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    SubjectRe: Is initramfs freed after kernel is booted?
    viro@parcelfarce.linux.theplanet.co.uk wrote:
    > On Mon, Nov 17, 2003 at 09:33:59PM +0300, Andrey Borzenkov wrote:
    >
    >>On Monday 17 November 2003 21:03, viro@parcelfarce.linux.theplanet.co.uk
    >>wrote:
    >>
    >>>On Mon, Nov 17, 2003 at 12:50:34PM -0500, Chris Friesen wrote:
    >>>
    >>>>viro@parcelfarce.linux.theplanet.co.uk 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", ...)
    >
    Nope. initramfs shares the superblock with 'rootfs', which has the
    MS_NOUSER flags set. Hence graft_tree() (which is the worker function
    for MS_BIND) refuses to work.
    Can't we just remove the MS_NOUSER flags if initramfs is active?
    Probably not the correct way, but certainly the quickest :-)
    The correct way would probably be to clone the superblock of initramfs,
    set the filesystem-type of initramfs to 'ramfs' so that initramfs
    appears to be a chroot()ed filesystem like initrd. Then we could do a
    pivot_root and we have the contents of initramfs still available.
    But needs someone with deeper fs-knowledge than myself to do it.

    Cheers,

    Hannes
    --
    Dr. Hannes Reinecke hare@suse.de
    SuSE Linux AG S390 & zSeries
    Deutschherrnstr. 15-19 +49 911 74053 688
    90429 Nürnberg http://www.suse.de

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