NFSD: Add a Kconfig setting to enable delegated timestamps

After three tries, we still see test failures with delegated
timestamps. Disable them by default, but leave the implementation
intact so that development can continue.

Cc: stable@vger.kernel.org # v6.14
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/Kconfig

@@ -172,6 +172,16 @@ config NFSD_LEGACY_CLIENT_TRACKING
 	  recoverydir, or spawn a process directly using a usermodehelper
 	  upcall.
 
-	  These legacy client tracking methods have proven to be probelmatic
+	  These legacy client tracking methods have proven to be problematic
 	  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.

fs/nfsd/nfs4state.c

@@ -5956,11 +5956,23 @@ 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)
+{
+	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,
 		    struct svc_fh *parent)
 {
-	bool deleg_ts = open->op_deleg_want & OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS;
+	bool deleg_ts = nfsd4_want_deleg_timestamps(open);
 	struct nfs4_client *clp = stp->st_stid.sc_client;
 	struct nfs4_file *fp = stp->st_stid.sc_file;
 	struct nfs4_clnt_odstate *odstate = stp->st_clnt_odstate;
@@ -6168,8 +6180,8 @@ static void
 nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
 		     struct svc_fh *currentfh)
 {
-	bool deleg_ts = open->op_deleg_want & OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS;
 	struct nfs4_openowner *oo = openowner(stp->st_stateowner);
+	bool deleg_ts = nfsd4_want_deleg_timestamps(open);
 	struct nfs4_client *clp = stp->st_stid.sc_client;
 	struct svc_fh *parent = NULL;
 	struct nfs4_delegation *dp;