[libvirt] [PATCH 1/2] qemu: Delete nvram store for transient domains too

[Michal Privoznik]

On 12.11.2014 19:10, Peter Krempa wrote:
> On 11/12/14 18:26, Michal Privoznik wrote:
>> There are two ways how to use nvram variable store file in
>> libvirt:
>>
>>    1) create it by hand and pass the path in domain XML
>>
>>    2) let libvirt generate path and create the file
>>
>> Now, we allow users to remove the file from case 2) by passing a
>> flag into the virDomainUndefineFlags(). But when implementing
>> this I forgot about transient domains. For them the file needs to
>> be removed in qemuProcessStop(). But not always, only if the file
>> was created by us.  For that reason new attribute to <nvram/> is
>> invented: @generated to keep the info between daemon restarts.
>> However, now that we are removing autogenerated file for
>> transient domains automatically, we should do the same for
>> persistent domains too without requiring the
>> VIR_DOMAIN_UNDEFINE_NVRAM flag.
>
> I agree that we should clean up the file once we create it as currently
> the guest would be started with the NVRAM generated for a different
> guest with the same name which might trigger some unwanted behavior.
>
> The existing behavior (introduced in 1.2.8) though might lead the users
> to use transient VMs with unspecified NVRAM path and rely on the fact
> that the NVRAM file is present from the last run.
>
> I think we should document that unless the NVRAM file is provided
> externally the settings don't persist between runs and users using
> transient VMs (hello oVirt) should take care of generating it by
> themselves as they might get unexpected results and we should do it
> rather sooner than later until somebody starts abusing it.

Okay, we should document that the file is left behind in case of 
transient domains and it's mgmt app responsibility to remove the file 
once not needed. What persuaded me is the fact, that it would be almost 
impossible for mgmt app to keep nvram file if this patch is merged. I 
mean, it's not possible from the host to tell when is the nvram file 
written or whether are some writes still pending in the guest. So the 
app can't just copy the file shortly before guest termination and hope 
for the best. Moreover, the guest can die without mgmt app knowledge 
beforehand.

Self NACK. Watch out for v2.

Michal