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Fri, 15 May 2020 10:04:16 +0000 (UTC) Date: Fri, 15 May 2020 11:04:13 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Lukas Straub Subject: Re: [PATCH 3/5] block/nbd.c: Add yank feature Message-ID: <20200515100413.GG1300305@redhat.com> References: <1e712fa7f08e4772c2a68197a851161bee51610f.1589193717.git.lukasstraub2@web.de> <20200511161909.GJ2811@work-vm> <20200511190524.3681e58c@luklap> <20200512085458.GE1191162@redhat.com> <20200515114818.25d9eb9c@luklap> MIME-Version: 1.0 In-Reply-To: <20200515114818.25d9eb9c@luklap> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 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=207.211.31.120; envelope-from=berrange@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/14 22:56:02 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -10 X-Spam_score: -1.1 X-Spam_bar: - X-Spam_report: (-1.1 / 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, FROM_EXCESS_BASE64=0.979, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN 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: Kevin Wolf , qemu-block , Juan Quintela , qemu-devel , Max Reitz , Paolo Bonzini , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, May 15, 2020 at 11:48:18AM +0200, Lukas Straub wrote: > On Tue, 12 May 2020 09:54:58 +0100 > Daniel P. Berrangé wrote: > > > On Mon, May 11, 2020 at 07:05:24PM +0200, Lukas Straub wrote: > > > On Mon, 11 May 2020 17:19:09 +0100 > > > "Dr. David Alan Gilbert" wrote: > > > > > > > * Lukas Straub (lukasstraub2@web.de) wrote: > > > > > Add yank option, pass it to the socket-channel and register a yank > > > > > function which sets s->state = NBD_CLIENT_QUIT. This is the same > > > > > behaviour as if an error occured. > > > > > > > > > > Signed-off-by: Lukas Straub > > > > > > > > > +static void nbd_yank(void *opaque) > > > > > +{ > > > > > + BlockDriverState *bs = opaque; > > > > > + BDRVNBDState *s = (BDRVNBDState *)bs->opaque; > > > > > + > > > > > + atomic_set(&s->state, NBD_CLIENT_QUIT); > > > > > > > > I think I was expecting a shutdown on the socket here - why doesn't it > > > > have one? > > > > > > For nbd, we register two yank functions: This one and we enable > > > the yank feature on the qio channel (see function > > > nbd_establish_connection below). > > > > As mentioned on the earlier patch, I don't want to see any yank > > code in the QIOChannel object directly. This nbd_yank function > > can simply call the qio_channel_shutdown() function directly > > and avoid need for modifying the QIOChannel object with yank > > support. > > Hi, > Looking at it again, the problem is not with registering the yank functions, but with tracking the lifetime of it. Suppose we add qio_channel_shutdown to the yank_nbd function. Then we need to unregister it whenever the QIOChannel object is freed. > > In the code that would lead to the following constructs in a lot of places: > if (local_err) { > yank_unregister_function(s->yank_name, yank_nbd, bs); > object_unref(OBJECT(sioc)); > error_propagate(errp, local_err); > return NULL; > } The nbd patch here already has a yank_unregister_function() so I'm not seeing anything changes in that respect. The "yank_nbd" function should check that the I/O channel is non-NULL before calling the qio_channel_shutdown method. > If you don't want the code in QIOChannel I guess I can create a > subclass (YankableChannelSocket?) of QIOChannelSocket. What do > you think? That's no better, and I don't see any compelling need for it as calling yank_unregister_function is something nbd already does in its nbd_close function. It isn't a burden for the other backends to do similarly. 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 :|