Currently, our handling of metadata is _ambiguous_ in some scenarios, that is, we end up returning unknown if the range only covers the mapping partially. For example, in the following case: $ xfs_io -c fsmap -d 0: 254:16 [0..7]: static fs metadata 8 1: 254:16 [8..15]: special 102:1 8 2: 254:16 [16..5127]: special 102:2 5112 3: 254:16 [5128..5255]: special 102:3 128 4: 254:16 [5256..5383]: special 102:4 128 5: 254:16 [5384..70919]: inodes 65536 6: 254:16 [70920..70967]: unknown 48 ... $ xfs_io -c fsmap -d 24 33 0: 254:16 [24..39]: unknown 16 <--- incomplete reporting $ xfs_io -c fsmap -d 24 33 (With patch) 0: 254:16 [16..5127]: special 102:2 5112 This is because earlier in ext4_getfsmap_meta_helper, we end up ignoring any extent that starts before our queried range, but overlaps it. While the man page [1] is a bit ambiguous on this, this fix makes the output make more sense since we are anyways returning an "unknown" extent. This is also consistent to how XFS does it: $ xfs_io -c fsmap -d ... 6: 254:16 [104..127]: free space 24 7: 254:16 [128..191]: inodes 64 ... $ xfs_io -c fsmap -d 137 150 0: 254:16 [128..191]: inodes 64 <-- full extent returned [1] https://man7.org/linux/man-pages/man2/ioctl_getfsmap.2.html Reported-by: Ritesh Harjani (IBM) Signed-off-by: Ojaswin Mujoo --- fs/ext4/fsmap.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/fs/ext4/fsmap.c b/fs/ext4/fsmap.c index 91185c40f755..22fc333244ef 100644 --- a/fs/ext4/fsmap.c +++ b/fs/ext4/fsmap.c @@ -74,7 +74,8 @@ static int ext4_getfsmap_dev_compare(const void *p1, const void *p2) static bool ext4_getfsmap_rec_before_low_key(struct ext4_getfsmap_info *info, struct ext4_fsmap *rec) { - return rec->fmr_physical < info->gfi_low.fmr_physical; + return rec->fmr_physical + rec->fmr_length <= + info->gfi_low.fmr_physical; } /* @@ -200,15 +201,18 @@ static int ext4_getfsmap_meta_helper(struct super_block *sb, ext4_group_first_block_no(sb, agno)); fs_end = fs_start + EXT4_C2B(sbi, len); - /* Return relevant extents from the meta_list */ + /* + * Return relevant extents from the meta_list. We emit all extents that + * partially/fully overlap with the query range + */ list_for_each_entry_safe(p, tmp, &info->gfi_meta_list, fmr_list) { - if (p->fmr_physical < info->gfi_next_fsblk) { + if (p->fmr_physical + p->fmr_length <= info->gfi_next_fsblk) { list_del(&p->fmr_list); kfree(p); continue; } - if (p->fmr_physical <= fs_start || - p->fmr_physical + p->fmr_length <= fs_end) { + if (p->fmr_physical <= fs_end && + p->fmr_physical + p->fmr_length > fs_start) { /* Emit the retained free extent record if present */ if (info->gfi_lastfree.fmr_owner) { error = ext4_getfsmap_helper(sb, info, -- 2.49.0