[bug report] xfs/802 failure due to mssing fstype report by lsblk

[Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>]

Hello Darrick,

Recently, my fstests run for null_blk (8GiB size) as SCRATCH_DEV failed at
xfs/802 [3]. I took a look and observed following points:

1) xfs_scrub_all command ran as expected. Even though SCRATCH_DEV is mounted,
   it did not scrub SCRATCH_DEV. Hence the failure.
2) xfs_scrub_all uses lsblk command to list all mounted xfs filesystems [1].
   However, lsblk command does not report that SCRATCH_DEV is mounted as xfs.
3) I leanred that lsblk command refers to udev database [2], and udev database
   sometimes fails to update the filesystem information. This is the case for
   the null_blk as SCRATCH_DEV on my test nodes.

Based on these observations, I think there are two points to improve:

1) I found "blkid -p" command reports that null_blk is mounted as xfs, even when
   lsblk does not report it. I think xfs_scrub_all can be modified to use
   "blkid -p" instead of lsblk to find out xfs filesystems mounted.
2) When there are other xfs filesystems on the test node than TEST_DEV or
   SCRATCH_DEV, xfs_scrub_all changes the status of them. This does not sound
   good to me since it affects system status out of the test targets block
   devices. I think he test case can be improved to check that there is no other
   xfs filesystems mounted other than TEST_DEV or SCRATCH_DEV/s. If not, the
   test case should be skipped.

At this moment, I don't have time to create patches for the improvements above.
If anyone can work on them, it will be appreciated.

[1] https://git.kernel.org/pub/scm/fs/xfs/xfsprogs-dev.git/tree/scrub/xfs_scrub_all.py.in#n55
[2] https://unix.stackexchange.com/questions/642598/lsblk-file-system-type-not-appears-from-lsblk#642600

[3] xfs/802 failure console message

xfs/802            - output mismatch (see /home/shin/kts/kernel-test-suite/src/xfstests/results//xfs/802.out.bad)
    --- tests/xfs/802.out       2026-02-04 20:44:52.254221182 +0900
    +++ /home/shin/kts/kernel-test-suite/src/xfstests/results//xfs/802.out.bad  2026-02-06 17:04:24.336536185 +0900
    @@ -2,4 +2,7 @@
     Format and populate
     Scrub Scratch FS
     Scrub Everything
    +Health status has not been collected for this filesystem.
    +Please run xfs_scrub(8) to remedy this situation.
    +cannot find evidence that /var/kts/scratch was scrubbed
     Scrub Done
    ...
    (Run 'diff -u /home/shin/kts/kernel-test-suite/src/xfstests/tests/xfs/802.out /home/shin/kts/kernel-test-suite/src/xfstests/results//xfs/802.out.bad'  to see the entire diff)