We construct a ramfs tree of "scaffolding" directories for all mount points, so
that a directory exists that each mount point can be mounted over.
We were creating these directories without write permissions, which meant that
they were not wribable even when underlayed under a writable filesystem. They
should be writable.
PiperOrigin-RevId: 242507789
Change-Id: I86645e35417560d862442ff5962da211dbe9b731
More helper structs have been added to the fsutil package to make it easier to
implement fs.InodeOperations and fs.FileOperations.
PiperOrigin-RevId: 229305982
Change-Id: Ib6f8d3862f4216745116857913dbfa351530223b