[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <023f37e35ee280cd9baac0296cbadcbe10995cab.1757058211.git.ojaswin@linux.ibm.com>
Date: Fri, 5 Sep 2025 13:44:46 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>
Cc: Ritesh Harjani <ritesh.list@...il.com>, Zhang Yi <yi.zhang@...wei.com>,
linux-kernel@...r.kernel.org, "Darrick J . Wong" <djwong@...nel.org>
Subject: [PATCH 1/2] ext4: Correctly handle queries for metadata mappings
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) <ritesh.list@...il.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
---
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
Powered by blists - more mailing lists