Re: [PATCH 0/3][try 1] init: enable system-on-initramfs

From: Bodo Eggert
Date: Fri Jul 13 2007 - 18:37:59 EST


On Fri, 13 Jul 2007, H. Peter Anvin wrote:
> Bodo Eggert wrote:

> > I toyed with setting up a diskless system in initramfs. In the process, I
> > came across some things:
> >
> > 1) There is no way to have the kernel not mount a filesystem,
> > unless you use /init or rdinit=.
>
> And? Just use rdinit=/sbin/init and no patch is needed.

rdinit is supposed to do a different job from /sbin/init, therefore it
will not do the security callbacks the original code would do.

And besides that, it feels like turning the wrong knob for that task.

> > 2a) I figured if you prepared the root fs to contain a running system, you
> > woud probably also set up a runnable system on it. Therefore I changed
> > the default to boot from tmpfs if there was no /init nor a root= option.
> > (If there is a /init, it will be executed as usural.)
> >
> > Unfortunately the way I do it, this will override the rdev setting, but
> > that should be OK, since rdev is dead. Isn't it?
>
> That's pretty hideous. There shouldn't be a need for doing that.
>
> rdev, unfortunately, isn't dead -- it lives on in the form of
> /proc/sys/kernel/real-root-dev, as I found out doing the klibc set.

It just missed it's own funeral:
"Obsolete root change mechanism
------------------------------

The following mechanism was used before the introduction of pivot_root.
Current kernels still support it, but you should _not_ rely on its
continued availability." (Documentation/initrd.txt)


I don't insist on changing the default, it was just a logical step from
preparing initramfs to hold a system.

--
Top 100 things you don't want the sysadmin to say:
48. Tell me again what that '-r' option to rm does
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