Btrfs: add a radix back bit tree

Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/bit-radix.c

@@ -0,0 +1,107 @@
+#include <linux/module.h>
+#include "bit-radix.h"
+
+#define BIT_ARRAY_BYTES 256
+#define BIT_RADIX_BITS_PER_ARRAY ((BIT_ARRAY_BYTES - sizeof(unsigned long)) * 8)
+
+int set_radix_bit(struct radix_tree_root *radix, unsigned long bit)
+{
+	unsigned long *bits;
+	unsigned long slot;
+	int bit_slot;
+	int ret;
+
+	slot = bit / BIT_RADIX_BITS_PER_ARRAY;
+	bit_slot = bit % BIT_RADIX_BITS_PER_ARRAY;
+
+	bits = radix_tree_lookup(radix, slot);
+	if (!bits) {
+		bits = kmalloc(BIT_ARRAY_BYTES, GFP_NOIO);
+		if (!bits)
+			return -ENOMEM;
+		memset(bits + 1, 0, BIT_ARRAY_BYTES - sizeof(unsigned long));
+		bits[0] = slot;
+		ret = radix_tree_insert(radix, slot, bits);
+		if (ret)
+			return ret;
+	}
+	set_bit(bit_slot, bits + 1);
+	return 0;
+}
+
+int test_radix_bit(struct radix_tree_root *radix, unsigned long bit)
+{
+	unsigned long *bits;
+	unsigned long slot;
+	int bit_slot;
+
+	slot = bit / BIT_RADIX_BITS_PER_ARRAY;
+	bit_slot = bit % BIT_RADIX_BITS_PER_ARRAY;
+
+	bits = radix_tree_lookup(radix, slot);
+	if (!bits)
+		return 0;
+	return test_bit(bit_slot, bits + 1);
+}
+
+int clear_radix_bit(struct radix_tree_root *radix, unsigned long bit)
+{
+	unsigned long *bits;
+	unsigned long slot;
+	int bit_slot;
+	int i;
+	int empty = 1;
+
+	slot = bit / BIT_RADIX_BITS_PER_ARRAY;
+	bit_slot = bit % BIT_RADIX_BITS_PER_ARRAY;
+
+	bits = radix_tree_lookup(radix, slot);
+	if (!bits)
+		return 0;
+	clear_bit(bit_slot, bits + 1);
+
+	for (i = 1; i < BIT_ARRAY_BYTES / sizeof(unsigned long); i++) {
+		if (bits[i]) {
+			empty = 0;
+			break;
+		}
+	}
+
+	if (empty) {
+		bits = radix_tree_delete(radix, slot);
+		BUG_ON(!bits);
+	}
+	return 0;
+}
+
+int find_first_radix_bit(struct radix_tree_root *radix, unsigned long *retbits,
+			 int nr)
+{
+	unsigned long *bits;
+	unsigned long *gang[4];
+	int found;
+	int ret;
+	int i;
+	int total_found = 0;
+
+	ret = radix_tree_gang_lookup(radix, (void *)&gang, 0, ARRAY_SIZE(gang));
+	for (i = 0; i < ret && nr > 0; i++) {
+		found = 0;
+		bits = gang[i];
+		while(nr > 0) {
+			found = find_next_bit(bits + 1,
+					      BIT_RADIX_BITS_PER_ARRAY,
+					      found);
+			if (found < BIT_RADIX_BITS_PER_ARRAY) {
+				*retbits = bits[0] *
+					BIT_RADIX_BITS_PER_ARRAY + found;
+				retbits++;
+				nr--;
+				total_found++;
+				found++;
+			} else
+				break;
+		}
+	}
+	return total_found;
+}