Implemented first test implementation of the new block cache and transaction API.

Moved from mutexes to benaphores.
Removed partial write support of the old API.
remove_cached_device_blocks() will now actually free all remaining blocks.


git-svn-id: file:///srv/svn/repos/haiku/trunk/current@9895 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/kernel/core/cache/block_cache.cpp

@@ -1,11 +1,14 @@
 /* 
-** Copyright 2004, Axel Dörfler, [email protected]. All rights reserved.
+ * Copyright 2004, Axel Dörfler, [email protected]. All rights reserved.
-** Distributed under the terms of the OpenBeOS License.
+ * Distributed under the terms of the MIT License.
-*/
+ */
 
 
 #include <KernelExport.h>
+#include <fs_cache.h>
 
+#include <util/kernel_cpp.h>
+#include <util/DoublyLinkedList.h>
 #include <cache.h>
 #include <khash.h>
 #include <lock.h>
@@ -15,24 +18,56 @@
 #include <string.h>
 
 
-/* Note, this is just a dump and simple cache implementation targeted to be
+// ToDo: this is a naive implementation to test the API:
- * compatible with the one found in BeOS.
+//	1) it does not have any useful memory management (just uses malloc/free)
- * This won't be the cache we end up using in R1, seriously :-)
+//	2) block reading/writing is not at all optimized for speed, it will
- */
+//	   just read and write single blocks.
+//	3) the locking could be improved; getting a block should not need to
+//	   wait for blocks to be written
+//	4) dirty blocks are only written back if asked for
+//	5) blocks are never removed yet
 
 
-struct cache_entry {
+struct cache_transaction;
-	cache_entry	*next;			// next in hash
+typedef DoublyLinked::Link block_link;
-	off_t		block_number;
+
-	void		*data;
+struct cached_block {
-	int32		ref_count;
+	cached_block	*next;			// next in hash
-	int32		lock;
+	cached_block	*transaction_next;
-	bool		is_dirty;
+	block_link		previous_transaction_link;
+	off_t			block_number;
+	void			*data;
+	void			*updated;
+	int32			ref_count;
+	int32			lock;
+	cache_transaction *transaction;
+	cache_transaction *previous_transaction;
+};
+
+struct block_cache {
+	hash_table	*hash;
+	benaphore	lock;
+	int			fd;
+	off_t		max_blocks;
+	size_t		block_size;
+	int32		next_transaction_id;
+	hash_table	*transaction_hash;
+};
+
+typedef DoublyLinked::List<cached_block, &cached_block::previous_transaction_link> block_list;
+
+struct cache_transaction {
+	int32			id;
+	int32			num_blocks;
+	cached_block	*first_block;
+	block_list		blocks;
+	transaction_notification_hook notification_hook;
+	bool			open;
 };
 
 struct cache {
 	hash_table	*hash;
-	mutex		lock;
+	benaphore	lock;
 	off_t		max_blocks;
 	size_t		block_size;
 };
@@ -42,38 +77,89 @@ struct cache sCaches[kNumCaches];
 	// we can cache the first 16 fds (I said we were dumb, right?)
 
 
-class MutexLocker {
+class BenaphoreLocker {
 	public:
-		MutexLocker(int fd)
+		BenaphoreLocker(int fd)
-			: fMutex(NULL)
+			: fBenaphore(NULL)
 		{
 			if (fd < 0 || fd >= kNumCaches)
 				return;
 
-			fMutex = &sCaches[fd].lock;
+			fBenaphore = &sCaches[fd].lock;
-			mutex_lock(fMutex);
+			benaphore_lock(fBenaphore);
 		}
 
-		~MutexLocker()
+		BenaphoreLocker(block_cache *cache)
+			: fBenaphore(&cache->lock)
 		{
-			if (fMutex != NULL)
+			benaphore_lock(fBenaphore);
-				mutex_unlock(fMutex);
+		}
+
+		~BenaphoreLocker()
+		{
+			if (fBenaphore != NULL)
+				benaphore_unlock(fBenaphore);
 		}
 
 		status_t InitCheck()
 		{
-			return fMutex != NULL ? B_OK : B_ERROR;
+			return fBenaphore != NULL ? B_OK : B_ERROR;
 		}
 
 	private:
-		mutex	*fMutex;
+		benaphore	*fBenaphore;
 };
 
