nilfs2: add document

	- info on Novell Netware(tm) filesystem using NCP protocol.

nfsroot.txt

	- short guide on setting up a diskless box with NFS root filesystem.

nilfs2.txt

	- info and mount options for the NILFS2 filesystem.

ntfs.txt

	- info and mount options for the NTFS filesystem (Windows NT).

ocfs2.txt

NILFS2

------

NILFS2 is a log-structured file system (LFS) supporting continuous

snapshotting.  In addition to versioning capability of the entire file

system, users can even restore files mistakenly overwritten or

destroyed just a few seconds ago.  Since NILFS2 can keep consistency

like conventional LFS, it achieves quick recovery after system

crashes.

NILFS2 creates a number of checkpoints every few seconds or per

synchronous write basis (unless there is no change).  Users can select

significant versions among continuously created checkpoints, and can

change them into snapshots which will be preserved until they are

changed back to checkpoints.

There is no limit on the number of snapshots until the volume gets

full.  Each snapshot is mountable as a read-only file system

concurrently with its writable mount, and this feature is convenient

for online backup.

The userland tools are included in nilfs-utils package, which is

available from the following download page.  At least "mkfs.nilfs2",

"mount.nilfs2", "umount.nilfs2", and "nilfs_cleanerd" (so called

cleaner or garbage collector) are required.  Details on the tools are

described in the man pages included in the package.

Project web page:    http://www.nilfs.org/en/

Download page:       http://www.nilfs.org/en/download.html

Git tree web page:   http://www.nilfs.org/git/

NILFS mailing lists: http://www.nilfs.org/mailman/listinfo/users

Caveats

=======

Features which NILFS2 does not support yet:

	- atime

	- extended attributes

	- POSIX ACLs

	- quotas

	- writable snapshots

	- remote backup (CDP)

	- data integrity

	- defragmentation

Mount options

=============

NILFS2 supports the following mount options:

(*) == default

barrier=on(*)		This enables/disables barriers. barrier=off disables

			it, barrier=on enables it.

errors=continue(*)	Keep going on a filesystem error.

errors=remount-ro	Remount the filesystem read-only on an error.

errors=panic		Panic and halt the machine if an error occurs.

cp=n			Specify the checkpoint-number of the snapshot to be

			mounted.  Checkpoints and snapshots are listed by lscp

			user command.  Only the checkpoints marked as snapshot

			are mountable with this option.  Snapshot is read-only,

			so a read-only mount option must be specified together.

order=relaxed(*)	Apply relaxed order semantics that allows modified data

			blocks to be written to disk without making a

			checkpoint if no metadata update is going.  This mode

			is equivalent to the ordered data mode of the ext3

			filesystem except for the updates on data blocks still

			conserve atomicity.  This will improve synchronous

			write performance for overwriting.

order=strict		Apply strict in-order semantics that preserves sequence

			of all file operations including overwriting of data

			blocks.  That means, it is guaranteed that no

			overtaking of events occurs in the recovered file

			system after a crash.

NILFS2 usage

============

To use nilfs2 as a local file system, simply:

 # mkfs -t nilfs2 /dev/block_device

 # mount -t nilfs2 /dev/block_device /dir

This will also invoke the cleaner through the mount helper program

(mount.nilfs2).

Checkpoints and snapshots are managed by the following commands.

Their manpages are included in the nilfs-utils package above.

  lscp     list checkpoints or snapshots.

  mkcp     make a checkpoint or a snapshot.

  chcp     change an existing checkpoint to a snapshot or vice versa.

  rmcp     invalidate specified checkpoint(s).

To mount a snapshot,

 # mount -t nilfs2 -r -o cp=<cno> /dev/block_device /snap_dir

where <cno> is the checkpoint number of the snapshot.

To unmount the NILFS2 mount point or snapshot, simply:

 # umount /dir

Then, the cleaner daemon is automatically shut down by the umount

helper program (umount.nilfs2).

Disk format

===========

A nilfs2 volume is equally divided into a number of segments except

for the super block (SB) and segment #0.  A segment is the container

of logs.  Each log is composed of summary information blocks, payload

blocks, and an optional super root block (SR):

   ______________________________________________________

  | |SB| | Segment | Segment | Segment | ... | Segment | |

  |_|__|_|____0____|____1____|____2____|_____|____N____|_|

  0 +1K +4K       +8M       +16M      +24M  +(8MB x N)

       .             .            (Typical offsets for 4KB-block)

    .                  .

  .______________________.

  | log | log |... | log |

  |__1__|__2__|____|__m__|

        .       .

      .               .

    .                       .

  .______________________________.

  | Summary | Payload blocks  |SR|

  |_blocks__|_________________|__|

The payload blocks are organized per file, and each file consists of

data blocks and B-tree node blocks:

    |<---       File-A        --->|<---       File-B        --->|

   _______________________________________________________________

    | Data blocks | B-tree blocks | Data blocks | B-tree blocks | ...

   _|_____________|_______________|_____________|_______________|_

Since only the modified blocks are written in the log, it may have

files without data blocks or B-tree node blocks.

The organization of the blocks is recorded in the summary information

blocks, which contains a header structure (nilfs_segment_summary), per

file structures (nilfs_finfo), and per block structures (nilfs_binfo):

  _________________________________________________________________________

 | Summary | finfo | binfo | ... | binfo | finfo | binfo | ... | binfo |...

 |_blocks__|___A___|_(A,1)_|_____|(A,Na)_|___B___|_(B,1)_|_____|(B,Nb)_|___

The logs include regular files, directory files, symbolic link files

and several meta data files.  The mata data files are the files used

to maintain file system meta data.  The current version of NILFS2 uses

the following meta data files:

 1) Inode file (ifile)             -- Stores on-disk inodes

 2) Checkpoint file (cpfile)       -- Stores checkpoints

 3) Segment usage file (sufile)    -- Stores allocation state of segments

 4) Data address translation file  -- Maps virtual block numbers to usual

    (DAT)                             block numbers.  This file serves to

                                      make on-disk blocks relocatable.

 5) Sketch file (sketch)           -- Keeps read-only data which can be

                                      associated with checkpoints (optional)

The following figure shows a typical organization of the logs:

  _________________________________________________________________________

 | Summary | regular file | file  | ... | ifile | cpfile | sufile | DAT |SR|

 |_blocks__|_or_directory_|_______|_____|_______|________|________|_____|__|

To stride over segment boundaries, this sequence of files may be split

into multiple logs.  The sequence of logs that should be treated as

logically one log, is delimited with flags marked in the segment

summary.  The recovery code of nilfs2 looks this boundary information

to ensure atomicity of updates.

The super root block is inserted for every checkpoints.  It includes

three special inodes, inodes for the DAT, cpfile, and sufile.  Inodes

of regular files, directories, symlinks and other special files, are

included in the ifile.  The inode of ifile itself is included in the

corresponding checkpoint entry in the cpfile.  Thus, the hierarchy

among NILFS2 files can be depicted as follows:

  Super block (SB)

       |

       v

  Super root block (the latest cno=xx)

       |-- DAT

       |-- sufile

       `-- cpfile

              |-- ifile (cno=c1)

              |-- ifile (cno=c2) ---- file (ino=i1)

              :        :          |-- file (ino=i2)

              `-- ifile (cno=xx)  |-- file (ino=i3)

                                  :        :

                                  `-- file (ino=yy)

                                    ( regular file, directory, or symlink )

For detail on the format of each file, please see include/linux/nilfs2_fs.h.