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

[Michael S. Tsirkin]

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:
> > > On Thu, 8 Sep 2016 10:59:26 +0200
> > > Cornelia Huck <address@hidden> wrote:
> > > 
> > > > On Wed, 07 Sep 2016 19:19:24 +0200
> > > > Greg Kurz <address@hidden> wrote:
> > > > 
> > > > > Calling assert() really makes sense when hitting a genuine bug, which 
> > > > > calls
> > > > > for a fix in QEMU. However, when something goes wrong because the 
> > > > > guest
> > > > > sends a malformed message, it is better to write down a more meaningul
> > > > > error message and exit.
> > > > > 
> > > > > Signed-off-by: Greg Kurz <address@hidden>
> > > > > ---
> > > > >  hw/9pfs/virtio-9p-device.c |   20 ++++++++++++++++++--
> > > > >  1 file changed, 18 insertions(+), 2 deletions(-)  
> > > > 
> > > > While this is an improvement over the current state, I don't think the
> > > > guest should be able to kill qemu just by doing something stupid.
> > > > 
> > > 
> > > Hi Connie,
> > > 
> > > I'm glad you're pointing this out... this was also my impression, but
> > > since there are a bunch of sanity checks in the virtio code that cause
> > > QEMU to exit (even recently added like 1e7aed70144b), I did not dare
> > > stand up :)
> > 
> > It's true that it's broken in many places but we should just
> > fix them all.
> > 
> > 
> > A separate question is how to log such hardware/guest bugs generally.
> > People already complained about disk filling up because of us printing
> > errors on each such bug.  Maybe print each message only N times, and
> > then set a flag to skip the log until management tells us to restart
> > logging again.
> 
> I'd expect to get the message just once per device if we set the device
> to broken (unless the guess continuously resets it again...)

Which it can do, so we should limit that anyway.

> Do we have
> a generic print/log ratelimit infrastructure in qemu?

There are actually two kinds of errors
host side ones and ones triggered by guests.

We should distinguish between them API-wise, then
we will be able to limit the logging of those
that guest can trigger.

-- 
MST