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Thu, 30 Jul 2020 16:40:25 +0000 (UTC) Date: Thu, 30 Jul 2020 17:40:23 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Eric Blake Subject: Re: [PATCH] osdep.h: Add doc comment for qemu_get_thread_id() Message-ID: <20200730164023.GQ3477223@redhat.com> References: <20200716154114.10838-1-peter.maydell@linaro.org> <0f8b8fea-2bd0-7616-292b-8fb0f87cec75@redhat.com> <87k0ylvy0t.fsf@dusky.pond.sub.org> <20200730155939.GP3477223@redhat.com> <4d2cba04-04d8-9b82-562f-acb84b6010d2@redhat.com> MIME-Version: 1.0 In-Reply-To: <4d2cba04-04d8-9b82-562f-acb84b6010d2@redhat.com> User-Agent: Mutt/1.14.5 (2020-06-23) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/30 03:51:24 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: QEMU Trivial , Peter Maydell , Markus Armbruster , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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 -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|