virtio: console: return -ENODEV on all read operations after unplug

If a port gets unplugged while a user is blocked on read(), -ENODEV is
returned.  However, subsequent read()s returned 0, indicating there's no
host-side connection (but not indicating the device went away).

This also happened when a port was unplugged and the user didn't have
any blocking operation pending.  If the user didn't monitor the SIGIO
signal, they won't have a chance to find out if the port went away.

Fix by returning -ENODEV on all read()s after the port gets unplugged.
write() already behaves this way.

CC: <stable@vger.kernel.org>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index e4845f1c9a0b..fc45567ad3ac 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -749,6 +749,10 @@ static ssize_t port_fops_read(struct file *filp, char __user *ubuf,
 
         port = filp->private_data;
 
+        /* Port is hot-unplugged. */
+        if (!port->guest_connected)
+                return -ENODEV;
+
         if (!port_has_data(port)) {
                 /*
                  * If nothing's connected on the host just return 0 in
@@ -765,7 +769,7 @@ static ssize_t port_fops_read(struct file *filp, char __user *ubuf,
                 if (ret < 0)
                         return ret;
         }
-        /* Port got hot-unplugged. */
+        /* Port got hot-unplugged while we were waiting above. */
         if (!port->guest_connected)
                 return -ENODEV;
         /*