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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 17 Mar 2015 18:19:15 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	dsterba@...e.cz, Omar Sandoval <osandov@...ndov.com>,
	linux-fsdevel@...r.kernel.org, linux-btrfs@...r.kernel.org,
	ceph-devel@...r.kernel.org, linux-cifs@...r.kernel.org,
	osd-dev@...n-osd.org, linux-ext4@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net,
	fuse-devel@...ts.sourceforge.net, cluster-devel@...hat.com,
	jfs-discussion@...ts.sourceforge.net, HPDD-discuss@...1.01.org,
	linux-nfs@...r.kernel.org, linux-nilfs@...r.kernel.org,
	ocfs2-devel@....oracle.com, reiserfs-devel@...r.kernel.org,
	v9fs-developer@...ts.sourceforge.net, xfs@....sgi.com,
	linux-kernel@...r.kernel.org, Chris Mason <clm@...com>,
	Josef Bacik <jbacik@...com>, Yan Zheng <zyan@...hat.com>,
	Sage Weil <sage@...hat.com>, Steve French <sfrench@...ba.org>,
	Boaz Harrosh <ooo@...ctrozaur.com>,
	Benny Halevy <bhalevy@...marydata.com>,
	Jan Kara <jack@...e.cz>, Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Jaegeuk Kim <jaegeuk@...nel.org>,
	Changman Lee <cm224.lee@...sung.com>,
	Miklos Szeredi <miklos@...redi.hu>,
	Steven Whitehouse <swhiteho@...hat.com>,
	Dave Kleikamp <shaggy@...nel.org>,
	Oleg Drokin <oleg.drokin@...el.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	Anna Schumaker <anna.schumaker@...app.com>,
	Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>,
	Mark Fasheh <mfasheh@...e.com>,
	Joel Becker <jlbec@...lplan.org>,
	Eric Van Hensbergen <ericvh@...il.com>,
	Ron Minnich <rminnich@...dia.gov>,
	Latchesar Ionkov <lucho@...kov.net>,
	Dave Chinner <david@...morbit.com>
Subject: Re: [RFC PATCH 1/5] new helper: iov_iter_rw()

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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/