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

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Date:   Fri, 11 Oct 2019 10:22:30 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        Jorgen Hansen <jhansen@...are.com>,
        "David S. Miller" <davem@...emloft.net>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Adit Ranadive <aditr@...are.com>,
        Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 1/2] vsock: add half-closed socket details in the
 implementation notes

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 <jhansen@...are.com>
> Cc: Adit Ranadive <aditr@...are.com>
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> ---
>  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