* You can now create the block cache in read-only mode (using an additional

parameter during construction).
* Doing so will now result in a kernel panic whenever your file system tries to
  write to a block.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@18719 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/os/drivers/fs_cache.h

@@ -31,7 +31,7 @@ extern int32 cache_blocks_in_sub_transaction(void *_cache, int32 id);
 
 /* block cache */
 extern void block_cache_delete(void *_cache, bool allowWrites);
-extern void *block_cache_create(int fd, off_t numBlocks, size_t blockSize);
+extern void *block_cache_create(int fd, off_t numBlocks, size_t blockSize, bool readOnly);
 extern status_t block_cache_sync(void *_cache);
 
 extern status_t block_cache_make_writable(void *_cache, off_t blockNumber, int32 transaction);

src/add-ons/kernel/file_systems/bfs/Volume.cpp

@@ -106,7 +106,7 @@ DeviceOpener::Open(const char *device, int mode)
 void *
 DeviceOpener::InitCache(off_t numBlocks, uint32 blockSize)
 {
-	return block_cache_create(fDevice, numBlocks, blockSize);
+	return block_cache_create(fDevice, numBlocks, blockSize, fMode == O_RDONLY);
 }
 
 

src/add-ons/kernel/file_systems/dos/dosfs.c

@@ -436,7 +436,8 @@ static status_t mount_fat_disk(const char *path, mount_id nsid,
 	}
 
 	// initialize block cache
-	vol->fBlockCache = block_cache_create(vol->fd, vol->total_sectors, vol->bytes_per_sector);
+	vol->fBlockCache = block_cache_create(vol->fd, vol->total_sectors,
+		vol->bytes_per_sector, (vol->flags & B_FS_IS_READONLY) != 0);
 	if (vol->fBlockCache == NULL) {
 		dprintf("error initializing block cache\n");
 		goto error;

src/add-ons/kernel/file_systems/iso9660/iso.c

@@ -267,7 +267,8 @@ ISOMount(const char *path, const int flags, nspace **newVol, bool allow_joliet)
 
 				/* Initialize access to the cache so that we can do cached i/o */
 				TRACE(("ISO9660: cache init: dev %d, max blocks %Ld\n", vol->fd, maxBlocks));
-				vol->fBlockCache = block_cache_create(vol->fd, maxBlocks, vol->logicalBlkSize[FS_DATA_FORMAT]);
+				vol->fBlockCache = block_cache_create(vol->fd, maxBlocks,
+					vol->logicalBlkSize[FS_DATA_FORMAT], true);
 				is_iso = true;
 			} else if ((*buffer == 0x02) && is_iso && allow_joliet) {
 				// ISO_VD_SUPPLEMENTARY
@@ -287,7 +288,6 @@ ISOMount(const char *path, const int flags, nspace **newVol, bool allow_joliet)
 					// update root directory record.
 					if (vol->joliet_level > 0)
 						InitNode(&(vol->rootDirRec), &buffer[156], NULL, 0);
-
 				}						
 			} else if (*(unsigned char *)buffer == 0xff) {
 				// ISO_VD_END

src/system/kernel/cache/block_cache.cpp

@@ -149,7 +149,7 @@ cached_block::Hash(void *_cacheEntry, const void *_block, uint32 range)
 //	#pragma mark - block_cache
 
 
-block_cache::block_cache(int _fd, off_t numBlocks, size_t blockSize)
+block_cache::block_cache(int _fd, off_t numBlocks, size_t blockSize, bool readOnly)
 	:
 	hash(NULL),
 	fd(_fd),
@@ -158,7 +158,8 @@ block_cache::block_cache(int _fd, off_t numBlocks, size_t blockSize)
 	next_transaction_id(1),
 	last_transaction(NULL),
 	transaction_hash(NULL),
-	ranges_hash(NULL)
+	ranges_hash(NULL),
+	read_only(readOnly)
 {
 	hash = hash_init(32, 0, &cached_block::Compare, &cached_block::Hash);
 	if (hash == NULL)
@@ -1078,9 +1079,9 @@ block_cache_delete(void *_cache, bool allowWrites)
 
 
 extern "C" void *
-block_cache_create(int fd, off_t numBlocks, size_t blockSize)
+block_cache_create(int fd, off_t numBlocks, size_t blockSize, bool readOnly)
 {
-	block_cache *cache = new block_cache(fd, numBlocks, blockSize);
+	block_cache *cache = new block_cache(fd, numBlocks, blockSize, readOnly);
 	if (cache == NULL)
 		return NULL;
 
@@ -1126,6 +1127,9 @@ block_cache_make_writable(void *_cache, off_t blockNumber, int32 transaction)
 	block_cache *cache = (block_cache *)_cache;
 	BenaphoreLocker locker(&cache->lock);
 
+	if (cache->read_only)
+		panic("tried to make block writable on a read-only cache!");
+
 	// ToDo: this can be done better!
 	void *block = get_writable_cached_block(cache, blockNumber,
 		blockNumber, 1, transaction, false);
@@ -1147,6 +1151,8 @@ block_cache_get_writable_etc(void *_cache, off_t blockNumber, off_t base,
 
 	TRACE(("block_cache_get_writable_etc(block = %Ld, transaction = %ld)\n",
 		blockNumber, transaction));
+	if (cache->read_only)
+		panic("tried to get writable block on a read-only cache!");
 
 	return get_writable_cached_block(cache, blockNumber, base, length,
 		transaction, false);
@@ -1169,6 +1175,8 @@ block_cache_get_empty(void *_cache, off_t blockNumber, int32 transaction)
 
 	TRACE(("block_cache_get_empty(block = %Ld, transaction = %ld)\n",
 		blockNumber, transaction));
+	if (cache->read_only)
+		panic("tried to get empty writable block on a read-only cache!");
 
 	return get_writable_cached_block((block_cache *)_cache, blockNumber,
 				blockNumber, 1, transaction, true);

src/system/kernel/cache/block_cache_private.h

@@ -116,7 +116,9 @@ struct block_cache {
 	block_list	unmapped_blocks;
 	block_list	unused_blocks;
 
-	block_cache(int fd, off_t numBlocks, size_t blockSize);
+	bool		read_only;
+
+	block_cache(int fd, off_t numBlocks, size_t blockSize, bool readOnly);
 	~block_cache();
 
 	status_t InitCheck();