Add Plymouth boot splash plugin

Manage the plymouthd lifecycle across boot, switch_root, and shutdown.
Activated by the "splash" kernel command line argument.

Author: aanderse

configure.ac

@@ -116,6 +116,7 @@ AC_PLUGIN([hotplug],       [yes], [Start udevd or mdev kernel event datamon])
 AC_PLUGIN([rtc],           [yes], [Save and restore RTC using hwclock])
 AC_PLUGIN([tty],           [yes], [Automatically activate new TTYs, e.g. USB-to-serial])
 AC_PLUGIN([urandom],       [yes], [Setup and save random seed at boot/shutdown])
+AC_PLUGIN([plymouth],      [no],  [Plymouth boot splash integration])
 AC_PLUGIN([testserv],      [no],  [Test plugin to start test serv daemon])
 
 # Check for extra arguments or packages

plugins/Makefile.am

@@ -29,6 +29,10 @@ if BUILD_NETLINK_PLUGIN
 libplug_la_SOURCES += netlink.c
 endif
 
+if BUILD_PLYMOUTH_PLUGIN
+libplug_la_SOURCES += plymouth.c
+endif
+
 if BUILD_RESOLVCONF_PLUGIN
 libplug_la_SOURCES += resolvconf.c
 endif
@@ -76,6 +80,10 @@ if BUILD_NETLINK_PLUGIN
 pkglib_LTLIBRARIES += netlink.la
 endif
 
+if BUILD_PLYMOUTH_PLUGIN
+pkglib_LTLIBRARIES += plymouth.la
+endif
+
 if BUILD_RESOLVCONF_PLUGIN
 pkglib_LTLIBRARIES += resolvconf.la
 endif

