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SubjectRe: [PATCH 1/3] vfs: dedpue: return s64
On Mon, May 07, 2018 at 01:32:09PM +0200, Miklos Szeredi wrote:
> On Mon, May 7, 2018 at 1:11 PM, Matthew Wilcox <willy@infradead.org> wrote:
> > 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.
>
> Next patch turns the offsets into loff_t and leaves "len" as u64. A
> size is definitely not an offset, I'd consider changing the type of
> "len" to loff_t a misuse.

Usually a size is the size of something in memory. The length of
something on storage is definitely an loff_t. Look at fallocate()
for an example. You could also argue that lseek where whence is set to
anything other than SEEK_SET is also being used as a length rather than
an absolute offset. We also already use 'loff_t len' as an argument to
vfs_dedupe_file_range_compare().

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