[RFC 0/8] Aufs2 documents

[hooanon05]

Hello,

This is my second trial to ask incorporating aufs into mainline.
Aufs2 is a refined version of old aufs1:
- to be reviewed easily and widely.
- to make the source files simpler and smaller by dropping several
  original features.

Before posting source files, here are some documents from aufs2 which
describes some of ideas, design or approaches which are implemented.
Kindly review and let me know your comments.

J. R. Okajima


----------------------------------------------------------------------

Aufs2 -- advanced multi layered unification filesystem version 2
http://aufs.sf.net
Junjiro R. Okajima


0. Introduction
----------------------------------------
In the early days, aufs was entirely re-designed and re-implemented
Unionfs Version 1.x series. After many original ideas, approaches,
improvements and implementations, it becomes totally different from
Unionfs while keeping the basic features.
Recently, Unionfs Version 2.x series begin taking some of the same
approaches to aufs1's.
Unionfs is being developed by Professor Erez Zadok at Stony Brook
University and his team.

This version of AUFS, aufs2 has several purposes.
- to be reviewed easily and widely.
- to make the source files simpler and smaller by dropping several
  original features.

Through this work, I found some bad things in aufs1 source code and
fixed them. Some of the dropped features will be reverted in the future,
but not all I'm afraid.
Aufs2 supports linux-2.6.27 and later. If you want older kernel version
support, try aufs1 from CVS on SourceForge.


1. Features
----------------------------------------
- unite several directories into a single virtual filesystem. The member
  directory is called as a branch.
- you can specify the permission flags to the branch, which are 'readonly',
  'readwrite' and 'whiteout-able.'
- by upper writable branch, internal copyup and whiteout, files/dirs on
  readonly branch are modifiable logically.
- dynamic branch manipulation, add, del.
- etc...

Also there are many enhancements in aufs1, such as:
- keep inode number by external inode number table
- keep the timestamps of file/dir in internal copyup operation
- seekable directory, supporting NFS readdir.
- support mmap(2) including /proc/PID/exe symlink, without page-copy
- whiteout is hardlinked in order to reduce the consumption of inodes
  on branch
- do not copyup, nor create a whiteout when it is unnecessary
- revert a single systemcall when an error occurs in aufs
- remount interface instead of ioctl
- maintain /etc/mtab by an external shell script, /sbin/mount.aufs.
- loopback mounted filesystem as a branch
- kernel thread for removing the dir who has a plenty of whiteouts
- support copyup sparse file (a file which has a 'hole' in it)
- default permission flags for branches
- selectable permission flags for ro branch, whether whiteout can
  exist or not
- export via NFS.
- support <sysfs>/fs/aufs.
- support multiple writable branches, some policies to select one
  among multiple writable branches.
- a new semantics for link(2) and rename(2) to support multiple
  writable branches.
- a delegation of the internal branch access to support task I/O
  accounting, which also supports Linux Security Modules (LSM) mainly
  for Suse AppArmor.
- nested mount, i.e. aufs as readonly no-whiteout branch of another aufs.
- copyup-on-open or copyup-on-write
- show-whiteout mode
- show configuration even out of kernel tree
- no glibc changes are required.
- pseudo hardlink (hardlink over branches)
- allow a direct access manually to a file on branch, e.g. bypassing aufs.
  including NFS or remote filesystem branch.
- and more...

Currently these features are dropped temporary from this version, aufs2.
See design/08plan.txt in detail.
- exporting via NFS
- test only the highest one for the directory permission (dirperm1)
- show whiteout mode (shwh)
- copyup on open (coo=)
- being another aufs's readonly branch (robr)
- statistics of aufs thread (/sys/fs/aufs/stat)
- delegation mode (dlgt)
- intent.open/create (file open in a single lookup)


2. Download
----------------------------------------
Kindly one of aufs user, the Center for Scientific Computing and Free
Software (C3SL), Federal University of Parana offered me a public GIT
tree space.

There are three GIT trees, aufs2-2.6, aufs2-standalone and aufs2-util.
While the aufs2-util is always necessary, you need either of aufs2-2.6
or aufs2-standalone.

The aufs2-2.6 tree includes the whole linux-2.6 GIT tree,
git://git.kernel.org/.../torvalds/linux-2.6.git.
And you cannot select CONFIG_AUFS_FS=m for this version, eg. you cannot
build aufs2 as an externel kernel module.
If you already have linux-2.6 GIT tree, you may want to pull and merge
the "aufs2" branch from this tree.

On the other hand, the aufs2-standalone tree has only aufs2 source files
and a necessary patch, and you can select CONFIG_AUFS_FS=m. In other
words, the aufs2-standalone tree is generated from aufs2-2.6 tree by,
- extract new files and modifications.
- generate a single patch file from modifications.
- generate a ChangeLog file from git-log.
- commit the files newly and no log messages. this is not git-pull.

