Better interop for NFS/SMB file share mode/reservation

[Jeremy Allison]

On Wed, Mar 06, 2019 at 03:31:08PM -0500, Jeff Layton wrote:
> On Wed, 2019-03-06 at 10:11 -0500, J. Bruce Fields wrote:
> > On Tue, Mar 05, 2019 at 04:47:48PM -0500, J. Bruce Fields wrote:
> > > On Thu, Feb 14, 2019 at 04:06:52PM -0500, J. Bruce Fields wrote:
> > > > After this:
> > > > 
> > > > 	https://marc.info/?l=linux-nfs&m=154966239918297&w=2
> > > > 
> > > > delegations would no longer conflict with opens from the same tgid.  So
> > > > if your threads all run in the same process and you're willing to manage
> > > > conflicts among your own clients, that should still allow you to do
> > > > multiple opens of the same file without giving up your lease/delegation.
> > > > 
> > > > I'd be curious to know whether that works with Samba's design.
> > > 
> > > Any idea whether that would work?
> > > 
> > > (Easy?  Impossible?  Possible, but realistically the changes required to
> > > Samba would be painful enough that it'd be unlikely to get done?)
> > 
> > Volker reminds me off-list that he'd like to see Ganesha and Samba work
> > out an API in userspace first before commiting to a user<->kernel API.
> > 
> > Jeff, wasn't there some work (on Ceph maybe?) on a userspace delegation
> > API?  Is that close to what's needed?
> > 
> 
> Here's the C headers for that stuff:
> 
>     https://github.com/ceph/ceph/blob/7ba6bece4187eda5d05a9b84211fe6ba8dd287bd/src/include/cephfs/libcephfs.h#L1734
> 
> It's simple enough and works for us in ganesha, and I think we can
> probably adapt it to samba without too much difficulty. The callback
> doesn't seem like it'll do for a kernel API though -- you'd almost
> certainly need to do something different there (signals? inotify?).

SMB3 leases have R/RW and Handle-based leases.

Handle leases allow multiple opens of the same pathname
that get different handles to share the lease, allowing
a client redirector to delay opens or closes locally
so long as it has a handle lease.

Here are the semantics:

https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-smb2/d8df943d-6ad7-4b30-9f58-96ae90fc6204

I'm not sure a simple file-descriptor based API is
enough for us. Can he have a uuid or token based
API instead where the server can chose what fd's
to cover with a token ?