Re: [PATCH 4/9 next] fs/io_uring Don't use the return value from import_iovec().

[Pavel Begunkov]

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@xxxxxxxxx>

>>
>> 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