Add find_next_zero_string to lib/ and bitops.h

Used to be x86-64 specific before it was removed. Readding
it as generic code because I need it for future patches.

This version assumes that most searches are for only a single
bit; it doesn't try to be particularly efficient for multiple
bits (but is also not too bad either)

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andi Kleen <andi@firstfloor.org>

---
 include/linux/bitops.h |    3 +++
 lib/Makefile           |    2 +-
 lib/bitstr.c           |   28 ++++++++++++++++++++++++++++
 3 files changed, 32 insertions(+), 1 deletion(-)

Index: linux/include/linux/bitops.h
===================================================================
--- linux.orig/include/linux/bitops.h
+++ linux/include/linux/bitops.h
@@ -72,4 +72,7 @@ static inline unsigned fls_long(unsigned
 	return fls64(l);
 }
 
+extern unsigned long find_next_zero_string(unsigned long *bitmap,
+					   long start, long nbits, int len);
+
 #endif
Index: linux/lib/bitstr.c
===================================================================
--- /dev/null
+++ linux/lib/bitstr.c
@@ -0,0 +1,27 @@
+#include <linux/module.h>
+#include <linux/bitops.h>
+
+/* Find string of zero bits in a bitmap */
+unsigned long
+find_next_zero_string(unsigned long *bitmap, long start, long nbits, int len)
+{
+	unsigned long n, end, i;
+
+ again:
+	n = find_next_zero_bit(bitmap, nbits, start);
+	if (n == -1)
+		return -1;
+
+	/* could test bitsliced, but it's hardly worth it */
+	end = n+len;
+	if (end >= nbits)
+		return -1;
+	for (i = n+1; i < end; i++) {
+		if (test_bit(i, bitmap)) {
+			start = i+1;
+			goto again;
+		}
+	}
+	return n;
+}
+EXPORT_SYMBOL(find_next_zero_string);
Index: linux/lib/Makefile
===================================================================
--- linux.orig/lib/Makefile
+++ linux/lib/Makefile
@@ -6,7 +6,7 @@ lib-y := ctype.o string.o vsprintf.o cmd
 	 rbtree.o radix-tree.o dump_stack.o \
 	 idr.o int_sqrt.o extable.o prio_tree.o \
 	 sha1.o irq_regs.o reciprocal_div.o argv_split.o \
-	 proportions.o prio_heap.o
+	 proportions.o prio_heap.o bitstr.o
 
 lib-$(CONFIG_MMU) += ioremap.o
 lib-$(CONFIG_SMP) += cpumask.o