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diff --git a/Documentation/rfkill.txt b/Documentation/rfkill.txt index 4d3ee317a4a..1b74b5f30af 100644 --- a/Documentation/rfkill.txt +++ b/Documentation/rfkill.txt @@ -1,575 +1,136 @@ -rfkill - RF switch subsystem support -==================================== +rfkill - RF kill switch support +=============================== -1 Introduction -2 Implementation details -3 Kernel driver guidelines -3.1 wireless device drivers -3.2 platform/switch drivers -3.3 input device drivers -4 Kernel API -5 Userspace support +1. Introduction +2. Implementation details +3. Kernel driver guidelines +4. Kernel API +5. Userspace support -1. Introduction: +1. Introduction -The rfkill switch subsystem exists to add a generic interface to circuitry that -can enable or disable the signal output of a wireless *transmitter* of any -type. By far, the most common use is to disable radio-frequency transmitters. +The rfkill subsystem provides a generic interface to disabling any radio +transmitter in the system. When a transmitter is blocked, it shall not +radiate any power. -Note that disabling the signal output means that the the transmitter is to be -made to not emit any energy when "blocked". rfkill is not about blocking data -transmissions, it is about blocking energy emission. +The subsystem also provides the ability to react on button presses and +disable all transmitters of a certain type (or all). This is intended for +situations where transmitters need to be turned off, for example on +aircraft. -The rfkill subsystem offers support for keys and switches often found on -laptops to enable wireless devices like WiFi and Bluetooth, so that these keys -and switches actually perform an action in all wireless devices of a given type -attached to the system. -The buttons to enable and disable the wireless transmitters are important in -situations where the user is for example using his laptop on a location where -radio-frequency transmitters _must_ be disabled (e.g. airplanes). -Because of this requirement, userspace support for the keys should not be made -mandatory. Because userspace might want to perform some additional smarter -tasks when the key is pressed, rfkill provides userspace the possibility to -take over the task to handle the key events. - -=============================================================================== -2: Implementation details +2. Implementation details The rfkill subsystem is composed of various components: the rfkill class, the rfkill-input module (an input layer handler), and some specific input layer events. -The rfkill class provides kernel drivers with an interface that allows them to -know when they should enable or disable a wireless network device transmitter. -This is enabled by the CONFIG_RFKILL Kconfig option. - -The rfkill class support makes sure userspace will be notified of all state -changes on rfkill devices through uevents. It provides a notification chain -for interested parties in the kernel to also get notified of rfkill state -changes in other drivers. It creates several sysfs entries which can be used -by userspace. See section "Userspace support". - -The rfkill-input module provides the kernel with the ability to implement a -basic response when the user presses a key or button (or toggles a switch) -related to rfkill functionality. It is an in-kernel implementation of default -policy of reacting to rfkill-related input events and neither mandatory nor -required for wireless drivers to operate. It is enabled by the -CONFIG_RFKILL_INPUT Kconfig option. - -rfkill-input is a rfkill-related events input layer handler. This handler will -listen to all rfkill key events and will change the rfkill state of the -wireless devices accordingly. With this option enabled userspace could either -do nothing or simply perform monitoring tasks. - -The rfkill-input module also provides EPO (emergency power-off) functionality -for all wireless transmitters. This function cannot be overridden, and it is -always active. rfkill EPO is related to *_RFKILL_ALL input layer events. - - -Important terms for the rfkill subsystem: - -In order to avoid confusion, we avoid the term "switch" in rfkill when it is -referring to an electronic control circuit that enables or disables a -transmitter. We reserve it for the physical device a human manipulates -(which is an input device, by the way): - -rfkill switch: - - A physical device a human manipulates. Its state can be perceived by - the