UBUNTU: SAUCE: Import aufs driver

Import aufs5.10 20210111 from https://github.com/sfjro/aufs5-standalone
commit e52be5a0f1290b2d113f8bb82f33527ffab8b790.

Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

Documentation/ABI/testing/debugfs-aufs

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+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>/xi0, xi1 ... xiN and xiN-N
+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.
+		Due to the file size limit, there may exist multiple
+		xino files per branch.  In this case, "-N" is added to
+		the filename and it corresponds to the index of the
+		internal xino array.  "-0" is omitted.
+		When the aufs mount option 'noxino' is specified, Those
+		entries won't exist.  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

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+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.