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From: Ken Y. <ke...@nl...> - 2000-11-08 06:17:49
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>Finally I found the problem: >"/src/etherboot.h" sets the constant DHCP_OPT_LEN to 312 (=0x138). >This seems to be the maximal length for _all_ DHCP options together. >I set it to 512 and encountered no problems with my dhcpd.conf: >The bootmenu appeared with all entries. For larger dhcpd.confs >the value has to be increased further. > >But the contstant hasn´t been defined just for fun, >so what purpose does the constant have ? And where >can I find information about it (e.g. RFC)? Ok, I took a look at the RFCs and the source. You are right that DHCP_OPT_LEN is the cause of the problem, but not in the obvious way. In the DHCPDISCOVER message, Etherboot already requests for the maximum packet size that can be accomodated in the buffer (1024 if the buffer is located at 0x93C00, otherwise sizeof(struct bootp_t) + 1024). The problem is the call to decode_rfc1533, where the decoding of the buffer is restricted by DHCP_OPT_LEN. There are several possible steps that can be taken, each with greater consequences: 1. Change the call near line 880 to pass DHCP_OPT_LEN + MAX_BOOTP_EXTLEN just like the line above, since the options extend into the extension area anyway. The EXTENSION_PATH option should be taken out of the DHCP options requested, so that Etherboot does not request it and have the contents of the file overwrite the extension area. Technically extension path (option 18) is still legal in DHCPDISCOVER requests. In practice it doesn't seem to be useful to DHCP because the buffer can be larger now. ISC dhcpd does not support this option directly, you would have to request for option-18. The one small problem with this is that you could not enable DHCP support and then use extension path with an bootp server. It could be argued that people who use bootp+extension path should be encouraged to migrate to DHCP. 2. More radically, rework the definitions of bootp_t and bootpd_t. The former is a definition of the minimal BOOTP/DHCP packet and is used for defining a DHCPDISCOVER packet in bootp() and so should not be bloated so we should probably leave bootp_t alone. The latter includes the extension area or additional options area. But it's not clear to me if anything needs changing in bootpd_t except that the member "bootp_extension" wrongly describes what is really the continuation of the DHCP options area. 3. Put the extension path handling code inside #ifdef NO_DHCP_SUPPORT, so that not only does enabling DHCP not request the extension path but it definitely cannot handle it. This would save a little bit of code space. If you (shredda) could try fix 1 and confirm this works, we have at least confirmation of my theory. |
