ftdev: respect O_NONBLOCK flag in ftdev_read()

Don't block if userspace wants to go on doing something else.

1 files changed, 11 insertions, 0 deletions

diff --git a/litmus/ftdev.c b/litmus/ftdev.c
index 3722a523b157..6de7b169df93 100644
--- a/litmus/ftdev.c
+++ b/litmus/ftdev.c
@@ -216,6 +216,17 @@ static ssize_t ftdev_read(struct file *filp,
                          * here with copied data because that data would get
                          * lost if the task is interrupted (e.g., killed).
                          */
+
+                        /* Before sleeping, check wether a non-blocking
+                         * read was requested.
+                         */
+                        if (filp->f_flags & O_NONBLOCK)
+                        {
+                                /* bug out, userspace doesn't want us to sleep */
+                                err = -EWOULDBLOCK;
+                                break;
+                        }
+
                         mutex_unlock(&ftdm->lock);
                         set_current_state(TASK_INTERRUPTIBLE);