tmpfiles: add support for config files on command line

Allow specifying one or more configuration files as command line
arguments instead of always processing all files in the standard
tmpfiles.d directories.

This enables targeted operations on specific config files:

    tmpfiles --create /etc/tmpfiles.d/myapp.conf
    tmpfiles --clean /tmp/test.conf /tmp/other.conf

When no config files are specified, the existing behavior of
processing all *.conf files in the standard directories is preserved.

Also refactors file processing into a helper function to reduce
code duplication.

src/tmpfiles.c

@@ -635,17 +635,44 @@ static void tmpfiles(char *line)
 		warn("Failed %s operation on path %s", type, path);
 }
 
+static void process_file(const char *fn)
+{
+	FILE *fp;
+
+	fp = fopen(fn, "r");
+	if (!fp) {
+		warn("Failed to open %s", fn);
+		return;
+	}
+
+	while (!feof(fp)) {
+		char *line;
+
+		line = fparseln(fp, NULL, NULL, NULL, FPARSELN_UNESCCOMM);
+		if (!line)
+			continue;
+
+		tmpfiles(line);
+		free(line);
+	}
+
+	fclose(fp);
+}
+
 static int usage(int rc)
 {
 	fprintf(stderr,
-		"Usage: tmpfiles [COMMAND...]\n"
+		"Usage: tmpfiles [OPTIONS] [CONFIGFILE...]\n"
 		"\n"
-		"Commands:\n"
+		"Options:\n"
 		"  -C, --clean               Clean files and directories based on age\n"
 		"  -c, --create              Create files and directories\n"
 		"  -d, --debug               Show developer debug messages\n"
 		"  -r, --remove              Remove files and directories marked for removal\n"
 		"  -h, --help                This help text\n"
+		"\n"
+		"If no CONFIGFILE is specified, all *.conf files in the standard\n"
+		"tmpfiles.d directories are processed.\n"
 		"\n");
 
 	return rc;
@@ -696,7 +723,16 @@ int main(int argc, char *argv[])
 		return 1;
 	}
 
+	/* If config files specified on command line, process only those */
+	if (optind < argc) {
+		for (int i = optind; i < argc; i++)
+			process_file(argv[i]);
+		return 0;
+	}
+
 	/*
+	 * No config files specified, process standard tmpfiles.d directories.
+	 *
 	 * Only the three last tmpfiles.d/ directories are defined in
 	 * tmpfiles.d(5) as system search paths.  Finit adds two more
 	 * before that to have Finit specific ones sorted first, and
@@ -723,7 +759,6 @@ int main(int argc, char *argv[])
 	for (i = 0; i < gl.gl_pathc; i++) {
 		char *fn = gl.gl_pathv[i];
 		size_t j;
-		FILE *fp;
 
 		/* check for overrides */
 		for (j = i + 1; j < gl.gl_pathc; j++) {
@@ -736,26 +771,12 @@ int main(int argc, char *argv[])
 		if (!fn)
 			continue; /* skip, override exists */
 
-		fp = fopen(fn, "r");
-		if (!fp)
-			continue;
-
-//		info("Parsing %s ...", fn);
-		while (!feof(fp)) {
-			char *line;
-
-			line = fparseln(fp, NULL, NULL, NULL, FPARSELN_UNESCCOMM);
-			if (!line)
-				continue;
-
-			tmpfiles(line);
-			free(line);
-		}
-
-		fclose(fp);
+		process_file(fn);
 	}
 
 	globfree(&gl);
+
+	return 0;
 }
 
 /**