tracing/ftrace: make nop tracer using tracer flags

Impact: give an example on how to use specific tracer flags

This patch propose to use the nop tracer to provide an
example for using the tracer's custom flags implementation.

V2: replace structures and defines just after the headers includes for
    cleanliness.
V3: replace defines by enum values.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Steven Noonan <steven@uplinklabs.net>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/trace_nop.c b/kernel/trace/trace_nop.c
index 0e77415..b9767ac 100644 (file)
--- a/kernel/trace/trace_nop.c
+++ b/kernel/trace/trace_nop.c
@@ -12,6 +12,27 @@
 
 #include "trace.h"
 
+/* Our two options */
+enum {
+       TRACE_NOP_OPT_ACCEPT = 0x1,
+       TRACE_NOP_OPT_REFUSE = 0x2
+};
+
+/* Options for the tracer (see trace_options file) */
+static struct tracer_opt nop_opts[] = {
+       /* Option that will be accepted by set_flag callback */
+       { TRACER_OPT(test_nop_accept, TRACE_NOP_OPT_ACCEPT) },
+       /* Option that will be refused by set_flag callback */
+       { TRACER_OPT(test_nop_refuse, TRACE_NOP_OPT_REFUSE) },
+       { } /* Always set a last empty entry */
+};
+
+static struct tracer_flags nop_flags = {
+       /* You can check your flags value here when you want. */
+       .val = 0, /* By default: all flags disabled */
+       .opts = nop_opts
+};
+
 static struct trace_array      *ctx_trace;
 
 static void start_nop_trace(struct trace_array *tr)
@@ -41,6 +62,35 @@ static void nop_trace_reset(struct trace_array *tr)
        stop_nop_trace(tr);
 }
 
+/* It only serves as a signal handler and a callback to
+ * accept or refuse tthe setting of a flag.
+ * If you don't implement it, then the flag setting will be
+ * automatically accepted.
+ */
+static int nop_set_flag(u32 old_flags, u32 bit, int set)
+{
+       /*
+        * Note that you don't need to update nop_flags.val yourself.
+        * The tracing Api will do it automatically if you return 0
+        */
+       if (bit == TRACE_NOP_OPT_ACCEPT) {
+               printk(KERN_DEBUG "nop_test_accept flag set to %d: we accept."
+                       " Now cat trace_options to see the result\n",
+                       set);
+               return 0;
+       }
+
+       if (bit == TRACE_NOP_OPT_REFUSE) {
+               printk(KERN_DEBUG "nop_test_refuse flag set to %d: we refuse."
+                       "Now cat trace_options to see the result\n",
+                       set);
+               return -EINVAL;
+       }
+
+       return 0;
+}
+
+
 struct tracer nop_trace __read_mostly =
 {
        .name           = "nop",
@@ -49,5 +99,7 @@ struct tracer nop_trace __read_mostly =
 #ifdef CONFIG_FTRACE_SELFTEST
        .selftest       = trace_selftest_startup_nop,
 #endif
+       .flags          = &nop_flags,
+       .set_flag       = nop_set_flag
 };