tree-wide: make specifier expansion --root= aware

This fixes repart's, systemctl's, sysusers' and tmpfiles' specifier
expansion to honour the root dir specified with --root=. This is
relevant for specifiers such as %m, %o, … which are directly sourced
from files on disk.

This doesn't try to be overly smart: specifiers referring to runtime
concepts (i.e. boot ID, architecture, hostname) rather than files on the
medium are left as is. There's certainly a point to be made that they
should fail in case --root= is specified, but I am not entirely convinced
about that, and it's certainly something we can look into later if
there's reason to.

I wondered for a while how to hook this up best, but given that quite a
large number of specifiers resolve to data from files on disks, and most
of our tools needs this, I ultimately decided to make the root dir a
first class parameter to specifier_printf().

Replaces: #16187
Fixes: #16183

1 files changed, 1 insertions, 0 deletions

diff --git a/src/shared/install.h b/src/shared/install.h
index c3a0249f5f..cdc5435035 100644
--- a/src/shared/install.h
+++ b/src/shared/install.h
@@ -79,6 +79,7 @@ enum UnitFileType {
 struct UnitFileInstallInfo {
         char *name;
         char *path;
+        char *root;
 
         char **aliases;
         char **wanted_by;