Subject: sysfs: Add /sys/kernel/realtime entry
From: Clark Williams <williams@redhat.com>
Date: Sat Jul 30 21:55:53 2011 -0500

From: Clark Williams <williams@redhat.com>

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: Thomas Gleixner <tglx@linutronix.de>


---
 kernel/ksysfs.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)
---
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -138,6 +138,15 @@ KERNEL_ATTR_RO(vmcoreinfo);
 
 #endif /* CONFIG_CRASH_CORE */
 
+#if defined(CONFIG_PREEMPT_RT)
+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)
@@ -229,6 +238,9 @@ static struct attribute * kernel_attrs[]
 	&rcu_expedited_attr.attr,
 	&rcu_normal_attr.attr,
 #endif
+#ifdef CONFIG_PREEMPT_RT
+	&realtime_attr.attr,
+#endif
 	NULL
 };