Input: evdev - add event-mask API

Hardware manufacturers group keys in the weirdest way possible. This may
cause a power-key to be grouped together with normal keyboard keys and
thus be reported on the same kernel interface.

However, user-space is often only interested in specific sets of events.
For instance, daemons dealing with system-reboot (like systemd-logind)
listen for KEY_POWER, but are not interested in any main keyboard keys.
Usually, power keys are reported via separate interfaces, however,
some i8042 boards report it in the AT matrix. To avoid waking up those
system daemons on each key-press, we had two ideas:
 - split off KEY_POWER into a separate interface unconditionally
 - allow filtering a specific set of events on evdev FDs

Splitting of KEY_POWER is a rather weird way to deal with this and may
break backwards-compatibility. It is also specific to KEY_POWER and might
be required for other stuff, too. Moreover, we might end up with a huge
set of input-devices just to have them properly split.

Hence, this patchset implements the second idea: An event-mask to specify
which events you're interested in. Two ioctls allow setting this mask for
each event-type. If not set, all events are reported. The type==0 entry is
used same as in EVIOCGBIT to set the actual EV_* mask of filtered events.
This way, you have a two-level filter.

We are heavily forward-compatible to new event-types and event-codes. So
new user-space will be able to run on an old kernel which doesn't know the
given event-codes or event-types.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

1 files changed, 60 insertions, 0 deletions

diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h
index 4f9f2a0f5573..2758687300b4 100644
--- a/include/uapi/linux/input.h
+++ b/include/uapi/linux/input.h
@@ -98,6 +98,12 @@ struct input_keymap_entry {
 	__u8  scancode[32];
 };
 
+struct input_mask {
+	__u32 type;
+	__u32 codes_size;
+	__u64 codes_ptr;
+};
+
 #define EVIOCGVERSION		_IOR('E', 0x01, int)			/* get driver version */
 #define EVIOCGID		_IOR('E', 0x02, struct input_id)	/* get device ID */
 #define EVIOCGREP		_IOR('E', 0x03, unsigned int[2])	/* get repeat settings */
@@ -155,6 +161,60 @@ struct input_keymap_entry {
 #define EVIOCGRAB		_IOW('E', 0x90, int)			/* Grab/Release device */
 #define EVIOCREVOKE		_IOW('E', 0x91, int)			/* Revoke device access */
 
+/**
+ * EVIOCGMASK - Retrieve current event mask
+ *
+ * This ioctl allows user to retrieve the current event mask for specific
+ * event type. The argument must be of type "struct input_mask" and
+ * specifies the event type to query, the address of the receive buffer and
+ * the size of the receive buffer.
+ *
+ * The event mask is a per-client mask that specifies which events are
+ * forwarded to the client. Each event code is represented by a single bit
+ * in the event mask. If the bit is set, the event is passed to the client
+ * normally. Otherwise, the event is filtered and will never be queued on
+ * the client's receive buffer.
+ *
+ * Event masks do not affect global state of the input device. They only
+ * affect the file descriptor they are applied to.
+ *
+ * The default event mask for a client has all bits set, i.e. all events
+ * are forwarded to the client. If the kernel is queried for an unknown
+ * event type or if the receive buffer is larger than the number of
+ * event codes known to the kernel, the kernel returns all zeroes for those
+ * codes.
+ *
+ * At maximum, codes_size bytes are copied.
+ *
+ * This ioctl may fail with ENODEV in case the file is revoked, EFAULT
+ * if the receive-buffer points to invalid memory, or EINVAL if the kernel
+ * does not implement the ioctl.
+ */
+#define EVIOCGMASK		_IOR('E', 0x92, struct input_mask)	/* Get event-masks */
+
+/**
+ * EVIOCSMASK - Set event mask
+ *
+ * This ioctl is the counterpart to EVIOCGMASK. Instead of receiving the
+ * current event mask, this changes the client's event mask for a specific
+ * type.  See EVIOCGMASK for a description of event-masks and the
+ * argument-type.
+ *
+ * This ioctl provides full forward compatibility. If the passed event type
+ * is unknown to the kernel, or if the number of event codes specified in
+ * the mask is bigger than what is known to the kernel, the ioctl is still
+ * accepted and applied. However, any unknown codes are left untouched and
+ * stay cleared. That means, the kernel always filters unknown codes
+ * regardless of what the client requests.  If the new mask doesn't cover
+ * all known event-codes, all remaining codes are automatically cleared and
+ * thus filtered.
+ *
+ * This ioctl may fail with ENODEV in case the file is revoked. EFAULT is
+ * returned if the receive-buffer points to invalid memory. EINVAL is returned
+ * if the kernel does not implement the ioctl.
+ */
+#define EVIOCSMASK		_IOW('E', 0x93, struct input_mask)	/* Set event-masks */
+
 #define EVIOCSCLOCKID		_IOW('E', 0xa0, int)			/* Set clockid to be used for timestamps */
 
 /*