* 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? 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 / dgilb...@redhat.com / Manchester, UK
