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Message-ID: <6065a76f32face0fa5cf84a238bcb1f2eebec7b5.camel@kernel.org>
Subject: Re: NFSv4.1 mandatory locks working in Linux nfsd ?
From: Jeff Layton <jlayton@kernel.org>
To: Dan Shelton <dan.f.shelton@gmail.com>
Cc: Roland Mainz <roland.mainz@nrubsig.org>, Linux NFS Mailing List
	 <linux-nfs@vger.kernel.org>
Date: Thu, 11 Jan 2024 20:24:57 -0500
In-Reply-To: <CAAvCNcCC7xB1oWoSxaL269T62TuOYx64A+49fRoJTFJZ6xD+EA@mail.gmail.com>
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On Fri, 2024-01-12 at 01:44 +0100, Dan Shelton wrote:
> On Thu, 11 Jan 2024 at 23:53, Jeff Layton <jlayton@kernel.org> wrote:
> >=20
> > On Thu, 2024-01-11 at 22:27 +0100, Roland Mainz wrote:
> > > On Thu, Jan 11, 2024 at 4:55=E2=80=AFPM Jeff Layton <jlayton@kernel.o=
rg> wrote:
> > > > On Thu, 2024-01-11 at 10:54 -0500, Jeff Layton wrote:
> > > > > On Sun, 2023-12-24 at 18:29 +0100, Roland Mainz wrote:
> > > > > > Are there any known issues with NFSv4.1 mandatory locking nfsd =
code in
> > > > > > the Linux 5.10.0-22-rt-amd64 kernel (technically the Debian Bul=
lseye
> > > > > > RT kernel) ? Is there any kernel or NFS test suite module which=
 covers
> > > > > > NFSv4.1 client mandatory locking ?
> > > > >=20
> > > > > Linux doesn't support mandatory locking at all since 2021 [1]. Th=
e Linux
> > > > > NFS client and server therefore do not support v4.1 mandatory loc=
king.
> > > >=20
> > > > Forgot the footnote!
> > > >=20
> > > > [1]: https://patchwork.kernel.org/project/linux-fsdevel/patch/20210=
820114046.69282-1-jlayton@kernel.org/
> > >=20
> > > OK, this is pretty bad in terms of interoperability.... ;-(
> > >=20
> > > What should a Windows NFSv4 client (Hummingbird, OpenText, Exceed,
> > > ms-nfs41-client, ...) do in this case ?
> > > It basically means that locking for these clients will fail if the
> > > server does not support it... ;-(
> > >=20
> >=20
> > I think they have two choices:
> >=20
> > Learn to deal with advisory locking, or contribute some sort of (sane)
> > mandatory locking implementation to the Linux kernel.
>=20
> None of this will happen.
> 1. Advisory locking cannot be mapped to Windows mandatory locking. End
> of story. They are incompatible. That is why the NFSv4 protocol had
> mandatory locking built in into the first place. That was the grand
> design and the grand dream. That is gone.

Yep, pretty much. Samba does set VFS-layer advisory locks that (mostly)
correspond to the locks that SMB clients set, but it's really just a
best-effort sort of thing. It has to emulate the windows semantics
internally.

> 2. No one is going to implement a giant set of code just so that SAMBA
> and NFSv4 can work. SAMBA has a builtin emulation so mandatory locking
> works between Windows clients, ignoring the Linux side and Linux
> advisory locking completely.
>=20

Also, pretty much. With a general purpose OS like Linux, we try to avoid
this sort of emulation. We do have that for the share/deny locking that
happens during OPEN, but there was really no choice there since we
couldn't reasonably implement that in the VFS, and it was a required
part of the NFSv4 protocol.

Mandatory locking is optional so we can just opt-out.

> The only option is option three: NFSv4 for Windows will become a 3rd
> class glorified FTP replacement with no functional locking. Just for
> copying files around. End of story.
>=20

More or less. FWIW, here's the LWN article from when we decided to start
getting rid of mandatory locking in Linux:

    https://lwn.net/Articles/667210/

No one used it. It was racy and there weren't great ways to fix that
that didn't slow down I/O.=20
--=20
Jeff Layton <jlayton@kernel.org>