diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst index a3e588dc8437ff3a0ff2c3ca567f51b44f89b3d4..1ef4ef38b542a8250da95838610ae4973851c5fd 100644 --- a/Documentation/filesystems/overlayfs.rst +++ b/Documentation/filesystems/overlayfs.rst @@ -97,11 +97,13 @@ directory trees to be in the same filesystem and there is no requirement that the root of a filesystem be given for either upper or lower. -The lower filesystem can be any filesystem supported by Linux and does -not need to be writable. The lower filesystem can even be another -overlayfs. The upper filesystem will normally be writable and if it -is it must support the creation of trusted.* extended attributes, and -must provide valid d_type in readdir responses, so NFS is not suitable. +A wide range of filesystems supported by Linux can be the lower filesystem, +but not all filesystems that are mountable by Linux have the features +needed for OverlayFS to work. The lower filesystem does not need to be +writable. The lower filesystem can even be another overlayfs. The upper +filesystem will normally be writable and if it is it must support the +creation of trusted.* extended attributes, and must provide valid d_type in +readdir responses, so NFS is not suitable. A read-only overlay of two read-only filesystems may use any filesystem type.