From owner-freebsd-net@FreeBSD.ORG Tue Dec 3 18:44:40 2013 Return-Path: Delivered-To: net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id D131A16C; Tue, 3 Dec 2013 18:44:40 +0000 (UTC) Received: from bigwig.baldwin.cx (bigwig.baldwin.cx [IPv6:2001:470:1f11:75::1]) (using TLSv1 with cipher ADH-CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id A7DE718C5; Tue, 3 Dec 2013 18:44:40 +0000 (UTC) Received: from jhbbsd.localnet (unknown [209.249.190.124]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id 1C200B972; Tue, 3 Dec 2013 13:44:39 -0500 (EST) From: John Baldwin To: freebsd-net@freebsd.org Subject: Re: Defaults for if_capenable and detecting user initiated changes Date: Tue, 3 Dec 2013 12:13:41 -0500 User-Agent: KMail/1.13.5 (FreeBSD/8.4-CBSD-20130906; KDE/4.5.5; amd64; ; ) References: <0E13D481-9D6D-4B52-A5AD-B671BF3A85AF@scsiguy.com> In-Reply-To: <0E13D481-9D6D-4B52-A5AD-B671BF3A85AF@scsiguy.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <201312031213.41677.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Tue, 03 Dec 2013 13:44:39 -0500 (EST) Cc: "Justin T. Gibbs" , Roger Pau =?utf-8?q?Monn=C3=A9?= , net@freebsd.org X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 03 Dec 2013 18:44:40 -0000 On Wednesday, November 27, 2013 12:59:08 pm Justin T. Gibbs wrote: > Hi net, >=20 > I=E2=80=99m reviewing a patch from Roger Pau Monn=C3=A9 for the Xen netfr= ont driver. The=20 goal of the change is to avoid disturbing the user=E2=80=99s settings for t= he=20 interface just because the backend device has changed or the connection to = the=20 backend was reset. I=E2=80=99ve attached the latest version of the patch. >=20 > The current patch leaves the interface settings alone if they can be=20 supported by the newly attached backend. What would be ideal is to enable= =20 capabilities that default to being enabled if they were not explicitly=20 disabled by the user and can be supported by the new backend. Unfortunatel= y,=20 I don=E2=80=99t think the if_capenable and if_capabilities fields are descr= iptive=20 enough to deal with an interface whose capabilities can change at runtime. = =20 Just as can be done with link speed, some of these settings need to allow a= n=20 =E2=80=9Cauto/default=E2=80=9D setting in addition to on or off. This woul= d allow the user to=20 explicitly disable a capability if needed, but generally allow the system t= o=20 chose the most optimal settings when they are supported. Would this be=20 difficult to add? Couldn't you maintain this state in the Xen netfront driver's softc? You already get the ioctls that track changes to the capenable field, so you when a change explicitly disables a capability you can set that in a 'forced off' or 'forced on' field. Perhaps more of a 'forced' field that you just update by doing: sc->capforced |=3D (oldcapenable ^ newcapenable) However, it's not clear to me if you can get the underlying adapters initial capenable list. If so, I think capforced should be all you need to handle this (though it might be easier if you have separate forcedon and forcedoff fields). =2D-=20 John Baldwin