4 files changed, 44 insertions, 4 deletions

diff --git a/sys/netinet/tcp.h b/sys/netinet/tcp.h
index e7c47e85bb7b..6dc7403aae28 100644
--- a/sys/netinet/tcp.h
+++ b/sys/netinet/tcp.h
@@ -210,6 +210,7 @@ struct tcphdr {
 #define	TCP_PCAP_OUT	2048	/* number of output packets to keep */
 #define	TCP_PCAP_IN	4096	/* number of input packets to keep */
 #define TCP_FUNCTION_BLK 8192	/* Set the tcp function pointers to the specified stack */
+#define TCP_FUNCTION_ALIAS 8193	/* Get the current tcp function pointer name alias */
 /* Options for Rack and BBR */
 #define	TCP_REUSPORT_LB_NUMA   1026	/* set listen socket numa domain */
 #define TCP_RACK_MBUF_QUEUE   1050 /* Do we allow mbuf queuing if supported */
diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
index 9d66086a383b..2752773a95fc 100644
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -473,6 +473,37 @@ find_and_ref_tcp_fb(struct tcp_function_block *blk)
 	return(rblk);
 }
 
+/* Find a matching alias for the given tcp_function_block. */
+int
+find_tcp_function_alias(struct tcp_function_block *blk,
+    struct tcp_function_set *fs)
+{
+	struct tcp_function *f;
+	int found;
+
+	found = 0;
+	rw_rlock(&tcp_function_lock);
+	TAILQ_FOREACH(f, &t_functions, tf_next) {
+		if ((f->tf_fb == blk) &&
+		    (strncmp(f->tf_name, blk->tfb_tcp_block_name,
+		        TCP_FUNCTION_NAME_LEN_MAX) != 0)) {
+			/* Matching function block with different name. */
+			strncpy(fs->function_set_name, f->tf_name,
+			    TCP_FUNCTION_NAME_LEN_MAX);
+			found = 1;
+			break;
+		}
+	}
+	/* Null terminate the string appropriately. */
+	if (found) {
+		fs->function_set_name[TCP_FUNCTION_NAME_LEN_MAX - 1] = '\0';
+	} else {
+		fs->function_set_name[0] = '\0';
+	}
+	rw_runlock(&tcp_function_lock);
+	return (found);
+}
+
 static struct tcp_function_block *
 find_and_ref_tcp_default_fb(void)
 {
diff --git a/sys/netinet/tcp_usrreq.c b/sys/netinet/tcp_usrreq.c
index e9f7fa541461..f004d54b4657 100644
--- a/sys/netinet/tcp_usrreq.c
+++ b/sys/netinet/tcp_usrreq.c
@@ -1894,10 +1894,17 @@ err_out:
 		INP_WUNLOCK(inp);
 		return (error);
 	} else if ((sopt->sopt_dir == SOPT_GET) &&
-	    (sopt->sopt_name == TCP_FUNCTION_BLK)) {
-		strncpy(fsn.function_set_name, tp->t_fb->tfb_tcp_block_name,
-		    TCP_FUNCTION_NAME_LEN_MAX);
-		fsn.function_set_name[TCP_FUNCTION_NAME_LEN_MAX - 1] = '\0';
+	    ((sopt->sopt_name == TCP_FUNCTION_BLK) ||
+	     (sopt->sopt_name == TCP_FUNCTION_ALIAS))) {
+		if (sopt->sopt_name == TCP_FUNCTION_ALIAS) {
+			memset(&fsn, 0, sizeof(fsn));
+			find_tcp_function_alias(tp->t_fb, &fsn);
+		} else {
+			strncpy(fsn.function_set_name,
+			    tp->t_fb->tfb_tcp_block_name,
+			    TCP_FUNCTION_NAME_LEN_MAX);
+			fsn.function_set_name[TCP_FUNCTION_NAME_LEN_MAX - 1] = '\0';
+		}
 		fsn.pcbcnt = tp->t_fb->tfb_refcnt;
 		INP_WUNLOCK(inp);
 		error = sooptcopyout(sopt, &fsn, sizeof fsn);
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
index d5b2963ef4dc..2775fb392a1a 100644
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -1020,6 +1020,7 @@ int register_tcp_functions_as_name(struct tcp_function_block *blk,
 int deregister_tcp_functions(struct tcp_function_block *blk, bool quiesce,
     bool force);
 struct tcp_function_block *find_and_ref_tcp_functions(struct tcp_function_set *fs);
+int find_tcp_function_alias(struct tcp_function_block *blk, struct tcp_function_set *fs);
 void tcp_switch_back_to_default(struct tcpcb *tp);
 struct tcp_function_block *
 find_and_ref_tcp_fb(struct tcp_function_block *fs);