Date: Tue, 3 Dec 2013 12:13:41 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-net@freebsd.org Cc: "Justin T. Gibbs" <gibbs@scsiguy.com>, Roger Pau =?utf-8?q?Monn=C3=A9?= <royger@freebsd.org>, net@freebsd.org Subject: Re: Defaults for if_capenable and detecting user initiated changes Message-ID: <201312031213.41677.jhb@freebsd.org> In-Reply-To: <0E13D481-9D6D-4B52-A5AD-B671BF3A85AF@scsiguy.com> References: <0E13D481-9D6D-4B52-A5AD-B671BF3A85AF@scsiguy.com>
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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
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