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The detailed info per renamed directory is stored in a regular file per
branch, ie. when each of two lower branches contains the same named
entry, then the created info files will be two.
The file is created internally by aufs rename(2) and loaded by lookup.
Also when the actual rename on the branch fails, the newly created or
stored info file should be all reverted.

When the renamed dir is renamed-back to the previous/original name, then
the info file has to be removed.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

DIRREN gives an identifier to every branch, and it is used as a part of
the filename of the detailed info file.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

This commits brings a list of the inode numbers which indicates the
logically renamed dir into a branch. The list will be referred in
lookup, and its lifetime is equivalent to the branch's, ie. the list is
loaded/created in adding a branch, and stored/deleted in deleting a
branch. The simple storing happens in remounting and unmounting aufs
too.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

This feature is definitely one of the things I really don't like.
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>

The permissions and attributes of a branch can be modified dynamically.
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>

Delete a branch which is not busy.
Aufs judges the branch is deletable by testing the opened files, the
cached dentries and inodes. Even if a directory is in use, as long as
the same named entry exist on another branch, then the branch is
deletable.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement an internal list of opened files to allow deleting a branch
which has an opened dir. Obviously I don't like such list.

There was such list in linux as sb->s_files, but in linux-3.12 s_files
became containing just a part of the opened files, and in linux-3.13 it
was totally gone.
Aufs still needs the file list, particularly for re-setting the branch
attribute from RW to RO.
After resetting to RO, aufs should return EROFS for write. In order to
support such case, aufs keeps the late s_files and mark_files_ro()
approach.

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

The interfaces to append and prepend branches.
They are the variations of "branch add" in another commit.
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>

->atomic_open() is another monster (the other is ->rename() of course).
It operates look-up, create, and open in a single method.
Strictly speaking the behaviour is not atomic from the branch fs's point
of view, while the atomicity is kept in aufs's. This is a second-best
approach. For details, refer to the design document in previous commit.

A simple list 'si_aopen' can be put into aufs inode object, but I don't
think it a good idea because the number of inodes is much larger than
the number of super_block. If I put it into inode, it can be an
un-interesting memory pressure I am afraid.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

This new function au_aopen_or_create() tries calling branch fs's
->atomic_open() first. If it is not set, call vfs_create() instead.
By putting this behaviour into aufs's add_simple(), many codes can be
shared.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Extend do_open_dir(), au_do_open_nondir() and au_do_open() to receive an
additional parameter h_file, which is an opened file object by branch
fs's ->atomic_open(). By this design/commit, aufs doesn't have to
duplicate many codes into a new aufs_atomic_open() (in later commit),
and can simply share them.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Following the design in another commit, aufs calls branch fs's
->atomic_open() if exits. Ideally it would be better to call
VFS:do_last, lookup_open() or atomic_open, but it is very hard for
aufs. This implementation is far from the best.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Refer to this document obviously.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement several f_op functions for non-dir.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

For details, read the document in this commit.
I don't like this approach, but there is no other way currently. But it
seems that UnionMount is trying add siblings of f_dentry and d_inode for
linux-4.0 or later. It may become another light for aufs too.

The finfo object which has ever mmapped is excluded from
refreshing (based upon fi_mmapped). Otherwise we may corrupt the process
memory space.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

By default, aufs doesn't copy-up the file in open(2).
The file write operation is one of the trigger of the copy-up.
Although I understand that O_RDWR or O_WRONLY should trigger the
copy-up, it is not a good idea for the case of open(O_RDWR) +
mmap(MAP_PRIVATE). In this case, all changes are not written-back to the
file on disk, and the copy-up is meaningless entirely.
In other words, aufs postpone the copy-up as possible.

This design also applies to the file operation after branch management.
Some of the opened file need to be refreshed after add/del/mod
branches. Eg. detect the revealed same named one, open it, close the old
one internally while the virtual file is kept opened.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement f_op->open() for non-directory.
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>

An enhancement for udba=none if possible.
The condition is same to the 'no ->d_revalidate()' patch series.
In this mode, i_op->getattr() is less important, and the default VFS
handler is enough.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement i_op->get/setattr().
setattr() is another trigger of the copy-up. The file may or may not be
opened. And some of sub-functions are commonly used to XATTR operations
in later commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement i_op->link().
As aufs supports 'pseudo-link', aufs_link() can make it without
copying-up. In the case of aufs_link() has to copy-up, the name of the
target file is used as-is, and it is pseudo-linked. In other words,
calling link(2) after the copy-up is unnecessary.

See also struct.txt in previous commit.
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 this version, the copy-up always happen.
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 i_op->rmdir() with supporting logical deletion by whiteout
including all children.

As struct.txt in previous commit described, the target dir is renamed to
a whiteout-ed temporary unique name in rmdir(2), and then removed
asynchronously by the system global workqueue.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement i_op->unlink() with supporting logical deletion by whiteout.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Here are entry adding inode operations, i_op->create(), symlink(),
mkdir(), mknod(), and tmpfile().
Obviously they return EOPNOTSUPP when the target branch fs doesn't
support the operation.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Implement dir.i_op->get_link().
I am afraid there may exist the case skipping updating the inode atime.
It means the aufs inode atime may be reverted by the real fs inode atime
silently.  But I don't think it a big problem.
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>

Maintain the internal array including corresponding XINO file and sysfs
entries.
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 opened files by counting the number of them,
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>