On Wed, Oct 08, 2014 at 11:34:22PM -0400, Mark Asselstine wrote: > On Wed, Oct 8, 2014 at 3:52 PM, Mark Asselstine <asselsm@xxxxxxxxx> wrote: > > On Wed, Oct 8, 2014 at 9:00 AM, Stanislaw Gruszka <sgruszka@xxxxxxxxxx> wrote: > >> > >> 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 :-) > > > > No just me being an idiot. I had thought > > frame == header + l2pad + payload > > not > > frame == payload > > > > By the way, I assumed that this due to the name and contents of > rt2x00queue_align_frame(). Where all the data (header and payload) are > aligned to a 4-byte boundary and the function is name 'align_frame'. I > assume your interpretation is the correct one, can you confirm? Frame term is used mostly to describe all data including header and payload. 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
