Re: [PATCH v15 10/30] ovl: Modify ovl_lookup() and friends to lookup metacopy dentry

[Vivek Goyal <vgoyal@redhat.com>]

On Thu, May 10, 2018 at 11:19:23AM +0200, Miklos Szeredi wrote:

[..]
> > @@ -925,18 +943,36 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >                  * When "verify_lower" feature is enabled, do not merge with a
> >                  * lower dir that does not match a stored origin xattr. In any
> >                  * case, only verified origin is used for index lookup.
> > +                *
> > +                * For non-dir dentry, make sure dentry found by lookup
> > +                * matches the origin stored in upper. Otherwise its an
> > +                * error.
> 
> Umm, why we need to be so strict?  This would  break the case where
> the layers are copied with xattr intact, but the origin pointer will
> obviously be "wrong", which shouldn't be a problem, since that's only
> needed to get a unique st_ino, nothing else.

So I have few questions at this point of time, I am not clear about what
should be the behavior.

- Layer copying does not work with index=on. So if index is on, it is fair
  to assume that layer copying will not be allowed and that configuration
  is not supported. If yes, then we could enforce this check with index=on
  and not in other cases.

- If we do not enforce ORIGIN verification for non-dir metacopy and
  overlay is mounted again after layer copy, then before data copy up we
  will report inode number of lowerstack[0]. And after data copy up it
  could be inode number of any of the following.

  A. lower inode (if previous overlay dentry has not been flushed, it will
  		  have CONST_INO set.).
  B. upper inode (if previous overlay dentry got flushed out, and new
     lookup could not decode ORIGIN).

  C. older lower inode (if previous overlay dentry got flushed out, and
     new lookup decoded previous inode before layer copy up.)

I guess both B and C will happen with existing code even with normal copy
up. So this behavior with metacopy files might not be a huge concern.

Thanks
Vivek