 
+//	private transaction functions
+
+
 static int
-cache_entry_compare(void *_cacheEntry, const void *_block)
+transaction_compare(void *_transaction, const void *_id)
 {
-	cache_entry *cacheEntry = (cache_entry *)_cacheEntry;
+	cache_transaction *transaction = (cache_transaction *)_transaction;
+	const int32 *id = (const int32 *)_id;
+
+	return transaction->id - *id;
+}
+
+
+static uint32
+transaction_hash(void *_transaction, const void *_id, uint32 range)
+{
+	cache_transaction *transaction = (cache_transaction *)_transaction;
+	const int32 *id = (const int32 *)_id;
+
+	if (transaction != NULL)
+		return transaction->id % range;
+
+	return *id % range;
+}
+
+
+static void
+delete_transaction(block_cache *cache, cache_transaction *transaction)
+{
+	hash_remove(cache->transaction_hash, transaction);
+	delete transaction;
+}
+
+
+static cache_transaction *
+lookup_transaction(block_cache *cache, int32 id)
+{
+	return (cache_transaction *)hash_lookup(cache->transaction_hash, &id);
+}
+
+
+//	#pragma mark -
+//	private cached block functions
+
+
+static int
+cached_block_compare(void *_cacheEntry, const void *_block)
+{
+	cached_block *cacheEntry = (cached_block *)_cacheEntry;
 	const off_t *block = (const off_t *)_block;
 
 	return cacheEntry->block_number - *block;
@@ -81,9 +167,9 @@ cache_entry_compare(void *_cacheEntry, const void *_block)
 
 
 static uint32
-cache_entry_hash(void *_cacheEntry, const void *_block, uint32 range)
+cached_block_hash(void *_cacheEntry, const void *_block, uint32 range)
 {
-	cache_entry *cacheEntry = (cache_entry *)_cacheEntry;
+	cached_block *cacheEntry = (cached_block *)_cacheEntry;
 	const off_t *block = (const off_t *)_block;
 
 	if (cacheEntry != NULL)
@@ -93,18 +179,473 @@ cache_entry_hash(void *_cacheEntry, const void *_block, uint32 range)
 }
 
 
-static status_t
+static void
-write_cache_entry(int fd, cache_entry *entry)
+free_cached_block(cached_block *block)
 {
-	ssize_t blockSize = sCaches[fd].block_size;
+	free(block->data);
-
+	if (block->data != block->updated)
-	return write_pos(fd, entry->block_number * blockSize,
+		free(block->updated);
-				entry->data, blockSize) < blockSize ? B_ERROR : B_OK;
+	free(block);
 }
 
