Add boot counting

[LorbusChris]

Introduces a boot_counter env var that counts down boot attempts to 0.

If 0 is reached it will set default=1 to boot the next older entry once (I don't need to set boot_once here for this, do I?)

Also introduces a fallback_active var that is set to true in this case, to make it easy to determine from userspace that this is a fallback boot.

As I need the automatic boot_success reset mechanism in all cases, I put this in 00_menu_auto_hide.in for now.

Use case: https://github.com/LorbusChris/greenboot/pull/16

RFC please
@jwrdegoede @dustymabe @jlebon @nullr0ute

[martinezjavier]

I don't think this belong to 00_menu_auto_hide.in, since this an independent feature I would add it in a new script file (i.e: 01_fallback_support).

That way we can for example ship the menu auto hide and fallback support independently depending on the Fedora variant that needs it, users can choose to disable one feature bit removing the script executable bit without affecting the other feature, etc.

[LorbusChris]

That way, both features couldn't be used at the same time. I'd like to have that option for workstations (even if it weren't active by default). I need the lines resetting and saving boot_success from this script. maybe @jwrdegoede has an idea how to separate things cleanly here?

[martinezjavier]

Probably you don't need this fallback_active variable, I would just use the boot_counter variable as an indication that the fallback entry was booted. For example you can set here boot_counter to -1 or unset it so user-space knows that the default entry failed to boot.

[LorbusChris]

ack

[LorbusChris]

Is this the distinction made between Server and Workstation editions?

[jlebon]

Nice! Just some minor comments below.

[jlebon]

Minor: can we just collapse these two as:

if [ "\${boot_counter}" -a "\${boot_success}" = "0" ]; then

?

[martinezjavier]

@jlebon I don't think we can since boot_counter not set is used as an indication that fallback is disabled on that system.

Otherwise you would need to have in the case statement:

elif [ "\${boot_counter}" ]; then

[jlebon]

Hmm, I'm not sure I understand this. Isn't

if A then
  if B then
    ...
  fi
fi

logically equivalent to:

if A and B then
  ...
fi

?

[martinezjavier]

@jlebon yes it is, but you are missing the else part in your example:

if A then
    if B then
    ...
    else
    ...
    fi
fi

if A and B then
    ...
else
    ...
fi

The else statement will be executed even if not A so then you need:

if A and B then
    ...
elif not A then
    ...
fi

[jlebon]

There is no else on the first two if-statements though, only the third. :)
Anyway, it's just a minor nit; not really worth discussing it more than we already have.

[martinezjavier]

@jlebon sorry, I misread and thought you were talking about the second if-statement. Yes, for the first one you are correct! cc @LorbusChris

[jlebon]

Minor: we can just factor out the save_env boot_counter outside the if-statement, right?

[martinezjavier]

@jlebon agreed.

[LorbusChris]

Changes since v1:

• Moved code into 01_fallback_support.in.
• Renamed 00_menu_auto_hide.in to 01_menu_auto_hide.in

[martinezjavier]

Renamed 00_menu_auto_hide.in to 01_menu_auto_hide.in

You are missing this bit though, it has to be on a preparatory commit before adding 01_fallback_support.in.

[LorbusChris]

done @martinezjavier @jlebon

[martinezjavier]

@LorbusChris the second patch looks good to me now. Could you please add a commit message in the same commit explaining why this rename is needed.

Also, could you please rebase on top of the latest fedora-29 branch?

[LorbusChris]

@martinezjavier please re-check =)

Edit: Changes v2 -> v3:
Named the new script 01_fallback_counting.in instead of 01_fallback_support.in as there seems to be another unrelated fallback feature (using fallback env var) in grub. Please tell if you have a better name in mind!

[martinezjavier]

Looks good to me now.