[tip:perf/core] perf: Comment /proc/sys/kernel/perf_event_paranoid to be part of user ABI

[tip-bot for Vince Weaver <vweaver1@eecs.utk.edu>]

Commit-ID:  aa4a221875873d2a1f9656cb7fd7e545e952b4fa
Gitweb:     http://git.kernel.org/tip/aa4a221875873d2a1f9656cb7fd7e545e952b4fa
Author:     Vince Weaver <vweaver1@eecs.utk.edu>
AuthorDate: Fri, 3 Jun 2011 17:54:40 -0400
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Sat, 4 Jun 2011 12:22:04 +0200

perf: Comment /proc/sys/kernel/perf_event_paranoid to be part of user ABI

Turns out that distro packages use this file as an indicator of
the perf event subsystem - this is easier to check for from scripts
than the existence of the system call.

This is easy enough to keep around for the kernel, so add a
comment to make sure it stays so.

Signed-off-by: Vince Weaver <vweaver1@eecs.utk.edu>
Cc: David Ahern <dsahern@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: paulus@samba.org
Cc: acme@redhat.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.00.1106031751170.29381@cl320.eecs.utk.edu
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/sysctl.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 4fc9244..f175d98 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -938,6 +938,12 @@ static struct ctl_table kern_table[] = {
 	},
 #endif
 #ifdef CONFIG_PERF_EVENTS
+	/*
+	 * User-space scripts rely on the existence of this file
+	 * as a feature check for perf_events being enabled.
+	 *
+	 * So it's an ABI, do not remove!
+	 */
 	{
 		.procname	= "perf_event_paranoid",
 		.data		= &sysctl_perf_event_paranoid,