Custom location for usage.db

[protist]

I can see in issue #3 there was some discussion about a custom location for usage.db. I can see the GUI option to make this /etc/config/usage.db, which would allow it to persist over reboots. However, I would like to move it to my external USB drive, to reduce writes to the router's flash drive. (luci-app-statistics allows a similar configuration).

How can I change the location? I'm happy to hack the source code, but couldn't find anything obvious. I could see some reference in /usr/lib/lua/luci/model/cbi/wrtbwmon/config.lua, but this seemed to be more about moving the file.

I also found a reference in the dependency package wrtbwmon, in the file /etc/init.d/wrtbwmon. However, I wasn't sure if hacks to this file would then filter down to luci-wrtbwmon itself.

EDIT

I also tried persisting the file at /etc/config/usage.db, copying it to my USB drive, then symlinking it back to /etc/config/usage.db, but it seems that this file gets overwritten with a "normal" file instead of back to the symlink.