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Fri, 31 Jul 2020 13:51:46 +0000 (UTC) Date: Fri, 31 Jul 2020 14:51:43 +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: <20200731135143.GG3641941@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> <87pn8ct9ga.fsf@dusky.pond.sub.org> <53b70f7f-1777-64e5-d80f-6af3d6c1252d@redhat.com> MIME-Version: 1.0 In-Reply-To: <53b70f7f-1777-64e5-d80f-6af3d6c1252d@redhat.com> User-Agent: Mutt/1.14.5 (2020-06-23) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.61; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/31 02:46:11 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=ham 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 Fri, Jul 31, 2020 at 08:46:40AM -0500, Eric Blake wrote: > On 7/31/20 2:44 AM, Markus Armbruster wrote: > > > > > 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). > > > > Options for systems where don't know how to compute a system-wide thread > > ID: > > > > 0. Return a bogus value: the PID. This is the status quo. > > > > 1. Return a more obviously bogus value: -1. Semantic compatibility > > break. Should be harmless, because a QMP client relying on the > > thread-id being the PID would be insane. > > > > 2. Make thread-id optional, present iff we can compute a value. > > > > This is what we should have done, but we didn't, and now it's a > > syntactic compatibility break. Matters only if it actually breaks > > QMP clients. We believe the one we know shouldn't break. > > > > Preferences? > > I'm in favor of 2, but can easily live with 1 if we decide to be that much > more conservative. Tooling that can't handle a missing value is not going > to fare any better with a value that is unusable because it is -1, but the > important point is that I don't think we have a scenario with such tooling > depending on the value (the tools that DO depend on the value are built on > platforms where the value is usable). I'm fine with (2) too. While technically a backcompat break, it won't hurt us in the real world, and so is the pragmatic choice that gets us to a long term better solution. 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 :|