When logical address of a regular extent is 0, the extent is sparse and consists of all zeros.

Without this when sparse extents are used in a file reading fails with Cannot map logical address 0 to physical

Signed-off-by: Marek Behún marek.behun@nic.cz --- fs/btrfs/extent-io.c | 6 ++++++ 1 file changed, 6 insertions(+)

diff --git a/fs/btrfs/extent-io.c b/fs/btrfs/extent-io.c index 66d0e1c7d6..2e4599cf64 100644 --- a/fs/btrfs/extent-io.c +++ b/fs/btrfs/extent-io.c @@ -78,6 +78,12 @@ u64 btrfs_read_extent_reg(struct btrfs_path *path, if (size > dlen - offset) size = dlen - offset;

+ /* sparse extent */ + if (extent->disk_bytenr == 0) { + memset(out, 0, size); + return size; + } + physical = btrfs_map_logical_to_physical(extent->disk_bytenr); if (physical == -1ULL) return -1ULL;