From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51959) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bxWOA-0007wF-DU for qemu-devel@nongnu.org; Fri, 21 Oct 2016 05:45:23 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bxWO7-0002Ni-CJ for qemu-devel@nongnu.org; Fri, 21 Oct 2016 05:45:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42974) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1bxWO7-0002Na-78 for qemu-devel@nongnu.org; Fri, 21 Oct 2016 05:45:19 -0400 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2FD0C7A495 for ; Fri, 21 Oct 2016 09:45:18 +0000 (UTC) Date: Fri, 21 Oct 2016 10:45:14 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20161021094514.GD2039@work-vm> References: <20161019122158.GS11194@redhat.com> <20161019180616.GF2035@work-vm> <87oa2fwg9z.fsf@dusky.pond.sub.org> <20161020090356.GD12145@redhat.com> <20161020095835.GC2039@work-vm> <87funrti86.fsf@dusky.pond.sub.org> <20161020110832.GG12145@redhat.com> <87insnqllc.fsf@dusky.pond.sub.org> <20161020175648.GN2039@work-vm> <8760omm5pu.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8760omm5pu.fsf@dusky.pond.sub.org> Subject: Re: [Qemu-devel] chardev's and fd's in monitors List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Markus Armbruster Cc: qemu-devel@nongnu.org * Markus Armbruster (armbru@redhat.com) wrote: > "Dr. David Alan Gilbert" writes: > > > * Markus Armbruster (armbru@redhat.com) wrote: > >> "Daniel P. Berrange" 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. It's detail I want in the initial error report rather than future debug; to give a real example: qemu-system-ppc64: 9223477658187168481 != 9223477658187151905 qemu-system-ppc64: Failed to load cpu:env.insns_flags qemu-system-ppc64: error while loading state for instance 0x0 of device 'cpu' qemu-system-ppc64: load of migration failed: Invalid argument I wouldn't want to log the value loaded from each field unless I'm in the pain of really bad debugging; but when one goes wrong like this getting the value mismatch, the field name, and the device that failed is what I want in the logs. One point here is that those lines each come from a different function as we come back up out of the failure; the one at the bottom doesn't have the information on the device it's loading, just that it's loading an integer and it's not the expected value. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK