ftrace: add README

make it easier for newbies to find their way around.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 39 insertions, 1 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 61d2f0228866..c736dd2e068d 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -995,6 +995,7 @@ print_trace_fmt(struct seq_file *m, struct trace_iterator *iter)
                         seq_printf(m, " <-");
                         seq_print_ip_sym(m, entry->fn.parent_ip, sym_flags);
                 }
+                seq_printf(m, "\n");
                 break;
         case TRACE_CTX:
                 S = entry->ctx.prev_state < sizeof(state_to_char) ?
@@ -1007,7 +1008,6 @@ print_trace_fmt(struct seq_file *m, struct trace_iterator *iter)
                            entry->ctx.next_prio);
                 break;
         }
-        seq_printf(m, "\n");
 }
 
 static int trace_empty(struct trace_iterator *iter)
@@ -1332,6 +1332,39 @@ static struct file_operations tracing_iter_fops = {
         .write = tracing_iter_ctrl_write,
 };
 
+static const char readme_msg[] =
+        "tracing mini-HOWTO:\n\n"
+        "# mkdir /debug\n"
+        "# mount -t debugfs nodev /debug\n\n"
+        "# cat /debug/tracing/available_tracers\n"
+        "wakeup preemptirqsoff preemptoff irqsoff ftrace sched_switch none\n\n"
+        "# cat /debug/tracing/current_tracer\n"
+        "none\n"
+        "# echo sched_switch > /debug/tracing/current_tracer\n"
+        "# cat /debug/tracing/current_tracer\n"
+        "sched_switch\n"
+        "# cat /debug/tracing/iter_ctrl\n"
+        "noprint-parent nosym-offset nosym-addr noverbose\n"
+        "# echo print-parent > /debug/tracing/iter_ctrl\n"
+        "# echo 1 > /debug/tracing/tracing_enabled\n"
+        "# cat /debug/tracing/trace > /tmp/trace.txt\n"
+        "echo 0 > /debug/tracing/tracing_enabled\n"
+;
+
+static ssize_t
+tracing_readme_read(struct file *filp, char __user *ubuf,
+                       size_t cnt, loff_t *ppos)
+{
+        return simple_read_from_buffer(ubuf, cnt, ppos,
+                                        readme_msg, strlen(readme_msg));
+}
+
+static struct file_operations tracing_readme_fops = {
+        .open = tracing_open_generic,
+        .read = tracing_readme_read,
+};
+
+
 static ssize_t
 tracing_ctrl_read(struct file *filp, char __user *ubuf,
                   size_t cnt, loff_t *ppos)
@@ -1598,6 +1631,11 @@ static __init void tracer_init_debugfs(void)
         if (!entry)
                 pr_warning("Could not create debugfs "
                            "'tracing_threash' entry\n");
+        entry = debugfs_create_file("README", 0644, d_tracer,
+                                    NULL, &tracing_readme_fops);
+        if (!entry)
+                pr_warning("Could not create debugfs 'README' entry\n");
+
 
 #ifdef CONFIG_DYNAMIC_FTRACE
         entry = debugfs_create_file("dyn_ftrace_total_info", 0444, d_tracer,