This option specifies the serial number to assign to the device.
@item addr=@var{addr}
Specify the controller's PCI address (if=virtio only).
+@item werror=@var{action},rerror=@var{action}
+Specify which @var{action} to take on write and read errors. Valid actions are:
+"ignore" (ignore the error and try to continue), "stop" (pause QEMU),
+"report" (report the error to the guest), "enospc" (pause QEMU only if the
+host disk is full; report the error to the guest otherwise).
+The default setting is @option{werror=enospc} and @option{rerror=report}.
+@item readonly
+Open drive @option{file} as read-only. Guest write attempts will fail.
@end table
By default, writethrough caching is used for all block device. This means that