1 files changed, 111 insertions, 52 deletions

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 48e708381d44..8acab0e176ef 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -676,84 +676,143 @@ int bitmap_bitremap(int oldbit, const unsigned long *old,
 }
 EXPORT_SYMBOL(bitmap_bitremap);
 
-/**
- *      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)
+/*
+ * Common code for bitmap_*_region() routines.
+ *      bitmap: array of unsigned longs corresponding to the bitmap
+ *      pos: the beginning of the region
+ *      order: region size (log base 2 of number of bits)
+ *      reg_op: operation(s) to perform on that region of bitmap
  *
- * 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).
+ * Can set, verify and/or release a region of bits in a bitmap,
+ * depending on which combination of REG_OP_* flag bits is set.
  *
- * The region is marked as set bits in the bitmap if a free one is
- * found.
+ * A region of a bitmap is a sequence of bits in the bitmap, of
+ * some size '1 << order' (a power of two), aligned to that same
+ * '1 << order' power of two.
  *
- * Returns either beginning of region or negative error
+ * Returns 1 if REG_OP_ISFREE succeeds (region is all zero bits).
+ * Returns 0 in all other cases and reg_ops.
  */
-int bitmap_find_free_region(unsigned long *bitmap, int bits, int order)
-{
-        unsigned long mask;
-        int pages = 1 << order;
-        int i;
 
-        if(pages > BITS_PER_LONG)
-                return -EINVAL;
+enum {
+        REG_OP_ISFREE,          /* true if region is all zero bits */
+        REG_OP_ALLOC,           /* set all bits in region */
+        REG_OP_RELEASE,         /* clear all bits in region */
+};
 
-        /* make a mask of the order */
-        mask = (1ul << (pages - 1));
+static int __reg_op(unsigned long *bitmap, int pos, int order, int reg_op)
+{
+        int nbits_reg;          /* number of bits in region */
+        int index;              /* index first long of region in bitmap */
+        int offset;             /* bit offset region in bitmap[index] */
+        int nlongs_reg;         /* num longs spanned by region in bitmap */
+        int nbitsinlong;        /* num bits of region in each spanned long */
+        unsigned long mask;     /* bitmask for one long of region */
+        int i;                  /* scans bitmap by longs */
+        int ret = 0;            /* return value */
+
+        /*
+         * Either nlongs_reg == 1 (for small orders that fit in one long)
+         * or (offset == 0 && mask == ~0UL) (for larger multiword orders.)
+         */
+        nbits_reg = 1 << order;
+        index = pos / BITS_PER_LONG;
+        offset = pos - (index * BITS_PER_LONG);
+        nlongs_reg = BITS_TO_LONGS(nbits_reg);
+        nbitsinlong = min(nbits_reg,  BITS_PER_LONG);
+
+        /*
+         * Can't do "mask = (1UL << nbitsinlong) - 1", as that
+         * overflows if nbitsinlong == BITS_PER_LONG.
+         */
+        mask = (1UL << (nbitsinlong - 1));
         mask += mask - 1;
+        mask <<= offset;
 
-        /* run up the bitmap pages bits at a time */
-        for (i = 0; i < bits; i += pages) {
-                int index = i/BITS_PER_LONG;
-                int offset = i - (index * BITS_PER_LONG);
-                if((bitmap[index] & (mask << offset)) == 0) {
-                        /* set region in bimap */
-                        bitmap[index] |= (mask << offset);
-                        return i;
+        switch (reg_op) {
+        case REG_OP_ISFREE:
+                for (i = 0; i < nlongs_reg; i++) {
+                        if (bitmap[index + i] & mask)
+                                goto done;
                 }
+                ret = 1;        /* all bits in region free (zero) */
+                break;
+
+        case REG_OP_ALLOC:
+                for (i = 0; i < nlongs_reg; i++)
+                        bitmap[index + i] |= mask;
+                break;
+
+        case REG_OP_RELEASE:
+                for (i = 0; i < nlongs_reg; i++)
+                        bitmap[index + i] &= ~mask;
+                break;
         }
-        return -ENOMEM;
+done:
+        return ret;
+}
+
+/**
+ * bitmap_find_free_region - find a contiguous aligned mem region
+ *      @bitmap: array of unsigned longs corresponding to the bitmap
+ *      @bits: number of bits in the bitmap
+ *      @order: region size (log base 2 of number of bits) to find
+ *
+ * Find a region of free (zero) bits in a @bitmap of @bits bits and
+ * allocate them (set them to one).  Only consider regions of length
+ * a power (@order) of two, aligned to that power of two, which
+ * makes the search algorithm much faster.
+ *
+ * Return the bit offset in bitmap of the allocated region,
+ * or -errno on failure.
+ */
+int bitmap_find_free_region(unsigned long *bitmap, int bits, int order)
+{
+        int pos;                /* scans bitmap by regions of size order */
+
+        for (pos = 0; pos < bits; pos += (1 << order))
+                if (__reg_op(bitmap, pos, order, REG_OP_ISFREE))
+                        break;
+        if (pos == bits)
+                return -ENOMEM;
+        __reg_op(bitmap, pos, order, REG_OP_ALLOC);
+        return pos;
 }
 EXPORT_SYMBOL(bitmap_find_free_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)
+ * bitmap_release_region - release allocated bitmap region
+ *      @bitmap: array of unsigned longs corresponding to the bitmap
+ *      @pos: beginning of bit region to release
+ *      @order: region size (log base 2 of number of bits) to release
  *
  * This is the complement to __bitmap_find_free_region and releases
  * the found region (by clearing it in the bitmap).
+ *
+ * No return value.
  */
 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 offset = pos - (index * BITS_PER_LONG);
-        mask += mask - 1;
-        bitmap[index] &= ~(mask << offset);
+        __reg_op(bitmap, pos, order, REG_OP_RELEASE);
 }
 EXPORT_SYMBOL(bitmap_release_region);
 
+/**
+ * bitmap_allocate_region - allocate bitmap region
+ *      @bitmap: array of unsigned longs corresponding to the bitmap
+ *      @pos: beginning of bit region to allocate
+ *      @order: region size (log base 2 of number of bits) to allocate
+ *
+ * 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 offset = pos - (index * BITS_PER_LONG);
-
-        /* We don't do regions of pages > 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);
-        mask += mask - 1;
-        if (bitmap[index] & (mask << offset))
+        if (!__reg_op(bitmap, pos, order, REG_OP_ISFREE))
                 return -EBUSY;
-        bitmap[index] |= (mask << offset);
+        __reg_op(bitmap, pos, order, REG_OP_ALLOC);
         return 0;
 }
 EXPORT_SYMBOL(bitmap_allocate_region);