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Tue, 21 Jul 2020 02:19:04 +0000 From: Damien Le Moal To: Matthew Wilcox CC: Kanchan Joshi , "hch@infradead.org" , Jens Axboe , Kanchan Joshi , "viro@zeniv.linux.org.uk" , "bcrl@kvack.org" , "asml.silence@gmail.com" , "linux-fsdevel@vger.kernel.org" , Matias Bj??rling , "linux-kernel@vger.kernel.org" , "linux-aio@kvack.org" , "io-uring@vger.kernel.org" , "linux-block@vger.kernel.org" , Selvakumar S , Nitesh Shetty , Javier Gonzalez Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append Thread-Topic: [PATCH v3 4/4] io_uring: add support for zone-append Thread-Index: AQHWUv1xEGaGdzUuiUilHzifWt+jQw== Date: Tue, 21 Jul 2020 02:19:04 +0000 Message-ID: References: <20200710131054.GB7491@infradead.org> <20200710134824.GK12769@casper.infradead.org> <20200710134932.GA16257@infradead.org> <20200710135119.GL12769@casper.infradead.org> <20200720171416.GY12769@casper.infradead.org> <20200721011509.GB15516@casper.infradead.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: infradead.org; 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x-ms-exchange-antispam-messagedata: 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 x-ms-exchange-transport-forked: True Content-Type: text/plain; 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: CY4PR04MB3751.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: e68f927a-cd10-4ccd-7204-08d82d1c7071 X-MS-Exchange-CrossTenant-originalarrivaltime: 21 Jul 2020 02:19:04.0582 (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: Ydrf1pWtGJ+Km92pDj2i4cmqcaSmwHjZ3BCG22reCv33zOioRVaJ538n/j9O87eS3ti8aFIJn+TeK314uXIKpg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR04MB1113 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/07/21 10:15, Matthew Wilcox wrote:=0A= > On Tue, Jul 21, 2020 at 12:59:59AM +0000, Damien Le Moal wrote:=0A= >> On 2020/07/21 5:17, Kanchan Joshi wrote:=0A= >>> On Mon, Jul 20, 2020 at 10:44 PM Matthew Wilcox w= rote:=0A= >>>> struct io_uring_cqe {=0A= >>>> __u64 user_data; /* sqe->data submission passed back */= =0A= >>>> - __s32 res; /* result code for this event */=0A= >>>> - __u32 flags;=0A= >>>> + union {=0A= >>>> + struct {=0A= >>>> + __s32 res; /* result code for this event = */=0A= >>>> + __u32 flags;=0A= >>>> + };=0A= >>>> + __s64 res64;=0A= >>>> + };=0A= >>>> };=0A= >>>>=0A= >>>> Return the value in bytes in res64, or a negative errno. Done.=0A= >>>=0A= >>> I concur. Can do away with bytes-copied. It's either in its entirety=0A= >>> or not at all.=0A= >>>=0A= >>=0A= >> SAS SMR drives may return a partial completion. So the size written may = be less=0A= >> than requested, but not necessarily 0, which would be an error anyway si= nce any=0A= >> condition that would lead to 0B being written will cause the drive to fa= il the=0A= >> command with an error.=0A= > =0A= > Why might it return a short write? And, given how assiduous programmers= =0A= > are about checking for exceptional conditions, is it useful to tell=0A= > userspace "only the first 512 bytes of your 2kB write made it to storage"= ?=0A= > Or would we rather just tell userspace "you got an error" and _not_=0A= > tell them that the first N bytes made it to storage?=0A= =0A= If the write hits a bad sector on disk half-way through, a SAS drive may re= turn=0A= a short write with a non 0 residual. SATA drives will fail the entire comma= nd=0A= and libata will retry the failed command. That said, if the drive fails to = remap=0A= a bad sector and return an error to the host, it is generally an indicator = that=0A= one should go to the store to get a new drive :)=0A= =0A= Yes, you have a good point. Returning an error for the entire write would b= e=0A= fine. The typical error handling for a failed write to a zone is for the us= er to=0A= first do a zone report to inspect the zone condition and WP position, resyn= c its=0A= view of the zone state and restart the write in the same zone or somewhere = else.=0A= So failing the entire write is OK.=0A= I am actually not 100% sure what the bio interface does if the "restart=0A= remaining" of a partially failed request fails again after all retry attemp= ts.=0A= The entire BIO is I think failed. Need to check. So the high level user wou= ld=0A= not see the partial failure as that stays within the scsi layer.=0A= =0A= >> Also, the completed size should be in res in the first cqe to follow io_= uring=0A= >> current interface, no ?. The second cqe would use the res64 field to ret= urn the=0A= >> written offset. Wasn't that the plan ?=0A= > =0A= > two cqes for one sqe seems like a bad idea to me.=0A= =0A= Yes, this is not very nice. I got lost in the thread. I thought that was th= e plan.=0A= =0A= =0A= -- =0A= Damien Le Moal=0A= Western Digital Research=0A=