kernel either directly (through a GPIO pin, ACPI GPE) or by its - effect on a rfkill line of a wireless device. - -rfkill controller: - - A hardware circuit that controls the state of a rfkill line, which a - kernel driver can interact with *to modify* that state (i.e. it has - either write-only or read/write access). - -rfkill line: - - An input channel (hardware or software) of a wireless device, which - causes a wireless transmitter to stop emitting energy (BLOCK) when it - is active. Point of view is extremely important here: rfkill lines are - always seen from the PoV of a wireless device (and its driver). - -soft rfkill line/software rfkill line: - - A rfkill line the wireless device driver can directly change the state - of. Related to rfkill_state RFKILL_STATE_SOFT_BLOCKED. - -hard rfkill line/hardware rfkill line: - - A rfkill line that works fully in hardware or firmware, and that cannot - be overridden by the kernel driver. The hardware device or the - firmware just exports its status to the driver, but it is read-only. - Related to rfkill_state RFKILL_STATE_HARD_BLOCKED. - -The enum rfkill_state describes the rfkill state of a transmitter: - -When a rfkill line or rfkill controller is in the RFKILL_STATE_UNBLOCKED state, -the wireless transmitter (radio TX circuit for example) is *enabled*. When the -it is in the RFKILL_STATE_SOFT_BLOCKED or RFKILL_STATE_HARD_BLOCKED, the -wireless transmitter is to be *blocked* from operating. - -RFKILL_STATE_SOFT_BLOCKED indicates that a call to toggle_radio() can change -that state. RFKILL_STATE_HARD_BLOCKED indicates that a call to toggle_radio() -will not be able to change the state and will return with a suitable error if -attempts are made to set the state to RFKILL_STATE_UNBLOCKED. - -RFKILL_STATE_HARD_BLOCKED is used by drivers to signal that the device is -locked in the BLOCKED state by a hardwire rfkill line (typically an input pin -that, when active, forces the transmitter to be disabled) which the driver -CANNOT override. - -Full rfkill functionality requires two different subsystems to cooperate: the -input layer and the rfkill class. The input layer issues *commands* to the -entire system requesting that devices registered to the rfkill class change -state. The way this interaction happens is not complex, but it is not obvious -either: - -Kernel Input layer: - - * Generates KEY_WWAN, KEY_WLAN, KEY_BLUETOOTH, SW_RFKILL_ALL, and - other such events when the user presses certain keys, buttons, or - toggles certain physical switches. - - THE INPUT LAYER IS NEVER USED TO PROPAGATE STATUS, NOTIFICATIONS OR THE - KIND OF STUFF AN ON-SCREEN-DISPLAY APPLICATION WOULD REPORT. It is - used to issue *commands* for the system to change behaviour, and these - commands may or may not be carried out by some kernel driver or - userspace application. It follows that doing user feedback based only - on input events is broken, as there is no guarantee that an input event - will be acted upon. - - Most wireless communication device drivers implementing rfkill - functionality MUST NOT generate these events, and have no reason to - register themselves with the input layer. Doing otherwise is a common - misconception. There is an API to propagate rfkill status change - information, and it is NOT the input layer. - -rfkill class: - - * Calls a hook in a driver to effectively change the wireless - transmitter state; - * Keeps track of the wireless transmitter state (with help from - the driver); - * Generates userspace notifications (uevents) and a call to a - notification chain (kernel) when there is a wireless transmitter - state change; - * Connects a wireless communications driver with the common rfkill - control system, which, for example, allows actions such as - "switch all bluetooth devices offline" to be carried out by - userspace or by rfkill-input. - - THE RFKILL CLASS NEVER ISSUES INPUT EVENTS. THE RFKILL CLASS DOES - NOT LISTEN TO INPUT EVENTS. NO DRIVER USING THE RFKILL CLASS SHALL - EVER LISTEN TO, OR ACT ON RFKILL INPUT EVENTS. Doing otherwise is - a layering violation. - - Most wireless data communication drivers in the kernel have just to - implement the rfkill class API to work properly. Interfacing to the - input layer is not often required (and is very often a *bug*) on - wireless drivers. - - Platform drivers often have to attach to the input layer to *issue* - (but never to listen to) rfkill events for rfkill switches, and also to - the rfkill class to export a control interface for the