Replace reboot(RB_SW_SUSPEND) w/ internal /sys/power/state API

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/api.c

@@ -250,10 +250,10 @@ static int do_reboot(int cmd, char *buf, size_t len)
 	case INIT_CMD_SUSPEND:
 		_d("suspend");
 		sync();
-		rc = reboot(RB_SW_SUSPEND);
+		rc = sys_suspend();
 		if (rc) {
 			if (errno == EINVAL)
-				snprintf(buf, len, "Kernel does not support suspend.");
+				snprintf(buf, len, "Kernel does not support suspend to RAM.");
 			else
 				snprintf(buf, len, "Failed: %s", strerror(errno));
 		}

src/reboot.c

@@ -160,6 +160,8 @@ int reboot_main(int argc, char *argv[])
 	transform(NULL);
 
 	if (force) {
+		sync();
+
 		switch (cmd) {
 		case CMD_REBOOT:
 			c = reboot(RB_AUTOBOOT);
@@ -174,9 +176,9 @@ int reboot_main(int argc, char *argv[])
 			break;
 
 		case CMD_SUSPEND:
-			c = reboot(RB_SW_SUSPEND);
+			c = suspend();
 			if (c && errno == EINVAL)
-				errx(1, "Kernel does not support suspend.");
+				errx(1, "Kernel does not support suspend to RAM.");
 			break;
 
 		case CMD_UNKNOWN:

src/util.c

@@ -235,6 +235,40 @@ int fngetint(char *path, int *val)
 	return 0;
 }
 
+/*
+ * This is a replacement for the non-working reboot(RB_SW_SUSPEND).  It
+ * checks for suspend to RAM support, assuming `mem_sleep` has a sane
+ * default, e.g. 'deep' or 's2idle'.  The latter should be possible to
+ * select from finit.conf, but for now we go with the kernel default.
+ * For more information on kernel sleep states, see:
+ * https://www.kernel.org/doc/html/latest/admin-guide/pm/sleep-states.html
+ */
+int suspend(void)
+{
+	char buf[80];
+	char *ptr;
+
+	if (fnread(buf, sizeof(buf), "/sys/power/state") <= 0) {
+	opnotsup:
+		errno = EINVAL;
+		return 1;
+	}
+
+	chomp(buf);
+
+	ptr = strtok(buf, " ");
+	while (ptr) {
+		if (!strcmp(ptr, "mem"))
+			break;
+
+		ptr = strtok(NULL, " ");
+	}
+	if (!ptr)
+		goto opnotsup;
+
+	return fnwrite("mem", "/sys/power/state");
+}
+
 int strtobytes(char *arg)
 {
 	int mod = 0, bytes;

src/util.h

@@ -59,6 +59,8 @@ int   fnread       (char *buf, size_t len, char *fmt, ...) __attribute__ ((forma
 int   fnwrite      (char *value, char *fmt, ...)           __attribute__ ((format (printf, 2, 3)));
 int   fngetint     (char *path, int *val);
 
+int   suspend      (void);
+
 int   strtobytes   (char *arg);
 char *sig2str      (int sig);
 int   str2sig      (char *sig);