Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
Message-ID: <9cd3cc84-a2a0-a827-3fb8-bd2928eabd28@linux.alibaba.com>
Date:   Tue, 22 Feb 2022 15:34:40 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.5.0
Subject: Re: [PATCH v2 4/4] io_uring: pre-increment f_pos on rw
Content-Language: en-US
To:     Dylan Yudaken <dylany@fb.com>, Jens Axboe <axboe@kernel.dk>,
        Pavel Begunkov <asml.silence@gmail.com>,
        io-uring@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, kernel-team@fb.com
References: <20220221141649.624233-1-dylany@fb.com>
 <20220221141649.624233-5-dylany@fb.com>
From:   Hao Xu <haoxu@linux.alibaba.com>
In-Reply-To: <20220221141649.624233-5-dylany@fb.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 2/21/22 22:16, Dylan Yudaken wrote:
> In read/write ops, preincrement f_pos when no offset is specified, and
> then attempt fix up the position after IO completes if it completed less
> than expected. This fixes the problem where multiple queued up IO will all
> obtain the same f_pos, and so perform the same read/write.
>
> This is still not as consistent as sync r/w, as it is able to advance the
> file offset past the end of the file. It seems it would be quite a
> performance hit to work around this limitation - such as by keeping track
> of concurrent operations - and the downside does not seem to be too
> problematic.
>
> The attempt to fix up the f_pos after will at least mean that in situations
> where a single operation is run, then the position will be consistent.
>
It's a little bit weird, when a read req returns x bytes read while f_pos

moves ahead y bytes where x isn't equal to y. Don't know if this causes

problems..