Bring back the hotplug-daemon-heuristic as a plugin

This way, the default behavior stays the same, but users can opt out
by disabling the plugin.

plugins/Makefile.am

@@ -17,6 +17,10 @@ if BUILD_DBUS_PLUGIN
 libplug_la_SOURCES += dbus.c
 endif
 
+if BUILD_HOTPLUG_PLUGIN
+libplug_la_SOURCES += hotplug.c
+endif
+
 if INETD
 if BUILD_INETD_ECHO_PLUGIN
 libplug_la_SOURCES += echo.c
@@ -62,6 +66,10 @@ if BUILD_DBUS_PLUGIN
 pkglib_LTLIBRARIES += dbus.la
 endif
 
+if BUILD_HOTPLUG_PLUGIN
+pkglib_LTLIBRARIES += hotplug.la
+endif
+
 if INETD
 if BUILD_INETD_ECHO_PLUGIN
 pkglib_LTLIBRARIES += echo.la

plugins/hotplug.c

@@ -0,0 +1,110 @@
+/* Heuristically find and initialize a suitable hotplug daemon
+ *
+ * Copyright (c) 2012-2020 Joachim Wiberg <troglobit@gmail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#include <stdio.h>
+
+#include "config.h"
+#include "conf.h"
+#include "finit.h"
+#include "helpers.h"
+#include "plugin.h"
+#include "service.h"
+
+static void setup(void *arg)
+{
+	char cmd[256];
+	char *path;
+
+	/*
+	 * Populate /dev and prepare for runtime events from kernel.
+	 * Prefer udev if mdev is also available on the system.
+	 */
+	path = which("udevd");
+	if (!path)
+		path = which("/lib/systemd/systemd-udevd");
+	if (path) {
+		/* Register udevd as a monitored service */
+		snprintf(cmd, sizeof(cmd), "[S12345789] pid:udevd %s "
+			 "-- Device event managing daemon", path);
+		if (service_register(SVC_TYPE_SERVICE, cmd, global_rlimit, NULL)) {
+			_pe("Failed registering %s", path);
+		} else {
+			snprintf(cmd, sizeof(cmd), ":1 [S] <svc%s> "
+				 "udevadm trigger -c add -t devices "
+				 "-- Requesting device events", path);
+			service_register(SVC_TYPE_RUN, cmd, global_rlimit, NULL);
+
+			snprintf(cmd, sizeof(cmd), ":2 [S] <svc%s> "
+				 "udevadm trigger -c add -t subsystems "
+				 "-- Requesting subsystem events", path);
+			service_register(SVC_TYPE_RUN, cmd, global_rlimit, NULL);
+		}
+
+		free(path);
+
+		/* Debian has this little script to copy generated
+		 * rules while the system was read-only. TODO: When
+		 * this functionality was hardcoded in finit.c, this
+		 * call was made in crank_worker(). Now that
+		 * filesystems are mounted earlier we should be able
+		 * to make this call directly after the triggers have
+		 * run, but this has not been tested AT ALL. */
+		if (fexist("/lib/udev/udev-finish"))
+			run_interactive("/lib/udev/udev-finish", "Finalizing udev");
+	} else {
+		path = which("mdev");
+		if (path) {
+			/* Embedded Linux systems usually have BusyBox mdev */
+			if (log_is_debug())
+				touch("/dev/mdev.log");
+
+			snprintf(cmd, sizeof(cmd), "%s -s", path);
+			free(path);
+
+			run_interactive(cmd, "Populating device tree");
+		}
+	}
+}
+
+static plugin_t plugin = {
+	.name = __FILE__,
+	.hook[HOOK_BASEFS_UP] = {
+		.cb  = setup
+	},
+};
+
+PLUGIN_INIT(plugin_init)
+{
+	plugin_register(&plugin);
+}
+
+PLUGIN_EXIT(plugin_exit)
+{
+	plugin_unregister(&plugin);
+}
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */