ftrace: provide an id file for each event

Since not every event has a format file to read the id from,
expose it explicitly in a separate file.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <20090319194233.372534033@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 36 insertions, 0 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index c88227b3b9db..7763db8fd0b3 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -412,6 +412,29 @@ event_format_read(struct file *filp, char __user *ubuf, size_t cnt,
         return r;
 }
 
+static ssize_t
+event_id_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;
+        int r;
+
+        if (*ppos)
+                return 0;
+
+        s = kmalloc(sizeof(*s), GFP_KERNEL);
+        if (!s)
+                return -ENOMEM;
+
+        trace_seq_init(s);
+        trace_seq_printf(s, "%d\n", call->id);
+
+        r = simple_read_from_buffer(ubuf, cnt, ppos,
+                                    s->buffer, s->len);
+        kfree(s);
+        return r;
+}
+
 static const struct seq_operations show_event_seq_ops = {
         .start = t_start,
         .next = t_next,
@@ -452,6 +475,11 @@ static const struct file_operations ftrace_event_format_fops = {
         .read = event_format_read,
 };
 
+static const struct file_operations ftrace_event_id_fops = {
+        .open = tracing_open_generic,
+        .read = event_id_read,
+};
+
 static struct dentry *event_trace_events_dir(void)
 {
         static struct dentry *d_tracer;
@@ -550,6 +578,14 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events)
                                    "'%s/enable' entry\n", call->name);
         }
 
+        if (call->id) {
+                entry = debugfs_create_file("id", 0444, call->dir, call,
+                                &ftrace_event_id_fops);
+                if (!entry)
+                        pr_warning("Could not create debugfs '%s/id' entry\n",
+                                        call->name);
+        }
+
         /* A trace may not want to export its format */
         if (!call->show_format)
                 return 0;