Hello,

The attached patch simplifies the target-stack by folding the "struct 
target_stack_item" into the "struct target_ops".  The field "struct 
target_ops . beneath" being added.

This in turn greatly simplifies the logic needed to walk the target 
stack (target_beneath becomes a one-liner), and that in turn lets me 
correctly implement the new target read/write partial methods I just posted.

Note that this implementation is still limited to a single target stack 
(due to all the target_ops vectors being static).  Follow-on changes can 
eliminate that restriction.

Once I've finished testing, I'll look to commit it in a day or so,
Andrew