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Wed, 22 Jul 2020 15:43:27 +0000 (UTC) Date: Wed, 22 Jul 2020 16:43:24 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH 3/4] io/channel-socket: implement non-blocking connect Message-ID: <20200722154324.GP2324845@redhat.com> References: <20200720180715.10521-4-vsementsov@virtuozzo.com> <20200720182923.GP643836@redhat.com> <840b762e-1ce1-af25-2ea0-b8cfdedba0d4@virtuozzo.com> <20200722112104.GC2324845@redhat.com> <20200722125303.GI2324845@redhat.com> <71bd9b95-6db6-bfaa-729e-df9d1493e5b7@virtuozzo.com> <46847ccc-22d0-59b9-6c43-16cb6af4b078@virtuozzo.com> <20200722152140.GO2324845@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.14.5 (2020-06-23) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 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=205.139.110.120; envelope-from=berrange@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/21 23:27:14 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: kwolf@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org, mreitz@redhat.com, kraxel@redhat.com, den@openvz.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 22, 2020 at 06:40:10PM +0300, Vladimir Sementsov-Ogievskiy wrote: > 22.07.2020 18:21, Daniel P. Berrangé wrote: > > On Wed, Jul 22, 2020 at 06:04:53PM +0300, Vladimir Sementsov-Ogievskiy wrote: > > > 22.07.2020 16:47, Vladimir Sementsov-Ogievskiy wrote: > > > > 22.07.2020 15:53, Daniel P. Berrangé wrote: > > > > > On Wed, Jul 22, 2020 at 03:43:54PM +0300, Vladimir Sementsov-Ogievskiy wrote: > > > > > > 22.07.2020 14:21, Daniel P. Berrangé wrote: > > > > > > > On Wed, Jul 22, 2020 at 02:00:25PM +0300, Vladimir Sementsov-Ogievskiy wrote: > > > > > > > > 20.07.2020 21:29, Daniel P. Berrangé wrote: > > > > > > > > > On Mon, Jul 20, 2020 at 09:07:14PM +0300, Vladimir Sementsov-Ogievskiy wrote: > > > > > > > > > > Utilize new socket API to make a non-blocking connect for inet sockets. > > > > > > > > > > > > > > > > > > > > Signed-off-by: Vladimir Sementsov-Ogievskiy > > > > > > > > > > --- > > > > > > > > > >     include/io/channel-socket.h | 14 +++++++ > > > > > > > > > >     io/channel-socket.c         | 74 +++++++++++++++++++++++++++++++++++++ > > > > > > > > > >     2 files changed, 88 insertions(+) > > > > > > > > > > > > > > > > > > > > diff --git a/include/io/channel-socket.h b/include/io/channel-socket.h > > > > > > > > > > index 777ff5954e..82e868bc02 100644 > > > > > > > > > > --- a/include/io/channel-socket.h > > > > > > > > > > +++ b/include/io/channel-socket.h > > > > > > > > > > @@ -94,6 +94,20 @@ int qio_channel_socket_connect_sync(QIOChannelSocket *ioc, > > > > > > > > > >                                         SocketAddress *addr, > > > > > > > > > >                                         Error **errp); > > > > > > > > > > +/** > > > > > > > > > > + * qio_channel_socket_connect_non_blocking_sync: > > > > > > > > > > + * @ioc: the socket channel object > > > > > > > > > > + * @addr: the address to connect to > > > > > > > > > > + * @errp: pointer to a NULL-initialized error object > > > > > > > > > > + * > > > > > > > > > > + * Attempt to connect to the address @addr using non-blocking mode of > > > > > > > > > > + * the socket. Function is synchronous, but being called from > > > > > > > > > > + * coroutine context will yield during connect operation. > > > > > > > > > > + */ > > > > > > > > > > +int qio_channel_socket_connect_non_blocking_sync(QIOChannelSocket *ioc, > > > > > > > > > > +                                                 SocketAddress *addr, > > > > > > > > > > +                                                 Error **errp); > > > > > > > > > > + > > > > > > > > > >     /** > > > > > > > > > >      * qio_channel_socket_connect_async: > > > > > > > > > >      * @ioc: the socket channel object > > > > > > > > > > diff --git a/io/channel-socket.c b/io/channel-socket.c > > > > > > > > > > index e1b4667087..076de7578a 100644 > > > > > > > > > > --- a/io/channel-socket.c > > > > > > > > > > +++ b/io/channel-socket.c > > > > > > > > > > @@ -22,6 +22,7 @@ > > > > > > > > > >     #include "qapi/error.h" > > > > > > > > > >     #include "qapi/qapi-visit-sockets.h" > > > > > > > > > >     #include "qemu/module.h" > > > > > > > > > > +#include "qemu/sockets.h" > > > > > > > > > >     #include "io/channel-socket.h" > > > > > > > > > >     #include "io/channel-watch.h" > > > > > > > > > >     #include "trace.h" > > > > > > > > > > @@ -29,6 +30,8 @@ > > > > > > > > > >     #define SOCKET_MAX_FDS 16 > > > > > > > > > > +static int qio_channel_socket_close(QIOChannel *ioc, Error **errp); > > > > > > > > > > + > > > > > > > > > >     SocketAddress * > > > > > > > > > >     qio_channel_socket_get_local_address(QIOChannelSocket *ioc, > > > > > > > > > >                                          Error **errp) > > > > > > > > > > @@ -157,6 +160,77 @@ int qio_channel_socket_connect_sync(QIOChannelSocket *ioc, > > > > > > > > > >         return 0; > > > > > > > > > >     } > > > > > > > > > > +static int qio_channel_inet_connect_non_blocking_sync(QIOChannelSocket *ioc, > > > > > > > > > > +        InetSocketAddress *addr, Error **errp) > > > > > > > > > > +{ > > > > > > > > > > +    Error *local_err = NULL; > > > > > > > > > > +    struct addrinfo *infos, *info; > > > > > > > > > > +    int sock = -1; > > > > > > > > > > + > > > > > > > > > > +    infos = inet_parse_connect_saddr(addr, errp); > > > > > > > > > > +    if (!infos) { > > > > > > > > > > +        return -1; > > > > > > > > > > +    } > > > > > > > > > > > > > > > > > > This call is blocking since it calls getaddrinfo whose design > > > > > > > > > offers no ability todo non-blocking DNS lookups. Given this > > > > > > > > > call, ... > > > > > > > > > > > > > > > > Oh, that's bad, thanks for taking a look on that early stage! > > > > > > > > > > > > > > > > > > > > > > > > > > > + > > > > > > > > > > +    for (info = infos; info != NULL; info = info->ai_next) { > > > > > > > > > > +        bool in_progress; > > > > > > > > > > + > > > > > > > > > > +        error_free(local_err); > > > > > > > > > > +        local_err = NULL; > > > > > > > > > > + > > > > > > > > > > +        sock = inet_connect_addr(addr, info, false, &in_progress, &local_err); > > > > > > > > > > +        if (sock < 0) { > > > > > > > > > > +            continue; > > > > > > > > > > +        } > > > > > > > > > > + > > > > > > > > > > +        if (qio_channel_socket_set_fd(ioc, sock, &local_err) < 0) { > > > > > > > > > > +            close(sock); > > > > > > > > > > +            continue; > > > > > > > > > > +        } > > > > > > > > > > + > > > > > > > > > > +        if (in_progress) { > > > > > > > > > > +            if (qemu_in_coroutine()) { > > > > > > > > > > +                qio_channel_yield(QIO_CHANNEL(ioc), G_IO_OUT); > > > > > > > > > > +            } else { > > > > > > > > > > +                qio_channel_wait(QIO_CHANNEL(ioc), G_IO_OUT); > > > > > > > > > > +            } > > > > > > > > > > > > > > > > > > ...this is offering false assurances of being non-blocking. > > > > > > > > > > > > > > > > > > If we don't want the current thread to be blocked then we > > > > > > > > > need to be using the existing qio_channel_socket_connect_async > > > > > > > > > method or similar. It uses a throw away background thread to > > > > > > > > > run the connection attempt, and then reports completion back > > > > > > > > > later, thus avoiding the getaddrinfo design flaw for the callers. > > > > > > > > > > > > > > > > > > I explicitly didn't want to add an method like the impl in this > > > > > > > > > patch, because getaddrinfo dooms it and we already had bugs in > > > > > > > > > the pre-QIOChannel code where QEMU thought it was non-blocking > > > > > > > > > but wasn't due to getaddrinfo lookups. > > > > > > > > > > > > > > > > > > > > > > > > > > > IIUC, the main appeal of this method is that the non-blocking > > > > > > > > > nature