RE: [PATCH net-next 3/6] vsock: add local transport support in the vsock core

Jorgen Hansen
2019-11-21T15:53:59Z

> From: Stefano Garzarella [mailto:sgarzare@redhat.com]
> Sent: Thursday, November 21, 2019 4:22 PM
>
> On Thu, Nov 21, 2019 at 03:04:18PM +0000, Jorgen Hansen wrote:
> > > From: Stefano Garzarella [mailto:sgarzare@redhat.com]
> > > Sent: Tuesday, November 19, 2019 12:01 PM
> > > To: netdev@vger.kernel.org
> > >
> > > This patch allows to register a transport able to handle
> > > local communication (loopback).
> > >
> > > Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> > > ---
> > > include/net/af_vsock.h | 2 ++
> > > net/vmw_vsock/af_vsock.c | 17 ++++++++++++++++-
> > > 2 files changed, 18 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> > > index 4206dc6d813f..b1c717286993 100644
> > > --- a/include/net/af_vsock.h
> > > +++ b/include/net/af_vsock.h
> > > @@ -98,6 +98,8 @@ struct vsock_transport_send_notify_data {
> > > #define VSOCK_TRANSPORT_F_G2H 0x00000002
> > > /* Transport provides DGRAM communication */
> > > #define VSOCK_TRANSPORT_F_DGRAM 0x00000004
> > > +/* Transport provides local (loopback) communication */
> > > +#define VSOCK_TRANSPORT_F_LOCAL 0x00000008
> > >
> > > struct vsock_transport {
> > > struct module *module;
> > > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> > > index cc8659838bf2..c9e5bad59dc1 100644
> > > --- a/net/vmw_vsock/af_vsock.c
> > > +++ b/net/vmw_vsock/af_vsock.c
> > > @@ -136,6 +136,8 @@ static const struct vsock_transport
> *transport_h2g;
> > > static const struct vsock_transport *transport_g2h;
> > > /* Transport used for DGRAM communication */
> > > static const struct vsock_transport *transport_dgram;
> > > +/* Transport used for local communication */
> > > +static const struct vsock_transport *transport_local;
> > > static DEFINE_MUTEX(vsock_register_mutex);
> > >
> > > /**** UTILS ****/
> > > @@ -2130,7 +2132,7 @@
> EXPORT_SYMBOL_GPL(vsock_core_get_transport);
> > >
> > > int vsock_core_register(const struct vsock_transport *t, int features)
> > > {
> > > - const struct vsock_transport *t_h2g, *t_g2h, *t_dgram;
> > > + const struct vsock_transport *t_h2g, *t_g2h, *t_dgram, *t_local;
> > > int err = mutex_lock_interruptible(&vsock_register_mutex);
> > >
> > > if (err)
> > > @@ -2139,6 +2141,7 @@ int vsock_core_register(const struct
> > > vsock_transport *t, int features)
> > > t_h2g = transport_h2g;
> > > t_g2h = transport_g2h;
> > > t_dgram = transport_dgram;
> > > + t_local = transport_local;
> > >
> > > if (features & VSOCK_TRANSPORT_F_H2G) {
> > > if (t_h2g) {
> > > @@ -2164,9 +2167,18 @@ int vsock_core_register(const struct
> > > vsock_transport *t, int features)
> > > t_dgram = t;
> > > }
> > >
> > > + if (features & VSOCK_TRANSPORT_F_LOCAL) {
> > > + if (t_local) {
> > > + err = -EBUSY;
> > > + goto err_busy;
> > > + }
> > > + t_local = t;
> > > + }
> > > +
> > > transport_h2g = t_h2g;
> > > transport_g2h = t_g2h;
> > > transport_dgram = t_dgram;
> > > + transport_local = t_local;
> > >
> > > err_busy:
> > > mutex_unlock(&vsock_register_mutex);
> > > @@ -2187,6 +2199,9 @@ void vsock_core_unregister(const struct
> > > vsock_transport *t)
> > > if (transport_dgram == t)
> > > transport_dgram = NULL;
> > >
> > > + if (transport_local == t)
> > > + transport_local = NULL;
> > > +
> > > mutex_unlock(&vsock_register_mutex);
> > > }
> > > EXPORT_SYMBOL_GPL(vsock_core_unregister);
> > > --
> > > 2.21.0
> >
> > Having loopback support as a separate transport fits nicely, but do we need
> to support
> > different variants of loopback? It could just be built in.
>
> I agree with you, indeed initially I developed it as built in, but
> DEPMOD found a cyclic dependency because vsock_transport use
> virtio_transport_common that use vsock, so if I include vsock_transport
> in the vsock module, DEPMOD is not happy.
>
> I don't know how to break this cyclic dependency, do you have any ideas?

One way to view this would be that the loopback transport and the support
it uses from virtio_transport_common are independent of virtio as such,
and could be part of the af_vsock module if loopback is configured. So
in a way, the virtio g2h and h2g transports would be extensions of the
built in loopback transport. But that brings in quite a bit of code so
it could be better to just keep it as is.

Thanks,
Jorgen