[PATCH v1 bpf-next 2/8] bpf: tcp: Introduce BPF_SOCK_OPS_RCVLOWAT_CB.

[Kuniyuki Iwashima <kuniyu@google.com>]

We will introduce a new type of opt-in hooks for BPF SOCK_OPS prog.

The hooks can be enabled on per-socket basis by bpf_setsockopt():

  int flag = BPF_SOCK_OPS_RCVLOWAT_CB_FLAG;

  bpf_setsockopt(sk, SOL_TCP, TCP_BPF_SOCK_OPS_CB_FLAGS,
                 &flags, sizeof(flags));

or via the SOCK_OPS specific helper:

  bpf_sock_ops_cb_flags_set(skops, BPF_SOCK_OPS_RCVLOWAT_CB_FLAG);

Once activated, the BPF prog will be invoked with bpf_sock_ops.op
set to BPF_SOCK_OPS_RCVLOWAT_CB upon the following events:

  1. TCP stack enqueues skb to sk->sk_receive_queue
  2. TCP recvmsg() completes

This will allow the BPF prog to dynamically adjust sk->sk_rcvlowat,
suppressing unnecessary EPOLLIN wakeups until sufficient data
(e.g., a full RPC frame) is available in the receive queue.

Note that is_locked_tcp_sock_ops() is left unchanged not to enable
bpf_setsockopt() unnecessarily.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 include/uapi/linux/bpf.h       | 18 +++++++++++++++++-
 tools/include/uapi/linux/bpf.h | 18 +++++++++++++++++-
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 552bc5d9afbd..e139a4e94ffd 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6952,6 +6952,9 @@ struct bpf_sock_ops {
 	 *					the 3WHS.
 	 * BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB: The ACK that concludes
 	 *					the 3WHS.
+	 * BPF_SOCK_OPS_RCVLOWAT_CB : No header included.  The payload is only
+	 *			      accessible by passing bpf_sock_ops to
+	 *			      bpf_skb_load_bytes().
 	 *
 	 * bpf_load_hdr_opt() can also be used to read a particular option.
 	 */
@@ -7023,8 +7026,16 @@ enum {
 	 * options first before the BPF program does.
 	 */
 	BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG = (1<<6),
+	/* Call bpf when TCP payload is queued to sk->sk_receive_queue
+	 * and after recvmsg().  The bpf prog will be called under
+	 * sock_ops->op == BPF_SOCK_OPS_RCVLOWAT_CB.
+	 *
+	 * It can be used to adjust sk->sk_rcvlowat and suppress
+	 * unnecessary wakeups before sufficient data is available.
+	 */
+	BPF_SOCK_OPS_RCVLOWAT_CB_FLAG = (1<<7),
 /* Mask of all currently supported cb flags */
-	BPF_SOCK_OPS_ALL_CB_FLAGS       = 0x7F,
+	BPF_SOCK_OPS_ALL_CB_FLAGS       = 0xFF,
 };
 
 enum {
@@ -7168,6 +7179,11 @@ enum {
 					 * sendmsg timestamp with corresponding
 					 * tskey.
 					 */
+	BPF_SOCK_OPS_RCVLOWAT_CB,	/* Called when TCP payload is queued to
+					 * sk->sk_receive_queue and after recvmsg()
+					 * to allow adjusting sk->sk_rcvlowat and
+					 * to suppress early wakeups.
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 677be9a47347..b5268a66ecb4 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6952,6 +6952,9 @@ struct bpf_sock_ops {
 	 *					the 3WHS.
 	 * BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB: The ACK that concludes
 	 *					the 3WHS.
+	 * BPF_SOCK_OPS_RCVLOWAT_CB : No header included.  The payload is only
+	 *			      accessible by passing bpf_sock_ops to
+	 *			      bpf_skb_load_bytes().
 	 *
 	 * bpf_load_hdr_opt() can also be used to read a particular option.
 	 */
@@ -7023,8 +7026,16 @@ enum {
 	 * options first before the BPF program does.
 	 */
 	BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG = (1<<6),
+	/* Call bpf when TCP payload is queued to sk->sk_receive_queue
+	 * and after recvmsg().  The bpf prog will be called under
+	 * sock_ops->op == BPF_SOCK_OPS_RCVLOWAT_CB.
+	 *
+	 * It can be used to adjust sk->sk_rcvlowat and suppress
+	 * unnecessary wakeups before sufficient data is available.
+	 */
+	BPF_SOCK_OPS_RCVLOWAT_CB_FLAG = (1<<7),
 /* Mask of all currently supported cb flags */
-	BPF_SOCK_OPS_ALL_CB_FLAGS       = 0x7F,
+	BPF_SOCK_OPS_ALL_CB_FLAGS       = 0xFF,
 };
 
 enum {
@@ -7168,6 +7179,11 @@ enum {
 					 * sendmsg timestamp with corresponding
 					 * tskey.
 					 */
+	BPF_SOCK_OPS_RCVLOWAT_CB,	/* Called when TCP payload is queued to
+					 * sk->sk_receive_queue and after recvmsg()
+					 * to allow adjusting sk->sk_rcvlowat and
+					 * to suppress early wakeups.
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
-- 
2.54.0.563.g4f69b47b94-goog