is hidden from the caller who can continue to treat it > > > > > > > > > as a synchronous call and have the coroutine magic happen in > > > > > > > > > behind the scenes. > > > > > > > > > > > > > > > > > > IOW, What's needed is a simple way to run the operation in a > > > > > > > > > thread, and sleep for completion while having the coroutine > > > > > > > > > yield. > > > > > > > > > > > > > > > > > > I think this could likely be achieved with QIOTask with an > > > > > > > > > alternate impl of the qio_task_wait_thread() method that is > > > > > > > > > friendly to coroutines instead of being based on pthread > > > > > > > > > condition variable waits. > > > > > > > > > > > > > > > > The most simple thing is just run qio_channel_socket_connect_sync in > > > > > > > > a thread with help of thread_pool_submit_co() which is coroutine-friendly. > > > > > > > > And this don't need any changes in io/channel. > > > > > > > > > > > > > > > > Actually, I've started with such design, but decided that better use > > > > > > > > non-blocking connect to not deal with cancelling the connecting thread > > > > > > > > on shutdown. > > > > > > > > > > > > > > > > I think, I'll resend based on thread_pool_submit_co(). > > > > > > > > > > > > > > > > === > > > > > > > > > > > > > > > > Hmm, there is async getaddrinfo_a function.. What do you think of it? > > > > > > > > > > > > > > It isn't portable, glibc only. > > > > > > > > > > > > > > > But seems simpler to use a thread than move to async interfaces everywhere. > > > > > > > > > > > > > > > > > > > > > > > > > > Hmm.. Still, on shutdown, how to cancel this connect and getaddrinfo ? I'm not sure > > > > > > how much time may getaddrinfo take, but connect can take about a minute. It's not really > > > > > > good to wait for it on shutdown. > > > > > > > > > > The intention was that if you don't want to carry on waiting for the > > > > > async operation to complete you just give and pretend it no longer > > > > > exists. Eventually it will fail or complete and the thread will exit. > > > > > The only important thing there is making sure that the callback you > > > > > are passing to the _async() method can cope with the cleanup when the > > > > > work eventually completes, even if you've given up. > > > > > > > > > > > > > At least it's not possible with thread_pool_submit_co as I wanted, because underlying > > > > thread pool waits for all its threads to complete on exit. > > > > > > > > > > > > > > > > > I'm trying to use qio_channel_socket_connect_async().. But callback > > > is not called. > > > > > > How to make it be executed? In tests/test-io-channel-socket.c it's > > > done by g_main_loop_new .. g_main_loop_run. But I need to yield. > > > socket_start_outgoing_migration uses qio_channel_socket_connect_async > > > as well, but is not doing any magic with g_main_loop. But it works. How? > > > > The _async() impls uses qio_task_run_in_thread to spawn the background > > thread. When the thread finishes, it uses g_idle_add to invoke the > > callback so that it runs in the context of the main thread, not the > > background thread. So something needs to be running the main loop > > in QEMU. > > I came to same idea. But still, I don't see where g_main_loop is > run inside qemu_main_loop(). Only iothread_run() does it. But > what if we don't have iothreads? There's no requirement to use g_main_loop, what matters is actually that something runs the default GMainContext. qemu_main_loop satisfies this. If you have a different GMainLoop that you want to use, then you can pass its GMainContext into the _async() functions, and the result will get dispatched from whatever thread runs that GMainContext/GMainLoop. So you could use this to get the callback to be invoked in your iothread context if that's desirable. If a NULL GMainContext is passed to _async(), then the callback is dispatched from qemu_main_loop() thread. 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 :|