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

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Message-ID: <Pine.LNX.4.58.0707132344140.13842@be1.lrz>
Date:	Sat, 14 Jul 2007 00:37:27 +0200 (CEST)
From:	Bodo Eggert <7eggert@....de>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Bodo Eggert <7eggert@....de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3][try 1] init: enable system-on-initramfs

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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