libext2fs: zero blocks via FALLOC_FL_ZERO_RANGE in ext2fs_zero_blocks

Plumb a new call into the IO manager to support translating
ext2fs_zero_blocks calls into the equivalent FALLOC_FL_ZERO_RANGE
fallocate flag primitive when possible.  This patch provides _only_
support for file-based images.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

lib/ext2fs/ext2_io.h

@@ -93,7 +93,9 @@ struct struct_io_manager {
 	errcode_t (*cache_readahead)(io_channel channel,
 				     unsigned long long block,
 				     unsigned long long count);
-	long	reserved[15];
+	errcode_t (*zeroout)(io_channel channel, unsigned long long block,
+			     unsigned long long count);
+	long	reserved[14];
 };
 
 #define IO_FLAG_RW		0x0001
@@ -125,6 +127,9 @@ extern errcode_t io_channel_write_blk64(io_channel channel,
 extern errcode_t io_channel_discard(io_channel channel,
 				    unsigned long long block,
 				    unsigned long long count);
+extern errcode_t io_channel_zeroout(io_channel channel,
+				    unsigned long long block,
+				    unsigned long long count);
 extern errcode_t io_channel_alloc_buf(io_channel channel,
 				      int count, void *ptr);
 extern errcode_t io_channel_cache_readahead(io_channel io,

lib/ext2fs/io_manager.c

@@ -112,6 +112,17 @@ errcode_t io_channel_discard(io_channel channel, unsigned long long block,
 	return EXT2_ET_UNIMPLEMENTED;
 }
 
+errcode_t io_channel_zeroout(io_channel channel, unsigned long long block,
+			     unsigned long long count)
+{
+	EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
+
+	if (channel->manager->zeroout)
+		return (channel->manager->zeroout)(channel, block, count);
+
+	return EXT2_ET_UNIMPLEMENTED;
+}
+
 errcode_t io_channel_alloc_buf(io_channel io, int count, void *ptr)
 {
 	size_t	size;

lib/ext2fs/mkjournal.c

@@ -170,6 +170,11 @@ errcode_t ext2fs_zero_blocks2(ext2_filsys fs, blk64_t blk, int num,
 	if (num <= 0)
 		return 0;
 
+	/* Try a zero out command, if supported */
+	retval = io_channel_zeroout(fs->io, blk, num);
+	if (retval == 0)
+		return 0;
+
 	/* Allocate the zeroizing buffer if necessary */
 	if (num > stride_length && stride_length < MAX_STRIDE_LENGTH) {
 		void *p;

lib/ext2fs/test_io.c

@@ -86,6 +86,7 @@ void (*test_io_cb_write_byte)
 #define TEST_FLAG_SET_OPTION		0x20
 #define TEST_FLAG_DISCARD		0x40
 #define TEST_FLAG_READAHEAD		0x80
+#define TEST_FLAG_ZEROOUT		0x100
 
 static void test_dump_block(io_channel channel,
 			    struct test_private_data *data,
@@ -507,6 +508,25 @@ static errcode_t test_cache_readahead(io_channel channel,
 	return retval;
 }
 
+static errcode_t test_zeroout(io_channel channel, unsigned long long block,
+			      unsigned long long count)
+{
+	struct test_private_data *data;
+	errcode_t	retval = 0;
+
+	EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
+	data = (struct test_private_data *) channel->private_data;
+	EXT2_CHECK_MAGIC(data, EXT2_ET_MAGIC_TEST_IO_CHANNEL);
+
+	if (data->real)
+		retval = io_channel_zeroout(data->real, block, count);
+	if (data->flags & TEST_FLAG_ZEROOUT)
+		fprintf(data->outfile,
+			"Test_io: zeroout(%llu, %llu) returned %s\n",
+			block, count, retval ? error_message(retval) : "OK");
+	return retval;
+}
+
 static struct struct_io_manager struct_test_manager = {
 	.magic		= EXT2_ET_MAGIC_IO_MANAGER,
 	.name		= "Test I/O Manager",
@@ -523,6 +543,7 @@ static struct struct_io_manager struct_test_manager = {
 	.write_blk64	= test_write_blk64,
 	.discard	= test_discard,
 	.cache_readahead	= test_cache_readahead,
+	.zeroout	= test_zeroout,
 };
 
 io_manager test_io_manager = &struct_test_manager;

lib/ext2fs/unix_io.c

@@ -987,6 +987,72 @@ unimplemented:
 	return EXT2_ET_UNIMPLEMENTED;
 }
 
+static errcode_t unix_zeroout(io_channel channel, unsigned long long block,
+			      unsigned long long count)
+{
+	struct unix_private_data *data;
+	int		ret;
+
+	EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
+	data = (struct unix_private_data *) channel->private_data;
+	EXT2_CHECK_MAGIC(data, EXT2_ET_MAGIC_UNIX_IO_CHANNEL);
+
+	if (getenv("UNIX_IO_NOZEROOUT"))
+		goto unimplemented;
+
+	if (channel->flags & CHANNEL_FLAGS_BLOCK_DEVICE) {
+		/* Not implemented until the BLKZEROOUT mess is fixed */
+		goto unimplemented;
+	} else {
+		/* Regular file, try to use truncate/punch/zero. */
+#if defined(HAVE_FALLOCATE) && (defined(FALLOC_FL_ZERO_RANGE) || \
+	(defined(FALLOC_FL_PUNCH_HOLE) && defined(FALLOC_FL_KEEP_SIZE)))
+		struct stat statbuf;
+
+		if (count == 0)
+			return 0;
+		/*
+		 * If we're trying to zero a range past the end of the file,
+		 * extend the file size, then punch (or zero_range) everything.
+		 */
+		ret = fstat(data->dev, &statbuf);
+		if (ret)
+			goto err;
+		if (statbuf.st_size < (block + count) * channel->block_size) {
+			ret = ftruncate(data->dev,
+					(block + count) * channel->block_size);
+			if (ret)
+				goto err;
+		}
+#if defined(FALLOC_FL_PUNCH_HOLE) && defined(FALLOC_FL_KEEP_SIZE)
+		ret = fallocate(data->dev,
+				FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+				(off_t)(block) * channel->block_size,
+				(off_t)(count) * channel->block_size);
+		if (ret == 0)
+			goto err;
+#endif
+#ifdef FALLOC_FL_ZERO_RANGE
+		ret = fallocate(data->dev,
+				FALLOC_FL_ZERO_RANGE,
+				(off_t)(block) * channel->block_size,
+				(off_t)(count) * channel->block_size);
+#endif
+#else
+		goto unimplemented;
+#endif /* HAVE_FALLOCATE && (ZERO_RANGE || (PUNCH_HOLE && KEEP_SIZE)) */
+	}
+err:
+	if (ret < 0) {
+		if (errno == EOPNOTSUPP)
+			goto unimplemented;
+		return errno;
+	}
+	return 0;
+unimplemented:
+	return EXT2_ET_UNIMPLEMENTED;
+}
+
 static struct struct_io_manager struct_unix_manager = {
 	.magic		= EXT2_ET_MAGIC_IO_MANAGER,
 	.name		= "Unix I/O Manager",
@@ -1003,6 +1069,7 @@ static struct struct_io_manager struct_unix_manager = {
 	.write_blk64	= unix_write_blk64,
 	.discard	= unix_discard,
 	.cache_readahead	= unix_cache_readahead,
+	.zeroout	= unix_zeroout,
 };
 
 io_manager unix_io_manager = &struct_unix_manager;