On Thu, Nov 21, 2019 at 03:04:18PM +0000, Jorgen Hansen wrote:

quoted

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?

Thanks,
Stefano