[Patch bpf-next v7 09/13] udp: implement ->read_sock() for sockmap

[Cong Wang <xiyou.wangcong@gmail.com>]

From: Cong Wang <cong.wang@bytedance.com>

This is similar to tcp_read_sock(), except we do not need
to worry about connections, we just need to retrieve skb
from UDP receive queue.

Note, the return value of ->read_sock() is unused in
sk_psock_verdict_data_ready().

Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jakub Sitnicki <jakub@cloudflare.com>
Cc: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
---
 include/net/udp.h   |  2 ++
 net/ipv4/af_inet.c  |  1 +
 net/ipv4/udp.c      | 35 +++++++++++++++++++++++++++++++++++
 net/ipv6/af_inet6.c |  1 +
 4 files changed, 39 insertions(+)

diff --git a/include/net/udp.h b/include/net/udp.h
index df7cc1edc200..347b62a753c3 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -329,6 +329,8 @@ struct sock *__udp6_lib_lookup(struct net *net,
 			       struct sk_buff *skb);
 struct sock *udp6_lib_lookup_skb(const struct sk_buff *skb,
 				 __be16 sport, __be16 dport);
+int udp_read_sock(struct sock *sk, read_descriptor_t *desc,
+		  sk_read_actor_t recv_actor);
 
 /* UDP uses skb->dev_scratch to cache as much information as possible and avoid
  * possibly multiple cache miss on dequeue()
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 1355e6c0d567..f17870ee558b 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1070,6 +1070,7 @@ const struct proto_ops inet_dgram_ops = {
 	.setsockopt	   = sock_common_setsockopt,
 	.getsockopt	   = sock_common_getsockopt,
 	.sendmsg	   = inet_sendmsg,
+	.read_sock	   = udp_read_sock,
 	.recvmsg	   = inet_recvmsg,
 	.mmap		   = sock_no_mmap,
 	.sendpage	   = inet_sendpage,
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 38952aaee3a1..04620e4d64ab 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1782,6 +1782,41 @@ struct sk_buff *__skb_recv_udp(struct sock *sk, unsigned int flags,
 }
 EXPORT_SYMBOL(__skb_recv_udp);
 
+int udp_read_sock(struct sock *sk, read_descriptor_t *desc,
+		  sk_read_actor_t recv_actor)
+{
+	int copied = 0;
+
+	while (1) {
+		int offset = 0, err;
+		struct sk_buff *skb;
+
+		skb = __skb_recv_udp(sk, 0, 1, &offset, &err);
+		if (!skb)
+			return err;
+		if (offset < skb->len) {
+			size_t len;
+			int used;
+
+			len = skb->len - offset;
+			used = recv_actor(desc, skb, offset, len);
+			if (used <= 0) {
+				if (!copied)
+					copied = used;
+				break;
+			} else if (used <= len) {
+				copied += used;
+				offset += used;
+			}
+		}
+		if (!desc->count)
+			break;
+	}
+
+	return copied;
+}
+EXPORT_SYMBOL(udp_read_sock);
+
 /*
  * 	This should be easy, if there is something there we
  * 	return it, otherwise we block.
diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index 802f5111805a..71de739b4a9e 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -714,6 +714,7 @@ const struct proto_ops inet6_dgram_ops = {
 	.getsockopt	   = sock_common_getsockopt,	/* ok		*/
 	.sendmsg	   = inet6_sendmsg,		/* retpoline's sake */
 	.recvmsg	   = inet6_recvmsg,		/* retpoline's sake */
+	.read_sock	   = udp_read_sock,
 	.mmap		   = sock_no_mmap,
 	.sendpage	   = sock_no_sendpage,
 	.set_peek_off	   = sk_set_peek_off,
-- 
2.25.1