Johannes and all mac80211 gurus, We encountered a problem that we use the extra_tx_headroom to reserve the headroom which we put the txdesc in. Current workaround is that we check our needed headroom size by skb_headroom() in the driver layer. Is extra_tx_headroom in struct ieee80211_hw always guaranteed? The header file describes: * @extra_tx_headroom: headroom to reserve in each transmit skb * for use by the driver (e.g. for transmit headers.) But when the skb goes through the ieee80211_amsdu_realloc_pad(), it does not take care of the extra_tx_headroom, i.e. the original reserved headroom might be eaten. Does the ieee80211_amsdu_realloc_pad() lacks some check for extra_tx_headroom or the extra_tx_headroom in mac80211 is not guaranteed? Furthermore, for the packet that would not be aggregate in A-MSDU and ndev->needed_headroom is not guaranteed, in this case whether mac80211 layer still guarantee the extra_tx_headroom ? Or mac80211 only guarantees the headroom of the skb which is built by itself ? Steven
