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    SubjectRe: [PATCH 14/15] rfkill: do not allow userspace to override ALL RADIOS OFF
    On Thursday 22 May 2008, Henrique de Moraes Holschuh wrote:
    > On Tue, 20 May 2008, Ivo van Doorn wrote:
    > > On Sunday 18 May 2008, Henrique de Moraes Holschuh wrote:
    > > > SW_RFKILL_ALL is the "emergency power-off all radios" input event. It must
    > > > be handled, and must always do the same thing as far as the rfkill system
    > > > is concerned: all transmitters are to go *immediately* offline.
    > >
    > > I don't quite agree here. The SW_RFKILL_ALL key is the one send by thinkpad-acpi,
    > > what makes that key so special that is has to be handled differently then a key
    > > that only controls a single radio type?
    > Well, first there is no KEY involved, it is a SWITCH :-) But that's not
    > the reason it is special.
    > What makes SW_RFKILL_ALL special, is that it is the kernel view of *The*
    > RFKill Switch. SW_RFKILL_ALL is the event you get when the user
    > manipulates the very *thing* that created the "rfkill switch" term.

    So do keys that are pressed that only send the KEY_WLAN, KEY_BLUETOOTH or
    KEY_UWB signals. They all indicate the key has been pressed and the radios
    should be turned on/off.

    > You get that event when someone moves that slider switch in the side/top
    > of a laptop which has to kill all RF output in hardware as far as safety
    > regulations go. Therefore, it refers to the only rfkill switch that has
    > guidelines that say that it must always work, and that it must not be
    > possible to override it in software.

    That is a valid point, and rfkill is supposed to do that, but making
    a difference between RFKILL_ALL and the individual types is wrong
    because that won't result in a clearly defined expected behavior for all
    rfkill keys.

    > Too bad that doesn't apply to "removable" radio transmitters, like
    > PCMCIA and ExpressCard WLAN cards, USB RF transmitters, and so on...
    > probably, the user is expected to yank them off when he moves the switch
    > to the "no radios working here!" position. Well, we can do better. We
    > can make it apply to these other radio transmitters, too.

    Through the write-only rfkill class right? ;)

    > So yes, it *is* special when it is doing its "power DOWN the
    > transmitters" function. It is not special at all when it is in the
    > "allow radios to function if they want to" position, which is why I
    > special-cased only the "OFF" state.
    > IMHO, that makes it special enough to implement it in a different way
    > that is not subject to, e.g., brain damage in userspace.
    > As for thinkpad-acpi being the only in-tree code issuing that event so
    > far, well... I have seen laptops from many vendors with that switch, and
    > it is likely that the firmware of at least some of these laptops let you
    > know the state of the switch (like the thinkpad firmware does), so I'd
    > expect more users of SW_RFKILL_ALL to show up soon. I am just paving
    > the way.
    > That, and as an user, I'd really like to be able to implement a
    > KEY_RFKILL_ALL keycode to use when I don't have a proper SW_RFKILL_ALL
    > in my laptop. But one thing at a time. Small steps.
    > > All keys should have the same rules when it is pressed, so either all keys should
    > > force the change, or none of them should.
    > IMO, "kill ALL radios" events are is the only kind of rfkill input event
    > that have to *always work*, even if something in userspace tried to
    > configure it not to.

    Well the definition of "ALL radios" is the part that is the question, when the KEY_WLAN is
    pressed it would be "ALL WLAN radios" and should still have the same rules for allowing
    or disallowing userspace to overwrite the status.


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