ftrace: add trace pipe header pluggin

This patch adds a method for open_pipe and open_read to the pluggins
so that they can add a header to the trace pipe call.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/trace/trace.c

@@ -2307,11 +2307,15 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
 	if (!iter)
 		return -ENOMEM;
 
+	mutex_lock(&trace_types_lock);
 	iter->tr = &global_trace;
 	iter->trace = current_trace;
-
 	filp->private_data = iter;
 
+	if (iter->trace->pipe_open)
+		iter->trace->pipe_open(iter);
+	mutex_unlock(&trace_types_lock);
+
 	return 0;
 }
 
@@ -2380,13 +2384,24 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 		return cnt;
 	}
 
+	mutex_lock(&trace_types_lock);
+	if (iter->trace->read) {
+		ret = iter->trace->read(iter, filp, ubuf, cnt, ppos);
+		if (ret) {
+			read = ret;
+			goto out;
+		}
+	}
+
 	trace_seq_reset(&iter->seq);
 	start = 0;
 
 	while (trace_empty(iter)) {
 
-		if ((filp->f_flags & O_NONBLOCK))
-			return -EAGAIN;
+		if ((filp->f_flags & O_NONBLOCK)) {
+			read = -EAGAIN;
+			goto out;
+		}
 
 		/*
 		 * This is a make-shift waitqueue. The reason we don't use
@@ -2400,16 +2415,22 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 		set_current_state(TASK_INTERRUPTIBLE);
 		iter->tr->waiter = current;
 
+		mutex_unlock(&trace_types_lock);
+
 		/* sleep for one second, and try again. */
 		schedule_timeout(HZ);
 
+		mutex_lock(&trace_types_lock);
+
 		iter->tr->waiter = NULL;
 
-		if (signal_pending(current))
-			return -EINTR;
+		if (signal_pending(current)) {
+			read = -EINTR;
+			goto out;
+		}
 
 		if (iter->trace != current_trace)
-			return 0;
+			goto out;
 
 		/*
 		 * We block until we read something and tracing is disabled.
@@ -2428,7 +2449,7 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 
 	/* stop when tracing is finished */
 	if (trace_empty(iter))
-		return 0;
+		goto out;
 
 	if (cnt >= PAGE_SIZE)
 		cnt = PAGE_SIZE - 1;
@@ -2518,6 +2539,9 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 	if (ret)
 		read = -EFAULT;
 
+out:
+	mutex_unlock(&trace_types_lock);
+
 	return read;
 }
 

kernel/trace/trace.h

@@ -135,9 +135,13 @@ struct tracer {
 	void			(*init)(struct trace_array *tr);
 	void			(*reset)(struct trace_array *tr);
 	void			(*open)(struct trace_iterator *iter);
+	void			(*pipe_open)(struct trace_iterator *iter);
 	void			(*close)(struct trace_iterator *iter);
 	void			(*start)(struct trace_iterator *iter);
 	void			(*stop)(struct trace_iterator *iter);
+	ssize_t			(*read)(struct trace_iterator *iter,
+					struct file *filp, char __user *ubuf,
+					size_t cnt, loff_t *ppos);
 	void			(*ctrl_update)(struct trace_array *tr);
 #ifdef CONFIG_FTRACE_STARTUP_TEST
 	int			(*selftest)(struct tracer *trace,
@@ -160,6 +164,7 @@ struct trace_seq {
 struct trace_iterator {
 	struct trace_array	*tr;
 	struct tracer		*trace;
+	void			*private;
 	long			last_overrun[NR_CPUS];
 	long			overrun[NR_CPUS];