USB: make usb-skeleton honor O_NONBLOCK in write path

usb:usb-skeleton: honor O_NONBLOCK in write path

nonblocking writes are allowed by using down_trylock if necessary
to reserve an URB

Signed-off-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 10 insertions, 3 deletions

diff --git a/drivers/usb/usb-skeleton.c b/drivers/usb/usb-skeleton.c
index 5ffa3e246856..768fda9064e9 100644
--- a/drivers/usb/usb-skeleton.c
+++ b/drivers/usb/usb-skeleton.c
@@ -399,9 +399,16 @@ static ssize_t skel_write(struct file *file, const char *user_buffer, size_t cou
                 goto exit;
 
         /* limit the number of URBs in flight to stop a user from using up all RAM */
-        if (down_interruptible(&dev->limit_sem)) {
-                retval = -ERESTARTSYS;
-                goto exit;
+        if (!file->f_flags & O_NONBLOCK) {
+                if (down_interruptible(&dev->limit_sem)) {
+                        retval = -ERESTARTSYS;
+                        goto exit;
+                }
+        } else {
+                if (down_trylock(&dev->limit_sem)) {
+                        retval = -EAGAIN;
+                        goto exit;
+                }
         }
 
         spin_lock_irq(&dev->err_lock);