Re: Minimizing isar-image-base

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2018-08-22 16:37, [ext] Jan Kiszka wrote:
>>> - Why do we pre-install dbus?
>>>
>>
>> Again, IIRC, without dbus there was dirty boot log in QEMU, some 
>> services failed to start.
> 
> I'll recheck that with stretch.

Removed it, but I'm not seeing any error messages nor does systemctl 
report failed services. Maybe the bug was solved in stretch. Christian, 
you said there is a harder dependency in reality than the "recommends" 
as Debian declares now. Any comments on this?

If it is really no longer needed, we could push the dbus dependency into 
debian-jessie.conf. Is raspbian-jessie on systemd as well? Then there as 
well.

> 
>>
>>> - Can we make apt optional? Installing it as transient package by
>>>    default, e.g. What would happen if a downstream image then puts it
>>>    into PREINSTALL again? Should we filter IMAGE_TRANSIENT_PACKAGES
>>>    against IMAGE_PREINSTALL?
>>
>> I could suppose how apt went to isar-image-base recipe, initially it 
>> was a copy of buildchroot one. So nobody actually cares about the list 
>> of packages, there was only one requirement - no error and warnings 
>> during image boot in QEMU.
>>
>> In buildchroot apt is needed to populate the dependencies.
>>
>> With current Isar implementation the apt is a must package for image. 
>> Let me explain why. Below is the whole chain to generate image:
>>
>> 1. At first, isar-debootstrap is called. This recipe fetches minimal 
>> *pure* Debian suite for specified architecture. It's stored in 
>> tmp/deploy folder.
>> 2. Image generation is started from copying this pre-fetched suite to 
>> work folder.
>> 3. Then you chroot to this *pure* minimal suite.
>> 4. And finally all the additional packages in pre-install list are 
>> installed via apt-get.
>>
>> So, the only way for current architecture - remove apt in post-build 
>> task.
> 
> Right, this is what I had in mind. I think we already have the tooling 
> for that, don't we?

We don't. IMAGE_TRANSIENT_PACKAGES is not suited.

Also, apt seems to get installed via debootstrap anyway. We should be 
fine removing it as explicit IMAGE_PREINSTALL entry. I'll propose a patch.

But we will need some explicit purging step that removes it again (and 
possibly more packages) after the image is done. And it should be under 
custom-image control, whether that step is run or not - or what the 
purge list contains. We could also use --exclude of debootstrap but that 
would imply forking the base bootstrap environment because we use the 
same for image and buildchroots so far. Probably not a good idea.

Jan

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