From owner-freebsd-current@FreeBSD.ORG Wed Jun 18 14:08:11 2014 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 2A12436E for ; Wed, 18 Jun 2014 14:08:11 +0000 (UTC) Received: from bigwig.baldwin.cx (bigwig.baldwin.cx [IPv6:2001:470:1f11:75::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 03B5C2781 for ; Wed, 18 Jun 2014 14:08:11 +0000 (UTC) Received: from jhbbsd.localnet (unknown [209.249.190.124]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id E300FB94B; Wed, 18 Jun 2014 10:08:09 -0400 (EDT) From: John Baldwin To: freebsd-current@freebsd.org Subject: Re: [RFC] Huge sysctl patch for the kernel coming - work in progress Date: Wed, 18 Jun 2014 09:44:17 -0400 User-Agent: KMail/1.13.5 (FreeBSD/8.4-CBSD-20140415; KDE/4.5.5; amd64; ; ) References: <53A179D5.8020604@selasky.org> In-Reply-To: <53A179D5.8020604@selasky.org> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201406180944.17762.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Wed, 18 Jun 2014 10:08:10 -0400 (EDT) Cc: Hans Petter Selasky X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 18 Jun 2014 14:08:11 -0000 On Wednesday, June 18, 2014 7:36:53 am Hans Petter Selasky wrote: > Hi, > > Sometimes sysctl's default value needs to be setup at boot time and not > when the rc.d/sysctl is running. Currently this is done by having two > statements in the kernel: > > TUNABLE_INT("net.graph.mppe.log_max_rekey", &mppe_log_max_rekey); > SYSCTL_INT(_net_graph_mppe, OID_AUTO, log_max_rekey, CTLFLAG_RW, > > I want to simplify this to: > > SYSCTL_INT(_net_graph_mppe, OID_AUTO, log_max_rekey, CTLFLAG_RWTUN, > > In other words if the existing CTLFLAG_TUN is set, the sysctl will > automatically be pre-loaded with values from /boot/loader.conf. > > The reason we don't want the current approach is: > > 1) It duplicates the sysctl path in the TUNABLE statement. > 2) It does not work very well for dynamically attached sysctls. There is > a lot of code overhead computing the TUNABLE() path before the TUNABLE() > can be fetched. > > Here is a work in progress: > > http://home.selasky.org:8192/sysctl_tunable.diff > > In most cases my patch is fine, but in some other cases I need some > input, like in the VM subsystem when doing init, I'm not sure if the > SYSINIT() for subsystem SI_SUB_KMEM, which sysctl's are using, has > already been executed. I think this is a good idea, but it's also true you can just leave separate TUNABLE_ statements without setting the CTLFLAG_TUN flag for cases you aren't sure about for now. It probably makes sense to do these changes in stages. I was going to suggest using sbuf() for building the tunable name, but that doesn't work since you have to build it in reverse. -- John Baldwin