NAME
mount_overlay —
mount an overlay
filesystem; demonstrate the use of an overlay file system layer
SYNOPSIS
mount_overlay |
[-o
options] /overlay
mount-point |
DESCRIPTION
The
mount_overlay command creates an overlay layer,
interposing the overlay filesystem between the over-mounted file store and
future pathname lookups.
A different device number for the virtual copy is returned by
stat(2), but in other respects it
is indistinguishable from the original.
The
mount_overlay filesystem differs from the null filesystem
in that the
mount_overlay filesystem does not replicate the
sub-tree, it places itself between the sub-tree and all future access.
The overlay layer has two purposes. First, it serves as a demonstration of
layering by providing a layer which does nothing other than insert itself over
the over-mounted file system. Second, the overlay layer can serve as a
prototype layer. Since it provides all necessary layer framework, new file
system layers which need to block access to the overlayed file system can be
created very easily by starting with an overlay layer.
The internal operation of the overlay layer is identical to that of the null
layer. See its documentation for details.
SEE ALSO
mount(8),
mount_null(8)
UCLA Technical Report CSD-910056,
Stackable Layers: an
Architecture for File System Development.
HISTORY
The
mount_overlay utility first appeared in
NetBSD 1.5.