[PATCH] bpf: tcp_bpf_recvmsg should return EAGAIN when nonblocking and no data

[John Fastabend <john.fastabend@gmail.com>]

We return 0 in the case of a nonblocking socket that has no data
available. However, this is incorrect and may confuse applications.
After this patch we do the correct thing and return the error
EAGAIN.

Quoting return codes from recvmsg manpage,

EAGAIN or EWOULDBLOCK
 The socket is marked nonblocking and the receive operation would
 block, or a receive timeout had been set and the timeout expired
 before data was received.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
 net/ipv4/tcp_bpf.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index b7918d4..3b45fe5 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -145,6 +145,7 @@ int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 			ret = err;
 			goto out;
 		}
+		copied = -EAGAIN;
 	}
 	ret = copied;
 out:
-- 
1.9.1