Better interop for NFS/SMB file share mode/reservation

[Amir Goldstein]

On Sun, Apr 28, 2019 at 6:08 PM Trond Myklebust <trondmy at hammerspace.com> wrote:
>
> On Sun, 2019-04-28 at 18:00 -0400, Amir Goldstein wrote:
> > On Sun, Apr 28, 2019 at 11:06 AM Trond Myklebust
> > <trondmy at hammerspace.com> wrote:
> > > On Sun, 2019-04-28 at 09:45 -0400, Amir Goldstein wrote:
> > > > On Sun, Apr 28, 2019 at 8:09 AM Jeff Layton <jlayton at kernel.org>
> > > > wrote:
> > > > > On Sat, 2019-04-27 at 16:16 -0400, Amir Goldstein wrote:
> > > > > > [adding back samba/nfs and fsdevel]
> > > > > >
> > > > >
> > > > > cc'ing Pavel too -- he did a bunch of work in this area a few
> > > > > years
> > > > > ago.
> > > > >
> > > > > > On Fri, Apr 26, 2019 at 6:22 PM Jeff Layton <
> > > > > > jlayton at kernel.org>
> > > > > > wrote:
> > > > > > > On Fri, 2019-04-26 at 10:50 -0400, J. Bruce Fields wrote:
> > > > > > > > On Fri, Apr 26, 2019 at 04:11:00PM +0200, Amir Goldstein
> > > > > > > > wrote:
> > > > > > > > > On Fri, Apr 26, 2019, 4:00 PM J. Bruce Fields <
> > > > > > > > > bfields at fieldses.org> wrote:
> > > > > > > > >
> > > > > > > That said, we could also look at a vfs-level mount option
> > > > > > > that
> > > > > > > would
> > > > > > > make the kernel enforce these for any opener. That could
> > > > > > > also
> > > > > > > be useful,
> > > > > > > and shouldn't be too hard to implement. Maybe even make it
> > > > > > > a
> > > > > > > vfsmount-
> > > > > > > level option (like -o ro is).
> > > > > > >
> > > > > >
> > > > > > Yeh, I am humbly going to leave this struggle to someone
> > > > > > else.
> > > > > > Not important enough IMO and completely independent effort to
> > > > > > the
> > > > > > advisory atomic open&lock API.
> > > > >
> > > > > Having the kernel allow setting deny modes on any open call is
> > > > > a
> > > > > non-
> > > > > starter, for the reasons Bruce outlined earlier. This _must_ be
> > > > > restricted in some fashion or we'll be opening up a ginormous
> > > > > DoS
> > > > > mechanism.
> > > > >
> > > > > My proposal was to make this only be enforced by applications
> > > > > that
> > > > > explicitly opt-in by setting O_SH*/O_EX* flags. It wouldn't be
> > > > > too
> > > > > difficult to also allow them to be enforced on a per-fs basis
> > > > > via
> > > > > mount
> > > > > option or something. Maybe we could expand the meaning of '-o
> > > > > mand'
> > > > > ?
> > > > >
> > > > > How would you propose that we restrict this?
> > > > >
> > > >
> > > > Our communication channel is broken.
> > > > I did not intend to propose any implicit locking.
> > > > If samba and nfsd can opt-in with O_SHARE flags, I do not
> > > > understand why a mount option is helpful for the cause of
> > > > samba/nfsd interop.
> > > >
> > > > If someone else is interested in samba/local interop than
> > > > yes, a mount option like suggested by Pavel could be a good
> > > > option,
> > > > but it is an orthogonal effort IMO.
> > >
> > > If an NFS client 'opts in' to set share deny, then that still makes
> > > it
> > > a non-optional lock for the other NFS clients, because all ordinary
> > > open() calls will be gated by the server whether or not their
> > > application specifies the O_SHARE flag. There is no flag in the NFS
> > > protocol that could tell the server to ignore deny modes.
> > >
> > > IOW: it would suffice for 1 client to use O_SHARE|O_DENY* to opt
> > > all
> > > the other clients in.
> > >
> >
> > Sorry for being thick, I don't understand if we are in agreement or
> > not.
> >
> > My understanding is that the network file server implementations
> > (i.e. samba, knfds, Ganesha) will always use share/deny modes.
> > So for example nfs v3 opens will always use O_DENY_NONE
> > in order to have correct interop with samba and nfs v4.
> >
> > If I am misunderstanding something, please enlighten me.
> > If there is a reason why mount option is needed for the sole purpose
> > of interop between network filesystem servers, please enlighten me.
> >
> >
>
> Same difference. As long as nfsd and/or Ganesha are translating
> OPEN4_SHARE_ACCESS_READ and OPEN4_SHARE_ACCESS_WRITE into share access
> locks, then those will conflict with any deny locks set by whatever
> application that uses them.
>
> IOW: any open(O_RDONLY) and open(O_RDWR) will conflict with an
> O_DENY_READ that is set on the server, and any open(O_WRONLY) and
> open(O_RDWR) will conflict with an O_DENY_WRITE that is set on the
> server. There is no opt-out for NFS clients on this issue, because
> stateful NFSv4 opens MUST set one or more of OPEN4_SHARE_ACCESS_READ
> and OPEN4_SHARE_ACCESS_WRITE.
>

Urgh! I *think* I understand the confusion.

I believe Jeff was talking about implementing a mount option
similar to -o mand for local fs on the server.
With that mount option, *any* open() by any app of file from
that mount will use O_DENY_NONE to interop correctly with
network servers that explicitly opt-in for interop on share modes.
I agree its a nice feature that is easy to implement - not important
for first version IMO.

I *think* you are talking on nfs client mount option for
opt-in/out of share modes? there was no such intention.

Thanks,
Amir.