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Subject[PATCH 2/3] 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.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
kernel/trace/trace_nop.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 48 insertions(+), 0 deletions(-)
diff --git a/kernel/trace/trace_nop.c b/kernel/trace/trace_nop.c
index 0e77415..1d8b4f8 100644
--- a/kernel/trace/trace_nop.c
+++ b/kernel/trace/trace_nop.c
@@ -41,6 +41,52 @@ static void nop_trace_reset(struct trace_array *tr)
stop_nop_trace(tr);
}

+#define TRACE_NOP_OPT_ACCEPT 0x1
+#define 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 the 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
+};
+
+/* 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 +95,7 @@ struct tracer nop_trace __read_mostly =
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_nop,
#endif
+ .flags = &nop_flags,
+ .set_flag = nop_set_flag
};

--
1.5.2.5

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