From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathias Krause Subject: Re: [PATCH net-next 3/3] net: allow to leave the buffer fragmented in skb_cow_data() Date: Wed, 06 Nov 2013 10:49:18 +0100 Message-ID: <527A109E.5040000@secunet.com> References: <14f30e8f5f8405c1ca73b6d3a554441c1736142d.1381923854.git.mathias.krause@secunet.com> <20131106093028.GA18435@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "David S. Miller" , Steffen Klassert , Dmitry Tarnyagin , netdev@vger.kernel.org To: Herbert Xu Return-path: Received: from a.mx.secunet.com ([195.81.216.161]:49020 "EHLO a.mx.secunet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753854Ab3KFJtV (ORCPT ); Wed, 6 Nov 2013 04:49:21 -0500 In-Reply-To: <20131106093028.GA18435@gondor.apana.org.au> Sender: netdev-owner@vger.kernel.org List-ID: On 06.11.2013 10:30, Herbert Xu wrote: > On Tue, Nov 05, 2013 at 02:54:11PM +0100, Mathias Krause wrote: >> - /* If skb is cloned or its head is paged, reallocate >> - * head pulling out all the pages (pages are considered not writable >> - * at the moment even if they are anonymous). >> + /* If skb is cloned reallocate head pulling out all the pages (pages are >> + * considered not writable at the moment even if they are anonymous). >> */ > > Hang on, you haven't explained why it is OK to write to pages. Why wouldn't it if the skb isn't cloned? > What if said page is owned by the virt host or some app? How would one detect such a case. I could image not by testing skb_shinfo(skb)->nr_frags as it is right now? Regards, Mathias