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?