diff --git a/lib/libc/gen/sched_getaffinity.c b/lib/libc/gen/sched_getaffinity.c
--- a/lib/libc/gen/sched_getaffinity.c
+++ b/lib/libc/gen/sched_getaffinity.c
@@ -54,3 +54,25 @@
 		errno = EINVAL;
 	return (error);
 }
+
+int
+cpuset_getmyaffinity_count(void)
+{
+	char *cac, *errstr;
+	cpuset_t mask;
+	int count;
+
+	cac = getenv("CPUSET_AFFINITY_COUNT");
+	if (cac != NULL) {
+		count = strtonum(optarg, 0, INT_MAX, &errstr);
+		if (errstr != NULL)
+			return (-1);
+		return (count);
+	}
+	if (cpuset_getaffinity(CPU_LEVEL_WHICH, CPU_WHICH_TID, -1, sizeof(mask),
+	    &mask) == 0) {
+		return CPU_COUNT(&mask);
+	}
+
+	return (-1);
+}