mac80211 ad-hoc problems

mac80211 ad-hoc problems

[Daniel Drake]

Hi,

I'm trying to implement ad-hoc mode in zd1211rw. I partially succeeded 
and posted a patch, but now I'm trying to investigate why I had trouble 
getting my laptops to talk...

I'm running iwl4965 on one box and zd1211rw on another, both running 
2.6.26-rc8

I create the network on the iwl4965 system:
	iwconfig wlan0 mode ad-hoc
	ifconfig wlan0 up
	iwconfig wlan0 essid dev

And then I try to connect on the zd1211rw system:
	iwconfig wlan0 mode ad-hoc
	ifconfig wlan0 up
	iwconfig wlan0 essid dev

If that's not the right way to create an ad-hoc network between 2 
systems, please discard the rest of this email and instead tell me how 
it should be done...


After running the 3rd command on the zd1211rw system, this happens:

<7>eth7: sta_find_ibss (active_ibss=0)
<7>   bssid=66:18:74:24:c1:d8 found
<7>   sta_find_ibss: selected 66:18:74:24:c1:d8 current 00:00:00:00:00:00
<7>   did not try to join ibss
<7>eth7: Trigger new scan to find an IBSS to join
<7>phy5: HW CONFIG: freq=2412
<7>phy5: HW CONFIG: freq=2417
<7>phy5: HW CONFIG: freq=2422
<7>phy5: HW CONFIG: freq=2427
<7>phy5: HW CONFIG: freq=2432
<7>phy5: HW CONFIG: freq=2437
<7>phy5: HW CONFIG: freq=2442
<7>phy5: HW CONFIG: freq=2447
<7>phy5: HW CONFIG: freq=2452
<7>phy5: HW CONFIG: freq=2457
<7>phy5: HW CONFIG: freq=2462
<7>phy5: HW CONFIG: freq=2467
<7>phy5: HW CONFIG: freq=2472
<4>__ratelimit: 4 messages suppressed
<7>phy5: HW CONFIG: freq=2462
<7>eth7: sta_find_ibss (active_ibss=0)
<7>   bssid=66:18:74:24:c1:d8 found
<7>   sta_find_ibss: selected 66:18:74:24:c1:d8 current 00:00:00:00:00:00
<7>   did not try to join ibss
<7>phy5: Adding new IBSS station 00:16:6f:47:00:46 (dev=eth7)
<7>phy5: Allocated STA 00:16:6f:47:00:46
<7>phy5: Inserted STA 00:16:6f:47:00:46
<7>eth7: sta_find_ibss (active_ibss=0)
<7>   bssid=66:18:74:24:c1:d8 found
<7>   sta_find_ibss: selected 66:18:74:24:c1:d8 current 00:00:00:00:00:00
<7>   did not try to join ibss
<7>eth7: Trigger new scan to find an IBSS to join
<7>phy5: HW CONFIG: freq=2412
<7>phy5: HW CONFIG: freq=2417

and soon after it creates its own IBSS.

Should it not have joined the IBSS it found? That one 
(66:18:74:24:c1:d8) is indeed the network I wanted it to connect to, 
hosted on my other laptop.

Looking at the code, ieee80211_sta_find_ibss() in mlme.c, I can't see 
how it's supposed to work.  It's clear why it said it found the other 
network, because the ESSID matches. But it's also clear why it didn't 
actually bother to try and connect: the ieee80211_sta_join_ibss() call 
is surrounded in an if condition which checks the BSSID - but I 
(intentionally) didn't specify one, so the condition evaluates as false.

Is this a bug, or am I required to specify an ESSID *and* a BSSID in 
order to connect to a pre-existing IBSS network?

Thanks,
Daniel

Re: mac80211 ad-hoc problems

[Daniel Drake]

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Daniel Drake wrote:
> Looking at the code, ieee80211_sta_find_ibss() in mlme.c, I can't see 
> how it's supposed to work.  It's clear why it said it found the other 
> network, because the ESSID matches. But it's also clear why it didn't 
> actually bother to try and connect: the ieee80211_sta_join_ibss() call 
> is surrounded in an if condition which checks the BSSID - but I 
> (intentionally) didn't specify one, so the condition evaluates as false.

Oh, I misread the code. I thought it was only looking for a 
user-specified BSSID (but I had not specified one). Actually it is 
checking that we aren't attempting to join the same network that we are 
already on.

The problem that was preventing me from getting connectivity was 
channel. It was only accepting IBSSes on local->hw.conf.channel, so I 
was required to do "iwconfig wlan0 channel X" first.

Is this by design, or is automatic channel selection a desirable 
feature? see attached patch, which seems to be working

Daniel

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[PATCH] mac80211: automatic IBSS channel selection

When joining an ad-hoc network, the user is currently required to specify
the channel. The network will not be joined otherwise, unless it happens
to be sitting on the currently active channel.

This patch implements automatic channel selection when the user has not
locked the interface onto a specific channel.

