What:		/sys/block/dm-<num>/bow/free
Date:		January 2023
KernelVersion:	5.15
Contact:	paullawrence@google.com
Description:	free space
		Free space on device in bytes. Only valid in state 0
Users:		Android vold to determine if there is sufficient space for expected size
		of checksum

What:		/sys/block/dm-<num>/bow/state
Date:		January 2023
KernelVersion:	5.15
Contact:	paullawrence@google.com
Description:	dm-bow state
		Read-write string containing 0, 1 or 2
		0: Trim mode
		1: Checkpoint mode
		2: Committed mode
		See Documentation/device-mapper/dm-bow for details