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Wed, 26 May 2021 02:55:57 +0000 From: Chaitanya Kulkarni To: Christoph Hellwig CC: Matthew Wilcox , "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "target-devel@vger.kernel.org" , "linux-btrfs@vger.kernel.org" , "axboe@kernel.dk" , "mb@lightnvm.io" , "martin.petersen@oracle.com" , "clm@fb.com" , "josef@toxicpanda.com" , "dsterba@suse.com" , Johannes Thumshirn , "ming.lei@redhat.com" , "osandov@fb.com" , "jefflexu@linux.alibaba.com" Subject: Re: [RFC PATCH 0/8] block: fix bio_add_XXX_page() return type Thread-Topic: [RFC PATCH 0/8] block: fix bio_add_XXX_page() return type Thread-Index: AQHXTUCZbkdV5W8mbU+6O2TFfy2HFA== Date: Wed, 26 May 2021 02:55:57 +0000 Message-ID: References: <20210520062255.4908-1-chaitanya.kulkarni@wdc.com> <20210524073527.GA24302@lst.de> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: lst.de; dkim=none (message not signed) header.d=none;lst.de; dmarc=none action=none header.from=wdc.com; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BYAPR04MB4965.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 6fd60881-8d8e-4488-937f-08d91ff1c965 X-MS-Exchange-CrossTenant-originalarrivaltime: 26 May 2021 02:55:57.5133 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: 7SGHYw4wP7GxduunB0G+dnjRIS1Pvbi4NRN96kd0u/04IVb7oCJsO9GdTEYUq7Jw2p4bW9BLT5/XiLqNe0mLw/pe3ajyBpBc9PAr1G5R05c= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR04MB3861 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Christoph,=0A= =0A= On 5/24/21 00:35, Christoph Hellwig wrote:=0A= > On Fri, May 21, 2021 at 12:30:45PM +0100, Matthew Wilcox wrote:=0A= >> On Wed, May 19, 2021 at 11:22:47PM -0700, Chaitanya Kulkarni wrote:=0A= >>> The helper functions bio_add_XXX_page() returns the length which is=0A= >>> unsigned int but the return type of those functions is defined=0A= >>> as int instead of unsigned int.=0A= >> I've been thinking about this for a few weeks as part of the folio=0A= >> patches:=0A= >>=0A= >> https://lore.kernel.org/linux-fsdevel/20210505150628.111735-72-willy@inf= radead.org/=0A= >>=0A= >> - len and off are measured in bytes=0A= >> - neither are permitted to be negative=0A= >> - for efficiency we only permit them to be up to 4GB=0A= >>=0A= >> I therefore believe the correct type for these parameters to be size_t,= =0A= >> and we should range-check them if they're too large. they should=0A= >> actually always fit within the page that they're associated with, but=0A= >> people do allocate non-compound pages and i'm not trying to break that= =0A= >> today.=0A= >>=0A= >> using size_t makes it clear that these are byte counts, not (eg) sector= =0A= >> counts. i do think it's good to make the return value unsigned so we=0A= >> don't have people expecting a negative errno on failure.=0A= > I think the right type is bool. We always return either 0 or the full=0A= > length we tried to add. Instead of optimizing for a partial add (which= =0A= > only makes sense for bio_add_hw_page anyway), I'd rather make the=0A= > interface as simple as possible.=0A= >=0A= =0A= Is above comment is on this series or on the API present in the folio=0A= patches [1] ?=0A= =0A= Since if we change the return type to bool for the functions in=0A= question [2] in this series we also need to modify the callers, I'm not sur= e=0A= that is worth it though.=0A= =0A= Please confirm.=0A= =0A= [1]=0A= https://lore.kernel.org/linux-fsdevel/20210505150628.111735-72-willy@infrad= ead.org/=0A= =0A= =0A= [2]=0A= bio_add_hw_page()=0A= bio_add_pc_page()=0A= bio_add_zone_append_page()=0A= bio_add page()=0A= =0A= =0A=