lib: bitmap: add alignment offset for bitmap_find_next_zero_area()

Add a bitmap_find_next_zero_area_off() function which works like
bitmap_find_next_zero_area() function except it allows an offset to be
specified when alignment is checked.  This lets caller request a bit such
that its number plus the offset is aligned according to the mask.

[[email protected]: Retrieved from https://patchwork.linuxtv.org/patch/6254/ and updated documentation]
Signed-off-by: Michal Nazarewicz <[email protected]>
Signed-off-by: Kyungmin Park <[email protected]>
Signed-off-by: Marek Szyprowski <[email protected]>
Signed-off-by: Gregory Fong <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Kukjin Kim <[email protected]>
Cc: Laurent Pinchart <[email protected]>
Cc: Laura Abbott <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/bitmap.h

@@ -45,6 +45,7 @@
  * bitmap_set(dst, pos, nbits)			Set specified bit area
  * bitmap_clear(dst, pos, nbits)		Clear specified bit area
  * bitmap_find_next_zero_area(buf, len, pos, n, mask)	Find bit free area
+ * bitmap_find_next_zero_area_off(buf, len, pos, n, mask)	as above
  * bitmap_shift_right(dst, src, n, nbits)	*dst = *src >> n
  * bitmap_shift_left(dst, src, n, nbits)	*dst = *src << n
  * bitmap_remap(dst, src, old, new, nbits)	*dst = map(old, new)(src)
@@ -114,11 +115,36 @@ extern int __bitmap_weight(const unsigned long *bitmap, unsigned int nbits);
 
 extern void bitmap_set(unsigned long *map, unsigned int start, int len);
 extern void bitmap_clear(unsigned long *map, unsigned int start, int len);
-extern unsigned long bitmap_find_next_zero_area(unsigned long *map,
-					 unsigned long size,
-					 unsigned long start,
-					 unsigned int nr,
-					 unsigned long align_mask);
+
+extern unsigned long bitmap_find_next_zero_area_off(unsigned long *map,
+						    unsigned long size,
+						    unsigned long start,
+						    unsigned int nr,
+						    unsigned long align_mask,
+						    unsigned long align_offset);
+
+/**
+ * bitmap_find_next_zero_area - find a contiguous aligned zero area
+ * @map: The address to base the search on
+ * @size: The bitmap size in bits
+ * @start: The bitnumber to start searching at
+ * @nr: The number of zeroed bits we're looking for
+ * @align_mask: Alignment mask for zero area
+ *
+ * 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.
+ */
+static inline unsigned long
+bitmap_find_next_zero_area(unsigned long *map,
+			   unsigned long size,
+			   unsigned long start,
+			   unsigned int nr,
+			   unsigned long align_mask)
+{
+	return bitmap_find_next_zero_area_off(map, size, start, nr,
+					      align_mask, 0);
+}
 
 extern int bitmap_scnprintf(char *buf, unsigned int len,
 			const unsigned long *src, int nbits);

lib/bitmap.c

@@ -326,30 +326,32 @@ void bitmap_clear(unsigned long *map, unsigned int start, int len)
 }
 EXPORT_SYMBOL(bitmap_clear);
 
-/*
- * bitmap_find_next_zero_area - find a contiguous aligned zero area
+/**
+ * bitmap_find_next_zero_area_off - find a contiguous aligned zero area
  * @map: The address to base the search on
  * @size: The bitmap size in bits
  * @start: The bitnumber to start searching at
  * @nr: The number of zeroed bits we're looking for
  * @align_mask: Alignment mask for zero area
+ * @align_offset: Alignment offset for zero area.
  *
  * 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.
+ * the bit offset of all zero areas this function finds plus @align_offset
+ * is multiple of that power of 2.
  */
-unsigned long bitmap_find_next_zero_area(unsigned long *map,
-					 unsigned long size,
-					 unsigned long start,
-					 unsigned int nr,
-					 unsigned long align_mask)
+unsigned long bitmap_find_next_zero_area_off(unsigned long *map,
+					     unsigned long size,
+					     unsigned long start,
+					     unsigned int nr,
+					     unsigned long align_mask,
+					     unsigned long align_offset)
 {
 	unsigned long index, end, i;
 again:
 	index = find_next_zero_bit(map, size, start);
 
 	/* Align allocation */
-	index = __ALIGN_MASK(index, align_mask);
+	index = __ALIGN_MASK(index + align_offset, align_mask) - align_offset;
 
 	end = index + nr;
 	if (end > size)
@@ -361,7 +363,7 @@ again:
 	}
 	return index;
 }
-EXPORT_SYMBOL(bitmap_find_next_zero_area);
+EXPORT_SYMBOL(bitmap_find_next_zero_area_off);
 
 /*
  * Bitmap printing & parsing functions: first version by Nadia Yvette Chambers,