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>

diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 674b23e..da32064 100644 (file)
--- 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 f9079e4..d9cb56f 100644 (file)
--- 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 a0676d3..5bf91c4 100644 (file)
--- 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);