remarkable: detect if launcher script has changed

And a complete restart from the parent launcher is needed.

frontend/device/remarkable/device.lua

@@ -426,6 +426,12 @@ function Remarkable:getDefaultCoverPath()
     return "/usr/share/remarkable/poweroff.png"
 end
 
+function Remarkable:isStartupScriptUpToDate()
+    local md5 = require("ffi/MD5")
+    -- Compare the hash of the *active* script to the *potential* one.
+    return md5.sumFile("/tmp/koreader.sh") == md5.sumFile(os.getenv("KOREADER_DIR") .. "/koreader.sh")
+end
+
 function Remarkable:setEventHandlers(UIManager)
     UIManager.event_handlers.Suspend = function()
         self:onPowerEvent("Suspend")

platform/remarkable/koreader.sh

@@ -1,7 +1,18 @@
 #!/bin/sh
+
+# Relocalize ourselves to /tmp: this is used by KOReader to detect if the
+# original script has changed after an update (requiring a complete restart
+# from the parent launcher).
+if [ "$(dirname "${0}")" != '/tmp' ]; then
+    cp -pf "${0}" '/tmp/koreader.sh'
+    chmod 777 '/tmp/koreader.sh'
+    exec '/tmp/koreader.sh' "$@"
+fi
+
 export LC_ALL="en_US.UTF-8"
+
 # working directory of koreader
-KOREADER_DIR="${0%/*}"
+export KOREADER_DIR="${0%/*}"
 UNPACK_DIR="${KOREADER_DIR%/*}"
 
 # we're always starting from our working directory