[patch] cope with buggy dhcp servers

[Denys Vlasenko]

On Saturday 24 November 2007 01:47, Cristian Ionescu-Idbohrn wrote:
> On Sat, 24 Nov 2007, Cristian Ionescu-Idbohrn wrote:
> > On Fri, 23 Nov 2007, Cristian Ionescu-Idbohrn wrote:
> > > Still...  This tweak is needed _only_ if the dhcp-server is brain
> > > dead, problem which most clients don't suffer of.
> >
> > This is what I could come out with.  Please comment.
>
> The difference to previous patch is just better wording of Config.in
> option.

+#define UDHCP_UDP_PACKET_SIZE_MIN ((sizeof(struct udp_dhcp_packet)) - \
+       (CONFIG_UDHCP_OPTIONS_SLACK_FOR_BUGGY_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 ? -1 : 1];
+               [sizeof(struct udp_dhcp_packet) !=
+                ((UDHCP_UDP_PACKET_SIZE_MIN) +
+                 (CONFIG_UDHCP_OPTIONS_SLACK_FOR_BUGGY_SERVERS)) ? -1 : 1];

This check as written above can never fail.

The sheck should have literal 576 - we are checking than neither we nor 
compiler goof up.

Maximum allowed slack size seems to be wrong, should be 1500 - 576 = 924.

See attached patch.

I changed the default from 0 to 300, it doesn't seem to have any effect on 
code size:

$ make bloatcheck
function                                             old     new   delta
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/0 up/down: 0/0)                 Total: 0 bytes
   text    data     bss     dec     hex filename
 776551     929    9100  786580   c0094 busybox_old
 776551     929    9100  786580   c0094 busybox_unstripped

Please test whether patch works for you.
--
vda
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