[U-Boot] DHCP Command Does Not Populate all DHCP Options supplied by DHCP Server

[Stefan Bruens <stefan.bruens@rwth-aachen.de>]

On Samstag, 4. Februar 2017 20:16:20 CET dh at synoia.com wrote:
> Stefan
> Thanks for the reply
> I suspect it is the offer response to the DHCP u-boot command.
> 
> Options 66/67 are important in the netboot scenario.
> 
> Regards Duncan Hare

Dear Duncan,

it would be good if you were more specific in your messages. Scenario, DHCP 
server, what do you want to achieve. You should also tell what you are 
referring to - messages on the wire, u-boot environment variables, ... Please 
be terse in your questions, but also give *all* necessary information. If in 
doubt, there is seldom to much information.

Of course bootserver and image url are typically [2] required for netboot 
scenarios. Although Option 66/67 is one possibility to specify this 
information, the "traditional"/non-PXE method of specifying these values is 
using the siaddr/sname/file fields. U-Boot currently evaluates siaddr and the 
file field. The sname field is ignored, as it would eventually require DNS 
resolution.

It is the obligation of the DHCP server to set these fields. The DHCP client 
*must not* use the sname/file fields in its DISCOVER/REQUEST (but for option 
overloading).

Specifically which information the DHCP *should* give to the client is 
specified in the DHCP Parameter Request List option (55). As u-boot uses 
siaddr/file for the bootstrapping, it omits the options 66/67. *If* a DHCP 
server sends out option 67 (bootfile name) although not requested, u-boot 
prefers its value over the file field.

Kind regards,

Stefan

[2] both values can be pre-set in the u-boot environment

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