Index: share/man/man9/Makefile
===================================================================
--- share/man/man9/Makefile
+++ share/man/man9/Makefile
@@ -623,6 +623,8 @@
 	bitset.9 BIT_FFS.9 \
 	bitset.9 BIT_FFS_AT.9 \
 	bitset.9 BIT_FLS.9 \
+	bitset.9 BIT_FOREACH_SET.9 \
+	bitset.9 BIT_FOREACH_CLR.9 \
 	bitset.9 BIT_COUNT.9 \
 	bitset.9 BIT_SUBSET.9 \
 	bitset.9 BIT_OVERLAP.9 \
Index: share/man/man9/bitset.9
===================================================================
--- share/man/man9/bitset.9
+++ share/man/man9/bitset.9
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd December 31, 2020
+.Dd September 20, 2021
 .Dt BITSET 9
 .Os
 .Sh NAME
@@ -45,6 +45,8 @@
 .Nm BIT_FFS ,
 .Nm BIT_FFS_AT ,
 .Nm BIT_FLS ,
+.Nm BIT_FOREACH_SET ,
+.Nm BIT_FOREACH_CLR ,
 .Nm BIT_COUNT ,
 .Nm BIT_SUBSET ,
 .Nm BIT_OVERLAP ,
@@ -92,9 +94,10 @@
 .Fn BIT_FFS_AT "const SETSIZE" "struct STRUCTNAME *bitset" "long start"
 .Ft long
 .Fn BIT_FLS "const SETSIZE" "struct STRUCTNAME *bitset"
+.Fn BIT_FOREACH_SET "const SETSIZE" "int i" "const struct STRUCTNAME *bitset"
+.Fn BIT_FOREACH_CLR "const SETSIZE" "int i" "const struct STRUCTNAME *bitset"
 .Ft long
 .Fn BIT_COUNT "const SETSIZE" "struct STRUCTNAME *bitset"
-.\"
 .Ft bool
 .Fo BIT_SUBSET
 .Fa "const SETSIZE" "struct STRUCTNAME *haystack" "struct STRUCTNAME *needle"
@@ -329,6 +332,25 @@
 macro, you must subtract one from the result.
 .Pp
 The
+.Fn BIT_FOREACH_SET
+macro can be used to iterate over all set bits in
+.Fa bitset .
+The index variable
+.Fa i
+must have been declared with type
+.Ft int ,
+and upon each iteration
+.Fa i
+is set to the index of successive set bits.
+The value of
+.Fa i
+after the loop terminates is undefined.
+Similarly,
+.Fn BIT_FOREACH_CLR
+iterates over all clear bits in
+.Fa bitset .
+.Pp
+The
 .Fn BIT_COUNT
 macro returns the total number of set bits in
 .Fa bitset .
Index: sys/sys/bitset.h
===================================================================
--- sys/sys/bitset.h
+++ sys/sys/bitset.h
@@ -271,6 +271,16 @@
 	__count;							\
 })
 
+/* Non-destructively loop over all set or clear bits in the set. */
+#define	_BIT_FOREACH(_s, i, p, op)					\
+	for (__size_t __i = 0; __i < __bitset_words(_s); __i++)		\
+		for (long __j = op((p)->__bits[__i]), __b = ffsl(__j);	\
+		    (i = (__b - 1) + __i * _BITSET_BITS), __j != 0;	\
+		    __j &= ~(1l << i), __b = ffsl(__j))
+
+#define	BIT_FOREACH_SET(_s, i, p)	_BIT_FOREACH(_s, i, p, )
+#define	BIT_FOREACH_CLR(_s, i, p)	_BIT_FOREACH(_s, i, p, ~)
+
 #define	BITSET_T_INITIALIZER(x)						\
 	{ .__bits = { x } }