tracing: add format files for ftrace default entries

Impact: allow user apps to read binary format of basic ftrace entries

Currently, only defined raw events export their formats so a binary
reader can parse them. There's no reason that the default ftrace entries
can't export their formats.

This patch adds a subsystem called "ftrace" in the events directory
that includes the ftrace entries for basic ftrace recorded items.

These only have three files in the events directory:

 type             : printf
 available_types  : printf
 format           : format for the event entry

For example:

 # cat /debug/tracing/events/ftrace/wakeup/format
name: wakeup
ID: 3
format:
        field:unsigned char type;       offset:0;       size:1;
        field:unsigned char flags;      offset:1;       size:1;
        field:unsigned char preempt_count;      offset:2;       size:1;
        field:int pid;  offset:4;       size:4;
        field:int tgid; offset:8;       size:4;

        field:unsigned int prev_pid;    offset:12;      size:4;
        field:unsigned char prev_prio;  offset:16;      size:1;
        field:unsigned char prev_state; offset:17;      size:1;
        field:unsigned int next_pid;    offset:20;      size:4;
        field:unsigned char next_prio;  offset:24;      size:1;
        field:unsigned char next_state; offset:25;      size:1;
        field:unsigned int next_cpu;    offset:28;      size:4;

print fmt: "%u:%u:%u  ==+ %u:%u:%u [%03u]"

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 210e71ff82d..4488d90e75e 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -656,11 +656,13 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events)
                 return -1;
         }
 
-        entry = debugfs_create_file("enable", 0644, call->dir, call,
-                                    &ftrace_enable_fops);
-        if (!entry)
-                pr_warning("Could not create debugfs "
-                           "'%s/enable' entry\n", call->name);
+        if (call->regfunc) {
+                entry = debugfs_create_file("enable", 0644, call->dir, call,
+                                            &ftrace_enable_fops);
+                if (!entry)
+                        pr_warning("Could not create debugfs "
+                                   "'%s/enable' entry\n", call->name);
+        }
 
         /* Only let type be writable, if we can change it */
         entry = debugfs_create_file("type",