mac80211: add utility function to get header length

Take a __le16 directly rather than a host-endian value.
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/net/mac80211.h

@@ -1547,6 +1547,12 @@ unsigned int ieee80211_get_hdrlen_from_skb(const struct sk_buff *skb);
  */
 int ieee80211_get_hdrlen(u16 fc);
 
+/**
+ * ieee80211_hdrlen - get header length in bytes from frame control
+ * @fc: frame control field in little-endian format
+ */
+unsigned int ieee80211_hdrlen(__le16 fc);
+
 /**
  * ieee80211_get_tkip_key - get a TKIP rc4 for skb
  *

net/mac80211/util.c

@@ -133,6 +133,38 @@ int ieee80211_get_hdrlen(u16 fc)
 }
 EXPORT_SYMBOL(ieee80211_get_hdrlen);
 
+unsigned int ieee80211_hdrlen(__le16 fc)
+{
+	unsigned int hdrlen = 24;
+
+	if (ieee80211_is_data(fc)) {
+		if (ieee80211_has_a4(fc))
+			hdrlen = 30;
+		if (ieee80211_is_data_qos(fc))
+			hdrlen += IEEE80211_QOS_CTL_LEN;
+		goto out;
+	}
+
+	if (ieee80211_is_ctl(fc)) {
+		/*
+		 * ACK and CTS are 10 bytes, all others 16. To see how
+		 * to get this condition consider
+		 *   subtype mask:   0b0000000011110000 (0x00F0)
+		 *   ACK subtype:    0b0000000011010000 (0x00D0)
+		 *   CTS subtype:    0b0000000011000000 (0x00C0)
+		 *   bits that matter:         ^^^      (0x00E0)
+		 *   value of those: 0b0000000011000000 (0x00C0)
+		 */
+		if ((fc & cpu_to_le16(0x00E0)) == cpu_to_le16(0x00C0))
+			hdrlen = 10;
+		else
+			hdrlen = 16;
+	}
+out:
+	return hdrlen;
+}
+EXPORT_SYMBOL(ieee80211_hdrlen);
+
 unsigned int ieee80211_get_hdrlen_from_skb(const struct sk_buff *skb)
 {
 	const struct ieee80211_hdr *hdr = (const struct ieee80211_hdr *)skb->data;