tracing: Add hist trigger support for pausing and continuing a trace

Allow users to append 'pause' or 'continue' to an existing trigger in
order to have it paused or to have a paused trace continue.

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

to this:

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

Link: http://lkml.kernel.org/r/b672a92c14702cb924cdf6fc27ea1809bed04907.1457029949.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>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d16fa8e1cdbf5b62490fed4abf49062186516b57..7d5c63dd410a97bd36eaf6a98cab9ec57c4ea015 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3837,6 +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            [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"
@@ -3851,7 +3852,11 @@ static const char readme_msg[] =
        "\t    used to specify more or fewer than the default 2048 entries\n"
        "\t    for the hashtable size.\n\n"
        "\t    Reading the 'hist' file for the event will dump the hash\n"
-       "\t    table in its entirety to stdout."
+       "\t    table in its entirety to stdout.\n\n"
+       "\t    The 'pause' parameter can be used to pause an existing hist\n"
+       "\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"
 #endif
 ;
 

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 03ba4530c08c684f278d799f8b0c8344fb588f43..e3fa9c89f12521d981fcd1af7a51bd1ceec996b8 100644 (file)
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -86,6 +86,8 @@ struct hist_trigger_attrs {
        char            *keys_str;
        char            *vals_str;
        char            *sort_key_str;
+       bool            pause;
+       bool            cont;
        unsigned int    map_bits;
 };
 
@@ -193,6 +195,11 @@ static struct hist_trigger_attrs *parse_hist_trigger_attrs(char *trigger_str)
                        attrs->vals_str = kstrdup(str, GFP_KERNEL);
                else if (strncmp(str, "sort=", strlen("sort=")) == 0)
                        attrs->sort_key_str = kstrdup(str, GFP_KERNEL);
+               else if (strcmp(str, "pause") == 0)
+                       attrs->pause = true;
+               else if ((strcmp(str, "cont") == 0) ||
+                        (strcmp(str, "continue") == 0))
+                       attrs->cont = true;
                else if (strncmp(str, "size=", strlen("size=")) == 0) {
                        int map_bits = parse_map_size(str);
 
@@ -871,7 +878,10 @@ static int event_hist_trigger_print(struct seq_file *m,
        if (data->filter_str)
                seq_printf(m, " if %s", data->filter_str);
 
-       seq_puts(m, " [active]");
+       if (data->paused)
+               seq_puts(m, " [paused]");
+       else
+               seq_puts(m, " [active]");
 
        seq_putc(m, '\n');
 
@@ -910,16 +920,30 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
                                 struct event_trigger_data *data,
                                 struct trace_event_file *file)
 {
+       struct hist_trigger_data *hist_data = data->private_data;
        struct event_trigger_data *test;
        int ret = 0;
 
        list_for_each_entry_rcu(test, &file->triggers, list) {
                if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
-                       ret = -EEXIST;
+                       if (hist_data->attrs->pause)
+                               test->paused = true;
+                       else if (hist_data->attrs->cont)
+                               test->paused = false;
+                       else
+                               ret = -EEXIST;
                        goto out;
                }
        }
 
+       if (hist_data->attrs->cont) {
+               ret = -ENOENT;
+               goto out;
+       }
+
+       if (hist_data->attrs->pause)
+               data->paused = true;
+
        if (data->ops->init) {
                ret = data->ops->init(data->ops, data);
                if (ret < 0)
@@ -1011,7 +1035,8 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
         * triggers registered a failure too.
         */
        if (!ret) {
-               ret = -ENOENT;
+               if (!(attrs->pause || attrs->cont))
+                       ret = -ENOENT;
                goto out_free;
        } else if (ret < 0)
                goto out_free;