linux-kernel - Re: [PATCH 6/8] ptrace: arch

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Date:	Fri, 21 Mar 2008 14:50:01 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Roland McGrath <roland@...hat.com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	David Miller <davem@...emloft.net>, sparclinux@...r.kernel.org,
	Paul Mackerras <paulus@...ba.org>, linuxppc-dev@...abs.org,
	Richard Henderson <rth@...ddle.net>, tony.luck@...el.com,
	linux-ia64@...r.kernel.org
Subject: Re: [PATCH 6/8] ptrace: arch_ptrace -ENOSYS return

On Thu, 20 Mar 2008, Roland McGrath wrote:
> > Wouldn't it be nicer to just let "arch_ptrace()" return a flag saying 
> > whether it handled things or not?
> 
> It would certainly be nicer.  I would prefer:
> 
> extern int arch_ptrace(struct task_struct *child, long request,
>        	    	       long addr, long data, long *retval);
> 
> where it returns an error code or it returns 0 and *retval is the value
> or it returns 1 and it didn't do anything.
>
> So this ugliness seemed like a better bet than waiting for 20 more
> arch sign-offs before any of it could go in.  You are certainly in a
> position to just change the generic signature and make every arch do
> the update (or fix your typos if you just tweak them all blind), and
> let them grumble.  I did not presume to do so.

What about adding a CONFIG_ARCH_HAS_PTRACE2, which is set by the archs
which are converted. For those which are not you add a fallback
implementation:

#ifndef CONFIG_ARCH_HAS_PTRACE2
static int arch_ptrace2(whatever your favourite interface)
{
	ret = arch_ptrace();
	return do_ugly_fixups(ret);
}
#endif

That way you introduce the new interface and convert one or two archs
initialy without breaking the other 22.

At the same time you mark arch_ptrace() deprecated so it will get the
attention of the arch maintainers pretty fast. Once all archs are
converted we can remove the config flag and the fallback quirk.

Thanks,
	tglx
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