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

["Daniel P. Berrangé" <berrange@redhat.com>]

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.

Regards,
Daniel
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