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=head1 NAME
nbdkit-cdi-plugin - export a layer from a container image
=head1 SYNOPSIS
nbdkit cdi [name=]NAME[:TAG|@DIGEST] [layer=N]
=head1 DESCRIPTION
C<nbdkit-cdi-plugin> (Containerized Data Importer plugin) is a plugin
for L<nbdkit(1)> which downloads a container image using
L<podman-pull(1)> and makes a single layer available over NBD. The
plugin is essentially a convenient wrapper around L<podman(1)> and
L<jq(1)> and requires both tools to be installed.
=head1 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 L<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 L<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 "$uri"'
export="":
export-size: 4294967296 (4G)
content: DOS/MBR boot sector
[...]
=head1 PARAMETERS
=over 4
=item [B<name=>]NAME[:TAG|@DIGEST]
The name or URI of the container image. This is passed to
L<podman-pull(1)>.
C<name=> __IS_MAGIC__
=item B<layer=>N
Export the N'th layer (instead of layer 0).
=back
=head1 ENVIRONMENT VARIABLES
=over 4
=item C<TMPDIR>
A temporary copy of the layer is created in C<TMPDIR>. If this
environment variable is not set then F</var/tmp> is used instead.
=back
=head1 FILES
=over 4
=item F<$plugindir/nbdkit-cdi-plugin.so>
The plugin.
Use C<nbdkit --dump-config> to find the location of C<$plugindir>.
=back
=head1 VERSION
C<nbdkit-cdi-plugin> first appeared in nbdkit 1.22.
=head1 SEE ALSO
L<nbdkit(1)>,
L<nbdkit-plugin(3)>,
L<nbdkit-qcow2dec-filter(1)>,
L<nbdkit-tar-filter(1)>,
L<podman(1)>,
L<podman-pull(1)>,
L<jq(1)>,
L<https://github.com/kubevirt/containerized-data-importer/blob/master/doc/image-from-registry.md>.
=head1 AUTHORS
Richard W.M. Jones
=head1 COPYRIGHT
Copyright Red Hat
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