tests: fix occasional LVM2-thinp test failures

[coiby]

Somehow LVM2-thinp test fails occasionally. It turns out the test fails
because /etc/lvm/devices/system.devices somehow becomes empty file after
a kernel panic,

[root@client ~]# journalctl -b0 |grep vdb
Aug 02 08:10:52 localhost kernel: virtio_blk virtio2: [vdb] 2097152 512-byte logical blocks (1.07 GB/1.00 GiB)
Aug 02 08:10:54 client lvm[712]: /dev/vdb excluded by devices file (checking PVID).

[root@client ~]# cat /etc/lvm/devices/system.devices
# empty result

[root@client ~]# pvscan -vvv
  /dev/vdb: Skipping (deviceid)

"sync -f /etc/lvm/devices/system.devices" doesn't work for this case. So
simply delete it to prevent an empty /etc/lvm/devices/system.devices. An
empty system.devices will filter out the LVM device (dev/vdb) [1].

Note the failure of this flaky test can happen 1/15 times,

log_dir=logs_dir
mkdir -p $log_dir
for i in {01..15}; do
  if tmt run  --environment KDUMP_UTILS_RPM=kdump-utils plan --name /plans/lvm2_thinp &> $log_dir/$i.log; then
    echo $i success
  else
    echo $i failure
    break
  fi
done

[1] https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/9/html/configuring_and_managing_logical_volumes/limiting-lvm-device-visibility-and-usage_configuring-and-managing-logical-volumes?extIdCarryOver=true&sc_cid=701f2000001Css5AAC#disabling-the-system-devices-file_the-lvm-devices-file

[coiby]

Hi @liutgnu, do you know why /etc/lvm/devices/system.devices will become empty?

[liutgnu]

Hi @liutgnu, do you know why /etc/lvm/devices/system.devices will become empty?

Hi coiby, Thanks for fixing the issue. I'm not sure, because I never encountered it. And I think delete the file is a good solution because according to 1, when the file is removed, it will use the device filter in lvm.conf instead, which is none in this case. So Ack for your patch.

[coiby]

@liutgnu Thanks for ack'ing the patch! Can you explicit approve this PR which is required by the workflow? Btw, I should have noted that /etc/lvm/devices/system.devices still has valid content before triggering the kernel panic. It's a kind of mysterious that sync -f /etc/lvm/devices/system.devices doesn't work.