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>

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 4fc9244..f175d98 100644 (file)
--- 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,