On Wed, Oct 19, 2016 at 07:06:16PM +0100, Dr. David Alan Gilbert wrote: > * Daniel P. Berrange (berra...@redhat.com) wrote: > > On Wed, Oct 19, 2016 at 02:16:05PM +0200, Markus Armbruster wrote: > > > "Daniel P. Berrange" <berra...@redhat.com> 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?
You have a problem of context - if you have multiple monitors, how do you know which to send the error back to if you're not in the event loop thread, and thus cur_mon is NULL. With Marc-Andre's series which allows proper async command processing it gets even harder, because there's potentially many outstanding commands associated with a monitor and you need to decide which the error should be given to. 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/ :|
