[OE-core] [OE-Core][PATCH] systemd: Default to non-stateless images

[Jonas Bonn]

Hi Alex,

On 06/05/2019 11:36, Alex Kiernan wrote:
> On Mon, May 6, 2019 at 5:54 AM Jonas Bonn <jonas at norrbonn.se> wrote:
>>
>> Hi Alex,
>>
>> The below is fine and looks good.  The one thing that bothers me about
>> this is that "stateless" isn't really a property of the "distro", rather
>> it's a property of the image/machine.
> 
> I agree it should be part of image, I'll respin it.
> 
>>   I suspect, in the same sense that
>> we have readonly-rootfs, that we should probably have image features
>> "stateless-rootfs" (no /etc, no /var) and "volatile-rootfs" (no /var).
>>
> 
> That makes sense to me
> 
>> Furthermore, if you want to boot with 'ro' on the command-line, I really
>> think you need to build your image with the "readonly-rootfs" feature
>> set.  The default should be writable+persistent /etc as that's the
>> configuration used 99% of the time (currently).  "readonly-rootfs" does
>> a bit more than just creating machine-id but it's all relevant to the
>> 'ro' case where /etc isn't writable.
>>
> 
> I think there's (at least) two use cases for ro boot:
> 
> - systems which boot ro and stay that way
> - systems which transition to rw during systemd-remount-fs
> 
> I'm in the second case as I have no initramfs and need the filesystem
> readonly until it's fscked/remounted rw.

I'd argue that you are abusing systemd for this because systemd 
explicity requires /etc to be writable.  The fact that it works on a 
read-only /etc is both incidental and fragile.

That said, I understand why you want to do this.  Have you considered 
putting the fsck in a "systemd generator" that doesn't return until fsck 
finishes?  Generators are kind of like units that run before systemd 
starts... or, at least, they can be (ab)used in this way.  Systemd won't 
start until all the generators are finished (the idea being that the 
generators may be responsible for creating units dynamically).

> 
>> Just for clarification:
>>
>> i)  volatile-rootfs:  means there's no point in prepopulating /var
>> because it's on a tmpfs and needs to be populated at boot time
>>
>> ii)  stateless-rootfs:  means there's no point in prepopulating neither
>> /etc nor /var because they are on a tmpfs and need to be populated at
>> boot time
>>
>> iii)  readonly-rootfs:  means that /etc is really not writable so it's
>> important that: the systemd first-boot stuff needs to be done at build
>> time:  machine-id, unit files set up, all tmpfiles.d snippets that touch
>> /etc and /var need to be done in advance.
>>
> 
> I'm assuming definitions from here?
> 
> http://0pointer.net/blog/projects/stateless.html
> 
> Either way, those work for me...

Correct.  Thanks for digging that up... I should have posted it myself.

/Jonas

> 
> 
> 
> 
> --
> Alex Kiernan
>