libvirt users - Oct 2022 - hook script for changing disk definition before guest start

On 10/21/22 15:30, Gionatan Danti wrote:
> Hi all,
> due to this [1] I am trying to change a guest's disk definition from
> "pool volume" to "file" via hook scripts.
This is downright libvirt bug and needs to be fixed.

For the libvirt developers on CC: when starting a domain, the QEMU
driver sets disk src->path to the actual file path in
virDomainDiskTranslateSourcePool() which is called from
qemuProcessPrepareDomainStorage(). I'm not sure whether the virt-aa
helper sees the translated path in the XML though. So maybe something as
trivial as the following might help?

diff --git i/src/security/virt-aa-helper.c w/src/security/virt-aa-helper.c
index a15971b9bb..f42c3f9a42 100644
--- i/src/security/virt-aa-helper.c
+++ w/src/security/virt-aa-helper.c
@@ -904,6 +904,7 @@ get_files(vahControl * ctl)
 #ifdef WITH_STORAGE
     virDriverLoadModule("storage", "storageRegister",
false);
 #endif
+    virDomainDiskTranslateSourcePool(ctl->def);
 
     for (i = 0; i < ctl->def->ndisks; i++) {
         virDomainDiskDef *disk = ctl->def->disks[i];
> 
> This seems an easy task via virsh detach-disk and virsh attach-disk, but
> virsh can not be called inside libvirt hook scripts. The best approach
> would be to change the disk definition right when a disk is attached,
> but I can not find any event calling a hook script when a disk is
> attache/detached.
You don't want to translate the path yourself. Libvirt has extensive
code for that.
> 
> Do you have any suggestion short of monitoring the directory
> /etc/libvirt/qemu itself for changed files?
> Thanks.
These are not the only files where libvirt stores its configuration. For
instance, if I'd 'virsh attach-device --live' then this new device
won't
appear in the XML stored under /etc/libvirt/qemu.

I hope we can resolve this libvirt bug soon and you can use fixed
version.

Michal

Il 2022-10-24 10:26 Michal Pr?vozn?k ha scritto:
> This is downright libvirt bug and needs to be fixed.
> ...
> I hope we can resolve this libvirt bug soon and you can use fixed
> version.
> 
> Michal
Hi Michal,
I agree that it would be _way_ better for 
libvirt/cockpit/virt-aa-helper/whatever to be fixed.

I only resorted to this "manually change the disk path" because it 
proved problematic to fix the underlying issue in virt-aa-helper (at 
least by reading here[1] and here[2]).

Thank you for having CC the appropriate peoples and for your proposed 
solution.
Regards.

[1] https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1677398
[2] https://gitlab.com/libvirt/libvirt/-/issues/135

-- 
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti at assyoma.it - info at assyoma.it
GPG public key ID: FF5F32A8