> VOP_LOCK() and friends are not advisory.
OK.  A reading of the Red Daemon book led me
to believe otherwise.  I realize that's
no longer a definitive source for NetBSD workings.
I mention it as the original BSD VFS/VOP design,
where the idea seems to be that VOP_LOCK() is merely a
hint to a file system that "hey, if you actually lock
something now, I'll guarantee consistent access to your
vnodes and you won't need to do any extra work."  I thought
all along, though, that any file system that felt up
to it could do that extra work if it wanted.

> While what you describe would be fine if we had only leaf file 
> systems, it
> won't work for layered file systems.
Aha.
>   They are implemented assuming that
> VOP_LOCK() and friends actually work.
Am I following you, here?  You're saying the implementation of the
layered, stackable file systems like nullfs require that
all leaf file systems implement VOP_LOCK()?  Err...sorry, not
"the implementation of layered f/s requires" but rather "the API for
implementing layered f/s requires?"

> Note that flock(2) locking is different. Those operations go through
> VOP_ADVLOCK().
Sure, sure, sure.  Different beastie.

> Bill
Chris <jepeway@blasted-heath.com>.