tcp: Add tcp_inq to get available receive bytes on socket

Create a common kernel function to get the number of bytes available
on a TCP socket. This is based on code in INQ getsockopt and we now call
the function for that getsockopt.

Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 24 insertions, 0 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index e90db8546806..0302636af98c 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1816,4 +1816,28 @@ static inline void skb_set_tcp_pure_ack(struct sk_buff *skb)
         skb->truesize = 2;
 }
 
+static inline int tcp_inq(struct sock *sk)
+{
+        struct tcp_sock *tp = tcp_sk(sk);
+        int answ;
+
+        if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
+                answ = 0;
+        } else if (sock_flag(sk, SOCK_URGINLINE) ||
+                   !tp->urg_data ||
+                   before(tp->urg_seq, tp->copied_seq) ||
+                   !before(tp->urg_seq, tp->rcv_nxt)) {
+
+                answ = tp->rcv_nxt - tp->copied_seq;
+
+                /* Subtract 1, if FIN was received */
+                if (answ && sock_flag(sk, SOCK_DONE))
+                        answ--;
+        } else {
+                answ = tp->urg_seq - tp->copied_seq;
+        }
+
+        return answ;
+}
+
 #endif  /* _TCP_H */