f2fs: fix to migrate blocks correctly during defragment

During defragment, we missed to trigger fragmented blocks migration
for below condition:

In defragment region:
- total number of valid blocks is smaller than 512;
- the tail part of the region are all holes;

In addtion, return zero to user via range->len if there is no
fragmented blocks.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -2383,8 +2383,10 @@ static int f2fs_defragment_range(struct f2fs_sb_info *sbi,
 		map.m_lblk += map.m_len;
 	}
 
-	if (!fragmented)
+	if (!fragmented) {
+		total = 0;
 		goto out;
+	}
 
 	sec_num = DIV_ROUND_UP(total, BLKS_PER_SEC(sbi));
 
@@ -2414,7 +2416,7 @@ static int f2fs_defragment_range(struct f2fs_sb_info *sbi,
 
 		if (!(map.m_flags & F2FS_MAP_FLAGS)) {
 			map.m_lblk = next_pgofs;
-			continue;
+			goto check;
 		}
 
 		set_inode_flag(inode, FI_DO_DEFRAG);
@@ -2438,8 +2440,8 @@ static int f2fs_defragment_range(struct f2fs_sb_info *sbi,
 		}
 
 		map.m_lblk = idx;
-
-		if (idx < pg_end && cnt < blk_per_seg)
+check:
+		if (map.m_lblk < pg_end && cnt < blk_per_seg)
 			goto do_map;
 
 		clear_inode_flag(inode, FI_DO_DEFRAG);