 
+static cached_block *
+new_cached_block(block_cache *cache, off_t blockNumber, bool cleared = false)
+{
+	cached_block *block = (cached_block *)malloc(sizeof(cached_block));
+	if (block == NULL)
+		return NULL;
+
+	if (!cleared) {
+		block->data = malloc(cache->block_size);
+		if (block->data == NULL) {
+			free(block);
+			return NULL;
+		}
+	} else
+		block->data = NULL;
+
+	block->block_number = blockNumber;
+	block->lock = 0;
+	block->transaction_next = NULL;
+	block->transaction = block->previous_transaction = NULL;
+	block->updated = NULL;
+
+	hash_insert(cache->hash, block);
+
+	return block;
+}
+
+
+static void
+put_cached_block(block_cache *cache, cached_block *block)
+{
+	block->lock--;
+}
+
+
+static void
+put_cached_block(block_cache *cache, off_t blockNumber)
+{
+	cached_block *block = (cached_block *)hash_lookup(cache->hash, &blockNumber);
+	if (block != NULL)
+		put_cached_block(cache, block);
+}
+
+
+static cached_block *
+get_cached_block(block_cache *cache, off_t blockNumber, bool cleared = false)
+{
+	cached_block *block = (cached_block *)hash_lookup(cache->hash, &blockNumber);
+	bool allocated = false;
+
+	if (block == NULL) {
+		// read block into cache
+		block = new_cached_block(cache, blockNumber, cleared);
+		if (block == NULL)
+			return NULL;
+
+		allocated = true;
+	}
+	
+	if (!allocated && block->data == NULL && !cleared) {
+		// there is no block yet, but we need one
+		block->data = malloc(cache->block_size);
+		if (block->data == NULL)
+			return NULL;
+
+		allocated = true;
+	}
+
+	if (allocated && !cleared) {
+		int32 blockSize = cache->block_size;
+
+		if (read_pos(cache->fd, blockNumber * blockSize, block->data, blockSize) < blockSize) {
+			free_cached_block(block);
+			return NULL;
+		}
+	}
+
+	block->lock++;
+	return block;
+}
+
+
+static void *
+get_writable_cached_block(block_cache *cache, off_t blockNumber, off_t base, off_t length,
+	int32 transactionID, bool cleared)
+{
+	BenaphoreLocker locker(cache);
+
+	cached_block *block = get_cached_block(cache, blockNumber, cleared);
+	if (block == NULL)
+		return NULL;
+
+	// if there is no transaction support, we just return the current block
+	if (transactionID == -1) {
+		if (cleared && block->data == NULL) {
+			block->data = malloc(cache->block_size);
+			if (block->data == NULL) {
+				put_cached_block(cache, block);
+				return NULL;
+			}
+		}
+		if (cleared)
+			memset(block->data, 0, cache->block_size);
+
+		block->updated = block->data;
+			// mark the block as dirty
+
+		return block->data;
+	}
+
+	// ToDo: note, even if we panic, we should probably put the cached block
+	//	back before we return
+
+	if (block->transaction != NULL && block->transaction->id != transactionID) {
+		// ToDo: we have to wait here until the other transaction is done.
+		//	Maybe we should even panic, since we can't prevent any deadlocks.
+		panic("block_cache_get_writable(): asked to get busy writable block\n");
+		return NULL;
+	}
+	if (block->transaction == NULL && transactionID != -1) {
+		// get new transaction
+		cache_transaction *transaction = lookup_transaction(cache, transactionID);
+		if (transaction == NULL) {
+			panic("block_cache_get_writable(): invalid transaction!\n");
+			return NULL;
+		}
+		if (!transaction->open) {
+			panic("block_cache_get_writable(): transaction already done!\n");
+			return NULL;
+		}
+
+		block->transaction = transaction;
+
+		// attach the block to the transaction block list
+		block->transaction_next = transaction->first_block;
+		transaction->first_block = block->transaction_next;
+		transaction->num_blocks++;
+	}
+
+	if (block->updated == NULL) {
+		block->updated = malloc(cache->block_size);
+		if (block->updated == NULL) {
+			put_cached_block(cache, block);
+			return NULL;
+		}
+
+		if (!cleared)
+			memcpy(block->updated, block->data, cache->block_size);
+	}
+
+	if (cleared)
+		memset(block->updated, 0, cache->block_size);
+	
+	return block->updated;
+}
+
+
+status_t
+write_cached_block(block_cache *cache, cached_block *block, bool deleteTransaction = true)
+{
+	cache_transaction *previous = block->previous_transaction;
+	int32 blockSize = cache->block_size;
+
+	if (write_pos(cache->fd, block->block_number * blockSize, block->data, blockSize) < blockSize) {
+		dprintf("could not write back block %Ld\n", block->block_number);
+		return B_IO_ERROR;
+	}
+
+	if (previous != NULL) {
+		previous->blocks.Remove(block);
+		block->previous_transaction = NULL;
+
+		if (--previous->num_blocks == 0) {
+			if (previous->notification_hook != NULL)
+				previous->notification_hook(previous->id);
+
+			if (deleteTransaction)
+				delete_transaction(cache, previous);
+		}
+	}
+
+	return B_OK;
+}
+
+
+//	#pragma mark -
+//	Transactions
+
+
+extern "C" int32
+cache_transaction_start(void *_cache, transaction_notification_hook hook)
+{
+	block_cache *cache = (block_cache *)_cache;
+
+	cache_transaction *transaction = new cache_transaction;
+	if (transaction == NULL)
+		return B_NO_MEMORY;
+
+	transaction->id = atomic_add(&cache->next_transaction_id, 1);
+	transaction->num_blocks = 0;
+	transaction->first_block = NULL;
+	transaction->notification_hook = hook;
+	transaction->open = true;
+
+	BenaphoreLocker locker(cache);
+	hash_insert(cache->transaction_hash, transaction);
+
+	return transaction->id;
+}
+
+
+extern "C" status_t
+cache_transaction_sync(void *_cache, int32 id)
+{
+	block_cache *cache = (block_cache *)_cache;
+	BenaphoreLocker locker(cache);
+	status_t status = B_ENTRY_NOT_FOUND;
+
+	hash_iterator iterator;
+	hash_open(cache->transaction_hash, &iterator);
+
+	cache_transaction *transaction;
+	while ((transaction = (cache_transaction *)hash_next(cache->transaction_hash, &iterator)) != NULL) {
+		// ToDo: fix hash interface to make this easier
