nbdkit-cdi-plugin - export a layer from a container image
nbdkit cdi [name=]NAME[:TAG|@DIGEST] [layer=N]nbdkit-cdi-plugin (Containerized Data Importer plugin) is a plugin for nbdkit(1) which downloads a container image using podman-pull(1) and makes a single layer available over NBD. The plugin is essentially a convenient wrapper around podman(1) and jq(1) and requires both tools to be installed.
Given a Containerized Data Importer (CDI) registry image containing a VM disk, you can export the whole layer using:
$ nbdkit cdi quay.io/kubevirt/fedora-cloud-container-disk-demoThe layer exported over NBD is a tar file:
$ nbdcopy nbd://localhost - | file -
-: POSIX tar archiveTo export only the VM disk image in this layer, combine this plugin with nbdkit-tar-filter(1). In the example below the file exposed inside the tar archive is a qcow2 image so you can turn it into a raw NBD export of the virtual machine using nbdkit-qcow2dec-filter(1):
┌──────────────────────────────────────────┐
│ fedora-cloud-container-disk-demo layer=0 │
│ (uncompressed tar file) │
│ ┌──────────────────────────────────────┐ │
│ │ ./disk/downloaded │ │
│ │ (qcow2 image) │ │
│ └──────────────────────────────────────┘ │
└──────────────────────────────────────────┘
$ nbdkit cdi \
--filter=qcow2dec \
--filter=tar tar-entry=./disk/downloaded \
quay.io/kubevirt/fedora-cloud-container-disk-demo \
--run 'nbdinfo "$uri"'
export="":
export-size: 4294967296 (4G)
content: DOS/MBR boot sector
[...]The name or URI of the container image. This is passed to podman-pull(1).
name= is a magic config key and may be omitted in most cases. See "Magic parameters" in nbdkit(1).
Export the N'th layer (instead of layer 0).
TMPDIRA temporary copy of the layer is created in TMPDIR. If this environment variable is not set then /var/tmp is used instead.
The plugin.
Use nbdkit --dump-config to find the location of $plugindir.
nbdkit-cdi-plugin first appeared in nbdkit 1.22.
nbdkit(1), nbdkit-plugin(3), nbdkit-qcow2dec-filter(1), nbdkit-tar-filter(1), podman(1), podman-pull(1), jq(1), https://github.com/kubevirt/containerized-data-importer/blob/master/doc/image-from-registry.md.
Richard W.M. Jones
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