The implementations are 90% copy&paste from the go standard library as
the existing code does not offer any way to read the symlink target
based on a filehandle.
Fall back to a standard readlink on platforms other than Linux and
Windows as those either don't even provide the necessary syscall or in
case of macOS are not yet available in Go.
Only the `Sys()` value from os.FileInfo is kept as field `sys` to
support Windows. The os.FileInfo removal ensures that for values like
`ModTime` that existed in both data structures there's no more confusion
which value is actually used.
Depending on the change packages, the VSS tests from ./cmd/restic and
the fs package may overlap in time. This causes the snapshot creation to
fail. Add retries in that case.
The actual implementation still relies on file paths, but with the
abstraction layer in place, an FS implementation can ensure atomic file
accesses in the future.
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.
