Extended attributes and security descriptors apparently cannot be
retrieved from a vss volume. Fix the volume check to correctly detect
vss volumes and just completely disable extended attributes for volumes.
Paths that only contain the volume shadow copy snapshot name require
special treatment. These paths must end with a slash for regular file
operations to work.
Previously, nodeRestoreTimestamps would do something like
if node.Type == restic.NodeTypeSymlink {
return nodeRestoreSymlinkTimestamps(...)
}
return syscall.UtimesNano(...)
where nodeRestoreSymlinkTimestamps was either a no-op or a
reimplementation of syscall.UtimesNano that handles symlinks, with some
repeated converting between timestamp types. The Linux implementation
was a bit clumsy, requiring three syscalls to set the timestamps.
In this new setup, there is a function utimesNano that has three
implementations:
* on Linux, it's a modified syscall.UtimesNano that uses
AT_SYMLINK_NOFOLLOW and AT_FDCWD so it can handle any type in a single
call;
* on other Unix platforms, it just calls the syscall function after
skipping symlinks;
* on Windows, it's the modified UtimesNano that was previously called
nodeRestoreSymlinkTimestamps, except with different arguments.
Previously, NodeFromFileInfo used the original file path to create the
node, which also meant that extended metadata was read from there
instead of within the vss snapshot.
This does not produce exactly the same messages, as it inserts newlines
instead of "; ". But given how long our error messages can be, that
might be a good thing.
Depending on parameters the paths in a snapshot do not directly
correspond to real paths on the filesystem. Therefore, reject funcs must
use the FS interface to work correctly.
The temp files used by the packer manager are either delete after
creation (unix) or marked as delete on close (windows). Thus, no
explicit cleanup is necessary.
The retry code path did not filter `ERROR_NOT_SUPPORTED`. Just call the
original function a second time to correctly follow the low privilege
code path.
Calling `Load()` twice for an atomic variable can return different
values each time. This resulted in trying to read the security
descriptor with high privileges, but then not entering the code path to
switch to low privileges when another thread has already done so
concurrently.
