Date:	Fri, 17 Oct 2008 16:42:51 +0100
From:	Phillip Lougher <phillip@...gher.demon.co.uk>
To:	akpm@...ux-foundation.org, linux-embedded@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	tim.bird@...sony.com
Subject: Subject: [PATCH 10/16] Squashfs: cache operations


Signed-off-by: Phillip Lougher <phillip@...gher.demon.co.uk>
---
 fs/squashfs/cache.c |  316 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 316 insertions(+), 0 deletions(-)

diff --git a/fs/squashfs/cache.c b/fs/squashfs/cache.c
new file mode 100644
index 0000000..0fe994f
--- /dev/null
+++ b/fs/squashfs/cache.c
@@ -0,0 +1,316 @@
+/*
+ * Squashfs - a compressed read only filesystem for Linux
+ *
+ * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
+ * Phillip Lougher <phillip@...gher.demon.co.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.
+ */
+
+#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/zlib.h>
+#include <linux/squashfs_fs.h>
+#include <linux/squashfs_fs_sb.h>
+#include <linux/squashfs_fs_i.h>
+
+#include "squashfs.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 *s,
+	struct squashfs_cache *cache, long long block, int length)
+{
+	int i, n;
+	struct squashfs_cache_entry *entry;
+
+	spin_lock(&cache->lock);
+
+	while (1) {
+		for (i = 0; i < cache->entries; i++)
+			if (cache->entry[i].block == block)
+				break;
+
+		if (i == cache->entries) {
+			/*
+			 * Block not in cache, if all cache entries are locked
+			 * go to sleep waiting for one to become available.
+			 */
+			if (cache->unused == 0) {
+				cache->waiting++;
+				spin_unlock(&cache->lock);
+				wait_event(cache->wait_queue, cache->unused);
+				spin_lock(&cache->lock);
+				cache->waiting--;
+				continue;
+			}
+
+			/*
+			 * At least one unlocked 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].locked == 0)
+					break;
+				i = (i + 1) % cache->entries;
+			}
+
+			cache->next_blk = (i + 1) % cache->entries;
+			entry = &cache->entry[i];
+
+			/*
+			 * Initialise choosen cache entry, and fill it in from
+			 * disk.
+			 */
+			cache->unused--;
+			entry->block = block;
+			entry->locked = 1;
+			entry->pending = 1;
+			entry->waiting = 0;
+			entry->error = 0;
+			spin_unlock(&cache->lock);
+
+			entry->length = squashfs_read_data(s, entry->data,
+				block, length, &entry->next_index,
+				cache->block_size);
+
+			spin_lock(&cache->lock);
+
+			if (entry->length == 0)
+				entry->error = 1;
+
+			entry->pending = 0;
+			spin_unlock(&cache->lock);
+
+			/*
+			 * 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->waiting)
+				wake_up_all(&entry->wait_queue);
+			goto out;
+		}
+
+		/*
+		 * Block already in cache.  Increment lock so it doesn't
+		 * get reused until we're finished with it, if it was
+		 * previously unlocked there's one less cache entry available
+		 * for reuse.
+		 */
+		entry = &cache->entry[i];
+		if (entry->locked == 0)
+			cache->unused--;
+		entry->locked++;
+
+		/*
+		 * If the entry is currently being filled in by another process
+		 * go to sleep waiting for it to become available.
+		 */
+		if (entry->pending) {
+			entry->waiting++;
+			spin_unlock(&cache->lock);
+			wait_event(entry->wait_queue, !entry->pending);
+			goto out;
+		}
+
+		spin_unlock(&cache->lock);
+		goto out;
+	}
+
+out:
+	TRACE("Got %s %d, start block %lld, locked %d, error %d\n", cache->name,
+		i, entry->block, entry->locked, entry->error);
+
+	if (entry->error)
+		ERROR("Unable to read %s cache entry [%llx]\n", cache->name,
+							block);
+	return entry;
+}
+
+
+/*
