Message-ID: <467AFB5F.6050100@errno.com>
Date: Thu, 21 Jun 2007 15:27:43 -0700
From: Sam Leffler <sam@errno.com>
MIME-Version: 1.0
To: Andy Green <andy@warmcat.com>
CC: Johannes Berg <johannes@sipsolutions.net>,
	linux-wireless <linux-wireless@vger.kernel.org>
Subject: Re: radiotap for TX
References: <1182375853.3714.103.camel@johannes.berg> <467AE460.1070606@errno.com> <467AE9D8.2030602@warmcat.com>
In-Reply-To: <467AE9D8.2030602@warmcat.com>
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Sender: linux-wireless-owner@vger.kernel.org

[radiotap mailing list dropped since it is members only]

Andy Green wrote:
> Sam Leffler wrote:
> 
>> Note that using a monitor mode interface for transmit is a bad idea.  It
>> is likely you will encounter devices that disallow any packet transmit
>> when operating in monitor mode.  In practice this can be worked around
>> by using a non-monitor operating mode for the device (e.g. adhoc mode
>> w/o setting up beacons) but exporting this notion to user mode is bad
>> IMO.  In net80211 there is an adhoc-demo mode which is essentially adhoc
>> mode which was originally added for functionality found in old lucent
>> cards but more recently has been used for building applications that
>> want a "raw 802.11 device".
> 
> Hi -
> 
> In mac80211 you can run multiple network interfaces off the one physical
> device, so you can have an associated WPA connection on one network
> interface and another logical "monitor mode" network interface up on the
> one physical device.  "Monitor mode" in this case can be the results of
> a promiscuous hardware RX that is filtered for the Managed mode logical
> interface ... this is AIUI.  So in that way "Monitor Mode" no longer
> means a single modal device setting, but really the delivery somehow of
> packets to a logical network interface that belongs to the physical device.

I've had working vap code for >3 years.

> 
> Injecting down a "monitor mode interface" then only means to use a
> logical network interface that locally is configured to "Monitor Mode",
> it doesn't have the same definite implication for physical device
> configuration as before mac80211.  (Well.. AIUI).  So hopefully this
> objection may not apply.

As I described, some devices may allow rx-only operation on channels 
otherwise disallowed by regulatory constraints.  As such overloading 
monitor operation with transmit is just a bad idea if you want to take 
full advantage of what h/w provides.  I'm just suggesting that you're 
defining an abstraction that's going to get you into trouble.

	Sam