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>

3 files changed, 22 insertions, 9 deletions

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index f0f7cd977667..7996ed7cbf18 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -619,7 +619,7 @@ static inline struct sk_buff *tap_alloc_skb(struct sock *sk, size_t prepad,
 #define TAP_RESERVE HH_DATA_OFF(ETH_HLEN)
 
 /* Get packet from user space buffer */
-static ssize_t tap_get_user(struct tap_queue *q, struct msghdr *m,
+static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
                             struct iov_iter *from, int noblock)
 {
         int good_linear = SKB_MAX_HEAD(TAP_RESERVE);
@@ -663,7 +663,7 @@ static ssize_t tap_get_user(struct tap_queue *q, struct msghdr *m,
         if (unlikely(len < ETH_HLEN))
                 goto err;
 
-        if (m && m->msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY)) {
+        if (msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY)) {
                 struct iov_iter i;
 
                 copylen = vnet_hdr.hdr_len ?
@@ -724,11 +724,11 @@ static ssize_t tap_get_user(struct tap_queue *q, struct msghdr *m,
         tap = rcu_dereference(q->tap);
         /* copy skb_ubuf_info for callback when skb has no error */
         if (zerocopy) {
-                skb_shinfo(skb)->destructor_arg = m->msg_control;
+                skb_shinfo(skb)->destructor_arg = msg_control;
                 skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
                 skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
-        } else if (m && m->msg_control) {
-                struct ubuf_info *uarg = m->msg_control;
+        } else if (msg_control) {
+                struct ubuf_info *uarg = msg_control;
                 uarg->callback(uarg, false);
         }
 
@@ -1150,7 +1150,13 @@ static int tap_sendmsg(struct socket *sock, struct msghdr *m,
                        size_t total_len)
 {
         struct tap_queue *q = container_of(sock, struct tap_queue, sock);
-        return tap_get_user(q, m, &m->msg_iter, m->msg_flags & MSG_DONTWAIT);
+        struct tun_msg_ctl *ctl = m->msg_control;
+
+        if (ctl && ctl->type != TUN_MSG_UBUF)
+                return -EINVAL;
+
+        return tap_get_user(q, ctl ? ctl->ptr : NULL, &m->msg_iter,
+                            m->msg_flags & MSG_DONTWAIT);
 }
 
 static int tap_recvmsg(struct socket *sock, struct msghdr *m,
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 3ae539374f6b..89779b58c7ca 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2431,11 +2431,15 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
         int ret;
         struct tun_file *tfile = container_of(sock, struct tun_file, socket);
         struct tun_struct *tun = tun_get(tfile);
+        struct tun_msg_ctl *ctl = m->msg_control;
 
         if (!tun)
                 return -EBADFD;
 
-        ret = tun_get_user(tun, tfile, m->msg_control, &m->msg_iter,
+        if (ctl && ctl->type != TUN_MSG_UBUF)
+                return -EINVAL;
+
+        ret = tun_get_user(tun, tfile, ctl ? ctl->ptr : NULL, &m->msg_iter,
                            m->msg_flags & MSG_DONTWAIT,
                            m->msg_flags & MSG_MORE);
         tun_put(tun);
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;