From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net-next] sk-filter: Add ability to get socket filter program (v2) Date: Thu, 01 Nov 2012 11:17:58 -0400 (EDT) Message-ID: <20121101.111758.587399436547929971.davem@davemloft.net> References: <509264AC.5090802@parallels.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: xemul@parallels.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:60173 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761978Ab2KAPSA (ORCPT ); Thu, 1 Nov 2012 11:18:00 -0400 In-Reply-To: <509264AC.5090802@parallels.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Pavel Emelyanov Date: Thu, 01 Nov 2012 16:01:48 +0400 > The SO_ATTACH_FILTER option is set only. I propose to add the get > ability by using SO_ATTACH_FILTER in getsockopt. To be less > irritating to eyes the SO_GET_FILTER alias to it is declared. This > ability is required by checkpoint-restore project to be able to > save full state of a socket. > > > There are two issues with getting filter back. > > First, kernel modifies the sock_filter->code on filter load, thus in > order to return the filter element back to user we have to decode it > into user-visible constants. Fortunately the modification in question > is interconvertible. > > Second, the BPF_S_ALU_DIV_K code modifies the command argument k to > speed up the run-time division by doing kernel_k = reciprocal(user_k). > Bad news is that different user_k may result in same kernel_k, so we > can't get the original user_k back. Good news is that we don't have > to do it. What we need to is calculate a user2_k so, that > > reciprocal(user2_k) == reciprocal(user_k) == kernel_k > > i.e. if it's re-loaded back the compiled again value will be exactly > the same as it was. That said, the user2_k can be calculated like this > > user2_k = reciprocal(kernel_k) > > with an exception, that if kernel_k == 0, then user2_k == 1. > > > The optlen argument is treated like this -- when zero, kernel returns > the amount of sock_fprog elements in filter, otherwise it should be > large enough for the sock_fprog array. > > changes since v1: > * Declared SO_GET_FILTER in all arch headers > * Added decode of vlan-tag codes > > Signed-off-by: Pavel Emelyanov Applied, thanks.