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dkim=none (message not signed) header.d=none;openvz.org; dmarc=none action=none header.from=virtuozzo.com; Received: from AM7PR08MB5494.eurprd08.prod.outlook.com (2603:10a6:20b:dc::15) by AM6PR08MB3030.eurprd08.prod.outlook.com (2603:10a6:209:46::26) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3216.20; Wed, 22 Jul 2020 12:43:56 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::a408:2f0f:bc6c:d312]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::a408:2f0f:bc6c:d312%3]) with mapi id 15.20.3195.026; Wed, 22 Jul 2020 12:43:56 +0000 Subject: Re: [PATCH 3/4] io/channel-socket: implement non-blocking connect To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= References: <20200720180715.10521-1-vsementsov@virtuozzo.com> <20200720180715.10521-4-vsementsov@virtuozzo.com> <20200720182923.GP643836@redhat.com> <840b762e-1ce1-af25-2ea0-b8cfdedba0d4@virtuozzo.com> <20200722112104.GC2324845@redhat.com> From: Vladimir Sementsov-Ogievskiy Message-ID: Date: Wed, 22 Jul 2020 15:43:54 +0300 User-Agent: Mozilla/5.0 (X11; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR05-AM6-obe.outbound.protection.outlook.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/22 08:58:59 X-ACL-Warn: Detected OS = Windows NT kernel [generic] [fuzzy] X-Spam_score_int: -37 X-Spam_score: -3.8 X-Spam_bar: --- X-Spam_report: (-3.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_PASS=-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: , 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" 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. So, it may make sense to split connect, and keep it true-async. And call getaddrinfo in a thread (or just keep it synchronous). -- Best regards, Vladimir