Re: [PATCH 04/10] virtio: console: return -ENODEV on all read operations after unplug

[Jason Wang <jasowang@redhat.com>]

On 07/19/2013 04:16 AM, Amit Shah wrote:
> 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>
> ---
>  drivers/char/virtio_console.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 6bf0df3..a39702a 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;
> +

What if the port is hot-unplugged after this check? Should we serialize
the hot plug with inbuf_lock here?
>  	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;
>  	/*