UBUNTU: SAUCE: AUFS

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

Documentation/ABI/testing/debugfs-aufs

+What:		/debug/aufs/si_<id>/
+Date:		March 2009
+Contact:	J. R. Okajima <hooanon05g@gmail.com>
+Description:
+		Under /debug/aufs, a directory named si_<id> is created
+		per aufs mount, where <id> is a unique id generated
+		internally.
+
+What:		/debug/aufs/si_<id>/plink
+Date:		Apr 2013
+Contact:	J. R. Okajima <hooanon05g@gmail.com>
+Description:
+		It has three lines and shows the information about the
+		pseudo-link. The first line is a single number
+		representing a number of buckets. The second line is a
+		number of pseudo-links per buckets (separated by a
+		blank). The last line is a single number representing a
+		total number of psedo-links.
+		When the aufs mount option 'noplink' is specified, it
+		will show "1\n0\n0\n".
+
+What:		/debug/aufs/si_<id>/xib
+Date:		March 2009
+Contact:	J. R. Okajima <hooanon05g@gmail.com>
+Description:
+		It shows the consumed blocks by xib (External Inode Number
+		Bitmap), its block size and file size.
+		When the aufs mount option 'noxino' is specified, it
+		will be empty. About XINO files, see the aufs manual.
+
+What:		/debug/aufs/si_<id>/xino0, xino1 ... xinoN
+Date:		March 2009
+Contact:	J. R. Okajima <hooanon05g@gmail.com>
+Description:
+		It shows the consumed blocks by xino (External Inode Number
+		Translation Table), its link count, block size and file
+		size.
+		When the aufs mount option 'noxino' is specified, it
+		will be empty. About XINO files, see the aufs manual.
+
+What:		/debug/aufs/si_<id>/xigen
+Date:		March 2009
+Contact:	J. R. Okajima <hooanon05g@gmail.com>
+Description:
+		It shows the consumed blocks by xigen (External Inode
+		Generation Table), its block size and file size.
+		If CONFIG_AUFS_EXPORT is disabled, this entry will not
+		be created.
+		When the aufs mount option 'noxino' is specified, it
+		will be empty. About XINO files, see the aufs manual.

Documentation/ABI/testing/sysfs-aufs

+What:		/sys/fs/aufs/si_<id>/
+Date:		March 2009
+Contact:	J. R. Okajima <hooanon05g@gmail.com>
+Description:
+		Under /sys/fs/aufs, a directory named si_<id> is created
+		per aufs mount, where <id> is a unique id generated
+		internally.
+
+What:		/sys/fs/aufs/si_<id>/br0, br1 ... brN
+Date:		March 2009
+Contact:	J. R. Okajima <hooanon05g@gmail.com>
+Description:
+		It shows the abolute path of a member directory (which
+		is called branch) in aufs, and its permission.
+
+What:		/sys/fs/aufs/si_<id>/brid0, brid1 ... bridN
+Date:		July 2013
+Contact:	J. R. Okajima <hooanon05g@gmail.com>
+Description:
+		It shows the id of a member directory (which is called
+		branch) in aufs.
+
+What:		/sys/fs/aufs/si_<id>/xi_path
+Date:		March 2009
+Contact:	J. R. Okajima <hooanon05g@gmail.com>
+Description:
+		It shows the abolute path of XINO (External Inode Number
+		Bitmap, Translation Table and Generation Table) file
+		even if it is the default path.
+		When the aufs mount option 'noxino' is specified, it
+		will be empty. About XINO files, see the aufs manual.

Documentation/filesystems/aufs/design/01intro.txt

+
+# Copyright (C) 2005-2015 Junjiro R. Okajima
+# 
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Introduction
+----------------------------------------
+
+aufs [ei ju: ef es] | [a u f s]
+1. abbrev. for "advanced multi-layered unification filesystem".
+2. abbrev. for "another unionfs".
+3. abbrev. for "auf das" in German which means "on the" in English.
+   Ex. "Butter aufs Brot"(G) means "butter onto bread"(E).
+   But "Filesystem aufs Filesystem" is hard to understand.
+
+AUFS is a filesystem with features:
+- multi layered stackable unification filesystem, the member directory
+  is called as a branch.
+- branch permission and attribute, 'readonly', 'real-readonly',
+  'readwrite', 'whiteout-able', 'link-able whiteout', etc. and their
+  combination.
+- internal "file copy-on-write".
+- logical deletion, whiteout.
+- dynamic branch manipulation, adding, deleting and changing permission.
+- allow bypassing aufs, user's direct branch access.
+- external inode number translation table and bitmap which maintains the
+  persistent aufs inode number.
+- seekable directory, including NFS readdir.
+- file mapping, mmap and sharing pages.
+- pseudo-link, hardlink over branches.
+- loopback mounted filesystem as a branch.
+- several policies to select one among multiple writable branches.
+- revert a single systemcall when an error occurs in aufs.
+- and more...
+
+
+Multi Layered Stackable Unification Filesystem
+----------------------------------------------------------------------
+Most people already knows what it is.
+It is a filesystem which unifies several directories and provides a
+merged single directory. When users access a file, the access will be
+passed/re-directed/converted (sorry, I am not sure which English word is
+correct) to the real file on the member filesystem. The member
+filesystem is called 'lower filesystem' or 'branch' and has a mode
+'readonly' and 'readwrite.' And the deletion for a file on the lower
+readonly branch is handled by creating 'whiteout' on the upper writable
+branch.
+
+On LKML, there have been discussions about UnionMount (Jan Blunck,
+Bharata B Rao and Valerie Aurora) and Unionfs (Erez Zadok). They took
+different approaches to implement the merged-view.
+The former tries putting it into VFS, and the latter implements as a
+separate filesystem.
+(If I misunderstand about these implementations, please let me know and
+I shall correct it. Because it is a long time ago when I read their
+source files last time).
+
+UnionMount's approach will be able to small, but may be hard to share
+branches between several UnionMount since the whiteout in it is
+implemented in the inode on branch filesystem and always
+shared. According to Bharata's post, readdir does not seems to be
+finished yet.
+There are several missing features known in this implementations such as
+- for users, the inode number may change silently. eg. copy-up.
+- link(2) may break by copy-up.
+- read(2) may get an obsoleted filedata (fstat(2) too).
+- fcntl(F_SETLK) may be broken by copy-up.
+- unnecessary copy-up may happen, for example mmap(MAP_PRIVATE) after
+  open(O_RDWR).
+
+In linux-3.18, "overlay" filesystem (formerly known as "overlayfs") was
+merged into mainline. This is another implementation of UnionMount as a
+separated filesystem. All the limitations and known problems which
+UnionMount are equally inherited to "overlay" filesystem.
+
+Unionfs has a longer history. When I started implementing a stackable
+filesystem (Aug 2005), it already existed. It has virtual super_block,
+inode, dentry and file objects and they have an array pointing lower
+same kind objects. After contributing many patches for Unionfs, I
+re-started my project AUFS (Jun 2006).
+
+In AUFS, the structure of filesystem resembles to Unionfs, but I
+implemented my own ideas, approaches and enhancements and it became
+totally different one.
+
+Comparing DM snapshot and fs based implementation
+- the number of bytes to be copied between devices is much smaller.
+- the type of filesystem must be one and only.
+- the fs must be writable, no readonly fs, even for the lower original
+  device. so the compression fs will not be usable. but if we use
+  loopback mount, we may address this issue.
+  for instance,
+	mount /cdrom/squashfs.img /sq
+	losetup /sq/ext2.img
+	losetup /somewhere/cow
+	dmsetup "snapshot /dev/loop0 /dev/loop1 ..."
+- it will be difficult (or needs more operations) to extract the
+  difference between the original device and COW.
+- DM snapshot-merge may help a lot when users try merging. in the
+  fs-layer union, users will use rsync(1).
+
+You may want to read my old paper "Filesystems in LiveCD"
+(http://aufs.sourceforge.net/aufs2/report/sq/sq.pdf).
+
+
+Several characters/aspects/persona of aufs
+----------------------------------------------------------------------
+
+Aufs has several characters, aspects or persona.
+1. a filesystem, callee of VFS helper
+2. sub-VFS, caller of VFS helper for branches
+3. a virtual filesystem which maintains persistent inode number
+4. reader/writer of files on branches such like an application
+
+1. Callee of VFS Helper
+As an ordinary linux filesystem, aufs is a callee of VFS. For instance,
+unlink(2) from an application reaches sys_unlink() kernel function and
+then vfs_unlink() is called. vfs_unlink() is one of VFS helper and it
+calls filesystem specific unlink operation. Actually aufs implements the
+unlink operation but it behaves like a redirector.
+
+2. Caller of VFS Helper for Branches
+aufs_unlink() passes the unlink request to the branch filesystem as if
+it were called from VFS. So the called unlink operation of the branch
+filesystem acts as usual. As a caller of VFS helper, aufs should handle
+every necessary pre/post operation for the branch filesystem.
+- acquire the lock for the parent dir on a branch
+- lookup in a branch
+- revalidate dentry on a branch
+- mnt_want_write() for a branch
+- vfs_unlink() for a branch
+- mnt_drop_write() for a branch
+- release the lock on a branch
+
+3. Persistent Inode Number
+One of the most important issue for a filesystem is to maintain inode
+numbers. This is particularly important to support exporting a
+filesystem via NFS. Aufs is a virtual filesystem which doesn't have a
+backend block device for its own. But some storage is necessary to
+keep and maintain the inode numbers. It may be a large space and may not
+suit to keep in memory. Aufs rents some space from its first writable
+branch filesystem (by default) and creates file(s) on it. These files
+are created by aufs internally and removed soon (currently) keeping
+opened.
+Note: Because these files are removed, they are totally gone after
+      unmounting aufs. It means the inode numbers are not persistent
+      across unmount or reboot. I have a plan to make them really
+      persistent which will be important for aufs on NFS server.
+
+4. Read/Write Files Internally (copy-on-write)
+Because a branch can be readonly, when you write a file on it, aufs will
+"copy-up" it to the upper writable branch internally. And then write the
+originally requested thing to the file. Generally kernel doesn't
+open/read/write file actively. In aufs, even a single write may cause a
+internal "file copy". This behaviour is very similar to cp(1) command.
+
+Some people may think it is better to pass such work to user space
+helper, instead of doing in kernel space. Actually I am still thinking
+about it. But currently I have implemented it in kernel space.

Documentation/filesystems/aufs/design/03atomic_open.txt

+
+# Copyright (C) 2015 Junjiro R. Okajima
+# 
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Support for a branch who has its ->atomic_open()
+----------------------------------------------------------------------
+The filesystems who implement its ->atomic_open() are not majority. For
+example NFSv4 does, and aufs should call NFSv4 ->atomic_open,
+particularly for open(O_CREAT|O_EXCL, 0400) case. Other than
+->atomic_open(), NFSv4 returns an error for this open(2). While I am not
+sure whether all filesystems who have ->atomic_open() behave like this,
+but NFSv4 surely returns the error.
+
+In order to support ->atomic_open() for aufs, there are a few
+approaches.
+
+A. Introduce aufs_atomic_open()
+   - calls one of VFS:do_last(), lookup_open() or atomic_open() for
+     branch fs.
+B. Introduce aufs_atomic_open() calling create, open and chmod. this is
+   an aufs user Pip Cet's approach
+   - calls aufs_create(), VFS finish_open() and notify_change().
+   - pass fake-mode to finish_open(), and then correct the mode by
+     notify_change().
+C. Extend aufs_open() to call branch fs's ->atomic_open()
+   - no aufs_atomic_open().
+   - aufs_lookup() registers the TID to an aufs internal object.
+   - aufs_create() does nothing when the matching TID is registered, but
+     registers the mode.
+   - aufs_open() calls branch fs's ->atomic_open() when the matching
+     TID is registered.
+D. Extend aufs_open() to re-try branch fs's ->open() with superuser's
+   credential
+   - no aufs_atomic_open().
+   - aufs_create() registers the TID to an internal object. this info
+     represents "this process created this file just now."
+   - when aufs gets EACCES from branch fs's ->open(), then confirm the
+     registered TID and re-try open() with superuser's credential.
+
+Pros and cons for each approach.
+
+A.
+   - straightforward but highly depends upon VFS internal.
+   - the atomic behavaiour is kept.
+   - some of parameters such as nameidata are hard to reproduce for
+     branch fs.
+   - large overhead.
+B.
+   - easy to implement.
+   - the atomic behavaiour is lost.
+C.
+   - the atomic behavaiour is kept.
+   - dirty and tricky.
+   - VFS checks whether the file is created correctly after calling
+     ->create(), which means this approach doesn't work.
+D.
+   - easy to implement.
+   - the atomic behavaiour is lost.
+   - to open a file with superuser's credential and give it to a user
+     process is a bad idea, since the file object keeps the credential
+     in it. It may affect LSM or something. This approach doesn't work
+     either.
+
+The approach A is ideal, but it hard to implement. So here is a
+variation of A, which is to be implemented.
+
+A-1. Introduce aufs_atomic_open()
+     - calls branch fs ->atomic_open() if exists. otherwise calls
+       vfs_create() and finish_open().
+     - the demerit is that the several checks after branch fs
+       ->atomic_open() are lost. in the ordinary case, the checks are
+       done by VFS:do_last(), lookup_open() and atomic_open(). some can
+       be implemented in aufs, but not all I am afraid.

Documentation/filesystems/aufs/design/03lookup.txt

+
+# Copyright (C) 2005-2015 Junjiro R. Okajima
+# 
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Lookup in a Branch
+----------------------------------------------------------------------
+Since aufs has a character of sub-VFS (see Introduction), it operates
+lookup for branches as VFS does. It may be a heavy work. But almost all
+lookup operation in aufs is the simplest case, ie. lookup only an entry
+directly connected to its parent. Digging down the directory hierarchy
+is unnecessary. VFS has a function lookup_one_len() for that use, and
+aufs calls it.
+
+When a branch is a remote filesystem, aufs basically relies upon its
+->d_revalidate(), also aufs forces the hardest revalidate tests for
+them.
+For d_revalidate, aufs implements three levels of revalidate tests. See
+"Revalidate Dentry and UDBA" in detail.
+
+
+Test Only the Highest One for the Directory Permission (dirperm1 option)
+----------------------------------------------------------------------
+Let's try case study.
+- aufs has two branches, upper readwrite and lower readonly.
+  /au = /rw + /ro
+- "dirA" exists under /ro, but /rw. and its mode is 0700.
+- user invoked "chmod a+rx /au/dirA"
+- the internal copy-up is activated and "/rw/dirA" is created and its
+  permission bits are set to world readable.
+- then "/au/dirA" becomes world readable?
+
+In this case, /ro/dirA is still 0700 since it exists in readonly branch,
+or it may be a natively readonly filesystem. If aufs respects the lower
+branch, it should not respond readdir request from other users. But user
+allowed it by chmod. Should really aufs rejects showing the entries
+under /ro/dirA?
+
+To be honest, I don't have a good solution for this case. So aufs
+implements 'dirperm1' and 'nodirperm1' mount options, and leave it to
+users.
+When dirperm1 is specified, aufs checks only the highest one for the
+directory permission, and shows the entries. Otherwise, as usual, checks
+every dir existing on all branches and rejects the request.
+
+As a side effect, dirperm1 option improves the performance of aufs
+because the number of permission check is reduced when the number of
+branch is many.
+
+
+Revalidate Dentry and UDBA (User's Direct Branch Access)
+----------------------------------------------------------------------
+Generally VFS helpers re-validate a dentry as a part of lookup.
+0. digging down the directory hierarchy.
+1. lock the parent dir by its i_mutex.
+2. lookup the final (child) entry.
+3. revalidate it.
+4. call the actual operation (create, unlink, etc.)
+5. unlock the parent dir
+
+If the filesystem implements its ->d_revalidate() (step 3), then it is
+called. Actually aufs implements it and checks the dentry on a branch is
+still valid.
+But it is not enough. Because aufs has to release the lock for the
+parent dir on a branch at the end of ->lookup() (step 2) and
+->d_revalidate() (step 3) while the i_mutex of the aufs dir is still
+held by VFS.
+If the file on a branch is changed directly, eg. bypassing aufs, after
+aufs released the lock, then the subsequent operation may cause
+something unpleasant result.
+
+This situation is a result of VFS architecture, ->lookup() and
+->d_revalidate() is separated. But I never say it is wrong. It is a good
+design from VFS's point of view. It is just not suitable for sub-VFS
+character in aufs.
+
+Aufs supports such case by three level of revalidation which is
+selectable by user.
+1. Simple Revalidate
+   Addition to the native flow in VFS's, confirm the child-parent
+   relationship on the branch just after locking the parent dir on the
+   branch in the "actual operation" (step 4). When this validation
+   fails, aufs returns EBUSY. ->d_revalidate() (step 3) in aufs still
+   checks the validation of the dentry on branches.
+2. Monitor Changes Internally by Inotify/Fsnotify
+   Addition to above, in the "actual operation" (step 4) aufs re-lookup
+   the dentry on the branch, and returns EBUSY if it finds different
+   dentry.
+   Additionally, aufs sets the inotify/fsnotify watch for every dir on branches
+   during it is in cache. When the event is notified, aufs registers a
+   function to kernel 'events' thread by schedule_work(). And the
+   function sets some special status to the cached aufs dentry and inode
+   private data. If they are not cached, then aufs has nothing to
+   do. When the same file is accessed through aufs (step 0-3) later,
+   aufs will detect the status and refresh all necessary data.
+   In this mode, aufs has to ignore the event which is fired by aufs
+   itself.
+3. No Extra Validation
+   This is the simplest test and doesn't add any additional revalidation
+   test, and skip the revalidation in step 4. It is useful and improves
+   aufs performance when system surely hide the aufs branches from user,
+   by over-mounting something (or another method).

Documentation/filesystems/aufs/design/04branch.txt

+
+# Copyright (C) 2005-2015 Junjiro R. Okajima
+# 
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Branch Manipulation
+
+Since aufs supports dynamic branch manipulation, ie. add/remove a branch
+and changing its permission/attribute, there are a lot of works to do.
+
+
+Add a Branch
+----------------------------------------------------------------------
+o Confirm the adding dir exists outside of aufs, including loopback
+  mount, and its various attributes.
+o Initialize the xino file and whiteout bases if necessary.
+  See struct.txt.
+
+o Check the owner/group/mode of the directory
+  When the owner/group/mode of the adding directory differs from the
+  existing branch, aufs issues a warning because it may impose a
+  security risk.
+  For example, when a upper writable branch has a world writable empty
+  top directory, a malicious user can create any files on the writable
+  branch directly, like copy-up and modify manually. If something like
+  /etc/{passwd,shadow} exists on the lower readonly branch but the upper
+  writable branch, and the writable branch is world-writable, then a
+  malicious guy may create /etc/passwd on the writable branch directly
+  and the infected file will be valid in aufs.
+  I am afraid it can be a security issue, but aufs can do nothing except
+  producing a warning.
+
+
+Delete a Branch
+----------------------------------------------------------------------
+o Confirm the deleting branch is not busy
+  To be general, there is one merit to adopt "remount" interface to
+  manipulate branches. It is to discard caches. At deleting a branch,
+  aufs checks the still cached (and connected) dentries and inodes. If
+  there are any, then they are all in-use. An inode without its
+  corresponding dentry can be alive alone (for example, inotify/fsnotify case).
+
+  For the cached one, aufs checks whether the same named entry exists on
+  other branches.
+  If the cached one is a directory, because aufs provides a merged view
+  to users, as long as one dir is left on any branch aufs can show the
+  dir to users. In this case, the branch can be removed from aufs.
+  Otherwise aufs rejects deleting the branch.
+
+  If any file on the deleting branch is opened by aufs, then aufs
+  rejects deleting.
+
+
+Modify the Permission of a Branch
+----------------------------------------------------------------------
+o Re-initialize or remove the xino file and whiteout bases if necessary.
+  See struct.txt.
+
+o rw --> ro: Confirm the modifying branch is not busy
+  Aufs rejects the request if any of these conditions are true.
+  - a file on the branch is mmap-ed.
+  - a regular file on the branch is opened for write and there is no
+    same named entry on the upper branch.

Documentation/filesystems/aufs/design/05wbr_policy.txt

+
+# Copyright (C) 2005-2015 Junjiro R. Okajima
+# 
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Policies to Select One among Multiple Writable Branches
+----------------------------------------------------------------------
+When the number of writable branch is more than one, aufs has to decide
+the target branch for file creation or copy-up. By default, the highest
+writable branch which has the parent (or ancestor) dir of the target
+file is chosen (top-down-parent policy).
+By user's request, aufs implements some other policies to select the
+writable branch, for file creation several policies, round-robin,
+most-free-space, and other policies. For copy-up, top-down-parent,
+bottom-up-parent, bottom-up and others.
+
+As expected, the round-robin policy selects the branch in circular. When
+you have two writable branches and creates 10 new files, 5 files will be
+created for each branch. mkdir(2) systemcall is an exception. When you
+create 10 new directories, all will be created on the same branch.
+And the most-free-space policy selects the one which has most free
+space among the writable branches. The amount of free space will be
+checked by aufs internally, and users can specify its time interval.
+
+The policies for copy-up is more simple,
+top-down-parent is equivalent to the same named on in create policy,
+bottom-up-parent selects the writable branch where the parent dir
+exists and the nearest upper one from the copyup-source,
+bottom-up selects the nearest upper writable branch from the
+copyup-source, regardless the existence of the parent dir.
+
+There are some rules or exceptions to apply these policies.
+- If there is a readonly branch above the policy-selected branch and
+  the parent dir is marked as opaque (a variation of whiteout), or the
+  target (creating) file is whiteout-ed on the upper readonly branch,
+  then the result of the policy is ignored and the target file will be
+  created on the nearest upper writable branch than the readonly branch.
+- If there is a writable branch above the policy-selected branch and
+  the parent dir is marked as opaque or the target file is whiteouted
+  on the branch, then the result of the policy is ignored and the target
+  file will be created on the highest one among the upper writable
+  branches who has diropq or whiteout. In case of whiteout, aufs removes
+  it as usual.
+- link(2) and rename(2) systemcalls are exceptions in every policy.
+  They try selecting the branch where the source exists as possible
+  since copyup a large file will take long time. If it can't be,
+  ie. the branch where the source exists is readonly, then they will
+  follow the copyup policy.
+- There is an exception for rename(2) when the target exists.
+  If the rename target exists, aufs compares the index of the branches
+  where the source and the target exists and selects the higher
+  one. If the selected branch is readonly, then aufs follows the
+  copyup policy.

Documentation/filesystems/aufs/design/06fhsm.txt

+
+# Copyright (C) 2011-2015 Junjiro R. Okajima
+# 
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+
+File-based Hierarchical Storage Management (FHSM)
+----------------------------------------------------------------------
+Hierarchical Storage Management (or HSM) is a well-known feature in the
+storage world. Aufs provides this feature as file-based with multiple
+writable branches, based upon the principle of "Colder, the Lower".
+Here the word "colder" means that the less used files, and "lower" means
+that the position in the order of the stacked branches vertically.
+These multiple writable branches are prioritized, ie. the topmost one
+should be the fastest drive and be used heavily.
+
+o Characters in aufs FHSM story
+- aufs itself and a new branch attribute.
+- a new ioctl interface to move-down and to establish a connection with
+  the daemon ("move-down" is a converse of "copy-up").
+- userspace tool and daemon.
+
+The userspace daemon establishes a connection with aufs and waits for
+the notification. The notified information is very similar to struct
+statfs containing the number of consumed blocks and inodes.
+When the consumed blocks/inodes of a branch exceeds the user-specified
+upper watermark, the daemon activates its move-down process until the
+consumed blocks/inodes reaches the user-specified lower watermark.
+
+The actual move-down is done by aufs based upon the request from
+user-space since we need to maintain the inode number and the internal
+pointer arrays in aufs.
+
+Currently aufs FHSM handles the regular files only. Additionally they
+must not be hard-linked nor pseudo-linked.
+
+
+o Cowork of aufs and the user-space daemon
+  During the userspace daemon established the connection, aufs sends a
+  small notification to it whenever aufs writes something into the
+  writable branch. But it may cost high since aufs issues statfs(2)
+  internally. So user can specify a new option to cache the
+  info. Actually the notification is controlled by these factors.
+  + the specified cache time.
+  + classified as "force" by aufs internally.
+  Until the specified time expires, aufs doesn't send the info
+  except the forced cases. When aufs decide forcing, the info is always
+  notified to userspace.
+  For example, the number of free inodes is generally large enough and
+  the shortage of it happens rarely. So aufs doesn't force the
+  notification when creating a new file, directory and others. This is
+  the typical case which aufs doesn't force.
+  When aufs writes the actual filedata and the files consumes any of new
+  blocks, the aufs forces notifying.
+
+
+o Interfaces in aufs
+- New branch attribute.
+  + fhsm
+    Specifies that the branch is managed by FHSM feature. In other word,
+    participant in the FHSM.
+    When nofhsm is set to the branch, it will not be the source/target
+    branch of the move-down operation. This attribute is set
+    independently from coo and moo attributes, and if you want full
+    FHSM, you should specify them as well.
+- New mount option.
+  + fhsm_sec
+    Specifies a second to suppress many less important info to be
+    notified.
+- New ioctl.
+  + AUFS_CTL_FHSM_FD
+    create a new file descriptor which userspace can read the notification
+    (a subset of struct statfs) from aufs.
+- Module parameter 'brs'
+  It has to be set to 1. Otherwise the new mount option 'fhsm' will not
+  be set.
+- mount helpers /sbin/mount.aufs and /sbin/umount.aufs
+  When there are two or more branches with fhsm attributes,
+  /sbin/mount.aufs invokes the user-space daemon and /sbin/umount.aufs
+  terminates it. As a result of remounting and branch-manipulation, the
+  number of branches with fhsm attribute can be one. In this case,
+  /sbin/mount.aufs will terminate the user-space daemon.
+
+
+Finally the operation is done as these steps in kernel-space.
+- make sure that,
+  + no one else is using the file.
+  + the file is not hard-linked.
+  + the file is not pseudo-linked.
+  + the file is a regular file.
+  + the parent dir is not opaqued.
+- find the target writable branch.
+- make sure the file is not whiteout-ed by the upper (than the target)
+  branch.
+- make the parent dir on the target branch.
+- mutex lock the inode on the branch.
+- unlink the whiteout on the target branch (if exists).
+- lookup and create the whiteout-ed temporary name on the target branch.
+- copy the file as the whiteout-ed temporary name on the target branch.
+- rename the whiteout-ed temporary name to the original name.
+- unlink the file on the source branch.
+- maintain the internal pointer array and the external inode number
+  table (XINO).
+- maintain the timestamps and other attributes of the parent dir and the
+  file.
+
+And of course, in every step, an error may happen. So the operation
+should restore the original file state after an error happens.

