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Message-ID: <b9e8fcbd0906240928h6c5db9a6va48e42799376149e@mail.gmail.com> Date: Wed, 24 Jun 2009 21:58:38 +0530 From: Nicholas Van Orton <turanammo@...il.com> To: Neil Horman <nhorman@...driver.com> Cc: netdev@...r.kernel.org Subject: Re: e100 skb allocation On Wed, Jun 24, 2009 at 4:17 PM, Neil Horman<nhorman@...driver.com> wrote: > 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. > Thanks a bunch for steering me in the right direction. Things are much clearer now. 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
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