On Thu, Aug 08, 2024 at 10:47:59PM +0800, Zizhi Wo wrote:
> In commit 63ef7a35912d ("xfs: fix interval filtering in multi-step fsmap
> queries"), Darrick has solved a fsmap bug about incorrect filter condition.
> But I still notice two problems in fsmap:
>
> [root@fedora ~]# xfs_io -c 'fsmap -vvvv' /mnt
> EXT: DEV BLOCK-RANGE OWNER FILE-OFFSET AG AG-OFFSET TOTAL
> 0: 253:32 [0..7]: static fs metadata 0 (0..7) 8
> 1: 253:32 [8..23]: per-AG metadata 0 (8..23) 16
> 2: 253:32 [24..39]: inode btree 0 (24..39) 16
> ......
>
> Bug 1:
> [root@fedora ~]# xfs_io -c 'fsmap -vvvv -d 3 7' /mnt
> [root@fedora ~]#
> Normally, we should be able to get [3, 7), but we got nothing.
Hmm, yes, that's a bug.
> Bug 2:
> [root@fedora ~]# xfs_io -c 'fsmap -vvvv -d 15 20' /mnt
> EXT: DEV BLOCK-RANGE OWNER FILE-OFFSET AG AG-OFFSET TOTAL
> 0: 253:32 [8..23]: per-AG metadata 0 (8..23) 16
> Normally, we should be able to get [15, 20), but we obtained a whole
> segment of extent.
Both filesystems implementing GETFSMAP (ext4 and xfs) can return larger
mapping than what was requested. Userspace can decide to trim the
mappings before using them, which is why the kernel doesn't do that on
its own.
> The first problem is caused by shifting. When the query interval is before
> the first extent which can be find in btree, no records can meet the
> requirement. And the gap will be obtained in the last query. However,
> rec_daddr is calculated based on the start_block recorded in key[1], which
> is converted by calling XFS_BB_TO_FSBT. Then if rec_daddr does not exceed
> info->next_daddr, which means keys[1].fmr_physical >> (mp)->m_blkbb_log
> <= info->next_daddr, no records will be displayed. In the above example,
> 3 >> (mp)->m_blkbb_log = 0 and 7 >> (mp)->m_blkbb_log = 0, so the two are
> reduced to 0 and the gap is ignored:
>
> before calculate ----------------> after shifting
> 3(st) 7(ed) 0(st/ed)
> |---------| |
> sector size block size
>
> Resolve this issue by introducing the "tail_daddr" field in
> xfs_getfsmap_info. This records |key[1].fmr_physical + key[1].length| at
> the granularity of sector. If the current query is the last, the rec_daddr
> is tail_daddr to prevent missing interval problems caused by shifting. We
> only need to focus on the last query, because xfs disks are internally
> aligned with disk blocksize that are powers of two and minimum 512, so
> there is no problem with shifting in previous queries.
Not sure what "tail_daddr" is; the patch adds {start,end}_daddr. I
agree that fsmap -vvvv -d 3 7 ought to return "static fs metadata"
instead of nothing, however.
Can you send a separate fix for "Bug 1", please?
--D
> The second problem is that the resulting range is not truncated precisely
> according to the boundary. Currently, the query display mechanism for owner
> and missing_owner is different. The query of missing_owner (e.g. freespace
> in rmapbt/ unknown space in bnobt) is obtained by subtraction (gap), which
> can accurately lock the range. In the query of owner which almostly finded
> by btree, as long as certain conditions met, the entire interval is
> recorded, regardless of the starting address of the key[0] and key[1]
> incoming from the user state. Focus on the following scenario:
>
> a b
> |-------|
> query
> c d
> |----------------|-------------|----------------|
> missing owner1 owner missing owner2
>
> Currently query is directly displayed as [c, d), the correct display should
> be [a, b). This problem is solved by calculating max(a, c) and min(b, d) to
> identify the head and tail of the range. To be able to determine the bounds
> of the low key, "start_daddr" is introduced in xfs_getfsmap_info. Although
> in some scenarios, similar results can be achieved without introducing
> "start_daddr" and relying solely on info->next_daddr (e.g. in bnobt), it is
> ineffective for overlapping scenarios in rmapbt.
>
> After applying this patch, both of the above issues have been fixed (the
> same applies to boundary queries for the log device and realtime device):
> 1)
> [root@fedora ~]# xfs_io -c 'fsmap -vvvv -d 3 7' /mnt
> EXT: DEV BLOCK-RANGE OWNER FILE-OFFSET AG AG-OFFSET TOTAL
> 0: 253:32 [3..6]: static fs metadata 0 (3..6) 4
> 2)
> [root@fedora ~]# xfs_io -c 'fsmap -vvvv -d 15 20' /mnt
> EXT: DEV BLOCK-RANGE OWNER FILE-OFFSET AG AG-OFFSET TOTAL
> 0: 253:32 [15..19]: per-AG metadata 0 (15..19) 5
>
> Note that due to the current query range being more precise, high.rm_owner
> needs to be handled carefully. When it is 0, set it to the maximum value to
> prevent missing intervals in rmapbt.
