[PATCH] nfsd: only register cld pipe notifier when CONFIG_NFSD_V4 is enabled

[Jeff Layton <jlayton@redhat.com>]

Otherwise, we get a warning or error similar to this when building with
CONFIG_NFSD_V4 disabled:

    ERROR: "nfsd4_cld_block" [fs/nfsd/nfsd.ko] undefined!

Fix this by wrapping the calls to rpc_pipefs_notifier_register and
..._unregister in another function and providing no-op replacements
when CONFIG_NFSD_V4 is disabled.

Reported-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/nfsd/netns.h       |   10 +++++++++-
 fs/nfsd/nfs4recover.c |   12 ++++++++++++
 fs/nfsd/nfsctl.c      |    6 +++---
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 66eac33..e87ba91 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -31,5 +31,13 @@ struct nfsd_net {
 };
 
 extern int nfsd_net_id;
-extern struct notifier_block nfsd4_cld_block;
+
+#if IS_ENABLED(CONFIG_NFSD_V4)
+extern int register_cld_notifier(void);
+extern void unregister_cld_notifier(void);
+#else /* IS_ENABLED(CONFIG_NFSD_V4) */
+#define register_cld_notifier() 0
+#define unregister_cld_notifier() do { } while(0)
+#endif /* IS_ENABLED(CONFIG_NFSD_V4) */
+
 #endif /* __NFSD_NETNS_H__ */
diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index eaaf948..4767429 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -1032,3 +1032,15 @@ rpc_pipefs_event(struct notifier_block *nb, unsigned long event, void *ptr)
 struct notifier_block nfsd4_cld_block = {
 	.notifier_call = rpc_pipefs_event,
 };
+
+int
+register_cld_notifier(void)
+{
+	return rpc_pipefs_notifier_register(&nfsd4_cld_block);
+}
+
+void
+unregister_cld_notifier(void)
+{
+	rpc_pipefs_notifier_unregister(&nfsd4_cld_block);
+}
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index dee6c1b..2c53be6 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1137,7 +1137,7 @@ static int __init init_nfsd(void)
 	int retval;
 	printk(KERN_INFO "Installing knfsd (copyright (C) 1996 okir@monad.swb.de).\n");
 
-	retval = rpc_pipefs_notifier_register(&nfsd4_cld_block);
+	retval = register_cld_notifier();
 	if (retval)
 		return retval;
 	retval = register_pernet_subsys(&nfsd_net_ops);
@@ -1186,7 +1186,7 @@ out_free_slabs:
 out_unregister_pernet:
 	unregister_pernet_subsys(&nfsd_net_ops);
 out_unregister_notifier:
-	rpc_pipefs_notifier_unregister(&nfsd4_cld_block);
+	unregister_cld_notifier();
 	return retval;
 }
 
@@ -1203,7 +1203,7 @@ static void __exit exit_nfsd(void)
 	nfsd_fault_inject_cleanup();
 	unregister_filesystem(&nfsd_fs_type);
 	unregister_pernet_subsys(&nfsd_net_ops);
-	rpc_pipefs_notifier_unregister(&nfsd4_cld_block);
+	unregister_cld_notifier();
 }
 
 MODULE_AUTHOR("Olaf Kirch <okir@monad.swb.de>");
-- 
1.7.7.6