Re: [Buildroot] [PATCH] system: Add option to maintain a supervision tree

["J. Neuschäfer via buildroot" <buildroot@buildroot.org>]

On Sun, Jul 14, 2024 at 11:11:57PM +0200, Arnout Vandecappelle wrote:
>  Hi J.,
>
> On 04/07/2024 21:00, J. Neuschäfer via buildroot wrote:
> > One of the major drawbacks of classic init/rc systems is that dead
> > daemons remain dead: Once started by the rc scripts, they are left to
> > look after themselves.
> >
> > A simple approach to keep them running reliably is to supervise them:
> > In a tree with PID 1 at its root, every process knows which children
> > ought to run under it, and it respawns them accordingly. This is the
> > supervision tree.
> >
> > Classic init already provides rudimentary supervision in the form of
> > inittab. This patch uses inittab to establish a more flexible
> > supervision tree based on runit's rvsvdir or s6's s6-svscan.
>
>  We discussed this patch here at the Buildroot hackaton. Although we fully
> agree that having a supervisor is extremely useful, we also feel that this
> patch is very invasive for something that is relatively simple to implement
> at the moment. The only thing you need to do is to select the supervisor you
> want to use, and put a custom inittab in the filesystem overlay that starts
> the supervisor. Oh, and you probably also want a post-build script to remove
> everything in /etc/init.d for which you created a service instead - but that
> part isn't even handled by this patch.
>
>  One of Buildroot's main principles is keeping it simple. Over the years,
> we've already collected way too much complexity. Therefore, we've decided to
> reject this patch.

Fair enough -- the particular design trade-offs can be a bit difficult
to see from the outside. For example (and this is not a reason to merge
my patch, just an explanation of my thought process), adding a custom
inittab requires knowing/copying the whole inittab, whereas the user of
this option would only need to know that they want a supervision tree,
which is from that perspective simpler.

>
>  Regardless, thank you for your contributions!

Again, thank you for your thoughtful and friendly reviews :)


-- jn
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