[PATCH] locks: breaking read lease should not block read open
jra at samba.org
Wed Jul 20 18:15:42 MDT 2011
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.
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