linux-kernel - Re: [RFC][Patch] Allow not mounting a root fs

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Date:	Sat, 07 Jul 2007 14:45:14 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
CC:	Bodo Eggert <7eggert@....de>, linux-kernel@...r.kernel.org
Subject: Re: [RFC][Patch] Allow not mounting a root fs

Jan Engelhardt wrote:
> 
> Come to speak of it, I think you can have it much easier by having the kernel
> exporting the cpio image as a virtual file inside rootfs, so that you could
> re-extract it inside a tmpfs. In other words:
> 
> mount -t tmpfs tmpfs /mnt;
> cd /mnt;
> cpio -diuv </initramfs.cpio;
> #
> # switch_root nukes rootfs, pivot_roots and execs some init
> klibc_switch_root .; # or something like that
> 
> Of course this needs double the memory than directly mounting tmpfs as 
> rootfs, but it's an idea too.
> 

Well, we're doing exactly this for non-initramfs initrd, however, it
would definitely be cleaner just to overmount rootfs with a tmpfs before
extraction -- it's an absolutely trivial amount of code; the biggest
complexity would be spotting the kernel command line option to invoke it.

Yet another variant, which works on existing kernels, is to have a
nested cpio, where your rootfs consists of a trivial /init which mounts
tmpfs and extracts another tar- or cpioball.

	-hpa

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