Re: [PATCH 01/39] vfs: dedpue: return loff_t

From: Miklos Szeredi
Date: Tue Jun 05 2018 - 04:33:30 EST

On Mon, Jun 4, 2018 at 10:43 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> 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...