~ubuntu-branches/ubuntu/intrepid/aufs/intrepid

Aufs -- Another Unionfs
Junjiro Okajima

# $Id: README,v 1.81 2008/06/30 03:47:53 sfjro Exp $


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 same
approaches to aufs's.
Unionfs is being developed by Professor Erez Zadok at Stony Brook
University and his team.
If you don't know Unionfs, I recommend you becoming familiar with it
before using aufs. Some terminology in aufs follows Unionfs's.

Bug reports (including my broken English), suggestions, comments
and donations are always welcome. Your bug report may help other users,
including future users. Especially the bug report which doesn't follow
unix/linux filesystem's semantics is important.


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... see Unionfs in detail.

Also there are many enhancements in aufs, 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.
- and more... see aufs manual in detail

Aufs is in still development stage, especially:
- 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.
- refine xino and revalidate
- pseudo-link in NFS-exporting

(current work)
- reorder the branch index without del/re-add.
- permanent xino files

(next work)
- an option for refreshing the opened files after add/del branches
- 'move' policy for copy-up between two writable branches, after
  checking free space.
- ioctl to manipulate file between branches.
- and documentation

(just an idea)
- remount option copy/move between two branches. (unnecessary?)
- O_DIRECT (unnecessary?)
- light version, without branch manipulation. (unnecessary?)
- SMP, because I don't have such machine. But several users reported
  aufs is working fine on SMP machines.
- copyup in userspace
- inotify in userspace
- xattr, acl


2. Download
----------------------------------------
CVS tree is in aufs project of SourceForge.
Here is simple instructions to get aufs source files. It is recommended to
refer to the document about CVS on SourceForge.
	$ mkdir aufs.wcvs
	$ cd aufs.wcvs
	$ cvs -d:pserver:anonymous@aufs.cvs.sourceforge.net:/cvsroot/aufs login
	(CVS password is empty)
	$ cvs -z3 -d:pserver:anonymous@aufs.cvs.sourceforge.net:/cvsroot/aufs co aufs

In order to update files after the first checkout,
	$ cd aufs.wcvs/aufs
	$ cvs update
Do not forget -A option for 'cvs update' if you have ever 'cvs update' with
specifying a file version.

In order to see what the difference between two versions (two dates) is,
	$ cd aufs.wcvs/aufs
	$ cvs diff -D20061212 -D20061219

Usually I am updating CVS tree on every Monday.
I always try putting the stable version in CVS, so you can try CVS
instead of SourceForge File Release. And every changes are summarized
and reported to aufs-users at lists.sourceforge.net ML. I'd like to
recommend you to join this ML.


3. Configuration and Compilation
----------------------------------------
Aufs is being developed and tested on linux-2.6.16 and later.
You need the correct environment to build a kernel module. Generally
it is an environment which your kernel was built.
The aufs source files are under ./fs/aufs or ./fs/aufs25, which are
for linux-2.6.16 - 2.6.24, and linux-2.6.25 and later respectively.
Aufs makefile refers the files which is generated by linux build
system.
If you are unsure that you got the correct environment, then I
recommend you to built your kernel by yourself. If it succeeds, you've
got the correct environment.

Currently aufs configuration is written in ./Kconfig.in. You can
generate the real ./fs/aufs/Kconfig file by make(1). And follow the
instructions which will be produced by make(1). The built
./fs/aufs/Kconfig depends upon the kernel version.
Before you build ./fs/aufs/Kconfig, you need to configure your kernel,
since this build refers to linux/include/version.h.
	$ make -f local.mk kconfig

The local.mk searches your kernel build path by
	KDIR = /lib/modules/$(shell uname -r)/build
If you are cross-compiling the aufs module, try
	$ make KDIR=/your/kernel/build/path -f local.mk kconfig
If you link aufs statically, the generated Kconfig will help you.

Also you can use ./local.mk to compile aufs as a module by simply,
	$ make -f local.mk
or
	$ make KDIR=/your/kernel/build/path -f local.mk

The default configuration is written in ./local.mk too, they will work
for you in most cases. You can edit this file and change the
configuration for your aufs module.
If you don't want to change the ./local.mk, then create a new file
./priv_def.mk and write the definitions your aufs configuration. The
./local.mk includes ./priv_def.mk if it exists.
When you configure aufs by modifying ./local.mk (or ./priv_dev.mk),
leave it blank/unset when you disable an aufs configuration, instead
of setting 'n.'

The aufs build system may refer some kernel source files for some
macros or internal functions which are not declared in their header
files. It depends upon the configuration whether these files will be
referred or not.
Even if you don't have these source files in your build environment,
aufs can be built safely, but works less efficiently in some cases.

There is a contributed Makefile for aufs users. You might want to try
it. Check
http://sourceforge.net/mailarchive/forum.php?thread_name=9c4865a10707241831r189f9646n5f2c4a9c303797d1%40mail.gmail.com&forum_name=aufs-users
and see the attachment.

Currently, CONFIG_DEBUG_PROVE_LOCKING (in linux kernel) is not
supported since MAX_LOCKDEP_SUBCLASSES is too small for a stackable
filesystem. I am trying reducing the depth of lock subclasses.
Until then, you need to increase the value of MAX_LOCKDEP_SUBCLASSES
macro in include/linux/lockdep.h, for example, 16UL, when you enable
CONFIG_DEBUG_PROVE_LOCKING.

When you test the performance, it is recommended to disable
CONFIG_AUFS_DEBUG. It is enabled by default for the feature test.

