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

commit 96f97a83910cdb9d89d127c5ee523f8fc040a804 upstream.

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.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 299532658bd2cbee7bb1471af4b6a077628e9036..c68b8ad957f9f7b16a953b274de98bde91fdc6eb 100644 (file)
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -637,6 +637,10 @@ 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
@@ -653,7 +657,7 @@ 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;
        /*