This patch adds the support of multiple transports in the
VSOCK core.

With the multi-transports support, we can use vsock with nested VMs
(using also different hypervisors) loading both guest->host and
host->guest transports at the same time.

Major changes:
- vsock core module can be loaded regardless of the transports
- vsock_core_init() and vsock_core_exit() are renamed to
  vsock_core_register() and vsock_core_unregister()
- vsock_core_register() has a feature parameter (H2G, G2H, DGRAM)
  to identify which directions the transport can handle and if it's
  support DGRAM (only vmci)
- each stream socket is assigned to a transport when the remote CID
  is set (during the connect() or when we receive a connection request
  on a listener socket).
  The remote CID is used to decide which transport to use:
  - remote CID > VMADDR_CID_HOST will use host->guest transport
  - remote CID <= VMADDR_CID_HOST will use guest->host transport
- listener sockets are not bound to any transports since no transport
  operations are done on it. In this way we can create a listener
  socket, also if the transports are not loaded or with VMADDR_CID_ANY
  to listen on all transports.
- DGRAM sockets are handled as before, since only the vmci_transport
  provides this feature.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
RFC -> v1:
- documented VSOCK_TRANSPORT_F_* flags
- fixed vsock_assign_transport() when the socket is already assigned
  (e.g connection failed)
- moved features outside of struct vsock_transport, and used as
  parameter of vsock_core_register()
---
 drivers/vhost/vsock.c                   |   5 +-
 include/net/af_vsock.h                  |  17 +-
 net/vmw_vsock/af_vsock.c                | 237 ++++++++++++++++++------
 net/vmw_vsock/hyperv_transport.c        |  26 ++-
 net/vmw_vsock/virtio_transport.c        |   7 +-
 net/vmw_vsock/virtio_transport_common.c |  28 ++-
 net/vmw_vsock/vmci_transport.c          |  31 +++-
 7 files changed, 270 insertions(+), 81 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 6d7e4f022748..b235f4bbe8ea 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c

@@ -831,7 +831,8 @@ static int __init vhost_vsock_init(void)
 {
        int ret;

-       ret = vsock_core_init(&vhost_transport.transport);
+       ret = vsock_core_register(&vhost_transport.transport,
+                                 VSOCK_TRANSPORT_F_H2G);
        if (ret < 0)
                return ret;
        return misc_register(&vhost_vsock_misc);

@@ -840,7 +841,7 @@ static int __init vhost_vsock_init(void)
 static void __exit vhost_vsock_exit(void)
 {
        misc_deregister(&vhost_vsock_misc);
-       vsock_core_exit();
+       vsock_core_unregister(&vhost_transport.transport);
 };

 module_init(vhost_vsock_init);

diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
index fa1570dc9f5c..27a3463e4892 100644
--- a/include/net/af_vsock.h
+++ b/include/net/af_vsock.h

@@ -91,6 +91,14 @@ struct vsock_transport_send_notify_data {
        u64 data2; /* Transport-defined. */
 };

+/* Transport features flags */
+/* Transport provides host->guest communication */
+#define VSOCK_TRANSPORT_F_H2G          0x00000001
+/* Transport provides guest->host communication */
+#define VSOCK_TRANSPORT_F_G2H          0x00000002
+/* Transport provides DGRAM communication */
+#define VSOCK_TRANSPORT_F_DGRAM                0x00000004
+
 struct vsock_transport {
        /* Initialize/tear-down socket. */
        int (*init)(struct vsock_sock *, struct vsock_sock *);

@@ -154,12 +162,8 @@ struct vsock_transport {

 /**** CORE ****/

-int __vsock_core_init(const struct vsock_transport *t, struct module *owner);
-static inline int vsock_core_init(const struct vsock_transport *t)
-{
-       return __vsock_core_init(t, THIS_MODULE);
-}
-void vsock_core_exit(void);
+int vsock_core_register(const struct vsock_transport *t, int features);
+void vsock_core_unregister(const struct vsock_transport *t);

 /* The transport may downcast this to access transport-specific functions */
 const struct vsock_transport *vsock_core_get_transport(struct vsock_sock *vsk);

@@ -190,6 +194,7 @@ struct sock *vsock_find_connected_socket(struct sockaddr_vm *src,
                                         struct sockaddr_vm *dst);
 void vsock_remove_sock(struct vsock_sock *vsk);
 void vsock_for_each_connected_socket(void (*fn)(struct sock *sk));
+int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk);

 /**** TAP ****/

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index d89381166028..dddd85d9a147 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c

@@ -130,7 +130,12 @@ static struct proto vsock_proto = {
 #define VSOCK_DEFAULT_BUFFER_MAX_SIZE (1024 * 256)
 #define VSOCK_DEFAULT_BUFFER_MIN_SIZE 128

-static const struct vsock_transport *transport_single;
+/* Transport used for host->guest communication */
+static const struct vsock_transport *transport_h2g;
+/* Transport used for guest->host communication */
+static const struct vsock_transport *transport_g2h;
+/* Transport used for DGRAM communication */
+static const struct vsock_transport *transport_dgram;
 static DEFINE_MUTEX(vsock_register_mutex);

 /**** UTILS ****/

@@ -182,7 +187,7 @@ static int vsock_auto_bind(struct vsock_sock *vsk)
        return __vsock_bind(sk, &local_addr);
 }

-static int __init vsock_init_tables(void)
+static void vsock_init_tables(void)
 {
        int i;

@@ -191,7 +196,6 @@ static int __init vsock_init_tables(void)

        for (i = 0; i < ARRAY_SIZE(vsock_connected_table); i++)
                INIT_LIST_HEAD(&vsock_connected_table[i]);
-       return 0;
 }

 static void __vsock_insert_bound(struct list_head *list,

@@ -376,6 +380,62 @@ void vsock_enqueue_accept(struct sock *listener, struct sock *connected)
 }
 EXPORT_SYMBOL_GPL(vsock_enqueue_accept);

+/* Assign a transport to a socket and call the .init transport callback.
+ *
+ * Note: for stream socket this must be called when vsk->remote_addr is set
+ * (e.g. during the connect() or when a connection request on a listener
+ * socket is received).
+ * The vsk->remote_addr is used to decide which transport to use:
+ *  - remote CID > VMADDR_CID_HOST will use host->guest transport
+ *  - remote CID <= VMADDR_CID_HOST will use guest->host transport
+ */
+int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
+{
+       const struct vsock_transport *new_transport;
+       struct sock *sk = sk_vsock(vsk);
+
+       switch (sk->sk_type) {
+       case SOCK_DGRAM:
+               new_transport = transport_dgram;
+               break;
+       case SOCK_STREAM:
+               if (vsk->remote_addr.svm_cid > VMADDR_CID_HOST)
+                       new_transport = transport_h2g;
+               else
+                       new_transport = transport_g2h;