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>

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index e4845f1c9a0b5cd6632c4dc6116dcc1fa5ead644..fc45567ad3acef079db496c9a2f495e19e5b5bba 100644 (file)
--- 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;
        /*