ftrace: trace_pipe implement NONBLOCK

This patch implements "NONBLOCK" for trace_pipe. If the trace_pipe is opened
with O_NONBLOCK, then the trace_pipe read will not block when buffer is empty.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2af940433e96..3b4eaf36ed5d 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2233,6 +2233,10 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
         start = 0;
 
         while (trace_empty(iter)) {
+
+                if ((filp->f_flags & O_NONBLOCK))
+                        return -EAGAIN;
+
                 /*
                  * This is a make-shift waitqueue. The reason we don't use
                  * an actual wait queue is because: