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Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id()
From: |
Daniel P . Berrangé |
Subject: |
Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id() |
Date: |
Thu, 30 Jul 2020 17:40:23 +0100 |
User-agent: |
Mutt/1.14.5 (2020-06-23) |
On Thu, Jul 30, 2020 at 11:24:51AM -0500, Eric Blake wrote:
> On 7/30/20 10:59 AM, Daniel P. Berrangé wrote:
>
> > > Well, I suspect that management-layer code currently has
> > > gone for "assume we're always running on Linux" and was
> > > written by people who knew they were getting a Linux tid...
> >
> > Yes, on the libvirt side, the functionality that relies on thread_is is
> > only compiled on Linux. If someone wants to use it on other OS, they'll
> > have to provide an impl using their platforms equivalent of
> > sched_setaffinity and friends since none of this stuff is standardized
> > across OS.
> >
> >
> > > > The PID is quite unlikely to be "an OS-specific identifier of the
> > > > current thread". Shouldn't we fail instead of lie when we don't know
> > > > how to compute the truth?
> > >
> > > Yeah, I think the default codepath is pretty bogus too. Should
> > > the QMP functions have a mechanism for saying "we don't know
> > > a thread-id on this platform" ?
> >
> > Thread_id should be optional and thus not filled in if we
> > can't provide a sensible value. Unfortunately we made it
> > mandatory in QMP.
>
> Normally, converting a mandatory output value to optional is a
> back-compatibility risk (we could break apps that depended on it being
> present). But if the only apps that depended on it being present are
> compiled on Linux, where the member will actually be present, I think that
> changing the schema to make it optional for non-Linux platforms won't be a
> back-compatibility nightmare (but we will have to be careful in our
> documentation).
FWIW, libvirt treats it as mandatory for query-iothreads, but optional
for query-cpus because it was missing in some older QEMU versions
entirely.
Libvirt explicitly only supports macOS, Linux and FreeBSD, so if those
platforms all report a value, libvirt won't care if you make it optional
and omit it for other platforms.
Regards,
Daniel
--
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- [PATCH] osdep.h: Add doc comment for qemu_get_thread_id(), Peter Maydell, 2020/07/16
- Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id(), Peter Maydell, 2020/07/28
- Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id(), Eric Blake, 2020/07/28
- Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id(), Peter Maydell, 2020/07/28
- Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id(), Markus Armbruster, 2020/07/30
- Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id(), Peter Maydell, 2020/07/30
- Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id(), Daniel P . Berrangé, 2020/07/30
- Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id(), Eric Blake, 2020/07/30
- Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id(),
Daniel P . Berrangé <=
- Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id(), Markus Armbruster, 2020/07/31
- Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id(), Eric Blake, 2020/07/31
- Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id(), Daniel P . Berrangé, 2020/07/31