From: Clark Williams <williams@redhat.com>
Date: Sat, 30 Jul 2011 21:55:53 -0500
Subject: sysfs: Add /sys/kernel/realtime entry
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 6c1a03be3e8b7d328d4b03d2e2c0588f19ec73d1
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

Add a /sys/kernel entry to indicate that the kernel is a
realtime kernel.

Clark says that he needs this for udev rules, udev needs to evaluate
if its a PREEMPT_RT kernel a few thousand times and parsing uname
output is too slow or so.

Are there better solutions? Should it exist and return 0 on !-rt?

Signed-off-by: Clark Williams <williams@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 kernel/ksysfs.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -140,6 +140,15 @@ KERNEL_ATTR_RO(vmcoreinfo);
 
 #endif /* CONFIG_CRASH_CORE */
 
+#if defined(CONFIG_PREEMPT_RT_FULL)
+static ssize_t  realtime_show(struct kobject *kobj,
+			      struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%d\n", 1);
+}
+KERNEL_ATTR_RO(realtime);
+#endif
+
 /* whether file capabilities are enabled */
 static ssize_t fscaps_show(struct kobject *kobj,
 				  struct kobj_attribute *attr, char *buf)
@@ -258,6 +267,9 @@ static struct attribute * kernel_attrs[]
 #ifdef CONFIG_SUSE_KERNEL_SUPPORTED
 	&supported_attr.attr,
 #endif
+#ifdef CONFIG_PREEMPT_RT_FULL
+	&realtime_attr.attr,
+#endif
 	NULL
 };