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This feature automatically handles MVDOWN in other commits.
In user-space, a daemon monitors the free space of the branch and issues
MVDOWN ioctl automatically when necessary. The main role is in
user-space and several options are implemented.
For a branch to join the FHSM circle, a new attribute 'fhsm' should be
specified.

See also the document in this commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

These are very old options.
Since Unionfs created 'diropq' unconditionally in mkdir(2), old users
may expect the same behaviour. But there are cases where 'diropq' is
unnecessary. The aufs default behaviour is to create 'diropq' only when
it is necessary.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Generally aufs hides the name of whiteouts. But in some cases, to show
them is very useful for users. For instance, creating a new middle layer
(branch) by merging existing layers.

See also the document in this commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

While most people (especially who use tmpfs as top writable branch)
doesn't care, I care and think it can be a security problem.
For example, when the lower readonly branch may contain
/etc/{passwd,shadow} and the permission bits of the upper empty
branch is world-writable, then a malicious user can make these files
manually with by-passing aufs.
Aufs can do nothing but produce a warning.

For details, see aufs manual in aufs-util.git.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Introduce the new mount options, dirren and nodirren, which activates
and deactivates DIRREN feature.
In remount and unmount, the inum-list per branch should be flushed to
the file.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Since aufs can have multiple writable branches, these options are
useful.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

This is a feature to optimize for rmdir and rename dir.
When the number of whiteouts under the target dir is very many, it may
take a long time to remove them all. To prevent this, 'dirwh=%d' option
specifies the watermark to decide when to remove them.

For details, see aufs manual in aufs-util.git.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Sometimes the aufs policy to respect the branch fs's permission bits
makes users confused. IE. the direcotry permission bits on the top branch
allows users to read, but the lower branch prohibts. This option may be
useful for such case.
See also the document in this commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement the user interface.
Since users often wonder "Why I cannot delete this branch?", 'verbose'
option was introduced.

You may think aufs should not hold several strings for the variation of
the option, and the mount helper (/sbin/mount.aufs) can convert all
variations to a single fixed string, and in kernel space aufs should
contain this only one string.
I agree, but in our real world, many users don't install
/sbin/mount.aufs. To be convenient, aufs contains these variations.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

This is very similar to file operations, including re-open after branch
management. The major part of readdir(3) is split into another object
called VDIR (in previous commit).
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Support for XATTR and ACL including several branch attributes to ignore
the copy error around XATTR and ACL.

NFS always sets MS_POSIXACL regardless its mount option 'noacl.'
When MS_POSIXACL is set, generic_permission() calls check_acl() (via
acl_permission_check()) and gets -EOPNOTSUPP because the NFS branch is
mounted as 'noacl.'
In aufs, h_permission() should not call generic_permission() in this
case.
The similar thing happens in coping-up XATTR. vfs_getxattr_alloc()
returns -EOPNOTSUPP.

See also the document in this commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

An enhancement for udba=none if possible.
The condition is same to the 'no ->d_revalidate()' patch series.
Refresh i_op in all cached inodes at the remount-time.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement i_op->rename().
This is a big monster and I don't like it.

In order to call d_move() in aufs lock section, FS_RENAME_DOES_D_MOVE is
set to fstype.f_flags.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement dir.i_op->lookup() and ->permission().
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Optimize out ->d_revalidate() if possible.
If the refreshing failed, then ->d_revalidate() remains. In this case,
aufs has two types of dentries. One has ->d_revalidate, the other
doesn't. I am afraid it will confuse me someday.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement d_op->d_revalidate().
This is another core part of UDBA (cf. lookup.txt in another commit).
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement basic sb_op->show_options(), statfs() and sync_fs() simply.
- show_options() doesn't print the default values (AuOpt_Def).
- statfs() will have an option to summarize the numbers from branches
  (in later commit).
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Call the functions in previous commits to refresh all.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

As a part of branch-management, aufs maintains all cached inodes,
dentries, and opened files in remounting.
This commits handles the cached inodes by counting the number of cached
inodes, generating an array of their pointers. I don't like such array
approach, but I don't have another idea.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Now aufs becomes mountable with very few features.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

The main part is in previous commit.
This commit handles the generation of aufs objects, to make sure the
inode in the file handle is still valid.
In order not to confuse NFSD, the various operation returns ESTALE for
NFSD where it used to return EBUSY.

See also the document in this commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Several policies to select one among multiple writable branches.
See also the document in previous commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Aufs can have multiple writable branches, and there are several
policies to select one among them.
This commit implements default "top-down-parent" for both of
creating-policy and copyup-policy.

See also the document in this commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

The branch path can be much longer and it is not suitable to print via
/proc/mounts as a part of mount options. Aufs can show it either
separately via sysfs or /proc/mounts (as a part of mount options).
This approach affects the lifetime of aufs objects and sbinfo contains
kobject (in another commit). Theoretically user can disable
CONFIG_SYSFS, but the lifetime management is always necessary. So
supporting sysfs is split into two files, sysaufs.c and sysfs.c.
sysaufs.c is always compiled, but sysfs.c is compiled only when
CONFIG_SYSFS is enabled.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

The structure is very similar to inode and dentry infos (in previous
commits), but the internal array is for 'struct au_branch' instead of
'superblock.' Additionally the lifetime of 'struct au_sbinfo' is managed
by kobject since it will be connected to sysfs by later commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

See the documents in this commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>