platform rfkill - controllers to the rfkill subsystem. This does NOT mean the rfkill - switch is attached to a rfkill class (doing so is almost always wrong). - It just means the same kernel module is the driver for different - devices (rfkill switches and rfkill controllers). - - -Userspace input handlers (uevents) or kernel input handlers (rfkill-input): - - * Implements the policy of what should happen when one of the input - layer events related to rfkill operation is received. - * Uses the sysfs interface (userspace) or private rfkill API calls - to tell the devices registered with the rfkill class to change - their state (i.e. translates the input layer event into real - action). - - * rfkill-input implements EPO by handling EV_SW SW_RFKILL_ALL 0 - (power off all transmitters) in a special way: it ignores any - overrides and local state cache and forces all transmitters to the - RFKILL_STATE_SOFT_BLOCKED state (including those which are already - supposed to be BLOCKED). - * rfkill EPO will remain active until rfkill-input receives an - EV_SW SW_RFKILL_ALL 1 event. While the EPO is active, transmitters - are locked in the blocked state (rfkill will refuse to unblock them). - * rfkill-input implements different policies that the user can - select for handling EV_SW SW_RFKILL_ALL 1. It will unlock rfkill, - and either do nothing (leave transmitters blocked, but now unlocked), - restore the transmitters to their state before the EPO, or unblock - them all. - -Userspace uevent handler or kernel platform-specific drivers hooked to the -rfkill notifier chain: - - * Taps into the rfkill notifier chain or to KOBJ_CHANGE uevents, - in order to know when a device that is registered with the rfkill - class changes state; - * Issues feedback notifications to the user; - * In the rare platforms where this is required, synthesizes an input - event to command all *OTHER* rfkill devices to also change their - statues when a specific rfkill device changes state. - - -=============================================================================== -3: Kernel driver guidelines - -Remember: point-of-view is everything for a driver that connects to the rfkill -subsystem. All the details below must be measured/perceived from the point of -view of the specific driver being modified. - -The first thing one needs to know is whether his driver should be talking to -the rfkill class or to the input layer. In rare cases (platform drivers), it -could happen that you need to do both, as platform drivers often handle a -variety of devices in the same driver. - -Do not mistake input devices for rfkill controllers. The only type of "rfkill -switch" device that is to be registered with the rfkill class are those -directly controlling the circuits that cause a wireless transmitter to stop -working (or the software equivalent of them), i.e. what we call a rfkill -controller. Every other kind of "rfkill switch" is just an input device and -MUST NOT be registered with the rfkill class. - -A driver should register a device with the rfkill class when ALL of the -following conditions are met (they define a rfkill controller): - -1. The device is/controls a data communications wireless transmitter; - -2. The kernel can interact with the hardware/firmware to CHANGE the wireless - transmitter state (block/unblock TX operation); - -3. The transmitter can be made to not emit any energy when "blocked": - rfkill is not about blocking data transmissions, it is about blocking - energy emission; - -A driver should register a device with the input subsystem to issue -rfkill-related events (KEY_WLAN, KEY_BLUETOOTH, KEY_WWAN, KEY_WIMAX, -SW_RFKILL_ALL, etc) when ALL of the folowing conditions are met: - -1. It is directly related to some physical device the user interacts with, to - command the O.S./firmware/hardware to enable/disable a data communications - wireless transmitter. - - Examples of the physical device are: buttons, keys and switches the user - will press/touch/slide/switch to enable or disable the wireless - communication device. - -2. It is NOT slaved to another device, i.e. there is no other device that - issues rfkill-related input events in preference to this one. - - Please refer to the corner cases and examples section for more details. - -When in doubt, do not issue input events. For drivers that should generate -input events in some platforms, but not in others (e.g. b43), the best solution -is to NEVER generate input events in the first place. That work should be -deferred to a platform-specific kernel module (which will know when to generate -events through the rfkill notifier chain) or to userspace. This avoids the -usual maintenance problems with DMI whitelisting. - - -Corner cases and examples: -==================================== - -1. If the device is an input device that, because of hardware or firmware, -causes wireless transmitters to be blocked regardless of the kernel's will, it -is still just an input device, and NOT to be registered with the rfkill class. - -2. If the wireless transmitter switch control is read-only, it is an input -device and not to be registered with the rfkill class (and maybe not to be made -an input layer event source either, see below). - -3. If there is some other device driver *closer* to the actual hardware the -user interacted with (the button/switch/key) to issue an input event, THAT is -the device driver that should be issuing input events. - -E.g: - [RFKILL slider switch] -- [GPIO hardware] -- [WLAN card rf-kill input] - (platform driver) (wireless card driver) - -The user is closer to the RFKILL slide switch plaform driver, so the driver -which must issue input events is the platform driver looking at the GPIO -hardware, and NEVER the wireless card driver (which is just a slave). It is -very likely that there are other leaves than just the WLAN card rf-kill input -(e.g. a bluetooth card, etc)... - -On the other hand, some embedded devices do this: - - [RFKILL slider switch] -- [WLAN card rf-kill input] - (wireless card driver) - -In this situation, the wireless card driver *could* register itself as an input -device and issue rf-kill related input events... but in order to AVOID the need -for DMI whitelisting, the wireless card driver does NOT do it. Userspace (HAL) -or a platform driver (that exists only on these embedded devices) will do the -dirty job of issuing the input events. - - -COMMON MISTAKES in kernel drivers, related to rfkill: -==================================== - -1. NEVER confuse input device keys and buttons with input device switches. - - 1a. Switches are always set or reset. They report the current state - (on position or off position). - - 1b. Keys and buttons are either in the pressed or not-pressed state, and - that's it. A "button" that latches down when you press it, and - unlatches when you press it again is in fact a switch as far as input - devices go. - -Add the SW_* events you need for switches, do NOT try to emulate a button using -KEY_* events just because there is no such SW_* event yet. Do NOT try to use, -for example, KEY_BLUETOOTH when you should be using SW_BLUETOOTH instead. - -2. Input device switches (sources of EV_SW events) DO store their current state -(so you *must* initialize it by issuing a gratuitous input layer event on -driver start-up and also when resuming from sleep), and that state CAN be -queried from userspace through IOCTLs. There is no sysfs interface for this, -but that doesn't mean you should break things trying to hook it to the rfkill -class to get a sysfs interface :-) - -3. Do not issue *_RFKILL_ALL events by default, unless you are sure it is the -correct event for your switch/button. These events are emergency power-off -events when they are trying to turn the transmitters off. An example of an -input device which SHOULD generate *_RFKILL_ALL events is the wireless-kill -switch in a laptop which is NOT a hotkey, but a real sliding/rocker switch. -An example of an input device which SHOULD NOT generate *_RFKILL_ALL events by -default, is any sort of hot key that is type-specific (e.g. the one for WLAN). - - -3.1 Guidelines for wireless device drivers ------------------------------------------- - -(in this text, rfkill->foo means the foo field of struct rfkill). - -1. Each independent transmitter in a wireless device (usually there is only one -transmitter per device) should have a SINGLE rfkill class attached to it. - -2. If the device does not have any sort of hardware assistance to allow the -driver to rfkill the device, the driver should emulate it by taking all actions -required to silence the transmitter. - -3. If it is impossible to silence the transmitter (i.e. it still emits energy, -even if it is just in brief pulses, when there is no data to transmit and there -is no hardware support to turn it off) do NOT lie to the users. Do not attach -it to a rfkill class. The rfkill subsystem does not deal with data -transmission, it deals with energy emission. If the transmitter is emitting -energy, it is not blocked in rfkill terms. - -4. It doesn't matter if the device has multiple rfkill input lines affecting -the same transmitter, their combined state is to be exported as a single state -per transmitter (see rule 1). - -This rule exists because users of the rfkill subsystem expect to get (and set, -when possible) the overall transmitter rfkill state, not of a particular rfkill -line. - -5. The wireless device driver MUST NOT leave the transmitter enabled during -suspend and hibernation unless: +The rfkill class is provided for kernel drivers to register their radio +transmitter with the kernel, provide methods for turning it on and off and, +optionally, letting the system know about hardware-disabled states that may +be implemented on the device. This code is enabled with the CONFIG_RFKILL +Kconfig option, which drivers can "select". - 5.1. The transmitter has to be enabled for some sort of functionality - like wake-on-wireless-packet or autonomous packed forwarding in a mesh - network, and that functionality is enabled for this suspend/hibernation - cycle. +The rfkill class code also notifies userspace of state changes, this is +achieved via uevents. It also provides some sysfs files for userspace to +check the status of radio transmitters. See the "Userspace support" section +below. -AND - 5.2. The device was not on a user-requested BLOCKED state before - the suspend (i.e. the driver must NOT unblock a device, not even - to support wake-on-wireless-packet or remain in the mesh). +The rfkill-input code implements a basic response to rfkill buttons -- it +implements turning on/off all devices of a certain class (or all). -In other words, there is absolutely no allowed scenario where a driver can -automatically take action to unblock a rfkill controller (obviously, this deals -with scenarios where soft-blocking or both soft and hard blocking is happening. -Scenarios where hardware rfkill lines are the only ones blocking the -transmitter are outside of this rule, since the wireless device driver does not -control its input hardware rfkill lines in the first place). +When the device is hard-blocked (either by a call to rfkill_set_hw_state() +or from query_hw_block) set_block() will be invoked but drivers can well +ignore the method call since they can use the return value of the function +rfkill_set_hw_state() to sync the software state instead of keeping track +of calls to set_block(). -6. During resume, rfkill will try to restore its previous state. -7. After a rfkill class is suspended, it will *not* call rfkill->toggle_radio -until it is resumed. +The entire functionality is spread over more than one subsystem: + * The kernel input layer generates KEY_WWAN, KEY_WLAN etc. and + SW_RFKILL_ALL -- when the user presses a button. Drivers for radio + transmitters generally do not register to the input layer, unless the + device really provides an input device (i.e. a button that has no + effect other than generating a button press event) -Example of a WLAN wireless driver connected to the rfkill subsystem: --------------------------------------------------------------------- + * The rfkill-input code hooks up to these events and switches the soft-block + of the various radio transmitters, depending on the button type. -A certain WLAN card has one input pin that causes it to block the transmitter -and makes the status of that input pin available (only for reading!) to the -kernel driver. This is a hard rfkill input line (it cannot be overridden by -the kernel driver). + * The rfkill drivers turn off/on their transmitters as requested. -The card also has one PCI register that, if manipulated by the driver, causes -it to block the transmitter. This is a soft rfkill input line. + * The rfkill class will generate userspace notifications (uevents) to tell + userspace what the current state is. -It has also a thermal protection circuitry that shuts down its transmitter if -the card overheats, and makes the status of that protection available (only for -reading!) to the kernel driver. This is also a hard rfkill input line. -If either one of these rfkill lines are active, the transmitter is blocked by -the hardware and forced offline. -The driver should allocate and attach to its struct device *ONE* instance of -the rfkill class (there is only one transmitter). +3. Kernel driver guidelines -It can implement the get_state() hook, and return RFKILL_STATE_HARD_BLOCKED if -either one of its two hard rfkill input lines are active. If the two hard -rfkill lines are inactive, it must return RFKILL_STATE_SOFT_BLOCKED if its soft -rfkill input line is active. Only if none of the rfkill input lines are -active, will it return RFKILL_STATE_UNBLOCKED. -Since the device has a hardware rfkill line, it IS subject to state changes -external to rfkill. Therefore, the driver must make sure that it calls -rfkill_force_state() to keep the status always up-to-date, and it must do a -rfkill_force_state() on resume from sleep. +Drivers for radio transmitters normally implement only the rfkill class. +These drivers may not unblock the transmitter based on own decisions, they +should act on information provided by the rfkill class only. -Every time the driver gets a notification from the card that one of its rfkill -lines changed state (polling might be needed on badly designed cards that don't -generate interrupts for such events), it recomputes the rfkill state as per -above, and calls rfkill_force_state() to update it. +Platform drivers might implement input devices if the rfkill button is just +that, a button. If that button influences the hardware then you need to +implement an rfkill class instead. This also applies if the platform provides +a way to turn on/off the transmitter(s). -The driver should implement the toggle_radio() hook, that: +During suspend/hibernation, transmitters should only be left enabled when +wake-on wlan or similar functionality requires it and the device wasn't +blocked before suspend/hibernate. Note that it may be necessary to update +the rfkill subsystem's idea of what the current state is at resume time if +the state may have changed over suspend. -1. Returns an error if one of the hardware rfkill lines are active, and the -caller asked for RFKILL_STATE_UNBLOCKED. -2. Activates the soft rfkill line if the caller asked for state -RFKILL_STATE_SOFT_BLOCKED. It should do this even if one of the hard rfkill -lines are active, effectively double-blocking the transmitter. -3. Deactivates the soft rfkill line if none of the hardware rfkill lines are -active and the caller asked for RFKILL_STATE_UNBLOCKED. - -=============================================================================== -4: Kernel API +4. Kernel API To build a driver with rfkill subsystem support, the driver should depend on -(or select) the Kconfig symbol RFKILL; it should _not_ depend on RKFILL_INPUT. +(or select) the Kconfig symbol RFKILL. The hardware the driver talks to may be write-only (where the current state of the hardware is unknown), or read-write (where the hardware can be queried about its current state). -The rfkill class will call the get_state hook of a device every time it needs -to know the *real* current state of the hardware. This can happen often, but -it does not do any polling, so it is not enough on hardware that is subject -to state changes outside of the rfkill subsystem. - -Therefore, calling rfkill_force_state() when a state change happens is -mandatory when the device has a hardware rfkill line, or when something else -like the firmware could cause its state to be changed without going through the -rfkill class. - -Some hardware provides events when its status changes. In these cases, it is -best for the driver to not provide a get_state hook, and instead register the -rfkill class *already* with the correct status, and keep it updated using -rfkill_force_state() when it gets an event from the hardware. - -rfkill_force_state() must be used on the device resume handlers to update the -rfkill status, should there be any chance of the device status changing during -the sleep. - -There is no provision for a statically-allocated rfkill struct. You must -use rfkill_allocate() to allocate one. - -You should: - - rfkill_allocate() - - modify rfkill fields (flags, name) - - modify state to the current hardware state (THIS IS THE ONLY TIME - YOU CAN ACCESS state DIRECTLY) - - rfkill_register() - -The only way to set a device to the RFKILL_STATE_HARD_BLOCKED state is through -a suitable return of get_state() or through rfkill_force_state(). +Calling rfkill_set_hw_state() when a state change happens is required from +rfkill drivers that control devices that can be hard-blocked unless they also +assign the poll_hw_block() callback (then the rfkill core will poll the +device). Don't do this unless you cannot get the event in any other way. -When a device is in the RFKILL_STATE_HARD_BLOCKED state, the only way to switch -it to a different state is through a suitable return of get_state() or