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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 AM6PR08MB4280.eurprd08.prod.outlook.com (2603:10a6:20b:b6::19) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3412.20; Wed, 23 Sep 2020 17:11:59 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b179:9641:7589:d692]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b179:9641:7589:d692%8]) with mapi id 15.20.3370.033; Wed, 23 Sep 2020 17:11:59 +0000 Subject: Re: [PATCH v6 2/5] block/io: bdrv_common_block_status_above: support include_base To: Alberto Garcia , qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, fam@euphon.net, stefanha@redhat.com, mreitz@redhat.com, kwolf@redhat.com, eblake@redhat.com, den@openvz.org References: <20200916122008.20303-1-vsementsov@virtuozzo.com> <20200916122008.20303-3-vsementsov@virtuozzo.com> From: Vladimir Sementsov-Ogievskiy Message-ID: <6181089a-8910-442e-35ed-e1bca0bde3eb@virtuozzo.com> Date: Wed, 23 Sep 2020 20:11:57 +0300 User-Agent: Mozilla/5.0 (X11; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR01-DB5-obe.outbound.protection.outlook.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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=-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" 23.09.2020 19:18, Alberto Garcia wrote: > On Wed 16 Sep 2020 02:20:05 PM CEST, Vladimir Sementsov-Ogievskiy wrote: >> - for (p = backing_bs(bs); p != base; p = backing_bs(p)) { >> + for (p = backing_bs(bs); include_base || p != base; p = backing_bs(p)) { >> ret = bdrv_co_block_status(p, want_zero, offset, bytes, pnum, map, >> file); >> if (ret < 0) { >> @@ -2420,6 +2422,11 @@ bdrv_co_common_block_status_above(BlockDriverState *bs, >> break; >> } >> >> + if (p == base) { >> + assert(include_base); >> + break; >> + } >> + > > Another option is something like: > > BlockDriverState *last_bs = include_base ? base : backing_bs(base); hmm, in case when include_base is false, last bs is not backing_bs(base) but the parent of base. > > and you get a simpler 'for' loop. > > But why do we need include_base at all? Can't the caller just pass > backing_bs(base) instead? I'm talking also about the existing case of > bdrv_is_allocated_above(). > include_base was introduced for the case when caller doesn't own backing_bs(base), and therefore shouldn't do operations that may yield (block_status can) dependent on backing_bs(base). In particular, in block stream, where link to base is not frozen. -- Best regards, Vladimir