IMO there should be a debug setting to turn this off, as it might
cause bugs in production environments. Similar to -O0 for cc, just in
case.

Ced

On Tue, 10 Jun 2025 at 14:03, Dai Ngo [off-list ref] wrote:

On 6/10/25 2:59 AM, Cedric Blancher wrote:

quoted

On Tue, 10 Jun 2025 at 02:17, Dai Ngo
[off-list ref] wrote:

quoted

On 6/9/25 4:35 PM, Rick Macklem wrote:

quoted

Hi,

I hope you don't mind a cross-post, but I thought both groups
might find this interesting...

I have been creating a compound RPC that does REMOVE and
then tries to determine if the file object has been removed and
I was surprised to see quite different results from the Linux knfsd
and Solaris 11.4 NFSv4.1/4.2 servers. I think both these servers
provide FH4_PERSISTENT file handles, although I suppose I
should check that?

First, the test OPEN/CREATEs a regular file called "foo" (only one
hard link) and acquires a write delegation for it.
Then a compound does the following:
...
REMOVE foo
PUTFH fh for foo
GETATTR

For the Solaris 11.4 server, the server CB_RECALLs the
delegation and then replies NFS4ERR_STALE for the PUTFH above.
(The FreeBSD server currently does the same.)

For a fairly recent Linux (6.12) knfsd, the above replies NFS_OK
with nlinks == 0 in the GETATTR reply.

Hmm. So I've looked in RFC8881 (I'm terrible at reading it so I
probably missed something) and I cannot find anything that states
either of the above behaviours is incorrect.
(NFS4ERR_STALE is listed as an error code for PUTFH, but the
description of PUTFH only says that it sets the CFH to the fh arg.
It does not say anything w.r.t. the fh arg. needing to be for a file
that still exists.) Neither of these servers sets
OPEN4_RESULT_PRESERVE_UNLINKED in the OPEN reply.

So, it looks like "file object no longer exists" is indicated either
by a NFS4ERR_STALE reply to either PUTFH or GETATTR
OR
by a successful reply, but with nlinks == 0 for the GETATTR reply.

To be honest, I kinda like the Linux knfsd version, but I am wondering
if others think that both of these replies is correct?

Also, is the CB_RECALL needed when the delegation is held by
the same client as the one doing the REMOVE?

The Linux NFSD detects the delegation belongs to the same client that
causes the conflict (due to REMOVE) and skips the CB_RECALL. This is
an optimization based on the assumption that the client would handle
the conflict locally.

Does Linux nfsd have a setting to turn such optimizations OFF (all of them)?

There is no setting to turn off the optimization of delegation recall from
the same client.

-Dai

quoted

Ced

-- 
Cedric Blancher [off-list ref]
[https://plus.google.com/u/0/+CedricBlancher/]
Institute Pasteur