Re: Better interop for NFS/SMB file share mode/reservation

Jeff Layton
2019-03-06T21:55:56Z

On Wed, 2019-03-06 at 13:07 -0800, Jeremy Allison wrote:
> 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 ?

The libcephfs API takes an opaque void * that could hold such a token.
It gets passed back to the callback function when it's called to handle
a delegation break.

I could envision a delegation storing something similar (maybe an
unsigned long or uint64_t) and pass it back in a delegation break. With
that you could set multiple delegations on a fd, and use that to store a
key for each one.

Would something like that work for samba, or am I misunderstanding what
it needs?

--
Jeff Layton <jlayton@kernel.org>