osbuild: support building kubevirt disks

[dustymabe]

Also a second commit for supporting the new platforms when symlinked.

[dustymabe]

Here is some data from two successive builds, one using cosa buildextend-kubevirt (the current code) and the other using cosa osbuild kubevirt.

It appears to compress a little better using OSBuild:

$ diffbuildsizes.py 41.20250305.dev.0 41.20250305.dev.1
    platform     | compression  | 41.20250305.dev.0 | 41.20250305.dev.1
---------------------------------------------------------------------
ostree           | compressed   | 750MiB           | 750MiB
ostree           | uncompressed | N/A              | N/A
oci-manifest     | compressed   | 15KiB            | 15KiB
oci-manifest     | uncompressed | N/A              | N/A
qemu             | compressed   | 1722MiB          | 1722MiB
qemu             | uncompressed | N/A              | N/A
kubevirt         | compressed   | 900MiB           | 876MiB
kubevirt         | uncompressed | N/A              | N/A

And most of the skopeo inspect and qemu-img info are equivalent:

41.20250305.dev.0 (using buildextend-kubevirt)

[dustymabe@media fcos]$ skopeo inspect oci-archive:./builds/41.20250305.dev.0/x86_64/fedora-coreos-41.20250305.dev.0-kubevirt.x86_64.ociarchive
{
    "Digest": "sha256:a4803fecbf1d3a8438bb1ac0d3e7a1084dc3de791b06688bb1141dc413ad55e5",
    "RepoTags": [],
    "Created": "2025-03-05T13:51:13.371096906Z",
    "DockerVersion": "",
    "Labels": {
        "io.buildah.version": "1.38.1",
        "version": "41.20250305.dev.0"
    },
    "Architecture": "amd64",
    "Os": "linux",
    "Layers": [
        "sha256:2afdacca5c5ad930169fbc6acbf838a8112c186f1ca1f8abd3bb77583af95c4b"
    ],
    "LayersData": [
        {
            "MIMEType": "application/vnd.oci.image.layer.v1.tar+gzip",
            "Digest": "sha256:2afdacca5c5ad930169fbc6acbf838a8112c186f1ca1f8abd3bb77583af95c4b",
            "Size": 943916860,
            "Annotations": null
        }
    ],
    "Env": [
        "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
    ]
}
[dustymabe@media fcos]$ podman unshare
[root@media fcos]$ podman pull oci-archive:./builds/41.20250305.dev.0/x86_64/fedora-coreos-41.20250305.dev.0-kubevirt.x86_64.ociarchive
Getting image source signatures
Copying blob 2afdacca5c5a done   | 
Copying config 572680e61f done   | 
Writing manifest to image destination
572680e61f2f993c464f7d2aaa4cf69a65a103adcd2c51716c19d2219888fefc
[root@media fcos]$ podman image mount 572680e6
/var/b/dustymabe-local-share-containers/storage/overlay/45edc52d9b6da5d2fefa9a15dcab553f6a54a0e6958f3e3a0fe89bf3460c422d/merged
[root@media fcos]$ qemu-img info /var/b/dustymabe-local-share-containers/storage/overlay/45edc52d9b6da5d2fefa9a15dcab553f6a54a0e6958f3e3a0fe89bf3460c422d/merged/disk/fedora-coreos-41.20250305.dev.0-kubevirt.x86_64.qcow2 
image: /var/b/dustymabe-local-share-containers/storage/overlay/45edc52d9b6da5d2fefa9a15dcab553f6a54a0e6958f3e3a0fe89bf3460c422d/merged/disk/fedora-coreos-41.20250305.dev.0-kubevirt.x86_64.qcow2
file format: qcow2
virtual size: 10 GiB (10737418240 bytes)
disk size: 1.68 GiB
cluster_size: 65536
Format specific information:
    compat: 1.1
    compression type: zlib
    lazy refcounts: false
    refcount bits: 16
    corrupt: false
    extended l2: false
Child node '/file':
    filename: /var/b/dustymabe-local-share-containers/storage/overlay/45edc52d9b6da5d2fefa9a15dcab553f6a54a0e6958f3e3a0fe89bf3460c422d/merged/disk/fedora-coreos-41.20250305.dev.0-kubevirt.x86_64.qcow2
    protocol type: file
    file length: 1.68 GiB (1806368768 bytes)
    disk size: 1.68 GiB

41.20250305.dev.1 (using OSBuild)

[dustymabe@media fcos]$ skopeo inspect oci-archive:./builds/41.20250305.dev.1/x86_64/fedora-coreos-41.20250305.dev.1-kubevirt.x86_64.ociarchive
{
    "Digest": "sha256:59786deaf153acaa2543993654244a9834cf5b64692dd54efd70768b2276a440",
    "RepoTags": [],
    "Created": "2025-03-05T13:57:41Z",
    "DockerVersion": "",
    "Labels": {
        "version": "41.20250305.dev.1"
    },
    "Architecture": "amd64",
    "Os": "linux",
    "Layers": [
        "sha256:589b28b0189762e7559c30a64f2f1a08e1f88ccbd10c7832d58c024e49d64e48"
    ],
    "LayersData": [
        {
            "MIMEType": "application/vnd.oci.image.layer.v1.tar+gzip",
            "Digest": "sha256:589b28b0189762e7559c30a64f2f1a08e1f88ccbd10c7832d58c024e49d64e48",
            "Size": 919207411,
            "Annotations": null
        }
    ],
    "Env": [
        "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
    ]
}
[dustymabe@media fcos]$ podman unshare
[root@media fcos]$ podman pull oci-archive:./builds/41.20250305.dev.1/x86_64/fedora-coreos-41.20250305.dev.1-kubevirt.x86_64.ociarchive
Getting image source signatures
Copying blob 589b28b01897 done   | 
Copying config 82498b4f4f done   | 
Writing manifest to image destination
82498b4f4fe7095d774336d23c02211449c09481b7ceef5850d0b5b49f0bb03d
[root@media fcos]$ podman image mount 82498b4f
/var/b/dustymabe-local-share-containers/storage/overlay/32942a119219c1e81ff2c7bf8c86dd9131f9a412652b424af5b8d1984d8a8d9c/merged
[root@media fcos]$ qemu-img info /var/b/dustymabe-local-share-containers/storage/overlay/32942a119219c1e81ff2c7bf8c86dd9131f9a412652b424af5b8d1984d8a8d9c/merged/disk/fedora-coreos-41.20250305.dev.1-kubevirt.x86_64.qcow2 
image: /var/b/dustymabe-local-share-containers/storage/overlay/32942a119219c1e81ff2c7bf8c86dd9131f9a412652b424af5b8d1984d8a8d9c/merged/disk/fedora-coreos-41.20250305.dev.1-kubevirt.x86_64.qcow2
file format: qcow2
virtual size: 10 GiB (10737418240 bytes)
disk size: 1.68 GiB
cluster_size: 65536
Format specific information:
    compat: 1.1
    compression type: zlib
    lazy refcounts: false
    refcount bits: 16
    corrupt: false
    extended l2: false
Child node '/file':
    filename: /var/b/dustymabe-local-share-containers/storage/overlay/32942a119219c1e81ff2c7bf8c86dd9131f9a412652b424af5b8d1984d8a8d9c/merged/disk/fedora-coreos-41.20250305.dev.1-kubevirt.x86_64.qcow2
    protocol type: file
    file length: 1.68 GiB (1806630912 bytes)
    disk size: 1.68 GiB