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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: Peter Zijlstra <peterz@infradead.org>
Date: Fri, 13 May 2011 14:43:32 +0200
Cc: James Morris <jmorris@namei.org>, Will Drewry <wad@chromium.org>, linux-kernel@vger.kernel.org, Steven Rostedt <rostedt@goodmis.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@lists.infradead.org, microblaze-uclinux@itee.uq.edu.au, 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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Original-recipient: rfc822;linux-mips@linux-mips.org
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Sender: linux-mips-bounce@linux-mips.org
On Fri, 2011-05-13 at 14:39 +0200, Peter Zijlstra wrote:
> 
> >       event_vfs_getname(result);
> >       result = check_event_vfs_getname(result); 

Another fundamental difference is how to treat the callback chains for
these two.

Observers won't have a return value and are assumed to never fail,
therefore we can always call every entry on the callback list.

Active things otoh do have a return value, and thus we need to have
semantics that define what to do with that during callback iteration,
when to continue and when to break. Thus for active elements its
impossible to guarantee all entries will indeed be called.


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