On Wed, Oct 08, 2014 at 07:46:33AM -0400, Mark Asselstine wrote: > > If rt2x00 does not remove the alignment from the frame before giving it back > > to mac80211 and the same frame comes into rt2x00 again it should be correctly > > aligned and no additional header space is required. So this should be fine. > > Then I would say this definitely hints at a design flaw in > rt2x00queue_insert_l2pad(). Take the following scenario. > > * skb's first arrival in rt2x00queue_insert_l2pad(), 3 bytes needed > for frame alignment, 2 bytes for l2pad results in 3 bytes of headroom > taken. Not quite realistic assumption - header length will have to be odd then. But if such situation would happen we will have: header_align=2, payload_align=3, l2pad=3 Since payload_align will be bigger than header_align, header_align will be increased to 6. Header will be moved by 6 bytes, frame will be moved by 3 bytes, between header and frame there will be l2pad equal to 3. > * rt2x00lib_txdone() returns 2 bytes of headroom Return 3 bytes. > * skb's second arrival in rt2x00queue_insert_l2pad(), 0 bytes needed > for frame alignment, 2 bytes for l2pad results in 4 bytes of headroom > taken. Header will be moved by 3 bytes. > * rt2x00lib_txdone() returns 2 bytes of headroom Return 3 bytes. > Basically as long as any bytes are required for l2pad the headroom > will lose 4 bytes again and again, never being returned by > rt2x00lib_txdone(). I think that's not true - you made a few mistakes in your scenario, but perhaps I'm wrong :-) Stanislaw -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
