From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: Netlink for kernel<->user space communication? Date: Mon, 7 May 2012 15:33:07 -0700 Message-ID: <20120507153307.551b29ed@nehalam.linuxnetplumber.net> References: <4FA817C8.9040204@xdin.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: "netdev@vger.kernel.org" To: Arvid Brodin Return-path: Received: from mail.vyatta.com ([76.74.103.46]:52583 "EHLO mail.vyatta.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753340Ab2EGWdL (ORCPT ); Mon, 7 May 2012 18:33:11 -0400 In-Reply-To: <4FA817C8.9040204@xdin.com> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 7 May 2012 18:43:23 +0000 Arvid Brodin wrote: > On Tue, 24 Apr 2012 16:57:55 -0700 > Stephen Hemminger wrote: > > On Tue, 24 Apr 2012 23:52:34 +0000 > > Arvid Brodin wrote: > > > >> Hi. > >> > >> I'm writing a kernel driver for the HSR protocol, a standard for high availability > >> networks. I want to send messages from the kernel to user space about broken network > >> links. I also want user space to be able to ask the kernel about its view of the status of > >> nodes on the network. > >> > >> Netlink seems like a good tool for this. (Is it?) > > > > Yes. > > > >> But do I use raw netlink? (Described here: http://www.linuxjournal.com/article/7356 - but > >> this seems a bit out of date, the kernel API description differs from today's kernel > >> implementation.) > > > > No. Your driver probably looks like a device so you should be > > using rtnetlink messages. > > I'm already using rtnetlink messages to add and remove my device, which works fine (see > e.g. http://www.spinics.net/lists/netdev/msg192817.html - although I didn't think it > meaningful to include the iproute2 patch here, until the kernel part is ready). > > The protocol specifies transmission of "supervision frames" every 2 seconds, e.g. to check > link integrity. Every such frame should be received from two directions in the ring - if > only one is received, then there is a link problem. Why not just manipulate the carrier or operational state (see Documentation/networking/operstate) and use the existing notification on link changes. If you don't get heartbeat then change the state of the device to indicate lower device is down with set_operstate(), the necessary link everts propgate back as netlink events. > I'd like to notify user space about every such occurence. Is there a rtnetlink message > type that fits this? The stuff in rtnetlink.h seems to be mostly concerned with specific > user space commands (there is something called RTNLGRP_NOTIFY but I couldn't find any > instances of it being used in the kernel, nor any documentation). > I am trying to steer you to use existing API's because then existing programs and infrastructure can deal with the new device type.