Re: [Qemu-devel] chardev's and fd's in monitors

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Daniel P. Berrange (berrange@redhat.com) wrote:
> On Fri, Oct 21, 2016 at 11:06:21AM +0200, Markus Armbruster wrote:
> > "Dr. David Alan Gilbert" <dgilbert@redhat.com> writes:
> > 
> > > * Markus Armbruster (armbru@redhat.com) wrote:
> > >> "Daniel P. Berrange" <berrange@redhat.com> writes:
> > [...]
> > >> > Realistically all the major backend subsystems (chardev, network, block,
> > >> > ui and migration) need to be converted to Error ** propagation, since
> > >> > they all ultimately call into some common code that reports Error **.
> > >> 
> > >> Infrastucture generally doesn't know how it's used, which means
> > >> error_report() is generally wrong there.  Sufficiently simple functions
> > >> can keep returning -errno, null, whatever, but the interesting stuff
> > >> needs to use Error.
> > >> > Very few places will end up being able to stick with -errno, or plain
> > >> > error_report in the long term.
> > >> 
> > >> Not sure about "very few".  Less than now.  We'll see.
> > >
> > > I'd also prefer we got the very-few level; Migration used to be
> > > characterised by getting a 'load of migration failed -22' and having
> > > no clue in the logs to why; I've slowly fought back to be able
> > > to get an error from the lowest level that caused the failure.
> > > I want more of that, so that when someone gets a rare failure in the field
> > > I can see why.
> > 
> > When it's about details that are only useful for debugging, logging
> > might be a practical alternative.  No excuse for shoddy error reporting,
> > of course.
> 
> FWIW, I would very much like it if incoming migration were able to report
> the error failing to load migration stream back via the monitor, instead
> of spitting them to stderr - the latter makes it hard for libvirt to
> provide good error report to the users.

As long as we also get them in the stderr log then that's fine.

Dave

> On the outgoing side we've now fed the errors back via the query-migrate
> command - the same approach could be used on the incoming side.
> 
> 
> Regards,
> Daniel
> -- 
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--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK