mac80211: send (QoS) Null if no buffered frames

For PS-poll, there's a possible race between
us expiring a frame and the station polling
for it -- send it a null frame in that case.

For uAPSD, the standard says that we have to
send a frame in each SP, so send null if we
don't have any other frames.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

3 files changed, 92 insertions, 12 deletions

diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 674b23ea14d7..da3206450192 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -1272,6 +1272,7 @@ void mac80211_ev_michael_mic_failure(struct ieee80211_sub_if_data *sdata, int ke
                                      struct ieee80211_hdr *hdr, const u8 *tsc,
                                      gfp_t gfp);
 void ieee80211_set_wmm_default(struct ieee80211_sub_if_data *sdata);
+void ieee80211_xmit(struct ieee80211_sub_if_data *sdata, struct sk_buff *skb);
 void ieee80211_tx_skb(struct ieee80211_sub_if_data *sdata, struct sk_buff *skb);
 void ieee802_11_parse_elems(u8 *start, size_t len,
                             struct ieee802_11_elems *elems);
diff --git a/net/mac80211/sta_info.c b/net/mac80211/sta_info.c
index f9079e478f77..d9cb56f548a9 100644
--- a/net/mac80211/sta_info.c
+++ b/net/mac80211/sta_info.c
@@ -24,6 +24,7 @@
 #include "sta_info.h"
 #include "debugfs_sta.h"
 #include "mesh.h"
+#include "wme.h"
 
 /**
  * DOC: STA information lifetime rules
@@ -247,10 +248,16 @@ static void sta_unblock(struct work_struct *wk)
                 ieee80211_sta_ps_deliver_wakeup(sta);
         else if (test_and_clear_sta_flags(sta, WLAN_STA_PSPOLL)) {
                 clear_sta_flags(sta, WLAN_STA_PS_DRIVER);
+
+                local_bh_disable();
                 ieee80211_sta_ps_deliver_poll_response(sta);
+                local_bh_enable();
         } else if (test_and_clear_sta_flags(sta, WLAN_STA_UAPSD)) {
                 clear_sta_flags(sta, WLAN_STA_PS_DRIVER);
+
+                local_bh_disable();
                 ieee80211_sta_ps_deliver_uapsd(sta);
+                local_bh_enable();
         } else
                 clear_sta_flags(sta, WLAN_STA_PS_DRIVER);
 }
@@ -1157,6 +1164,70 @@ void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta)
 #endif /* CONFIG_MAC80211_VERBOSE_PS_DEBUG */
 }
 
+static void ieee80211_send_null_response(struct ieee80211_sub_if_data *sdata,
+                                         struct sta_info *sta, int tid,
+                                         bool uapsd)
+{
+        struct ieee80211_local *local = sdata->local;
+        struct ieee80211_qos_hdr *nullfunc;
+        struct sk_buff *skb;
+        int size = sizeof(*nullfunc);
+        __le16 fc;
+        bool qos = test_sta_flags(sta, WLAN_STA_WME);
+        struct ieee80211_tx_info *info;
+
+        if (qos) {
+                fc = cpu_to_le16(IEEE80211_FTYPE_DATA |
+                                 IEEE80211_STYPE_QOS_NULLFUNC |
+                                 IEEE80211_FCTL_FROMDS);
+        } else {
+                size -= 2;
+                fc = cpu_to_le16(IEEE80211_FTYPE_DATA |
+                                 IEEE80211_STYPE_NULLFUNC |
+                                 IEEE80211_FCTL_FROMDS);
+        }
+
+        skb = dev_alloc_skb(local->hw.extra_tx_headroom + size);
+        if (!skb)
+                return;
+
+        skb_reserve(skb, local->hw.extra_tx_headroom);
+
+        nullfunc = (void *) skb_put(skb, size);
+        nullfunc->frame_control = fc;
+        nullfunc->duration_id = 0;
+        memcpy(nullfunc->addr1, sta->sta.addr, ETH_ALEN);
+        memcpy(nullfunc->addr2, sdata->vif.addr, ETH_ALEN);
+        memcpy(nullfunc->addr3, sdata->vif.addr, ETH_ALEN);
+
+        if (qos) {
+                skb->priority = tid;
+
+                skb_set_queue_mapping(skb, ieee802_1d_to_ac[tid]);
+
+                nullfunc->qos_ctrl = cpu_to_le16(tid);
+
+                if (uapsd)
+                        nullfunc->qos_ctrl |=
+                                cpu_to_le16(IEEE80211_QOS_CTL_EOSP);
+        }
+
+        info = IEEE80211_SKB_CB(skb);
+
+        /*
+         * Tell TX path to send this frame even though the
+         * STA may still remain is PS mode after this frame
+         * exchange.
+         */
+        info->flags |= IEEE80211_TX_CTL_POLL_RESPONSE;
+
+        if (uapsd)
+                info->flags |= IEEE80211_TX_STATUS_EOSP |
+                               IEEE80211_TX_CTL_REQ_TX_STATUS;
+
+        ieee80211_xmit(sdata, skb);
+}
+
 static void
 ieee80211_sta_ps_deliver_response(struct sta_info *sta,
                                   int n_frames, u8 ignored_acs,
@@ -1228,19 +1299,28 @@ ieee80211_sta_ps_deliver_response(struct sta_info *sta,
         }
 
         if (!found) {
-#ifdef CONFIG_MAC80211_VERBOSE_PS_DEBUG
+                int tid;
+
                 /*
-                 * FIXME: This can be the result of a race condition between
-                 *        us expiring a frame and the station polling for it.
-                 *        Should we send it a null-func frame indicating we
-                 *        have nothing buffered for it?
+                 * For PS-Poll, this can only happen due to a race condition
+                 * when we set the TIM bit and the station notices it, but
+                 * before it can poll for the frame we expire it.
+                 *
+                 * For uAPSD, this is said in the standard (11.2.1.5 h):
+                 *      At each unscheduled SP for a non-AP STA, the AP shall
+                 *      attempt to transmit at least one MSDU or MMPDU, but no
+                 *      more than the value specified in the Max SP Length field
+                 *      in the QoS Capability element from delivery-enabled ACs,
+                 *      that are destined for the non-AP STA.
+                 *
+                 * Since we have no other MSDU/MMPDU, transmit a QoS null frame.
                  */
-                if (reason == IEEE80211_FRAME_RELEASE_PSPOLL)
-                        printk(KERN_DEBUG "%s: STA %pM sent PS Poll even "
-                               "though there are no buffered frames for it\n",
-                               sdata->name, sta->sta.addr);
-#endif /* CONFIG_MAC80211_VERBOSE_PS_DEBUG */
 
+                /* This will evaluate to 1, 3, 5 or 7. */
+                tid = 7 - ((ffs(~ignored_acs) - 1) << 1);
+
+                ieee80211_send_null_response(sdata, sta, tid,
+                                reason == IEEE80211_FRAME_RELEASE_UAPSD);
                 return;
         }
 
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index a0676d39fe8f..5bf91c43c88c 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1520,8 +1520,7 @@ static int ieee80211_skb_resize(struct ieee80211_sub_if_data *sdata,
         return 0;
 }
 
-static void ieee80211_xmit(struct ieee80211_sub_if_data *sdata,
-                           struct sk_buff *skb)
+void ieee80211_xmit(struct ieee80211_sub_if_data *sdata, struct sk_buff *skb)
 {
         struct ieee80211_local *local = sdata->local;
         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);