[Bug 1579130] Re: need to support renaming of devices in container and on first boot

[Scott Moser]

I have fixes for this in cloud-init in my branch at https://launchpad.net/~smoser/+archive/ubuntu/cloud-init-dev/+packages
that is available in the ppa at https://launchpad.net/~smoser/+archive/ubuntu/cloud-init-dev/+packages

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Title:
  need to support renaming of devices in container and on first boot

Status in cloud-init package in Ubuntu:
  Confirmed
Status in systemd package in Ubuntu:
  Triaged

Bug description:
  We're interested in supporting network configuration of cloud
  instances including lxc containers via maas/cloud-init yaml format.

  For Containers, the end goal is to do:
  $ lxc init xenial x1
  $ ncpath=/var/lib/cloud/seed/nocloud-net/network-config
  $ sudo tee /var/lib/lxd/containers/x1/rootfs/$ncpath <<EOF
  version: 1
  config:
    - type: physical
      mac_address: "00:16:3e:3b:01:7a"
      name: foo2
      subnets:
        - type: dhcp
          control: auto
  EOF

  $ lxc start x1
  $ lxc exec x1 /bin/bash

  From inside we expect to have a device named 'foo2' at this point that
  has dhcp'd.

  Currently cloud-init is writing files named:
   /etc/systemd/network/50-cloud-init-eth0.link
  and expecting systemd.link(5) to rename them.

  We've run into a number of issues with this.
   a.) we don't get coldplug events for devices in a container, so writing systemd.link (or 70-persistent-net.rules style udev rules files) wont "just work" to apply the name changes.

   b.) systemd.link does not rename devices that have been renamed previously, and all lxd instance devices are renamed (from the kernel returned veth<random> into 'eth0').
   That is implemented by check of /sys/devices/virtual/net/eth0/name_assign_type . Value of 4 means renamed.

   c.) systemd.link will not attempt to rename a device that does not have a driver.
     To see that run: udevadm test-builtin net_setup_link /sys/class/net/eth0
     http://paste.ubuntu.com/16261974/

   d.) on first boot of a cloud instance, the systemd.link files in the
  initramfs are either pristine or from the previous instance.  The
  devices will leave the initramfs either named incorrectly or named
  with standard persistent naming and will have already been renamed.

  To force these systemd.link files to run in spite of 'b' on kvm guests
  or bare metal, we have found that unbind and rebind of the device will
  clear the state and rename would occur.  that can be done as shown in
  https://bugs.launchpad.net/ubuntu/+source/cloud-
  init/+bug/1577844/comments/3 but since there is no 'driver' we cannot
  unbind and rebind veth devices.

  To do this right, we need to support:
   1.) renaming on first boot with initramfs and with 'stale' initramfs
   2.) renaming in lxc containers
   3.) user updating whatever files or mechanism is used post first boot.  For example, if the user wrote a 25-my-rules.link after first boot, a reboot should prefer their provided names to whatever were originally there.
   4.) if cloud-init networking is disabled, the renaming should not occur.

  
  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: udev 229-4ubuntu4
  ProcVersionSignature: Ubuntu 4.4.0-21.37-generic 4.4.6
  Uname: Linux 4.4.0-21-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2
  Architecture: amd64
  Date: Fri May  6 15:42:52 2016
  MachineType: LENOVO 33672B7
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-21-generic.efi.signed root=UUID=19ac97d5-6973-4193-9a09-2e6bbfa38262 ro quiet splash vt.handoff=7
  SourcePackage: systemd
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 12/18/2013
  dmi.bios.vendor: LENOVO
  dmi.bios.version: G8ET96WW (2.56 )
  dmi.board.asset.tag: Not Available
  dmi.board.name: 33672B7
  dmi.board.vendor: LENOVO
  dmi.board.version: Not Defined
  dmi.chassis.asset.tag: No Asset Information
  dmi.chassis.type: 10
  dmi.chassis.vendor: LENOVO
  dmi.chassis.version: Not Available
  dmi.modalias: dmi:bvnLENOVO:bvrG8ET96WW(2.56):bd12/18/2013:svnLENOVO:pn33672B7:pvrThinkPadX131e:rvnLENOVO:rn33672B7:rvrNotDefined:cvnLENOVO:ct10:cvrNotAvailable:
  dmi.product.name: 33672B7
  dmi.product.version: ThinkPad X131e
  dmi.sys.vendor: LENOVO

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