plugins/plymouth.c

@@ -0,0 +1,310 @@
+/* Plymouth boot splash plugin for Finit
+ *
+ * Copyright (c) 2012-2026  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.
+ */
+
+/*
+ * This plugin integrates the Plymouth boot splash screen with Finit.
+ * It manages the plymouthd lifecycle across the full boot process:
+ *
+ *  - HOOK_BANNER:      Start plymouthd early, before console output.
+ *                      In initramfs, starts fresh.  In stage 2, reuses
+ *                      the daemon carried over from initramfs if alive.
+ *  - HOOK_ROOTFS_UP .. HOOK_SYSTEM_UP: Display status messages.
+ *  - HOOK_SVC_UP:      Tear down plymouth once boot is complete.
+ *  - HOOK_SWITCH_ROOT: Notify plymouth of root filesystem change so
+ *                      the daemon survives the initramfs -> rootfs
+ *                      transition.
+ *  - HOOK_SHUTDOWN:    Restart plymouthd in shutdown mode for a
+ *                      splash during poweroff/reboot.
+ *
+ * The plugin is only activated when "splash" is present on the kernel
+ * command line.  Plymouth requires devpts for VT takeover, which may
+ * not be mounted yet at HOOK_BANNER time (before fs_finalize), so the
+ * plugin mounts it if needed.
+ *
+ * NOTE: The initramfs must include /etc/initrd-release.  Plymouth
+ * checks for this file and, when present, prefixes its argv[0] with
+ * '@' so that the process is not killed during switch_root.  Without
+ * it, plymouthd will not survive the initramfs-to-rootfs transition.
+ */
+
+#include <sys/mount.h>
+#include <sys/stat.h>
+
+#include "config.h"
+#include "finit.h"
+#include "helpers.h"
+#include "conf.h"
+#include "pid.h"
+#include "plugin.h"
+#include "sig.h"
+#include "util.h"
+#include "log.h"
+
+#ifndef PLYMOUTH_PATH
+#define PLYMOUTH_PATH "/sbin/plymouth"
+#endif
+#ifndef PLYMOUTHD_PATH
+#define PLYMOUTHD_PATH "/sbin/plymouthd"
+#endif
+
+#define PLYMOUTH_PIDFILE  "/run/plymouthd.pid"
+
+static pid_t daemon_pid;
+static int   switching_root;
+static int   in_initramfs;
+
+static int plymouth_cmd(const char *action)
+{
+	char cmd[256];
+
+	snprintf(cmd, sizeof(cmd), PLYMOUTH_PATH " %s", action);
+	return run(cmd, NULL);
+}
+
+static void plymouth_message(const char *msg)
+{
+	pid_t pid;
+
+	pid = fork();
+	if (pid == 0) {
+		sig_unblock();
+		execl(PLYMOUTH_PATH, PLYMOUTH_PATH,
+		      "display-message", "--text", msg, NULL);
+		_exit(EX_OSERR);
+	}
+}
+
+static int plymouth_alive(void)
+{
+	return daemon_pid > 0 && pid_alive(daemon_pid);
+}
+
+/*
+ * Start plymouthd in the given mode ("boot" or "shutdown").
+ *
+ * Mounts devpts if needed -- HOOK_BANNER fires before fs_finalize(),
+ * so /dev/pts may not exist yet.  Plymouth needs it for --attach-to-session
+ * which gives it control of the VT for rendering.
+ */
+static void plymouth_start(const char *mode)
+{
+	char cmd[256];
+	int rc;
+
+	if (plymouth_alive())
+		return;
+
+	/* Mount devpts if not already mounted (needed for --attach-to-session) */
+	if (!fismnt("/dev/pts")) {
+		mkdir("/dev/pts", 0755);
+		mount("devpts", "/dev/pts", "devpts",
+		      MS_NOSUID | MS_NOEXEC, "ptmxmode=0666,mode=0620");
+	}
+
+	snprintf(cmd, sizeof(cmd),
+		 PLYMOUTHD_PATH " --attach-to-session --mode %s --pid-file %s",
+		 mode, PLYMOUTH_PIDFILE);
+	rc = run(cmd, NULL);
+	if (rc) {
+		warnx("plymouthd failed to start (exit %d)", rc);
+		return;
+	}
+
+	daemon_pid = pid_file_read(PLYMOUTH_PIDFILE);
+	if (daemon_pid <= 0) {
+		warnx("plymouthd started but no PID in %s", PLYMOUTH_PIDFILE);
+		return;
+	}
+
+	rc = plymouth_cmd("show-splash");
+	if (rc)
+		warnx("plymouth show-splash failed (exit %d)", rc);
+}
+
+static void plymouth_stop(void)
+{
+	if (!plymouth_alive())
+		return;
+
+	plymouth_cmd("quit");
+
+	/*
+	 * Don't poll -- we're in a finit hook, so finit's event loop
+	 * is blocked and can't reap children.  Trust that plymouthd
+	 * exits after receiving the quit command.
+	 */
+	daemon_pid = 0;
+	unlink(PLYMOUTH_PIDFILE);
+}
+
+/*
+ * HOOK_BANNER - earliest possible hook, before any console output.
+ *
+ * In initramfs: start plymouthd fresh.
+ * In stage 2:   reuse plymouthd from initramfs if still alive,
+ *               otherwise start a new instance.
+ */
+static void plymouth_boot(void *arg)
+{
+	in_initramfs = fexist("/etc/initrd-release");
+
+	if (rescue)
+		return;
+
+	enable_progress(0);
+
+	if (!in_initramfs) {
+		if (plymouth_cmd("--ping") == 0) {
+			daemon_pid = pid_file_read(PLYMOUTH_PIDFILE);
+			if (daemon_pid <= 0)
+				daemon_pid = 1; /* alive but unknown pid */
+			return;
+		}
+	}
+
+	plymouth_start("boot");
+}
+
+/*
+ * HOOK_SVC_UP - all services launched.
+ *
+ * In initramfs: keep splash alive for switch_root.
+ * In stage 2:   boot is done, tear down plymouth.
+ */
+static void plymouth_boot_done(void *arg)
+{
+	if (in_initramfs)
+		return;
+
+	plymouth_stop();
+	enable_progress(1);
+}
+
+/* HOOK_SWITCH_ROOT - initramfs transitioning to real root. */
+static void plymouth_switchroot(void *arg)
+{
+	switching_root = 1;
+
+	plymouth_message("Switching to root filesystem...");
+
+	if (plymouth_alive())
+		run(PLYMOUTH_PATH " update-root-fs --new-root-dir=/sysroot", NULL);
+
+	enable_progress(1);
+}
+
+/* HOOK_SHUTDOWN - entering runlevel 0 or 6. */
+static void plymouth_shutdown(void *arg)
+{
+	if (rescue || switching_root)
+		return;
+
+	enable_progress(0);
+	plymouth_start("shutdown");
+}
+
+static void on_rootfs_up(void *arg)
+{
+	plymouth_message("Root filesystem mounted");
+}
+
+static void on_mount_post(void *arg)
+{
+	plymouth_message("Mounting filesystems...");
+}
+
+static void on_basefs_up(void *arg)
+{
+	plymouth_message("All filesystems mounted");
+}
+
+static void on_network_up(void *arg)
+{
+	plymouth_message("Network is up");
+}
+
+static void on_system_up(void *arg)
+{
+	plymouth_message("System ready");
+}
+
+static plugin_t plugin = {
+	.name = "plymouth",
+	.hook[HOOK_BANNER]      = { .cb  = plymouth_boot       },
+	.hook[HOOK_ROOTFS_UP]   = { .cb  = on_rootfs_up        },
+	.hook[HOOK_MOUNT_POST]  = { .cb  = on_mount_post       },
+	.hook[HOOK_BASEFS_UP]   = { .cb  = on_basefs_up        },
+	.hook[HOOK_NETWORK_UP]  = { .cb  = on_network_up       },
+	.hook[HOOK_SYSTEM_UP]   = { .cb  = on_system_up        },
+	.hook[HOOK_SVC_UP]      = { .cb  = plymouth_boot_done  },
+	.hook[HOOK_SWITCH_ROOT] = { .cb  = plymouth_switchroot },
+	.hook[HOOK_SHUTDOWN]    = { .cb  = plymouth_shutdown   },
+};
+
+/*
+ * Check kernel command line for "splash" argument.  Plymouth should
+ * only be activated when the user explicitly requests it.
+ */
+static int has_splash_arg(void)
+{
+	char line[LINE_SIZE], *tok, *saveptr;
+	FILE *fp;
+
+	fp = fopen("/proc/cmdline", "r");
+	if (!fp)
+		return 0;
+
+	if (!fgets(line, sizeof(line), fp)) {
+		fclose(fp);
+		return 0;
+	}
+	fclose(fp);
+
+	for (tok = strtok_r(line, " \t\n", &saveptr); tok;
+	     tok = strtok_r(NULL, " \t\n", &saveptr)) {
+		if (!strcmp(tok, "splash"))
+			return 1;
+	}
+
+	return 0;
+}
+
+PLUGIN_INIT(__init)
+{
+	if (!has_splash_arg())
+		return;
+
+	plugin_register(&plugin);
+}
+
+PLUGIN_EXIT(__exit)
+{
+	plugin_unregister(&plugin);
+}
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */