f2fs: introduce __find_rev_next(_zero)_bit

When f2fs_set_bit is used, in a byte MSB and LSB is reversed,
in that case we can use __find_rev_next_bit or __find_rev_next_zero_bit.

Signed-off-by: Changman Lee <cm224.lee@samsung.com>
[Jaegeuk Kim: change the function names]
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index fa284d397199faed53f1c8ffb4de611440ad2e73..aa1d30d76719ca11a79ad2f56a07e7d71cea45ef 100644 (file)
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -20,6 +20,154 @@
 #include "node.h"
 #include <trace/events/f2fs.h>
 
+#define __reverse_ffz(x) __reverse_ffs(~(x))
+
+/*
+ * __reverse_ffs is copied from include/asm-generic/bitops/__ffs.h since
+ * MSB and LSB are reversed in a byte by f2fs_set_bit.
+ */
+static inline unsigned long __reverse_ffs(unsigned long word)
+{
+       int num = 0;
+
+#if BITS_PER_LONG == 64
+       if ((word & 0xffffffff) == 0) {
+               num += 32;
+               word >>= 32;
+       }
+#endif
+       if ((word & 0xffff) == 0) {
+               num += 16;
+               word >>= 16;
+       }
+       if ((word & 0xff) == 0) {
+               num += 8;
+               word >>= 8;
+       }
+       if ((word & 0xf0) == 0)
+               num += 4;
+       else
+               word >>= 4;
+       if ((word & 0xc) == 0)
+               num += 2;
+       else
+               word >>= 2;
+       if ((word & 0x2) == 0)
+               num += 1;
+       return num;
+}
+
+/*
+ * __find_rev_next(_zero)_bit is copied from lib/find_next_bit.c becasue
+ * f2fs_set_bit makes MSB and LSB reversed in a byte.
+ * Example:
+ *                             LSB <--> MSB
+ *   f2fs_set_bit(0, bitmap) => 0000 0001
+ *   f2fs_set_bit(7, bitmap) => 1000 0000
+ */
+static unsigned long __find_rev_next_bit(const unsigned long *addr,
+                       unsigned long size, unsigned long offset)
+{
+       const unsigned long *p = addr + BIT_WORD(offset);
+       unsigned long result = offset & ~(BITS_PER_LONG - 1);
+       unsigned long tmp;
+       unsigned long mask, submask;
+       unsigned long quot, rest;
+
+       if (offset >= size)
+               return size;
+
+       size -= result;
+       offset %= BITS_PER_LONG;
+       if (!offset)
+               goto aligned;
+
+       tmp = *(p++);
+       quot = (offset >> 3) << 3;
+       rest = offset & 0x7;
+       mask = ~0UL << quot;
+       submask = (unsigned char)(0xff << rest) >> rest;
+       submask <<= quot;
+       mask &= submask;
+       tmp &= mask;
+       if (size < BITS_PER_LONG)
+               goto found_first;
+       if (tmp)
+               goto found_middle;
+
+       size -= BITS_PER_LONG;
+       result += BITS_PER_LONG;
+aligned:
+       while (size & ~(BITS_PER_LONG-1)) {
+               tmp = *(p++);
+               if (tmp)
+                       goto found_middle;
+               result += BITS_PER_LONG;
+               size -= BITS_PER_LONG;
+       }
+       if (!size)
+               return result;
+       tmp = *p;
+found_first:
+       tmp &= (~0UL >> (BITS_PER_LONG - size));
+       if (tmp == 0UL)         /* Are any bits set? */
+               return result + size;   /* Nope. */
+found_middle:
+       return result + __reverse_ffs(tmp);
+}
+
+static unsigned long __find_rev_next_zero_bit(const unsigned long *addr,
+                       unsigned long size, unsigned long offset)
+{
+       const unsigned long *p = addr + BIT_WORD(offset);
+       unsigned long result = offset & ~(BITS_PER_LONG - 1);
+       unsigned long tmp;
+       unsigned long mask, submask;
+       unsigned long quot, rest;
+
+       if (offset >= size)
+               return size;
+
+       size -= result;
+       offset %= BITS_PER_LONG;
+       if (!offset)
+               goto aligned;
+
+       tmp = *(p++);
+       quot = (offset >> 3) << 3;
+       rest = offset & 0x7;
+       mask = ~(~0UL << quot);
+       submask = (unsigned char)~((unsigned char)(0xff << rest) >> rest);
+       submask <<= quot;
+       mask += submask;
+       tmp |= mask;
+       if (size < BITS_PER_LONG)
+               goto found_first;
+       if (~tmp)
+               goto found_middle;
+
+       size -= BITS_PER_LONG;
+       result += BITS_PER_LONG;
+aligned:
+       while (size & ~(BITS_PER_LONG - 1)) {
+               tmp = *(p++);
+               if (~tmp)
+                       goto found_middle;
+               result += BITS_PER_LONG;
+               size -= BITS_PER_LONG;
+       }
+       if (!size)
+               return result;
+       tmp = *p;
+
+found_first:
+       tmp |= ~0UL << size;
+       if (tmp == ~0UL)        /* Are any bits zero? */
+               return result + size;   /* Nope. */
+found_middle:
+       return result + __reverse_ffz(tmp);
+}
+
 /*
  * This function balances dirty node and dentry pages.
  * In addition, it controls garbage collection.