net: sock: introduce SOCK_XDP

This patch introduces a new sock flag - SOCK_XDP. This will be used
for notifying the upper layer that XDP program is attached on the
lower socket, and requires for extra headroom.

TUN will be the first user.
Signed-off-by: NJason Wang <jasowang@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -869,6 +869,9 @@ static int tun_attach(struct tun_struct *tun, struct file *file,
 		tun_napi_init(tun, tfile, napi);
 	}
 
+	if (rtnl_dereference(tun->xdp_prog))
+		sock_set_flag(&tfile->sk, SOCK_XDP);
+
 	tun_set_real_num_queues(tun);
 
 	/* device is allowed to go away first, so no need to hold extra
@@ -1241,13 +1244,29 @@ static int tun_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 		       struct netlink_ext_ack *extack)
 {
 	struct tun_struct *tun = netdev_priv(dev);
+	struct tun_file *tfile;
 	struct bpf_prog *old_prog;
+	int i;
 
 	old_prog = rtnl_dereference(tun->xdp_prog);
 	rcu_assign_pointer(tun->xdp_prog, prog);
 	if (old_prog)
 		bpf_prog_put(old_prog);
 
+	for (i = 0; i < tun->numqueues; i++) {
+		tfile = rtnl_dereference(tun->tfiles[i]);
+		if (prog)
+			sock_set_flag(&tfile->sk, SOCK_XDP);
+		else
+			sock_reset_flag(&tfile->sk, SOCK_XDP);
+	}
+	list_for_each_entry(tfile, &tun->disabled, next) {
+		if (prog)
+			sock_set_flag(&tfile->sk, SOCK_XDP);
+		else
+			sock_reset_flag(&tfile->sk, SOCK_XDP);
+	}
+
 	return 0;
 }
 

include/net/sock.h

@@ -800,6 +800,7 @@ enum sock_flags {
 	SOCK_SELECT_ERR_QUEUE, /* Wake select on error queue */
 	SOCK_RCU_FREE, /* wait rcu grace period in sk_destruct() */
 	SOCK_TXTIME,
+	SOCK_XDP, /* XDP is attached */
 };
 
 #define SK_FLAGS_TIMESTAMP ((1UL << SOCK_TIMESTAMP) | (1UL << SOCK_TIMESTAMPING_RX_SOFTWARE))