linux-kernel - Re: [PATCH 1/3] vfs: dedpue: return s64

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Message-ID: <20180507111142.GA18116@bombadil.infradead.org>
Date:   Mon, 7 May 2018 04:11:42 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, Amir Goldstein <amir73il@...il.com>
Subject: Re: [PATCH 1/3] vfs: dedpue: return s64

On Mon, May 07, 2018 at 10:21:06AM +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).
> 
> Returning s64 should be good, since clone_verify_area() makes sure that the
> supplied length doesn't overflow.

Why s64 rather than loff_t?  Particularly since the next patch turns
the paramters into loff_t.