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

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@vmware.com>
Cc: Adit Ranadive <aditr@vmware.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 net/vmw_vsock/af_vsock.c | 4 ++++
 1 file changed, 4 insertions(+)

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@vmware.com>
> Cc: Adit Ranadive <aditr@vmware.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.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

On Fri, Oct 11, 2019 at 10:22:30AM -0400, Michael S. Tsirkin wrote:
> 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@vmware.com>
> > Cc: Adit Ranadive <aditr@vmware.com>
> > Signed-off-by: Stefano Garzarella <sgarzare@redhat.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.

Thanks for explaining.
Discard this patch, I'll try to add a getsockopt() to allow the tests
(and applications) to understand if half-closed socket is supported or not.

Stefano