need some insight in udhcp structures size

[Denys Vlasenko]

On Friday 23 November 2007 03:03, Cristian Ionescu-Idbohrn wrote:
> Thanks Denys,
>
> On Thu, 22 Nov 2007, Denys Vlasenko wrote:
> > 576 is a RFC-mandated max dhcp packet size (including IP header).
>
> Yes.  I now took the time to look even at that part of rfc2131 ;)
>
> > 308, 128 and 64 are sizes of the fields, should be changed:
> >
> > -   length = 308;
> > +   length = sizeof(packet->options);
>
> Yes.  I'll do that on the magic numbers.

It's already done in svn. Take a look.

> * what you suggest: bump the size of options, or
> * add a pad-variable to the structure

First. This way, sizeof() of options field will give correct value,
and no code changes will be needed.

> > Please document which devices need that:
> >
> > /* Should be 0 but there are buggy DHCP servers in the wild:
> >  * <name of the device with buggy server> - needs N bytes
> >  * ... ...
> >  */
> > #define SPACE_FOR_BUGGY_DHCP_SERVERS 500
> > ...
> >         options[308 + SPACE_FOR_BUGGY_DHCP_SERVERS];
> > ...
> > /* Let's see whether compiler understood us right */
> > struct BUG_bad_sizeof_struct_udp_dhcp_packet {
> >         char BUG_bad_sizeof_struct_udp_dhcp_packet
> >                 [sizeof(struct udp_dhcp_packet) != (576 +
> > SPACE_FOR_BUGGY_DHCP_SERVERS) ? -1 : 1]; };
>
> I thought of doing that with a configuration option instead of hard
> coding.  What do you think?

Config options are needed when people may want to exclude functionality
and save on code size. Here code size will be the same.
--
vda