Author: me@beroal.in.ua http://www.beroal.in.ua/
Title: config file on command line, multiple Xorg displays

This patch adds to SLiM version 1.3.5:
* A command line option "-c $CONFIGURATION_FILENAME". Options in CONFIGURATION_FILENAME overrides options in "/etc/slim.conf".
* An option "display_name" for use in its configuration file.
These allows to start SLiM in several processes on different virtual terminals and displays. Example https://bbs.archlinux.org/viewtopic.php?pid=1192964#p1192964 .
There are similar old patches on developer's website, see https://developer.berlios.de/patch/?func=detailpatch&patch_id=2695&group_id=2663 and https://developer.berlios.de/patch/?func=detailpatch&patch_id=2207&group_id=2663

diff -u a/app.cpp b/app.cpp
--- a/app.cpp	2012-12-31 15:03:42.000000000 +0200
+++ b/app.cpp	2013-03-25 19:08:47.444065483 +0200
@@ -137,12 +137,13 @@
 	mcookie = string(App::mcookiesize, 'a');
 	daemonmode = false;
 	force_nodaemon = false;
+	confArgIs = false;
 	firstlogin = true;
 	Dpy = NULL;
 
 	/* Parse command line
 	   Note: we force a option for nodaemon switch to handle "-nodaemon" */
-	while((tmp = getopt(argc, argv, "vhp:n:d?")) != EOF) {
+	while((tmp = getopt(argc, argv, "c:vhp:n:d?")) != EOF) {
 		switch (tmp) {
 		case 'p':	/* Test theme */
 			testtheme = optarg;
@@ -163,6 +164,10 @@
 			std::cout << APPNAME << " version " << VERSION << endl;
 			exit(OK_EXIT);
 			break;
+		case 'c':
+			confArgIs = true;
+			confArgFn = optarg;
+			break;
 		case '?':	/* Illegal */
 			logStream << endl;
 		case 'h':   /* Help */
@@ -186,7 +191,14 @@
 }
 
 void App::Run() {
-	DisplayName = DISPLAY;
+	// Read configuration and theme
+	cfg = new Cfg;
+	cfg->readConf(CFGFILE);
+	if (confArgIs) {
+		cfg->readConf(confArgFn);
+	}
+
+	DisplayName = cfg->getOption("display_name").c_str();
 
 #ifdef XNEST_DEBUG
 	char* p = getenv("DISPLAY");
@@ -196,9 +208,6 @@
 	}
 #endif
 
-	/* Read configuration and theme */
-	cfg = new Cfg;
-	cfg->readConf(CFGFILE);
 	string themebase = "";
 	string themefile = "";
 	string themedir = "";
@@ -892,9 +901,7 @@
 	static const int MAX_XSERVER_ARGS = 256;
 	static char* server[MAX_XSERVER_ARGS+2] = { NULL };
 	server[0] = (char *)cfg->getOption("default_xserver").c_str();
-	string argOption = cfg->getOption("xserver_arguments");
-	/* Add mandatory -xauth option */
-	argOption = argOption + " -auth " + cfg->getOption("authfile");
+	string argOption = cfg->getOption("display_name") + " " + cfg->getOption("xserver_arguments") + " -auth " + cfg->getOption("authfile");
 	char* args = new char[argOption.length()+2]; /* NULL plus vt */
 	strcpy(args, argOption.c_str());
 
@@ -1213,7 +1220,7 @@
 	authfile = cfg->getOption("authfile");
 	remove(authfile.c_str());
 	putenv(StrConcat("XAUTHORITY=", authfile.c_str()));
-	Util::add_mcookie(mcookie, ":0", cfg->getOption("xauth_path"),
+	Util::add_mcookie(mcookie, cfg->getOption("display_name").c_str(), cfg->getOption("xauth_path"),
 	  authfile);
 }
 
diff -u a/app.h b/app.h
--- a/app.h	2012-12-31 15:03:42.000000000 +0200
+++ b/app.h	2013-03-25 19:09:18.623946895 +0200
@@ -104,6 +104,8 @@
 	bool firstlogin;
 	bool daemonmode;
 	bool force_nodaemon;
+	bool confArgIs;
+	const char* confArgFn;
 	/* For testing themes */
 	char *testtheme;
 	bool testing;
diff -u a/cfg.cpp b/cfg.cpp
--- a/cfg.cpp	2012-12-31 15:03:42.000000000 +0200
+++ b/cfg.cpp	2013-03-25 19:10:25.057027305 +0200
@@ -30,6 +30,7 @@
 	/* Configuration options */
 	options.insert(option("default_path","/bin:/usr/bin:/usr/local/bin"));
 	options.insert(option("default_xserver","/usr/bin/X"));
+	options.insert(option("display_name",":0.0"));
 	options.insert(option("xserver_arguments",""));
 	options.insert(option("numlock",""));
 	options.insert(option("daemon",""));
diff -u a/switchuser.cpp b/switchuser.cpp
--- a/switchuser.cpp	2012-12-31 15:03:42.000000000 +0200
+++ b/switchuser.cpp	2013-03-25 19:10:55.040246585 +0200
@@ -55,6 +55,6 @@
 	string home = string(Pw->pw_dir);
 	string authfile = home + "/.Xauthority";
 	remove(authfile.c_str());
-	r = Util::add_mcookie(mcookie, ":0", cfg->getOption("xauth_path"),
+	r = Util::add_mcookie(mcookie, displayName.c_str(), cfg->getOption("xauth_path"),
 	  authfile);
 }