---

yaml
---
r: 134086
b: refs/heads/master
c: d1c3a37
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 2bf30fabadbdcb535b057afc92aba015884847dc
+refs/heads/master: d1c3a37ceeb1a5ea02991a0476355f1a1d3b3e83

trunk/Documentation/DocBook/mac80211.tmpl

@@ -165,8 +165,8 @@ usage should require reading the full document.
 !Pinclude/net/mac80211.h Frame format
       </sect1>
       <sect1>
-        <title>Alignment issues</title>
-        <para>TBD</para>
+        <title>Packet alignment</title>
+!Pnet/mac80211/rx.c Packet alignment
       </sect1>
       <sect1>
         <title>Calling into mac80211 from interrupts</title>

trunk/net/mac80211/rx.c

@@ -102,7 +102,7 @@ ieee80211_rx_radiotap_len(struct ieee80211_local *local,
 	return len;
 }
 
-/**
+/*
  * ieee80211_add_rx_radiotap_header - add radiotap header
  *
  * add a radiotap header containing all the fields which the hardware provided.
@@ -371,39 +371,50 @@ static void ieee80211_parse_qos(struct ieee80211_rx_data *rx)
 	rx->skb->priority = (tid > 7) ? 0 : tid;
 }
 
-static void ieee80211_verify_ip_alignment(struct ieee80211_rx_data *rx)
+/**
+ * DOC: Packet alignment
+ *
+ * Drivers always need to pass packets that are aligned to two-byte boundaries
+ * to the stack.
+ *
+ * Additionally, should, if possible, align the payload data in a way that
+ * guarantees that the contained IP header is aligned to a four-byte
+ * boundary. In the case of regular frames, this simply means aligning the
+ * payload to a four-byte boundary (because either the IP header is directly
+ * contained, or IV/RFC1042 headers that have a length divisible by four are
+ * in front of it).
+ *
+ * With A-MSDU frames, however, the payload data address must yield two modulo
+ * four because there are 14-byte 802.3 headers within the A-MSDU frames that
+ * push the IP header further back to a multiple of four again. Thankfully, the
+ * specs were sane enough this time around to require padding each A-MSDU
+ * subframe to a length that is a multiple of four.
+ *
+ * Padding like Atheros hardware adds which is inbetween the 802.11 header and
+ * the payload is not supported, the driver is required to move the 802.11
+ * header to be directly in front of the payload in that case.
+ */
+static void ieee80211_verify_alignment(struct ieee80211_rx_data *rx)
 {
-#ifdef CONFIG_MAC80211_DEBUG_PACKET_ALIGNMENT
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)rx->skb->data;
 	int hdrlen;
 
+#ifndef CONFIG_MAC80211_DEBUG_PACKET_ALIGNMENT
+	return;
+#endif
+
+	if (WARN_ONCE((unsigned long)rx->skb->data & 1,
+		      "unaligned packet at 0x%p\n", rx->skb->data))
+		return;
+
 	if (!ieee80211_is_data_present(hdr->frame_control))
 		return;
 
-	/*
-	 * Drivers are required to align the payload data in a way that
-	 * guarantees that the contained IP header is aligned to a four-
-	 * byte boundary. In the case of regular frames, this simply means
-	 * aligning the payload to a four-byte boundary (because either
-	 * the IP header is directly contained, or IV/RFC1042 headers that
-	 * have a length divisible by four are in front of it.
-	 *
-	 * With A-MSDU frames, however, the payload data address must
-	 * yield two modulo four because there are 14-byte 802.3 headers
-	 * within the A-MSDU frames that push the IP header further back
-	 * to a multiple of four again. Thankfully, the specs were sane
-	 * enough this time around to require padding each A-MSDU subframe
-	 * to a length that is a multiple of four.
-	 *
-	 * Padding like atheros hardware adds which is inbetween the 802.11
-	 * header and the payload is not supported, the driver is required
-	 * to move the 802.11 header further back in that case.
-	 */
 	hdrlen = ieee80211_hdrlen(hdr->frame_control);
 	if (rx->flags & IEEE80211_RX_AMSDU)
 		hdrlen += ETH_HLEN;
-	WARN_ON_ONCE(((unsigned long)(rx->skb->data + hdrlen)) & 3);
-#endif
+	WARN_ONCE(((unsigned long)(rx->skb->data + hdrlen)) & 3,
+		  "unaligned IP payload at 0x%p\n", rx->skb->data + hdrlen);
 }
 
 
@@ -1267,10 +1278,37 @@ ieee80211_deliver_skb(struct ieee80211_rx_data *rx)
 	}
 
 	if (skb) {
-		/* deliver to local stack */
-		skb->protocol = eth_type_trans(skb, dev);
-		memset(skb->cb, 0, sizeof(skb->cb));
-		netif_rx(skb);
+		int align __maybe_unused;
+
+#if defined(CONFIG_MAC80211_DEBUG_PACKET_ALIGNMENT) || !defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
+		/*
+		 * 'align' will only take the values 0 or 2 here
+		 * since all frames are required to be aligned
+		 * to 2-byte boundaries when being passed to
+		 * mac80211. That also explains the __skb_push()
+		 * below.
+		 */
+		align = (unsigned long)skb->data & 4;
+		if (align) {
+			if (WARN_ON(skb_headroom(skb) < 3)) {
+				dev_kfree_skb(skb);
+				skb = NULL;
+			} else {
+				u8 *data = skb->data;
+				size_t len = skb->len;
+				u8 *new = __skb_push(skb, align);
+				memmove(new, data, len);
+				__skb_trim(skb, len);
+			}
+		}
+#endif
+
+		if (skb) {
+			/* deliver to local stack */
+			skb->protocol = eth_type_trans(skb, dev);
+			memset(skb->cb, 0, sizeof(skb->cb));
+			netif_rx(skb);
+		}
 	}
 
 	if (xmit_skb) {
@@ -1339,14 +1377,20 @@ ieee80211_rx_h_amsdu(struct ieee80211_rx_data *rx)
 		if (remaining <= subframe_len + padding)
 			frame = skb;
 		else {
-			frame = dev_alloc_skb(local->hw.extra_tx_headroom +
-					      subframe_len);
+			/*
+			 * Allocate and reserve two bytes more for payload
+			 * alignment since sizeof(struct ethhdr) is 14.
+			 */
+			frame = dev_alloc_skb(
+				ALIGN(local->hw.extra_tx_headroom, 4) +
+				subframe_len + 2);
 
 			if (frame == NULL)
 				return RX_DROP_UNUSABLE;
 
-			skb_reserve(frame, local->hw.extra_tx_headroom +
-				    sizeof(struct ethhdr));
+			skb_reserve(frame,
+				    ALIGN(local->hw.extra_tx_headroom, 4) +
+				    sizeof(struct ethhdr) + 2);
 			memcpy(skb_put(frame, ntohs(len)), skb->data,
 				ntohs(len));
 
@@ -1976,7 +2020,7 @@ static void __ieee80211_rx_handle_packet(struct ieee80211_hw *hw,
 		rx.flags |= IEEE80211_RX_IN_SCAN;
 
 	ieee80211_parse_qos(&rx);
-	ieee80211_verify_ip_alignment(&rx);
+	ieee80211_verify_alignment(&rx);
 
 	skb = rx.skb;