bpf: Add access to snd_cwnd and others in sock_ops

Adds read access to snd_cwnd and srtt_us fields of tcp_sock. Since these
fields are only valid if the socket associated with the sock_ops program
call is a full socket, the field is_fullsock is also added to the
bpf_sock_ops struct. If the socket is not a full socket, reading these
fields returns 0.

Note that in most cases it will not be necessary to check is_fullsock to
know if there is a full socket. The context of the call, as specified by
the 'op' field, can sometimes determine whether there is a full socket.

The struct bpf_sock_ops has the following fields added:

  __u32 is_fullsock;      /* Some TCP fields are only valid if
                           * there is a full socket. If not, the
                           * fields read as zero.
			   */
  __u32 snd_cwnd;
  __u32 srtt_us;          /* Averaged RTT << 3 in usecs */

There is a new macro, SOCK_OPS_GET_TCP32(NAME), to make it easier to add
read access to more 32 bit tcp_sock fields.

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 4e09398009c1..89a656077884 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -2012,10 +2012,12 @@ static inline int tcp_call_bpf(struct sock *sk, int op)
 	struct bpf_sock_ops_kern sock_ops;
 	int ret;
 
-	if (sk_fullsock(sk))
+	memset(&sock_ops, 0, sizeof(sock_ops));
+	if (sk_fullsock(sk)) {
+		sock_ops.is_fullsock = 1;
 		sock_owned_by_me(sk);
+	}
 
-	memset(&sock_ops, 0, sizeof(sock_ops));
 	sock_ops.sk = sk;
 	sock_ops.op = op;