Date: Fri, 6 Dec 2013 09:25:48 -0700 From: "Justin T. Gibbs" <gibbs@scsiguy.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-net@freebsd.org, =?iso-8859-1?Q?Roger_Pau_Monn=E9?= <royger@freebsd.org>, net@freebsd.org Subject: Re: Defaults for if_capenable and detecting user initiated changes Message-ID: <526A243B-7B66-45BD-9B45-3BFB04F1E16D@scsiguy.com> In-Reply-To: <201312031213.41677.jhb@freebsd.org> References: <0E13D481-9D6D-4B52-A5AD-B671BF3A85AF@scsiguy.com> <201312031213.41677.jhb@freebsd.org>
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On Dec 3, 2013, at 10:13 AM, John Baldwin <jhb@freebsd.org> wrote: > On Wednesday, November 27, 2013 12:59:08 pm Justin T. Gibbs wrote: >> Hi net, >> >> I’m reviewing a patch from Roger Pau Monné for the Xen netfront driver. The > goal of the change is to avoid disturbing the user’s settings for the > interface just because the backend device has changed or the connection to the > backend was reset. I’ve attached the latest version of the patch. >> >> The current patch leaves the interface settings alone if they can be > supported by the newly attached backend. What would be ideal is to enable > capabilities that default to being enabled if they were not explicitly > disabled by the user and can be supported by the new backend. Unfortunately, > I don’t think the if_capenable and if_capabilities fields are descriptive > enough to deal with an interface whose capabilities can change at runtime. > Just as can be done with link speed, some of these settings need to allow an > “auto/default” setting in addition to on or off. This would allow the user to > explicitly disable a capability if needed, but generally allow the system to > chose the most optimal settings when they are supported. Would this be > 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 |= (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). > > -- > John Baldwin Certainly this could be done in the Xen driver. The reason I posted my question, however, was to ask whether this should be more generically tracked by the if layer instead of handled by the underlying driver. Lots of user interfaces support a “restore defaults” capability (e.g. for the novice administrator who screws up, or as a step in writing a script/procedure that starts by getting to a known state), so I think this is interesting for more than this particular Xen issue. — Justin
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