Since switching to extract_first_word with no flags for parsing
unit names in 4c9565eea5, escape
characters will be stripped from escaped unit names such as
"mnt-persistent\x2dvolume.mount" resulting in the unit not being
configured as defined. Preserve escape characters again for
compatibility with existing preset definitions.
This informs chase_symlinks that symlinks should be treated as if
the path given by --root= is the root of their file system.
With the parent commit, this allows tmpfiles to create files as the
root user under a prefix that may be owned by an unprivileged user.
In particular, this fixes the case where tmpfiles generates initial
files in a staging root directory for packaging under a directory
owned by the unprivileged packager user (e.g. in Gentoo).
When chase_symlinks is given a root path, it is assumed that all
processed symlinks are restricted under that path. It should not
be necessary to verify components of that prefix path since they
are not relevant to the symlinks.
This change skips unsafe UID transitions in this root prefix, i.e.
it now ignores when an unprivileged user's directory contains a
root-owned directory above the symlink root.
David Michael