Write event -> dm_read_invis?

[Ben Myers <dative@xxxxxxxxxxx>]

Hi,

I'm working on a small data migration app.  I'm getting DM_EVENT_WRITE
events, responding with DM_RESP_CONTINUE, and wanting to immediately
turn a round and dm_read_invis() on that handle from de_offset to
de_length and spit it out (with some other info) towards my tape
drive.  

Can I assume that a dm_read_invis will get me only the change affected
by the write event i responded to?  What behavior should I expect for
overlapping writes, and how can I tell when a write is finished and it's
ok to copy the data out to tape?

Thanks for any help,
-Ben

-- 
Ben Myers <dative@xxxxxxxxxxx>