ftrace: inject markers via trace_marker file

Allow a user to inject a marker (TRACE_PRINT entry) into the trace ring
buffer. The related file operations are derived from code by Frédéric
Weisbecker <fweisbec@gmail.com>.

Signed-off-by: Pekka Paalanen <pq@iki.fi>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Documentation/tracers/mmiotrace.txt

diff --git a/Documentation/tracers/mmiotrace.txt b/Documentation/tracers/mmiotrace.txt
index a4afb56..5bbbe20 100644
--- a/Documentation/tracers/mmiotrace.txt
+++ b/Documentation/tracers/mmiotrace.txt
@@ -36,7 +36,7 @@
 $ echo mmiotrace > /debug/tracing/current_tracer
 $ cat /debug/tracing/trace_pipe > mydump.txt &
 Start X or whatever.
-$ echo "X is up" > /debug/tracing/marker
+$ echo "X is up" > /debug/tracing/trace_marker
 $ echo none > /debug/tracing/current_tracer
 Check for lost events.
 
@@ -59,9 +59,8 @@
 Load the driver you want to trace and use it. Mmiotrace will only catch MMIO
 accesses to areas that are ioremapped while mmiotrace is active.
 
-[Unimplemented feature:]
 During tracing you can place comments (markers) into the trace by
-$ echo "X is up" > /debug/tracing/marker
+$ echo "X is up" > /debug/tracing/trace_marker
 This makes it easier to see which part of the (huge) trace corresponds to
 which action. It is recommended to place descriptive markers about what you
 do.

kernel/trace/trace.c

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 7e7154f..eee1fd9 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2879,6 +2879,66 @@
 	return cnt;
 }
 
+static int tracing_open_mark(struct inode *inode, struct file *filp)
+{
+	int ret;
+
+	ret = tracing_open_generic(inode, filp);
+	if (ret)
+		return ret;
+
+	if (current_trace == &no_tracer)
+		return -ENODEV;
+
+	return 0;
+}
+
+static int mark_printk(const char *fmt, ...)
+{
+	int ret;
+	va_list args;
+	va_start(args, fmt);
+	ret = trace_vprintk(0, fmt, args);
+	va_end(args);
+	return ret;
+}
+
+static ssize_t
+tracing_mark_write(struct file *filp, const char __user *ubuf,
+					size_t cnt, loff_t *fpos)
+{
+	char *buf;
+	char *end;
+	struct trace_array *tr = &global_trace;
+
+	if (current_trace == &no_tracer || !tr->ctrl || tracing_disabled)
+		return -EINVAL;
+
+	if (cnt > TRACE_BUF_SIZE)
+		cnt = TRACE_BUF_SIZE;
+
+	buf = kmalloc(cnt + 1, GFP_KERNEL);
+	if (buf == NULL)
+		return -ENOMEM;
+
+	if (copy_from_user(buf, ubuf, cnt)) {
+		kfree(buf);
+		return -EFAULT;
+	}
+
+	/* Cut from the first nil or newline. */
+	buf[cnt] = '\0';
+	end = strchr(buf, '\n');
+	if (end)
+		*end = '\0';
+
+	cnt = mark_printk("%s\n", buf);
+	kfree(buf);
+	*fpos += cnt;
+
+	return cnt;
+}
+
 static struct file_operations tracing_max_lat_fops = {
 	.open		= tracing_open_generic,
 	.read		= tracing_max_lat_read,
@@ -2910,6 +2970,11 @@
 	.write		= tracing_entries_write,
 };
 
+static struct file_operations tracing_mark_fops = {
+	.open		= tracing_open_mark,
+	.write		= tracing_mark_write,
+};
+
 #ifdef CONFIG_DYNAMIC_FTRACE
 
 static ssize_t
@@ -3027,6 +3092,12 @@
 		pr_warning("Could not create debugfs "
 			   "'trace_entries' entry\n");
 
+	entry = debugfs_create_file("trace_marker", 0220, d_tracer,
+				    NULL, &tracing_mark_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs "
+			   "'trace_marker' entry\n");
+
 #ifdef CONFIG_DYNAMIC_FTRACE
 	entry = debugfs_create_file("dyn_ftrace_total_info", 0444, d_tracer,
 				    &ftrace_update_tot_cnt,
@@ -3040,11 +3111,6 @@
 #endif
 }
 
-#define TRACE_BUF_SIZE 1024
-#define TRACE_PRINT_BUF_SIZE \
-	(sizeof(struct trace_field) - offsetof(struct trace_field, print.buf))
-#define TRACE_CONT_BUF_SIZE sizeof(struct trace_field)
-
 int trace_vprintk(unsigned long ip, const char *fmt, va_list args)
 {
 	static DEFINE_SPINLOCK(trace_buf_lock);

kernel/trace/trace.h

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 648433d..42f65d0 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -124,6 +124,10 @@
 };
 
 #define TRACE_ENTRY_SIZE	sizeof(struct trace_entry)
+#define TRACE_BUF_SIZE		1024
+#define TRACE_PRINT_BUF_SIZE \
+	(sizeof(struct trace_field) - offsetof(struct trace_field, print.buf))
+#define TRACE_CONT_BUF_SIZE	sizeof(struct trace_field)
 
 /*
  * The CPU trace array - it consists of thousands of trace entries