Message-ID: <3BD5ABF3.1040404@usa.net>
Date: Tue, 23 Oct 2001 10:42:11 -0700
From: Eric <ebrower@usa.net>
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To: linux-kernel@vger.kernel.org
Subject: Re: [Q] pivot_root and initrd
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Would it even be worthwhile to propose a patch that would set a flag 
when pivot_root is called during an initrd and prevent change_root from 
occuring once the linuxrc thread exits?

Your method of placing "initrx=xxx" and "root=xxx" is similar to my 
method of stuffing those values into /proc/sys/kernel/real_root_dev once 
the pivot_root is complete; I am not really happy with that solution, 
not the least of which because it is an undocumented work-around and 
somewhat unexpected behavior for a system call that is to (presumably) 
replace or augment change_root.

I was also hoping that Warner or Hans would chime-in either in defense 
of the current documentation or with clarifications...

E

HPA wrote:
>> 
>> I am mystified that the call to 'exec /sbin/init' works 
>> if you are using the standard (you mention "based on RedHat7.1"
>> util-linux") /sbin/init proggie, and that a standard RH7.1 
>> initscripts would not complain when the root filesystem is already 
>> mounted r/w.
>> 
>> I would also guess that you are susceptible to the kernel's 
>> change_root call if your /sbin/init terminates. I'll have to 
>> play with the disk a bit.
>> 
> 
> I modify the initscripts to not try to fsck and remount the root -- 
> its a ramfs (tmpfs in a later version) after all. If I had been 
> mounting a filesystem off the harddisk I would either have mounted it 
> readonly and left the init scripts as-is, or fscked it before 
> mounting. 
> 
> I pass the following command line options to the kernel (this is set 
> up in isolinux.cfg): 
> 
>         append initrd=initrd.gz root=/dev/ram0 init=/linuxrc single 
> 
> By specifying root=/dev/ram0 and an explicit init (which I'm calling 
> /linuxrc but could just as easily have called /sbin/init) I'm telling 
> the kernel that this is the final root, and effectively turn off most 
> of the initrd legacy weirdness. 
> 
> If /sbin/init exits, the kernel panics, just like it would normally do 
> if init goes away. 


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