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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Tue, 5 Jun 2018 10:33:22 +0200
Message-ID: <CAJfpegun8HyjODXguHstxYrGE2nuSoCCicaHT3yfYWMkxxmVWg@mail.gmail.com>
Subject: Re: [PATCH 01/39] vfs: dedpue: return loff_t
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Miklos Szeredi <mszeredi@redhat.com>,
        overlayfs <linux-unionfs@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-xfs <linux-xfs@vger.kernel.org>, ocfs2-devel@oss.oracle.com
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On Mon, Jun 4, 2018 at 10:43 AM, Christoph Hellwig <hch@infradead.org> wrote:
> On Tue, May 29, 2018 at 04:43:01PM +0200, Miklos Szeredi wrote:
>> f_op->dedupe_file_range() gets a u64 length to dedup and returns an ssize_t
>> actual length deduped.  This breaks badly on 32bit archs since the returned
>> length will be truncated and possibly overflow into the sign bit (xfs and
>> ocfs2 are affected, btrfs limits actual length to 16MiB).
>
> Can we just make it return 0 vs errno?  The only time we return
> a different length than the one passed in is due to the btrfs cap.
>
> Given that this API started out on btrfs we should just do the cap
> everywhere to not confuse userspace.

And that's a completely arbitrary cap; sure btrfs started out with
that, but there's no fundamental reason for that becoming the global
limit.  Xfs now added a different, larger limit, so based on what
reason should that limit be reduced?

I don't care either way, but at this stage I'm not going to change
this patch, unless there's a very good reason to do so, because if I
do someone will come and suggest another improvement, ad-infinitum...

Thanks,
Miklos