The WCOW layer support does not support creating sandboxes with no
parent. Instead, parentless scratch layers must be layed out as a
directory containing only a directory named 'Files', and all data stored
inside 'Files'. At commit-time, this will be converted in-place into a
read-only layer suitable for use as a parent layer.
The WCOW layer support also does not deal with making read-only layers,
i.e. layers that are prepared to be parent layers, visible in a
read-only manner. A bind-mount or junction point cannot be made
read-only, so a view must instead be a small sandbox layer that we can
mount via WCOW, and discard later, to protect the layer against
accidental or deliberate modification.
Signed-off-by: Paul "TBBle" Hampson <Paul.Hampson@Pobox.com>
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