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Date: Fri, 5 Oct 2012 16:17:12 +0200 From: Daniel Borkmann <danborkmann@...earbox.net> To: Paul Chavent <Paul.Chavent@...ra.fr> Cc: davem@...emloft.net, edumazet@...gle.com, xemul@...allels.com, herbert@...dor.hengli.com.au, netdev@...r.kernel.org, johann.baudy@...-log.net, uaca@...mni.uv.es Subject: Re: [PATCH] Packet mmap : allow the user to choose the offset of the tx payload. On Fri, Oct 5, 2012 at 3:10 PM, Paul Chavent <Paul.Chavent@...ra.fr> wrote: > The tx offset of packet mmap tx ring used to be : > (TPACKET2_HDRLEN - sizeof(struct sockaddr_ll)) > > The problem is that depending on the usage of SOCK_DGRAM or > SOCK_RAW, the payload could be aligned or not. > > This patch allow to let the user give an offset for it's tx > payload if he desires. > > Signed-off-by: Paul Chavent <paul.chavent@...ra.fr> Can you provide an example when it doesn't hit TPACKET_ALIGNMENT? On the first look, could it be that your patch currently enforces the use of your tp_net's offset for *all* TX_RING users, even if they don't care about it? So in case off==0, you probably get a negative offset in case of SOCK_RAW, thus it won't hit the second if-statement. Sure, but this does not look intuitive in my opinion. Maybe, it's better to only enter this path if the offset *is* used by someone. Also, to my knowledge tp_net is currently only applied in receive path. So, if for whatever reason people did not explicitly set tp_net to 0, it might break their code, if there's a random offset in it, right? Best, Daniel -- 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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