grub-config-flags usage of $GRUB_CMDLINE_LINUX_DEFAULT does not work to keep previously configured kernel parameters

[Mauricio Faria de Oliveira]

The sysconfig charm's README.md says:

 """
 To add or keep kernel parameters you had previously configured see the grub-config-flags option below.

 ...

 For instance, if you need to set the kernel parameter "nvme_core.multipath=0" you would add:

 juju config sysconfig grub-config-flags='GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT nvme_core.multipath=0"
 """

But it does not work.

Without the charm:

 $ cat /etc/default/grub
 GRUB_CMDLINE_LINUX_DEFAULT="important=option"

 $ sudo update-grub

 $ grep -w -m1 ' linux' /boot/grub/grub.cfg
         linux /vmlinuz-4.15.0-106-generic root=... ro important=option

Now with the charm, but grub-config-flags option unset: (overrides it, as documented.)

 $ grep -w -m1 ' linux' /boot/grub/grub.cfg
         linux /vmlinuz-4.15.0-106-generic root=... ro console=tty0 console=ttyS0,115200 console=ttyS1,115200 pti=off

Now with the charm, AND grub-config-flags option set as suggested:

 $ juju config sysconfig-ubuntu grub-config-flags='GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT something=else"'

 $ grep -w -m1 ' linux' /boot/grub/grub.cfg
         linux /vmlinuz-4.15.0-106-generic root=... ro console=tty0 console=ttyS0,115200 console=ttyS1,115200 pti=off something=else

Note that the 'important=option' is lost.

With this fix:

@ https://code.launchpad.net/~mfo/charm-sysconfig/+git/charm-sysconfig/+merge/386280

 $ juju upgrade-charm --path .../sysconfig sysconfig-ubuntu

 $ grep -w -m1 ' linux' /boot/grub/grub.cfg
  linux /vmlinuz-4.15.0-106-generic root=... ro important=option something=else console=tty0 console=ttyS0,115200 console=ttyS1,115200 pti=off

Now all options are there:
- previously configured 'important=option'
- newly configured 'something=else'
- charm configured options.

And if we reset the option (keep current behavior)

 $ juju config sysconfig-ubuntu --reset grub-config-flags

 $ grep -w -m1 ' linux' /boot/grub/grub.cfg
  linux /vmlinuz-4.15.0-106-generic root=... ro console=tty0 console=ttyS0,115200 console=ttyS1,115200 pti=off

[Zachary Zehring (zzehring)]

Thanks for the detailed bug report and associated MR. We'll get this change through our MR process.

[Xav Paice (xavpaice)]

cs:~bootstack-charmers-next/sysconfig-4 has this merged.

[Mauricio Faria de Oliveira (mfo)]

Hi Xav / Bootstack Charmers,

Could you please clarify whether there is an ETA on landing this fix to the stable charms, and/or how your release process works?

Thank you!
Mauricio

[Arif Ali (arif-ali)]

cs:sysconfig now has the fix