linux-kernel - Re: [PATCH 4/9 next] fs/io_uring Don't use the return value from import

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Message-ID: <47e7d21b-28ae-80d7-8e1a-403f180b0e70@gmail.com>
Date:   Mon, 21 Sep 2020 19:01:40 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     David Laight <David.Laight@...LAB.COM>,
        'Christoph Hellwig' <hch@...radead.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "io-uring@...r.kernel.org" <io-uring@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>,
        "David S. Miller" <davem@...emloft.net>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 4/9 next] fs/io_uring Don't use the return value from
 import_iovec().

On 21/09/2020 17:38, David Laight wrote:
> From: Christoph Hellwig
>> Sent: 21 September 2020 15:15
>>
>> On Tue, Sep 15, 2020 at 02:55:20PM +0000, David Laight wrote:
>>>
>>> This is the only code that relies on import_iovec() returning
>>> iter.count on success.
>>> This allows a better interface to import_iovec().

Reviewed-by: Pavel Begunkov <asml.silence@...il.com>

>>
>> This looks generall sane, but a comment below:
>>
>>> @@ -3123,7 +3123,7 @@ static int io_read(struct io_kiocb *req, bool force_nonblock,
>>>  	if (ret < 0)
>>>  		return ret;
>>>  	iov_count = iov_iter_count(iter);
>>> -	io_size = ret;
>>> +	io_size = iov_count;
>>>  	req->result = io_size;
>>>  	ret = 0;
>>>
>>> @@ -3246,7 +3246,7 @@ static int io_write(struct io_kiocb *req, bool force_nonblock,
>>>  	if (ret < 0)
>>>  		return ret;
>>>  	iov_count = iov_iter_count(iter);
>>> -	io_size = ret;
>>> +	io_size = iov_count;
>>>  	req->result = io_size;
>>
>> I tink the local iov_count variable can go away in both functions,
>> as io_size only changes after the last use of iov_count (io_read) or
>> not at all (io_write).

Yes, iov_count should be killed, now or later.

> 
> Yes, the compiler will probably make that optimisation.
> I did a minimal change because my head hurts whenever I look at io_uring.c.
> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 

-- 
Pavel Begunkov