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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 AS8PR08MB6870.eurprd08.prod.outlook.com (2603:10a6:20b:39a::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4020.18; Thu, 8 Apr 2021 10:03:58 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133%7]) with mapi id 15.20.4020.017; Thu, 8 Apr 2021 10:03:58 +0000 Subject: DROP THIS Re: [PATCH 00/14] nbd: move reconnect-thread to separate file To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, mreitz@redhat.com, kwolf@redhat.com, eblake@redhat.com, rvkagan@yandex-team.ru, den@openvz.org References: <20210407104637.36033-1-vsementsov@virtuozzo.com> From: Vladimir Sementsov-Ogievskiy Message-ID: <13074b0f-3b83-8db5-2ef4-a5e0060d15cc@virtuozzo.com> Date: Thu, 8 Apr 2021 13:03:55 +0300 User-Agent: Mozilla/5.0 (X11; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR04-HE1-obe.outbound.protection.outlook.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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, SPF_HELO_PASS=-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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 07.04.2021 13:46, Vladimir Sementsov-Ogievskiy wrote: > Hi all! > > There are problems with nbd driver: > > - nbd reconnect is cancelled on drain, which is bad as Roman describes > in his "[PATCH 0/7] block/nbd: decouple reconnect from drain" > - nbd driver is too complicated around drained sections and aio context > switch. It's nearly impossible to follow all the logic, including > abuse of bs->in_flight, which is temporary decreased in some places > (like nbd_read_eof()). Additional reconnect thread and two different > state machines (we have BDRVNBDState::state and > BDRVNBDState::connect_thread->state) doesn't make things simpler :) > > So, I have a plan: > > 1. Move nbd negotiation to connect_thread > > 2. Do receive NBD replies in request coroutines, not in connection_co > > At this point we can drop connection_co, and when we don't have > endless running coroutine, NBD driver becomes a usual block driver, > and we can drop abuse of bs->in_flight, and probably drop most of > complicated logic around drained section and aio context switch in > nbd driver. > > 3. Still, as Roman describes, with [2] we loose a possibility to > reconnect immediately when connection breaks (with current code we > have endless read in reconnect_co, but actually for this to work > keep-alive should be setup correctly). So, we'll need to reinvent it, > checking connection periodically by timeout, with help of getsockopt > or just sending a kind of PING request (zero-length READ or something > like this). > > And this series a kind of preparation. The main point of it is moving > connect-thread to a separate file. > Finally I don't like it. I'm in progress of creating new series to substitute this one, so don't waste your time on review. -- Best regards, Vladimir