From: Al Viro <viro@ZenIV.linux.org.uk>
To: dsterba@suse.cz, Omar Sandoval <osandov@osandov.com>,
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Ron Minnich <rminnich@sandia.gov>,
Latchesar Ionkov <lucho@ionkov.net>,
Dave Chinner <david@fromorbit.com>
Subject: Re: [RFC PATCH 1/5] new helper: iov_iter_rw()
Date: Tue, 17 Mar 2015 18:19:15 +0000 [thread overview]
Message-ID: <20150317181910.GK29656@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20150317093151.GS20767@twin.jikos.cz>
On Tue, Mar 17, 2015 at 10:31:51AM +0100, David Sterba wrote:
> 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.
... and you are getting
a) use of rather lousy gccism when plain C would do
b) double evaluation since you've got it wrong (should've been
__iter.type & RW_MASK, if you do it that way). As it is, if argument has
any side effects, your variant will trigger those twice - even if the
destination of the assignment is never used, the side effects remain.
I agree that it could use /* use ?: for typechecking */, but let's not go into
({...}) land unless we absolutely have to.
next prev parent reply other threads:[~2015-03-17 18:21 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
2015-03-17 18:19 ` Al Viro [this message]
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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