Subject: Re: diffs for UVM/UBC improvements available
To: Chuck Silvers <>
From: Bill Studenmund <>
List: tech-kern
Date: 05/29/2001 12:43:48
On Wed, 23 May 2001, Bill Studenmund wrote:

> On Tue, 22 May 2001, Chuck Silvers wrote:
> > On Tue, May 22, 2001 at 08:32:29PM -0700, Bill Studenmund wrote:
> > > Hmmm... I should look at the diff. My thought was we'd keep the struct
> > > vnode *, which would just point into the fs-private data.
> > 
> > actually, here's a reason why this isn't preferable:  it means that
> > a filesystem which does not use a struct lock to implement VOP_LOCK()
> > would not work with the layered filesystems.  an example of such a
> > filesystem would be a cluster filesystem which would need to use a
> > cluster-wide vnode lock.
> That was already covered - if the exported struct lock * was NULL, then
> layer_{,un}lock() called the underlying VOP_LOCK(). This idea already came
> up so we could support a layered fs over a unionfs system (which has to do
> its own lock gyrations).
> Any other reason?

More to the point, could you please not remove the struct lock * part? In
addition to being used as a way of exporting lock information, I was
planning on using it for some of the other things from John Heidemann's
disseratation. If you remove it, I'll probably have to re-add it later,
which seems like a waste.

And as above, we have clustered file systems covered with the existing

Take care,