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+===== What this is about =====
+For an introduction see the [[http://pdxplumbers.osuosl.org/2010/ocw/system/presentations/639/original/lpc-p2p.pdf|slides]] for the "Wi-Fi Peer-to-Peer on Linux" talk given by Johannes Berg during the Linux Plumbers Conference 2010.
+===== Basic P2P Architecture Stack =====
+<code>          |  <---------- D-Bus Application API
++--------------------+
+| connection manager |
+| or p2p control app |
++--------------------+
+          |  <---------- D-Bus supplicant API
+          |              or socket control interface
++--------------------+
+| wpa_supplicant     |
++--------------------+
+          |  <---------- nl80211
++--------------------+
+| cfg80211           |
++--------------------+
+          |  <---------- struct API
++--------------------+
+| mac80211           |
++--------------------+
+          |  <---------- mac80211's driver API
++--------------------+
+| driver             |
++--------------------+</code>
+===== Interfaces =====
+==== D-Bus Application API ====
+<code>NOTE: This doesn't exist yet! There's no integration
+      with connection managers or any other control
+      application yet!</code>
+We're currently working on seeing if this is at all feasible to define, but it would be good if applications could use a standard API that the connection manager offers. There are multiple reasons for having the connection manager offer this, like the need for a coordinator of all wifi usage.
+Since there are multiple connections managers, a good approach to defining this would be a freedesktop.org standard.
+==== supplicant API ====
+=== D-Bus API ===
+API has been posted for review: [[http://thread.gmane.org/gmane.linux.drivers.hostap/22469|http://thread.gmane.org/gmane.linux.drivers.hostap/22469]]
+=== socket control interface ===
+This interface offers basic P2P primitives like p2p_find, p2p_stop_find, p2p_connect, etc.
+Here's a full list:
+  * p2p_find
+  * p2p_stop_find
+  * p2p_connect
+  * p2p_listen
+  * p2p_group_remove
+  * p2p_group_add
+  * p2p_prov_disc
+  * p2p_get_passphrase
+  * p2p_serv_disc_req
+  * p2p_serv_disc_cancel_req
+  * p2p_serv_disc_resp
+  * p2p_service_update
+  * p2p_serv_disc_external
+  * p2p_service_flush
+  * p2p_service_add
+  * p2p_service_del
+  * p2p_reject
+  * p2p_invite
+  * p2p_peers
+  * p2p_peer
+  * p2p_set
+  * p2p_flush
+  * p2p_presence_req
+  * p2p_ext_listen This API can be used on dedicated/embedded systems like a printer, but applications that must play together with other applications can't really use it.
+Both D-Bus and socket interfaces (will) also have events indicating when new P2P devices were found, etc.
+==== nl80211 ====
+Currently, the P2P-related extensions are:
+    * NL80211_CMD_REMAIN_ON_CHANNEL
+    * NL80211_CMD_CANCEL_REMAIN_ON_CHANNEL
+    *  * This indicates to the device that it should stay on a given channel for a given time, to implement a P2P listen phase. Can also be canceled, since it is also used to implement off-channel TX for group negotiation or invitation (but see below)
+    *   NL80211_CMD_FRAME (previously NL80211_CMD_ACTION)
+    *    * Transmit a management frame, with channel checking. This can be used during a remain-on-channel phase to transmit frames on that channel, or at other times to transmit on the operating channel. This also allows off-channel transmission, i.e. transmit on a given channel and wait for a response for a given time (including the ability to cancel the wait) which in a sense combines REMAIN_ON_CHANNEL and MGMT_TX into just a single MGMT_TX for some operations. (wpa_supplicant changes for this enhanced offload haven't been merged upstream yet)
+    *     NL80211_CMD_REGISTER_FRAME
+    *      * Allow a userspace application to register for receiving a given type of (management) frame through nl80211, and also replying to it. Applications can also specify a filter so for example they don't have to handle all the different action frames but just a subset. For action frames, a side effect is that the kernel will not reply to unknown action frames when they are registered by userspace. Used by wpa_supplicant for P2P also for probe requests. Related events: NL80211_CMD_FRAME, NL80211_CMD_FRAME_TX_STATUS. Prior to some work, this was called NL80211_CMD_REGISTER_ACTION, NL80211_CMD_ACTION, NL80211_CMD_ACTION_TX_STATUS.
+    *       (not a command) the ability to restrict the supported rates so
+    *        * that the P2P requirement of not using 11b rates can be fulfilled. This is still somewhat WIP for scanning, action frame TX etc.
+==== cfg80211's struct API ====
+This just mirrors nl80211 with function/method calls etc.
+==== mac80211's driver API ====
+    *         * A remain_on_channel (see above in nl80211) hardware offload
+    *         *  * complete with canceling it and events
+    *         *   WIP: complete hardware offload for mgmt-tx (see above in nl80211)
+    *         *    * through a single function call
+===== Interface types =====
+nl80211/cfg80211 currently define the P2P interface types P2P_CLIENT and P2P_GO, but wpa_supplicant doesn't use them, it still uses regular STA/AP interfaces. This is mostly because we haven't figured out a good way in the supplicant to distinguish between normal "STA" and P2P-client yet. The new P2P interface types will be needed later.
+===== Driver considerations =====
+Drivers must currently only support AP and STA modes, and must be able to function during off-channel periods. They must also be able to receive probe requests even while in station mode, as indicated by mac80211 by the FIF_PROBE_REQ filter flag.
+With the patches that I'm working on, drivers may optionally implement the p2p_start_listen/stop_listen callback to allow offload to the device for these operations. Additionally, they will be able to implement off-channel TX callbacks (but this is still WIP).

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