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[49.180.20.59]) by smtp.gmail.com with ESMTPSA id y22-20020aa78056000000b00692b6fe1c7asm32069pfm.179.2023.10.04.15.48.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Oct 2023 15:48:27 -0700 (PDT) Received: from dave by dread.disaster.area with local (Exim 4.96) (envelope-from ) id 1qoAfI-009Wtm-33; Thu, 05 Oct 2023 09:48:24 +1100 Date: Thu, 5 Oct 2023 09:48:24 +1100 From: Dave Chinner To: John Garry Cc: Bart Van Assche , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, martin.petersen@oracle.com, djwong@kernel.org, himanshu.madhani@oracle.com Subject: Re: [PATCH 2/4] readv.2: Document RWF_ATOMIC flag Message-ID: References: <20230929093717.2972367-1-john.g.garry@oracle.com> <20230929093717.2972367-3-john.g.garry@oracle.com> <9ba10b14-931b-42db-b7c2-e6f9aa95e477@acm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Wed, Oct 04, 2023 at 09:47:24AM +0100, John Garry wrote: > On 03/10/2023 20:25, Bart Van Assche wrote: > > On 9/29/23 02:37, John Garry wrote: > > > +.BR RWF_ATOMIC " (since Linux 6.7)" > > > +Allows block-based filesystems to indicate that write operations > > > will be issued > > > +with torn-write protection. Torn-write protection means that for a > > > power or any > > > +other hardware failure, all or none of the data from the write will > > > be stored, > > > +but never a mix of old and new data. This flag is meaningful only for > > > +.BR pwritev2 (), > > > +and its effect applies only to the data range written by the system > > > call. > > > +The total write length must be power-of-2 and must be sized between > > > +stx_atomic_write_unit_min and stx_atomic_write_unit_max, both > > > inclusive. The > > > +write must be at a natural offset within the file with respect to > > > the total > > > +write length. Torn-write protection only works with > > > +.B O_DIRECT > > > +flag, i.e. buffered writes are not supported. To guarantee > > > consistency from > > > +the write between a file's in-core state with the storage device, > > > > It seems wrong to me to start the first sentence with "Allows". Atomic > > behavior should be mandatory if RWF_ATOMIC has been set. > > Yes, I agree that this has been poorly worded. Flag RWF_ATOMIC does not > indicate anything. I will fix it. > > > > > Additionally, shouldn't it be documented what value will be stored in > > errno if the atomic write has been rejected? > > So I was treating all atomic writes errors which don't follow the "rules" as > low-level I/O errors, which is -EIO. However, yes, I can document this. > Further to that, based on description of an error for O_DIRECT, which is to > return -EINVAL for misaligned, I think that -EINVAL may be better for any > atomic write rule violations. OK? Agreed - I was going to make that comment myself about using EINVAL instead of EIO... -Dave. -- Dave Chinner david@fromorbit.com