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

To: Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filtering
From: Steven Rostedt <rostedt@goodmis.org>
Date: Mon, 16 May 2011 13:03:42 -0400
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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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.

> 
> > [...] 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! :)

The above is rather trivial to implement. I don't think it complicates
anything.

-- Steve



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