Re: overlayfs: issue with a replaced lower squashfs with export-table

[Vivek Goyal <vgoyal@redhat.com>]

On Wed, Jul 08, 2020 at 11:50:29AM +0300, Amir Goldstein wrote:
> On Wed, Jul 8, 2020 at 11:37 AM Miklos Szeredi <miklos@szeredi.hu> wrote:
> >
> > On Wed, Jul 8, 2020 at 10:31 AM Amir Goldstein <amir73il@gmail.com> wrote:
> >
> > >
> > > 1) is not problematic IMO and the simple patch I posted may be applied
> > > for fixing the reported issue, but it only solved the special case of null uuid.
> > > The problem still exists with re-creating lower on xfs/ext4, e.g. by
> > > rm -rf and unpacking image tar.
> >
> > How so?  st_ino may be reused but the fh is guaranteed to be unique.
> >
> 
> Doh! You are right. I was talking nonsense.
> The only problem would be with re-creating an xfs/ext4 lower image
> with the same uuid maybe because a basic image is cloned.
> 
> In any case, it's a corner of a corner of a corner.
> I will post the patch to fix null uuid.

It will also be good if we can bring some clarity to the documentation
for future references in section "Sharing and copying layers".

So if IIUC,

- sharing layers should work with all features of overlayfs.

- copying layers works only if index and nfs_export is not enabled. Even
  if index is not enabled, copying layers will change inode number
  reporting behavior (as origin verification will fail). We probably
  say something about this.

- Modifying/recreating lower layer only works when
  metacopy/index/nfs_export are not enabled at any point of time. This
  also will change inode number reporting behavior.

Is that a fair understanding? I am not sure how exactly inode number
reporting will change when lower layers are copied or recreated.

Thanks
Vivek