wifi: mac80211: add a helper to fragment an element

The way this works is that you add all the element data,
keeping a pointer to the length field of the element.
Then call this helper function, which will fragment the
element if there was more than 255 bytes in the element,
memmove()ing the data back if needed.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/net/mac80211/util.c b/net/mac80211/util.c
index 6d6ba23aa074..2ff8d1ec564c 100644
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -4780,3 +4780,31 @@ u8 *ieee80211_ie_build_eht_cap(u8 *pos,
 
 	return pos;
 }
+
+void ieee80211_fragment_element(struct sk_buff *skb, u8 *len_pos)
+{
+	unsigned int elem_len;
+
+	if (!len_pos)
+		return;
+
+	elem_len = skb->data + skb->len - len_pos - 1;
+
+	while (elem_len > 255) {
+		/* this one is 255 */
+		*len_pos = 255;
+		/* remaining data gets smaller */
+		elem_len -= 255;
+		/* make space for the fragment ID/len in SKB */
+		skb_put(skb, 2);
+		/* shift back the remaining data to place fragment ID/len */
+		memmove(len_pos + 255 + 3, len_pos + 255 + 1, elem_len);
+		/* place the fragment ID */
+		len_pos += 255 + 1;
+		*len_pos = WLAN_EID_FRAGMENT;
+		/* and point to fragment length to update later */
+		len_pos++;
+	}
+
+	*len_pos = elem_len;
+}