From 9d311e11fc1f5581d5ec2df0f87ea5a0193c41ad Mon Sep 17 00:00:00 2001 From: Robbie Ko Date: Mon, 7 May 2018 16:42:04 +0800 Subject: [PATCH] Btrfs: fiemap: pass correct bytenr when fm_extent_count is zero [BUG] fm_mapped_extents is not correct when fm_extent_count is 0 Like: # mount /dev/vdb5 /mnt/btrfs # dd if=/dev/zero bs=16K count=4 oflag=dsync of=/mnt/btrfs/file # xfs_io -c "fiemap -v" /mnt/btrfs/file /mnt/btrfs/file: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..127]: 25088..25215 128 0x1 When user space wants to get the number of file extents, set fm_extent_count to 0 to run fiemap and then read fm_mapped_extents. In the above example, fiemap will return with fm_mapped_extents set to 4, but it should be 1 since there's only one entry in the output. [REASON] The problem seems to be that disko is only set if fieinfo->fi_extents_max is set. And this member is initialized, in the generic ioctl_fiemap function, to the value of used-passed fm_extent_count. So when the user passes 0 then fi_extent_max is also set to zero and this causes btrfs to not initialize disko at all. Eventually this leads emit_fiemap_extent being called with a bogus 'phys' argument preventing proper fiemap entries merging. [FIX] Move the disko initialization earlier in extent_fiemap making it independent of user-passed arguments, allowing emit_fiemap_extent to properly handle consecutive extent entries. Signed-off-by: Robbie Ko Signed-off-by: David Sterba --- fs/btrfs/extent_io.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index af2f0408c6e4..8e4a7cdbc9f5 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4545,7 +4545,7 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo, offset_in_extent = em_start - em->start; em_end = extent_map_end(em); em_len = em_end - em_start; - disko = 0; + disko = em->block_start + offset_in_extent; flags = 0; /* @@ -4568,8 +4568,6 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo, u64 bytenr = em->block_start - (em->start - em->orig_start); - disko = em->block_start + offset_in_extent; - /* * As btrfs supports shared space, this information * can be exported to userspace tools via