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+++ This bug was initially created as a clone of Bug #1734625 +++
Description:
When disable 'io' controller, the error message is code-level when try to set values to blk related params
Versions:
libvirt-5.5.0-2.module+el8.1.0+3773+7dd501bf.x86_64
How reproducible:
100%
Pls note:
This is a regression but not a serious issue.
And happens with cgroup v1 and v2.
Steps:
1. Disable blkio controller with qemu.conf
$ cat /etc/libvirt/qemu.conf | grep "^cgroup"
cgroup_controllers = [ "cpu", "devices", "memory", "cpuset", "cpuacct" ]
$ systemctl restart libvirtd
2. Try to use 'blkiotune' cmd to set values to some params
$ virsh blkiotune avocado-vt-vm1 --device-read-iops-sec /dev/sda,330 --device-write-iops-sec /dev/sda,293
error: Unable to change blkio parameters
error: internal error: failed to get cgroup backend for 'setBlkioDeviceWriteIops'
$ virsh blkiotune avocado-vt-vm1 --device-weights /dev/sda,100
error: Unable to change blkio parameters
error: internal error: failed to get cgroup backend for 'setBlkioDeviceWeight'
$ virsh blkiotune avocado-vt-vm1 --weight 100
error: Unable to change blkio parameters
error: internal error: failed to get cgroup backend for 'setBlkioWeight'
<==== we can see these "internal error" is code level, not suitable for end-user
Additional info:
1. When just try to getting the values, the error message is clear
virsh blkiotune avocado-vt-vm1
error: Unable to get blkio parameters
error: Requested operation is not valid: blkio cgroup isn't mounted
2. other controllers don't have this problem.
3. With rhel7.7 libvirt-4.5.0-23.el7.x86_64, the error message is clear
# virsh blkiotune avocado-vt-vm1 --weight 100
error: Unable to change blkio parameters
error: internal error: Controller 'blkio' is not mounted
3
Expected result:
Should keep the error message as before.
I don't think this is critical enough to backport it to RHEL. There is a separate BZ for RHEL-AV where it will eventually get by rebase once we address this issue in upstream and it will eventually get into RHEL as well. The error message is not ideal but it's good enough to figure out that cgroups are not working.