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Re: [RFC PATCH 1/5] new helper: iov_iter_rw()

To: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Subject: Re: [RFC PATCH 1/5] new helper: iov_iter_rw()
From: David Sterba <dsterba@xxxxxxx>
Date: Tue, 17 Mar 2015 10:31:51 +0100
Cc: Omar Sandoval <osandov@xxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, linux-btrfs@xxxxxxxxxxxxxxx, ceph-devel@xxxxxxxxxxxxxxx, linux-cifs@xxxxxxxxxxxxxxx, osd-dev@xxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx, fuse-devel@xxxxxxxxxxxxxxxxxxxxx, cluster-devel@xxxxxxxxxx, jfs-discussion@xxxxxxxxxxxxxxxxxxxxx, HPDD-discuss@xxxxxxxxxxx, linux-nfs@xxxxxxxxxxxxxxx, linux-nilfs@xxxxxxxxxxxxxxx, ocfs2-devel@xxxxxxxxxxxxxx, reiserfs-devel@xxxxxxxxxxxxxxx, v9fs-developer@xxxxxxxxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Chris Mason <clm@xxxxxx>, Josef Bacik <jbacik@xxxxxx>, David Sterba <dsterba@xxxxxxx>, Yan Zheng <zyan@xxxxxxxxxx>, Sage Weil <sage@xxxxxxxxxx>, Steve French <sfrench@xxxxxxxxx>, Boaz Harrosh <ooo@xxxxxxxxxxxxxxx>, Benny Halevy <bhalevy@xxxxxxxxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Theodore Ts'o <tytso@xxxxxxx>, Andreas Dilger <adilger.kernel@xxxxxxxxx>, Jaegeuk Kim <jaegeuk@xxxxxxxxxx>, Changman Lee <cm224.lee@xxxxxxxxxxx>, Miklos Szeredi <miklos@xxxxxxxxxx>, Steven Whitehouse <swhiteho@xxxxxxxxxx>, Dave Kleikamp <shaggy@xxxxxxxxxx>, Oleg Drokin <oleg.drokin@xxxxxxxxx>, Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>, Anna Schumaker <anna.schumaker@xxxxxxxxxx>, Ryusuke Konishi <konishi.ryusuke@xxxxxxxxxxxxx>, Mark Fasheh <mfasheh@xxxxxxxx>, Joel Becker <jlbec@xxxxxxxxxxxx>, Eric Van Hensbergen <ericvh@xxxxxxxxx>, Ron Minnich <rminnich@xxxxxxxxxx>, Latchesar Ionkov <lucho@xxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>
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Mail-followup-to: dsterba@xxxxxxx, Al Viro <viro@xxxxxxxxxxxxxxxxxx>, Omar Sandoval <osandov@xxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, linux-btrfs@xxxxxxxxxxxxxxx, ceph-devel@xxxxxxxxxxxxxxx, linux-cifs@xxxxxxxxxxxxxxx, osd-dev@xxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx, fuse-devel@xxxxxxxxxxxxxxxxxxxxx, cluster-devel@xxxxxxxxxx, jfs-discussion@xxxxxxxxxxxxxxxxxxxxx, HPDD-discuss@xxxxxxxxxxx, linux-nfs@xxxxxxxxxxxxxxx, linux-nilfs@xxxxxxxxxxxxxxx, ocfs2-devel@xxxxxxxxxxxxxx, reiserfs-devel@xxxxxxxxxxxxxxx, v9fs-developer@xxxxxxxxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Chris Mason <clm@xxxxxx>, Josef Bacik <jbacik@xxxxxx>, Yan Zheng <zyan@xxxxxxxxxx>, Sage Weil <sage@xxxxxxxxxx>, Steve French <sfrench@xxxxxxxxx>, Boaz Harrosh <ooo@xxxxxxxxxxxxxxx>, Benny Halevy <bhalevy@xxxxxxxxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Theodore Ts'o <tytso@xxxxxxx>, Andreas Dilger <adilger.kernel@xxxxxxxxx>, Jaegeuk Kim <jaegeuk@xxxxxxxxxx>, Changman Lee <cm224.lee@xxxxxxxxxxx>, Miklos Szeredi <miklos@xxxxxxxxxx>, Steven Whitehouse <swhiteho@xxxxxxxxxx>, Dave Kleikamp <shaggy@xxxxxxxxxx>, Oleg Drokin <oleg.drokin@xxxxxxxxx>, Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>, Anna Schumaker <anna.schumaker@xxxxxxxxxx>, Ryusuke Konishi <konishi.ryusuke@xxxxxxxxxxxxx>, Mark Fasheh <mfasheh@xxxxxxxx>, Joel Becker <jlbec@xxxxxxxxxxxx>, Eric Van Hensbergen <ericvh@xxxxxxxxx>, Ron Minnich <rminnich@xxxxxxxxxx>, Latchesar Ionkov <lucho@xxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>
References: <cover.1426502566.git.osandov@xxxxxxxxxxx> <34dc78b262546e9343e0ed872232a97f5eaa5f15.1426502566.git.osandov@xxxxxxxxxxx> <20150316173605.GX29656@xxxxxxxxxxxxxxxxxx>
Reply-to: dsterba@xxxxxxx
User-agent: Mutt/1.5.23.1-rc1 (2014-03-12)
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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