Using symlinks for bind mounts means we are not protecting an RO-mounted
layer against modification. Windows doesn't currently appear to offer a
better approach though, as we cannot create arbitrary empty WCOW scratch
layers at this time.
For windows-layer mounts, Unmount does not have access to the mounts
used to create it. So we store the relevant data in an Alternate Data
Stream on the mountpoint in order to be able to Unmount later.
Based on approach in https://github.com/containerd/containerd/pull/2366,
with sign-offs recorded as 'Based-on-work-by' trailers below.
This also partially-reverts some changes made in #6034 as they are not
needed with this mounting implmentation, which no longer needs to be
handled specially by the caller compared to non-Windows mounts.
Signed-off-by: Paul "TBBle" Hampson <Paul.Hampson@Pobox.com>
Based-on-work-by: Michael Crosby <crosbymichael@gmail.com>
Based-on-work-by: Darren Stahl <darst@microsoft.com>
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