upslug2 is a command line program intended to allow the upgrade of a
LinkSys NSLU2 firmware to new or different versions. Unlike upslug and
the LinkSys (Sercomm) upgrade utilities upslug2 will synthesise a
complete 'image' from a kernel and a root file system, as such it
duplicates part of the functionality of 'slugimage'.

upslug2 also optimises the upload to avoid transmitted parts of the
image which need not be written or are 'blank' (set to the erased flash
value of all 1's).