f2fs: support large nat bitmap

Previously, we will store all nat version bitmap in checkpoint pack block,
so our total node entry number has a limitation which caused total node
number can not exceed (3900 * 8) block * 455 node/block = 14196000. So
that once user wants to create more nodes in large size image, it becomes
a bottleneck, that's unreasonable.

This patch detects the new layout of nat/sit version bitmap in image in
order to enable supporting large nat bitmap.
Signed-off-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -1762,6 +1762,12 @@ static inline void *__bitmap_ptr(struct f2fs_sb_info *sbi, int flag)
 	struct f2fs_checkpoint *ckpt = F2FS_CKPT(sbi);
 	int offset;
 
+	if (is_set_ckpt_flags(sbi, CP_LARGE_NAT_BITMAP_FLAG)) {
+		offset = (flag == SIT_BITMAP) ?
+			le32_to_cpu(ckpt->nat_ver_bitmap_bytesize) : 0;
+		return &ckpt->sit_nat_version_bitmap + offset;
+	}
+
 	if (__cp_payload(sbi) > 0) {
 		if (flag == NAT_BITMAP)
 			return &ckpt->sit_nat_version_bitmap;

include/linux/f2fs_fs.h

@@ -116,6 +116,7 @@ struct f2fs_super_block {
 /*
  * For checkpoint
  */
+#define CP_LARGE_NAT_BITMAP_FLAG	0x00000400
 #define CP_NOCRC_RECOVERY_FLAG	0x00000200
 #define CP_TRIMMED_FLAG		0x00000100
 #define CP_NAT_BITS_FLAG	0x00000080