Description of problem:

When importing a gzipped raw image, nbdkid is started with the following args:

I0523 14:20:31.215028       1 nbdkit.go:238] Start nbdkit with: ['--foreground' '--readonly' '--exit-with-parent' '-U' '/var/run/nbdkit.sock' '--pidfile' '/var/run/nbdkit.pid' '--filter=gzip' '-r' 'curl' 'url=http://cdi-file-host.cdi/tinyCore.iso.gz']

The gzip plugin is specified.  Internally, the gzip plugin downloads/uncompresses the target file to a temporary dir when it is initially accessed.  See [1].  Unfortunately, that temp dir is on the container filesystem, not a PVC.  This is obviously problematic for large images.


[1] https://github.com/libguestfs/nbdkit/blob/v1.31.7/filters/gzip/gzip.c#L126-L250


Version-Release number of selected component (if applicable):


How reproducible:  100%


Steps to Reproduce:
1.  make cluster-up cluster-sync


2.  Create this DataVolume

apiVersion: cdi.kubevirt.io/v1beta1
kind: DataVolume
metadata:
  name: dv1
  annotations:
    "cdi.kubevirt.io/storage.pod.retainAfterCompletion": "true"
spec:
  source:
      http:
         url: "http://cdi-file-host.cdi/tinyCore.iso.gz"
  pvc:
    volumeMode: Filesystem
    accessModes:
      - ReadWriteOnce
    resources:
      requests:
        storage: 1Gi

3.  Check pod log to confirm that gzip plugin is used

Actual results:

Image is downloaded/uncompressed to container filesystem


Expected results:

It should be possible for the image to be downloaded/uncompressed directly to the target PVC with no temporary space


Additional info: