tmpfiles: add --cat-config

This implements similar logic as conf_files_cat(), but with slightly different
file gathering logic. I also want to add support for replacement files later on,
so it seems better to keep those two file-gathering functions separate.

src/basic/conf-files.c

@@ -259,6 +259,41 @@ int conf_files_list_nulstr(char ***strv, const char *suffix, const char *root, u
         return conf_files_list_strv_internal(strv, suffix, root, flags, d);
 }
 
+int conf_files_list_with_replacement(
+                const char *root,
+                char **config_dirs,
+                const char *replacement,
+                char ***files,
+                char **replace_file) {
+
+        _cleanup_strv_free_ char **f = NULL;
+        _cleanup_free_ char *p = NULL;
+        int r;
+
+        assert(config_dirs);
+        assert(files);
+        assert(replace_file || !replacement);
+
+        r = conf_files_list_strv(&f, ".conf", root, 0, (const char* const*) config_dirs);
+        if (r < 0)
+                return log_error_errno(r, "Failed to enumerate config files: %m");
+
+        if (replacement) {
+                r = conf_files_insert(&f, root, config_dirs, replacement);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to extend config file list: %m");
+
+                p = path_join(root, replacement, NULL);
+                if (!p)
+                        return log_oom();
+        }
+
+        *files = TAKE_PTR(f);
+        if (replace_file)
+                *replace_file = TAKE_PTR(p);
+        return 0;
+}
+
 int conf_files_cat(const char *name) {
         _cleanup_strv_free_ char **dirs = NULL, **files = NULL;
         const char *dir;

src/basic/conf-files.h

@@ -17,4 +17,10 @@ int conf_files_list_strv(char ***ret, const char *suffix, const char *root, unsi
 int conf_files_list_nulstr(char ***ret, const char *suffix, const char *root, unsigned flags, const char *dirs);
 int conf_files_insert(char ***strv, const char *root, char **dirs, const char *path);
 int conf_files_insert_nulstr(char ***strv, const char *root, const char *dirs, const char *path);
+int conf_files_list_with_replacement(
+                const char *root,
+                char **config_dirs,
+                const char *replacement,
+                char ***files,
+                char **replace_file);
 int conf_files_cat(const char *name);