examples/shutdown-1.0: an example of reboot which does not signal init

For one, my inits know nothing about the concept of "shutting down the system".

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

examples/shutdown-1.0/script/hardshutdown.c

@@ -0,0 +1,168 @@
+/* Including <unistd.h> makes sure that on a glibc system
+ * <features.h> is included, which again defines __GLIBC__
+ */
+
+#include <unistd.h>
+#include <stdio.h>	/* puts */
+#include <time.h>	/* nanosleep */
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+
+
+/*
+ * Magic values required to use _reboot() system call.
+ */
+#define	LINUX_REBOOT_MAGIC1	0xfee1dead
+#define	LINUX_REBOOT_MAGIC2	672274793
+#define	LINUX_REBOOT_MAGIC2A	85072278
+#define	LINUX_REBOOT_MAGIC2B	369367448
+/*
+ * Commands accepted by the _reboot() system call.
+ *
+ * RESTART     Restart system using default command and mode.
+ * HALT        Stop OS and give system control to ROM monitor, if any.
+ * CAD_ON      Ctrl-Alt-Del sequence causes RESTART command.
+ * CAD_OFF     Ctrl-Alt-Del sequence sends SIGINT to init task.
+ * POWER_OFF   Stop OS and remove all power from system, if possible.
+ * RESTART2    Restart system using given command string.
+ */
+#define	LINUX_REBOOT_CMD_RESTART	0x01234567
+#define	LINUX_REBOOT_CMD_HALT		0xCDEF0123
+#define	LINUX_REBOOT_CMD_CAD_ON		0x89ABCDEF
+#define	LINUX_REBOOT_CMD_CAD_OFF	0x00000000
+#define	LINUX_REBOOT_CMD_POWER_OFF	0x4321FEDC
+#define	LINUX_REBOOT_CMD_RESTART2	0xA1B2C3D4
+
+
+#define USE_LIBC
+
+#ifdef USE_LIBC
+
+/* libc version */
+#if defined __GLIBC__ && __GLIBC__ >= 2
+#  include <sys/reboot.h>
+#  define REBOOT(cmd) reboot(cmd)
+#else
+extern int reboot(int, int, int);
+#  define REBOOT(cmd) reboot(LINUX_REBOOT_MAGIC1,LINUX_REBOOT_MAGIC2,(cmd))
+#endif
+
+static int my_reboot(int cmd)
+{
+	return REBOOT(cmd);
+}
+
+#else /* no USE_LIBC */
+
+/* direct syscall version */
+#include <linux/unistd.h>
+
+#ifdef _syscall3
+_syscall3(int,  reboot,  int,  magic, int, magic_too, int, cmd);
+#else
+/* Let us hope we have a 3-argument reboot here */
+extern int reboot(int, int, int);
+#endif
+
+static int my_reboot(int cmd)
+{
+	return reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, cmd);
+}
+
+#endif
+
+
+static void do_reboot(void)
+{
+	my_reboot(LINUX_REBOOT_CMD_RESTART);
+}
+static void do_poweroff(void)
+{
+	my_reboot(LINUX_REBOOT_CMD_POWER_OFF);
+}
+static void do_halt(void)
+{
+	my_reboot(LINUX_REBOOT_CMD_HALT);
+}
+
+static void usage(void)
+{
+	puts(
+	    "Usage: hardshutdown -h|-r|-p [NN]\n"
+	    "	NN - seconds to sleep before requested action"
+	);
+	exit(1);
+}
+
+enum action_t {
+	SHUTDOWN,	// do nothing
+	HALT,
+	POWEROFF,
+	REBOOT
+};
+
+int main(int argc, char *argv[])
+{
+	struct timespec t = {0,0};
+	enum action_t action = SHUTDOWN;
+	int c, i;
+	char *prog, *ptr;
+
+	//if (*argv[0] == '-') argv[0]++; /* allow shutdown as login shell */
+	prog = argv[0];
+	ptr = strrchr(prog,'/');
+	if (ptr)
+		prog = ptr+1;
+
+	for (c=1; c < argc; c++) {
+		if (argv[c][0] >= '0' && argv[c][0] <= '9') {
+			t.tv_sec = strtol(argv[c], NULL, 10);
+			continue;
+		}
+		if (argv[c][0] != '-') {
+			usage();
+			return 1;
+		}
+		for (i=1; argv[c][i]; i++) {
+			switch (argv[c][i]) {
+			case 'h':
+				action = HALT;
+				break;
+			case 'p':
+				action = POWEROFF;
+				break;
+			case 'r':
+				action = REBOOT;
+				break;
+			default:
+				usage();
+				return 1;
+			}
+		}
+	}
+
+	if (action==SHUTDOWN) {
+		usage();
+		return 1;
+	}
+
+	chdir("/");
+	while (nanosleep(&t,&t)<0)
+		if (errno!=EINTR) break;
+
+	switch (action) {
+	case HALT:
+		do_halt();
+		break;
+	case POWEROFF:
+		do_poweroff();
+		break;
+	case REBOOT:
+		do_reboot();
+		break;
+	default: /* SHUTDOWN */
+		break;
+	}
+	return 1;
+}