linux-ext4 - Re: [RFC PATCH 1/5] new helper: iov_iter

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Message-ID: <20150317093151.GS20767@twin.jikos.cz>
Date:	Tue, 17 Mar 2015 10:31:51 +0100
From:	David Sterba <dsterba@...e.cz>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Omar Sandoval <osandov@...ndov.com>, linux-fsdevel@...r.kernel.org,
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	Latchesar Ionkov <lucho@...kov.net>,
	Dave Chinner <david@...morbit.com>
Subject: Re: [RFC PATCH 1/5] new helper: iov_iter_rw()

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.
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