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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 AM6PR08MB3287.eurprd08.prod.outlook.com (2603:10a6:209:41::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4264.18; Thu, 24 Jun 2021 09:15:16 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::75ce:1d52:cb60:e955]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::75ce:1d52:cb60:e955%6]) with mapi id 15.20.4264.020; Thu, 24 Jun 2021 09:15:16 +0000 Subject: Re: [PATCH v2 3/6] block: Clarify that @bytes is no limit on *pnum To: Max Reitz , qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, Kevin Wolf , Eric Blake References: <20210623150143.188184-1-mreitz@redhat.com> <20210623150143.188184-4-mreitz@redhat.com> From: Vladimir Sementsov-Ogievskiy Message-ID: Date: Thu, 24 Jun 2021 12:15:15 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR03-DB5-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, NICE_REPLY_A=-0.001, 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" 23.06.2021 18:01, Max Reitz wrote: > .bdrv_co_block_status() implementations are free to return a *pnum that > exceeds @bytes, because bdrv_co_block_status() in block/io.c will clamp > *pnum as necessary. > > On the other hand, if drivers' implementations return values for *pnum > that are as large as possible, our recently introduced block-status > cache will become more effective. > > So, make a note in block_int.h that @bytes is no upper limit for *pnum. > > Suggested-by: Eric Blake > Signed-off-by: Max Reitz > --- > include/block/block_int.h | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/include/block/block_int.h b/include/block/block_int.h > index fcb599dd1c..f85b96ed99 100644 > --- a/include/block/block_int.h > +++ b/include/block/block_int.h > @@ -347,6 +347,11 @@ struct BlockDriver { > * clamped to bdrv_getlength() and aligned to request_alignment, > * as well as non-NULL pnum, map, and file; in turn, the driver > * must return an error or set pnum to an aligned non-zero value. > + * > + * Note that @bytes is just a hint on how big of a region the > + * caller wants to inspect. It is not a limit on *pnum. > + * Implementations are free to return larger values of *pnum if > + * doing so does not incur a performance penalty. Worth mention that the cache will benefit of it? Reviewed-by: Vladimir Sementsov-Ogievskiy > */ > int coroutine_fn (*bdrv_co_block_status)(BlockDriverState *bs, > bool want_zero, int64_t offset, int64_t bytes, int64_t *pnum, > -- Best regards, Vladimir