rfkill: export persistent attribute in sysfs

This information allows userspace to implement a hybrid policy where
it can store the rfkill soft-blocked state in platform non-volatile
storage if available, and if not then file-based storage can be used.

Some users prefer platform non-volatile storage because of the behaviour
when dual-booting multiple versions of Linux, or if the rfkill setting
is changed in the BIOS setting screens, or if the BIOS responds to
wireless-toggle hotkeys itself before the relevant platform driver has
been loaded.
Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

Documentation/rfkill.txt

@@ -111,6 +111,8 @@ following attributes:
 
 	name: Name assigned by driver to this key (interface or driver name).
 	type: Driver type string ("wlan", "bluetooth", etc).
+	persistent: Whether the soft blocked state is initialised from
+	            non-volatile storage at startup.
 	state: Current state of the transmitter
 		0: RFKILL_STATE_SOFT_BLOCKED
 			transmitter is turned off by software

include/linux/rfkill.h

@@ -259,8 +259,9 @@ bool rfkill_set_sw_state(struct rfkill *rfkill, bool blocked);
  * userspace) of their initial state.  It should only be used before
  * registration.
  *
- * In addition, it marks the device as "persistent".  Persistent devices
- * are expected to preserve preserve their own state when suspended.
+ * In addition, it marks the device as "persistent", an attribute which
+ * can be read by userspace.  Persistent devices are expected to preserve
+ * their own state when suspended.
  */
 void rfkill_init_sw_state(struct rfkill *rfkill, bool blocked);
 

net/rfkill/core.c

@@ -610,6 +610,15 @@ static ssize_t rfkill_idx_show(struct device *dev,
 	return sprintf(buf, "%d\n", rfkill->idx);
 }
 
+static ssize_t rfkill_persistent_show(struct device *dev,
+			       struct device_attribute *attr,
+			       char *buf)
+{
+	struct rfkill *rfkill = to_rfkill(dev);
+
+	return sprintf(buf, "%d\n", rfkill->persistent);
+}
+
 static u8 user_state_from_blocked(unsigned long state)
 {
 	if (state & RFKILL_BLOCK_HW)
@@ -668,6 +677,7 @@ static struct device_attribute rfkill_dev_attrs[] = {
 	__ATTR(name, S_IRUGO, rfkill_name_show, NULL),
 	__ATTR(type, S_IRUGO, rfkill_type_show, NULL),
 	__ATTR(index, S_IRUGO, rfkill_idx_show, NULL),
+	__ATTR(persistent, S_IRUGO, rfkill_persistent_show, NULL),
 	__ATTR(state, S_IRUGO|S_IWUSR, rfkill_state_show, rfkill_state_store),
 	__ATTR(claim, S_IRUGO|S_IWUSR, rfkill_claim_show, rfkill_claim_store),
 	__ATTR_NULL