linux-kernel - Re: [PATCH v2 2/2] nfsd: remove NFSD_V4_DELEG

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Message-Id: <a6960530-c872-4bc8-a125-0834f12a6108@app.fastmail.com>
Date: Sun, 25 Jan 2026 11:43:21 -0500
From: "Chuck Lever" <cel@...nel.org>
To: "Jeff Layton" <jlayton@...nel.org>,
 "Chuck Lever" <chuck.lever@...cle.com>, NeilBrown <neil@...wn.name>,
 "Olga Kornievskaia" <okorniev@...hat.com>, "Dai Ngo" <Dai.Ngo@...cle.com>,
 "Tom Talpey" <tom@...pey.com>
Cc: linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] nfsd: remove NFSD_V4_DELEG_TIMESTAMPS Kconfig option



On Sun, Jan 25, 2026, at 7:24 AM, Jeff Layton wrote:
> Now that there is a runtime debugfs switch, eliminate the compile-time
> switch and always build in support for delegated timestamps.
>
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
>  fs/nfsd/Kconfig     | 10 ----------
>  fs/nfsd/nfs4state.c |  7 -------
>  2 files changed, 17 deletions(-)
>
> diff --git a/fs/nfsd/Kconfig b/fs/nfsd/Kconfig
> index 
> 4fd6e818565ea24e4e16844a3f82e808dbc558f8..fc0e87eaa25714d621aa893c99dabe4ce34228df 
> 100644
> --- a/fs/nfsd/Kconfig
> +++ b/fs/nfsd/Kconfig
> @@ -177,16 +177,6 @@ config NFSD_LEGACY_CLIENT_TRACKING
>  	  and will be removed in the future. Say Y here if you need support
>  	  for them in the interim.
> 
> -config NFSD_V4_DELEG_TIMESTAMPS
> -	bool "Support delegated timestamps"
> -	depends on NFSD_V4
> -	default n
> -	help
> -	  NFSD implements delegated timestamps according to
> -	  draft-ietf-nfsv4-delstid-08 "Extending the Opening of Files". This
> -	  is currently an experimental feature and is therefore left disabled
> -	  by default.
> -
>  config NFSD_V4_POSIX_ACLS
>  	bool "Support NFSv4 POSIX draft ACLs"
>  	depends on NFSD_V4
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 
> 95f2e87141a7ab5dd3da6741859bdcae28a8c6c0..e2f29ba490c6335e2cb6c3a411770b3a19755095 
> 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -6047,19 +6047,12 @@ nfsd4_verify_setuid_write(struct nfsd4_open 
> *open, struct nfsd_file *nf)
>  	return 0;
>  }
> 
> -#ifdef CONFIG_NFSD_V4_DELEG_TIMESTAMPS
>  static bool nfsd4_want_deleg_timestamps(const struct nfsd4_open *open)
>  {
>  	if (!nfsd_delegts_enabled)
>  		return false;
>  	return open->op_deleg_want & OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS;
>  }
> -#else /* CONFIG_NFSD_V4_DELEG_TIMESTAMPS */
> -static bool nfsd4_want_deleg_timestamps(const struct nfsd4_open *open)
> -{
> -	return false;
> -}
> -#endif /* CONFIG NFSD_V4_DELEG_TIMESTAMPS */
> 
>  static struct nfs4_delegation *
>  nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
>
> -- 
> 2.52.0

Thanks for jumping on the robot report.

This time around, LLM review produced some comments related to
documentation that seem pretty sensible to me, so I'm passing
these along verbatim:

  Key Concerns:                                                                                                                                 

  1. Behavioral change: Systems that previously disabled this experimental feature at compile-time will now have it enabled by default after upgrade. While the runtime switch allows disabling, administrators are not informed of this change.
  2. Documentation gap: The commit message is minimal and doesn't explain the transition rationale, migration path, or the loss of the RFC specification reference that was in the Kconfig help text.

[ cel: Perhaps some of the context provided in the cover letter
is not visible to the LLM -- but note, that context won't appear
in the commit history either ]

  Recommendations:                                                                                                                              
                                                                                                                                                
  1. Consider whether nfsd_delegts_enabled should default to false to preserve the conservative default of the removed Kconfig option, or document the intentional policy shift
  2. Expand commit message to include migration guidance:                                                                                       
  Administrators who previously disabled this feature at compile time can disable it at runtime via:
    echo 0 > /sys/kernel/debug/nfsd/delegated_timestamps                                                                                        
  3. Add a brief comment above nfsd4_want_deleg_timestamps() documenting the debugfs control and RFC reference


As the new debugfs switch is intended to be undocumented and
temporary, I think adding some code comments and a little more
beef to the commit message (sorry vegans) would be helpful. You
don't need to go crazy with it.


-- 
Chuck Lever