bitmap: Return size when no zero area is found

Return the bitmap size, rather than size + 1, when
bitmap_find_next_zero_area_off() cannot find a suitable area. This
matches the conventional find_bit() failure sentinel and still lets
callers detect failure with an out-of-range check.

Document the public failure contract as a value greater than or equal
to the bitmap size, without requiring callers to depend on the exact
sentinel.

Signed-off-by: Yury Norov <ynorov@nvidia.com>

include/linux/bitmap.h

@@ -209,6 +209,9 @@ unsigned long bitmap_find_next_zero_area_off(unsigned long *map,
  * The @align_mask should be one less than a power of 2; the effect is that
  * the bit offset of all zero areas this function finds is multiples of that
  * power of 2. A @align_mask of 0 means no alignment is required.
+ *
+ * Return: The bit offset of the found area or a value >= @size
+ * if no area is found.
  */
 static __always_inline
 unsigned long bitmap_find_next_zero_area(unsigned long *map,

lib/bitmap.c

@@ -424,6 +424,9 @@ EXPORT_SYMBOL(__bitmap_clear);
  * The @align_mask should be one less than a power of 2; the effect is that
  * the bit offset of all zero areas this function finds plus @align_offset
  * is multiple of that power of 2.
+ *
+ * Return: The bit offset of the found area or a value greater than or equal
+ * to @size if no area is found.
  */
 unsigned long bitmap_find_next_zero_area_off(unsigned long *map,
 					     unsigned long size,
@@ -448,12 +451,7 @@ unsigned long bitmap_find_next_zero_area_off(unsigned long *map,
 		start = i;
 	}
 
-	/*
-	 * Here, returning size + 1 is to maintain consistency
-	 * with the old version, where the return value is always
-	 * greater than size when no zero areas are found.
-	 */
-	return size + 1;
+	return size;
 }
 EXPORT_SYMBOL(bitmap_find_next_zero_area_off);