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+What:           /sys/devices/.../online
+Date:           April 2013
+Contact:        Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+Description:
+                The /sys/devices/.../online attribute is only present for
+                devices whose bus types provide .online() and .offline()
+                callbacks.  The number read from it (0 or 1) reflects the value
+                of the device's 'offline' field.  If that number is 1 and '0'
+                (or 'n', or 'N') is written to this file, the device bus type's
+                .offline() callback is executed for the device and (if
+                successful) its 'offline' field is updated accordingly.  In
+                turn, if that number is 0 and '1' (or 'y', or 'Y') is written to
+                this file, the device bus type's .online() callback is executed
+                for the device and (if successful) its 'offline' field is
+                updated as appropriate.
+
+                After a successful execution of the bus type's .offline()
+                callback the device cannot be used for any purpose until either
+                it is removed (i.e. device_del() is called for it), or its bus
+                type's .online() is exeucted successfully.