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

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Date:   Mon, 21 Sep 2020 14:38:02 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     '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().

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().
> 
> 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, the compiler will probably make that optimisation.
I did a minimal change because my head hurts whenever I look at io_uring.c.

	David

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