vhost-user-scsi: Introduce vhost-user-scsi host device

This commit introduces a vhost-user device for SCSI. This is based
on the existing vhost-scsi implementation, but done over vhost-user
instead. It also uses a chardev to connect to the backend. Unlike
vhost-scsi (today), VMs using vhost-user-scsi can be live migrated.

To use it, start Qemu with a command line equivalent to:

qemu-system-x86_64 \
       -chardev socket,id=vus0,path=/tmp/vus.sock \
       -device vhost-user-scsi-pci,chardev=vus0,bus=pci.0,addr=...

A separate commit presents a sample application linked with libiscsi to
provide a backend for vhost-user-scsi.

Signed-off-by: Felipe Franciosi <felipe@nutanix.com>
Message-Id: <1488479153-21203-4-git-send-email-felipe@nutanix.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/hw/scsi/Makefile.objs b/hw/scsi/Makefile.objs
index 54d8754..b188f72 100644
--- a/hw/scsi/Makefile.objs
+++ b/hw/scsi/Makefile.objs
@@ -11,4 +11,5 @@
 ifeq ($(CONFIG_VIRTIO),y)
 obj-y += virtio-scsi.o virtio-scsi-dataplane.o
 obj-$(CONFIG_VHOST_SCSI) += vhost-scsi-common.o vhost-scsi.o
+obj-$(CONFIG_VHOST_USER_SCSI) += vhost-scsi-common.o vhost-user-scsi.o
 endif