tracing: splice support for tracing_pipe

Added and implemented tracing_pipe_fops->splice_read(). This allows
userspace programs to get tracing data more efficiently.

Signed-off-by: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>

kernel/trace/trace.h

@@ -353,6 +353,12 @@ struct tracer {
 	ssize_t			(*read)(struct trace_iterator *iter,
 					struct file *filp, char __user *ubuf,
 					size_t cnt, loff_t *ppos);
+	ssize_t			(*splice_read)(struct trace_iterator *iter,
+					       struct file *filp,
+					       loff_t *ppos,
+					       struct pipe_inode_info *pipe,
+					       size_t len,
+					       unsigned int flags);
 #ifdef CONFIG_FTRACE_STARTUP_TEST
 	int			(*selftest)(struct tracer *trace,
 					    struct trace_array *tr);