fs: btrfs: support sparse extents

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>

diff --git a/fs/btrfs/extent-io.c b/fs/btrfs/extent-io.c
index 66d0e1c7d65faf5a91da5ca985fdbdaace2825df..2e4599cf64abc39232637b00b3837844b6328a32 100644 (file)
--- 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;