Both of aufs2-2.6 and aufs2-standalone trees have a branch whose name is
in form of "aufs2-xx" where "xx" represents the linux kernel version,
"linux-2.6.xx".

o aufs2-2.6 tree
$ git clone --reference /your/linux-2.6/git/tree \
	http://git.c3sl.ufpr.br/pub/scm/aufs/aufs2-2.6.git \
	aufs2-2.6.git
- if you don't have linux-2.6 GIT tree, then remove "--reference ..."
$ cd aufs2-2.6.git
$ git checkout aufs2-xx	# for instance, aufs2-27 for linux-2.6.27

o aufs2-standalone tree
$ git clone http://git.c3sl.ufpr.br/pub/scm/aufs/aufs2-standalone.git \
	aufs2-standalone.git
$ cd aufs2-standalone.git
$ git checkout aufs2-xx	# for instance, aufs2-27 for linux-2.6.27
- apply "aufs2-standalone.patch" to your kernel source files.

o aufs2-util tree
$ git clone http://git.c3sl.ufpr.br/pub/scm/aufs/aufs2-util.git \
	aufs2-util.git
$ cd aufs2-util.git
- no particular tag/branch currently.


3. Configuration and Compilation
----------------------------------------
For aufs2-2.6 tree,
- enable CONFIG_EXPERIMENTAL and CONFIG_AUFS_FS.
- set other aufs configurations if necessary.

For aufs2-standalone tree,
- enable CONFIG_EXPERIMENTAL and CONFIG_AUFS_FS, you can select =m.
- edit fs/aufs/config.mk and set other aufs configurations if necessary.

And then,
- build your kernel (or a module) by "make"
- install it and reboot your system
- read README in aufs2-util, build and install it


4. Usage
----------------------------------------
At first, make sure aufs2-util are installed, and please read the aufs
manual, ./Documentation/filesystems/aufs/aufs.5.
$ man -l aufs.5

And then,
$ mkdir /tmp/rw /tmp/aufs
# mount -t aufs -o br=/tmp/rw:${HOME}=ro none /tmp/aufs

Here is another example. The result is equivalent.
# mount -t aufs -o br=/tmp/rw:${HOME} none /tmp/aufs
  Or
# mount -t aufs -o br:/tmp/rw none /tmp/aufs
# mount -o remount,append:${HOME} /tmp/aufs

Then, you can see whole tree of your home dir through /tmp/aufs. If
you modify a file under /tmp/aufs, the one on your home directory is
not affected, instead the same named file will be newly created under
/tmp/rw. And all of your modification to a file will be applied to
the one under /tmp/rw. This is called the file based Copy on Write
(COW) method.
Aufs mount options are described in aufs.5.

Additionally, there are some sample usages of aufs which are a
diskless system with network booting, and LiveCD over NFS.
See sample dir in CVS tree on SourceForge.


5. Contact
----------------------------------------
When you have any problems or strange behaviour in aufs, please let me
know with:
- /proc/mounts (instead of the output of mount(8))
- /sys/fs/aufs/* (if you have them)
- /sys/module/aufs/*
- linux kernel version
  if your kernel is not plain, for example modified by distributor,
  the url where i can download its source is necessary too.
- aufs version which was printed at loading the module or booting the
  system, instead of the date you downloaded.
- configuration (define/undefine CONFIG_AUFS_xxx)
- kernel configuration or /proc/config.gz (if you have it)
- behaviour which you think to be incorrect
- actual operation, reproducible one is better
- mailto: aufs-users at lists.sourceforge.net

Usually, I don't watch the Public Areas(Bugs, Support Requests, Patches,
and Feature Requests) on SourceForge. Please join and write to
aufs-users ML.


6. Acknowledgements
----------------------------------------
Thanks to everyone who have tried and are using aufs, whoever
have reported a bug or any feedback.

Especially donors:
Tomas Matejicek(slax.org) made a donation (much more than once).
Dai Itasaka made a donation (2007/8).
Chuck Smith made a donation (2008/4, 10 and 12).
Henk Schoneveld made a donation (2008/9).
Chih-Wei Huang, ASUS, CTC donated Eee PC 4G (2008/10).
Francois Dupoux made a donation (2008/11).
Bruno Cesar Ribas and Luis Carlos Erpen de Bona, C3SL serves public GIT
tree (2009/2).

Thank you very much.
Donations are always, including future donations, very important and
helpful for me to keep on developing aufs.


7.
----------------------------------------
If you are an experienced user, no explanation is needed. Aufs is
just a linux filesystem.


Enjoy!

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