From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754061Ab1GFXYU (ORCPT ); Wed, 6 Jul 2011 19:24:20 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:34246 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753887Ab1GFXYT (ORCPT ); Wed, 6 Jul 2011 19:24:19 -0400 Subject: Re: [PATCH V8 2/4 net-next] skbuff: skb supports zero-copy buffers From: Shirley Ma To: Zan Lynx Cc: David Miller , mst@redhat.com, netdev@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <4E14E939.5040904@acm.org> References: <1309990932.10209.19.camel@localhost.localdomain> <4E14E939.5040904@acm.org> Content-Type: text/plain; charset="UTF-8" Date: Wed, 06 Jul 2011 16:24:14 -0700 Message-ID: <1309994654.10209.29.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 (2.28.3-1.fc12) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2011-07-06 at 17:01 -0600, Zan Lynx wrote: > On 7/6/2011 4:22 PM, Shirley Ma wrote: > > This patch adds userspace buffers support in skb shared info. A new > > struct skb_ubuf_info is needed to maintain the userspace buffers > > argument and index, a callback is used to notify userspace to > release > > the buffers once lower device has done DMA (Last reference to that > skb > > has gone). > > > > If there is any userspace apps to reference these userspace buffers, > > then these userspaces buffers will be copied into kernel. This way > we > > can prevent userspace apps from holding these userspace buffers too > long. > > > > Use destructor_arg to point to the userspace buffer info; a new tx > flags > > SKBTX_DEV_ZEROCOPY is added for zero-copy buffer check. > > > > Signed-off-by: Shirley Ma > > I was just reading this patch and noticed that you check if > uarg->callback is set before calling it in skb_release_data, but you > do > not check before calling it in skb_copy_ubufs. > > I was only skimming so I have probably missed something... It is a redundant check. The userspace buffer info always has a callback to release the buffers. I should have removed it after using tx_flags. Thanks Shirley