Re: [PATCH 1/4] fs/notify: fdinfo can report unsupported file handles.

[Al Viro]

On Mon, Dec 11, 2017 at 05:04:05PM +1100, NeilBrown wrote:
> @@ -385,7 +385,9 @@ int exportfs_encode_inode_fh(struct inode *inode, struct fid *fid,
>  {
>  	const struct export_operations *nop = inode->i_sb->s_export_op;
>  
> -	if (nop && nop->encode_fh)
> +	if (nop)
> +		return FILEID_INVALID;
> +	if (nop->encode_fh)
>  		return nop->encode_fh(inode, fid->raw, max_len, parent);

This might as well have been

	if (nop)
		return FILEID_INVALID;
	BUG();

Have you ever tested that?