocate %s cache\n", name);
    		return NULL;
    	}
    
    	cache->entry = kcalloc(entries, sizeof(*(cache->entry)), GFP_KERNEL);
    	if (cache->entry == NULL) {
    		ERROR("Failed to allocate %s cache\n", name);
    		goto cleanup;
    	}
    
    	cache->curr_blk = 0;
    	cache->next_blk = 0;
    	cache->unused = entries;
    	cache->entries = entries;
    	cache->block_size = block_size;
    	cache->pages = block_size >> PAGE_CACHE_SHIFT;
    	cache->pages = cache->pages ? cache->pages : 1;
    	cache->name = name;
    	cache->num_waiters = 0;
    	spin_lock_init(&cache->lock);
    	init_waitqueue_head(&cache->wait_queue);
    
    	for (i = 0; i < entries; i++) {
    		struct squashfs_cache_entry *entry = &cache->entry[i];
    
    		init_waitqueue_head(&cache->entry[i].wait_queue);
    		entry->cache = cache;
    		entry->block = SQUASHFS_INVALID_BLK;
    		entry->data = kcalloc(cache->pages, sizeof(void *), GFP_KERNEL);
    		if (entry->data == NULL) {
    			ERROR("Failed to allocate %s cache entry\n", name);
    			goto cleanup;
    		}
    
    		for (j = 0; j < cache->pages; j++) {
    			entry->data[j] = kmalloc(PAGE_CACHE_SIZE, GFP_KERNEL);
    			if (entry->data[j] == NULL) {
    				ERROR("Failed to allocate %s buffer\n", name);
    				goto cleanup;
    			}
    		}
    
    		entry->actor = squashfs_page_actor_init(entry->data,
    						cache->pages, 0);
    		if (entry->actor == NULL) {
    			ERROR("Failed to allocate %s cache entry\n", name);
    			goto cleanup;
    		}
    	}
    
    	return cache;
    
    cleanup:
    	squashfs_cache_delete(cache);
    	return NULL;
    }
    
    
    /*
     * Copy up to length bytes from cache entry to buffer starting at offset bytes
     * into the cache entry.  If there's not length bytes then copy the number of
     * bytes available.  In all cases return the number of bytes copied.
     */
    int squashfs_copy_data(void *buffer, struct squashfs_cache_entry *entry,
    		int offset, int length)
    {
    	int remaining = length;
    
    	if (length == 0)
    		return 0;
    	else if (buffer == NULL)
    		return min(length, entry->length - offset);
    
    	while (offset < entry->length) {
    		void *buff = entry->data[offset / PAGE_CACHE_SIZE]
    				+ (offset % PAGE_CACHE_SIZE);
    		int bytes = min_t(int, entry->length - offset,
    				PAGE_CACHE_SIZE - (offset % PAGE_CACHE_SIZE));
    
    		if (bytes >= remaining) {
    			memcpy(buffer, buff, remaining);
    			remaining = 0;
    			break;
    		}
    
    		memcpy(buffer, buff, bytes);
    		buffer += bytes;
    		remaining -= bytes;
    		offset += bytes;
    	}
    
    	return length - remaining;
    }
    
    
    /*
     * Read length bytes from metadata position <block, offset> (block is the
     * start of the compressed block on disk, and offset is the offset into
     * the block once decompressed).  Data is packed into consecutive blocks,
     * and length bytes may require reading more than one block.
     */
    int squashfs_read_metadata(struct super_block *sb, void *buffer,
    		u64 *block, int *offset, int length)
    {
    	struct squashfs_sb_info *msblk = sb->s_fs_info;
    	int bytes, res = length;
    	struct squashfs_cache_entry *entry;
    
    	TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);
    
    	while (length) {
    		entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
    		if (entry->error) {
    			res = entry->error;
    			goto error;
    		} else if (*offset >= entry->length) {
    			res = -EIO;
    			goto error;
    		}
    
    		bytes = squashfs_copy_data(buffer, entry, *offset, length);
    		if (buffer)
    			buffer += bytes;
    		length -= bytes;
    		*offset += bytes;
    
    		if (*offset == entry->length) {
    			*block = entry->next_index;
    			*offset = 0;
    		}
    
    		squashfs_cache_put(entry);
    	}
    
    	return res;
    
    error:
    	squashfs_cache_put(entry);
    	return res;
    }
    
    
    /*
     * Look-up in the fragmment cache the fragment located at <start_block> in the
     * filesystem.  If necessary read and decompress it from disk.
     */
    struct squashfs_cache_entry *squashfs_get_fragment(struct super_block *sb,
    				u64 start_block, int length)
    {
    	struct squashfs_sb_info *msblk = sb->s_fs_info;
    
    	return squashfs_cache_get(sb, msblk->fragment_cache, start_block,
    		length);
    }
    
    
    /*
     * Read and decompress the datablock located at <start_block> in the
     * filesystem.  The cache is used here to avoid duplicating locking and
     * read/decompress code.
     */
    struct squashfs_cache_entry *squashfs_get_datablock(struct super_block *sb,
    				u64 start_block, int length)
    {
    	struct squashfs_sb_info *msblk = sb->s_fs_info;
    
    	return squashfs_cache_get(sb, msblk->read_page, start_block, length);
    }
    
    
    /*
     * Read a filesystem table (uncompressed sequence of bytes) from disk
     */
    void *squashfs_read_table(struct super_block *sb, u64 block, int length)
    {
    	int pages = (length + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
    	int i, res;
    	void *table, *buffer, **data;
    	struct squashfs_page_actor *actor;
    
    	table = buffer = kmalloc(length, GFP_KERNEL);
    	if (table == NULL)
    		return ERR_PTR(-ENOMEM);
    
    	data = kcalloc(pages, sizeof(void *), GFP_KERNEL);
    	if (data == NULL) {
    		res = -ENOMEM;
    		goto failed;
    	}
    
    	actor = squashfs_page_actor_init(data, pages, length);
    	if (actor == NULL) {
    		res = -ENOMEM;
    		goto failed2;
    	}
    
    	for (i = 0; i < pages; i++, buffer += PAGE_CACHE_SIZE)
    		data[i] = buffer;
    
    	res = squashfs_read_data(sb, block, length |
    		SQUASHFS_COMPRESSED_BIT_BLOCK, NULL, actor);
    
    	kfree(data);
    	kfree(actor);
    
    	if (res < 0)
    		goto failed;
    
    	return table;
    
    failed2:
    	kfree(data);
    failed:
    	kfree(table);
    	return ERR_PTR(res);
    }