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Mon, 23 Mar 2020 17:41:10 +0000 (UTC) Received: from linux.fritz.box (ovpn-114-85.ams2.redhat.com [10.36.114.85]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E9E235C1AD; Mon, 23 Mar 2020 17:41:09 +0000 (UTC) Date: Mon, 23 Mar 2020 18:41:08 +0100 From: Kevin Wolf To: Markus Armbruster Subject: Re: [PATCH v5 3/4] qmp: Move dispatcher to a coroutine Message-ID: <20200323174108.GD8049@linux.fritz.box> References: <20200218154036.28562-1-kwolf@redhat.com> <20200218154036.28562-4-kwolf@redhat.com> <87d09965g3.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87d09965g3.fsf@dusky.pond.sub.org> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 216.205.24.74 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: , Cc: marcandre.lureau@gmail.com, qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 18.03.2020 um 16:36 hat Markus Armbruster geschrieben: > Kevin Wolf writes: >=20 > > This moves the QMP dispatcher to a coroutine and runs all QMP command > > handlers that declare 'coroutine': true in coroutine context so they > > can avoid blocking the main loop while doing I/O or waiting for other > > events. > > > > For commands that are not declared safe to run in a coroutine, the > > dispatcher drops out of coroutine context by calling the QMP command > > handler from a bottom half. > > > > Signed-off-by: Kevin Wolf >=20 > Uh, what about @cur_mon? >=20 > @cur_mon points to the current monitor while a command executes. > Initial value is null. It is set in three places (not counting unit > tests), and all three save, set, do something that may use @cur_mon, > restore: >=20 > * monitor_qmp_dispatch(), for use within qmp_dispatch() > * monitor_read(), for use within handle_hmp_command() > * qmp_human_monitor_command(), also for use within handle_hmp_command() >=20 > Therefore, @cur_mon is null unless we're running within qmp_dispatch() > or handle_hmp_command(). Can we make it NULL for coroutine-enabled handlers? > Example of use: error_report() & friends print "to current monitor if we > have one, else to stderr." Makes sharing code between HMP and CLI > easier. Uses @cur_mon under the hood. error_report() eventually prints to stderr both for cur_mon =3D=3D NULL and for QMP monitors. Is there an important difference between both cases? There is error_vprintf_unless_qmp(), which behaves differently for both cases. However, it is only used in VNC code, so that code would have to keep coroutines disabled. Is cur_mon used much in other functions called by QMP handlers? > @cur_mon is thread-local. >=20 > I'm afraid we have to save, clear and restore @cur_mon around a yield. That sounds painful enough that I'd rather avoid it. Kevin