Re: [Xen-devel] [PATCH 5/6] xen/netback: try to pull a minimum of 72 bytes into the skb data area

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

Something odd happened with git-formatpatch here, there was a commit
message originally:

        xen/netback: try to pull a minimum of 72 bytes into the skb data area
        when receiving a packet into netback.  The previous number, 64, tended
        to place a fragment boundary in the middle of the TCP header options
        and led to unnecessary fragmentation in Windows <-> Windows
        networking.

Ian.

On Tue, 2010-02-23 at 16:47 +0000, Ian Campbell wrote:
> From: Steven Smith <ssmith@xxxxxxxxxxxxx>
> 
> ---
>  drivers/xen/netback/netback.c |    9 +++------
>  1 files changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/xen/netback/netback.c b/drivers/xen/netback/netback.c
> index e668704..0bc6398 100644
> --- a/drivers/xen/netback/netback.c
> +++ b/drivers/xen/netback/netback.c
> @@ -116,13 +116,10 @@ static inline int netif_page_index(struct page *pg)
>  /*
>   * This is the amount of packet we copy rather than map, so that the
>   * guest can't fiddle with the contents of the headers while we do
> - * packet processing on them (netfilter, routing, etc).  This could
> - * probably do with being larger, since 1) 64-bytes isn't necessarily
> - * long enough to cover a full christmas-tree ip+tcp header, let alone
> - * packet contents, and 2) the data is probably in cache anyway
> - * (though perhaps some other cpu's cache).
> + * packet processing on them (netfilter, routing, etc). 72 is enough
> + * to cover TCP+IP headers including options.
>   */
> -#define PKT_PROT_LEN 64
> +#define PKT_PROT_LEN 72
>  
>  static struct pending_tx_info {
>       struct xen_netif_tx_request req;



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