fsck.f2fs checks file system consistency, but does not repair a broken
file system yet.
dump.f2fs shows the information of a specific inode and makes dump file
of SSA and SIT.
f2fs checks file system consistency as follows:
 o When data about used area and its metadata are identical,
   f2fs is considered consistent. To verify such consistency, we use
   three bitmaps: nat_area_bitmap, sit_area_bitmap, and main_area_bitmap.
   First, each bit in nat_area_bitmap corresponds to a nid in NAT.
   Second, each bit in sit_area_bitmap corresponds to a valid block in a
   segment. This bitmap is same to the total valid_map of f2fs_sit_entries
   in SIT.
   Last, each bit in main_area_bitmap corresponds to a block in main area
   except meta area.
   After a consistency check of each block, we set or clear the
   corresponding bit of each bitmap.
   From the root node, we start consistency check. The verified
   information varies according to block type.
   1. NODE
     - Read information of node block from NAT
     - Check if block address is allocated using node info.
     - Check if the type of f2fs_summary related to nid in SSA is NODE.
     - Update the corresponding bit in nat_area_bitmap.
     - Update the corresponding bit in sit_area_bitmap.
     - Set the corresponding bit in main_area_bitmap to 1.
     - Then, read node block. According to its attribute, explore
       inode/direct node/indirect node/double indirect node
       recursively.
     - If it is an inode block, we also check its xattr and hard link.
   2. DATA
     - Check if the type of f2fs_summary related to nid in SSA is DATA.
     - Set the corresponding bits of sit_area_bitmap and
       main_area_bitmap to visited
     - If it is a dentry block, traverse each dentries that may be
       regular
       file or directory. At this time, it will check inode block again.
   Finally, we verify whether
     - every nat_area_bitmap is visited
     - any unreachable hard link exists
     - values of sit_area_bitmap and main_area_bitmap are identical
     - total_valid_block_count/node_count/inode_count are correct

Usage:
 o fsck.f2fs
   # fsck.f2fs /dev/sdx
   options:
     -d debug level [default:0]
 o dump.f2fs
   # dump.f2fs -i [ino] /dev/sdx
   # dump.f2fs -s 0~-1 /dev/sdx (SIT dump)
   # dump.f2fs -a 0~-1 /dev/sdx (SSA dump)
   options:
     -d debug level [default:0]
     -i inode no (hex)
     -s [SIT dump segno from #1~#2 (decimal), for all 0~-1]
     -a [SSA dump segno from #1~#2 (decimal), for all 0~-1]

Note: To use dump.f2fs, please run make install or ln -s fsck.f2fs
dump.f2fs

Signed-off-by: Changman Lee <cm224.lee@samsung.com>
Signed-off-by: Byoung Geun Kim <bgbg.kim@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>