Re: [Buildroot] [PATCH v3 1/3] package/tinyinit: new package

["Yann E. MORIN" <yann.morin.1998@free.fr>]

Thomas, All,

On 2024-08-23 18:17 +0200, Thomas Petazzoni spake thusly:
> On Thu, 22 Aug 2024 20:37:40 +0200
> Dario Binacchi <dario.binacchi@amarulasolutions.com> wrote:
[--SNIP--]
> We also need to change busybox.mk to ensure that tinyinit is built
> before Busybox:
> 
> # Packages that provide commands that may also be busybox applets:
> BUSYBOX_DEPENDENCIES = \
> 	...
> 	$(if $(BR2_PACKAGE_TINYINIT),tinyinit) \

Good catch! We also need that for tini, then.

> > diff --git a/package/tinyinit/Config.in b/package/tinyinit/Config.in
> > new file mode 100644
> > index 000000000000..2ceb8e191e23
> > --- /dev/null
> > +++ b/package/tinyinit/Config.in
> > @@ -0,0 +1,10 @@
> > +config BR2_PACKAGE_TINYINIT
> > +	bool "tinyinit"
> > +	depends on BR2_INIT_NONE
> > +	help
> > +	  A Linux tiny initialization script suitable for resource
> > +	  limited systems, which can be used as an alternative to the
> > +	  one provided by Busybox.
> > +
> > +comment "tinyinit needs BR2_INIT_NONE, i. e. no init system installed"
> > +	depends on !BR2_INIT_NONE
> I find this a bit odd. In the end, shouldn't we simply promote tinyinit
> as an init implementation, and have its own BR2_INIT_TINYINIT entry?

As Dario already pointed out, that was my suggestion to drop it from the
init selection.

The reasoning is that we need to know the init system when we need some
infra for it. For example, for busybox/sysvinit, we need to install init
scripts, for systemd, the units, and for openrc, the openrc "units".

And the "None" init choice really is "Custom", in that there is always a
PID-1 process, whether in a real system, a VM, or a container: it is the
first process that is started in that environment. Now, whether that
process is a real init system, a stub, or directly the final applicaiton,
it is still a PID-1, and thus treated as 'init' by the kernel.

The existing tini package is to be used a a PID-1 in containers (I use
it extensively in that situation) and it does not need any infra in
Buildroot (it can only spawn a single child and is a reaper); to my
eyes, tiny-init is also very simple and does not require any infra in
Buildroot. Both tini and tiny-init are cases for a "Custom" init
(currently labelled "None").

Regards,
Yann E. MORIN.

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