From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AE880C2D0DB for ; Fri, 24 Jan 2020 14:52:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7562520838 for ; Fri, 24 Jan 2020 14:52:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579877567; bh=SWQtWFvP2yM5RTM0cJf3qzdhWsmk+CUpbrJZ2ck+Zxs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=eDI2+EZk2E4wa5O7yvH0VPRsFwwixxrfhmyJHH6fmJYgp1CLQOZUl93p2nf98UuSy gryg+hs55FsRU/fNvadGZHwa5lGKN4GbVOHzJNVbMMMn4EmM4d/XiPpaooPUjlfckL HDgPp19I63qrcF/ffswk4rdxafehEQY3F2uU3hHY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730964AbgAXOwq (ORCPT ); Fri, 24 Jan 2020 09:52:46 -0500 Received: from mail.kernel.org ([198.145.29.99]:44680 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730287AbgAXOwq (ORCPT ); Fri, 24 Jan 2020 09:52:46 -0500 Received: from cakuba (c-73-93-4-247.hsd1.ca.comcast.net [73.93.4.247]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A720720704; Fri, 24 Jan 2020 14:52:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579877565; bh=SWQtWFvP2yM5RTM0cJf3qzdhWsmk+CUpbrJZ2ck+Zxs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=OCVmpaFORc4TqvptdkWJvnSmyl70Z5uEf4IYVdy2heKCgllI6QmjqNjE5dPmwoMc5 alByYmV1Ni3acbhUsPp8oHgHQwlQGcgyxLMskSrIWb1kCQj5giif02TdhILDTAV40O JnSNpt0ygT2a7bzyGY/sTqSgY1yvQldsjg1z3OsY= Date: Fri, 24 Jan 2020 06:52:44 -0800 From: Jakub Kicinski To: Daniel Borkmann Cc: Luigi Rizzo , netdev@vger.kernel.org, Jesper Dangaard Brouer , "David S. Miller" , sameehj@amazon.com, toke@redhat.com Subject: Re: [PATCH net-next] v2 net-xdp: netdev attribute to control xdpgeneric skb linearization Message-ID: <20200124065244.4cafef68@cakuba> In-Reply-To: <3a7e66da-7506-47a0-8733-8d48674176f9@iogearbox.net> References: <20200123232054.183436-1-lrizzo@google.com> <3a7e66da-7506-47a0-8733-8d48674176f9@iogearbox.net> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, 24 Jan 2020 10:55:19 +0100, Daniel Borkmann wrote: > > diff --git a/net/core/dev.c b/net/core/dev.c > > index 4dcc1b390667..13a671e45b61 100644 > > --- a/net/core/dev.c > > +++ b/net/core/dev.c > > @@ -4484,8 +4484,8 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb, > > * of XDP_PACKET_HEADROOM bytes. This is the guarantee that also > > * native XDP provides, thus we need to do it here as well. > > */ > > - if (skb_is_nonlinear(skb) || > > - skb_headroom(skb) < XDP_PACKET_HEADROOM) { > > + if (skb->dev->xdp_linearize && (skb_is_nonlinear(skb) || > > + skb_headroom(skb) < XDP_PACKET_HEADROOM)) { > > int hroom = XDP_PACKET_HEADROOM - skb_headroom(skb); > > int troom = skb->tail + skb->data_len - skb->end; > > I still think in order for this knob to be generally useful, we would need to > provide an equivalent of bpf_skb_pull_data() helper, which in generic XDP would then > pull in more data from non-linear section, and in native XDP would be a "no-op" since > the frame is already linear. Otherwise, as mentioned in previous thread, users would > have no chance to examine headers if they are not pre-pulled by the driver. Which takes us to the point of the ongoing work to allow multi-buffer frames in native mode. Sorry if this was already mentioned but this seems like the other side of the same coin, once we have multi-buffer semantics in native mode we can likely just replicate them for skbs, no?