ibft: Expose iBFT acpi header via sysfs

Some ethernet adapter vendors are supplying products which support optional
(payed license) features. On some adapters this includes a hardware iscsi
initiator.  The same adapters in a normal (no extra licenses) mode of
operation can be used as a software iscsi initiator.  In addition, software
iscsi boot initiators are becoming a standard part of many vendors uefi
implementations.  This is creating difficulties during early boot/install
determining the proper configuration method for these adapters when they
are used as a boot device.

The attached patch creates sysfs entries to expose information from the
acpi header of the ibft table.  This information allows for a method to
easily determining if an ibft table was created by a ethernet card's
firmware or the system uefi/bios.  In the case of a hardware initiator this
information in combination with the pci vendor and device id can be used
to ascertain any vendor specific behaviors that need to be accommodated.

Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: David Bond <dbond@suse.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Documentation/ABI/testing/sysfs-ibft

@@ -21,3 +21,13 @@ Contact:	Konrad Rzeszutek <ketuzsezr@darnok.org>
 Description:	The /sys/firmware/ibft/ethernetX directory will contain
 		files that expose the iSCSI Boot Firmware Table NIC data.
 		Usually this contains the IP address, MAC, and gateway of the NIC.
+
+What:		/sys/firmware/ibft/acpi_header
+Date:		March 2016
+Contact:	David Bond <dbond@suse.com>
+Description:	The /sys/firmware/ibft/acpi_header directory will contain files
+		that expose the SIGNATURE, OEM_ID, and OEM_TABLE_ID fields of the
+		acpi table header of the iBFT structure.  This will allow for
+		identification of the creator of the table which is useful in
+		determining quirks associated with some adapters when used in
+		hardware vs software iscsi initiator mode.