From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48663) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f9SRo-0006cr-Cn for qemu-devel@nongnu.org; Fri, 20 Apr 2018 05:35:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f9SRm-0006RW-Ro for qemu-devel@nongnu.org; Fri, 20 Apr 2018 05:35:16 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:43468 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1f9SRm-0006Qo-KU for qemu-devel@nongnu.org; Fri, 20 Apr 2018 05:35:14 -0400 Date: Fri, 20 Apr 2018 10:34:57 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Message-ID: <20180420093457.GE21035@redhat.com> Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20180417224054.26363-1-lersek@redhat.com> <87po2wzysh.fsf@dusky.pond.sub.org> <8a52bb49-4194-3b91-8b67-a0e5700fd6ed@redhat.com> <87in8nvdpn.fsf@dusky.pond.sub.org> <20180419075629.GC10259@redhat.com> <5ed8b01f-7faa-b23d-5fd2-f4715294e061@redhat.com> <20180419091201.GI10259@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [libvirt] [qemu RFC v2] qapi: add "firmware.json" List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Laszlo Ersek Cc: Markus Armbruster , Peter Maydell , Thomas Huth , Peter Krempa , Ard Biesheuvel , libvir-list@redhat.com, Michal Privoznik , qemu-devel@nongnu.org, Alexander Graf , Gary Ching-Pang Lin , Gerd Hoffmann , Paolo Bonzini , David Gibson On Fri, Apr 20, 2018 at 10:11:08AM +0200, Laszlo Ersek wrote: > On 04/19/18 11:12, Daniel P. Berrang=C3=A9 wrote: > > On Thu, Apr 19, 2018 at 10:39:32AM +0200, Laszlo Ersek wrote: > >> On 04/19/18 09:56, Daniel P. Berrang=C3=A9 wrote: > >>> On Thu, Apr 19, 2018 at 09:48:36AM +0200, Markus Armbruster wrote: > >>>> Laszlo Ersek writes: > >>>> > >>>>> On 04/18/18 10:47, Markus Armbruster wrote: > >>>>>> Laszlo Ersek writes: > >>>> Replacing CpuInfoArch by such an enum will change the discriminato= r > >>>> value from "other" to the real architecture, with the obvious > >>>> compatibility concerns. But we've accepted similar changes twice > >>>> already: commit 9d0306dfdfb and commit 25fa194b7b1, both v2.12.0-r= c0. > >>>> > >>>> "other" was a bad idea. Hindsight 20/20. > >>>> > >>>> Getting rid of it in one go rather than piecemeal seems like the l= east > >>>> bad way out. Too late for 2.12, though. Eric, what do you think? > >>> > >>> Given the context in which this "other" value is used, I think it i= s > >>> reasonable to kill it and put a full arch list in there. > >>> > >>> No app is likely to be accessing the struct under "other" because i= t > >>> is just an empty placeholder. > >> > >> Commit 9d0306dfdfb added "s390" and "CpuInfoS390", which I guess had= the > >> potential to confuse QMP clients that didn't expect "s390", but > >> otherwise it didn't mess with preexistent enum values / structures. > >=20 > > NB, qemu-system-s390x would previously have returned "other" in > > this field, and now it returns "s390". So while it didn't > > remove "other" from the list of things that could potentially > > exist, it did change what the s390x binary will actually report. > >=20 > >> The same applies to commit 25fa194b7b1, just with "riscv" / > >> "CpuInfoRISCV" substituted. > >> > >> Removing "other" might confuse QMP clients that expect it, except > >> (according to Daniel) no such client exists, probably. > >=20 > > When I say removing "other", I imply that we add an explicit arch > > for all those which we currently are missing. IOW, all qemu-system-XX= X > > binaries which currently report "other" would change to report their > > respective "XXX" values. > >=20 > > So in this way, it is exactly the same as what we did when we > > introduced "s390" as an option. > >=20 > > The only difference is that once we have every binary reporting the > > correct arch, we can now also remove "other" from the schema itself > > as it will then be unused. >=20 > Can we please translate this into more actionable items for me, because > I'm getting confused :) >=20 > First, if I add "i386" and "x86_64" to the enum list, we'll have all > three of "i386", "x86_64" and "x86". Is that useful? How will that work= ? Hmm, yes, on closer look this is a big mess as it is. We've been using generic terms for covering multiple architectures :-( 'x86' for both i386 and x86_64, 'sparc' for sparc and sparc64, etc. If we try to fix that we'll be entering a world of backcompat hurt :-( Since your schema is likely to end up just being a file in docs/specs, rather than directly part of our existnig qapi schema, I suggest we just ignore whats there. Just define an arch enum in your spec which is right, and let someone else worry about fixing the mess > Second, assuming I add constants for the ~10 (?) softmmu arches, can I > still use @CpuInfoOther as the type for the corresponding new members i= n > @CpuInfo? What C code changes will be necessary? Yes, we could still use the CpuInfoOther struct, since struct names are invisible to consumers, but as above, lets ignore the mess Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|