Re: Re: Question about ESTALE error whene deleting upper directory file.

["YoungJun.Park" <her0gyugyu@gmail.com>]

On Mon, Nov 07, 2022 at 08:40:02AM +0200, Amir Goldstein wrote:
> On Mon, Nov 7, 2022 at 6:38 AM YoungJun.Park <her0gyugyu@gmail.com> wrote:
> >
> > Here is my curious scenario.
> >
> > 1. create a file on overlayfs.
> > 2. delete a file on upper directory.
> > 3. can see file contents using read sys call. (may file operations all success)
> > 4. cannot remove, rename. it return -ESTALE error (may inode operations fail)
> >
> > I understand this scenario onto the code level.
> > But I don't understand this situation itself.
> >
> > I found a overlay kernel docs and it comments
> > Changes to underlying filesystems section
> >
> > ...
> > Changes to the underlying filesystems while part of a mounted overlay filesystem are not allowed.
> > If the underlying filesystem is changed, the behavior of the overlay is undefined,
> > though it will not result in a crash or deadlock.
> > ....
> >
> > So here is my question (may it is suggestion)
> >
> > 1. underlying file system change is not allowed, then how about implementing shadow upper directory from user?
> > 2. if read, write system call is allowed, how about changing remove, rename(and more I does not percept) operation success?
> >
> 
> What is your use case?
> Why do you think this is worth spending time on?
> If anything, we could implement revalidate to return ESTALE also from open
> in such a case.
> But again, why do you think that would matter?
> 
> Thanks,
> Amir.

Thank you for replying.
I develop antivirus scanner.
When developing, I am confronted the situaion below.

1. make a docker container using overlayfs
2. our antivirus scanner detect on upperdir and remove it.
3. When I check container, the file contents can be read, buf file cannot be removed.(-ESTALE error)

And as I think, the reason is upperdir is touchable. So it is better to hide upperdir.
If it is hard to implement(or maybe there is a other reson that I don' know)
it is better to make the situation is clear 
(file operation error, inode operations error or file operation success , inode operation success)

Thank you again Amir.
Best regards