// SPDX-License-Identifier: GPL-2.0-or-later/* * Squashfs - a compressed read only filesystem for Linux * * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008 * Phillip Lougher <phillip@squashfs.org.uk> * * 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_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" /* * Waiters on cache->wait_queue are keyed by the block they want, so a wakeup * can name who it is for.  A NULL key is a capacity wakeup: one entry became * free, so wake one waiter.  A block key is a publication wakeup: that block * now has an entry, so wake every waiter which can share it. */struct squashfs_cache_wait {	wait_queue_entry_t	wait;	u64			block;	bool			capacity_wake;}; static int squashfs_cache_wake_function(wait_queue_entry_t *wait,					unsigned int mode, int sync, void *key){	struct squashfs_cache_wait *cache_wait =		container_of(wait, struct squashfs_cache_wait, wait);	u64 *block = key; 	if (block && cache_wait->block != *block)		return 0; 	WRITE_ONCE(cache_wait->capacity_wake, !block); 	/*	 * Wake and unlink unconditionally instead of using	 * autoremove_wake_function(), which unlinks only when it changed the	 * task state.  A waiter can be made runnable by something which does	 * not go through this queue: wake_up_process() takes TASK_NORMAL, and	 * a cgroup v2 thaw calls it on every task in the cgroup, as do	 * free_pid() on a pid namespace init and a late rcuwait_wake_up().	 * try_to_wake_up() then fails.  Leaving such a waiter queued with a	 * reason already recorded would let it act on a freed entry it was not	 * given, and the failure would not consume the exclusive budget, so a	 * second waiter would be woken for the same entry.	 *	 * list_del_init_careful() must be the last access to @cache_wait: it	 * releases the waiter, whose wait structure lives on its stack, and it	 * pairs with list_empty_careful() in finish_wait() to publish the	 * store above.  __wake_up_common() samples ->flags and the next entry	 * before calling here, so it does not touch @wait afterwards either.	 */	default_wake_function(wait, mode, sync, key);	list_del_init_careful(&wait->entry); 	return 1;} static void squashfs_cache_wake_block(struct squashfs_cache *cache, u64 block){	/* nr_exclusive == 0: wake every waiter which matches the key. */	__wake_up(&cache->wait_queue, TASK_NORMAL, 0, &block);} /* * Look-up block in cache, and increment usage count.  If not in cache, read * and decompress it from disk. * * A caller which finds no free entry sleeps on cache->wait_queue as an * exclusive waiter, so squashfs_cache_put() releasing one entry wakes exactly * one task.  Because a wakee may find its block published in the meantime and * share that entry rather than claim the free one, a wakee which shares hands * its wakeup on to the next waiter. */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;	bool capacity_wake = false; 	spin_lock(&cache->lock); 	while (1) {		bool pending, wake_next, wake_block; 		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) {				struct squashfs_cache_wait wait = {					.block		= block,					.capacity_wake	= false,				}; 				init_wait_func(&wait.wait,					       squashfs_cache_wake_function);				cache->num_waiters++;				/*				 * Enqueue while still holding cache->lock, so				 * that a concurrent lookup either sees us				 * queued or we see the block it publishes.				 */				prepare_to_wait_exclusive(&cache->wait_queue,						&wait.wait, TASK_UNINTERRUPTIBLE);				spin_unlock(&cache->lock);				schedule();				finish_wait(&cache->wait_queue, &wait.wait);				capacity_wake = READ_ONCE(wait.capacity_wake);				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;			wake_block = cache->num_waiters > 0;			spin_unlock(&cache->lock); 			/*			 * The entry is now findable, so release everybody			 * queued for this block to share it rather than each			 * waiting for an entry of their own.  They will block			 * on entry->wait_queue below until the read completes.			 */			if (wake_block)				squashfs_cache_wake_block(cache, block); 			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--;			/* This claims the capacity we were woken for. */			capacity_wake = false;		}		entry->refcount++; 		/*		 * If the entry is currently being filled in by another process		 * go to sleep waiting for it to become available.		 */		pending = entry->pending;		if (pending)			entry->num_waiters++; 		/*		 * We were woken because an entry became free, but shared a		 * block instead of claiming it.  Hand the wakeup on, otherwise		 * the free entry sits unclaimed while others sleep.		 */		wake_next = capacity_wake && cache->unused && cache->num_waiters;		spin_unlock(&cache->lock); 		if (wake_next)			wake_up(&cache->wait_queue);		if (pending)			wait_event(entry->wait_queue, !entry->pending); 		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 (IS_ERR(cache) || 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_SIZE buffers. */struct squashfs_cache *squashfs_cache_init(char *name, int entries,	int block_size){	int i, j;	struct squashfs_cache *cache; 	if (entries == 0)		return NULL; 	cache = kzalloc_obj(*cache);	if (cache == NULL) {		ERROR("Failed to allocate %s cache\n", name);		return ERR_PTR(-ENOMEM);	} 	cache->entry = kzalloc_objs(*(cache->entry), entries);	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_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_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 ERR_PTR(-ENOMEM);}  /* * 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 || offset < 0)		return 0;	else if (buffer == NULL)		return min(length, entry->length - offset); 	while (offset < entry->length) {		void *buff = entry->data[offset / PAGE_SIZE]				+ (offset % PAGE_SIZE);		int bytes = min_t(int, entry->length - offset,				PAGE_SIZE - (offset % PAGE_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); 	if (unlikely(length < 0))		return -EIO; 	if (unlikely(*offset < 0 || *offset >= SQUASHFS_METADATA_SIZE))		return -EIO; 	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

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