fff-sysupgrade/fff-web: Free cache before upgrade

This might reduce the chance to break devices with 32 MB RAM
during sysupgrade.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Fabian Bläse <fabian@blaese.de>

src/packages/fff/fff-sysupgrade/files/etc/sysupgrade.sh

@@ -97,6 +97,10 @@ else
     read -p "sha256 sums correct. Should I start upgrading the firmware (y/N)? " yn
     case $yn in
         [Yy]*|[Jj]*)
+            echo ""
+            echo "Freeing caches ..."
+            echo 3 > /proc/sys/vm/drop_caches
+
             echo ""
             echo "Starting firmware upgrade. Don't touch me until I reboot."
             echo ""

src/packages/fff/fff-web/files/www/ssl/cgi-bin/upgrade.html

@@ -70,6 +70,8 @@ if [ "$do_reset" = "1" ] ; then
 	echo "</pre>"
 elif [ "$do_sysupgrade" = "1" ] ; then
 	echo "<pre>"
+	echo "# Freeing caches ..."
+	echo 3 > /proc/sys/vm/drop_caches
 	echo "# sysupgrade $args $HASERL_firmware_path"
 	sysupgrade $args $HASERL_firmware_path
 	echo "</pre>"