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Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filt

To: Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filtering
From: Ingo Molnar <mingo@elte.hu>
Date: Mon, 16 May 2011 18:52:49 +0200
Cc: Peter Zijlstra <peterz@infradead.org>, James Morris <jmorris@namei.org>, Will Drewry <wad@chromium.org>, linux-kernel@vger.kernel.org, Frederic Weisbecker <fweisbec@gmail.com>, Eric Paris <eparis@redhat.com>, kees.cook@canonical.com, agl@chromium.org, "Serge E. Hallyn" <serge@hallyn.com>, Ingo Molnar <mingo@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>, Michal Marek <mmarek@suse.cz>, Oleg Nesterov <oleg@redhat.com>, Roland McGrath <roland@redhat.com>, Jiri Slaby <jslaby@suse.cz>, David Howells <dhowells@redhat.com>, Russell King <linux@arm.linux.org.uk>, Michal Simek <monstr@monstr.eu>, Ralf Baechle <ralf@linux-mips.org>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, linux390@de.ibm.com, Paul Mundt <lethal@linux-sh.org>, "David S. Miller" <davem@davemloft.net>, Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org, linux-arm-kernel <linux-arm-kernel@lists.infradead.org>, linux-mips@linux-mips.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, Linus Torvalds <torvalds@linux-foundation.org>
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* Steven Rostedt <rostedt@goodmis.org> wrote:

> I'm a bit nervous about the 'active' role of (trace_)events, because of the 
> way multiple callbacks can be registered. How would:
> 
>       err = event_x();
>       if (err == -EACCESS) {
> 
> be handled? [...]

The default behavior would be something obvious: to trigger all callbacks and 
use the first non-zero return value.

> [...] Would we need a way to prioritize which call back gets the return 
> value? One way I guess would be to add a check_event option, where you pass 
> in an ENUM of the event you want:
> 
>       event_x();
>       err = check_event_x(MYEVENT);
> 
> If something registered itself as "MYEVENT" to event_x, then you get the 
> return code of MYEVENT. If the MYEVENT was not registered, a -ENODEV or 
> something could be returned. I'm sure we could even optimize it such a way if 
> no active events have been registered to event_x, that check_event_x() will 
> return -ENODEV without any branches.

I would keep it simple and extensible - that way we can complicate it when the 
need arises! :)

Thanks,

        Ingo

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