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

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Message-ID: <20191011143741.frgdjcyee25wpcmf@steredhat>
Date:   Fri, 11 Oct 2019 16:37:41 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Michael S. Tsirkin" <mst@...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 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@...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.

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