Index: share/man/man9/bitset.9
===================================================================
--- share/man/man9/bitset.9
+++ share/man/man9/bitset.9
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd December 12, 2019
+.Dd Auguest 10, 2020
 .Dt BITSET 9
 .Os
 .Sh NAME
@@ -43,6 +43,7 @@
 .Nm BIT_EMPTY ,
 .Nm BIT_ISFULLSET ,
 .Nm BIT_FFS ,
+.Nm BIT_FFS_AT ,
 .Nm BIT_FLS ,
 .Nm BIT_COUNT ,
 .Nm BIT_SUBSET ,
@@ -86,6 +87,8 @@
 .Ft int
 .Fn BIT_FFS "const SETSIZE" "struct STRUCTNAME *bitset"
 .Ft int
+.Fn BIT_FFS_AT "const SETSIZE" "struct STRUCTNAME *bitset" "int start"
+.Ft int
 .Fn BIT_FLS "const SETSIZE" "struct STRUCTNAME *bitset"
 .Ft int
 .Fn BIT_COUNT "const SETSIZE" "struct STRUCTNAME *bitset"
@@ -285,6 +288,18 @@
 macro, you must subtract one from the result.
 .Pp
 The
+.Fn BIT_FFS_AT
+macro returns the 1-index of the first (lowest) set bit in
+.Fa bitset ,
+which is greater than the given
+.Fa start ,
+or zero if no bits in
+.Fa bitset
+greater than
+.Fa start
+are set.
+.Pp
+The
 .Fn BIT_FLS
 macro returns the 1-index of the last (highest) set bit in
 .Fa bitset ,
@@ -518,7 +533,8 @@
 .Fn BITSET_DEFINE .
 .Pp
 Unlike every other reference to individual set members, which are zero-indexed,
-.Fn BIT_FFS
+.Fn BIT_FFS ,
+.Fn BIT_FFS_AT
 and
 .Fn BIT_FLS
 return a one-indexed result (or zero if the set is empty).
Index: sys/sys/bitset.h
===================================================================
--- sys/sys/bitset.h
+++ sys/sys/bitset.h
@@ -222,6 +222,24 @@
 	__bit;								\
 })
 
+#define	BIT_FFS_AT(_s, p, start) __extension__ ({			\
+	__size_t __i;							\
+	int __bit;							\
+	long __test;							\
+									\
+	__bit = 0;							\
+	__i = __bitset_word(_s, start);					\
+	if (__i < __bitset_words((_s))) {				\
+		__test = (p)->__bits[__i] &				\
+		    (~0UL << ((start) % _BITSET_BITS));			\
+		while (__test == 0 && ++__i < __bitset_words((_s)))	\
+			__test = (p)->__bits[__i];			\
+		if (__i < __bitset_words((_s)))				\
+			__bit = ffsl(__test) + __i * _BITSET_BITS;	\
+	}								\
+	__bit;								\
+})
+
 #define	BIT_FLS(_s, p) __extension__ ({					\
 	__size_t __i;							\
 	int __bit;							\