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Re: [Qemu-devel] chardev's and fd's in monitors
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] chardev's and fd's in monitors |
Date: |
Wed, 19 Oct 2016 19:06:16 +0100 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
* Daniel P. Berrange (address@hidden) wrote:
> On Wed, Oct 19, 2016 at 02:16:05PM +0200, Markus Armbruster wrote:
> > "Daniel P. Berrange" <address@hidden> writes:
> >
> > > On Wed, Oct 19, 2016 at 11:05:53AM +0100, Dr. David Alan Gilbert wrote:
> > >>
> > >> We need a way to be able to report an error without plumbing error_setg
> > >> up the stack; if you're saying error_report isn't suitable then we
> > >> should just recommend we switch everything in migration back to
> > >> fprintf(stderr,
> >
> > In the cases where error_report() isn't suitable, fprintf() is just as
> > unsuitable for the exact same reasons.
> >
> > > Well both error_report() + fprintf are broken from POV of anything
> > > using QMP. error_report() is slightly less broken for HMP,
> >
> > error_report() is not broken at all for HMP code. The trouble is code
> > that can't know whether it's running in a context where error_report()
> > is suitable.
> >
> > > but doesn't
> > > help QMP.
> >
> > Correct.
> >
> > > In the short term we should just make error_report be threadsafe in
> > > its usage of the monitor.
> >
> > Any problems left once cur_mon is thread-local (which it should be
> > anyway)?
>
> If we make cur_mon a thread-local, then error_report() is equivalent
> to fprintf(stderr) for the migration code, since the migration
> code runs in a different thread thread, and so would always see
> cur_mon == NULL.
Yes, that would become safe; it does sound the best fix for the current
worry.
If we had that, then why not wire up error_report to pass errors back to QMP
as well?
Dave
> > > Beyond the short term we have no choice but
> > > to plumb in error_setg throughout, otherwise QMP will continue to
> > > have useless error reporting in this area of code.
> >
> > Actually, no choice but propagate errors up the stack until they reach a
> > spot that knows how to report them. error_setg() is *one* way to do
> > that. Its prime advantage is ability to carry an error message. Its
> > disadvantage is boilerplate. Use it as needed. Just don't convert back
> > and forth between Error and other representations while propagating up
> > the stack.
>
> Regards,
> Daniel
> --
> |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :|
> |: http://libvirt.org -o- http://virt-manager.org :|
> |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] chardev's and fd's in monitors, (continued)
- Re: [Qemu-devel] chardev's and fd's in monitors, Markus Armbruster, 2016/10/19
- Re: [Qemu-devel] chardev's and fd's in monitors, Dr. David Alan Gilbert, 2016/10/19
- Re: [Qemu-devel] chardev's and fd's in monitors, Daniel P. Berrange, 2016/10/19
- Re: [Qemu-devel] chardev's and fd's in monitors, Markus Armbruster, 2016/10/19
- Re: [Qemu-devel] chardev's and fd's in monitors, Dr. David Alan Gilbert, 2016/10/19
- Re: [Qemu-devel] chardev's and fd's in monitors, Daniel P. Berrange, 2016/10/19
- Re: [Qemu-devel] chardev's and fd's in monitors, Markus Armbruster, 2016/10/19
- Re: [Qemu-devel] chardev's and fd's in monitors, Daniel P. Berrange, 2016/10/19
- Re: [Qemu-devel] chardev's and fd's in monitors,
Dr. David Alan Gilbert <=
- Re: [Qemu-devel] chardev's and fd's in monitors, Daniel P. Berrange, 2016/10/20
- Re: [Qemu-devel] chardev's and fd's in monitors, Marc-André Lureau, 2016/10/20
- Re: [Qemu-devel] chardev's and fd's in monitors, Markus Armbruster, 2016/10/20
- Re: [Qemu-devel] chardev's and fd's in monitors, Paolo Bonzini, 2016/10/20
- Re: [Qemu-devel] chardev's and fd's in monitors, Markus Armbruster, 2016/10/21
- Re: [Qemu-devel] chardev's and fd's in monitors, Paolo Bonzini, 2016/10/21
- Re: [Qemu-devel] chardev's and fd's in monitors, Markus Armbruster, 2016/10/24
- Re: [Qemu-devel] chardev's and fd's in monitors, Daniel P. Berrange, 2016/10/21
- Re: [Qemu-devel] chardev's and fd's in monitors, Dr. David Alan Gilbert, 2016/10/20
- Re: [Qemu-devel] chardev's and fd's in monitors, Markus Armbruster, 2016/10/20