On Fri, Nov 14, 2014 at 03:57:40PM +0900, Marcel Holtmann wrote: > Hi Luca, > > >>>>> I've updated wireless code on RHEL and get complain that now > >>>>> cfg80211 and rfkill modules are loaded on machines that do not have > >>>>> wireless hardware. Modules are auto-loaded because NetworkManager send > >>>>> nl80211 messages to check if there are wireless devices in the system. > >>>>> > >>>>> Hence my question, can we revert commit fb4e156886ce > >>>>> "nl80211: Add generic netlink module alias for cfg80211/nl80211" ? > >>>> > >>>> Realistically, we can't revert it, but only remove the > >>>> MODULE_ALIAS_GENL_FAMILY() line. > >>>> > >>>>> Auto loading nl80211 does not seems to be necessary, if there are > >>>>> wireless devices nl80211 will be loaded anyway. > >>>> > >>>> Maybe other applications would like to see an empty list of devices? But > >>>> OTOH, if they're robust at all, they have to cope with kernels not even > >>>> compiled with nl80211, so I guess for me I don't really see a big > >>>> difference in whether the module alias exists or not. > >>> > >>> auto-loading cfg80211 module when userspace requests nl80211 netlink > >>> family is exactly the right thing to do. Systems compiled without nl80211 > >>> support and systems with no wireless device attached are two different > >>> things. > >>> > >>> Someone can fix NetworkManager to not send nl80211 messages or just plain > >>> accept that cfg80211 will be loaded. > >> > >> NM uses nl80211 initially to determine whether *any* ethernet-type > >> interface (a) is actually WiFi, and (b) should be driven by nl80211 or > >> WEXT. Because of the variety of drivers (both in-kernel and > >> out-of-kernel) and the variety of kernel versions (NM supports back to > >> early 3.x series) we cannot rely on specific behavior. > >> > >> So given an ethernet-type interface, how do we determine that it is > >> wifi? > >> > >> DEVTYPE=wlan - not always reliable due to driver and kernel versions > >> > >> "phy80211" in sysfs: same reason; also doesn't capture WEXT or > >> out-of-tree drivers > >> > >> nl80211 calls: this is the only 100% reliable mechanism to detect > >> whether an ethernet-type interface is actually WiFi and nl80211-capable. > >> > >> And unfortunately calling nl80211 loads the module... > > > > So, basically the conclusion is: there's no way around it. If someone > > in userspace uses nl80211 it must be loaded, regardless of whether > > nl80211 is automatically loaded or if depmod bring it in. > > yes, that is how it should be. And actually that is how every other subsystem > does. Including modules that get loaded because we have a socket() system > call for an address family.
On other subsystems auto loading make sense. For example on netfiler, we really want to load netfiler modules when user-space want to configure it and started talking to it by socket. But here situation is different. If there is no hardware we can not configure it. Stanislaw -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
