buildroot: support OSTree trees as buildroots

[dustymabe]

In a filesystem layout in OSTree the software is in a deployment under /ostree/deploy/<name>/deploy/*/. If the specified buildroot is an OSTree tree then let's just use the deployment root as the rootdir here.

An example where this will help us is in RHCOS, where we'd like to not maintain a separate buildroot definition since our OSTree we already build has all the exact versions of the software we want to use already.

[mvo5]

I like the idea - I wonder if this is already possible via the org.osbuild.ostree.deployment mount stage and the new "org.osbuild.bind" stage? Here is what we do in bib to get a deployment mount:

          "devices": {
            "disk": {
              "type": "org.osbuild.loopback",
              "options": {
                "filename": "disk.raw",
                "partscan": true
              }
            }
          },
          "mounts": [
            {
              "name": "part4",
              "type": "org.osbuild.xfs",
              "source": "disk",
              "target": "/",
              "partition": 4
            },
            {
              "name": "part3",
              "type": "org.osbuild.ext4",
              "source": "disk",
              "target": "/boot",
              "partition": 3
            },
            {
              "name": "part2",
              "type": "org.osbuild.fat",
              "source": "disk",
              "target": "/boot/efi",
              "partition": 2
            },
            {
              "name": "ostree.deployment",
              "type": "org.osbuild.ostree.deployment",
              "options": {
                "source": "mount",
                "deployment": {
                  "default": true
                }
              }
            },
            {
              "name": "bind-ostree-deployment-to-tree",
              "type": "org.osbuild.bind",
              "target": "tree://",
              "options": {
                "source": "mount://"
              }
            }
          ]

now of course this does not directly apply (as you would not use the loopback etc) but maybe a similar idea would work? Do you have a link to an example manifest that you use today so that we could experiment ?

[dustymabe]

I like the idea - I wonder if this is already possible via the org.osbuild.ostree.deployment mount stage and the new "org.osbuild.bind" stage?

Not really. Using mounts here requires there to already be a disk image. What I'd like to do is use an OSTree buildroot to create the disk image, partitioning, and filesystems (that would then later be mountable).

[dustymabe]

Also, the bind mount stuff only affects the tree:/// right, not the buildroot?

[dustymabe]

it looks like org.osbuild.container-deploy is what is being used to create the buildroot for bib. I guess that doesn't have this problem because it copies the filesystem directly from the container which has been normalized (i.e. software is available in /usr/bin/ from the start).

[dustymabe]

Closing this out since we used an alternative implementation in coreos/coreos-assembler#3808