tun: switch to new type of msg_control

This patch introduces to a new tun/tap specific msg_control:

#define TUN_MSG_UBUF 1
#define TUN_MSG_PTR  2
struct tun_msg_ctl {
       int type;
       void *ptr;
};

This allows us to pass different kinds of msg_control through
sendmsg(). The first supported type is ubuf (TUN_MSG_UBUF) which will
be used by the existed vhost_net zerocopy code. The second is XDP
buff, which allows vhost_net to pass XDP buff to TUN. This could be
used to implement accepting an array of XDP buffs from vhost_net in
the following patches.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 4e656f89cb22..fb01ce6d981c 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -620,6 +620,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
                 .msg_controllen = 0,
                 .msg_flags = MSG_DONTWAIT,
         };
+        struct tun_msg_ctl ctl;
         size_t len, total_len = 0;
         int err;
         struct vhost_net_ubuf_ref *uninitialized_var(ubufs);
@@ -664,8 +665,10 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
                         ubuf->ctx = nvq->ubufs;
                         ubuf->desc = nvq->upend_idx;
                         refcount_set(&ubuf->refcnt, 1);
-                        msg.msg_control = ubuf;
-                        msg.msg_controllen = sizeof(ubuf);
+                        msg.msg_control = &ctl;
+                        ctl.type = TUN_MSG_UBUF;
+                        ctl.ptr = ubuf;
+                        msg.msg_controllen = sizeof(ctl);
                         ubufs = nvq->ubufs;
                         atomic_inc(&ubufs->refcount);
                         nvq->upend_idx = (nvq->upend_idx + 1) % UIO_MAXIOV;