From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59077) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z5Ax1-0002sd-Cf for qemu-devel@nongnu.org; Wed, 17 Jun 2015 06:52:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z5Awt-00019h-6Q for qemu-devel@nongnu.org; Wed, 17 Jun 2015 06:52:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46831) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z5Awt-00019G-1o for qemu-devel@nongnu.org; Wed, 17 Jun 2015 06:52:03 -0400 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) by mx1.redhat.com (Postfix) with ESMTPS id 29314337651 for ; Wed, 17 Jun 2015 10:52:02 +0000 (UTC) Date: Wed, 17 Jun 2015 11:51:57 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20150617105157.GD2122@work-vm> References: <1434480849-23093-1-git-send-email-dgilbert@redhat.com> <558124BD.8010807@redhat.com> <20150617094829-mutt-send-email-mst@redhat.com> <55812BC4.3000600@redhat.com> <20150617121148-mutt-send-email-mst@redhat.com> <87381q7grj.fsf@neno.neno> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87381q7grj.fsf@neno.neno> Subject: Re: [Qemu-devel] [PATCH] Migration compatibility for serial List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Juan Quintela Cc: amit.shah@redhat.com, Paolo Bonzini , qemu-devel@nongnu.org, "Michael S. Tsirkin" * Juan Quintela (quintela@redhat.com) wrote: > "Michael S. Tsirkin" wrote: > > On Wed, Jun 17, 2015 at 10:11:48AM +0200, Paolo Bonzini wrote: > >> > >> > >> On 17/06/2015 09:52, Michael S. Tsirkin wrote: > >> > > No, please. Upstream QEMU doesn't want to get into judgement about when > >> > > migration quality might be "good enough" that you can drop subsections. > >> > > It's one thing to perfect the .needed functions to make the appearance > >> > > of subsections as unlikely as possible, but adding flags is not > >> > > something we've done so far---and not something at least *I* want to do. > >> > > >> > Not like this, sure. But e.g. patches that force specific fields to > >> > behave in a way consistent with QEMU 2.2, with appropriate > >> > doducmentation would be ok I think. > >> > >> That's not what 2.2 means in "pc-i440fx-2.2". It means "same hardware > >> as 2.2", not "bug-compatible with 2.2". > >> > >> Refining the .needed functions (e.g. see commit bfa7362889) is just > >> that: describing when a subsection is needed. Forcing specific fields > >> to behave in a way consistent with QEMU 2.2 is bug compatibility. > >> > >> Paolo > > > > We do bug-compatible if it's not a big pain, too. > > In this case, there is disagreement about what is better: > - correct solution > - bug compatible > > We can't have both in this case :-( > > Notice that if "both" are 2.2 , i.e. 2.3 with -M > pc-i440fx-2.2, we also got the correct behaviour. So the matrix is > something like: > > Source: 2.2 Destination: 2.2 -> bug compatible 2.2 > Source: 2.3 Destination: 2.2 -> breaks if serial is being used, works otherwise > Source: 2.3 Destination: 2.3 with -M pc-i440fx-2.2: works always To be fair the 2.3->2.2 is more subtle; opening it is unlikely to generate the subsections; it needs a bit more than that (certainly on Linux) figuring out exactly what triggers each subsection is trickier. Dave > > > So the problem is 2.3 -> 2.2 when serial is being used (notice that just > opening it it is using). That is what we are differing about what is > the right thing to do. As Paolo says, in upstream, we have done in the > past the correct thing, in downstream, it depends. > > Notice that adding this patch makes that the three cases are bug > compatible, i.e. there is no way to detect breakage neither a way to fix > the issue (fix without the patch is just upgrade both binaries. > ) > > Later, Juan. -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK