>> So, I'd like to add to parameters to VOP_FSYNC: start (off_t) and end (off_t).
> 
> I would suggest using start and len instead so you don't need to worry
> about handling cases where end < start.

Good idea, especially if you also define len==0 to mean "all".

Any time I see a conceptually unsigned argument using a -1 value
for anything, I get this vague uneasy feeling...

Todd Whitesel
toddpw @ best.com