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