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

[Laszlo Ersek <lersek@redhat.com>]

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@redhat.com> writes:
>>>>
>>>>> On 04/18/18 10:47, Markus Armbruster wrote:
>>>>>> Laszlo Ersek <lersek@redhat.com> 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?

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?

Thanks
Laszlo