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Received: from VI0PR08MB10656.eurprd08.prod.outlook.com (2603:10a6:800:20a::12) by PA4PR08MB6128.eurprd08.prod.outlook.com (2603:10a6:102:f2::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.382.10; Thu, 3 Sep 2026 14:56:12 +0000 Received: from VI0PR08MB10656.eurprd08.prod.outlook.com ([fe80::4e37:b189:ddcd:3dd8]) by VI0PR08MB10656.eurprd08.prod.outlook.com ([fe80::4e37:b189:ddcd:3dd8%7]) with mapi id 15.21.0382.007; Thu, 3 Sep 2026 14:56:12 +0000 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Subject: Re: [QEMU HCI-8.0 PATCH 4/5] vhost-blk: watch the device for resize events From: Andrey Drobyshev To: Andrey Zhadchenko Cc: svt-core@virtuozzo.com, den@openvz.org, andrey.drobyshev@virtuozzo.com In-Reply-To: <20260903123204.24035-5-andrey.zhadchenko@virtuozzo.com> References: <20260903123204.24035-1-andrey.zhadchenko@virtuozzo.com> <20260903123204.24035-5-andrey.zhadchenko@virtuozzo.com> Date: Thu, 03 Sep 2026 17:56:04 +0300 Message-Id: <178844736480.581266.1644890129890342175.b4-review@b4> X-Mailer: b4 0.16.0 X-ClientProxiedBy: FR5P281CA0017.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:f1::9) To VI0PR08MB10656.eurprd08.prod.outlook.com (2603:10a6:800:20a::12) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VI0PR08MB10656:EE_|PA4PR08MB6128:EE_ X-MS-Office365-Filtering-Correlation-Id: ae45f98b-4eb4-4539-a42a-08df09cb7dbb X-LD-Processed: 0bc7f26d-0264-416e-a6fc-8352af79c58f,ExtAddr List-Id: svt-core@virtuozzo.com X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|52116014|366016|1800799024|376014|23010399003|22082099003|18002099003|5113699003|4143699003|56012099006|10067099003|38350700014; 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So, QEMU must get the knowledge about updated size. It can only do so by getting this knowledge from libvirt (as it used to be with qmp_block_resize) or from the kernel via some kind of notification. So our options: 1. Another QMP command sent directly from libvirt, smth like 'vhost-blk-config-update id=virtio-disk0 data={...}' 2. Patching the kernel so it knows the size, caches it. Making ploop send an ioctl to inform the kernel about new size. Then establishing eventfd from vhost-blk backend -> qemu, and processing the events. I think 1st is cleaner and requires less work. Andrey -- Andrey Drobyshev