Documentation/filesystems/aufs/design/06mmap.txt

+
+# Copyright (C) 2005-2015 Junjiro R. Okajima
+# 
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+mmap(2) -- File Memory Mapping
+----------------------------------------------------------------------
+In aufs, the file-mapped pages are handled by a branch fs directly, no
+interaction with aufs. It means aufs_mmap() calls the branch fs's
+->mmap().
+This approach is simple and good, but there is one problem.
+Under /proc, several entries show the mmapped files by its path (with
+device and inode number), and the printed path will be the path on the
+branch fs's instead of virtual aufs's.
+This is not a problem in most cases, but some utilities lsof(1) (and its
+user) may expect the path on aufs.
+
+To address this issue, aufs adds a new member called vm_prfile in struct
+vm_area_struct (and struct vm_region). The original vm_file points to
+the file on the branch fs in order to handle everything correctly as
+usual. The new vm_prfile points to a virtual file in aufs, and the
+show-functions in procfs refers to vm_prfile if it is set.
+Also we need to maintain several other places where touching vm_file
+such like
+- fork()/clone() copies vma and the reference count of vm_file is
+  incremented.
+- merging vma maintains the ref count too.
+
+This is not a good approach. It just fakes the printed path. But it
+leaves all behaviour around f_mapping unchanged. This is surely an
+advantage.
+Actually aufs had adopted another complicated approach which calls
+generic_file_mmap() and handles struct vm_operations_struct. In this
+approach, aufs met a hard problem and I could not solve it without
+switching the approach.
+
+There may be one more another approach which is
+- bind-mount the branch-root onto the aufs-root internally
+- grab the new vfsmount (ie. struct mount)
+- lazy-umount the branch-root internally
+- in open(2) the aufs-file, open the branch-file with the hidden
+  vfsmount (instead of the original branch's vfsmount)
+- ideally this "bind-mount and lazy-umount" should be done atomically,
+  but it may be possible from userspace by the mount helper.
+
+Adding the internal hidden vfsmount and using it in opening a file, the
+file path under /proc will be printed correctly. This approach looks
+smarter, but is not possible I am afraid.
+- aufs-root may be bind-mount later. when it happens, another hidden
+  vfsmount will be required.
+- it is hard to get the chance to bind-mount and lazy-umount
+  + in kernel-space, FS can have vfsmount in open(2) via
+    file->f_path, and aufs can know its vfsmount. But several locks are
+    already acquired, and if aufs tries to bind-mount and lazy-umount
+    here, then it may cause a deadlock.
+  + in user-space, bind-mount doesn't invoke the mount helper.
+- since /proc shows dev and ino, aufs has to give vma these info. it
+  means a new member vm_prinode will be necessary. this is essentially
+  equivalent to vm_prfile described above.
+
+I have to give up this "looks-smater" approach.

Documentation/filesystems/aufs/design/06xattr.txt

+
+# Copyright (C) 2014-2015 Junjiro R. Okajima
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+
+Listing XATTR/EA and getting the value
+----------------------------------------------------------------------
+For the inode standard attributes (owner, group, timestamps, etc.), aufs
+shows the values from the topmost existing file. This behaviour is good
+for the non-dir entries since the bahaviour exactly matches the shown
+information. But for the directories, aufs considers all the same named
+entries on the lower branches. Which means, if one of the lower entry
+rejects readdir call, then aufs returns an error even if the topmost
+entry allows it. This behaviour is necessary to respect the branch fs's
+security, but can make users confused since the user-visible standard
+attributes don't match the behaviour.
+To address this issue, aufs has a mount option called dirperm1 which
+checks the permission for the topmost entry only, and ignores the lower
+entry's permission.
+
+A similar issue can happen around XATTR.
+getxattr(2) and listxattr(2) families behave as if dirperm1 option is
+always set. Otherwise these very unpleasant situation would happen.
+- listxattr(2) may return the duplicated entries.
+- users may not be able to remove or reset the XATTR forever,
+
+
+XATTR/EA support in the internal (copy,move)-(up,down)
+----------------------------------------------------------------------
+Generally the extended attributes of inode are categorized as these.
+- "security" for LSM and capability.
+- "system" for posix ACL, 'acl' mount option is required for the branch
+  fs generally.
+- "trusted" for userspace, CAP_SYS_ADMIN is required.
+- "user" for userspace, 'user_xattr' mount option is required for the
+  branch fs generally.
+
+Moreover there are some other categories. Aufs handles these rather
+unpopular categories as the ordinary ones, ie. there is no special
+condition nor exception.
+
+In copy-up, the support for XATTR on the dst branch may differ from the
+src branch. In this case, the copy-up operation will get an error and
+the original user operation which triggered the copy-up will fail. It
+can happen that even all copy-up will fail.
+When both of src and dst branches support XATTR and if an error occurs
+during copying XATTR, then the copy-up should fail obviously. That is a
+good reason and aufs should return an error to userspace. But when only
+the src branch support that XATTR, aufs should not return an error.
+For example, the src branch supports ACL but the dst branch doesn't
+because the dst branch may natively un-support it or temporary
+un-support it due to "noacl" mount option. Of course, the dst branch fs
+may NOT return an error even if the XATTR is not supported. It is
+totally up to the branch fs.
+
+Anyway when the aufs internal copy-up gets an error from the dst branch
+fs, then aufs tries removing the just copied entry and returns the error
+to the userspace. The worst case of this situation will be all copy-up
+will fail.
+
+For the copy-up operation, there two basic approaches.
+- copy the specified XATTR only (by category above), and return the
+  error unconditionally if it happens.
+- copy all XATTR, and ignore the error on the specified category only.
+
+In order to support XATTR and to implement the correct behaviour, aufs
+chooses the latter approach and introduces some new branch attributes,
+"icexsec", "icexsys", "icextr", "icexusr", and "icexoth".
+They correspond to the XATTR namespaces (see above). Additionally, to be
+convenient, "icex" is also provided which means all "icex*" attributes
+are set (here the word "icex" stands for "ignore copy-error on XATTR").
+
+The meaning of these attributes is to ignore the error from setting
+XATTR on that branch.
+Note that aufs tries copying all XATTR unconditionally, and ignores the
+error from the dst branch according to the specified attributes.
+
+Some XATTR may have its default value. The default value may come from
+the parent dir or the environment. If the default value is set at the
+file creating-time, it will be overwritten by copy-up.
+Some contradiction may happen I am afraid.
+Do we need another attribute to stop copying XATTR? I am unsure. For
+now, aufs implements the branch attributes to ignore the error.

Documentation/filesystems/aufs/design/07export.txt

+
+# Copyright (C) 2005-2015 Junjiro R. Okajima
+# 
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Export Aufs via NFS
+----------------------------------------------------------------------
+Here is an approach.
+- like xino/xib, add a new file 'xigen' which stores aufs inode
+  generation.
+- iget_locked(): initialize aufs inode generation for a new inode, and
+  store it in xigen file.
+- destroy_inode(): increment aufs inode generation and store it in xigen
+  file. it is necessary even if it is not unlinked, because any data of
+  inode may be changed by UDBA.
+- encode_fh(): for a root dir, simply return FILEID_ROOT. otherwise
+  build file handle by
+  + branch id (4 bytes)
+  + superblock generation (4 bytes)
+  + inode number (4 or 8 bytes)
+  + parent dir inode number (4 or 8 bytes)
+  + inode generation (4 bytes))
+  + return value of exportfs_encode_fh() for the parent on a branch (4
+    bytes)
+  + file handle for a branch (by exportfs_encode_fh())
+- fh_to_dentry():
+  + find the index of a branch from its id in handle, and check it is
+    still exist in aufs.
+  + 1st level: get the inode number from handle and search it in cache.
+  + 2nd level: if not found in cache, get the parent inode number from
+    the handle and search it in cache. and then open the found parent
+    dir, find the matching inode number by vfs_readdir() and get its
+    name, and call lookup_one_len() for the target dentry.
+  + 3rd level: if the parent dir is not cached, call
+    exportfs_decode_fh() for a branch and get the parent on a branch,
+    build a pathname of it, convert it a pathname in aufs, call
+    path_lookup(). now aufs gets a parent dir dentry, then handle it as
+    the 2nd level.
+  + to open the dir, aufs needs struct vfsmount. aufs keeps vfsmount
+    for every branch, but not itself. to get this, (currently) aufs
+    searches in current->nsproxy->mnt_ns list. it may not be a good
+    idea, but I didn't get other approach.
+  + test the generation of the gotten inode.
+- every inode operation: they may get EBUSY due to UDBA. in this case,
+  convert it into ESTALE for NFSD.
+- readdir(): call lockdep_on/off() because filldir in NFSD calls
+  lookup_one_len(), vfs_getattr(), encode_fh() and others.

Documentation/filesystems/aufs/design/08shwh.txt

+
+# Copyright (C) 2005-2015 Junjiro R. Okajima
+# 
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Show Whiteout Mode (shwh)
+----------------------------------------------------------------------
+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.
+
+(borrowing aufs1 HOW-TO from a user, Michael Towers)
+When you have three branches,
+- Bottom: 'system', squashfs (underlying base system), read-only
+- Middle: 'mods', squashfs, read-only
+- Top: 'overlay', ram (tmpfs), read-write
+
+The top layer is loaded at boot time and saved at shutdown, to preserve
+the changes made to the system during the session.
+When larger changes have been made, or smaller changes have accumulated,
+the size of the saved top layer data grows. At this point, it would be
+nice to be able to merge the two overlay branches ('mods' and 'overlay')
+and rewrite the 'mods' squashfs, clearing the top layer and thus
+restoring save and load speed.
+
+This merging is simplified by the use of another aufs mount, of just the
+two overlay branches using the 'shwh' option.
+# mount -t aufs -o ro,shwh,br:/livesys/overlay=ro+wh:/livesys/mods=rr+wh \
+	aufs /livesys/merge_union
+
+A merged view of these two branches is then available at
+/livesys/merge_union, and the new feature is that the whiteouts are
+visible!
+Note that in 'shwh' mode the aufs mount must be 'ro', which will disable
+writing to all branches. Also the default mode for all branches is 'ro'.
+It is now possible to save the combined contents of the two overlay
+branches to a new squashfs, e.g.:
+# mksquashfs /livesys/merge_union /path/to/newmods.squash
+
+This new squashfs archive can be stored on the boot device and the
+initramfs will use it to replace the old one at the next boot.

Documentation/filesystems/aufs/design/10dynop.txt

+
+# Copyright (C) 2010-2015 Junjiro R. Okajima
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Dynamically customizable FS operations
+----------------------------------------------------------------------
+Generally FS operations (struct inode_operations, struct
+address_space_operations, struct file_operations, etc.) are defined as
+"static const", but it never means that FS have only one set of
+operation. Some FS have multiple sets of them. For instance, ext2 has
+three sets, one for XIP, for NOBH, and for normal.
+Since aufs overrides and redirects these operations, sometimes aufs has
+to change its behaviour according to the branch FS type. More importantly
+VFS acts differently if a function (member in the struct) is set or
+not. It means aufs should have several sets of operations and select one
+among them according to the branch FS definition.
+
+In order to solve this problem and not to affect the behaviour of VFS,
+aufs defines these operations dynamically. For instance, aufs defines
+dummy direct_IO function for struct address_space_operations, but it may
+not be set to the address_space_operations actually. When the branch FS
+doesn't have it, aufs doesn't set it to its address_space_operations
+while the function definition itself is still alive. So the behaviour
+itself will not change, and it will return an error when direct_IO is
+not set.
+
+The lifetime of these dynamically generated operation object is
+maintained by aufs branch object. When the branch is removed from aufs,
+the reference counter of the object is decremented. When it reaches
+zero, the dynamically generated operation object will be freed.
+
+This approach is designed to support AIO (io_submit), Direct I/O and
+XIP (DAX) mainly.
+Currently this approach is applied to address_space_operations for
+regular files only.

