the kernel), which encapsulates the information needed to refer to an
external buffer.  Under normal operation, this can just be a void *
equivalent, but under -DKEEP_IT_REAL it would be a segoff_t equivalent.

Use this concept to avoid the need for bounce buffers in int13.c,
which reduces memory usage and opens up the possibility of using
multi-sector reads.

Extend the block-device API and the SCSI block device implementation
to support multi-sector reads.

Update iscsi.c to use user buffers.

Move the obsolete portions of realmode.h to old_realmode.h.

MS-DOS now boots an order of magnitude faster over iSCSI (~10 seconds
from power-up to C:> prompt in bochs).

Use .text16.data section with "aw" attributes, to avoid section type
conflicts when placing both code and data into .text16.

Add __from_{text16,data16}.

interrupt vectors, for example, will be easiest to handle if placed in
.text16.

.data16.  librm will need to supply "char *data16", i.e. the virtual
address of the start of .data16.

advantage of the fact that we have to have a permanently-resident block
in base memory.