lib/find_bit: Introduce find_next_andnot_bit()

In preparation of introducing for_each_cpu_andnot(), add a variant of
find_next_bit() that negate the bits in @addr2 when ANDing them with the
bits in @addr1.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>

include/linux/find.h

@@ -12,6 +12,8 @@ unsigned long _find_next_bit(const unsigned long *addr1, unsigned long nbits,
 				unsigned long start);
 unsigned long _find_next_and_bit(const unsigned long *addr1, const unsigned long *addr2,
 					unsigned long nbits, unsigned long start);
+unsigned long _find_next_andnot_bit(const unsigned long *addr1, const unsigned long *addr2,
+					unsigned long nbits, unsigned long start);
 unsigned long _find_next_zero_bit(const unsigned long *addr, unsigned long nbits,
 					 unsigned long start);
 extern unsigned long _find_first_bit(const unsigned long *addr, unsigned long size);
@@ -91,6 +93,37 @@ unsigned long find_next_and_bit(const unsigned long *addr1,
 }
 #endif
 
+#ifndef find_next_andnot_bit
+/**
+ * find_next_andnot_bit - find the next set bit in *addr1 excluding all the bits
+ *                        in *addr2
+ * @addr1: The first address to base the search on
+ * @addr2: The second address to base the search on
+ * @size: The bitmap size in bits
+ * @offset: The bitnumber to start searching at
+ *
+ * Returns the bit number for the next set bit
+ * If no bits are set, returns @size.
+ */
+static inline
+unsigned long find_next_andnot_bit(const unsigned long *addr1,
+		const unsigned long *addr2, unsigned long size,
+		unsigned long offset)
+{
+	if (small_const_nbits(size)) {
+		unsigned long val;
+
+		if (unlikely(offset >= size))
+			return size;
+
+		val = *addr1 & ~*addr2 & GENMASK(size - 1, offset);
+		return val ? __ffs(val) : size;
+	}
+
+	return _find_next_andnot_bit(addr1, addr2, size, offset);
+}
+#endif
+
 #ifndef find_next_zero_bit
 /**
  * find_next_zero_bit - find the next cleared bit in a memory region

lib/find_bit.c

@@ -164,6 +164,15 @@ unsigned long _find_next_and_bit(const unsigned long *addr1, const unsigned long
 EXPORT_SYMBOL(_find_next_and_bit);
 #endif
 
+#ifndef find_next_andnot_bit
+unsigned long _find_next_andnot_bit(const unsigned long *addr1, const unsigned long *addr2,
+					unsigned long nbits, unsigned long start)
+{
+	return FIND_NEXT_BIT(addr1[idx] & ~addr2[idx], /* nop */, nbits, start);
+}
+EXPORT_SYMBOL(_find_next_andnot_bit);
+#endif
+
 #ifndef find_next_zero_bit
 unsigned long _find_next_zero_bit(const unsigned long *addr, unsigned long nbits,
 					 unsigned long start)