[libvirt] [PATCH v4 3/3] qemuDomainPMSuspendForDuration: check for wake-up support

[Michal Privoznik]

On 4/25/19 1:31 PM, Daniel Henrique Barboza wrote:
> 
>
> Thanks for the explanation and fixing before pushing. I was under the 
> impression
> that the now extinct line:
> 
> 
> "if (qemuDomainObjBeginAgentJob(driver, vm, QEMU_AGENT_JOB_MODIFY) < 0)"
> 
> 
> Was enough to hold the lock context for all the VM resources, not only 
> the QEMU
> agent. Mostly because I saw the usage of:
> 
>      if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_MODIFY) < 0)
> 
> Right below, in qemuDomainPMWakeup(), that access the monitor in the same
> function.
> 
> But now that I'm putting it all together I noticed that the functions
> are all different .... so qemuDomainObjBeginJob() locks the monitor,
> qemuDomainObjBeginAgentJob() locks the agent, and
> qemuDomainObjBeginJobWithAgent() can lock both, depending if
> job isn't QEMU_JOB_NONE. Is this somewhat close to the actual usage?

Exactly. Previously we had only one job condition where all threads had 
to serialize. I mean one condition per VM. So even if you had two APIs: 
one wanted to talk on monitor and the other wanted to talk to the guest 
agent they would serialize. This is obviously suboptimal. So I've split 
the condition into two. The downside is that we have to be more careful 
which job we must take (and there's no job promotion as in 'I already 
have say monitor job and now I realized I need an agent job too').

Michal