On Wed, Sep 9, 2015 at 1:09 PM, Chris Mason <c...@fb.com> wrote: > On Tue, Sep 08, 2015 at 04:08:43PM -0700, Andy Lutomirski wrote: >> On Tue, Sep 8, 2015 at 3:39 PM, Darrick J. Wong <darrick.w...@oracle.com> >> wrote: >> > On Tue, Sep 08, 2015 at 02:45:39PM -0700, Andy Lutomirski wrote: >> >> What I meant by this was: if you ask for "regular copy", you may end >> >> up with a reflink anyway. Anyway, how can you reflink a range and >> >> have the contents *not* be the same? >> > >> > reflink forcibly remaps fd_dest's range to fd_src's range. If they didn't >> > match before, they will afterwards. >> > >> > dedupe remaps fd_dest's range to fd_src's range only if they match, of >> > course. >> > >> > Perhaps I should have said "...if the contents are the same before the >> > call"? >> > >> >> Oh, I see. >> >> Can we have a clean way to figure out whether two file ranges are the >> same in a way that allows false negatives? I.e. return 1 if the >> ranges are reflinks of each other and 0 if not? Pretty please? I've >> implemented that in the past on btrfs by syncing the ranges and then >> comparing FIEMAP output, but that's hideous. > > I'd almost rather have a separate call, maybe unshare_file_range()? > > Is that the end goal to the sharing check?
My use case was archival. I can reflink data between a working copy and some archived copy and then I can very efficiently tell if the working copy has been changed by checking if the reflink is still linked. It would be even better if I could enumerate which parts of one file match which parts of another file. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
