radiotap feature discovery

Johannes Berg <[email protected]> Thu, 16 Apr 2009 18:02:37 +0200

Newsgroups	org.netbsd.radiotap
Message-ID	<[email protected]>

Hi!

With all these injection things, we'll invariably find devices that do
not support some of them, e.g. will not support not setting the sequence
number because the hardware always assigns them.

Thus, I think we need a way to do feature discovery. This isn't relevant
for RX -- there the driver just provides what it has -- but is for TX
where tools would like to know what they can do.

One way I could think of would be to define a whole bunch of flags for
the various injection features, and export those somehow. Not sure I
like this, since it means we need to keep track of yet another bitmap.

The other way I could imagine would be to export, in a yet to be defined
way, a radiotap header that lists the capabilities. For example, upon
feature query you'd return a header like this:

	0x00, 0x00,		// <-- radiotap version
	0x0b, 0x00,		// <- radiotap header length
	0x04, 0x84, 0x00, 0x00,	// <-- bitmap
	0x00,			// <-- rate
	0x00,			// <-- tx power
	0x08, 0x00		// <-- tx flags

This would indicate support for controlling
 * rate
 * tx power
 * tx flags - only no-ACK

How to export this information is to be determined and would most likely
be platform dependent though.

Thoughts?

johannes

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