Re: Replace lockmgr for vnodes

[Andrew Doran <ad%netbsd.org@localhost>]

On Thu, Feb 28, 2008 at 10:44:14PM -0800, Jason Thorpe wrote:

> On Feb 28, 2008, at 10:15 PM, David Holland wrote:
> 
> >I am still not convinced of this, for two reasons: first, I don't
> >think layers are going to work unless locks are exported and shared;
> >and second, if every fs does its own locking, it gives every fs the
> >opportunity to do it wrong, and there'll furthermore tend to be a lot
> >of cut&paste code with all the attendant problems.
> 
> The reason file systems can get it so wrong is because of the nutty  
> rules that we currently have.

The nutty rules and over-clever code result in all kinds of fun bugs and
deadlocks, in part because it's ~impossible to have a full understanding of
what the rules are.

It has been maybe 13 years since Lite2 was released, and even though some
smart people have spent a lot of time on it, we are still trying to make
vnode based locking work reliably. I'd classify that as a dead end!

Andrew