1 files changed, 24 insertions, 1 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c2e2c2310374..9e3120b8a2ad 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2400,6 +2400,27 @@ static void test_ftrace_alive(struct seq_file *m)
         seq_printf(m, "#          MAY BE MISSING FUNCTION EVENTS\n");
 }
 
+#ifdef CONFIG_TRACER_MAX_TRACE
+static void print_snapshot_help(struct seq_file *m, struct trace_iterator *iter)
+{
+        if (iter->trace->allocated_snapshot)
+                seq_printf(m, "#\n# * Snapshot is allocated *\n#\n");
+        else
+                seq_printf(m, "#\n# * Snapshot is freed *\n#\n");
+
+        seq_printf(m, "# Snapshot commands:\n");
+        seq_printf(m, "# echo 0 > snapshot : Clears and frees snapshot buffer\n");
+        seq_printf(m, "# echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.\n");
+        seq_printf(m, "#                      Takes a snapshot of the main buffer.\n");
+        seq_printf(m, "# echo 2 > snapshot : Clears snapshot buffer (but does not allocate)\n");
+        seq_printf(m, "#                      (Doesn't have to be '2' works with any number that\n");
+        seq_printf(m, "#                       is not a '0' or '1')\n");
+}
+#else
+/* Should never be called */
+static inline void print_snapshot_help(struct seq_file *m, struct trace_iterator *iter) { }
+#endif
+
 static int s_show(struct seq_file *m, void *v)
 {
         struct trace_iterator *iter = v;
@@ -2411,7 +2432,9 @@ static int s_show(struct seq_file *m, void *v)
                         seq_puts(m, "#\n");
                         test_ftrace_alive(m);
                 }
-                if (iter->trace && iter->trace->print_header)
+                if (iter->snapshot && trace_empty(iter))
+                        print_snapshot_help(m, iter);
+                else if (iter->trace && iter->trace->print_header)
                         iter->trace->print_header(m);
                 else
                         trace_default_header(m);