Re: [ovirt-devel] Issue: Device path changed after adding disks to guest VM
On Wed, Jan 06, 2021 at 17:16:24 +0200, Nir Soffer wrote:
On Wed, Dec 2, 2020 at 4:57 PM Joy Li <joooy.li(a)gmail.com>
wrote:
[...]
Comparing to state before reboot:
# virsh -r domblklist disk-mapping
Target Source
---------------------------------------------------------------------------------------------------------------------------------------------------------------
sdc -
sda
/rhev/data-center/mnt/blockSD/84dc4e3c-00fd-4263-84e8-fc246eeee6e9/images/40018b33-2b11-4d10-82e4-604a5b135fb2/40f455c4-8c92-4f8f-91c2-991b0ddfc2f5
vda /dev/mapper/3600140594af345ed76d42058f2b1a454
vdb /dev/mapper/360014050058f2f8a0474dc7a8a7cc6a5
vdc /dev/mapper/36001405b4d0c0b7544d47438b21296ef
# ls -lh /dev/disk/by-id/virtio-*
lrwxrwxrwx. 1 root root 9 Jan 6 09:42
/dev/disk/by-id/virtio-b97e68b2-87ea-45ca-9 -> ../../vda
lrwxrwxrwx. 1 root root 9 Jan 6 09:42
/dev/disk/by-id/virtio-d9a29187-f492-4a0d-a -> ../../vdb
lrwxrwxrwx. 1 root root 9 Jan 6 09:51
/dev/disk/by-id/virtio-e801c2e4-dc2e-4c53-b -> ../../vdc
In the guest disks are mapped to the same device name.
It looks like libivrt domblklist is not correct - vdb and vdc are switched.
Peter, this expected?
The names in 'virsh domblklist' are unfortunately and confusingly chosen
to match the expected /dev/ device node name, but it's at kernel's
discretion to name /dev/ nodes.
This means that it's not guaranteed that what you see in 'virsh
domblklist' will match the state in the guest.
In this case I think the reorder happens as the PCI address of vdb is
larger than the address of vdc.
A partial workaround can be to use the data provided by the qemu guest
agent, for exampe via 'virsh domfsinfo':
$ virsh domfsinfo fedora32
Mountpoint Name Type Target
------------------------------------
/ dm-0 xfs vda
/boot vda1 xfs vda
Here the guest-host matching is established via the PCI address so the
'Target' field accurately refers to the target in the VM XML.
Similarly the linux kernel recently changed enumeration of SCSI devices
so they are not guaranteed to match either. Libguestfs for example
needed a workaround.
https://github.com/libguestfs/libguestfs/commit/bca9b94fc593771b3801b09b9...