Re: [libvirt] [PATCH 3/5] qemu_domain: Introduce qemuDomainObjBeginJobInstant

>> qemuDomainObjPrivatePtr priv = obj->privateData; >> unsigned long long now; >> @@ -6395,12 +6400,18 @@ qemuDomainObjBeginJobInternal(virQEMUDriverPtr driver, >> } >> >> while (!nested && !qemuDomainNestedJobAllowed(priv, job)) { >> + if (instant) >> + goto cleanup; >> + > > If async is not supported for this (as I believe seen in the new API), > then is this path possible? Of course. For instance, if there's an async job running and another thread is trying to start a sync, non-nested job that is not allowed for the async job. Say, thread A is doing a snapshot which sets job mask (=allowed sync jobs) to: query, destroy, abort, suspend, migration-op. Then there's a thread B which is executing qemuDomainSetUserPassword(). This threads tries to grab modify job. However, since grabbing modify is not allowed (due to job mask) thread B sits and waits until thread A releases the async job. At that point, thread B can safely grab modify job because there's no other (nor async) job running. Long story short, not only synchronous jobs serialize, also async (and any combination of those two) do.

>> +int >> +qemuDomainObjBeginJobInstant(virQEMUDriverPtr driver, >> + virDomainObjPtr obj, >> + qemuDomainJob job) >> +{ >> + return qemuDomainObjBeginJobInternal(driver, obj, job, >> + QEMU_ASYNC_JOB_NONE, true); > ^^^^^^^^^^^^^^^^^^^^ > Doesn't this mean async jobs are not supported. I'm not quite sure what do you mean. You mean whether grabbing a sync job while there's async job already running? This is supported. The fact that asyncJob is QEMU_ASYNC_JOB_NONE does not mean "set sync job to @job and async job to QEMU_ASYNC_JOB_NONE". In fact, qemuDomainObjBeginJobInternal() is capable of grabbing either sync or async job but not both at the same time. When grabbing a sync job, @asynJob == QEMU_ASYNC_JOB_NONE and when grabbing an async job, @job == QEMU_JOB_ASYNC. Anyway, the point of BeginJobInstant() is to be drop-in replacement for plain BeginJob(), so whatever the latter passes to BeginJobInternal() the former should mimic it. But then again, I'm not quite sure I understand what you mean.