What:		/sys/devices/.../sun
Date:		October 2012
Contact:	Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Description:
		The file contains a Slot-unique ID which provided by the _SUN
		method in the ACPI namespace. The value is written in Advanced
		Configuration and Power Interface Specification as follows:

		"The _SUN value is required to be unique among the slots of
		the same type. It is also recommended that this number match
		the slot number printed on the physical slot whenever possible."

		So reading the sysfs file, we can identify a physical position
		of the slot in the system.