Signed-off-by: Daniel Drake <dsd@gentoo.org>

Index: linux-2.6.26-rc8/net/mac80211/mlme.c
===================================================================
--- linux-2.6.26-rc8.orig/net/mac80211/mlme.c
+++ linux-2.6.26-rc8/net/mac80211/mlme.c
@@ -3582,6 +3582,7 @@ static int ieee80211_sta_find_ibss(struc
 	int found = 0;
 	u8 bssid[ETH_ALEN];
 	int active_ibss;
+	int search_freq;
 	DECLARE_MAC_BUF(mac);
 	DECLARE_MAC_BUF(mac2);
 
@@ -3614,11 +3615,21 @@ static int ieee80211_sta_find_ibss(struc
 	printk(KERN_DEBUG "   sta_find_ibss: selected %s current "
 	       "%s\n", print_mac(mac, bssid), print_mac(mac2, ifsta->bssid));
 #endif /* CONFIG_MAC80211_IBSS_DEBUG */
-	if (found && memcmp(ifsta->bssid, bssid, ETH_ALEN) != 0 &&
-	    (bss = ieee80211_rx_bss_get(dev, bssid,
-					local->hw.conf.channel->center_freq,
-					ifsta->ssid, ifsta->ssid_len))) {
+
+	if (found && memcmp(ifsta->bssid, bssid, ETH_ALEN) != 0) {
 		int ret;
+		int search_freq;
+
+		if (ifsta->flags & IEEE80211_STA_AUTO_CHANNEL_SEL)
+			search_freq = bss->freq;
+		else
+			search_freq = local->hw.conf.channel->center_freq;
+
+		bss = ieee80211_rx_bss_get(dev, bssid, search_freq,
+					   ifsta->ssid, ifsta->ssid_len);
+		if (!bss)
+			goto dont_join;
+
 		printk(KERN_DEBUG "%s: Selected IBSS BSSID %s"
 		       " based on configured SSID\n",
 		       dev->name, print_mac(mac, bssid));
@@ -3626,6 +3637,8 @@ static int ieee80211_sta_find_ibss(struc
 		ieee80211_rx_bss_put(dev, bss);
 		return ret;
 	}
+
+dont_join:
 #ifdef CONFIG_MAC80211_IBSS_DEBUG
 	printk(KERN_DEBUG "   did not try to join ibss\n");
 #endif /* CONFIG_MAC80211_IBSS_DEBUG */

Re: mac80211 ad-hoc problems

[Johannes Berg]

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> Oh, I misread the code. I thought it was only looking for a 
> user-specified BSSID (but I had not specified one). Actually it is 
> checking that we aren't attempting to join the same network that we are 
> already on.
> 
> The problem that was preventing me from getting connectivity was 
> channel. It was only accepting IBSSes on local->hw.conf.channel, so I 
> was required to do "iwconfig wlan0 channel X" first.

Heh. I might have done that, yeah.

> Is this by design, or is automatic channel selection a desirable 
> feature? see attached patch, which seems to be working

Seems we should do automatic selection, the patch looks ok to me.

I wonder though, if we decide to create a new IBSS, which channel will
we choose?

> Daniel
> plain text document attachment (ibss-channel.txt)
> [PATCH] mac80211: automatic IBSS channel selection
> 
> When joining an ad-hoc network, the user is currently required to specify
> the channel. The network will not be joined otherwise, unless it happens
> to be sitting on the currently active channel.
> 
> This patch implements automatic channel selection when the user has not
> locked the interface onto a specific channel.
> 
> Signed-off-by: Daniel Drake <dsd@gentoo.org>

Acked-by: Johannes Berg <johannes@sipsolutions.net>

> 
> Index: linux-2.6.26-rc8/net/mac80211/mlme.c
> ===================================================================
> --- linux-2.6.26-rc8.orig/net/mac80211/mlme.c
> +++ linux-2.6.26-rc8/net/mac80211/mlme.c
> @@ -3582,6 +3582,7 @@ static int ieee80211_sta_find_ibss(struc
>  	int found = 0;
>  	u8 bssid[ETH_ALEN];
>  	int active_ibss;
> +	int search_freq;
>  	DECLARE_MAC_BUF(mac);
>  	DECLARE_MAC_BUF(mac2);
>  
> @@ -3614,11 +3615,21 @@ static int ieee80211_sta_find_ibss(struc
>  	printk(KERN_DEBUG "   sta_find_ibss: selected %s current "
>  	       "%s\n", print_mac(mac, bssid), print_mac(mac2, ifsta->bssid));
>  #endif /* CONFIG_MAC80211_IBSS_DEBUG */
> -	if (found && memcmp(ifsta->bssid, bssid, ETH_ALEN) != 0 &&
> -	    (bss = ieee80211_rx_bss_get(dev, bssid,
> -					local->hw.conf.channel->center_freq,
> -					ifsta->ssid, ifsta->ssid_len))) {
> +
> +	if (found && memcmp(ifsta->bssid, bssid, ETH_ALEN) != 0) {
>  		int ret;
> +		int search_freq;
> +
> +		if (ifsta->flags & IEEE80211_STA_AUTO_CHANNEL_SEL)
> +			search_freq = bss->freq;
> +		else
> +			search_freq = local->hw.conf.channel->center_freq;
> +
> +		bss = ieee80211_rx_bss_get(dev, bssid, search_freq,
> +					   ifsta->ssid, ifsta->ssid_len);
> +		if (!bss)
> +			goto dont_join;
> +
>  		printk(KERN_DEBUG "%s: Selected IBSS BSSID %s"
>  		       " based on configured SSID\n",
>  		       dev->name, print_mac(mac, bssid));
> @@ -3626,6 +3637,8 @@ static int ieee80211_sta_find_ibss(struc
>  		ieee80211_rx_bss_put(dev, bss);
>  		return ret;
>  	}
> +
> +dont_join:
>  #ifdef CONFIG_MAC80211_IBSS_DEBUG
>  	printk(KERN_DEBUG "   did not try to join ibss\n");
>  #endif /* CONFIG_MAC80211_IBSS_DEBUG */

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