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envelope-from=vsementsov@virtuozzo.com; helo=EUR02-HE1-obe.outbound.protection.outlook.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/22 09:47:21 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 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. -- Best regards, Vladimir