udp: Implement udp_bpf_recvmsg() for sockmap

We have to implement udp_bpf_recvmsg() to replace the ->recvmsg()
to retrieve skmsg from ingress_msg.

Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210331023237.41094-14-xiyou.wangcong@gmail.com

Author: Cong Wang

net/ipv4/udp_bpf.c

@@ -4,14 +4,75 @@
 #include <linux/skmsg.h>
 #include <net/sock.h>
 #include <net/udp.h>
+#include <net/inet_common.h>
+
+#include "udp_impl.h"
+
+static struct proto *udpv6_prot_saved __read_mostly;
+
+static int sk_udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
+			  int noblock, int flags, int *addr_len)
+{
+#if IS_ENABLED(CONFIG_IPV6)
+	if (sk->sk_family == AF_INET6)
+		return udpv6_prot_saved->recvmsg(sk, msg, len, noblock, flags,
+						 addr_len);
+#endif
+	return udp_prot.recvmsg(sk, msg, len, noblock, flags, addr_len);
+}
+
+static int udp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
+			   int nonblock, int flags, int *addr_len)
+{
+	struct sk_psock *psock;
+	int copied, ret;
+
+	if (unlikely(flags & MSG_ERRQUEUE))
+		return inet_recv_error(sk, msg, len, addr_len);
+
+	psock = sk_psock_get(sk);
+	if (unlikely(!psock))
+		return sk_udp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
+
+	lock_sock(sk);
+	if (sk_psock_queue_empty(psock)) {
+		ret = sk_udp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
+		goto out;
+	}
+
+msg_bytes_ready:
+	copied = sk_msg_recvmsg(sk, psock, msg, len, flags);
+	if (!copied) {
+		int data, err = 0;
+		long timeo;
+
+		timeo = sock_rcvtimeo(sk, nonblock);
+		data = sk_msg_wait_data(sk, psock, flags, timeo, &err);
+		if (data) {
+			if (!sk_psock_queue_empty(psock))
+				goto msg_bytes_ready;
+			ret = sk_udp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
+			goto out;
+		}
+		if (err) {
+			ret = err;
+			goto out;
+		}
+		copied = -EAGAIN;
+	}
+	ret = copied;
+out:
+	release_sock(sk);
+	sk_psock_put(sk, psock);
+	return ret;
+}
 
 enum {
 	UDP_BPF_IPV4,
 	UDP_BPF_IPV6,
 	UDP_BPF_NUM_PROTS,
 };
 
-static struct proto *udpv6_prot_saved __read_mostly;
 static DEFINE_SPINLOCK(udpv6_prot_lock);
 static struct proto udp_bpf_prots[UDP_BPF_NUM_PROTS];
 
@@ -20,6 +81,7 @@ static void udp_bpf_rebuild_protos(struct proto *prot, const struct proto *base)
 	*prot        = *base;
 	prot->unhash = sock_map_unhash;
 	prot->close  = sock_map_close;
+	prot->recvmsg = udp_bpf_recvmsg;
 }
 
 static void udp_bpf_check_v6_needs_rebuild(struct proto *ops)