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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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