All uses of frame-xchg were for action frames, and the frame type
was hard coded. Soon other frame types will be needed so the type
must now be specified in the frame_xchg_prefix structure.
In 98cf2bf3ec frame_xchg_stop was removed
and its use in p2p.c was changed to frame_xchg_cancel with the slight
complication that the ID returned by frame_xchg_start had do be stored.
Re-add frame_xchg_stop, (renamed as frame_xchg_stop_wdev) to simplify
this bit in p2p.c.
In order to first integrate frame-xchg some refactoring needed to
be done. First it is useful to allow queueing frames up rather than
requiring the module (p2p, anqp etc) to wait for the last frame to
finish. This can be aided by radio management but frame-xchg needed
some refactoring as well.
First was getting rid of this fx pointer re-use. It looks like this
was done to save a bit of memory but things get pretty complex
needed to check if the pointer is stale or has been reset. Instead
of this we now just allocate a new pointer each frame-xchg. This
allows for the module to queue multiple requests as well as removes
the complexity of needed to check if the fx pointer is stale.
Next was adding the ability to track frame-xchgs by ID. If a module
can queue up multiple requests it also needs to be able to cancel
them individually vs per-wdev. This comes free with the wiphy work
queue since it returns an ID which can be given directly to the
caller.
Then radio management was simply piped in by adding the
insert/done APIs.
In some cases a P2P peer will ACK our frame but not reply on the first
attempt, and other implementations seem to handle this by going back to
retransmitting the frame at a high rate until it gets ACKed again, at
which point they will again give the peer a longer time to tx the
response frame. Implement the same logic here by adding a
retries_on_ack parameter that takes the number of additional times we
want to restart the normal retransmit counter after we received no
response frame on the first attempt. So passing 0 maintains the
current behaviour, 1 for 1 extra attempt, etc.
In effect we may retransmit a frame about 15 * (retry_on_ack + 1) *
<in-kernel retransmit limit> times. The kernel/driver retransmits a
frame a number of times if there's no ACK (I've seen about 20 normally)
at a high frequency, if that fails we retry the whole process 15 times
inside frame-xchg.c and if we still get no ACK at any point, we give up.
If we do get an ACK, we wait for a response frame and if we don't get
that we will optionally reset the retry counter and restart the whole
thing retry_on_ack times.
Add a little state machine and a related API, to simplify sending out a
frame, receiving the Ack / No-ack status and (if acked) waiting for a
response frame from the target device, one of a list of possible
frame prefixes. The nl80211 API for this makes it complicated
enough that this new API seems to be justified, on top of that there's a
quirk when using the brcmfmac driver where the nl80211 response
(containing the operation's cookie), the Tx Status event and the response
Frame event are received from nl80211 in reverse order (not seen with
other drivers so far), further complicating what should be a pretty
simple task.
This new API is independent of netdev.c and allows actually
unregistering from receiving notifications of frames, although with some
quirks. The current API only allowed the callback for a registration to
be forgotten but our process and/or the kernel would still be woken up
when matching frames were received because the kernel had no frame
unregister call. In the new API you can supply a group-id paramter when
registering frames. If it is non-zero the frame_watch_group_remove() call
can be used to remove all frame registrations that had a given group-id
by closing the netlink socket on which the notifications would be
received. This means though that it's a slightly costly operation.
The file is named frame-xchg.c because I'm thinking of also adding
utilities for sending frames and waiting for one of a number of replies
and handling the acked/un-acked information.
James Prestwood