Re: [Devel] Re: LXC container, unmounting unneeded mount points (from the container namespace)

["Michael H. Warfield" <mhw-BetbSzk+GohWk0Htik3J/w@public.gmane.org>]

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Added lxc-devel to the cc list since this seems to be more appropriate
over there (maybe) and I've just joined that one as well.

On Fri, 2010-01-08 at 15:35 +0100, Daniel Lezcano wrote: 
> Ciprian Dorin, Craciun wrote:
> > On Fri, Jan 8, 2010 at 4:17 PM, Daniel Lezcano <daniel.lezcano-GANU6spQydw@public.gmane.org> wrote:
> >   
> >> Ciprian Dorin, Craciun wrote:
> >>     
> >>>    Hy all!
> >>>
> >>>    Today I've started to play with the LXC containers, and I've got a
> >>> question: when starting a container (with it's own mount point
> >>> namespace), and I do a `cat /proc/mounts` I also see the mount points
> >>> from my host system.
> >>>
> >>>    So the question is: how can I force `lxc-create` to remove any
> >>> uneeded mount points (maybe all)?
> >>>
> >>>       
> >> Committed today :)
> >>
> >> http://git.lab.toulouse-stg.fr.ibm.com/?p=lxc.git;a=commit;h=ed83715df7666879116d1657b1dd54a8fc6513f6
> >>     

> Oops, this one:

> http://lxc.git.sourceforge.net/git/gitweb.cgi?p=lxc/lxc;a=commit;h=bf601689a9e0cea1ceaf17e4f7f853f5392c2827

Nice.  This is EXACTLY what I've been looking for as well.  Only problem
is...  It didn't work.  It complains about:

lxc-start: could not umount 1 mounts"

Then terminates saying it can't start the container.

When I throw in some debugging prints, I find out that it's complaining
that it can't umount {pivotdir}/dev.  Commented out the return -1's in
that routine so it starts the container anyways and jump into the
running container and I discover that {pivotdir}/dev/shm is still
mounted even though it thinks it umounted it.  I can see from the
debugging prints that it seems to have successfully umount it (the
debugging message indicates that it umounted it - so it saw it had it
and tried and got a good return from the attempt) but it's apparently
still mount.  If I umount that {pivotdir}/dev/shm inside the container,
I can then umount {pivotdir}/dev and {pivotdir}. 

Tried it both by defining lxc.pivotdir and by letting it choose a
temporary one.  Tried two different containers.  Same result.

This is what I get with the "return -1"'s commented out in the function
and laced with my own debugging prints to print each step of the umount
loop (this is with lxc.pivotdir = /rootfs):

===
[root@Berserker-Base ~]# lxc-start -n 1009
still mounted '/rootfs/dev'
umounted '/rootfs/dev/pts'
umounted '/rootfs/dev/shm'
still mounted '/rootfs/proc'
umounted '/rootfs/proc/bus/usb'
umounted '/rootfs/proc/sys/fs/binfmt_misc'
umounted '/rootfs/sys'
umounted '/rootfs/home'
still mounted '/rootfs/var'
umounted '/rootfs/var/lib/cgroup'
umounted '/rootfs/var/lib/nfs/rpc_pipefs'
umounted '/rootfs/usr'
umounted '/rootfs/boot'
still mounted '/rootfs/srv'
umounted '/rootfs/misc'
umounted '/rootfs/net'
still mounted '/rootfs/srv/lxc/root/1009'
umounted '/rootfs/srv/lxc/root/1009/export'
umounted '/rootfs/srv/lxc/root/1009/srv/shared'
umounted '/rootfs/srv/lxc/root/1009/dev/pts'
umounted '/rootfs/srv/lxc/root/1009/proc'
umounted '/rootfs/srv/lxc/root/1009/sys'
umounted '/rootfs/srv/lxc/root/1009/dev/shm'
umounted '/rootfs/srv/lxc/root/1009/dev/console'
umounted '/rootfs/srv/lxc/root/1009/dev/tty1'
umounted '/rootfs/srv/lxc/root/1009/dev/tty2'
umounted '/rootfs/srv/lxc/root/1009/dev/tty3'
umounted '/rootfs/srv/lxc/root/1009/dev/tty4'
umounted '/rootfs/srv/lxc/root/1009/dev/tty5'
umounted '/rootfs/srv/lxc/root/1009/dev/tty6'
still mounted '/rootfs/dev'
umounted '/rootfs/proc'
umounted '/rootfs/var'
still mounted '/rootfs/srv'
umounted '/rootfs/srv/lxc/root/1009'
still mounted '/rootfs/dev'
umounted '/rootfs/srv'
still mounted '/rootfs/dev'
lxc-start: could not umount 1 mounts
lxc-start: Device or resource busy - could not unmount old rootfs
INIT: version 2.86 booting
===

Container now continues to boot, since I commented out the error
returns.  Jumping into that container:

=== 
[root@Berserker ~]# df
Filesystem           1K-blocks      Used Available Use% Mounted on
rootfs               288433504 240305660  33476248  88% /
/dev/sda6              2063504    662116   1296568  34% /rootfs
udev                   1031280       200   1031080   1% /rootfs/dev
/dev/shm               1031280         0   1031280   0% /rootfs/dev/shm
/dev/mapper/VolGroup00-LogVol00
                     288433504 240305660  33476248  88% /
/dev/sda6              2063504    662116   1296568  34% /export
/dev/sda7            693727244 554704408 103783460  85% /srv/shared
none                   1031280         0   1031280   0% /dev/shm
[root@Berserker ~]# umount /rootfs/dev/shm
[root@Berserker ~]# umount /rootfs/dev    
[root@Berserker ~]# umount /rootfs    
[root@Berserker ~]# df
Filesystem           1K-blocks      Used Available Use% Mounted on
rootfs               288433504 240305672  33476236  88% /
/dev/mapper/VolGroup00-LogVol00
                     288433504 240305672  33476236  88% /
/dev/sda6              2063504    662116   1296568  34% /export
/dev/sda7            693727244 554704408 103783460  85% /srv/shared
none                   1031280         0   1031280   0% /dev/shm
===

Of course we also have the strange "rootfs" entry there as well.

Host system is Fedora 12.
Host kernel is: 2.6.31.9-174.fc12.i686
Guest system in each case is CentOS 5.4

Regards,
Mike
-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw-BetbSzk+GohWk0Htik3J/w@public.gmane.org
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!

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