Re: constant st_ino/st_dev for non-samefs case

[Chandan Rajendra <chandan@linux.vnet.ibm.com>]

On Wednesday, May 24, 2017 2:03:29 AM IST Amir Goldstein wrote:
> On Tue, May 23, 2017 at 4:19 PM, Chandan Rajendra
> <chandan@linux.vnet.ibm.com> wrote:
> > On Tuesday, May 23, 2017 6:27:42 PM IST Amir Goldstein wrote:
> >> On Wed, May 17, 2017 at 3:46 PM, Chandan Rajendra
> >> <chandan@linux.vnet.ibm.com> wrote:
> >> > On Wednesday, May 17, 2017 5:56:31 PM IST Amir Goldstein wrote:
> >> >> On Wed, May 17, 2017 at 2:42 PM, Chandan Rajendra
> >>
> >> >> There is actually one task that should be very simple to do and can also
> >> >> bring large benefit for many users.
> >> >>
> >> >> In his pull request for kernel 4.12 Miklos writes:
> >> >> "The biggest part of this is making st_dev/st_ino on the overlay behave like a
> >> >> normal filesystem ... future work will move the general case towards more sane
> >> >> behavior."
> >> >> https://marc.info/?l=linux-unionfs&m=149442365202823&w=2
> >> >>
> >> >> The work towards constant st_dev/st_ino for the general case is not within my
> >> >> immediate scope of interest, but it shouldn't be hard. The basic idea was
> >> >> explained by  Miklos here:
> >> >> https://marc.info/?l=linux-unionfs&m=149259338809700&w=2
> >> >>
> >> > Amir, I will work on this task. Thanks for the guidance.
> >> >
> >>
> >> Hi Chandan,
> >>
> >> Were you able to figure out the scope of the task?
> >> Or didn't get around to it yet?
> >
> > Hi Amir,
> >
> > I spent time understanding current overlayfs code. I am now starting to
> > work on the problem statement.
> >
> > I should be able to post the patches to the mailing list by the end of
> > this week.
> >
> ...
> >>
> >> Please let me know if you intend to work on this soon, because I may be
> >> working on some parts of this task for a different feature.
> 
> Chandan,
> 
> My apologies for biting into your task, but as I wrote, I needed some parts
> for another feature, so implemented partial non-samefs support [1].
> At least one of the 2 "relax same fs" patches was not as trivial as I indented
> for your task to be.
> 
> You still need to implement this part:
> "The only extra thing needed compared to the samefs case is the allocation
> of dummy device numbers for lower layers."
> 
> I also fixes unionmount-testsuite to check constant inode for non samefs [2].
> 
> The problem now is that all the test pass, although, as I wrote, I only
> implemented partial support for non samefs. This means that the test coverage
> for constant st_ino/st_dev is insufficient to validate the results of your task.
> Which is good, because it will give you an opportunity to enhance the tests :)
> 
> It would be great if you could add validation to the fact that the
> overlay st_ino/
> st_dev pair is different from the underlying inode st_ino/st_dev.
> That is not the case with upstream overlayfs and that is not the case with
> my partial work on non same fs constant st_ino.
> 
> A new overlay xfstest, along the lines of overlay/017 that validates
> the uniqueness of st_ino/st_dev would also be a good idea.

Amir, Thanks for informing me. I will base my work on top of your patches.

> 
> Thanks,
> Amir.
> 
> [1] https://github.com/amir73il/linux/commits/ovl-constino
> [2] https://github.com/amir73il/unionmount-testsuite/commits/ovl-constino
> 
> 


-- 
chandan