+ * Release block, once usage count is zero it can be reused.
+ */
+void squashfs_cache_put(struct squashfs_cache *cache,
+				struct squashfs_cache_entry *entry)
+{
+	spin_lock(&cache->lock);
+	entry->locked--;
+	if (entry->locked == 0) {
+		cache->unused++;
+		spin_unlock(&cache->lock);
+		/*
+		 * If there's any processes waiting for a block to become
+		 * available, wake one up.
+		 */
+		if (cache->waiting)
+			wake_up(&cache->wait_queue);
+	} else {
+		spin_unlock(&cache->lock);
+	}
+}
+
+
+void squashfs_cache_delete(struct squashfs_cache *cache)
+{
+	int i;
+
+	if (cache == NULL)
+		return;
+
+	for (i = 0; i < cache->entries; i++)
+		if (cache->entry[i].data) {
+			if (cache->use_vmalloc)
+				vfree(cache->entry[i].data);
+			else
+				kfree(cache->entry[i].data);
+		}
+
+	kfree(cache);
+}
+
+
+struct squashfs_cache *squashfs_cache_init(char *name, int entries,
+	int block_size, int use_vmalloc)
+{
+	int i;
+	struct squashfs_cache *cache = kzalloc(sizeof(*cache) + entries *
+			sizeof(*(cache->entry)), GFP_KERNEL);
+
+	if (cache == NULL) {
+		ERROR("Failed to allocate %s cache\n", name);
+		goto failed;
+	}
+
+	cache->next_blk = 0;
+	cache->unused = entries;
+	cache->entries = entries;
+	cache->block_size = block_size;
+	cache->use_vmalloc = use_vmalloc;
+	cache->name = name;
+	cache->waiting = 0;
+	spin_lock_init(&cache->lock);
+	init_waitqueue_head(&cache->wait_queue);
+
+	for (i = 0; i < entries; i++) {
+		init_waitqueue_head(&cache->entry[i].wait_queue);
+		cache->entry[i].block = SQUASHFS_INVALID_BLK;
+		cache->entry[i].data = use_vmalloc ? vmalloc(block_size) :
+				kmalloc(block_size, GFP_KERNEL);
+		if (cache->entry[i].data == NULL) {
+			ERROR("Failed to allocate %s cache entry\n", name);
+			goto cleanup;
+		}
+	}
+
+	return cache;
+
+cleanup:
+	squashfs_cache_delete(cache);
+failed:
+	return NULL;
+}
+
+
+/*
+ * 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 *s, void *buffer,
+				long long block, unsigned int offset,
+				int length, long long *next_block,
+				unsigned int *next_offset)
+{
+	struct squashfs_sb_info *msblk = s->s_fs_info;
+	int bytes, return_length = length;
+	struct squashfs_cache_entry *entry;
+
+	TRACE("Entered squashfs_read_metadata [%llx:%x]\n", block, offset);
+
+	while (1) {
+		entry = squashfs_cache_get(s, msblk->block_cache, block, 0);
+		bytes = entry->length - offset;
+
+		if (entry->error || bytes < 1) {
+			return_length = 0;
+			goto finish;
+		} else if (bytes >= length) {
+			if (buffer)
+				memcpy(buffer, entry->data + offset, length);
+			if (entry->length - offset == length) {
+				*next_block = entry->next_index;
+				*next_offset = 0;
+			} else {
+				*next_block = block;
+				*next_offset = offset + length;
+			}
+			goto finish;
+		} else {
+			if (buffer) {
+				memcpy(buffer, entry->data + offset, bytes);
+				buffer += bytes;
+			}
+			block = entry->next_index;
+			squashfs_cache_put(msblk->block_cache, entry);
+			length -= bytes;
+			offset = 0;
+		}
+	}
+
+finish:
+	squashfs_cache_put(msblk->block_cache, entry);
+	return return_length;
+}
+
+
+struct squashfs_cache_entry *get_cached_fragment(struct super_block *s,
+				long long start_block, int length)
+{
+	struct squashfs_sb_info *msblk = s->s_fs_info;
+
+	return squashfs_cache_get(s, msblk->fragment_cache, start_block,
+		length);
+}
+
+
+void release_cached_fragment(struct squashfs_sb_info *msblk,
+				struct squashfs_cache_entry *fragment)
+{
+	squashfs_cache_put(msblk->fragment_cache, fragment);
+}
+
-- 
1.5.2.5

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