systemd: enable required kernel features.

When systemd is chosen as init system, the required kernel features are
enabled.

Signed-off-by: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

linux/linux.mk

@@ -195,7 +195,11 @@ define LINUX_CONFIGURE_CMDS
 		$(call KCONFIG_ENABLE_OPT,CONFIG_FUNCTION_TRACER,$(@D)/.config))
 	$(if $(BR2_PACKAGE_SYSTEMD),
 		$(call KCONFIG_ENABLE_OPT,CONFIG_CGROUPS,$(@D)/.config)
-		$(call KCONFIG_ENABLE_OPT,CONFIG_INOTIFY_USER,$(@D)/.config))
+		$(call KCONFIG_ENABLE_OPT,CONFIG_INOTIFY_USER,$(@D)/.config)
+		$(call KCONFIG_ENABLE_OPT,CONFIG_FHANDLE,$(@D)/.config)
+		$(call KCONFIG_ENABLE_OPT,CONFIG_AUTOFS4_FS,$(@D)/.config)
+		$(call KCONFIG_ENABLE_OPT,CONFIG_TMPFS_POSIX_ACL,$(@D)/.config)
+		$(call KCONFIG_ENABLE_OPT,CONFIG_TMPFS_POSIX_XATTR,$(@D)/.config))
 	$(if $(BR2_LINUX_KERNEL_APPENDED_DTB),
 		$(call KCONFIG_ENABLE_OPT,CONFIG_ARM_APPENDED_DTB,$(@D)/.config))
 	yes '' | $(TARGET_MAKE_ENV) $(MAKE1) $(LINUX_MAKE_FLAGS) -C $(@D) oldconfig

package/systemd/Config.in

@@ -26,8 +26,20 @@ config BR2_PACKAGE_SYSTEMD
 	  elaborate transactional dependency-based service control logic.
 	  It can work as a drop-in replacement for sysvinit.
 
-	  Systemd requires a Linux kernel >= 3.0, with inotify, devtmpfs,
-	  tmpfs vfs and tmpfs POSIX ACL enabled.
+	  Systemd requires a Linux kernel >= 3.0 with the following options
+	  enabled:
+
+	  - CONFIG_CGROUPS
+	  - CONFIG_INOTIFY_USER
+	  - CONFIG_FHANDLE
+	  - CONFIG_AUTOFS4_FS
+	  - CONFIG_TMPFS_POSIX_ACL
+	  - CONFIG_TMPFS_XATTR
+
+	  These options will be automatically enabled by Buildroot if
+	  it is responsible for building the kernel. Otherwise, if you
+	  are building your kernel outside of Buildroot, make sure
+	  these options are enabled.
 
 	  Systemd also provides udev, the userspace device daemon.