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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 11:04:56 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 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? -- Best regards, Vladimir