[SCSI] tcm_loop: Add multi-fabric Linux/SCSI LLD fabric module

This patch adds the TCM_Loop Linux/SCSI LLD fabric module for
accessing TCM device backstores as locally accessable SCSI LUNs in
virtual SAS, FC, and iSCSI Target ports using the generic fabric
TransportID and Target Port WWN naming handlers from TCM's
target_core_fabric_lib.c The TCM_Loop module uses the generic fabric
configfs infratructure provided by target_core_fabric_configfs.c and
adds a module dependent attribute for the creation/release of the
virtual I_T Nexus connected the TCM_Loop Target and Initiator Ports.

TCM_Loop can also be used with scsi-generic and BSG drivers so that
STGT userspace fabric modules, QEMU-KVM and other hypervisor SCSI
passthrough support can access TCM device backstore and control CDB
emulation.

For more information please see:

http://linux-iscsi.org/wiki/Tcm_loop

[jejb: fixed up checkpatch stuff]
Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

drivers/target/Kconfig

@@ -29,4 +29,6 @@ config TCM_PSCSI
 	Say Y here to enable the TCM/pSCSI subsystem plugin for non-buffered
 	passthrough access to Linux/SCSI device
 
+source "drivers/target/loopback/Kconfig"
+
 endif

drivers/target/Makefile

@@ -21,3 +21,6 @@ obj-$(CONFIG_TARGET_CORE)	+= target_core_mod.o
 obj-$(CONFIG_TCM_IBLOCK)	+= target_core_iblock.o
 obj-$(CONFIG_TCM_FILEIO)	+= target_core_file.o
 obj-$(CONFIG_TCM_PSCSI)		+= target_core_pscsi.o
+
+# Fabric modules
+obj-$(CONFIG_LOOPBACK_TARGET)	+= loopback/

drivers/target/loopback/Kconfig

@@ -0,0 +1,11 @@
+config LOOPBACK_TARGET
+	tristate "TCM Virtual SAS target and Linux/SCSI LDD fabric loopback module"
+	help
+	  Say Y here to enable the TCM Virtual SAS target and Linux/SCSI LLD
+	  fabric loopback module.
+
+config LOOPBACK_TARGET_CDB_DEBUG
+	bool "TCM loopback fabric module CDB debug code"
+	depends on LOOPBACK_TARGET
+	help
+	  Say Y here to enable the TCM loopback fabric module CDB debug code

drivers/target/loopback/Makefile

@@ -0,0 +1 @@
+obj-$(CONFIG_LOOPBACK_TARGET)	+= tcm_loop.o