NFSv4: Turn off open-by-filehandle and NFS re-export for NFSv4.0

The NFSv4.0 protocol only supports open() by name. It cannot therefore
be used with open_by_handle() and friends, nor can it be re-exported by
knfsd.

Reported-by: Chuck Lever III <chuck.lever@oracle.com>
Fixes: 20fa190 ("nfs: add export operations")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/super.c

@@ -1051,22 +1051,31 @@ static void nfs_fill_super(struct super_block *sb, struct nfs_fs_context *ctx)
 	if (ctx->bsize)
 		sb->s_blocksize = nfs_block_size(ctx->bsize, &sb->s_blocksize_bits);
 
-	if (server->nfs_client->rpc_ops->version != 2) {
-		/* The VFS shouldn't apply the umask to mode bits. We will do
-		 * so ourselves when necessary.
+	switch (server->nfs_client->rpc_ops->version) {
+	case 2:
+		sb->s_time_gran = 1000;
+		sb->s_time_min = 0;
+		sb->s_time_max = U32_MAX;
+		break;
+	case 3:
+		/*
+		 * The VFS shouldn't apply the umask to mode bits.
+		 * We will do so ourselves when necessary.
 		 */
 		sb->s_flags |= SB_POSIXACL;
 		sb->s_time_gran = 1;
-		sb->s_export_op = &nfs_export_ops;
-	} else
-		sb->s_time_gran = 1000;
-
-	if (server->nfs_client->rpc_ops->version != 4) {
 		sb->s_time_min = 0;
 		sb->s_time_max = U32_MAX;
-	} else {
+		sb->s_export_op = &nfs_export_ops;
+		break;
+	case 4:
+		sb->s_flags |= SB_POSIXACL;
+		sb->s_time_gran = 1;
 		sb->s_time_min = S64_MIN;
 		sb->s_time_max = S64_MAX;
+		if (server->caps & NFS_CAP_ATOMIC_OPEN_V1)
+			sb->s_export_op = &nfs_export_ops;
+		break;
 	}
 
 	sb->s_magic = NFS_SUPER_MAGIC;