[PATCH v2] nfs: add dummy definition for nfsd_file

[Mike Snitzer <snitzer@kernel.org>]

Add dummy definition for nfsd_file in both nfslocalio.c and localio.c
so various compilers (e.g. gcc 8.5.0 and 9.5.0) can be used. Otherwise
RCU code (rcu_dereference and rcu_access_pointer) will dereference
what should just be an opaque pointer (by using typeof(*ptr)).

Fixes: 86e00412254a ("nfs: cache all open LOCALIO nfsd_file(s) in client")
Cc: stable@vger.kernel.org
Tested-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>
Tested-by: Pali Rohár <pali@kernel.org>
Tested-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
---
 fs/nfs/localio.c           | 8 ++++++++
 fs/nfs_common/nfslocalio.c | 8 ++++++++
 2 files changed, 16 insertions(+)

v2: fix email used in S-o-B, added 3 Tested-by:s and adjust commit header.

diff --git a/fs/nfs/localio.c b/fs/nfs/localio.c
index 5c21caeae075..830078e5866b 100644
--- a/fs/nfs/localio.c
+++ b/fs/nfs/localio.c
@@ -46,6 +46,14 @@ struct nfs_local_fsync_ctx {
 	struct completion	*done;
 };
 
+/*
+ * nfsd_file structure is purposely kept opaque to NFS client.
+ * This is a dummy definition to make RCU compilation happy.
+ */
+struct nfsd_file {
+	int undefined__;
+};
+
 static bool localio_enabled __read_mostly = true;
 module_param(localio_enabled, bool, 0644);
 
diff --git a/fs/nfs_common/nfslocalio.c b/fs/nfs_common/nfslocalio.c
index 6a0bdea6d644..f3274a70ce5e 100644
--- a/fs/nfs_common/nfslocalio.c
+++ b/fs/nfs_common/nfslocalio.c
@@ -271,6 +271,14 @@ struct nfsd_file *nfs_open_local_fh(nfs_uuid_t *uuid,
 }
 EXPORT_SYMBOL_GPL(nfs_open_local_fh);
 
+/*
+ * nfsd_file structure is purposely kept opaque to NFS client.
+ * This is a dummy definition to make RCU compilation happy.
+ */
+struct nfsd_file {
+	int undefined__;
+};
+
 void nfs_close_local_fh(struct nfs_file_localio *nfl)
 {
 	struct nfsd_file *ro_nf = NULL;
-- 
2.44.0