handle hard links and whiteouts in different layers about docker2aci

[alban]

/cc @josephschorr @jakedt

The same bug exists in the quay.io Docker image squasher. I uploaded my busybox-hardlinks Docker image into quay.io/alban/busybox-hardlinks and then downloaded a squashed image from the quay.io web interface (click on Fetch tag / Squashed Docker image). Then, the image also has a dangling hard link, so it cannot be extracted:

$ tar tvf /tmp/quay.io-alban-busybox-hardlinks-latest.squash.aci | grep LINK
hrw-r--r-- 0/0               0 2015-10-21 23:26 rootfs/LINK-Z link to rootfs/LINK-A
$ tar xf /tmp/quay.io-alban-busybox-hardlinks-latest.squash.aci
tar: rootfs/LINK-Z: Cannot hard link to ‘rootfs/LINK-A’: No such file or directory
$ sudo docker load < /tmp/quay.io-alban-busybox-hardlinks-latest.squash.aci
Error response from daemon: Untar re-exec error: exit status 1: output: link /rootfs/LINK-A /rootfs/LINK-Z: no such file or directory

[josephschorr]

@alban: I just tried this locally without any errors. I pulled the image from DockerHub, pushed to my local Quay, then squash pulled image. Do you have another repro case I can try?

[alban]

@josephschorr : there is also the image https://hub.docker.com/r/zopyx/xmldirector-plone/ but given its size (854MB), it is easier to try with my image https://hub.docker.com/r/albanc/busybox-hardlinks/ (1MB). I could reproduce the issue just now. I think I mixed the explanation in my comment above between downloading the aci and the Docker squashed image. I can see the problem when using:

$ curl -L -f https://alban+squashedrobot:[email protected]/c1/squash/alban/busybox-hardlinks/latest 2>/dev/null | sudo docker load
Error response from daemon: ApplyLayer exit status 1 stdout:  stderr: link /LINK-A /LINK-Z: no such file or directory

[josephschorr]

Hmm, I tried that image. Will try again tomorrow.