Subject: Re: [PATCH net 1/2] vsock: add half-closed socket details in the implementation notes

From: "Michael S. Tsirkin" <[email-masked]>
Date: Fri, 11 Oct 2019 10:22:30 -0400

On Fri, Oct 11, 2019 at 03:07:57PM +0200, Stefano Garzarella wrote:
> vmci_transport never allowed half-closed socket on the host side.
> Since we want to have the same behaviour across all transports, we
> add a section in the "Implementation notes".
> 
> Cc: Jorgen Hansen <[email-masked]>
> Cc: Adit Ranadive <[email-masked]>
> Signed-off-by: Stefano Garzarella <[email-masked]>
> ---
>  net/vmw_vsock/af_vsock.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 2ab43b2bba31..27df57c2024b 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -83,6 +83,10 @@
>   *   TCP_ESTABLISHED - connected
>   *   TCP_CLOSING - disconnecting
>   *   TCP_LISTEN - listening
> + *
> + * - Half-closed socket is supported only on the guest side. recv() on the host
> + * side should return EOF when the guest closes a connection, also if some
> + * data is still in the receive queue.
>   */
>  
>  #include <linux/types.h>

That's a great way to lose data in a way that's hard to debug.

VMCI sockets connect to a hypervisor so there's tight control
of what the hypervisor can do.

But vhost vsocks connect to a fully fledged Linux, so
you can't assume this is safe. And application authors do not read
kernel source.

> -- 
> 2.21.0