Re: [PATCH] locks: breaking read lease should not block read open

[Jeremy Allison <jra@samba.org>]

On Wed, Jul 20, 2011 at 08:07:58PM -0400, J. Bruce Fields wrote:
> On Fri, Jun 10, 2011 at 09:48:59AM -0400, J. Bruce Fields wrote:
> > On Fri, Jun 10, 2011 at 09:56:49AM +0200, Volker Lendecke wrote:
> > > Without having looked too deeply, just let me point out that
> > > Samba here has a plain flaw. Early Linux Kernel versions
> > > that we programmed against did not properly support read
> > > only leases, so we did not implement that initially. If I
> > > remember correctly we never got around to finally do it once
> > > it became available. Eventually we will probably, as read
> > > only leases are a pretty important feature to present to
> > > CIFS clients.
> > 
> > Thanks, I didn't know that.  (Or I did, and I forgot.)
> > 
> > When you *do* implement that, is there any chance you'd have this need
> > to be able to downgrade to a read lease in the case of a conflict?
> 
> So it's a question about the protocols samba implements:
> 
> 	- Do they allow an atomic downgrade from an exclusive to a
> 	  shared oplock?  (Or to a level 2 oplock, or whatever the right
> 	  term is).

Yes. Exclusive can go to level 2 - in fact that's the default
downgrade we do (unless an smb.conf option explicity denies it).

> 	- If so, can that happen as a response to a conflicting open?
> 	  (So, if you're holding an exclusive oplock, and a conflicting
> 	  open comes in, can the server-to-client break message say "now
> 	  you're getting a shared oplock instead"?  Or is the client
> 	  left without any oplock until it requests a new one?)

Yes, this can happen.

In SMB, we only break to no lease when a write request comes
in on a exclusive or level2 oplock (read-lease) handle.

Jeremy.