Re: [Qemu-devel] QMP: RFC: I/O error info & query-stop-reason

[Luiz Capitulino <lcapitulino@redhat.com>]

On Thu, 02 Jun 2011 13:32:25 -0500
Anthony Liguori <anthony@codemonkey.ws> wrote:

> On 06/02/2011 01:01 PM, Luiz Capitulino wrote:
> > On Thu, 02 Jun 2011 09:02:30 -0500
> > Anthony Liguori<anthony@codemonkey.ws>  wrote:
> >
> >> On 06/02/2011 08:24 AM, Jiri Denemark wrote:
> >>> On Thu, Jun 02, 2011 at 08:08:35 -0500, Anthony Liguori wrote:
> >>>> On 06/02/2011 04:06 AM, Daniel P. Berrange wrote:
> >>>>>>> B. query-stop-reason
> >>>>>>> --------------------
> >>>>>>>
> >>>>>>> I also have a simple solution for item 2. The vm_stop() accepts a reason
> >>>>>>> argument, so we could store it somewhere and return it as a string, like:
> >>>>>>>
> >>>>>>> ->     { "execute": "query-stop-reason" }
> >>>>>>> <- { "return": { "reason": "user" } }
> >>>>>>>
> >>>>>>> Valid reasons could be: "user", "debug", "shutdown", "diskfull" (hey,
> >>>>>>> this should be "ioerror", no?), "watchdog", "panic", "savevm", "loadvm",
> >>>>>>> "migrate".
> >>>>>>>
> >>>>>>> Also note that we have a STOP event. It should be extended with the
> >>>>>>> stop reason too, for completeness.
> >>>>>>
> >>>>>>
> >>>>>> Can we just extend query-block?
> >>>>>
> >>>>> Primarily we want 'query-stop-reason' to tell us what caused the VM
> >>>>> CPUs to stop. If that reason was 'ioerror', then 'query-block' could
> >>>>> be used to find out which particular block device(s) caused the IO
> >>>>> error to occurr&    get the "reason" that was in the BLOCK_IO_ERROR
> >>>>> event.
> >>>>
> >>>> My concern is that we're over abstracting here.  We're not going to add
> >>>> additional stop reasons in the future.
> >>>>
> >>>> Maybe just add an 'io-error': True to query-state.
> >>>
> >>> Sure, adding a new field to query-state response would work as well. And it
> >>> seems like a good idea to me since one already needs to call query-status to
> >>> check if CPUs are stopped or not so it makes sense to incorporate the
> >>> additional information there as well. And if you want to be safe for the
> >>> future, the new field doesn't have to be boolean 'io-error' but it can be the
> >>> string 'reason' which Luiz suggested above.
> >>
> >>
> >> String enumerations are a Bad Thing.  It's impossible to figure out what
> >> strings are valid and it lacks type safety.
> >>
> >> Adding more booleans provides better type safety, and when we move to
> >> QAPI with a queryable schema, provides a way to figure out exactly what
> >> combinations are supported by QEMU.
> >
> > To summarize:
> >
> >   1. Add a 'io-error' field to query-status (which is only present if
> >      field 'running' is false)
> 
> It may or may not be present.  Lack of presence does not tell you anything.
> 
> It is only true when running is false AND the guest was stopped because 
> of an io error.

Right.

> >
> >   2. Extend query-block to contain error information associated with the
> >      device. This is interesting, because this information will be available
> >      even if the error didn't cause the VM to stop
> 
> Well we need at least some way to indicate that a block device is in a 
> failed state.  For instance, if you have two block device, but you miss 
> the IO_ERROR event, you need to figure out which of the two devices is 
> giving errors.

Can't query-block be used for that? The 'io-error' key will only be present
for the failing device(s).

> 
> But I was thinking of something that had the semantics of, last_iop_failed.
> 
> Regards,
> 
> Anthony Liguori
> 
> > Seems good enough to me, comments?
> >
>