MAINTAINERS

@@ -2029,6 +2029,19 @@ F:	include/linux/audit.h
 F:	include/uapi/linux/audit.h
 F:	kernel/audit*
 
+AUFS (advanced multi layered unification filesystem) FILESYSTEM
+M:	"J. R. Okajima" <hooanon05g@gmail.com>
+L:	linux-unionfs@vger.kernel.org
+L:	aufs-users@lists.sourceforge.net (members only)
+W:	http://aufs.sourceforge.net
+T:	git://github.com/sfjro/aufs4-linux.git
+S:	Supported
+F:	Documentation/filesystems/aufs/
+F:	Documentation/ABI/testing/debugfs-aufs
+F:	Documentation/ABI/testing/sysfs-aufs
+F:	fs/aufs/
+F:	include/uapi/linux/aufs_type.h
+
 AUXILIARY DISPLAY DRIVERS
 M:	Miguel Ojeda Sandonis <miguel.ojeda.sandonis@gmail.com>
 W:	http://miguelojeda.es/auxdisplay.htm

drivers/block/loop.c

@@ -556,7 +556,7 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
 }
 
 struct switch_request {
-	struct file *file;
+	struct file *file, *virt_file;
 	struct completion wait;
 };
 
@@ -582,6 +582,7 @@ static void do_loop_switch(struct loop_device *lo, struct switch_request *p)
 	mapping = file->f_mapping;
 	mapping_set_gfp_mask(old_file->f_mapping, lo->old_gfp_mask);
 	lo->lo_backing_file = file;
+	lo->lo_backing_virt_file = p->virt_file;
 	lo->lo_blocksize = S_ISBLK(mapping->host->i_mode) ?
 		mapping->host->i_bdev->bd_block_size : PAGE_SIZE;
 	lo->old_gfp_mask = mapping_gfp_mask(mapping);
@@ -594,11 +595,13 @@ static void do_loop_switch(struct loop_device *lo, struct switch_request *p)
  * First it needs to flush existing IO, it does this by sending a magic
  * BIO down the pipe. The completion of this BIO does the actual switch.
  */
-static int loop_switch(struct loop_device *lo, struct file *file)
+static int loop_switch(struct loop_device *lo, struct file *file,
+		       struct file *virt_file)
 {
 	struct switch_request w;
 
 	w.file = file;
+	w.virt_file = virt_file;
 
 	/* freeze queue and wait for completion of scheduled requests */
 	blk_mq_freeze_queue(lo->lo_queue);
@@ -617,7 +620,16 @@ static int loop_switch(struct loop_device *lo, struct file *file)
  */
 static int loop_flush(struct loop_device *lo)
 {
-	return loop_switch(lo, NULL);
+	return loop_switch(lo, NULL, NULL);
+}
+
+static struct file *loop_real_file(struct file *file)
+{
+	struct file *f = NULL;
+
+	if (file->f_path.dentry->d_sb->s_op->real_loop)
+		f = file->f_path.dentry->d_sb->s_op->real_loop(file);
+	return f;
 }
 
 static void loop_reread_partitions(struct loop_device *lo,
@@ -654,6 +666,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 			  unsigned int arg)
 {
 	struct file	*file, *old_file;
+	struct file	*f, *virt_file = NULL, *old_virt_file;
 	struct inode	*inode;
 	int		error;
 
@@ -670,9 +683,16 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 	file = fget(arg);
 	if (!file)
 		goto out;
+	f = loop_real_file(file);
+	if (f) {
+		virt_file = file;
+		file = f;
+		get_file(file);
+	}
 
 	inode = file->f_mapping->host;
 	old_file = lo->lo_backing_file;
+	old_virt_file = lo->lo_backing_virt_file;
 
 	error = -EINVAL;
 
@@ -684,17 +704,21 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 		goto out_putf;
 
 	/* and ... switch */
-	error = loop_switch(lo, file);
+	error = loop_switch(lo, file, virt_file);
 	if (error)
 		goto out_putf;
 
 	fput(old_file);
+	if (old_virt_file)
+		fput(old_virt_file);
 	if (lo->lo_flags & LO_FLAGS_PARTSCAN)
 		loop_reread_partitions(lo, bdev);
 	return 0;
 
  out_putf:
 	fput(file);
+	if (virt_file)
+		fput(virt_file);
  out:
 	return error;
 }
@@ -706,6 +730,24 @@ static inline int is_loop_device(struct file *file)
 	return i && S_ISBLK(i->i_mode) && MAJOR(i->i_rdev) == LOOP_MAJOR;
 }
 
+/*
+ * for AUFS
+ * no get/put for file.
+ */
+struct file *loop_backing_file(struct super_block *sb)
+{
+	struct file *ret;
+	struct loop_device *l;
+
+	ret = NULL;
+	if (MAJOR(sb->s_dev) == LOOP_MAJOR) {
+		l = sb->s_bdev->bd_disk->private_data;
+		ret = l->lo_backing_file;
+	}
+	return ret;
+}
+EXPORT_SYMBOL(loop_backing_file);
+
 /* loop sysfs attributes */
 
 static ssize_t loop_attr_show(struct device *dev, char *page,
@@ -863,7 +905,7 @@ static int loop_prepare_queue(struct loop_device *lo)
 static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 		       struct block_device *bdev, unsigned int arg)
 {
-	struct file	*file, *f;
+	struct file	*file, *f, *virt_file = NULL;
 	struct inode	*inode;
 	struct address_space *mapping;
 	unsigned lo_blocksize;
@@ -878,6 +920,12 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 	file = fget(arg);
 	if (!file)
 		goto out;
+	f = loop_real_file(file);
+	if (f) {
+		virt_file = file;
+		file = f;
+		get_file(file);
+	}
 
 	error = -EBUSY;
 	if (lo->lo_state != Lo_unbound)
@@ -930,6 +978,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 	lo->lo_device = bdev;
 	lo->lo_flags = lo_flags;
 	lo->lo_backing_file = file;
+	lo->lo_backing_virt_file = virt_file;
 	lo->transfer = NULL;
 	lo->ioctl = NULL;
 	lo->lo_sizelimit = 0;
@@ -962,6 +1011,8 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 
  out_putf:
 	fput(file);
+	if (virt_file)
+		fput(virt_file);
  out:
 	/* This is safe: open() is still holding a reference. */
 	module_put(THIS_MODULE);
@@ -1008,6 +1059,7 @@ loop_init_xfer(struct loop_device *lo, struct loop_func_table *xfer,
 static int loop_clr_fd(struct loop_device *lo)
 {
 	struct file *filp = lo->lo_backing_file;
+	struct file *virt_filp = lo->lo_backing_virt_file;
 	gfp_t gfp = lo->old_gfp_mask;
 	struct block_device *bdev = lo->lo_device;
 
@@ -1039,6 +1091,7 @@ static int loop_clr_fd(struct loop_device *lo)
 	spin_lock_irq(&lo->lo_lock);
 	lo->lo_state = Lo_rundown;
 	lo->lo_backing_file = NULL;
+	lo->lo_backing_virt_file = NULL;
 	spin_unlock_irq(&lo->lo_lock);
 
 	loop_release_xfer(lo);
@@ -1083,6 +1136,8 @@ static int loop_clr_fd(struct loop_device *lo)
 	 * bd_mutex which is usually taken before lo_ctl_mutex.
 	 */
 	fput(filp);
+	if (virt_filp)
+		fput(virt_filp);
 	return 0;
 }
 

drivers/block/loop.h

@@ -46,7 +46,7 @@ struct loop_device {
 	int		(*ioctl)(struct loop_device *, int cmd, 
 				 unsigned long arg); 
 
-	struct file *	lo_backing_file;
+	struct file *	lo_backing_file, *lo_backing_virt_file;
 	struct block_device *lo_device;
 	unsigned	lo_blocksize;
 	void		*key_data; 

fs/Kconfig

@@ -221,6 +221,7 @@ source "fs/pstore/Kconfig"
 source "fs/sysv/Kconfig"
 source "fs/ufs/Kconfig"
 source "fs/exofs/Kconfig"
+source "fs/aufs/Kconfig"
 
 endif # MISC_FILESYSTEMS
 

fs/Makefile

@@ -126,3 +126,4 @@ obj-y				+= exofs/ # Multiple modules
 obj-$(CONFIG_CEPH_FS)		+= ceph/
 obj-$(CONFIG_PSTORE)		+= pstore/
 obj-$(CONFIG_EFIVAR_FS)		+= efivarfs/
+obj-$(CONFIG_AUFS_FS)           += aufs/

fs/aufs/Kconfig

+config AUFS_FS
+	tristate "Aufs (Advanced multi layered unification filesystem) support"
+	help
+	Aufs is a stackable unification filesystem such as Unionfs,
+	which unifies several directories and provides a merged single
+	directory.
+	In the early days, aufs was entirely re-designed and
+	re-implemented Unionfs Version 1.x series. Introducing many
+	original ideas, approaches and improvements, it becomes totally
+	different from Unionfs while keeping the basic features.
+
+if AUFS_FS
+choice
+	prompt "Maximum number of branches"
+	default AUFS_BRANCH_MAX_127
+	help
+	Specifies the maximum number of branches (or member directories)
+	in a single aufs. The larger value consumes more system
+	resources and has a minor impact to performance.
+config AUFS_BRANCH_MAX_127
+	bool "127"
+	help
+	Specifies the maximum number of branches (or member directories)
+	in a single aufs. The larger value consumes more system
+	resources and has a minor impact to performance.
+config AUFS_BRANCH_MAX_511
+	bool "511"
+	help
+	Specifies the maximum number of branches (or member directories)
+	in a single aufs. The larger value consumes more system
+	resources and has a minor impact to performance.
+config AUFS_BRANCH_MAX_1023
+	bool "1023"
+	help
+	Specifies the maximum number of branches (or member directories)
+	in a single aufs. The larger value consumes more system
+	resources and has a minor impact to performance.
+config AUFS_BRANCH_MAX_32767
+	bool "32767"
+	help
+	Specifies the maximum number of branches (or member directories)
+	in a single aufs. The larger value consumes more system
+	resources and has a minor impact to performance.
+endchoice
+
+config AUFS_SBILIST
+	bool
+	depends on AUFS_MAGIC_SYSRQ || PROC_FS
+	default y
+	help
+	Automatic configuration for internal use.
+	When aufs supports Magic SysRq or /proc, enabled automatically.
+
+config AUFS_HNOTIFY
+	bool "Detect direct branch access (bypassing aufs)"
+	help
+	If you want to modify files on branches directly, eg. bypassing aufs,
+	and want aufs to detect the changes of them fully, then enable this
+	option and use 'udba=notify' mount option.
+	Currently there is only one available configuration, "fsnotify".
+	It will have a negative impact to the performance.
+	See detail in aufs.5.
+
+choice
+	prompt "method" if AUFS_HNOTIFY
+	default AUFS_HFSNOTIFY
+config AUFS_HFSNOTIFY
+	bool "fsnotify"
+	select FSNOTIFY
+endchoice
+
+config AUFS_EXPORT
+	bool "NFS-exportable aufs"
+	depends on EXPORTFS
+	help
+	If you want to export your mounted aufs via NFS, then enable this
+	option. There are several requirements for this configuration.
+	See detail in aufs.5.
+
+config AUFS_INO_T_64
+	bool
+	depends on AUFS_EXPORT
+	depends on 64BIT && !(ALPHA || S390)
+	default y
+	help
+	Automatic configuration for internal use.
+	/* typedef unsigned long/int __kernel_ino_t */
+	/* alpha and s390x are int */
+
+config AUFS_XATTR
+	bool "support for XATTR/EA (including Security Labels)"
+	help
+	If your branch fs supports XATTR/EA and you want to make them
+	available in aufs too, then enable this opsion and specify the
+	branch attributes for EA.
+	See detail in aufs.5.
+
+config AUFS_FHSM
+	bool "File-based Hierarchical Storage Management"
+	help
+	Hierarchical Storage Management (or HSM) is a well-known feature
+	in the storage world. Aufs provides this feature as file-based.
+	with multiple branches.
+	These multiple branches are prioritized, ie. the topmost one
+	should be the fastest drive and be used heavily.
+
+config AUFS_RDU
+	bool "Readdir in userspace"
+	help
+	Aufs has two methods to provide a merged view for a directory,
+	by a user-space library and by kernel-space natively. The latter
+	is always enabled but sometimes large and slow.
+	If you enable this option, install the library in aufs2-util
+	package, and set some environment variables for your readdir(3),
+	then the work will be handled in user-space which generally
+	shows better performance in most cases.
+	See detail in aufs.5.
+
+config AUFS_SHWH
+	bool "Show whiteouts"
+	help
+	If you want to make the whiteouts in aufs visible, then enable
+	this option and specify 'shwh' mount option. Although it may
+	sounds like philosophy or something, but in technically it
+	simply shows the name of whiteout with keeping its behaviour.
+
+config AUFS_BR_RAMFS
+	bool "Ramfs (initramfs/rootfs) as an aufs branch"
+	help
+	If you want to use ramfs as an aufs branch fs, then enable this
+	option. Generally tmpfs is recommended.
+	Aufs prohibited them to be a branch fs by default, because
+	initramfs becomes unusable after switch_root or something
+	generally. If you sets initramfs as an aufs branch and boot your
+	system by switch_root, you will meet a problem easily since the
+	files in initramfs may be inaccessible.
+	Unless you are going to use ramfs as an aufs branch fs without
+	switch_root or something, leave it N.
+
+config AUFS_BR_FUSE
+	bool "Fuse fs as an aufs branch"
+	depends on FUSE_FS
+	select AUFS_POLL
+	help
+	If you want to use fuse-based userspace filesystem as an aufs
+	branch fs, then enable this option.
+	It implements the internal poll(2) operation which is
+	implemented by fuse only (curretnly).
+
+config AUFS_POLL
+	bool
+	help
+	Automatic configuration for internal use.
+
+config AUFS_BR_HFSPLUS
+	bool "Hfsplus as an aufs branch"
+	depends on HFSPLUS_FS
+	default y
+	help
+	If you want to use hfsplus fs as an aufs branch fs, then enable
+	this option. This option introduces a small overhead at
+	copying-up a file on hfsplus.
+
+config AUFS_BDEV_LOOP
+	bool
+	depends on BLK_DEV_LOOP
+	default y
+	help
+	Automatic configuration for internal use.
+	Convert =[ym] into =y.
+
+config AUFS_DEBUG
+	bool "Debug aufs"
+	help
+	Enable this to compile aufs internal debug code.
+	It will have a negative impact to the performance.
+
+config AUFS_MAGIC_SYSRQ
+	bool
+	depends on AUFS_DEBUG && MAGIC_SYSRQ
+	default y
+	help
+	Automatic configuration for internal use.
+	When aufs supports Magic SysRq, enabled automatically.
+endif

fs/aufs/Makefile

+
+include ${src}/magic.mk
+ifeq (${CONFIG_AUFS_FS},m)
+include ${src}/conf.mk
+endif
+-include ${src}/priv_def.mk
+
+# cf. include/linux/kernel.h
+# enable pr_debug
+ccflags-y += -DDEBUG
+# sparse requires the full pathname
+ifdef M
+ccflags-y += -include ${M}/../../include/uapi/linux/aufs_type.h
+else
+ccflags-y += -include ${srctree}/include/uapi/linux/aufs_type.h
+endif
+
+obj-$(CONFIG_AUFS_FS) += aufs.o
+aufs-y := module.o sbinfo.o super.o branch.o xino.o sysaufs.o opts.o \
+	wkq.o vfsub.o dcsub.o \
+	cpup.o whout.o wbr_policy.o \
+	dinfo.o dentry.o \
+	dynop.o \
+	finfo.o file.o f_op.o \
+	dir.o vdir.o \
+	iinfo.o inode.o i_op.o i_op_add.o i_op_del.o i_op_ren.o \
+	mvdown.o ioctl.o
+
+# all are boolean
+aufs-$(CONFIG_PROC_FS) += procfs.o plink.o
+aufs-$(CONFIG_SYSFS) += sysfs.o
+aufs-$(CONFIG_DEBUG_FS) += dbgaufs.o
+aufs-$(CONFIG_AUFS_BDEV_LOOP) += loop.o
+aufs-$(CONFIG_AUFS_HNOTIFY) += hnotify.o
+aufs-$(CONFIG_AUFS_HFSNOTIFY) += hfsnotify.o
+aufs-$(CONFIG_AUFS_EXPORT) += export.o
+aufs-$(CONFIG_AUFS_XATTR) += xattr.o
+aufs-$(CONFIG_FS_POSIX_ACL) += posix_acl.o
+aufs-$(CONFIG_AUFS_FHSM) += fhsm.o
+aufs-$(CONFIG_AUFS_POLL) += poll.o
+aufs-$(CONFIG_AUFS_RDU) += rdu.o
+aufs-$(CONFIG_AUFS_BR_HFSPLUS) += hfsplus.o
+aufs-$(CONFIG_AUFS_DEBUG) += debug.o
+aufs-$(CONFIG_AUFS_MAGIC_SYSRQ) += sysrq.o

fs/aufs/aufs.h

+/*
+ * Copyright (C) 2005-2015 Junjiro R. Okajima
+ *
+ * This program, aufs is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * all header files
+ */
+
+#ifndef __AUFS_H__
+#define __AUFS_H__
+
+#ifdef __KERNEL__
+
+#define AuStub(type, name, body, ...) \
+	static inline type name(__VA_ARGS__) { body; }
+
+#define AuStubVoid(name, ...) \
+	AuStub(void, name, , __VA_ARGS__)
+#define AuStubInt0(name, ...) \
+	AuStub(int, name, return 0, __VA_ARGS__)
+
+#include "debug.h"
+
+#include "branch.h"
+#include "cpup.h"
+#include "dcsub.h"
+#include "dbgaufs.h"
+#include "dentry.h"
+#include "dir.h"
+#include "dynop.h"
+#include "file.h"
+#include "fstype.h"
+#include "inode.h"
+#include "loop.h"
+#include "module.h"
+#include "opts.h"
+#include "rwsem.h"
+#include "spl.h"
+#include "super.h"
+#include "sysaufs.h"
+#include "vfsub.h"
+#include "whout.h"
+#include "wkq.h"
+
+#endif /* __KERNEL__ */
+#endif /* __AUFS_H__ */

fs/aufs/branch.h

+/*
+ * Copyright (C) 2005-2015 Junjiro R. Okajima
+ *
+ * This program, aufs is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * branch filesystems and xino for them
+ */
+
+#ifndef __AUFS_BRANCH_H__
+#define __AUFS_BRANCH_H__
+
+#ifdef __KERNEL__
+
+#include <linux/mount.h>
+#include "dynop.h"
+#include "rwsem.h"
+#include "super.h"
+
+/* ---------------------------------------------------------------------- */
+
+/* a xino file */
+struct au_xino_file {
+	struct file		*xi_file;
+	struct mutex		xi_nondir_mtx;
+
+	/* todo: make xino files an array to support huge inode number */
+
+#ifdef CONFIG_DEBUG_FS
+	struct dentry		 *xi_dbgaufs;
+#endif
+};
+
+/* File-based Hierarchical Storage Management */
+struct au_br_fhsm {
+#ifdef CONFIG_AUFS_FHSM
+	struct mutex		bf_lock;
+	unsigned long		bf_jiffy;
+	struct aufs_stfs	bf_stfs;
+	int			bf_readable;
+#endif
+};
+
+/* members for writable branch only */
+enum {AuBrWh_BASE, AuBrWh_PLINK, AuBrWh_ORPH, AuBrWh_Last};
+struct au_wbr {
+	struct au_rwsem		wbr_wh_rwsem;
+	struct dentry		*wbr_wh[AuBrWh_Last];
+	atomic_t		wbr_wh_running;
+#define wbr_whbase		wbr_wh[AuBrWh_BASE]	/* whiteout base */
+#define wbr_plink		wbr_wh[AuBrWh_PLINK]	/* pseudo-link dir */
+#define wbr_orph		wbr_wh[AuBrWh_ORPH]	/* dir for orphans */
+
+	/* mfs mode */
+	unsigned long long	wbr_bytes;
+};
+
+/* ext2 has 3 types of operations at least, ext3 has 4 */
+#define AuBrDynOp (AuDyLast * 4)
+
+#ifdef CONFIG_AUFS_HFSNOTIFY
+/* support for asynchronous destruction */
+struct au_br_hfsnotify {
+	struct fsnotify_group	*hfsn_group;
+};
+#endif
+
+/* sysfs entries */
+struct au_brsysfs {
+	char			name[16];
+	struct attribute	attr;
+};
+
+enum {
+	AuBrSysfs_BR,
+	AuBrSysfs_BRID,
+	AuBrSysfs_Last
+};
+
+/* protected by superblock rwsem */
+struct au_branch {
+	struct au_xino_file	br_xino;
+
+	aufs_bindex_t		br_id;
+
+	int			br_perm;
+	struct path		br_path;
+	spinlock_t		br_dykey_lock;
+	struct au_dykey		*br_dykey[AuBrDynOp];
+	atomic_t		br_count;
+
+	struct au_wbr		*br_wbr;
+	struct au_br_fhsm	*br_fhsm;
+
+	/* xino truncation */
+	atomic_t		br_xino_running;
+
+#ifdef CONFIG_AUFS_HFSNOTIFY
+	struct au_br_hfsnotify	*br_hfsn;
+#endif
+
+#ifdef CONFIG_SYSFS
+	/* entries under sysfs per mount-point */
+	struct au_brsysfs	br_sysfs[AuBrSysfs_Last];
+#endif
+};
+
+/* ---------------------------------------------------------------------- */
+
+static inline struct vfsmount *au_br_mnt(struct au_branch *br)
+{
+	return br->br_path.mnt;
+}
+
+static inline struct dentry *au_br_dentry(struct au_branch *br)
+{
+	return br->br_path.dentry;
+}
+
+static inline struct super_block *au_br_sb(struct au_branch *br)
+{
+	return au_br_mnt(br)->mnt_sb;
+}
+
+static inline int au_br_rdonly(struct au_branch *br)
+{
+	return ((au_br_sb(br)->s_flags & MS_RDONLY)
+		|| !au_br_writable(br->br_perm))
+		? -EROFS : 0;
+}
+
+static inline int au_br_hnotifyable(int brperm __maybe_unused)
+{
+#ifdef CONFIG_AUFS_HNOTIFY
+	return !(brperm & AuBrPerm_RR);
+#else
+	return 0;
+#endif
+}
+
+static inline int au_br_test_oflag(int oflag, struct au_branch *br)
+{
+	int err, exec_flag;
+
+	err = 0;
+	exec_flag = oflag & __FMODE_EXEC;
+	if (unlikely(exec_flag && path_noexec(&br->br_path)))
+		err = -EACCES;
+
+	return err;
+}
+
+/* ---------------------------------------------------------------------- */
+
+/* branch.c */
+struct au_sbinfo;
+void au_br_free(struct au_sbinfo *sinfo);
+int au_br_index(struct super_block *sb, aufs_bindex_t br_id);
+struct au_opt_add;
+int au_br_add(struct super_block *sb, struct au_opt_add *add, int remount);
+struct au_opt_del;
+int au_br_del(struct super_block *sb, struct au_opt_del *del, int remount);
+long au_ibusy_ioctl(struct file *file, unsigned long arg);
+#ifdef CONFIG_COMPAT
+long au_ibusy_compat_ioctl(struct file *file, unsigned long arg);
+#endif
+struct au_opt_mod;
+int au_br_mod(struct super_block *sb, struct au_opt_mod *mod, int remount,
+	      int *do_refresh);
+struct aufs_stfs;
+int au_br_stfs(struct au_branch *br, struct aufs_stfs *stfs);
+
+/* xino.c */
+static const loff_t au_loff_max = LLONG_MAX;
+
+int au_xib_trunc(struct super_block *sb);
+ssize_t xino_fread(vfs_readf_t func, struct file *file, void *buf, size_t size,
+		   loff_t *pos);
+ssize_t xino_fwrite(vfs_writef_t func, struct file *file, void *buf,
+		    size_t size, loff_t *pos);
+struct file *au_xino_create2(struct file *base_file, struct file *copy_src);
+struct file *au_xino_create(struct super_block *sb, char *fname, int silent);
+ino_t au_xino_new_ino(struct super_block *sb);
+void au_xino_delete_inode(struct inode *inode, const int unlinked);
+int au_xino_write(struct super_block *sb, aufs_bindex_t bindex, ino_t h_ino,
+		  ino_t ino);
+int au_xino_read(struct super_block *sb, aufs_bindex_t bindex, ino_t h_ino,
+		 ino_t *ino);
+int au_xino_br(struct super_block *sb, struct au_branch *br, ino_t hino,
+	       struct file *base_file, int do_test);
+int au_xino_trunc(struct super_block *sb, aufs_bindex_t bindex);
+
+struct au_opt_xino;
+int au_xino_set(struct super_block *sb, struct au_opt_xino *xino, int remount);
+void au_xino_clr(struct super_block *sb);
+struct file *au_xino_def(struct super_block *sb);
+int au_xino_path(struct seq_file *seq, struct file *file);
+
+/* ---------------------------------------------------------------------- */
+
+/* Superblock to branch */
+static inline
+aufs_bindex_t au_sbr_id(struct super_block *sb, aufs_bindex_t bindex)
+{
+	return au_sbr(sb, bindex)->br_id;
+}
+
+static inline
+struct vfsmount *au_sbr_mnt(struct super_block *sb, aufs_bindex_t bindex)
+{
+	return au_br_mnt(au_sbr(sb, bindex));
+}
+
+static inline
+struct super_block *au_sbr_sb(struct super_block *sb, aufs_bindex_t bindex)
+{
+	return au_br_sb(au_sbr(sb, bindex));
+}
+
+static inline void au_sbr_put(struct super_block *sb, aufs_bindex_t bindex)
+{
+	atomic_dec(&au_sbr(sb, bindex)->br_count);
+}
+
+static inline int au_sbr_perm(struct super_block *sb, aufs_bindex_t bindex)
+{
+	return au_sbr(sb, bindex)->br_perm;
+}
+
+static inline int au_sbr_whable(struct super_block *sb, aufs_bindex_t bindex)
+{
+	return au_br_whable(au_sbr_perm(sb, bindex));
+}
+
+/* ---------------------------------------------------------------------- */
+
+/*
+ * wbr_wh_read_lock, wbr_wh_write_lock
+ * wbr_wh_read_unlock, wbr_wh_write_unlock, wbr_wh_downgrade_lock
+ */
+AuSimpleRwsemFuncs(wbr_wh, struct au_wbr *wbr, &wbr->wbr_wh_rwsem);
+
+#define WbrWhMustNoWaiters(wbr)	AuRwMustNoWaiters(&wbr->wbr_wh_rwsem)
+#define WbrWhMustAnyLock(wbr)	AuRwMustAnyLock(&wbr->wbr_wh_rwsem)
+#define WbrWhMustWriteLock(wbr)	AuRwMustWriteLock(&wbr->wbr_wh_rwsem)
+
+/* ---------------------------------------------------------------------- */
+
+#ifdef CONFIG_AUFS_FHSM
+static inline void au_br_fhsm_init(struct au_br_fhsm *brfhsm)
+{
+	mutex_init(&brfhsm->bf_lock);
+	brfhsm->bf_jiffy = 0;
+	brfhsm->bf_readable = 0;
+}
+
+static inline void au_br_fhsm_fin(struct au_br_fhsm *brfhsm)
+{
+	mutex_destroy(&brfhsm->bf_lock);
+}
+#else
+AuStubVoid(au_br_fhsm_init, struct au_br_fhsm *brfhsm)
+AuStubVoid(au_br_fhsm_fin, struct au_br_fhsm *brfhsm)
+#endif
+
+#endif /* __KERNEL__ */
+#endif /* __AUFS_BRANCH_H__ */

fs/aufs/conf.mk

+
+AuConfStr = CONFIG_AUFS_FS=${CONFIG_AUFS_FS}
+
+define AuConf
+ifdef ${1}
+AuConfStr += ${1}=${${1}}
+endif
+endef
+
+AuConfAll = BRANCH_MAX_127 BRANCH_MAX_511 BRANCH_MAX_1023 BRANCH_MAX_32767 \
+	SBILIST \
+	HNOTIFY HFSNOTIFY \
+	EXPORT INO_T_64 \
+	XATTR \
+	FHSM \
+	RDU \
+	SHWH \
+	BR_RAMFS \
+	BR_FUSE POLL \
+	BR_HFSPLUS \
+	BDEV_LOOP \
+	DEBUG MAGIC_SYSRQ
+$(foreach i, ${AuConfAll}, \
+	$(eval $(call AuConf,CONFIG_AUFS_${i})))
+
+AuConfName = ${obj}/conf.str
+${AuConfName}.tmp: FORCE
+	@echo ${AuConfStr} | tr ' ' '\n' | sed -e 's/^/"/' -e 's/$$/\\n"/' > $@
+${AuConfName}: ${AuConfName}.tmp
+	@diff -q $< $@ > /dev/null 2>&1 || { \
+	echo '  GEN    ' $@; \
+	cp -p $< $@; \
+	}
+FORCE:
+clean-files += ${AuConfName} ${AuConfName}.tmp
+${obj}/sysfs.o: ${AuConfName}
+
+-include ${srctree}/${src}/conf_priv.mk

fs/aufs/cpup.h

+/*
+ * Copyright (C) 2005-2015 Junjiro R. Okajima
+ *
+ * This program, aufs is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * copy-up/down functions
+ */
+
+#ifndef __AUFS_CPUP_H__
+#define __AUFS_CPUP_H__
+
+#ifdef __KERNEL__
+
+#include <linux/path.h>
+
+struct inode;
+struct file;
+struct au_pin;
+
+void au_cpup_attr_flags(struct inode *dst, unsigned int iflags);
+void au_cpup_attr_timesizes(struct inode *inode);
+void au_cpup_attr_nlink(struct inode *inode, int force);
+void au_cpup_attr_changeable(struct inode *inode);
+void au_cpup_igen(struct inode *inode, struct inode *h_inode);
+void au_cpup_attr_all(struct inode *inode, int force);
+
+/* ---------------------------------------------------------------------- */
+
+struct au_cp_generic {
+	struct dentry	*dentry;
+	aufs_bindex_t	bdst, bsrc;
+	loff_t		len;
+	struct au_pin	*pin;
+	unsigned int	flags;
+};
+
+/* cpup flags */
+#define AuCpup_DTIME		1		/* do dtime_store/revert */
+#define AuCpup_KEEPLINO		(1 << 1)	/* do not clear the lower xino,
+						   for link(2) */
+#define AuCpup_RENAME		(1 << 2)	/* rename after cpup */
+#define AuCpup_HOPEN		(1 << 3)	/* call h_open_pre/post() in
+						   cpup */
+#define AuCpup_OVERWRITE	(1 << 4)	/* allow overwriting the
+						   existing entry */
+#define AuCpup_RWDST		(1 << 5)	/* force write target even if
+						   the branch is marked as RO */
+
+#define au_ftest_cpup(flags, name)	((flags) & AuCpup_##name)
+#define au_fset_cpup(flags, name) \
+	do { (flags) |= AuCpup_##name; } while (0)
+#define au_fclr_cpup(flags, name) \
+	do { (flags) &= ~AuCpup_##name; } while (0)
+
+int au_copy_file(struct file *dst, struct file *src, loff_t len);
+int au_sio_cpup_simple(struct au_cp_generic *cpg);
+int au_sio_cpdown_simple(struct au_cp_generic *cpg);
+int au_sio_cpup_wh(struct au_cp_generic *cpg, struct file *file);
+
+int au_cp_dirs(struct dentry *dentry, aufs_bindex_t bdst,
+	       int (*cp)(struct dentry *dentry, aufs_bindex_t bdst,
+			 struct au_pin *pin,
+			 struct dentry *h_parent, void *arg),
+	       void *arg);
+int au_cpup_dirs(struct dentry *dentry, aufs_bindex_t bdst);
+int au_test_and_cpup_dirs(struct dentry *dentry, aufs_bindex_t bdst);
+
+/* ---------------------------------------------------------------------- */
+
+/* keep timestamps when copyup */
+struct au_dtime {
+	struct dentry *dt_dentry;
+	struct path dt_h_path;
+	struct timespec dt_atime, dt_mtime;
+};
+void au_dtime_store(struct au_dtime *dt, struct dentry *dentry,
+		    struct path *h_path);
+void au_dtime_revert(struct au_dtime *dt);
+
+#endif /* __KERNEL__ */
+#endif /* __AUFS_CPUP_H__ */

fs/aufs/dbgaufs.c

+/*
+ * Copyright (C) 2005-2015 Junjiro R. Okajima
+ *
+ * This program, aufs is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * debugfs interface
+ */
+
+#include <linux/debugfs.h>
+#include "aufs.h"
+
+#ifndef CONFIG_SYSFS
+#error DEBUG_FS depends upon SYSFS
+#endif
+
+static struct dentry *dbgaufs;
+static const mode_t dbgaufs_mode = S_IRUSR | S_IRGRP | S_IROTH;
+
+/* 20 is max digits length of ulong 64 */
+struct dbgaufs_arg {
+	int n;
+	char a[20 * 4];
+};
+
+/*
+ * common function for all XINO files
+ */
+static int dbgaufs_xi_release(struct inode *inode __maybe_unused,
+			      struct file *file)
+{
+	kfree(file->private_data);
+	return 0;
+}
+
+static int dbgaufs_xi_open(struct file *xf, struct file *file, int do_fcnt)
+{
+	int err;
+	struct kstat st;
+	struct dbgaufs_arg *p;
+
+	err = -ENOMEM;
+	p = kmalloc(sizeof(*p), GFP_NOFS);
+	if (unlikely(!p))
+		goto out;
+
+	err = 0;
+	p->n = 0;
+	file->private_data = p;
+	if (!xf)
+		goto out;
+
+	err = vfs_getattr(&xf->f_path, &st);
+	if (!err) {
+		if (do_fcnt)
+			p->n = snprintf
+				(p->a, sizeof(p->a), "%ld, %llux%lu %lld\n",
+				 (long)file_count(xf), st.blocks, st.blksize,
+				 (long long)st.size);
+		else
+			p->n = snprintf(p->a, sizeof(p->a), "%llux%lu %lld\n",
+					st.blocks, st.blksize,
+					(long long)st.size);
+		AuDebugOn(p->n >= sizeof(p->a));
+	} else {
+		p->n = snprintf(p->a, sizeof(p->a), "err %d\n", err);
+		err = 0;
+	}
+
+out:
+	return err;
+
+}
+
+static ssize_t dbgaufs_xi_read(struct file *file, char __user *buf,
+			       size_t count, loff_t *ppos)
+{
+	struct dbgaufs_arg *p;
+
+	p = file->private_data;
+	return simple_read_from_buffer(buf, count, ppos, p->a, p->n);
+}
+
+/* ---------------------------------------------------------------------- */
+
+struct dbgaufs_plink_arg {
+	int n;
+	char a[];
+};
+
+static int dbgaufs_plink_release(struct inode *inode __maybe_unused,
+				 struct file *file)
+{
+	free_page((unsigned long)file->private_data);
+	return 0;
+}
+
+static int dbgaufs_plink_open(struct inode *inode, struct file *file)
+{
+	int err, i, limit;
+	unsigned long n, sum;
+	struct dbgaufs_plink_arg *p;
+	struct au_sbinfo *sbinfo;
+	struct super_block *sb;
+	struct au_sphlhead *sphl;
+
+	err = -ENOMEM;
+	p = (void *)get_zeroed_page(GFP_NOFS);
+	if (unlikely(!p))
+		goto out;
+
+	err = -EFBIG;
+	sbinfo = inode->i_private;
+	sb = sbinfo->si_sb;
+	si_noflush_read_lock(sb);
+	if (au_opt_test(au_mntflags(sb), PLINK)) {
+		limit = PAGE_SIZE - sizeof(p->n);
+
+		/* the number of buckets */
+		n = snprintf(p->a + p->n, limit, "%d\n", AuPlink_NHASH);
+		p->n += n;
+		limit -= n;
+
+		sum = 0;
+		for (i = 0, sphl = sbinfo->si_plink;
+		     i < AuPlink_NHASH;
+		     i++, sphl++) {
+			n = au_sphl_count(sphl);
+			sum += n;
+
+			n = snprintf(p->a + p->n, limit, "%lu ", n);
+			p->n += n;
+			limit -= n;
+			if (unlikely(limit <= 0))
+				goto out_free;
+		}
+		p->a[p->n - 1] = '\n';
+
+		/* the sum of plinks */
+		n = snprintf(p->a + p->n, limit, "%lu\n", sum);
+		p->n += n;
+		limit -= n;
+		if (unlikely(limit <= 0))
+			goto out_free;
+	} else {
+#define str "1\n0\n0\n"
+		p->n = sizeof(str) - 1;
+		strcpy(p->a, str);
+#undef str
+	}
+	si_read_unlock(sb);
+
+	err = 0;
+	file->private_data = p;
+	goto out; /* success */
+
+out_free:
+	free_page((unsigned long)p);
+out:
+	return err;
+}
+
+static ssize_t dbgaufs_plink_read(struct file *file, char __user *buf,
+				  size_t count, loff_t *ppos)
+{
+	struct dbgaufs_plink_arg *p;
+
+	p = file->private_data;
+	return simple_read_from_buffer(buf, count, ppos, p->a, p->n);
+}
+
+static const struct file_operations dbgaufs_plink_fop = {
+	.owner		= THIS_MODULE,
+	.open		= dbgaufs_plink_open,
+	.release	= dbgaufs_plink_release,
+	.read		= dbgaufs_plink_read
+};
+
+/* ---------------------------------------------------------------------- */
+
+static int dbgaufs_xib_open(struct inode *inode, struct file *file)
+{
+	int err;
+	struct au_sbinfo *sbinfo;
+	struct super_block *sb;
+
+	sbinfo = inode->i_private;
+	sb = sbinfo->si_sb;
+	si_noflush_read_lock(sb);
+	err = dbgaufs_xi_open(sbinfo->si_xib, file, /*do_fcnt*/0);
+	si_read_unlock(sb);
+	return err;
+}
+
+static const struct file_operations dbgaufs_xib_fop = {
+	.owner		= THIS_MODULE,
+	.open		= dbgaufs_xib_open,
+	.release	= dbgaufs_xi_release,
+	.read		= dbgaufs_xi_read
+};
+
+/* ---------------------------------------------------------------------- */
+
+#define DbgaufsXi_PREFIX "xi"
+
+static int dbgaufs_xino_open(struct inode *inode, struct file *file)
+{
+	int err;
+	long l;
+	struct au_sbinfo *sbinfo;
+	struct super_block *sb;
+	struct file *xf;
+	struct qstr *name;
+
+	err = -ENOENT;
+	xf = NULL;
+	name = &file->f_path.dentry->d_name;
+	if (unlikely(name->len < sizeof(DbgaufsXi_PREFIX)
+		     || memcmp(name->name, DbgaufsXi_PREFIX,
+			       sizeof(DbgaufsXi_PREFIX) - 1)))
+		goto out;
+	err = kstrtol(name->name + sizeof(DbgaufsXi_PREFIX) - 1, 10, &l);
+	if (unlikely(err))
+		goto out;
+
+	sbinfo = inode->i_private;
+	sb = sbinfo->si_sb;
+	si_noflush_read_lock(sb);
+	if (l <= au_sbend(sb)) {
+		xf = au_sbr(sb, (aufs_bindex_t)l)->br_xino.xi_file;
+		err = dbgaufs_xi_open(xf, file, /*do_fcnt*/1);
+	} else
+		err = -ENOENT;
+	si_read_unlock(sb);
+
+out:
+	return err;
+}
+
+static const struct file_operations dbgaufs_xino_fop = {
+	.owner		= THIS_MODULE,
+	.open		= dbgaufs_xino_open,
+	.release	= dbgaufs_xi_release,
+	.read		= dbgaufs_xi_read
+};
+
+void dbgaufs_brs_del(struct super_block *sb, aufs_bindex_t bindex)
+{
+	aufs_bindex_t bend;
+	struct au_branch *br;
+	struct au_xino_file *xi;
+
+	if (!au_sbi(sb)->si_dbgaufs)
+		return;
+
+	bend = au_sbend(sb);
+	for (; bindex <= bend; bindex++) {
+		br = au_sbr(sb, bindex);
+		xi = &br->br_xino;
+		debugfs_remove(xi->xi_dbgaufs);
+		xi->xi_dbgaufs = NULL;
+	}
+}
+
+void dbgaufs_brs_add(struct super_block *sb, aufs_bindex_t bindex)
+{
+	struct au_sbinfo *sbinfo;
+	struct dentry *parent;
+	struct au_branch *br;
+	struct au_xino_file *xi;
+	aufs_bindex_t bend;
+	char name[sizeof(DbgaufsXi_PREFIX) + 5]; /* "xi" bindex NULL */
+
+	sbinfo = au_sbi(sb);
+	parent = sbinfo->si_dbgaufs;
+	if (!parent)
+		return;
+
+	bend = au_sbend(sb);
+	for (; bindex <= bend; bindex++) {
+		snprintf(name, sizeof(name), DbgaufsXi_PREFIX "%d", bindex);
+		br = au_sbr(sb, bindex);
+		xi = &br->br_xino;
+		AuDebugOn(xi->xi_dbgaufs);
+		xi->xi_dbgaufs = debugfs_create_file(name, dbgaufs_mode, parent,
+						     sbinfo, &dbgaufs_xino_fop);
+		/* ignore an error */
+		if (unlikely(!xi->xi_dbgaufs))
+			AuWarn1("failed %s under debugfs\n", name);
+	}
+}
+
+/* ---------------------------------------------------------------------- */
+
+#ifdef CONFIG_AUFS_EXPORT
+static int dbgaufs_xigen_open(struct inode *inode, struct file *file)
+{
+	int err;
+	struct au_sbinfo *sbinfo;
+	struct super_block *sb;
+
+	sbinfo = inode->i_private;
+	sb = sbinfo->si_sb;
+	si_noflush_read_lock(sb);
+	err = dbgaufs_xi_open(sbinfo->si_xigen, file, /*do_fcnt*/0);
+	si_read_unlock(sb);
+	return err;
+}
+
+static const struct file_operations dbgaufs_xigen_fop = {
+	.owner		= THIS_MODULE,
+	.open		= dbgaufs_xigen_open,
+	.release	= dbgaufs_xi_release,
+	.read		= dbgaufs_xi_read
+};
+
+static int dbgaufs_xigen_init(struct au_sbinfo *sbinfo)
+{
+	int err;
+
+	/*
+	 * This function is a dynamic '__init' function actually,
+	 * so the tiny check for si_rwsem is unnecessary.
+	 */
+	/* AuRwMustWriteLock(&sbinfo->si_rwsem); */
+
+	err = -EIO;
+	sbinfo->si_dbgaufs_xigen = debugfs_create_file
+		("xigen", dbgaufs_mode, sbinfo->si_dbgaufs, sbinfo,
+		 &dbgaufs_xigen_fop);
+	if (sbinfo->si_dbgaufs_xigen)
+		err = 0;
+
+	return err;
+}
+#else
+static int dbgaufs_xigen_init(struct au_sbinfo *sbinfo)
+{
+	return 0;
+}
+#endif /* CONFIG_AUFS_EXPORT */
+
+/* ---------------------------------------------------------------------- */
+
+void dbgaufs_si_fin(struct au_sbinfo *sbinfo)
+{
+	/*
+	 * This function is a dynamic '__fin' function actually,
+	 * so the tiny check for si_rwsem is unnecessary.
+	 */
+	/* AuRwMustWriteLock(&sbinfo->si_rwsem); */
+
+	debugfs_remove_recursive(sbinfo->si_dbgaufs);
+	sbinfo->si_dbgaufs = NULL;
+	kobject_put(&sbinfo->si_kobj);
+}
+
+int dbgaufs_si_init(struct au_sbinfo *sbinfo)
+{
+	int err;
+	char name[SysaufsSiNameLen];
+
+	/*
+	 * This function is a dynamic '__init' function actually,
+	 * so the tiny check for si_rwsem is unnecessary.
+	 */
+	/* AuRwMustWriteLock(&sbinfo->si_rwsem); */
+
+	err = -ENOENT;
+	if (!dbgaufs) {
+		AuErr1("/debug/aufs is uninitialized\n");
+		goto out;
+	}
+
+	err = -EIO;
+	sysaufs_name(sbinfo, name);
+	sbinfo->si_dbgaufs = debugfs_create_dir(name, dbgaufs);
+	if (unlikely(!sbinfo->si_dbgaufs))
+		goto out;
+	kobject_get(&sbinfo->si_kobj);
+
+	sbinfo->si_dbgaufs_xib = debugfs_create_file
+		("xib", dbgaufs_mode, sbinfo->si_dbgaufs, sbinfo,
+		 &dbgaufs_xib_fop);
+	if (unlikely(!sbinfo->si_dbgaufs_xib))
+		goto out_dir;
+
+	sbinfo->si_dbgaufs_plink = debugfs_create_file
+		("plink", dbgaufs_mode, sbinfo->si_dbgaufs, sbinfo,
+		 &dbgaufs_plink_fop);
+	if (unlikely(!sbinfo->si_dbgaufs_plink))
+		goto out_dir;
+
+	err = dbgaufs_xigen_init(sbinfo);
+	if (!err)
+		goto out; /* success */
+
+out_dir:
+	dbgaufs_si_fin(sbinfo);
+out:
+	return err;
+}
+
+/* ---------------------------------------------------------------------- */
+
+void dbgaufs_fin(void)
+{
+	debugfs_remove(dbgaufs);
+}
+
+int __init dbgaufs_init(void)
+{
+	int err;
+
+	err = -EIO;
+	dbgaufs = debugfs_create_dir(AUFS_NAME, NULL);
+	if (dbgaufs)
+		err = 0;
+	return err;
+}

fs/aufs/dbgaufs.h

+/*
+ * Copyright (C) 2005-2015 Junjiro R. Okajima
+ *
+ * This program, aufs is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * debugfs interface
+ */
+
+#ifndef __DBGAUFS_H__
+#define __DBGAUFS_H__
+
+#ifdef __KERNEL__
+
+struct super_block;
+struct au_sbinfo;
+
+#ifdef CONFIG_DEBUG_FS
+/* dbgaufs.c */
+void dbgaufs_brs_del(struct super_block *sb, aufs_bindex_t bindex);
+void dbgaufs_brs_add(struct super_block *sb, aufs_bindex_t bindex);
+void dbgaufs_si_fin(struct au_sbinfo *sbinfo);
+int dbgaufs_si_init(struct au_sbinfo *sbinfo);
+void dbgaufs_fin(void);
+int __init dbgaufs_init(void);
+#else
+AuStubVoid(dbgaufs_brs_del, struct super_block *sb, aufs_bindex_t bindex)
+AuStubVoid(dbgaufs_brs_add, struct super_block *sb, aufs_bindex_t bindex)
+AuStubVoid(dbgaufs_si_fin, struct au_sbinfo *sbinfo)
+AuStubInt0(dbgaufs_si_init, struct au_sbinfo *sbinfo)
+AuStubVoid(dbgaufs_fin, void)
+AuStubInt0(__init dbgaufs_init, void)
+#endif /* CONFIG_DEBUG_FS */
+
+#endif /* __KERNEL__ */
+#endif /* __DBGAUFS_H__ */

