RFC: enhancing the root mount logic

[Bakul Shah]

On Mon, 23 Aug 2010 16:43:15 PDT Marcel Moolenaar <xcllnt at mac.com>  wrote:
> 
> On Aug 23, 2010, at 4:12 PM, M. Warner Losh wrote:
> 
> *snip*
> 
> > However, all this scripting sounds a bit like a very simple shell in
> > the kernel.  What advantages are there to this approach vs having the
> > ability to run a simple shell script or executable and "pivot" the root
> > to a new location?
> 
> The 2 reasons for doing this in the kernel are:
> 1.  resiliency against ABI changes.
> 2.  allowing /sbin/init to come from the actual root file system.
> 
> Both points are impossible to handle efficiently or correctly if
> you need user space support in getting to your actual root file
> system. You basically have a catch-22 or bootstrap problem, which
> a pure in-kernel solution doesn't have.

How about just bundling a small compressed ramfs with the
kernel.  The kernel unpacks it, uses it as the initial rootfs
and runs init from it. A forth/scheme/lua based program
wouldn't add more than a % or so (given that the GENERIC
kernel is over 10MB now!).