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>

include/hw/virtio/virtio-scsi.h

@@ -21,6 +21,7 @@
 #include "hw/virtio/virtio.h"
 #include "hw/pci/pci.h"
 #include "hw/scsi/scsi.h"
+#include "chardev/char-fe.h"
 #include "sysemu/iothread.h"
 
 #define TYPE_VIRTIO_SCSI_COMMON "virtio-scsi-common"
@@ -53,6 +54,7 @@ struct VirtIOSCSIConf {
     char *vhostfd;
     char *wwpn;
 #endif
+    CharBackend chardev;
     uint32_t boot_tpgt;
     IOThread *iothread;
 };