Re: [PATCH v2 01/18] overlay: implement fsck utility

[Vivek Goyal <vgoyal@redhat.com>]

On Fri, Dec 15, 2017 at 03:18:58PM +0100, Miklos Szeredi wrote:
> On Thu, Dec 14, 2017 at 5:29 PM, Amir Goldstein <amir73il@gmail.com> wrote:
> > On Thu, Dec 14, 2017 at 5:48 PM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> >> On Thu, Dec 14, 2017 at 4:18 PM, Amir Goldstein <amir73il@gmail.com> wrote:
> >>> On Thu, Dec 14, 2017 at 5:10 PM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> > [...]
> >>> Yes :) Docker uses tar alright.
> >>> But for example "origin" xattr cannot be exported as is to a portable format.
> >>> Need to decode file handles during export and change them to "redirect"
> >>> for directories and possible to "redirect" for files as well, that
> >>> would be converted
> >>> back to "origin" on import.
> >>
> >> Is it worth preserving origin for non-hardlinks?  Same story as "cp
> >> -a", inode numbers will change, so there doesn't appear to be a reason
> >> to preserve the connection between origin and the copied up file.
> >
> > Besides metacopy, no reason.
> >
> >>
> >>> Exporting index is a challenge for the same reason and also because tar can
> >>> break hardlinks on extract. Probably index should be rebuilt from scratch on
> >>> import, based on "redirect".
> >>
> >> Yes, hard links need special handling, so will metacopy.  Might be
> >> worth adding "redirect" to hard links and metacopy to make this issue
> >> less of a problem.
> >>
> >
> > Do you mean add it now in kernel? hmm, that's just another thing that
> > can become inconsistent, so I don't see the immediate value.
> 
> The immediate value is that no need for a special pack/unpack tool for
> transferring the overlay "image".

Hi Miklos,

So idea is that I should use use REDIRECT xattr instead of ORIGIN for
metacopy. I guess it should work for atleast metacopy feature. Just
that order of lower dirs during mount will not be detected and IIUC,
we might end up doing a copy up of wrong file.

Vivek