librc: add build option to set default RC_PATH

distros, namely debian, want to keep sysvinit scripts for compatibility,
while moving to openrc native scripts slowly

having /etc/init.d in the search path before /usr/libexec/rc/init.d
makes that transition almost impossible

the recommendation for most distros is to leave the path untouched or as
close to the default as possible

Author: navi-desu

meson_options.txt

@@ -27,3 +27,11 @@ option('uucp_group', type : 'string', value : 'uucp',
 option('agetty', type: 'array',
   value: ['tty1', 'tty2', 'tty3', 'tty4', 'tty5', 'tty6'],
   description : 'agetty symlinks to install when sysvinit is also specified')
+option('rc_path', type: 'array',
+  description : '''compile-time default RC_PATH, if unset, defaults to:
+    $sysconfdir/rc, $sysconfdir, $local_prefix/etc/rc, $local_prefix, $libexecdir/rc
+
+    consider using the runtime environment variable RC_PATH over setting this, though
+    if setting a custom compile-time time is strictly necessary, it is recommended to
+    set it as close to the default as possible
+  ''')

src/librc/librc.c

@@ -555,21 +555,7 @@ rc_runlevel_stacks(const char *runlevel)
 	return stack;
 }
 
-static const char *config_path[] = {
-	RC_SYSCONFDIR "/rc",
-	RC_SYSCONFDIR,
-#ifdef RC_LOCAL_PREFIX
-	RC_LOCAL_PREFIX "/etc/rc",
-	RC_LOCAL_PREFIX "/etc",
-#endif
-#ifdef RC_PKG_PREFIX
-	RC_PKG_PREFIX "/etc/rc",
-	RC_PKG_PREFIX "/etc",
-#endif
-	RC_LIBEXECDIR,
-	RC_SVCDIR,
-	NULL,
-};
+static const char *config_path[] = { _RC_PATH, NULL };
 
 static struct {
 	bool set;

src/librc/meson.build

@@ -12,13 +12,27 @@ librc_sources = [
   'librc-stringlist.c',
 ]
 
+sysconfdir = get_option('sysconfdir')
+rc_path = get_option('rc_path')
+if rc_path.length() == 0
+  rc_path = [
+    sysconfdir / 'rc',
+    sysconfdir,
+    local_prefix / 'rc',
+    local_prefix,
+    rc_libexecdir,
+  ]
+endif
+rc_path += '/run/openrc'
+
 rc_h = configure_file(input : 'rc.h.in', output : 'rc.h',
   configuration : rc_h_conf_data)
 
 rc = declare_dependency(
   include_directories: '.',
   sources: rc_h,
   link_with: library('rc', librc_sources,
+    c_args: [ '-D_RC_PATH="@0@"'.format('","'.join(rc_path)) ],
     dependencies: kvm_dep,
     include_directories : incdir,
     link_depends : 'rc.map',