nbdkit-cdi-plugin1

Usage

Overview

"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.

Examples

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-demo

The layer exported over NBD is a tar file:

 $ nbdcopy nbd://localhost - | file -
 -: POSIX tar archive

To 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
 [...]

Parameters

[name=]NAME[:TAG|@DIGEST]

The name or URI of the container image. This is passed to podman-pull(1).

"name=" prefix may be omitted in most cases. See "Magic parameters" in nbdkit(1).

layer=N

Export the N'th layer (instead of layer 0).

Environment

"TMPDIR"

A temporary copy of the layer is created in "TMPDIR". If this environment variable is not set then /var/tmp is used instead.

Files

$plugindir/nbdkit-cdi-plugin.so

The plugin.

Use "nbdkit --dump-config" to find the location of $plugindir.

Version

"nbdkit-cdi-plugin" first appeared in nbdkit 1.22.