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

From: Daniel P. Berrange
Subject: Re: [Qemu-devel] chardev's and fd's in monitors
Date: Fri, 21 Oct 2016 10:37:56 +0100
User-agent: Mutt/1.7.0 (2016-08-17)

On Fri, Oct 21, 2016 at 11:06:21AM +0200, Markus Armbruster wrote:
> "Dr. David Alan Gilbert" <address@hidden> writes:
> > * Markus Armbruster (address@hidden) wrote:
> >> "Daniel P. Berrange" <address@hidden> 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.

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.

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