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    Subject[for-next][PATCH 13/30] tracing: Add hist trigger support for clearing a trace
    From: Tom Zanussi <tom.zanussi@linux.intel.com>

    Allow users to append 'clear' to an existing trigger in order to have
    the hash table cleared.

    This expands the hist trigger syntax from this:
    # echo hist:keys=xxx:vals=yyy:sort=zzz.descending:pause/cont \
    [ if filter] >> event/trigger

    to this:

    # echo hist:keys=xxx:vals=yyy:sort=zzz.descending:pause/cont/clear \
    [ if filter] >> event/trigger

    Link: http://lkml.kernel.org/r/ae15dd0d9b2f7af07a37c1ff682063e2dbcdf160.1457029949.git.tom.zanussi@linux.intel.com

    Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
    Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Reviewed-by: Namhyung Kim <namhyung@kernel.org>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    kernel/trace/trace.c | 5 ++++-
    kernel/trace/trace_events_hist.c | 24 ++++++++++++++++++++++--
    2 files changed, 26 insertions(+), 3 deletions(-)

    diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
    index 7d5c63dd410a..4097cd3763f7 100644
    --- a/kernel/trace/trace.c
    +++ b/kernel/trace/trace.c
    @@ -3837,7 +3837,7 @@ static const char readme_msg[] =
    "\t [:values=<field1[,field2,...]>]\n"
    "\t [:sort=<field1[,field2,...]>]\n"
    "\t [:size=#entries]\n"
    - "\t [:pause][:continue]\n"
    + "\t [:pause][:continue][:clear]\n"
    "\t [if <filter>]\n\n"
    "\t When a matching event is hit, an entry is added to a hash\n"
    "\t table using the key(s) and value(s) named, and the value of a\n"
    @@ -3857,6 +3857,9 @@ static const char readme_msg[] =
    "\t trigger or to start a hist trigger but not log any events\n"
    "\t until told to do so. 'continue' can be used to start or\n"
    "\t restart a paused hist trigger.\n\n"
    + "\t The 'clear' parameter will clear the contents of a running\n"
    + "\t hist trigger and leave its current paused/active state\n"
    + "\t unchanged.\n\n"
    #endif
    ;

    diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
    index e3fa9c89f125..83cb25e067ad 100644
    --- a/kernel/trace/trace_events_hist.c
    +++ b/kernel/trace/trace_events_hist.c
    @@ -88,6 +88,7 @@ struct hist_trigger_attrs {
    char *sort_key_str;
    bool pause;
    bool cont;
    + bool clear;
    unsigned int map_bits;
    };

    @@ -200,6 +201,8 @@ static struct hist_trigger_attrs *parse_hist_trigger_attrs(char *trigger_str)
    else if ((strcmp(str, "cont") == 0) ||
    (strcmp(str, "continue") == 0))
    attrs->cont = true;
    + else if (strcmp(str, "clear") == 0)
    + attrs->clear = true;
    else if (strncmp(str, "size=", strlen("size=")) == 0) {
    int map_bits = parse_map_size(str);

    @@ -916,6 +919,21 @@ static struct event_trigger_ops *event_hist_get_trigger_ops(char *cmd,
    return &event_hist_trigger_ops;
    }

    +static void hist_clear(struct event_trigger_data *data)
    +{
    + struct hist_trigger_data *hist_data = data->private_data;
    + bool paused;
    +
    + paused = data->paused;
    + data->paused = true;
    +
    + synchronize_sched();
    +
    + tracing_map_clear(hist_data->map);
    +
    + data->paused = paused;
    +}
    +
    static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
    struct event_trigger_data *data,
    struct trace_event_file *file)
    @@ -930,13 +948,15 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
    test->paused = true;
    else if (hist_data->attrs->cont)
    test->paused = false;
    + else if (hist_data->attrs->clear)
    + hist_clear(test);
    else
    ret = -EEXIST;
    goto out;
    }
    }

    - if (hist_data->attrs->cont) {
    + if (hist_data->attrs->cont || hist_data->attrs->clear) {
    ret = -ENOENT;
    goto out;
    }
    @@ -1035,7 +1055,7 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
    * triggers registered a failure too.
    */
    if (!ret) {
    - if (!(attrs->pause || attrs->cont))
    + if (!(attrs->pause || attrs->cont || attrs->clear))
    ret = -ENOENT;
    goto out_free;
    } else if (ret < 0)
    --
    2.8.0.rc3

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