Re: [PATCH bpf-next v5 05/11] bpf: Adds field bpf_sock_ops_flags to tcp_sock

Adds field bpf_sock_ops_flags to tcp_sock and bpf_sock_ops. Its primary
use is to determine if there should be calls to sock_ops bpf program at
various points in the TCP code. The field is initialized to zero,
disabling the calls. A sock_ops BPF program can set, per connection and
as necessary, when the connection is established.

It also adds support for reading and writting the field within a
sock_ops BPF program.

Examples of where to call the bpf program:

1) When RTO fires
2) When a packet is retransmitted
3) When the connection terminates
4) When a packet is sent
5) When a packet is received

Signed-off-by: Lawrence Brakmo <redacted>
---
 include/linux/tcp.h      | 8 ++++++++
 include/uapi/linux/bpf.h | 1 +
 net/core/filter.c        | 7 +++++++
 3 files changed, 16 insertions(+)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 4f93f095..62f4388 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h

@@ -373,6 +373,14 @@ struct tcp_sock {
 	 */
 	struct request_sock *fastopen_rsk;
 	u32	*saved_syn;
+
+/* Sock_ops bpf program related variables */
+#ifdef CONFIG_BPF
+	u32     bpf_sock_ops_flags;     /* values defined in uapi/linux/tcp.h */
+#define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) (TP->bpf_sock_ops_flags & ARG)
+#else
+#define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) 0
+#endif
 };