Overlay filesystem support

modulename: overlay.ko


Linux Kernel Configuration
└─>File systems
└─>Overlay filesystem support
In linux kernel since version 3.10 (release Date: 2013-06-30)  
An overlay filesystem combines two filesystems - an 'upper' filesystem
and a 'lower' filesystem. When a name exists in both filesystems, the
object in the 'upper' filesystem is visible while the object in the
'lower' filesystem is either hidden or, in the case of directories,
merged with the 'upper' object.

For more information see Documentation/filesystems/overlayfs.rst

source code: