[libvirt] [RFC PATCH] qemu: Fail APIs not allowed during async job

[Jiri Denemark]

On Fri, Jul 15, 2011 at 09:09:52 -0600, Eric Blake wrote:
> On 07/15/2011 08:41 AM, Jiri Denemark wrote:
> > When an asynchronous job is running while another API that is
> > incompatible with that job is called, we now try to wait until the job
> > finishes and either run the API or fail with timeout. I guess nicer
> > solution is to just fail such API immediately and let the application
> > retry once the asynchronous job ends.
> > ---
> >  src/qemu/THREADS.txt   |    5 ++---
> >  src/qemu/qemu_domain.c |   28 +++++++++++++++-------------
> >  2 files changed, 17 insertions(+), 16 deletions(-)
> 
> If all such APIs have a flag argument, then we could make the behavior
> configurable - passing 0 blocks until possible, and passing
> VIR_DOMAIN_OPERATION_NONBLOCK as a flag returns immediately.
> 
> But we probably don't have uniform flags arguments.  Which APIs are
> affected?

All APIs that modify state, currently the following list (qemu driver names):

    Resume
    Shutdown
    Reboot
    SetMemoryFlags
    InjectNMI
    SetVcpusFlags
    Suspend
    Restore
    ModifyDeviceFlags
    SnapshotCreateActive
    RevertToSnapshot
    SnapshotDelete
    MonitorCommand

> If we can't control things by a flag, then returning a specific failure
> seems like the best way to go (it is easier to write an app that can
> retry than it is to write an app that doesn't suffer from unintended
> blocking).
> 
> So this patch seems sane to me, although I'd still like a list of all
> affected APIs before giving ack.

BTW, the patch is not complete so acking or not would only affect the idea.

Jirka