configure.ac: make cgroup2 configurable (#406)

configure.ac

@@ -67,6 +67,10 @@ AC_ARG_ENABLE(fsckfix,
         AS_HELP_STRING([--enable-fsckfix], [Run fsck fix mode (options: -yf) on filesystems listed in /etc/fstab]),,[
 	enable_fsckfix=no])
 
+AC_ARG_ENABLE(cgroup,
+        AS_HELP_STRING([--disable-cgroup], [Disable cgroup v2 support, default: autodetect from /sys/fs/cgroup]),,[
+        enable_cgroup=yes])
+
 AC_ARG_ENABLE(redirect,
         AS_HELP_STRING([--disable-redirect], [Disable redirection of service output to /dev/null]),,[
 	enable_redirect=yes])
@@ -188,6 +192,9 @@ AS_IF([test "x$enable_kernel_cmdline" = "xyes"], [
 AS_IF([test "x$enable_kernel_logging" = "xyes"], [
         AC_DEFINE(KERNEL_LOGGING, 1, [Keep kernel warn/err logs to console])])
 
+AS_IF([test "x$enable_cgroup" = "xyes"], [
+        AC_DEFINE(CGROUP2_ENABLED, 1, [Autodetect cgroup v2 support from /sys/fs/cgroup])])
+
 AS_IF([test "x$enable_fastboot" = "xyes"], [
 	AC_DEFINE(FAST_BOOT, 1, [Skip fsck check on filesystems listed in /etc/fstab])])
 
@@ -388,6 +395,7 @@ Optional features:
   Built-in sulogin......: $with_sulogin $sulogin
   Built-in watchdogd....: $with_watchdog $watchdog
   Built-in logrotate....: $enable_logrotate
+  Use cgroup v2.........: $enable_cgroup
   Parse kernel cmdline..: $enable_kernel_cmdline
   Keep kernel logging...: $enable_kernel_logging
   Skip fsck check.......: $enable_fastboot

src/cgroup.c

@@ -463,6 +463,11 @@ void cgroup_init(uev_ctx_t *ctx)
 	FILE *fp;
 	int fd;
 
+#ifndef CGROUP2_ENABLED
+	avail = 0;
+	return;
+#endif
+
 	if (mount("none", FINIT_CGPATH, "cgroup2", opts, NULL)) {
 		if (errno == ENOENT)
 			logit(LOG_INFO, "Kernel does not support cgroups v2, disabling.");