linux-kernel - Re: [PATCH v6 02/34] iov_iter: Use IOCB/IOMAP_WRITE/op_is

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Date:   Wed, 18 Jan 2023 22:18:53 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     David Howells <dhowells@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 02/34] iov_iter: Use IOCB/IOMAP_WRITE/op_is_write
 rather than iterator direction

On Mon, Jan 16, 2023 at 11:55:08PM -0800, Christoph Hellwig wrote:
> On Mon, Jan 16, 2023 at 11:08:17PM +0000, David Howells wrote:
> > Use information other than the iterator direction to determine the
> > direction of the I/O:
> > 
> >  (*) If a kiocb is available, use the IOCB_WRITE flag.
> > 
> >  (*) If an iomap_iter is available, use the IOMAP_WRITE flag.
> > 
> >  (*) If a request is available, use op_is_write().
> 
> The really should be three independent patches.  Plus another one
> to drop the debug checks in cifs.
> 
> The changes themselves look good to me.
> 
> >  
> > +static unsigned char iov_iter_rw(const struct iov_iter *i)
> > +{
> > +	return i->data_source ? WRITE : READ;
> > +}
> 
> It might as well make sense to just open code this in the only
> caller as well (yet another patch).

Especially since
		/* if it's a destination, tell g-u-p we want them writable */
                if (!i->data_source)
			gup_flags |= FOLL_WRITE;
is less confusing than the current
                if (iov_iter_rw(i) != WRITE)
			gup_flags |= FOLL_WRITE;