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From: Omar Sandoval <osandov@osandov.com>
To: David Sterba <dsterba@suse.cz>
Cc: Al Viro <viro@ZenIV.linux.org.uk>,
	linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org,
	ceph-devel@vger.kernel.org, linux-cifs@vger.kernel.org,
	osd-dev@open-osd.org, linux-ext4@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net,
	fuse-devel@lists.sourceforge.net, cluster-devel@redhat.com,
	jfs-discussion@lists.sourceforge.net, HPDD-discuss@ml01.01.org,
	linux-nfs@vger.kernel.org, linux-nilfs@vger.kernel.org,
	ocfs2-devel@oss.oracle.com, reiserfs-devel@vger.kernel.org,
	v9fs-developer@lists.sourceforge.net, xfs@oss.sgi.com,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/5] new helper: iov_iter_rw()
Date: Tue, 17 Mar 2015 03:18:35 -0700	[thread overview]
Message-ID: <20150317101835.GA31649@mew> (raw)
In-Reply-To: <20150317093151.GS20767@twin.jikos.cz>

On Tue, Mar 17, 2015 at 10:31:51AM +0100, David Sterba wrote:
> On Mon, Mar 16, 2015 at 05:36:05PM +0000, Al Viro wrote:
> > On Mon, Mar 16, 2015 at 04:33:49AM -0700, Omar Sandoval wrote:
> > > Get either READ or WRITE out of iter->type.
> > 
> > Umm...  
> > 
> > > + * Get one of READ or WRITE out of iter->type without any other flags OR'd in
> > > + * with it.
> > > + */
> > > +static inline int iov_iter_rw(const struct iov_iter *i)
> > > +{
> > > +	return i->type & RW_MASK;
> > > +}
> > 
> > TBH, I would turn that into a macro.  Reason: indirect includes.
> 
> Agreed, but the proposed define is rather cryptic and I was not able to
> understand the meaning on the first glance.
> 
> > #define iov_iter_rw(i) ((0 ? (struct iov_iter *)0 : (i))->type & RW_MASK)
> 
> This worked for me, does not compile with anything else than
> 'struct iov_iter*' as i:
> 
> #define iov_iter_rw(i)	({			\
> 	struct iov_iter __iter = *(i);		\
> 	(i)->type & RW_MASK;			\
> 	})
> 
> The assignment is optimized out.

[-cc individual fs maintainers to avoid all of these email bounces,
should've looked a bit closer at that get_maintainer.pl output...]

I agree that this is a bit more readable, but it evaluates i twice.
That's an easy fix, just do __iter.type instead of (i)->type, but
there's still the possibility of someone passing in something called
__iter as i, and the fix for that tends to be "add more underscores". At
the very least, Al's macro could probably use a comment explaining
what's going on there, though.

-- 
Omar

  reply	other threads:[~2015-03-17 10:18 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-16 11:33 [RFC PATCH 0/5] Remove rw parameter from direct_IO() Omar Sandoval
2015-03-16 11:33 ` [RFC PATCH 1/5] new helper: iov_iter_rw() Omar Sandoval
2015-03-16 17:36   ` Al Viro
2015-03-17  1:20     ` [RFC PATCH v2 " Omar Sandoval
2015-03-17  9:31     ` [RFC PATCH " David Sterba
2015-03-17 10:18       ` Omar Sandoval [this message]
2015-03-17 18:19       ` Al Viro
2015-03-17 21:04         ` [RFC PATCH v3 " Omar Sandoval
2015-03-18 13:42           ` David Sterba
2015-03-16 11:33 ` [RFC PATCH 2/5] Remove rw from {,__,do_}blockdev_direct_IO() Omar Sandoval
2015-03-16 11:33 ` [RFC PATCH 3/5] Remove rw from dax_{do_,}io() Omar Sandoval
2015-03-16 11:33 ` [RFC PATCH 4/5] direct_IO: use iov_iter_rw() instead of rw everywhere Omar Sandoval
2015-03-16 11:33 ` [RFC PATCH 5/5] direct_IO: remove rw from a_ops->direct_IO() Omar Sandoval
2015-03-16 18:15 ` [RFC PATCH 0/5] Remove rw parameter from direct_IO() Al Viro
2015-04-05 16:27 ` Al Viro

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