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Date: Mon, 11 Dec 2017 06:29:47 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: NeilBrown <neilb@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
        Amir Goldstein <amir73il@gmail.com>,
        lkml <linux-kernel@vger.kernel.org>,
        Lennart Poettering <lennart@poettering.net>
Subject: Re: [PATCH 1/4] fs/notify: fdinfo can report unsupported file
 handles.
Message-ID: <20171211062946.GX21978@ZenIV.linux.org.uk>
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 <151297224512.7818.18333908109878259066.stgit@noble>
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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?