Hi, > Agreed. I guess I just view nl80211.h as a sort of combination between > a uapi file and an actual manpage. And manpages do mention which kernel > version a certain feature/flag/whatever was added. Such info can be > useful in many ways, e.g. figuring out which kernel version might be > required for a certain piece of hardware, etc. Yeah, fair point, I just think it's better to document that behaviour as dependent on the flag, not the kernel version; this will continue to be true for drivers that don't set the flag in future kernels after all. IOW, I don't see how it does you any good to know that you're running on kernel version 5.4, when the flag isn't set you still have to follow the 4 steps you outlined. > > > + * @NL80211_EXT_FEATURE_LIVE_IFTYPE_CHANGE: This device supports switching > > > + * the IFTYPE of an interface without having to bring the device DOWN > > > + * first via RTNL. Exact semantics of this feature is driver > > > + * implementation dependent. > > > > That's not really nice. > > Sorry. This came from some doc changes I have pending. I think I wrote > this after looking at some fullmac drivers and how they handle mode > changes and the wording reflects the exasperation I felt at the time. > > Do you want to suggest some alternate wording? I think it is worth it > to have some fair warning in the docs stating that prior to version so > and so the semantics are completely driver dependent. Well, but you're trying to document/advertise the restrictions now. So this feels a bit insufficient, by advertising the feature flag the device is now saying "it's possible I can switch, but don't ask me how or when". (Cont'd below) So I don't really think it's the wording that bothers me so much as the fact that you're basically going only half the way documenting this. We have nothing now, which I can agree isn't a good thing, but adding a flag that says "maybe you can do it on this device" doesn't really change the status quo *much*, since that was already true before. It seems to me you'd rather want a definitive statement. > > > For mac80211, the following restrictions > > > + * apply: > > > + * - Only devices currently in IFTYPE AP, P2P_GO, P2P_CLIENT, > > > + * STATION, ADHOC and OCB can be switched. > > > + * - The target IFTYPE must be one of: AP, P2P_GO, P2P_CLIENT, > > > + * STATION, ADHOC or OCB. > > > + * Other drivers are expected to follow similar restrictions. > > > > Maybe we should instead have a "bitmask of interface types that can be > > switched while live" or something like that? > > > > I'm fine with that, but this would only apply to newer kernels, no? Sure, but all that you're doing here does. > Don't we at least want to attempt to state what the rules are for older > ones? That's what you did above for the NL80211_CMD_SET_INTERFACE documentation update, I don't think it would belong into the documentation for NL80211_EXT_FEATURE_LIVE_IFTYPE_CHANGE? And you wrote that this is what happens when the flag is *set* which by definition cannot happen in older kernels. > An alternative might be to simply state what the restrictions are and > just enforce those at the cfg80211 level. Sounds good to me, we do that for a lot of things. Basically that just takes it one step further - I said above we could advertise the restrictions, but once we do that cfg80211 knows and can also enforce it. johannes
