saner calling conventions for nfs_fs_mount_common()

Allow it to take ERR_PTR() for server and return ERR_CAST() of it in
such case.  All callers used to open-code that...

Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/nfs4super.c

@@ -110,21 +110,12 @@ nfs4_remote_mount(struct file_system_type *fs_type, int flags,
 {
 	struct nfs_mount_info *mount_info = info;
 	struct nfs_server *server;
-	struct dentry *mntroot = ERR_PTR(-ENOMEM);
 
 	mount_info->set_security = nfs_set_sb_security;
 
 	/* Get a volume representation */
 	server = nfs4_create_server(mount_info, &nfs_v4);
-	if (IS_ERR(server)) {
-		mntroot = ERR_CAST(server);
-		goto out;
-	}
-
-	mntroot = nfs_fs_mount_common(server, flags, dev_name, mount_info, &nfs_v4);
-
-out:
-	return mntroot;
+	return nfs_fs_mount_common(server, flags, dev_name, mount_info, &nfs_v4);
 }
 
 static struct vfsmount *nfs_do_root_mount(struct file_system_type *fs_type,
@@ -280,11 +271,6 @@ nfs4_remote_referral_mount(struct file_system_type *fs_type, int flags,
 
 	/* create a new volume representation */
 	server = nfs4_create_referral_server(mount_info.cloned, mount_info.mntfh);
-	if (IS_ERR(server)) {
-		mntroot = ERR_CAST(server);
-		goto out;
-	}
-
 	mntroot = nfs_fs_mount_common(server, flags, dev_name, &mount_info, &nfs_v4);
 out:
 	nfs_free_fhandle(mount_info.mntfh);

fs/nfs/super.c

@@ -1903,9 +1903,6 @@ struct dentry *nfs_try_mount(int flags, const char *dev_name,
 	else
 		server = nfs_mod->rpc_ops->create_server(mount_info, nfs_mod);
 
-	if (IS_ERR(server))
-		return ERR_CAST(server);
-
 	return nfs_fs_mount_common(server, flags, dev_name, mount_info, nfs_mod);
 }
 EXPORT_SYMBOL_GPL(nfs_try_mount);
@@ -2666,6 +2663,9 @@ struct dentry *nfs_fs_mount_common(struct nfs_server *server,
 	};
 	int error;
 
+	if (IS_ERR(server))
+		return ERR_CAST(server);
+
 	if (server->flags & NFS_MOUNT_UNSHARED)
 		compare_super = NULL;
 
@@ -2814,9 +2814,6 @@ nfs_xdev_mount(struct file_system_type *fs_type, int flags,
 	/* create a new volume representation */
 	server = nfs_mod->rpc_ops->clone_server(NFS_SB(data->sb), data->fh, data->fattr, data->authflavor);
 
-	if (IS_ERR(server))
-		mntroot = ERR_CAST(server);
-	else
 	mntroot = nfs_fs_mount_common(server, flags,
 				dev_name, &mount_info, nfs_mod);