On Tue, Jun 05, 2018 at 10:33:22AM +0200, Miklos Szeredi wrote: > 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... I think we should hoist the MAX_RW_COUNT/2 limit to the VFS helpers since afaict we generally cap max IO per call at MAX_RW_COUNT. (I probably should've capped ocfs2 back when I did xfs, but forgot). If btrfs wants to keep their lower (16M) limit then they're free to do so; the interface documentation allows for this. One of the btrfs developers seems to be working on a patch series to raise the limit[1] anyway. --D [1] https://www.spinics.net/lists/linux-btrfs/msg78392.html > > Thanks, > Miklos
