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>

1 files changed, 52 insertions, 0 deletions

diff --git a/kernel/trace/trace_nop.c b/kernel/trace/trace_nop.c
index 0e77415caed3..b9767acd30ac 100644
--- 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
 };