+
+		if (transaction->id <= id && !transaction->open) {
+			while (transaction->num_blocks > 0) {
+				status = write_cached_block(cache, block_list::GetItem(transaction->blocks.Head()), false);
+				if (status != B_OK)
+					return status;
+			}
+			delete_transaction(cache, transaction);
+			hash_rewind(cache->transaction_hash, &iterator);
+		}
+	}
+
+	hash_close(cache->transaction_hash, &iterator, false);
+	return B_OK;
+}
+
+
+extern "C" status_t
+cache_transaction_end(void *_cache, int32 id)
+{
+	block_cache *cache = (block_cache *)_cache;
+	BenaphoreLocker locker(cache);
+
+	cache_transaction *transaction = lookup_transaction(cache, id);
+	if (transaction == NULL) {
+		panic("cache_transaction_end(): invalid transaction ID\n");
+		return B_BAD_VALUE;
+	}
+
+	// iterate through all blocks and make the updated contents current
+
+	cached_block *block = transaction->first_block, *next;
+	for (; block != NULL; block = next) {
+		next = block->transaction_next;
+
+		if (block->previous_transaction != NULL) {
+			// need to write back pending changes
+			write_cached_block(cache, block);
+		}
+			
+		// ToDo: unfortunately, at least for now, we have to keep the
+		//	block data pointer constant. Therefore, we have to copy
+		//	the data.
+		if (block->data != NULL) {
+			memcpy(block->data, block->updated, cache->block_size);
+			free(block->updated);
+		} else
+			block->data = block->updated;
+
+		block->updated = NULL;
+
+		// move the block to the previous transaction list
+		transaction->blocks.Add(block);
+
+		block->previous_transaction = transaction;
+		block->transaction_next = NULL;
+		block->transaction = NULL;
+	}
+
+	transaction->open = false;
+
+	return B_OK;
+}
+
+
+extern "C" status_t
+cache_transaction_abort(void *_cache, int32 id)
+{
+	block_cache *cache = (block_cache *)_cache;
+	BenaphoreLocker locker(cache);
+
+	return B_OK;
+}
+
+
+//	#pragma mark -
+//	public interface
+
+
+extern "C" void
+block_cache_delete(void *_cache, bool allowWrites)
+{
+	block_cache *cache = (block_cache *)_cache;
+
+	if (allowWrites)
+		block_cache_sync(cache);
+
+	// free all blocks
+
+	uint32 cookie = 0;
+	cached_block *block;
+	while ((block = (cached_block *)hash_remove_first(cache->hash, &cookie)) != NULL) {
+		free_cached_block(block);
+	}
+	
+	// free all transactions (they will all be aborted)	
+
+	cookie = 0;
+	cache_transaction *transaction;
+	while ((transaction = (cache_transaction *)hash_remove_first(cache->transaction_hash, &cookie)) != NULL) {
+		delete transaction;
+	}
+
+	hash_uninit(cache->hash);
+	hash_uninit(cache->transaction_hash);
+	benaphore_destroy(&cache->lock);
+
+	delete cache;
+}
+
+
+extern "C" void *
+block_cache_create(int fd, off_t numBlocks, size_t blockSize)
+{
+	block_cache *cache = new block_cache;
+	if (cache == NULL)
+		return NULL;
+
+	cache->hash = hash_init(32, 0, &cached_block_compare, &cached_block_hash);
+	if (cache->hash == NULL)
+		goto err1;
+
+	cache->transaction_hash = hash_init(16, 0, &transaction_compare, &transaction_hash);
+	if (cache->transaction_hash == NULL)
+		goto err2;
+
+	if (benaphore_init(&cache->lock, "block cache") < B_OK)
+		goto err3;
+
+	cache->fd = fd;
+	cache->max_blocks = numBlocks;
+	cache->block_size = blockSize;
+
+	return cache;
+
+err3:
+	hash_uninit(cache->transaction_hash);
+err2:
+	hash_uninit(cache->hash);
+err1:
+	delete cache;
+	return NULL;
+}
+
+
+extern "C" status_t
+block_cache_sync(void *_cache)
+{
+	block_cache *cache = (block_cache *)_cache;
+
+	// we will sync all dirty blocks to disk that have a completed
+	// transaction or no transaction only
+
+	BenaphoreLocker locker(cache);
+	hash_iterator iterator;
+	hash_open(cache->hash, &iterator);
+
+	cached_block *block;
+	while ((block = (cached_block *)hash_next(cache->hash, &iterator)) != NULL) {
+		if (block->previous_transaction != NULL
+			|| (block->transaction == NULL && block->updated)) {
+			status_t status = write_cached_block(cache, block);
+			if (status != B_OK)
+				return status;
+		}
+	}
+
+	hash_close(cache->hash, &iterator, false);
+	return B_OK;
+}
+
+
+extern "C" void *
+block_cache_get_writable_etc(void *_cache, off_t blockNumber, off_t base, off_t length,
+	int32 transaction)
+{
+	return get_writable_cached_block((block_cache *)_cache, blockNumber,
+				base, length, transaction, false);
+}
+
+
+extern "C" void *
+block_cache_get_writable(void *_cache, off_t blockNumber, int32 transaction)
+{
+	return block_cache_get_writable_etc(_cache, blockNumber, blockNumber, 1, transaction);
+}
+
+
+extern "C" void *
+block_cache_get_empty(void *_cache, off_t blockNumber, int32 transaction)
+{
+	return get_writable_cached_block((block_cache *)_cache, blockNumber,
+				blockNumber, 1, transaction, true);
+}
+
+
+extern "C" const void *
+block_cache_get_etc(void *_cache, off_t blockNumber, off_t base, off_t length)
+{
+	block_cache *cache = (block_cache *)_cache;
+	BenaphoreLocker locker(cache);
+
+	cached_block *block = get_cached_block(cache, blockNumber);
+	if (block == NULL)
+		return NULL;
+
+	return block->data;
+}
+
+
+extern "C" const void *
+block_cache_get(void *_cache, off_t blockNumber)
+{
+	return block_cache_get_etc(_cache, blockNumber, blockNumber, 1);
+}
+
+
+extern "C" void
+block_cache_put(void *_cache, off_t blockNumber)
+{
+	block_cache *cache = (block_cache *)_cache;
+	BenaphoreLocker locker(cache);
+
+	put_cached_block(cache, blockNumber);
+}
+
+
+//	#pragma mark -
+//	private BeOS compatible interface (to be removed)
+
+
 void
-put_cache_entry(int fd, cache_entry *entry)
+put_cache_entry(int fd, cached_block *entry)
 {
 	if (entry == NULL)
 		return;
@@ -112,21 +653,16 @@ put_cache_entry(int fd, cache_entry *entry)
 	if (--entry->ref_count > 0)
 		return;
 
