Use writeback rather then the default writethrough for compression

[kronos30]

The following PR is to help increase the speed of compression/conversions. The default option is writethrough, which is a slower process then writeback. For our purposes, it appears it takes close to 15 minutes, perhaps even more for the compression/conversion to take place. This change is in the attempts to improve the speed of this conversion by switching to use writeback.

Reference: https://opendev.org/openstack/nova/commit/e7b64eaad82db38dd46f586b650da4ddde42533b
and https://linux.die.net/man/1/qemu-img

[garyservin]

LGTM

[bearrito]

This builds for me, but will not produce an image.

sudo packer build template.json
qemu-chroot: output will be in this color.

==> qemu-chroot: Creating output directory output-qemu-chroot...
==> qemu-chroot: Copying source image...
==> qemu-chroot: Finding available device...
==> qemu-chroot: Connecting source image as a network block device to /dev/nbd0...
==> qemu-chroot: Mounting the root device at /mnt/packer-builder-qemu-chroot/nbd0...
==> qemu-chroot: Mounting additional paths within the chroot...
    qemu-chroot: Mounting: /proc
    qemu-chroot: Mounting: /sys
    qemu-chroot: Mounting: /dev
    qemu-chroot: Mounting: /dev/pts
    qemu-chroot: Mounting: /proc/sys/fs/binfmt_misc
==> qemu-chroot: Copying files from host to chroot...
    qemu-chroot: /etc/resolv.conf
==> qemu-chroot: Provisioning with shell script: /tmp/packer-shell3352148920
==> qemu-chroot:
==> qemu-chroot: WARNING: apt does not have a stable CLI interface. Use with caution in scripts.
==> qemu-chroot:
    qemu-chroot: Hit:1 http://archive.ubuntu.com/ubuntu jammy InRelease
    qemu-chroot: Get:2 http://archive.ubuntu.com/ubuntu jammy-updates InRelease [119 kB]
    qemu-chroot: Reading state information...
    qemu-chroot: 20 packages can be upgraded. Run 'apt list --upgradable' to see them.
==> qemu-chroot: Unmounting the root device...
==> qemu-chroot: Error cleaning up: Error unmounting root device: exit status 32
==> qemu-chroot: Unmounting the root device...
==> qemu-chroot: Error unmounting root device: exit status 32
==> qemu-chroot: Disconnecting the source image from /dev/nbd0...
==> qemu-chroot: Deleting output directory...
Build 'qemu-chroot' errored after 15 seconds 966 milliseconds: Error cleaning up: Error unmounting root device: exit status 32

==> Wait completed after 15 seconds 966 milliseconds

==> Some builds didn't complete successfully and had errors:
--> qemu-chroot: Error cleaning up: Error unmounting root device: exit status 32

==> Builds finished but no artifacts were created.

@kronos30 When we talked I seem to remember you having an issue with building? Did I misremember that?

[kronos30]

This builds for me, but will not produce an image.

sudo packer build template.json
qemu-chroot: output will be in this color.

==> qemu-chroot: Creating output directory output-qemu-chroot...
==> qemu-chroot: Copying source image...
==> qemu-chroot: Finding available device...
==> qemu-chroot: Connecting source image as a network block device to /dev/nbd0...
==> qemu-chroot: Mounting the root device at /mnt/packer-builder-qemu-chroot/nbd0...
==> qemu-chroot: Mounting additional paths within the chroot...
    qemu-chroot: Mounting: /proc
    qemu-chroot: Mounting: /sys
    qemu-chroot: Mounting: /dev
    qemu-chroot: Mounting: /dev/pts
    qemu-chroot: Mounting: /proc/sys/fs/binfmt_misc
==> qemu-chroot: Copying files from host to chroot...
    qemu-chroot: /etc/resolv.conf
==> qemu-chroot: Provisioning with shell script: /tmp/packer-shell3352148920
==> qemu-chroot:
==> qemu-chroot: WARNING: apt does not have a stable CLI interface. Use with caution in scripts.
==> qemu-chroot:
    qemu-chroot: Hit:1 http://archive.ubuntu.com/ubuntu jammy InRelease
    qemu-chroot: Get:2 http://archive.ubuntu.com/ubuntu jammy-updates InRelease [119 kB]
    qemu-chroot: Reading state information...
    qemu-chroot: 20 packages can be upgraded. Run 'apt list --upgradable' to see them.
==> qemu-chroot: Unmounting the root device...
==> qemu-chroot: Error cleaning up: Error unmounting root device: exit status 32
==> qemu-chroot: Unmounting the root device...
==> qemu-chroot: Error unmounting root device: exit status 32
==> qemu-chroot: Disconnecting the source image from /dev/nbd0...
==> qemu-chroot: Deleting output directory...
Build 'qemu-chroot' errored after 15 seconds 966 milliseconds: Error cleaning up: Error unmounting root device: exit status 32

==> Wait completed after 15 seconds 966 milliseconds

==> Some builds didn't complete successfully and had errors:
--> qemu-chroot: Error cleaning up: Error unmounting root device: exit status 32

==> Builds finished but no artifacts were created.

@kronos30 When we talked I seem to remember you having an issue with building? Did I misremember that?

I was try to build locally using the instructions in the repo and the issue was my packer-sdc was not being found.

I haven't had a chance to re-try it, as I suspect I may be doing something incorrectly.

[bearrito]

@kronos30

After building packer-sdc, Likely need the following

export PATH=$PATH:/home/klad/go/bin/

Here is my template

{
  "builders": [
    {
      "type": "qemu-chroot",
      "source_image": "/home/bstrausser/Downloads/ubuntu-22.04-server-cloudimg-amd64.img",
      "image_name": "ubuntu-22.04.img",
      "compression": true
    }
  ],
  "provisioners": [

    {
      "type": "shell",
      "inline": [
        "echo '#!/bin/sh' > /usr/sbin/policy-rc.d",
        "echo 'exit 101' >> /usr/sbin/policy-rc.d",
        "chmod a+x /usr/sbin/policy-rc.d"
      ]
      
    },

    {
      "type": "shell",
      "inline": [
        "apt update"
      ]
    },

    {
      "type": "shell",
      "inline": [
        "rm -f /usr/sbin/policy-rc.d"
      ]
    }
    ,
    {
      "type": "shell",
      "inline": [
        "cat /proc/mounts"
      ]
    }


    

  ]
}

You need to add the policy statements so that no services get started.