[Bug 1923268] Re: grubnet default grub.cfg should try /grub/grub.cfg-${net_default_mac} before /grub/grub.cfg

[Lee Trager]

lp:maas-images produces the bootloaders stream. It was previously
pointed to Bionic for i386(pxelinux), amd64(shim+grub-signed), and
arm64(grub) while PPC64(grub) is pointed to Xenial. In an attempt to get
secure boot working I upgraded i386, amd64, and arm64 to Focal. arm64
and PPC64 had their grub "built" with grub-mkimage as they don't use the
signed package. Part of this process included a custom grub.cfg which
did the right thing. Our build host is still using Precise and the team
managing it doesn't have time to upgrade it. I noticed that grub-signed
is now available for arm64 so I moved arm64 to shim+grub-signed.

We test all changes to the stream however our current process doesn't
test enlistment, only commissioning, testing, and deployment. We noticed
this bug in our CI and filed it. A resolution is being discussed this
week at the sprint.

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https://bugs.launchpad.net/bugs/1923268

Title:
  grubnet default grub.cfg should try /grub/grub.cfg-${net_default_mac}
  before /grub/grub.cfg

Status in MAAS:
  New
Status in grub2-signed package in Ubuntu:
  Confirmed

Bug description:
  MAAS uses the signed network GRUB bootloader when a machine network
  boots on AMD64 and ARM64. The configuration MAAS produces depends on
  the machine which are identified by MAC address. The default grub.cfg
  in the boot loader downloads /grub/grub.cfg from the remote host. As
  that doesn't provide the MAC address MAAS provides a default
  configuration file:

  configfile /grub/grub.cfg-${net_default_mac}
  configfile /grub/grub.cfg-default-amd64

  There are two issues with this:

  1. This causes an additional unnecessary request.
  2. It is assumed an known machine is amd64.

  Can the default grub.cfg embedded in grubnet<arch>.efi be updated to

  configfile /grub/grub.cfg-${net_default_mac}
  configfile /grub/grub.cfg-default-<ARCH>
  configfile /grub/grub.cfg

  This would be similar to what PXELinux[1] does.

  [1] https://wiki.syslinux.org/wiki/index.php?title=PXELINUX

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