Resize /system in boot

Is it really safe?
Tested on Allview V3 Viper and Huawei Mate 9

base.mk

@@ -43,5 +43,8 @@ PRODUCT_COPY_FILES += \
 PRODUCT_COPY_FILES += \
 	device/phh/treble/nfc/libnfc-nci.conf:system/etc/libnfc-nci.conf
 
+PRODUCT_COPY_FILES += \
+	device/phh/treble/resize-system.sh:system/bin/resize-system.sh
+
 PRODUCT_PACKAGES += \
 	treble-environ-rc

resize-system.sh

@@ -0,0 +1,11 @@
+#!/system/bin/sh
+
+set -e
+
+if [ "grep ' /system ' /proc/mounts  |cut -d ' ' -f 1 |wc -l" -ne 1 ];then
+	exit 0
+fi
+
+mount -o remount,rw /system
+resize2fs $(grep ' /system ' /proc/mounts |cut -d ' ' -f 1)
+mount -o remount,ro /system

sepolicy/file_contexts

@@ -1,3 +1,4 @@
 /system/bin/phh-su                   u:object_r:phhsu_exec:s0
 /system/bin/vndk-detect			u:object_r:vndk_detect_exec:s0
 /system/etc/usb_audio_policy_configuration.xml	u:object_r:vendor_configs_file:s0
+/system/bin/resize-system.sh u:object_r:update_engine_exec:s0

sepolicy/resize.te

@@ -0,0 +1,6 @@
+allow update_engine { toolbox_exec system_file }:file rx_file_perms;
+allow update_engine labeledfs:filesystem remount;
+
+allow update_engine sysfs_fs_ext4_features:dir r_dir_perms;
+allow update_engine sysfs_fs_ext4_features:file r_file_perms;
+allow update_engine self:capability { sys_resource };

vndk.rc

@@ -1,4 +1,5 @@
 on post-fs
 	exec - root -- /system/bin/vndk-detect
+	exec - root -- /system/bin/resize-system.sh
 	mount none /system/etc/usb_audio_policy_configuration.xml /vendor/etc/usb_audio_policy_configuration.xml bind
 	export LD_CONFIG_FILE /system/etc/ld.config.${persist.sys.vndk}.txt