scsi: Allow scsi controller to associate with an IO thread.

This enable data-plane for scsi. All drives attached to the
scsi controller will have their IO processed in a single separate
IO thread instead of qemu's main event loop.

Signed-off-by: Archana Shinde <archana.m.shinde@intel.com>

qemu/qemu.go

@@ -841,6 +841,9 @@ type SCSIController struct {
 
 	// DisableModern prevents qemu from relying on fast MMIO.
 	DisableModern bool
+
+	// IOThread is the IO thread on which IO will be handled
+	IOThread string
 }
 
 // Valid returns true if the SCSIController structure is valid and complete.
@@ -867,6 +870,9 @@ func (scsiCon SCSIController) QemuParams(config *Config) []string {
 	if scsiCon.DisableModern {
 		devParams = append(devParams, fmt.Sprintf("disable-modern=true"))
 	}
+	if scsiCon.IOThread != "" {
+		devParams = append(devParams, fmt.Sprintf("iothread=%s", scsiCon.IOThread))
+	}
 
 	qemuParams = append(qemuParams, "-device")
 	qemuParams = append(qemuParams, strings.Join(devParams, ","))