>
> Signed-off-by: Zizhi Wo <wozizhi@xxxxxxxxxx>
> ---
> fs/xfs/xfs_fsmap.c | 42 ++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 40 insertions(+), 2 deletions(-)
>
> diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c
> index 85dbb46452ca..e7bb21497e5c 100644
> --- a/fs/xfs/xfs_fsmap.c
> +++ b/fs/xfs/xfs_fsmap.c
> @@ -162,6 +162,8 @@ struct xfs_getfsmap_info {
> xfs_daddr_t next_daddr; /* next daddr we expect */
> /* daddr of low fsmap key when we're using the rtbitmap */
> xfs_daddr_t low_daddr;
> + xfs_daddr_t start_daddr; /* daddr of low fsmap key */
> + xfs_daddr_t end_daddr; /* daddr of high fsmap key */
> u64 missing_owner; /* owner of holes */
> u32 dev; /* device id */
> /*
> @@ -276,6 +278,7 @@ xfs_getfsmap_helper(
> struct xfs_mount *mp = tp->t_mountp;
> bool shared;
> int error;
> + int trunc_len;
>
> if (fatal_signal_pending(current))
> return -EINTR;
> @@ -283,6 +286,13 @@ xfs_getfsmap_helper(
> if (len_daddr == 0)
> len_daddr = XFS_FSB_TO_BB(mp, rec->rm_blockcount);
>
> + /*
> + * Determine the maximum boundary of the query to prepare for
> + * subsequent truncation.
> + */
> + if (info->last && info->end_daddr)
> + rec_daddr = info->end_daddr;
> +
> /*
> * Filter out records that start before our startpoint, if the
> * caller requested that.
> @@ -348,6 +358,21 @@ xfs_getfsmap_helper(
> return error;
> fmr.fmr_offset = XFS_FSB_TO_BB(mp, rec->rm_offset);
> fmr.fmr_length = len_daddr;
> + /* If the start address of the record is before the low key, truncate left. */
> + if (info->start_daddr > rec_daddr) {
> + trunc_len = info->start_daddr - rec_daddr;
> + fmr.fmr_physical += trunc_len;
> + fmr.fmr_length -= trunc_len;
> + /* need to update the offset in rmapbt. */
> + if (info->missing_owner == XFS_FMR_OWN_FREE)
> + fmr.fmr_offset += trunc_len;
> + }
> + /* If the end address of the record exceeds the high key, truncate right. */
> + if (info->end_daddr) {
> + fmr.fmr_length = umin(fmr.fmr_length, info->end_daddr - fmr.fmr_physical);
> + if (fmr.fmr_length == 0)
> + goto out;
> + }
> if (rec->rm_flags & XFS_RMAP_UNWRITTEN)
> fmr.fmr_flags |= FMR_OF_PREALLOC;
> if (rec->rm_flags & XFS_RMAP_ATTR_FORK)
> @@ -364,7 +389,7 @@ xfs_getfsmap_helper(
>
> xfs_getfsmap_format(mp, &fmr, info);
> out:
> - rec_daddr += len_daddr;
> + rec_daddr = fmr.fmr_physical + fmr.fmr_length;
> if (info->next_daddr < rec_daddr)
> info->next_daddr = rec_daddr;
> return 0;
> @@ -655,6 +680,13 @@ __xfs_getfsmap_datadev(
> error = xfs_fsmap_owner_to_rmap(&info->high, &keys[1]);
> if (error)
> break;
> + /*
> + * Set the owner of high_key to the maximum again to
> + * prevent missing intervals during the query.
> + */
> + if (info->high.rm_owner == 0 &&
> + info->missing_owner == XFS_FMR_OWN_FREE)
> + info->high.rm_owner = ULLONG_MAX;
> xfs_getfsmap_set_irec_flags(&info->high, &keys[1]);
> }
>
> @@ -946,6 +978,9 @@ xfs_getfsmap(
>
> info.next_daddr = head->fmh_keys[0].fmr_physical +
> head->fmh_keys[0].fmr_length;
> + /* Assignment is performed only for the first time. */
> + if (head->fmh_keys[0].fmr_length == 0)
> + info.start_daddr = info.next_daddr;
> info.fsmap_recs = fsmap_recs;
> info.head = head;
>
> @@ -966,8 +1001,10 @@ xfs_getfsmap(
> * low key, zero out the low key so that we get
> * everything from the beginning.
> */
> - if (handlers[i].dev == head->fmh_keys[1].fmr_device)
> + if (handlers[i].dev == head->fmh_keys[1].fmr_device) {
> dkeys[1] = head->fmh_keys[1];
> + info.end_daddr = dkeys[1].fmr_physical + dkeys[1].fmr_length;
> + }
> if (handlers[i].dev > head->fmh_keys[0].fmr_device)
> memset(&dkeys[0], 0, sizeof(struct xfs_fsmap));
>
> @@ -991,6 +1028,7 @@ xfs_getfsmap(
> xfs_trans_cancel(tp);
> tp = NULL;
> info.next_daddr = 0;
> + info.start_daddr = 0;
> }
>
> if (tp)
> --
> 2.39.2
>
>
