This patch adds the initial code for tcm_vhost, a Vhost level TCM
fabric driver for virtio SCSI initiators into KVM guest.

This code is currently up and running on v3.5-rc2 host+guest
from target-pending/for-next-merge.

Using tcm_vhost requires Zhi's -> Stefan -> nab's qemu vhost-scsi tree here:

http://git.kernel.org/?p=virt/kvm/nab/qemu-kvm.git;a=shortlog;h=refs/heads/vhost-scsi

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Changelog v4 -> v5:

Expose ABI version via VHOST_SCSI_GET_ABI_VERSION + use Rev 0 as
starting point for v3.6-rc code (Stefan + ALiguori + nab)
Convert vhost_scsi_handle_vq() to vq_err() (nab + MST)
Minor style fixes from checkpatch (nab)

Changelog v3 -> v4:

Rename vhost_vring_target -> vhost_scsi_target (mst + nab)
Use TRANSPORT_IQN_LEN in vhost_scsi_target->vhost_wwpn[] def (nab)
Move back to drivers/vhost/, and just use drivers/vhost/Kconfig.tcm (mst)
Move TCM_VHOST related ioctl defines from include/linux/vhost.h ->
drivers/vhost/tcm_vhost.h as requested by MST (nab)
Move Kbuild.tcm include from drivers/staging -> drivers/vhost/, and
just use 'if STAGING' around 'source drivers/vhost/Kbuild.tcm'

Changelog v2 -> v3:

Unlock on error in tcm_vhost_drop_nexus() (DanC)
Fix strlen() doesn't count the terminator (DanC)
Call kfree() on an error path (DanC)
Convert tcm_vhost_write_pending to use target_execute_cmd (hch + nab)
Fix another strlen() off by one in tcm_vhost_make_tport (DanC)
Add option under drivers/staging/Kconfig, and move to drivers/vhost/tcm/
as requested by MST (nab)

Changelog v1 -> v2:

Fix tv_cmd completion -> release SGL memory leak (nab)
Fix sparse warnings for static variable usage ((Fengguang Wu)
Fix sparse warnings for min() typing + printk format specs (Fengguang Wu)
Convert to cmwq submission for I/O dispatch (nab + hch)

Changelog v0 -> v1:

Merge into single source + header file, and move to drivers/vhost/

Acked-by: Michael S. Tsirkin
Cc: Stefan Hajnoczi
Cc: Anthony Liguori
Cc: Zhi Yong Wu
Cc: Paolo Bonzini
Cc: Christoph Hellwig
Cc: Hannes Reinecke
Cc: Jens Axboe
Signed-off-by: Nicholas Bellinger