ftrace: sysrq-z to dump the buffers

Impact: add SysRq-z support to dump trace buffers

Allows one to force an ftrace dump from sysrq
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

drivers/char/sysrq.c

@@ -274,6 +274,22 @@ static struct sysrq_key_op sysrq_showstate_blocked_op = {
 	.enable_mask	= SYSRQ_ENABLE_DUMP,
 };
 
+#ifdef CONFIG_TRACING
+#include <linux/ftrace.h>
+
+static void sysrq_ftrace_dump(int key, struct tty_struct *tty)
+{
+	ftrace_dump();
+}
+static struct sysrq_key_op sysrq_ftrace_dump_op = {
+	.handler	= sysrq_ftrace_dump,
+	.help_msg	= "dumpZ-ftrace-buffer",
+	.action_msg	= "Dump ftrace buffer",
+	.enable_mask	= SYSRQ_ENABLE_DUMP,
+};
+#else
+#define sysrq_ftrace_dump_op (*(struct sysrq_key_op *)0)
+#endif
 
 static void sysrq_handle_showmem(int key, struct tty_struct *tty)
 {
@@ -406,7 +422,7 @@ static struct sysrq_key_op *sysrq_key_table[36] = {
 	NULL,				/* x */
 	/* y: May be registered on sparc64 for global register dump */
 	NULL,				/* y */
-	NULL				/* z */
+	&sysrq_ftrace_dump_op,		/* z */
 };
 
 /* key2index calculation, -1 on invalid index */