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Tsirkin" , Stefan Hajnoczi , Paolo Bonzini , Jason Wang Subject: Re: [PATCH V14 06/15] monitor: track IOThread users with QOM paths In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Wed, 2 Sep 2026 17:17:02 +0100") References: <20260831160038.221776-1-zhangckid@gmail.com> <20260831160038.221776-7-zhangckid@gmail.com> <8733vtbk16.fsf@pond.sub.org> <87qzjb3nf6.fsf@pond.sub.org> <87jyp31zyf.fsf@pond.sub.org> Date: Fri, 04 Sep 2026 10:33:18 +0200 Message-ID: <8733vph0vl.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Daniel P. Berrang=C3=A9 writes: > On Wed, Sep 02, 2026 at 04:37:44PM +0200, Markus Armbruster wrote: >> Daniel P. Berrang=C3=A9 writes: >>=20 >> > On Wed, Sep 02, 2026 at 01:25:33PM +0200, Markus Armbruster wrote: >> >> Zhang Chen writes: >> >>=20 >> >> > On Tue, Sep 1, 2026 at 1:47=E2=80=AFPM Markus Armbruster wrote: >> >> >> >> >> >> Zhang Chen writes: >> >> >> >> >> >> > Monitors that require an IOThread share the internal mon_iothrea= d. >> >> >> > Account for each monitor explicitly in IOThread holder tracking,= using >> >> >> > the monitor's canonical QOM path to distinguish holders. >> >> >> > >> >> >> > Acquire the shared monitor IOThread AioContext once, using the m= onitor >> >> >> > QOM path as the holder, and reuse the stored context for later >> >> >> > operations. >> >> >> > >> >> >> > Release the holder from the Monitor ObjectClass::unparent callba= ck, >> >> >> > while the canonical QOM path is still available. This covers eve= ry >> >> >> > object_unparent() path and avoids duplicating the cleanup in >> >> >> > monitor_cleanup() and monitor_qmp_prepare_delete(). >> >> >> > >> >> >> > The internal mon_iothread remains hidden from query-iothreads, a= s before. >> >> >> > Management applications therefore cannot use it to determine whi= ch >> >> >> > monitors are using the IOThread. Nevertheless, track the monitor >> >> >> > holders so that they follow the same explicit holder and >> >> >> > IOThread reference lifecycle as other AioContext users. >> >> >> > >> >> >> > Signed-off-by: Zhang Chen >> >> >> >> >> >> I have a question for our QOM experts (Paolo and Daniel). >> >> >> >> >> >> This patch takes a reference in its UserCreatableClass method >> >> >> complete(), and relinquishes it in its ObjectClass unparent() meth= od. >> >> >> Is that correct and clean? Or should complete() pair with >> >> >> prepare_delete()? >> >> > >> >> > >> >> > Add some background information in previous reviews for here: >> >> > https://lists.gnu.org/archive/html/qemu-devel/2026-08/msg05318.html >> >>=20 >> >> Aha, Stefan asked for monitor_finalize(), which doesn't exist. You t= hen >> >> moved it to the unparent() method. >> > >> > monitor_finalize() does exist as of about a month ago. It was >> > introduced as part of my series that turned Monitor into a QOM >> > object. >>=20 >> I was on an old branch. Sorry for the noise! >>=20 >> >> My question for the QOM maintainers remains: is it okay to pair >> >> complete() with unparent(), or should it pair with prepare_delete()? >> > >> > In general most things done in complete() can/should be undone in the >> > finalize() callback IMHO. >>=20 >> I can't see a finalize() callback, and I *am* on current master now. Do >> you mean unparent(), or do you mean monitor_finalize()? > > Sorry for the ambiguity. The latter. > > When I wrote "finalize()" I meant to say "instance_finalize()", as the > generic name of the callback field in the Type, which is > "monitor_finalize()" in the specific Monitor implementation. If I understand you correctly, the code this patch puts in monitor_unparent() should instead go into monitor_finalize(). Fair?