linux-kernel - Re: [PATCH] ifdef struct task

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Message-Id: <20070806220833.4040f861.akpm@linux-foundation.org>
Date:	Mon, 6 Aug 2007 22:08:33 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	Alexey Dobriyan <adobriyan@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ifdef struct task_struct::security

On Mon, 6 Aug 2007 15:31:12 -0500 "Serge E. Hallyn" <serge@...lyn.com> wrote:

> Quoting Alexey Dobriyan (adobriyan@...il.com):
> > For those who don't care about CONFIG_SECURITY.
> 
> I'm quite sure we started that way, but the ifdefs were considered
> too much of an eyesore.

argh, y'all stop top-posting at me.

> If this is now acceptable, then the same thing might be considered
> for inode->i_security, kern_ipc_perm.security, etc.  Getting rid of
> just the task->security seems overly half-hearted.
> 
> -serge
> 
> > Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> > ---
> > 
> >  include/linux/sched.h |    3 ++-
> >  kernel/fork.c         |    2 ++
> >  2 files changed, 4 insertions(+), 1 deletion(-)
> > 
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1086,8 +1086,9 @@ struct task_struct {
> >  	int (*notifier)(void *priv);
> >  	void *notifier_data;
> >  	sigset_t *notifier_mask;
> > -	
> > +#ifdef CONFIG_SECURITY
> >  	void *security;
> > +#endif
> >  	struct audit_context *audit_context;
> >  	seccomp_t seccomp;
> >  
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -1066,7 +1066,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
> >  	do_posix_clock_monotonic_gettime(&p->start_time);
> >  	p->real_start_time = p->start_time;
> >  	monotonic_to_bootbased(&p->real_start_time);
> > +#ifdef CONFIG_SECURITY
> >  	p->security = NULL;
> > +#endif
> >  	p->io_context = NULL;
> >  	p->io_wait = NULL;
> >  	p->audit_context = NULL;
> > 

I think it's OK.  Removing 4 or 8 bytes from the task_struct is a decent win,
and an ifdef at the definition site (unavoidable) and at a single
initialisation site where there are lots of other similar ifdefs is pretty
minimal hurt.

In fact, looking through all those "= 0" and "= NULL" statements in
copy_process() makes one wonder whether we should be memsetting that guy to
zero then selectively copying things out of current, rather than the
present vice-versa.

A possibly-neat way of doing this would be to move all the task_struct fields which
are zeroed in copy_process() into a separate anonymous struct in
task_struct, then wipe only that in copy_process().  One would need to be
careful about the hand-arranged grouping which has been done in the
task_struct however.

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