Merge ~mfo/charm-sysconfig:fix-grub-cmdline-linux-default into charm-sysconfig:master

[Mauricio Faria de Oliveira]

grub.j2: fix grub-config-flags that use $GRUB_CMDLINE_LINUX_DEFAULT

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:

 $ 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

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

This merge proposal is being monitored by mergebot. Change the status to Approved to merge.

[Zachary Zehring (zzehring)]

Looks good to me. I'll ask for an approval from an approved Bootstack Reviewer.

review: Approve

[Mauricio Faria de Oliveira (mfo)]

Hi Zachary,

Thanks for reviewing.

Friendly reminder for review from an approved Bootstack Reviewer, per your comment.

cheers,
Mauricio

[Arif Ali (arif-ali)]

Hey all, we're keen to get this reviewed and checked. We would greatly appreciate someone looking at this, so that we can move with the customer

Thanks,
Arif

[Adam Dyess (addyess)]

LGTM

review: Approve

[Xav Paice (xavpaice)]

lgtm

review: Approve

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

Change successfully merged at revision 237ca16bb97e18334d02b13814e1a512732f4a8b

diff --git a/src/templates/grub.j2 b/src/templates/grub.j2
index f29ed5c..756025e 100644
--- a/src/templates/grub.j2
+++ b/src/templates/grub.j2
@@ -5,7 +5,18 @@
 # For full documentation of the options in this file, see:
 #   info -f grub -n 'Simple configuration'
 
-GRUB_CMDLINE_LINUX_DEFAULT="console=tty0 console=ttyS0,115200 console=ttyS1,115200"
+# Evaluate grub-config-flags first, in case it uses $GRUB_CMDLINE_LINUX_DEFAULT.
+# However, if grub-config-flags is not specified, ignore that (current behavior.)
+{% if grub_config_flags is defined and grub_config_flags -%}
+# config-flags
+{% for key, value in grub_config_flags.items() -%}
+{{ key }}={{ value }}
+{% endfor -%}
+{% else -%}
+GRUB_CMDLINE_LINUX_DEFAULT=""
+{% endif -%}
+
+GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT console=tty0 console=ttyS0,115200 console=ttyS1,115200"
 {% if cpu_range is defined and cpu_range -%}
 GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT isolcpus={{ cpu_range }}"
 {% endif -%}
@@ -33,10 +44,3 @@ GRUB_CMDLINE_LINUX=""
 # Uncomment to disable graphical terminal (grub-pc only)
 #GRUB_TERMINAL=console
 GRUB_TERMINAL=serial
-
-{% if grub_config_flags is defined and grub_config_flags -%}
-# config-flags
-{% for key, value in grub_config_flags.items() -%}
-{{ key }}={{ value }}
-{% endfor -%}
-{% endif -%}