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dkim=none (message not signed) header.d=none;redhat.com; dmarc=none action=none header.from=virtuozzo.com; Received: from AM7PR08MB5494.eurprd08.prod.outlook.com (2603:10a6:20b:dc::15) by AM6PR08MB3223.eurprd08.prod.outlook.com (2603:10a6:209:4d::25) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3370.16; Fri, 11 Sep 2020 11:06:12 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b179:9641:7589:d692]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b179:9641:7589:d692%7]) with mapi id 15.20.3348.019; Fri, 11 Sep 2020 11:06:12 +0000 Subject: Re: [PATCH v3 2/2] qcow2: Skip copy-on-write when allocating a zero cluster To: Alberto Garcia , qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, Kevin Wolf , Max Reitz References: <0350dd55702eacd701e0aea924b101db7448a517.1599759873.git.berto@igalia.com> <7f0ae868-07ca-2267-eb27-2787ff86e801@virtuozzo.com> From: Vladimir Sementsov-Ogievskiy Message-ID: <5642b34f-cc33-f7c5-2070-a7285b9e0acf@virtuozzo.com> Date: Fri, 11 Sep 2020 14:06:04 +0300 User-Agent: Mozilla/5.0 (X11; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR03-VE1-obe.outbound.protection.outlook.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/11 07:06:15 X-ACL-Warn: Detected OS = Windows NT kernel [generic] [fuzzy] X-Spam_score_int: -52 X-Spam_score: -5.3 X-Spam_bar: ----- X-Spam_report: (-5.3 / 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, NICE_REPLY_A=-2.469, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, 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" 11.09.2020 13:04, Alberto Garcia wrote: > On Fri 11 Sep 2020 11:34:37 AM CEST, Vladimir Sementsov-Ogievskiy wrote: >>> - if (!is_zero_cow(bs, m)) { >>> + ret = is_zero_cow(bs, m); >>> + if (ret < 0) { >>> + return ret; >> >> It's a common practice to treat block-status errors as "unknown" >> status and not error-out immediately: >> >> - really, it's not critical, we can continue assuming non-zero >> - if there are real problems with IO, we'll most probably fail on >> real read or write operation, and report its status, which seems >> better for user than block-status error > > But what's the problem exactly, does this complicate the code too much? > :-? Of course not :) Hmm. OK, I don't know, I'm just used to this practice in block jobs. Patch is correct as is: Reviewed-by: Vladimir Sementsov-Ogievskiy > >> So, I'd keep existing logic in handle_alloc_space(). And, if you agree >> and resend, probably good to split this patch into two, one for >> block.h/io.c and one for qcow2.c (still, I'm OK with it as one patch). > > Sure, I can split the patch if I have to resend it. > > Berto > -- Best regards, Vladimir