Re: [mac80211-next:cfg80211-mac80211-multi-bssid 8/20] ERROR: "__umoddi3" [net/wireless/cfg80211.ko] undefined!

[Jouni Malinen <j@w1.fi>]

On Sat, Feb 09, 2019 at 09:08:20AM +0100, Johannes Berg wrote:

> but maybe the whole thing is more readable as
> 
> static inline void cfg80211_gen_new_bssid(const u8 *bssid_addr, u8 max_bssid,
>                                           u8 mbssid_index, u8 *new_bssid_addr)
> {
>         u64 bssid = ether_addr_to_u64(bssid_addr);
>         u64 mask = GENMASK_ULL(max_bssid - 1, 0);
>         u64 new_bssid;
> 
>         new_bssid &= bssid & ~mask;

That should be "=" not "&="..

>         new_bssid |= ((bssid & mask) + mbssid_index) & mask;
> 
>         u64_to_ether_addr(new_bssid, new_bssid_addr);
> }

but other than that, this version looks much nicer than the other
alternatives.

> However, isn't it true that 0 <= mbssid_index < max_bssid? Then the
> whole masking isn't really needed at all?

0 <= mbssid_index < 2^max_bssid. The transmitted BSSID (i.e., that
bssid_addr argument) is not required to be the first BSSID in the range,
so the masking is needed to cover wraparound for addition modulo
2^mbssid_index when max_bssid LSBs of bssid are not zeros.

-- 
Jouni Malinen                                            PGP id EFC895FA