Re: [libvirt] [Qemu-devel] [qemu RFC v2] qapi: add "firmware.json"

On Fri, Apr 20, 2018 at 10:11:08AM +0200, Laszlo Ersek wrote: > On 04/19/18 11:12, Daniel P. Berrangé wrote: > > On Thu, Apr 19, 2018 at 10:39:32AM +0200, Laszlo Ersek wrote: > >> On 04/19/18 09:56, Daniel P. Berrangé wrote: > >>> On Thu, Apr 19, 2018 at 09:48:36AM +0200, Markus Armbruster wrote: > >>>> Laszlo Ersek <lersek(a)redhat.com&gt; writes: > >>>> > >>>>> On 04/18/18 10:47, Markus Armbruster wrote: > >>>>>> Laszlo Ersek <lersek(a)redhat.com&gt; writes: > >>>> Replacing CpuInfoArch by such an enum will change the discriminator > >>>> 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-rc0. > >>>> > >>>> "other" was a bad idea. Hindsight 20/20. > >>>> > >>>> Getting rid of it in one go rather than piecemeal seems like the least > >>>> 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 is > >>> reasonable to kill it and put a full arch list in there. > >>> > >>> No app is likely to be accessing the struct under "other" because it > >>> 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. > > > > 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. > > > >> 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. > > > > 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-XXX > > binaries which currently report "other" would change to report their > > respective "XXX" values. > > > > So in this way, it is exactly the same as what we did when we > > introduced "s390" as an option. > > > > 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. > > Can we please translate this into more actionable items for me, because > I'm getting confused :) > > 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 in > @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