ports, binaries & iovecs

[Vance Shipley]

I am finding that sending binaries to a port with port_command/2,
and receiving them with outputv(), doesn't work the way I had
expected.  The problem is that I can't seem to control how the 
ErlIOVec is created.  I had expected, and hoped, that if I create
two seperate binaries in Erlang and send them with port_command/2
that my outputv() driver call back would receive them as seperate
SysIOVec structures.  Instead I find that the emulator is making
up it's own mind:

1> port_command(Port, [<<0:32>>, <<0:32>>]).
my_outputv:
ev->vsize = 2    
ev->size = 8 
true                         
2> port_command(Port, [<<0:128/integer-unit:8>>, <<0:32/integer-unit:8>>]).
netaccess_outputv
ev->vsize = 3    
ev->size = 160
true

Can anyone tell me what the rules are?

	-Vance