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Date: Wed, 24 Jun 2009 06:47:50 -0400 From: Neil Horman <nhorman@...driver.com> To: Nicholas Van Orton <turanammo@...il.com> Cc: netdev@...r.kernel.org Subject: Re: e100 skb allocation On Wed, Jun 24, 2009 at 02:19:48PM +0530, Nicholas Van Orton wrote: > Hello, > > For the Intel 8256 Ethernet Controller (e100.c), I notice that at the > time of skb allocation using netdev_alloc_skb() and just before > calling skb_reserve(), rx->skb->head and rx->skb->tail do not point to > the same location. In fact they are already 16bytes apart. After > calling skb_reserve(), which would add a 2 byte padding, head and > tail would be 18 bytes apart. Is this behaviour correct? Shouldn't the > ethernet header be 14+2 bytes after padding? Why aren't head and tail > at the same location at the beginning? > Yes, its fine (although IIRC it should be 32, rather than 16 bytes). netdev_alloc_skb, in its implementation, allocates an skb that is NET_SKB_PAD bytes larger than the caller requested, then it calls skb_reserve internally to add NET_SKB_PAD bytes of data to the skb's buffer. Neil > > Thanks and regards, > Nicholas > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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