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

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Date:   Thu, 21 Nov 2019 16:21:48 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jorgen Hansen <jhansen@...are.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        Dexuan Cui <decui@...rosoft.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next 3/6] vsock: add local transport support in the
 vsock core

On Thu, Nov 21, 2019 at 03:04:18PM +0000, Jorgen Hansen wrote:
> > From: Stefano Garzarella [mailto:sgarzare@...hat.com]
> > Sent: Tuesday, November 19, 2019 12:01 PM
> > To: netdev@...r.kernel.org
> >
> > This patch allows to register a transport able to handle
> > local communication (loopback).
> > 
> > Signed-off-by: Stefano Garzarella <sgarzare@...hat.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?

Thanks,
Stefano