-	// write out entry if necessary
-	if (entry->is_dirty
-		&& write_cache_entry(fd, entry) != B_OK)
-		panic("could not write back entry\n");
-
 	hash_remove(sCaches[fd].hash, entry);
 	free(entry->data);
 	free(entry);
 }
 
 
-cache_entry *
+cached_block *
 new_cache_entry(int fd, off_t blockNumber, size_t blockSize)
 {
-	cache_entry *entry = (cache_entry *)malloc(sizeof(cache_entry));
+	cached_block *entry = (cached_block *)malloc(sizeof(cached_block));
 	if (entry == NULL)
 		return NULL;
 
@@ -142,7 +678,6 @@ new_cache_entry(int fd, off_t blockNumber, size_t blockSize)
 	entry->block_number = blockNumber;
 	entry->ref_count = 1;
 	entry->lock = 0;
-	entry->is_dirty = false;
 
 	hash_insert(sCaches[fd].hash, entry);
 
@@ -150,10 +685,10 @@ new_cache_entry(int fd, off_t blockNumber, size_t blockSize)
 }
 
 
-cache_entry *
+static cached_block *
 lookup_cache_entry(int fd, off_t blockNumber)
 {
-	cache_entry *entry = (cache_entry *)hash_lookup(sCaches[fd].hash, &blockNumber);
+	cached_block *entry = (cached_block *)hash_lookup(sCaches[fd].hash, &blockNumber);
 	if (entry == NULL)
 		return NULL;
 
@@ -163,7 +698,7 @@ lookup_cache_entry(int fd, off_t blockNumber)
 
 
 //	#pragma mark -
-//	public BeOS compatible interface
+//	public BeOS compatible read-only interface (to be removed)
 
 
 extern "C" void
@@ -194,8 +729,8 @@ init_cache_for_device(int fd, off_t max_blocks)
 	if (sCaches[fd].hash != NULL)
 		return B_BUSY;
 
