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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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