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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: Tue, 17 May 2011 14:42:12 +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:

> On Mon, 2011-05-16 at 18:52 +0200, Ingo Molnar wrote:
> > * 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.
> 
> But how do we know which callback that was from? There's no ordering of what 
> callbacks are called first.

We do not have to know that - nor do the calling sites care in general. Do you 
have some specific usecase in mind where the identity of the callback that 
generates a match matters?

Thanks,

        Ingo

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