-	sCaches[fd].hash = hash_init(32, 0, &cache_entry_compare, &cache_entry_hash);
+	sCaches[fd].hash = hash_init(32, 0, &cached_block_compare, &cached_block_hash);
-	return mutex_init(&sCaches[fd].lock, "block cache");
+	return benaphore_init(&sCaches[fd].lock, "block cache");
 }
 
 
@@ -205,35 +740,29 @@ remove_cached_device_blocks(int fd, int allowWrite)
 	if (fd < 0 || fd >= kNumCaches || sCaches[fd].hash == NULL)
 		return B_ERROR;
 
-	if (allowWrite) {
+	hash_table *hash = sCaches[fd].hash;
-		hash_iterator iterator;
+
-		hash_open(sCaches[fd].hash, &iterator);
+	uint32 cookie = 0;
-		
+	cached_block *block;
-		cache_entry *entry;
+	while ((block = (cached_block *)hash_remove_first(hash, &cookie)) != NULL) {
-		while ((entry = (cache_entry *)hash_next(sCaches[fd].hash, &iterator)) != NULL) {
+		free_cached_block(block);
-			// write out entry if necessary
-			if (entry->is_dirty
-				&& write_cache_entry(fd, entry) != B_OK)
-				panic("write failed!\n");
-		}
-		hash_close(sCaches[fd].hash, &iterator, false);
 	}
 
-	hash_uninit(sCaches[fd].hash);
+	hash_uninit(hash);
-	mutex_destroy(&sCaches[fd].lock);
+	benaphore_destroy(&sCaches[fd].lock);
 
-	return 0;
+	return B_OK;
 }
 
 
 extern "C" void *
 get_block(int fd, off_t blockNumber, int blockSize)
 {
-	MutexLocker locker(fd);
+	BenaphoreLocker locker(fd);
 	if (locker.InitCheck() != B_OK)
 		return NULL;
 
-	cache_entry *entry = lookup_cache_entry(fd, blockNumber);
+	cached_block *entry = lookup_cache_entry(fd, blockNumber);
 	if (entry == NULL) {
 		// read entry into cache
 		entry = new_cache_entry(fd, blockNumber, blockSize);
@@ -256,11 +785,11 @@ get_block(int fd, off_t blockNumber, int blockSize)
 extern "C" void *
 get_empty_block(int fd, off_t blockNumber, int blockSize)
 {
-	MutexLocker locker(fd);
+	BenaphoreLocker locker(fd);
 	if (locker.InitCheck() != B_OK)
 		return NULL;
 
-	cache_entry *entry = lookup_cache_entry(fd, blockNumber);
+	cached_block *entry = lookup_cache_entry(fd, blockNumber);
 	if (entry == NULL) {
 		// create new cache entry
 		entry = new_cache_entry(fd, blockNumber, blockSize);
@@ -278,11 +807,11 @@ get_empty_block(int fd, off_t blockNumber, int blockSize)
 extern "C" int
 release_block(int fd, off_t blockNumber)
 {
-	MutexLocker locker(fd);
+	BenaphoreLocker locker(fd);
 	if (locker.InitCheck() != B_OK)
 		return B_ERROR;
 
-	cache_entry *entry = lookup_cache_entry(fd, blockNumber);
+	cached_block *entry = lookup_cache_entry(fd, blockNumber);
 	if (entry == NULL)
 		panic("release_block() called on block %Ld that was not cached\n", blockNumber);
 
@@ -302,7 +831,7 @@ mark_blocks_dirty(int fd, off_t blockNumber, int numBlocks)
 extern "C" int
 cached_read(int fd, off_t blockNumber, void *data, off_t numBlocks, int blockSize)
 {
-	MutexLocker locker(fd);
+	BenaphoreLocker locker(fd);
 	if (locker.InitCheck() != B_OK)
 		return B_ERROR;
 
@@ -310,16 +839,6 @@ cached_read(int fd, off_t blockNumber, void *data, off_t numBlocks, int blockSiz
 	if (read_pos(fd, blockNumber * blockSize, data, bytes) < bytes)
 		return -1;
 
-	// check if there are any cached blocks in that range shadowing the device contents
-
-	for (off_t blockOffset = 0; blockOffset < numBlocks; blockOffset++) {
-		cache_entry *entry = lookup_cache_entry(fd, blockNumber + blockOffset);
-		if (entry != NULL) {
-			if (entry->is_dirty)
-				memcpy((void *)((addr_t)data + blockOffset * blockSize), entry->data, blockSize);
-			put_cache_entry(fd, entry);
-		}
-	}
 	return 0;
 }