Issues with OvelayFS + 9P FS

[Miguel Bernal Marin]

Hi Miklos,

I've seen issues when I try to use a Qemu/KVM + 9P and a Overlay FS.

The issue started to show from v4.14 and I bisected the guilty commit to

4edb83bb1041 ("ovl: constant d_ino for non-merge dirs")

The issue is showed when ovl_iterate_real(file, ctx) is called, if I
commented out that *if* block to just load iterate_dir(od->realfile, ctx),
everything works fine.

To reproduce the issue just create a OverlayFS and use the merged
directory as a 9P share directory to the VM.
You will see that the upper ONLY files/directories are seen good, but 
when you try to list the lower and merged files the process couldn't
finish and ends with a "ls: Memory exhausted"

I've tried to fix it but my knowledge is not enough on FS.
I've done small script to reproduce the issue, they are at
https://github.com/miguelinux/overlay-9p-issue

-- 
Regards,

Miguel Bernal Marin                     Open Source Technology Center
https://clearlinux.org                              Intel Corporation