diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 8d5d9b0..aafd309 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7056,6 +7056,11 @@ enum {
 					 * when SK_BPF_CB_TX_TIMESTAMPING
 					 * feature is on.
 					 */
+	BPF_SOCK_OPS_TSTAMP_SENDMSG_CB,	/* Called when every sendmsg syscall
+					 * is triggered. It's used to correlate
+					 * sendmsg timestamp with corresponding
+					 * tskey.
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect