[PATCH v2 5/5] ovl: Add documentation on nesting of overlayfs mounts

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Signed-off-by: Alexander Larsson <alexl@xxxxxxxxxx>
---
 Documentation/filesystems/overlayfs.rst | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst
index 35853906accb..e38b2f5fadaf 100644
--- a/Documentation/filesystems/overlayfs.rst
+++ b/Documentation/filesystems/overlayfs.rst
@@ -492,6 +492,28 @@ directory tree on the same or different underlying filesystem, and even
 to a different machine.  With the "inodes index" feature, trying to mount
 the copied layers will fail the verification of the lower root file handle.
 
+Nesting overlayfs mounts
+------------------------
+
+It is possible to use a lower directory that is stored on an overlayfs
+mount. For regular files this does not need any special care. However, files
+that have overlayfs attributes, such as whiteouts or `overlay.*` xattrs will
+be interpreted by the underlying overlayfs mount and stripped out. In order to
+allow the second overlayfs mount to see the attributes they must be escaped.
+
+Overlayfs specific xattrs are escaped by using a special prefix of
+`overlay.overlay.`. So, a file with a `trusted.overlay.overlay.metacopy` xattr
+in the lower dir will be exposed as a regular file with a
+`trusted.overlay.metacopy` xattr in the overlayfs mount. This can be nested
+by repeating the prefix multiple time, as each instance only removes one
+prefix.
+
+Whiteouts files marked with a `overlay.nowhiteout` xattr will cause overlayfs
+not to treat them as a whiteout. Since this xattr is then stripped out, the
+next layer will instead apply the whiteout.
+
+Files created via overlayfs will automatically be created with the right
+escapes in the upper directory.
 
 Non-standard behavior
 ---------------------
-- 
2.41.0




[Index of Archives]     [Linux Filesystems Devel]     [Linux NFS]     [Linux NILFS]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux