binfmt,tmpfiles,modules-load,sysctl: rework the various early-boot services that work on .d/ directories

This unifies much of the logic behind them:

- All four will now ofllow the rule that the earlier file and earlier
  assignment in the .d/ directories wins. Before, sysctl was the only
  outlier, where the later setting always won.

- All four now support getopt() and --help on the command line.

- All four can now handle specification of configuration file names on
  the command line to apply. The tools will automatically find them, and
  apply them. Previously only tmpfiles could do that. This is useful for
  %post scripts in RPMs and suchlike.

- This fixes various error path issues in conf_files_list()

src/tmpfiles/tmpfiles.c

@@ -106,16 +106,15 @@ static bool arg_remove = false;
 
 static const char *arg_prefix = NULL;
 
-static const char * const conf_file_dirs[] = {
-        "/etc/tmpfiles.d",
-        "/run/tmpfiles.d",
-        "/usr/local/lib/tmpfiles.d",
-        "/usr/lib/tmpfiles.d",
+static const char conf_file_dirs[] =
+        "/etc/tmpfiles.d\0"
+        "/run/tmpfiles.d\0"
+        "/usr/local/lib/tmpfiles.d\0"
+        "/usr/lib/tmpfiles.d\0"
 #ifdef HAVE_SPLIT_USR
-        "/lib/tmpfiles.d",
+        "/lib/tmpfiles.d\0"
 #endif
-        NULL
-};
+        ;
 
 #define MAX_DEPTH 256
 
@@ -1289,20 +1288,19 @@ static int parse_argv(int argc, char *argv[]) {
 static int read_config_file(const char *fn, bool ignore_enoent) {
         FILE *f;
         unsigned v = 0;
-        int r = 0;
+        int r;
         Iterator iterator;
         Item *i;
 
         assert(fn);
 
-        f = fopen(fn, "re");
-        if (!f) {
-
-                if (ignore_enoent && errno == ENOENT)
+        r = search_and_fopen_nulstr(fn, "re", conf_file_dirs, &f);
+        if (r < 0) {
+                if (ignore_enoent && r == -ENOENT)
                         return 0;
 
-                log_error("Failed to open %s: %m", fn);
-                return -errno;
+                log_error("Failed to open '%s', ignoring: %s", fn, strerror(-r));
+                return r;
         }
 
         log_debug("apply: %s\n", fn);
@@ -1363,32 +1361,8 @@ static int read_config_file(const char *fn, bool ignore_enoent) {
         return r;
 }
 
-static char *resolve_fragment(const char *fragment, const char **search_paths) {
-        const char **p;
-        char *resolved_path;
-
-        if (is_path(fragment))
-                return strdup(fragment);
-
-        STRV_FOREACH(p, search_paths) {
-                resolved_path = strjoin(*p, "/", fragment, NULL);
-                if (resolved_path == NULL) {
-                        log_oom();
-                        return NULL;
-                }
-
-                if (access(resolved_path, F_OK) == 0)
-                        return resolved_path;
-
-                free(resolved_path);
-        }
-
-        errno = ENOENT;
-        return NULL;
-}
-
 int main(int argc, char *argv[]) {
-        int r;
+        int r, k;
         Item *i;
         Iterator iterator;
 
@@ -1408,46 +1382,36 @@ int main(int argc, char *argv[]) {
         globs = hashmap_new(string_hash_func, string_compare_func);
 
         if (!items || !globs) {
-                log_oom();
-                r = EXIT_FAILURE;
+                r = log_oom();
                 goto finish;
         }
 
-        r = EXIT_SUCCESS;
+        r = 0;
 
         if (optind < argc) {
                 int j;
 
                 for (j = optind; j < argc; j++) {
-                        char *fragment;
-
-                        fragment = resolve_fragment(argv[j], (const char **)conf_file_dirs);
-                        if (!fragment) {
-                                log_error("Failed to find a %s file: %m", argv[j]);
-                                r = EXIT_FAILURE;
-                                goto finish;
-                        }
-                        if (read_config_file(fragment, false) < 0)
-                                r = EXIT_FAILURE;
-                        free(fragment);
+                        k = read_config_file(argv[j], false);
+                        if (k < 0 && r == 0)
+                                r = k;
                 }
 
         } else {
-                char **files, **f;
+                _cleanup_strv_free_ char **files = NULL;
+                char **f;
 
-                r = conf_files_list_strv(&files, ".conf", NULL, (const char **)conf_file_dirs);
+                r = conf_files_list_nulstr(&files, ".conf", NULL, conf_file_dirs);
                 if (r < 0) {
                         log_error("Failed to enumerate tmpfiles.d files: %s", strerror(-r));
-                        r = EXIT_FAILURE;
                         goto finish;
                 }
 
                 STRV_FOREACH(f, files) {
-                        if (read_config_file(*f, true) < 0)
-                                r = EXIT_FAILURE;
+                        k = read_config_file(*f, true);
+                        if (k < 0 && r == 0)
+                                r = k;
                 }
-
-                strv_free(files);
         }
 
         HASHMAP_FOREACH(i, globs, iterator)
@@ -1470,5 +1434,5 @@ finish:
 
         label_finish();
 
-        return r;
+        return r < 0 ? EXIT_FAILURE : EXIT_SUCCESS;
 }