From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH] net: af_packet: Don't initialize vnet_hdr Date: Thu, 12 May 2011 17:36:08 -0400 (EDT) Message-ID: <20110512.173608.1652572492952866283.davem@davemloft.net> References: <18a010357eb63dfd50751c5eb529f6261cf90ecd.1305232529.git.joe@perches.com> <20110512.172623.220889608152651989.davem@davemloft.net> <1305236000.6124.67.camel@Joe-Laptop> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org To: joe@perches.com Return-path: In-Reply-To: <1305236000.6124.67.camel@Joe-Laptop> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org From: Joe Perches Date: Thu, 12 May 2011 14:33:20 -0700 > On Thu, 2011-05-12 at 17:26 -0400, David Miller wrote: >> From: Joe Perches >> Date: Thu, 12 May 2011 13:36:10 -0700 >> >> > Save a memset, initialize only the portion necessary. >> > >> > packet_snd either gets this structure completely from >> > memcpy_fromiovec or uses only the hdr_len set to 0, >> > so don't always initialize the structure to 0. >> > >> > Signed-off-by: Joe Perches >> >> On ARM this won't be tightly packed, therefore you'll leave >> uninitialized pieces of padding in this structure and this >> thing is an "on-the-wire" network header. >> >> I'm not applying this. > > I believe that it's only sent when po->has_vnet_hdr > is set. In that case, it's completely filled from > memcpy_fromiovec. In the not set po->has_vnet_hdr case, > only vnet_hdr.hdr_len is accessed by packet_alloc_skb. I think with the way this code is protecting accesses to vnet_hdr, it's going to start warning that some parts "may" be use uninitialized. It's also slightly ugly to partially initialize these on-stack things. I would rather see the code rearranged such that this sort of hackish scheme isn't necessary. Again, I'm not applying this.