Re: Is initramfs freed after kernel is booted?

[viro]

On Mon, Nov 17, 2003 at 09:33:59PM +0300, Andrey Borzenkov wrote:
> On Monday 17 November 2003 21:03, viro@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
> wrote:
> > On Mon, Nov 17, 2003 at 12:50:34PM -0500, Chris Friesen wrote:
> > > viro@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx wrote:
> > > >On Mon, Nov 17, 2003 at 11:06:48AM -0500, Chris Friesen wrote:
> > > >>Anyone know why it overmounts rather than pivots?
> > > >
> > > >Because amount of extra code you lose that way takes more memory than
> > > >empty roots takes.
> > > >
> > > >Remove whatever files you don't need and be done with that.
> > >
> > > How do you remove files from the old rootfs after the new one has been
> > > mounted on top of it?
> >
> > You do that before ;-)
> 
> would the following work?
> 
> pivot_root . /initramfs
> cd /initramfs && rm -rf *

No.  pivot_root() will not move the absolute root of tree elsewhere.

> ?? doing it before is rather hard ... you apparently still need something to 
> execute your mounts :)

You do, but you can trivially call unlink() on the executable itself.  It
will be freed after it does exec() of final /sbin/init...

Alternatively, you could
mkdir /root
mount final root on /root

chdir("/root");
mount("/", "initramfs", NULL, MS_BIND, NULL);
mount(".", "/", NULL, MS_MOVE, NULL);
chroot(".");
execve("/sbin/init", ...)

and have init scripts do rm -rf /initramfs/*; umount /initramfs
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