On Wed, 2008-01-23 at 15:48 +0100, Johannes Berg wrote:
> > enable IBSS cell merging. if an IBSS beacon with the same ESSID and a TSF
> > higher than the local TSF (mactime) is received, we have to join its BSSID.
>
> Can you back that up with standard references? I see no such requirement
> in the standard text. I can see that under some circumstances this may
> be desirable, but maybe not.
>
> In fact, this seems to *break* standard behaviour, as per 11.1.3.1:
> (emphasis mine)
The way I understood Ad-Hoc to work was that if you weren't using the
SSID + BSSID as somebody else, you weren't part of that adhoc network.
Ad-Hoc + roaming isn't supported and is even less defined, which is what
this patch would enable IIUC. When joining an adhoc network, your
card/driver must scan around to find the SSID + (optionally) BSSID of
that adhoc network. If it finds one that matches criteria, it joins
that adhoc network, which means using the same BSSID. If it doesn't, it
creates a new adhoc network with a generated BSSID and the specified
SSID.
If this patch were applied, then you'd pretty quickly get split adhoc
networks where some people were automatically moved to a different BSSID
and the rest are left on the old BSSID (maybe missed a beacon, or
whatever), and therefore can't talk to each other. If only because
mac80211 would jump adhoc BSSIDs, while all other drivers (including
fullmac parts) would not.
A cell is identified uniquely by the combination of BSSID + SSID,
nothing less. You don't combine infrastructure networks of the same
SSID and a different BSSID, nor does this happen for adhoc.
Dan
> When a STA starts a BSS, that STA shall determine the BSSID of
> the BSS. If the BSSType indicates an infrastructure BSS, then
> the STA shall start an infrastructure BSS and the BSSID shall be
> equal to the STA’s dot11StationID. ***The value of the BSSID
> shall remain unchanged***, even if the value of dot11StationID
> is changed after the completion of the MLME-START.request. If
> the BSSType indicates an IBSS, the STA shall start an IBSS, and
> the BSSID shall be an individual locally administered IEEE MAC
> address as defined in 5.2 of IEEE Std 802-1990. The remaining 46
> bits of that MAC address shall be a number selected in a manner
> that minimizes the probability of STAs generating the same
> number, even when those STAs are subjected to the same initial
> conditions.
>
> Remember that BSSIDs, *not* SSIDs are used to identify BSSes uniquely.
>
> Of course you could argue that "merging" is simply tearing down the own
> and then joining the other IBSS.
>
> Comments on the code now.
>
> > --- a/net/mac80211/ieee80211_sta.c
> > +++ b/net/mac80211/ieee80211_sta.c
> > @@ -80,6 +80,9 @@ static void ieee80211_rx_bss_put(struct net_device *dev,
> > struct ieee80211_sta_bss *bss);
> > static int ieee80211_sta_find_ibss(struct net_device *dev,
> > struct ieee80211_if_sta *ifsta);
> > +static int ieee80211_sta_join_ibss(struct net_device *dev,
> > + struct ieee80211_if_sta *ifsta,
> > + struct ieee80211_sta_bss *bss);
>
> No way, order the code properly, this mess needs to be cleaned up not
> added to.
>
> > - if (bss->probe_resp && beacon) {
> > + if (sdata->vif.type != IEEE80211_IF_TYPE_IBSS &&
> > + bss->probe_resp && beacon) {
> > /* Do not allow beacon to override data from Probe Response. */
>
> Ahem. Comment update required.
>
> > + /* check if we need to merge IBSS */
>
> Could use a plural, but whatever.
>
> > + if (sdata->vif.type == IEEE80211_IF_TYPE_IBSS && beacon &&
> > + !local->sta_sw_scanning && !local->sta_hw_scanning &&
> > + mgmt->u.beacon.capab_info & WLAN_CAPABILITY_IBSS &&
> > + memcmp(elems.ssid, sdata->u.sta.ssid, sdata->u.sta.ssid_len) == 0) {
>
> I think that needs a check "&& ssid_len" or something. Someone's bound
> to try making an IBSS with a hidden SSID and we really don't want that
> to work.
>
> > +#ifdef CONFIG_MAC80211_IBSS_DEBUG
> > + static unsigned long last_tsf_debug;
> > +#endif
>
> Let's just get rid of that, it's not usable with multiple devices.
>
> > + if (rx_status->flag & RX_FLAG_TSFT)
> > + mactime = rx_status->mactime;
> > + else {
> > + mactime = -1LLU;
> > + printk(KERN_WARNING "%s: IBSS mode needs mactime for "
> > + "beacons\n", dev->name);
>
> Very bad, you'll be flooded by this when others send beacons. Also, I
> doubt its truthfulness.
>
> > + printk(KERN_DEBUG "%s: beacon TSF higher than local TSF"
> > + " -> IBSS merge with BSSID %s\n",
> > + dev->name, print_mac(mac, mgmt->bssid));
>
> No way. At the very least you need to ratelimit this.
>
> johannes
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