Re: [PATCH v10 07/18] ovl: Add mechanism to create a chain of origin dentries

[Vivek Goyal <vgoyal@redhat.com>]

On Tue, Jan 23, 2018 at 03:47:29PM +0200, Amir Goldstein wrote:
> On Tue, Jan 23, 2018 at 3:45 PM, Vivek Goyal <vgoyal@redhat.com> wrote:
> > On Mon, Jan 22, 2018 at 09:46:33PM +0200, Amir Goldstein wrote:
> >> On Mon, Jan 22, 2018 at 9:34 PM, Amir Goldstein <amir73il@gmail.com> wrote:
> >> > On Mon, Jan 22, 2018 at 8:39 PM, Vivek Goyal <vgoyal@redhat.com> wrote:
> >> >> There is a need to support metacopy dentry in midlayer. That means there
> >> >> could be a chain of metacopy dentries.
> >> >>
> >> >> For example, upper could be metacopy, midlayer lower could be metacopy and
> >> >> lowest layer could be actual data inode. This means when we copy up actual
> >> >> data, we should be able to reach to lowest data inode and copy up data from
> >> >> there. And that means we should keep track of all the dentries in origin
> >> >> chain which lead to data inode.
> >> >>
> >> >> Current ovl_check_origin() logic only looks for one origin dentry. This patch
> >> >> enhances ovl_check_origin() to continue to follow origin chain and return
> >> >> all the origin entries found. This is done only if caller of the function
> >> >> set "follow_chain" argument.
> >> >>
> >> >
> >> > We don't really need to keep the entire chain do we?
> >> > We can follow chain but keep only the one inode that is not a metacopy inode.
> >> > All the rest are useless, no?
> >> > Then we don't create a new type of object - non-dir with numlower > 1.
> >> >
> >>
> >> Seems like if you don't keep the entire chain, then no need for
> >> patches 14 and 15.
> >
> > I will need to have atleast 2 lower dentries. One will be top most
> > metadata copy and other lower most data dentry. IOW, both the ends of
> > the chain need to be there.
> >
> >> Also with upper metacopy, you can fix upper origin xattr after
> >> following to the data
> >> origin and forget about middle layer metacopies forever.
> >
> > If upper metacopy is alreday there, then I agree that lower top most
> > becomes inner node of chain and we can get rid of it.
> >
> >>
> >> Am I missing something?
> >
> > I think you are missing the case when there is no upper and lower has
> > a metacopy chain. In that case we need to retain two dentries. One for
> > data copy up and one for metadata copy up.
> >
> 
> OK. so you can get rid of all the middle metacopies while following
> the origin chain. no reason to keep those.

Sure, will do that. As of now there are no users of intermediate nodes.
Once somebody needs these, code can be modified.

Vivek