According to lxc.container.conf manual page lxc.hook.pre-start is "A hook to be run in the host's namespace".
But from what I see it's not quite so:
1. /etc/pve/lxc/125.conf contains the following line
lxc.hook.pre-mount: /etc/pve/lxc/${LXC_NAME}.mount
2. /etc/pve/lxc/125.mount is a shell...