through -rfkill_force_state(). -If toggle_radio() is called to set a device to state RFKILL_STATE_SOFT_BLOCKED -when that device is already at the RFKILL_STATE_HARD_BLOCKED state, it should -not return an error. Instead, it should try to double-block the transmitter, -so that its state will change from RFKILL_STATE_HARD_BLOCKED to -RFKILL_STATE_SOFT_BLOCKED should the hardware blocking cease. - -Please refer to the source for more documentation. - -=============================================================================== -5: Userspace support - -rfkill devices issue uevents (with an action of "change"), with the following -environment variables set: - -RFKILL_NAME -RFKILL_STATE -RFKILL_TYPE -The ABI for these variables is defined by the sysfs attributes. It is best -to take a quick look at the source to make sure of the possible values. +5. Userspace support -It is expected that HAL will trap those, and bridge them to DBUS, etc. These -events CAN and SHOULD be used to give feedback to the user about the rfkill -status of the system. - -Input devices may issue events that are related to rfkill. These are the -various KEY_* events and SW_* events supported by rfkill-input.c. - -******IMPORTANT****** -When rfkill-input is ACTIVE, userspace is NOT TO CHANGE THE STATE OF AN RFKILL -SWITCH IN RESPONSE TO AN INPUT EVENT also handled by rfkill-input, unless it -has set to true the user_claim attribute for that particular switch. This rule -is *absolute*; do NOT violate it. -******IMPORTANT****** - -Userspace must not assume it is the only source of control for rfkill switches. -Their state CAN and WILL change due to firmware actions, direct user actions, -and the rfkill-input EPO override for *_RFKILL_ALL. - -When rfkill-input is not active, userspace must initiate a rfkill status -change by writing to the "state" attribute in order for anything to happen. - -Take particular care to implement EV_SW SW_RFKILL_ALL properly. When that -switch is set to OFF, *every* rfkill device *MUST* be immediately put into the -RFKILL_STATE_SOFT_BLOCKED state, no questions asked. - -The following sysfs entries will be created: +The following sysfs entries exist for every rfkill device: name: Name assigned by driver to this key (interface or driver name). type: Name of the key type ("wlan", "bluetooth", etc). state: Current state of the transmitter 0: RFKILL_STATE_SOFT_BLOCKED - transmitter is forced off, but one can override it - by a write to the state attribute; + transmitter is turned off by software 1: RFKILL_STATE_UNBLOCKED - transmiter is NOT forced off, and may operate if - all other conditions for such operation are met - (such as interface is up and configured, etc); + transmitter is (potentially) active 2: RFKILL_STATE_HARD_BLOCKED transmitter is forced off by something outside of - the driver's control. One cannot set a device to - this state through writes to the state attribute; - claim: 1: Userspace handles events, 0: Kernel handles events - -Both the "state" and "claim" entries are also writable. For the "state" entry -this means that when 1 or 0 is written, the device rfkill state (if not yet in -the requested state), will be will be toggled accordingly. - -For the "claim" entry writing 1 to it means that the kernel no longer handles -key events even though RFKILL_INPUT input was enabled. When "claim" has been -set to 0, userspace should make sure that it listens for the input events or -check the sysfs "state" entry regularly to correctly perform the required tasks -when the rkfill key is pressed. - -A note about input devices and EV_SW events: - -In order to know the current state of an input device switch (like -SW_RFKILL_ALL), you will need to use an IOCTL. That information is not -available through sysfs in a generic way at this time, and it is not available -through the rfkill class AT ALL. + the driver's control. + claim: 0: Kernel handles events (currently always reads that value) + +rfkill devices also issue uevents (with an action of "change"), with the +following environment variables set: + +RFKILL_NAME +RFKILL_STATE +RFKILL_TYPE + +The contents of these variables corresponds to the "name", "state" and +"type" sysfs files explained above. + +An alternative userspace interface exists as a misc device /dev/rfkill, +which allows userspace to obtain and set the state of rfkill devices and +sets of devices. It also notifies userspace about device addition and +removal. The API is a simple read/write API that is defined in +linux/rfkill.h. |