linux-kernel - Re: [PATCH 5/5] CUSE: implement CUSE

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Message-Id: <20080828153235.b005748f.akpm@linux-foundation.org>
Date:	Thu, 28 Aug 2008 15:32:35 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Greg KH <greg@...ah.com>
Cc:	tj@...nel.org, fuse-devel@...ts.sourceforge.net, miklos@...redi.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] CUSE: implement CUSE - Character device in
 Userspace

On Thu, 28 Aug 2008 15:15:25 -0700
Greg KH <greg@...ah.com> wrote:

> On Thu, Aug 28, 2008 at 01:07:40PM -0700, Andrew Morton wrote:
> > On Fri, 29 Aug 2008 03:19:04 +0900
> > Tejun Heo <tj@...nel.org> wrote:
> > > +#define fc_to_cc(_fc)		container_of((_fc), struct cuse_conn, fc)
> > > +#define cdev_to_cc(_cdev)	container_of((_cdev), struct cuse_conn, cdev)
> > > +#define cuse_conn_get(cc)	({mntget((cc)->mnt); cc;})
> > > +#define cuse_conn_put(cc)	mntput((cc)->mnt)
> > 
> > I believe all the above could be implemented in C.
> 
> "traditionally" container_of() is used in #define, not a function call
> as it is just pointer math that can be done at compile time.
> 

Well yeah.  But it isn't a very good tradition.

static inline struct cuse_conn *cdev_to_cc(struct cdev *cdev)
{
	return container_of(cdev, struct cuse_conn, cdev);
}

should generate the same code and is prettier.

Unfortunately it has no additional type-safety.  You can still pass it
the address of a tty_driver.cdev instead of a cuse_conn.cdev and the
compiler will happily swallow it.  Not a big problem in practice though.

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