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Tsirkin" , Stefan Weil , Paolo Bonzini , Jason Wang , Samuel Thibault , Anthony Perard , Laine Stump Subject: Re: [PATCH v13 17/17] net: stream: add QAPI events to report connection state Message-ID: <20221024140431.2e93dd2b@elisabeth> In-Reply-To: <87tu3tsczq.fsf@pond.sub.org> References: <20221020162558.123284-1-lvivier@redhat.com> <20221020162558.123284-18-lvivier@redhat.com> <87pmel4th4.fsf@pond.sub.org> <52e989b9-6f8d-99c6-ef04-3ce32006b002@redhat.com> <87lep935hn.fsf@pond.sub.org> <87tu3tsczq.fsf@pond.sub.org> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=sbrivio@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.503, 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=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Qemu-devel" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, 24 Oct 2022 13:00:09 +0200 Markus Armbruster wrote: > Markus Armbruster writes: > > > Cc: Stefano Brivio > > > > Laurent Vivier writes: > > > >> On 10/21/22 07:48, Markus Armbruster wrote: > >>> Laurent Vivier writes: > >>> > >>>> The netdev reports NETDEV_STREAM_CONNECTED event when the backend > >>>> is connected, and NETDEV_STREAM_DISCONNECTED when it is disconnected. > >>> > >>> Use cases? > >> > >> This is asked by Stefano Brivio to allow libvirt to detect if connection to passt is lost and to restart passt. > > [...] > > >>> Could similar event signalling be useful for other kinds of netdev > >>> backends? > >> > >> I was wondering, but it becomes more complicated to be generic. > > > > Making something complicated and generic where a simpler special > > solution would do is the worst. > > > > Not quite as bad (but still plenty bad) is making a few special > > solutions first, then replace them all with a generic solution. > > > > I believe we should have a good, hard think on possible applications of > > a generic solution now. > > > > There is no need to hold back this series for that. > > > > If we conclude a generic solution is called for, we better replace this > > special solution before it becomes ABI. Either by replacing it before > > we release it, or by keeping it unstable until we replace it. > > Stefano, any thoughts on this? Actually, to me, it already looks as generic as it can be: stream back-ends are the only ones connecting and disconnecting. I quickly tried to think about possible, similar events for other back-ends: - user: handled by libslirp, there's no connection, and probably not much we can or want to export from libslirp itself - tap, bridge: the closest equivalent would be interfaces changing states, but that's something that's also externally observable with a netlink socket, in case one needs to know. And in any case, it's logically very different from a connection or disconnection. If we want events for that, they should have different names - vhost-user, vde: we could implement something similar if the need arises, but it should logically have a different name - l2tpv3: stateless, same as datagram-oriented socket. No states, no events to report, I guess. All in all, to me, NETDEV_STREAM_{,DIS}CONNECTED events here don't look very "special" or hackish. -- Stefano