[Buildroot] [PATCH 1/1] package/skeleton-init-common: Create /lib/modules directory

[Yann E. MORIN]

Norbert, All,

On 2019-03-18 19:11 +0100, Norbert Lange spake thusly:
> Am Mo., 18. März 2019 um 18:44 Uhr schrieb Yann E. MORIN
> <yann.morin.1998 at free.fr>:
> > On 2019-03-18 17:30 +0100, Norbert Lange spake thusly:
> > > For read-only root file systems, the kernel-modules
> > > will be mounted over this directory.
> >
> > This does not mean anything.
> >
> > Either you build your kernel with Buildroot, and the kernel does the
> > installation of modules in /lib/modules, and thus you do not need to
> > create it, or you build your kernel outside of Buildroot and you install
> > the modules at build time in there.
> >
> > So, having a read-only filesystem is of no consequence here.
> >
> > Also, I don;t see how "the kernel-modules will be mounted over this
> > directory", which imply this is done at runtime. If your system uses
> > special means to store the kernel modules, then it's your duty to
> > provide it on your own, like as an overlay (or a specific package) that
> > install those files/direcoties.
> 
> If you prepare a kernel with an builtin initramfs containing
> the modules and an initscript to mount those over /lib/modules,
> then you wont have to touch the root fs.
> (can be replaced independently of each other).

*That* is the real reason, and that's what you should have explained in
your commit log.

(Incidentally, I knew where this was coming from; I just wanted it to be
explained by you, not I.)

> > > This directory should always exist for this reason,
> > This is wrong: one can have a no-module kernel, in which case
> > /lib/modules is useless.
> One could also have nothing to use with  /mnt, /media and /opt.
> 
> > > just as /mnt and /opt are in the skeleton.
> > Those are madanted by the FHS [0].
> Ok, if I red that right, then /boot and /srv would be required/mandated aswell?

"red"? But who am I for pointing at others typoes? Hehe! ;-)

And sorry, I wrote "mandated" (with typoes, at that), when I should have
written "documented". So, I was just pointing out that /mnt and /opt do
have some standard backing them, while /lib/modules does not, and thus
/lib/modules does not have to "always exist like /mnt/ or /opt" as you
wrote.

Additionally, if one is building a filesystem (possibly readonly) to run
in a container, they'd probably have no use for /lib/modules either. So,
again, /lib/modules does not *have* to always exist.

> I guess I wont get the change up-streamed, and thats fine (minor annoyance
> that I cant use verbatim buildroot's with such kernels).

As I said, you need not do that in skeleton. You can do it in an
overlay, or as a custom package, or even as a custom skeleton. And if
you do not want to "pollute" your Buildroot tree with your custom stuff,
you can host it in a br2-external tree, for example. My professional
alter-ego gave a talk about that some time ago:
    https://elinux.org/images/8/8e/2017-10-24_-_ELCE-Buildroot.pdf

And Arnout wrote a nice summary of the presentation:
    https://mindlinux.wordpress.com/2017/10/24/buildroot-making-embedded-linux-easy-a-real-life-example-yann-morin-orange/

> But this seems
> to be pretty arbitrary given that buildroot seems rather lenient
> otherwise (for good reasons).

Given the proper explanations for a change, we'd consider it, yes. But I
just pointed out that your explanations were not correct/accurate, as
the conditions you *described* did not *require* that change. The
explanations above is the real reason, and that is what you have said in
your commit log instead, and that would have given it a better chance to
get applied.

And yes, drawing the boundary line is arbitrary at times.

Regards,
Yann E. MORIN.

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