tracing: add format file to describe event struct fields
[linux-2.6.git] / kernel / trace / trace_events.c
index 26069fa..d57a772 100644 (file)
@@ -3,6 +3,9 @@
  *
  * Copyright (C) 2008 Red Hat Inc, Steven Rostedt <srostedt@redhat.com>
  *
+ *  - Added format output of fields of the trace point.
+ *    This was based off of work by Tom Zanussi <tzanussi@gmail.com>.
+ *
  */
 
 #include <linux/debugfs.h>
@@ -444,6 +447,42 @@ event_available_types_read(struct file *filp, char __user *ubuf, size_t cnt,
        return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
 }
 
+static ssize_t
+event_format_read(struct file *filp, char __user *ubuf, size_t cnt,
+                 loff_t *ppos)
+{
+       struct ftrace_event_call *call = filp->private_data;
+       struct trace_seq *s;
+       char *buf;
+       int r;
+
+       s = kmalloc(sizeof(*s), GFP_KERNEL);
+       if (!s)
+               return -ENOMEM;
+
+       trace_seq_init(s);
+
+       if (*ppos)
+               return 0;
+
+       r = call->show_format(s);
+       if (!r) {
+               /*
+                * ug!  The format output is bigger than a PAGE!!
+                */
+               buf = "FORMAT TOO BIG\n";
+               r = simple_read_from_buffer(ubuf, cnt, ppos,
+                                             buf, strlen(buf));
+               goto out;
+       }
+
+       r = simple_read_from_buffer(ubuf, cnt, ppos,
+                                   s->buffer, s->len);
+ out:
+       kfree(s);
+       return r;
+}
+
 static const struct seq_operations show_event_seq_ops = {
        .start = t_start,
        .next = t_next,
@@ -490,6 +529,11 @@ static const struct file_operations ftrace_available_types_fops = {
        .read = event_available_types_read,
 };
 
+static const struct file_operations ftrace_event_format_fops = {
+       .open = tracing_open_generic,
+       .read = event_format_read,
+};
+
 static struct dentry *event_trace_events_dir(void)
 {
        static struct dentry *d_tracer;
@@ -602,7 +646,17 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events)
                                    &ftrace_available_types_fops);
        if (!entry)
                pr_warning("Could not create debugfs "
-                          "'%s/type' available_types\n", call->name);
+                          "'%s/available_types' entry\n", call->name);
+
+       /* A trace may not want to export its format */
+       if (!call->show_format)
+               return 0;
+
+       entry = debugfs_create_file("format", 0444, call->dir, call,
+                                   &ftrace_event_format_fops);
+       if (!entry)
+               pr_warning("Could not create debugfs "
+                          "'%s/format' entry\n", call->name);
 
        return 0;
 }