The 'host_no' element is a change in lk 2.4 kernels. [In the lk 2.2 series
and earlier, it was 'low_inode & 0xff' from the procfs entry
corresponding to the host.] This change makes the use of the
SCSI_IOCTL_GET_BUS_NUMBER ioctl() superfluous.
The advantage of this ioctl() is that it can be called on any SCSI file
descriptor.