[PATCH] bitmap: region cleanup

[mirror_ubuntu-artful-kernel.git] / lib / bitmap.c

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 48e708381d44d0fb4ce1810aa24fc819ceaf7e2d..3fab1ce9ac65b2a7c7f5ab6c2b34ddd4c21e30f4 100644 (file)
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -677,39 +677,38 @@ int bitmap_bitremap(int oldbit, const unsigned long *old,
 EXPORT_SYMBOL(bitmap_bitremap);
 
 /**
- *     bitmap_find_free_region - find a contiguous aligned mem region
+ * bitmap_find_free_region - find a contiguous aligned mem region
  *     @bitmap: an array of unsigned longs corresponding to the bitmap
  *     @bits: number of bits in the bitmap
  *     @order: region size to find (size is actually 1<<order)
  *
- * This is used to allocate a memory region from a bitmap.  The idea is
- * that the region has to be 1<<order sized and 1<<order aligned (this
- * makes the search algorithm much faster).
+ * Find a sequence of free (zero) bits in a bitmap and allocate
+ * them (set them to one).  Only consider sequences of length a
+ * power ('order') of two, aligned to that power of two, which
+ * makes the search algorithm much faster.
  *
- * The region is marked as set bits in the bitmap if a free one is
- * found.
- *
- * Returns either beginning of region or negative error
+ * Return the bit offset in bitmap of the allocated sequence,
+ * or -errno on failure.
  */
 int bitmap_find_free_region(unsigned long *bitmap, int bits, int order)
 {
        unsigned long mask;
-       int pages = 1 << order;
+       int nbits = 1 << order;
        int i;
 
-       if(pages > BITS_PER_LONG)
+       if (nbits > BITS_PER_LONG)
                return -EINVAL;
 
        /* make a mask of the order */
-       mask = (1ul << (pages - 1));
+       mask = (1UL << (nbits - 1));
        mask += mask - 1;
 
-       /* run up the bitmap pages bits at a time */
-       for (i = 0; i < bits; i += pages) {
-               int index = i/BITS_PER_LONG;
+       /* run up the bitmap nbits at a time */
+       for (i = 0; i < bits; i += nbits) {
+               int index = i / BITS_PER_LONG;
                int offset = i - (index * BITS_PER_LONG);
-               if((bitmap[index] & (mask << offset)) == 0) {
-                       /* set region in bimap */
+               if ((bitmap[index] & (mask << offset)) == 0) {
+                       /* set region in bitmap */
                        bitmap[index] |= (mask << offset);
                        return i;
                }
@@ -719,7 +718,7 @@ int bitmap_find_free_region(unsigned long *bitmap, int bits, int order)
 EXPORT_SYMBOL(bitmap_find_free_region);
 
 /**
- *     bitmap_release_region - release allocated bitmap region
+ * bitmap_release_region - release allocated bitmap region
  *     @bitmap: a pointer to the bitmap
  *     @pos: the beginning of the region
  *     @order: the order of the bits to release (number is 1<<order)
@@ -729,27 +728,40 @@ EXPORT_SYMBOL(bitmap_find_free_region);
  */
 void bitmap_release_region(unsigned long *bitmap, int pos, int order)
 {
-       int pages = 1 << order;
-       unsigned long mask = (1ul << (pages - 1));
-       int index = pos/BITS_PER_LONG;
+       int nbits = 1 << order;
+       unsigned long mask = (1UL << (nbits - 1));
+       int index = pos / BITS_PER_LONG;
        int offset = pos - (index * BITS_PER_LONG);
+
        mask += mask - 1;
        bitmap[index] &= ~(mask << offset);
 }
 EXPORT_SYMBOL(bitmap_release_region);
 
+/**
+ * bitmap_allocate_region - allocate bitmap region
+ *     @bitmap: a pointer to the bitmap
+ *     @pos: the beginning of the region
+ *     @order: the order of the bits to allocate (number is 1<<order)
+ *
+ * Allocate (set bits in) a specified region of a bitmap.
+ * Return 0 on success, or -EBUSY if specified region wasn't
+ * free (not all bits were zero).
+ */
 int bitmap_allocate_region(unsigned long *bitmap, int pos, int order)
 {
-       int pages = 1 << order;
-       unsigned long mask = (1ul << (pages - 1));
-       int index = pos/BITS_PER_LONG;
+       int nbits = 1 << order;
+       unsigned long mask = (1UL << (nbits - 1));
+       int index = pos / BITS_PER_LONG;
        int offset = pos - (index * BITS_PER_LONG);
 
-       /* We don't do regions of pages > BITS_PER_LONG.  The
+       /*
+        * We don't do regions of nbits > BITS_PER_LONG.  The
         * algorithm would be a simple look for multiple zeros in the
         * array, but there's no driver today that needs this.  If you
-        * trip this BUG(), you get to code it... */
-       BUG_ON(pages > BITS_PER_LONG);
+        * trip this BUG(), you get to code it...
+        */
+       BUG_ON(nbits > BITS_PER_LONG);
        mask += mask - 1;
        if (bitmap[index] & (mask << offset))
                return -EBUSY;