fs/aufs/dcsub.c

+/*
+ * Copyright (C) 2005-2015 Junjiro R. Okajima
+ *
+ * This program, aufs is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * sub-routines for dentry cache
+ */
+
+#include "aufs.h"
+
+static void au_dpage_free(struct au_dpage *dpage)
+{
+	int i;
+	struct dentry **p;
+
+	p = dpage->dentries;
+	for (i = 0; i < dpage->ndentry; i++)
+		dput(*p++);
+	free_page((unsigned long)dpage->dentries);
+}
+
+int au_dpages_init(struct au_dcsub_pages *dpages, gfp_t gfp)
+{
+	int err;
+	void *p;
+
+	err = -ENOMEM;
+	dpages->dpages = kmalloc(sizeof(*dpages->dpages), gfp);
+	if (unlikely(!dpages->dpages))
+		goto out;
+
+	p = (void *)__get_free_page(gfp);
+	if (unlikely(!p))
+		goto out_dpages;
+
+	dpages->dpages[0].ndentry = 0;
+	dpages->dpages[0].dentries = p;
+	dpages->ndpage = 1;
+	return 0; /* success */
+
+out_dpages:
+	kfree(dpages->dpages);
+out:
+	return err;
+}
+
+void au_dpages_free(struct au_dcsub_pages *dpages)
+{
+	int i;
+	struct au_dpage *p;
+
+	p = dpages->dpages;
+	for (i = 0; i < dpages->ndpage; i++)
+		au_dpage_free(p++);
+	kfree(dpages->dpages);
+}
+
+static int au_dpages_append(struct au_dcsub_pages *dpages,
+			    struct dentry *dentry, gfp_t gfp)
+{
+	int err, sz;
+	struct au_dpage *dpage;
+	void *p;
+
+	dpage = dpages->dpages + dpages->ndpage - 1;
+	sz = PAGE_SIZE / sizeof(dentry);
+	if (unlikely(dpage->ndentry >= sz)) {
+		AuLabel(new dpage);
+		err = -ENOMEM;
+		sz = dpages->ndpage * sizeof(*dpages->dpages);
+		p = au_kzrealloc(dpages->dpages, sz,
+				 sz + sizeof(*dpages->dpages), gfp);
+		if (unlikely(!p))
+			goto out;
+
+		dpages->dpages = p;
+		dpage = dpages->dpages + dpages->ndpage;
+		p = (void *)__get_free_page(gfp);
+		if (unlikely(!p))
+			goto out;
+
+		dpage->ndentry = 0;
+		dpage->dentries = p;
+		dpages->ndpage++;
+	}
+
+	AuDebugOn(au_dcount(dentry) <= 0);
+	dpage->dentries[dpage->ndentry++] = dget_dlock(dentry);
+	return 0; /* success */
+
+out:
+	return err;
+}
+
+/* todo: BAD approach */
+/* copied from linux/fs/dcache.c */
+enum d_walk_ret {
+	D_WALK_CONTINUE,
+	D_WALK_QUIT,
+	D_WALK_NORETRY,
+	D_WALK_SKIP,
+};
+
+extern void d_walk(struct dentry *parent, void *data,
+		   enum d_walk_ret (*enter)(void *, struct dentry *),
+		   void (*finish)(void *));
+
+struct ac_dpages_arg {
+	int err;
+	struct au_dcsub_pages *dpages;
+	struct super_block *sb;
+	au_dpages_test test;
+	void *arg;
+};
+
+static enum d_walk_ret au_call_dpages_append(void *_arg, struct dentry *dentry)
+{
+	enum d_walk_ret ret;
+	struct ac_dpages_arg *arg = _arg;
+
+	ret = D_WALK_CONTINUE;
+	if (dentry->d_sb == arg->sb
+	    && !IS_ROOT(dentry)
+	    && au_dcount(dentry) > 0
+	    && au_di(dentry)
+	    && (!arg->test || arg->test(dentry, arg->arg))) {
+		arg->err = au_dpages_append(arg->dpages, dentry, GFP_ATOMIC);
+		if (unlikely(arg->err))
+			ret = D_WALK_QUIT;
+	}
+
+	return ret;
+}
+
+int au_dcsub_pages(struct au_dcsub_pages *dpages, struct dentry *root,
+		   au_dpages_test test, void *arg)
+{
+	struct ac_dpages_arg args = {
+		.err	= 0,
+		.dpages	= dpages,
+		.sb	= root->d_sb,
+		.test	= test,
+		.arg	= arg
+	};
+
+	d_walk(root, &args, au_call_dpages_append, NULL);
+
+	return args.err;
+}
+
+int au_dcsub_pages_rev(struct au_dcsub_pages *dpages, struct dentry *dentry,
+		       int do_include, au_dpages_test test, void *arg)
+{
+	int err;
+
+	err = 0;
+	write_seqlock(&rename_lock);
+	spin_lock(&dentry->d_lock);
+	if (do_include
+	    && au_dcount(dentry) > 0
+	    && (!test || test(dentry, arg)))
+		err = au_dpages_append(dpages, dentry, GFP_ATOMIC);
+	spin_unlock(&dentry->d_lock);
+	if (unlikely(err))
+		goto out;
+
+	/*
+	 * RCU for vfsmount is unnecessary since this is a traverse in a single
+	 * mount
+	 */
+	while (!IS_ROOT(dentry)) {
+		dentry = dentry->d_parent; /* rename_lock is locked */
+		spin_lock(&dentry->d_lock);
+		if (au_dcount(dentry) > 0
+		    && (!test || test(dentry, arg)))
+			err = au_dpages_append(dpages, dentry, GFP_ATOMIC);
+		spin_unlock(&dentry->d_lock);
+		if (unlikely(err))
+			break;
+	}
+
+out:
+	write_sequnlock(&rename_lock);
+	return err;
+}
+
+static inline int au_dcsub_dpages_aufs(struct dentry *dentry, void *arg)
+{
+	return au_di(dentry) && dentry->d_sb == arg;
+}
+
+int au_dcsub_pages_rev_aufs(struct au_dcsub_pages *dpages,
+			    struct dentry *dentry, int do_include)
+{
+	return au_dcsub_pages_rev(dpages, dentry, do_include,
+				  au_dcsub_dpages_aufs, dentry->d_sb);
+}
+
+int au_test_subdir(struct dentry *d1, struct dentry *d2)
+{
+	struct path path[2] = {
+		{
+			.dentry = d1
+		},
+		{
+			.dentry = d2
+		}
+	};
+
+	return path_is_under(path + 0, path + 1);
+}

fs/aufs/dcsub.h

+/*
+ * Copyright (C) 2005-2015 Junjiro R. Okajima
+ *
+ * This program, aufs is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * sub-routines for dentry cache
+ */
+
+#ifndef __AUFS_DCSUB_H__
+#define __AUFS_DCSUB_H__
+
+#ifdef __KERNEL__
+
+#include <linux/dcache.h>
+#include <linux/fs.h>
+
+struct au_dpage {
+	int ndentry;
+	struct dentry **dentries;
+};
+
+struct au_dcsub_pages {
+	int ndpage;
+	struct au_dpage *dpages;
+};
+
+/* ---------------------------------------------------------------------- */
+
+/* dcsub.c */
+int au_dpages_init(struct au_dcsub_pages *dpages, gfp_t gfp);
+void au_dpages_free(struct au_dcsub_pages *dpages);
+typedef int (*au_dpages_test)(struct dentry *dentry, void *arg);
+int au_dcsub_pages(struct au_dcsub_pages *dpages, struct dentry *root,
+		   au_dpages_test test, void *arg);
+int au_dcsub_pages_rev(struct au_dcsub_pages *dpages, struct dentry *dentry,
+		       int do_include, au_dpages_test test, void *arg);
+int au_dcsub_pages_rev_aufs(struct au_dcsub_pages *dpages,
+			    struct dentry *dentry, int do_include);
+int au_test_subdir(struct dentry *d1, struct dentry *d2);
+
+/* ---------------------------------------------------------------------- */
+
+/*
+ * todo: in linux-3.13, several similar (but faster) helpers are added to
+ * include/linux/dcache.h. Try them (in the future).
+ */
+
+static inline int au_d_hashed_positive(struct dentry *d)
+{
+	int err;
+	struct inode *inode = d_inode(d);
+
+	err = 0;
+	if (unlikely(d_unhashed(d)
+		     || d_is_negative(d)
+		     || !inode->i_nlink))
+		err = -ENOENT;
+	return err;
+}
+
+static inline int au_d_linkable(struct dentry *d)
+{
+	int err;
+	struct inode *inode = d_inode(d);
+
+	err = au_d_hashed_positive(d);
+	if (err
+	    && d_is_positive(d)
+	    && (inode->i_state & I_LINKABLE))
+		err = 0;
+	return err;
+}
+
+static inline int au_d_alive(struct dentry *d)
+{
+	int err;
+	struct inode *inode;
+
+	err = 0;
+	if (!IS_ROOT(d))
+		err = au_d_hashed_positive(d);
+	else {
+		inode = d_inode(d);
+		if (unlikely(d_unlinked(d)
+			     || d_is_negative(d)
+			     || !inode->i_nlink))
+			err = -ENOENT;
+	}
+	return err;
+}
+
+static inline int au_alive_dir(struct dentry *d)
+{
+	int err;
+
+	err = au_d_alive(d);
+	if (unlikely(err || IS_DEADDIR(d_inode(d))))
+		err = -ENOENT;
+	return err;
+}
+
+static inline int au_qstreq(struct qstr *a, struct qstr *b)
+{
+	return a->len == b->len
+		&& !memcmp(a->name, b->name, a->len);
+}
+
+/*
+ * by the commit
+ * 360f547 2015-01-25 dcache: let the dentry count go down to zero without
+ *			taking d_lock
+ * the type of d_lockref.count became int, but the inlined function d_count()
+ * still returns unsigned int.
+ * I don't know why. Maybe it is for every d_count() users?
+ * Anyway au_dcount() lives on.
+ */
+static inline int au_dcount(struct dentry *d)
+{
+	return (int)d_count(d);
+}
+
+#endif /* __KERNEL__ */
+#endif /* __AUFS_DCSUB_H__ */

fs/aufs/dir.h

+/*
+ * Copyright (C) 2005-2015 Junjiro R. Okajima
+ *
+ * This program, aufs is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * directory operations
+ */
+
+#ifndef __AUFS_DIR_H__
+#define __AUFS_DIR_H__
+
+#ifdef __KERNEL__
+
+#include <linux/fs.h>
+
+/* ---------------------------------------------------------------------- */
+
+/* need to be faster and smaller */
+
+struct au_nhash {
+	unsigned int		nh_num;
+	struct hlist_head	*nh_head;
+};
+
+struct au_vdir_destr {
+	unsigned char	len;
+	unsigned char	name[0];
+} __packed;
+
+struct au_vdir_dehstr {
+	struct hlist_node	hash;
+	struct au_vdir_destr	*str;
+} ____cacheline_aligned_in_smp;
+
+struct au_vdir_de {
+	ino_t			de_ino;
+	unsigned char		de_type;
+	/* caution: packed */
+	struct au_vdir_destr	de_str;
+} __packed;
+
+struct au_vdir_wh {
+	struct hlist_node	wh_hash;
+#ifdef CONFIG_AUFS_SHWH
+	ino_t			wh_ino;
+	aufs_bindex_t		wh_bindex;
+	unsigned char		wh_type;
+#else
+	aufs_bindex_t		wh_bindex;
+#endif
+	/* caution: packed */
+	struct au_vdir_destr	wh_str;
+} __packed;
+
+union au_vdir_deblk_p {
+	unsigned char		*deblk;
+	struct au_vdir_de	*de;
+};
+
+struct au_vdir {
+	unsigned char	**vd_deblk;
+	unsigned long	vd_nblk;
+	struct {
+		unsigned long		ul;
+		union au_vdir_deblk_p	p;
+	} vd_last;
+
+	unsigned long	vd_version;
+	unsigned int	vd_deblk_sz;
+	unsigned long	vd_jiffy;
+} ____cacheline_aligned_in_smp;
+
+/* ---------------------------------------------------------------------- */
+
+/* dir.c */
+extern const struct file_operations aufs_dir_fop;
+void au_add_nlink(struct inode *dir, struct inode *h_dir);
+void au_sub_nlink(struct inode *dir, struct inode *h_dir);
+loff_t au_dir_size(struct file *file, struct dentry *dentry);
+void au_dir_ts(struct inode *dir, aufs_bindex_t bsrc);
+int au_test_empty_lower(struct dentry *dentry);
+int au_test_empty(struct dentry *dentry, struct au_nhash *whlist);
+
+/* vdir.c */
+unsigned int au_rdhash_est(loff_t sz);
+int au_nhash_alloc(struct au_nhash *nhash, unsigned int num_hash, gfp_t gfp);
+void au_nhash_wh_free(struct au_nhash *whlist);
+int au_nhash_test_longer_wh(struct au_nhash *whlist, aufs_bindex_t btgt,
+			    int limit);
+int au_nhash_test_known_wh(struct au_nhash *whlist, char *name, int nlen);
+int au_nhash_append_wh(struct au_nhash *whlist, char *name, int nlen, ino_t ino,
+		       unsigned int d_type, aufs_bindex_t bindex,
+		       unsigned char shwh);
+void au_vdir_free(struct au_vdir *vdir);
+int au_vdir_init(struct file *file);
+int au_vdir_fill_de(struct file *file, struct dir_context *ctx);
+
+/* ioctl.c */
+long aufs_ioctl_dir(struct file *file, unsigned int cmd, unsigned long arg);
+
+#ifdef CONFIG_AUFS_RDU
+/* rdu.c */
+long au_rdu_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
+#ifdef CONFIG_COMPAT
+long au_rdu_compat_ioctl(struct file *file, unsigned int cmd,
+			 unsigned long arg);
+#endif
+#else
+AuStub(long, au_rdu_ioctl, return -EINVAL, struct file *file,
+       unsigned int cmd, unsigned long arg)
+#ifdef CONFIG_COMPAT
+AuStub(long, au_rdu_compat_ioctl, return -EINVAL, struct file *file,
+       unsigned int cmd, unsigned long arg)
+#endif
+#endif
+
+#endif /* __KERNEL__ */
+#endif /* __AUFS_DIR_H__ */

fs/aufs/magic.mk

+
+# defined in ${srctree}/fs/fuse/inode.c
+# tristate
+ifdef CONFIG_FUSE_FS
+ccflags-y += -DFUSE_SUPER_MAGIC=0x65735546
+endif
+
+# defined in ${srctree}/fs/xfs/xfs_sb.h
+# tristate
+ifdef CONFIG_XFS_FS
+ccflags-y += -DXFS_SB_MAGIC=0x58465342
+endif
+
+# defined in ${srctree}/fs/configfs/mount.c
+# tristate
+ifdef CONFIG_CONFIGFS_FS
+ccflags-y += -DCONFIGFS_MAGIC=0x62656570
+endif
+
+# defined in ${srctree}/fs/ubifs/ubifs.h
+# tristate
+ifdef CONFIG_UBIFS_FS
+ccflags-y += -DUBIFS_SUPER_MAGIC=0x24051905
+endif
+
+# defined in ${srctree}/fs/hfsplus/hfsplus_raw.h
+# tristate
+ifdef CONFIG_HFSPLUS_FS
+ccflags-y += -DHFSPLUS_SUPER_MAGIC=0x482b
+endif