Add an optional 'type' attribute to <target> element of serial port
device. There are two choices for its value, 'isa-serial' and
'usb-serial'. For backward compatibility, when attribute 'type' is
missing the 'isa-serial' will be chosen as before.
Libvirt XML sample
<serial type='pty'>
<target type='usb-serial' port='0'/>
<address type='usb' bus='0' port='1'/>
</serial>
qemu commandline:
qemu ${other_vm_args} \
-chardev pty,id=charserial0 \
-device usb-serial,chardev=charserial0,id=serial0,bus=usb.0,port=1
e3a04455fa