Since aufs supports several versions of linux kernel, it uses the
condition like this,
	#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 18)
On the other hand, some distributions modify their kernel by their own
patches. For example, just a piece of code is brought from v2.6.18 and
merged into a distribution kernel which calls itself as v2.6.17.
Finally, the conditions in aufs will not work correctly.
You may or may not find them when you compile aufs.
You need to modify aufs source code for 'custom-version' kernel
(cf. patch/ubuntu-edgy.patch).


o Patches
There are several patches for linux kernel, in order to use aufs.
All of them are not necessary essentially, but in some cases you need
them. It is up to your environment and aufs usage.
All these patches are just for exporting a kernel internal function to
modules. If the function was already declared as extern and you link
aufs statically to your kernel, then you don't need such patch. If the
function was not extern and you want the feature, you need to apply
the patch.
When you apply a patch, you need to enable the corresponding aufs
configuration.
All these patches are under CVS_TREE/aufs/patch.

- sec_perm-2.6.24.patch
  For linux-2.6.24 and later.
  When you compile aufs as a module and enable CONFIG_SECURITY, this
  patch is required.
- splice-2.6.23.patch
  For linux-2.6.23 and later.
  When you use splice(2) (sendfile(2) in linux-2.6.23 and later), or
  loopback-mount an fs-image file in aufs, this patch is
  required. Aufs doesn't support splice(2) in linux-2.6.22 and
  earlier.
  If unionfs patch v2.3 or later is applied to your kernel, then you
  don't need this patch.
- put_filp.patch
  For linux-2.6.19 and later.
  When you compile aufs as a module and use NFS as an aufs branch
  filesystem, this patch is required.
- lhash.patch
  For linux-2.6.19 and later till linux-2.6.21.
  When you use NFS as an aufs branch filesystem, this patch is
  required.
- lhash-2.6.22.patch
  Same above, but this patch is for linux-2.6.22 only.
- fsync_super-2.6.16.patch
  For linux-2.6.16 and later.
  When you compile aufs as a module, apply this patch and enable a
  configuration, aufs tries flushing everything for branch filesystems
  which are not marked as 'rr' or 'rr+wh' at umount or remount time.
- fsync_super-2.6.19.patch
  Same above, but this patch is for linux-2.6.19 and later.
- deny_write_access.patch
  For linux-2.6.17 and later.
  When you compile aufs as a module, applied this patch and enabled a
  configuration, a minor security enhancement will be available at
  execve(2).
  You can omit this if you don't care the writing to a running
  executable on a lower branch filesystem which was invoked through
  aufs.
- ksize.patch
  For linux-2.6.22 and earlier.
  When you compile aufs as a module and applied this patch, an
  optimization inside aufs will be available at adding or deleting a
  branch filesystem. You can omit this if you don't care the aufs
  performance.

Additionally, there are patches for aufs which will be necessary when
you use non-standard kernel modules or patches. Some of them have been
tested by several people, but not all.
See also the comments in the patches.
- ubuntu-2.6.22-14.46.patch
  For Ubuntu kernel
  (http://archive.ubuntu.com/ubuntu/pool/main/l/linux-source-2.6.22/
  linux-source-2.6.22_2.6.22-14.46_all.deb) which is modified a lot by
  ubuntu people.
- ubuntu-2.6.24-5.8.patch
  For http://archive.ubuntu.com/ubuntu/pool/main/l/linux/
  linux-source-2.6.24_2.6.24-5.8_all.deb.
- ubuntu-edgy.patch
  For Ubuntu Edgy kernel which calls itself as 2.6.17, while its
  umount_begin() interface has arguments of 2.6.18.
- rt-compat.patch
  For realtime patch (http://people.redhat.com/mingo/realtime-preempt).
- vserver.patch
  For linux-vserver module (http://linux-vserver.org).
- openvz_028stab039.1.patch
  For openvz module (http://openvz.org).


4. Usage
----------------------------------------
After 'make',
	$ man -l ./aufs.5
	# install -m 500 -p mount.aufs umount.aufs auplink aulchown /sbin (recommended)
	# echo FLUSH=ALL > /etc/default/auplink (recommended)
	# insmod ./aufs.ko
	$ mkdir /tmp/rw /tmp/aufs
	# mount -t aufs -o dirs=/tmp/rw:${HOME}=ro none /tmp/aufs

If you are familiar with Unionfs Version 1.x series and want to use
unionctl(8), you can try the sample unionctl script under sample/
directory too.

Here is another example.

	# mount -t aufs -o br:/tmp/rw:${HOME}=ro none /tmp/aufs
	or
	# mount -t aufs -o br:/tmp/rw none /tmp/aufs
	# mount -o remount,append:${HOME}=ro /tmp/aufs

If you disable CONFIG_AUFS_COMPAT in your configuration, you can remove the
default branch permission '=ro' since '=rw' is set to the first branch
only by default.

	# mount -t aufs -o br:/tmp/rw:${HOME} none /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 the 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 the generated ./aufs.5.

Additionally, there are some sample usages of aufs which are a
diskless system with network booting, and LiveCD over NFS.
See ./sample/diskless in detail.


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, or plain local.mk is
  used or not)
- 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, especially who
have reported a bug or any feedback.

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).

Thank you very much.
Donations are always, including future donations, very important and
helpful for me to keep on developing aufs.
If you have a plan to develop or customize linux, feel free to ask me
a job with some donations or payments.


7.
----------------------------------------
If you are an experienced user, no explanation is needed. Aufs is
just a linux filesystem module. take a glance at ./local.mk,
aufs.5, and Unionfs.


Enjoy!

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