busybox udhcp settings/options help

[Denys Vlasenko]

On Thu, Jan 26, 2017 at 10:22 PM,  <bch at shroggslodge.freeserve.co.uk> wrote:
> Please can anyone explain what the 'boot_file'  parameter is specifically
> for  and what udhcp does with it ?
> Also, what is the difference between that 'boot_file' parameter and then the
> optional 'opt bootfile <filename>' parameter ?

There is a fixed-size 128-byte boot_file field in DHCP packets,
it is a feature inherited from BOOTP
(new, DHCP options use variable-sized storage in the packet).

If it is not starting with zero byte, udhcpc (client) exports it
into $boot_file env var for its script (the -s SCRIPT thing)
to use in whatever way SCRIPT wants.

udhcpd (server) will fill it with zeroes inlees you specify
    boot_file FILE
in udhcpd.conf.
In the same file,
    opt bootfile FILE
sets the value of DHCP option 67, not of the boot_file field.