From: Johannes Berg <johannes@xxxxxxxxxxxxxxxx> Date: Sun, 04 May 2008 23:32:25 +0200 > --- everything.orig/net/mac80211/iface.c 2008-05-04 23:24:17.000000000 +0200 > +++ everything/net/mac80211/iface.c 2008-05-04 23:31:46.000000000 +0200 > @@ -53,6 +53,15 @@ int ieee80211_if_add(struct net_device * > if (!ndev) > return -ENOMEM; > > + ndev->needed_headroom = local->tx_headroom + > + 4*6 /* four MAC addresses */ > + + 2 + 2 + 2 + 2 /* ctl, dur, seq, qos */ > + + 6 /* mesh */ > + + 8 /* rfc1042/bridge tunnel */ > + - ETH_HLEN /* ethernet hard_header_len */ > + + IEEE80211_ENCRYPT_HEADROOM; > + ndev->needed_tailroom = IEEE80211_ENCRYPT_TAILROOM; > + > ret = dev_alloc_name(ndev, ndev->name); > if (ret < 0) > goto fail; Where is the patch that adds these new members to struct netdevice, and where is the code that uses these new values? I even searched the netdev archives and couldn't find it. Anyways I see your basic idea and this may be the best way to handle the problem. The invariants would be: 1) LL_MAX_HEADER has to include all of these bits. 2) LL_RESERVED_SPACE*() has to take the new needed_headroom into account. Your patch which I can't find, which adds netdev->needed_*, probably does all of that. But I'm just making sure :-) Note that what would be really nice is if we could assert, in dev_queue_xmit, that the SKB has all of the necessary headroom, and give a WARN_ON_ONCE() backtrace if not. If we can ensure that, things like mac80211 and others will not need to skb_realloc_headroom() or anything like that unless they need to modify packet contents after skb->data and the packet is shared (ie. the pskb_expand_headroom(skb, 0, 0, GFP_*) case the TSO drivers use). -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
