fast reboot fails when kernel parameters get too long
a fast reboot initiated via
/usr/sbin/reboot -f -- dataset -B kernel,parameters
will fail if the part after "-B" gets too long.
In fact the kernel,parameters can't be that long as a GRUB menu entry... .
The limit seems to be about 150 characters, but I didn't find where exactly this is enforced within the sources (as in reboot.c or a routine called by that has a limit of 512 characters when copying the reboot arguments...)