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

[Cornelia Huck]

On Fri, 9 Sep 2016 10:46:25 +0200
Greg Kurz <address@hidden> wrote:

> On Fri, 9 Sep 2016 10:30:53 +0200
> Cornelia Huck <address@hidden> wrote:
> 
> > On Thu, 8 Sep 2016 19:55:16 +0300
> > "Michael S. Tsirkin" <address@hidden> 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" <address@hidden> 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" <address@hidden> 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.

Stefan had already sent
<address@hidden> ages ago, but
it has not yet made it anywhere...

Anyhow, I was concerned with host signalling (sorry for being unclear),
and I still do not think we need to alert host monitoring software to
guest stupidity.

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