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

[Peter Kjellerstedt]

> -----Original Message-----
> From: openembedded-core-bounces at lists.openembedded.org <openembedded-
> core-bounces at lists.openembedded.org> On Behalf Of Jonas Bonn
> Sent: den 6 maj 2019 06:54
> To: Alex Kiernan <alex.kiernan at gmail.com>; openembedded-
> core at lists.openembedded.org
> Subject: Re: [OE-core] [OE-Core][PATCH] systemd: Default to non-
> stateless images
> 
> 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 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).
> 
> 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.
> 
> 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

This doesn't really say anything about the state of the rootfs outside 
of /var, i.e., is it writable or read-only?

> 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

Same here.

> 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.
> 
> /Jonas

Maybe we need some more generic way of describing the intended 
structure of the image? E.g., what are the expected behavior of 
/etc, /var and the rest of the rootfs? For each they can typically 
be "read-only", "persistent" (writable and survives reboots) or 
"volatile" (writable, but doesn't survive a reboot).

//Peter