Re: [Qemu-devel] [PATCH 1/2] virtio-9p: print error message and exit instead of BUG_ON()

[Greg Kurz <groug@kaod.org>]

On Fri, 9 Sep 2016 10:30:53 +0200
Cornelia Huck <cornelia.huck@de.ibm.com> wrote:

> On Thu, 8 Sep 2016 19:55:16 +0300
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Thu, Sep 08, 2016 at 06:26:52PM +0200, Greg Kurz wrote:  
> > > On Thu, 8 Sep 2016 18:19:27 +0300
> > > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > >   
> > > > On Thu, Sep 08, 2016 at 05:04:47PM +0200, Cornelia Huck wrote:  
> > > > > On Thu, 8 Sep 2016 18:00:28 +0300
> > > > > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > > > >     
> > > > > > On Thu, Sep 08, 2016 at 11:12:16AM +0200, Greg Kurz wrote:    
> 
> > > If it continues
> > > execution, this means we're expecting the guest or the host to do something
> > > to fix the error condition. This requires QEMU to emit an event of some
> > > sort, but not necessarily to log an error message in a file. I guess this
> > > depends if QEMU is run by some tooling, or by a human.  
> > 
> > I'm not sure we need an event if tools are not expected to
> > do anything with it. If we limit # of times error
> > is printed, tools will need to reset this counter,
> > so we will need an event on overflow.  
> 
> If the device goes into a broken state, it should be discoverable from
> outside. I'm not sure we need an actual event signalling this if this
> happens due to the guest doing something wrong: That would be a task
> for tools monitoring _inside_ the guest. 

Well, in case of a virtio device being broken, section 2.1.2 in the spec
suggests to set the status to DEVICE_NEEDS_RESET and to notify it to
the guest (aka. event signalling). I'll send a patch shortly.

> For tools monitoring the
> health of the machine (from the host perspective), the discovery
> interface would probably be enough?
> 

Yeah, probably.

Cheers.

--
Greg