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mount --bind Bug in OpenVZ? [message #35793]

Wed, 22 April 2009 21:20

divB
Messages: 79
Registered: April 2009

Member

Hi,

The following scenario without OpenVZ:

# mount /dev/sda1 /home
# mount --bind /home /dest1
# mount --bind /home /dest2
...

Now the content from /home is mapped to dest1 and dest2. Now I want to unmount these mapping but never ever the original mount to /home:

# umount /dest1
# umound /dest2
...
# ls /home
(there are files)

Well this is how should bind-mounts work. Now OpenVZ comes into play. In $VEID.mount, I have the following command:

mount --bind /home /var/lib/vz/root/${VEID}/home

When the VE starts everything is fine. In the $VEID.unmount-Skript I have the following command:

umount /home /var/lib/vz/root/${VEID}/home

But now suddenly /home has been unmounted too on the host!! But this should never ever happen!

# ls /home
. ..

When I just ignore unmounting the bind-mounts it seems to work without problems but it seems to be not elegant to me.

I just don't understand it. Without the mount-Scripts everything works fine. But inside the mount/umount script, the original mount (/dev/sda1 to /home on VE0) is unmounted too.

And this is a fiasco: I have mounted /home into multiple VEs stopping one VE which has /home mounted removes /home from all other VEs!

Does anybody know something about this issue?

Regards,
divB

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Re: mount --bind Bug in OpenVZ? [message #35800 is a reply to message #35793]

Thu, 23 April 2009 06:53

maratrus
Messages: 1495
Registered: August 2007
Location: Moscow

Senior Member

Hi,

Quote:

umount /home /var/lib/vz/root/${VEID}/home

This is a wrong syntax.
Invoking such command from HN tells your system to umount home. No wonder that /home is umounted.

Don't put anything in umount script in such situation because /home directory will be properly umounted from inside a VE when a VE is stopped.
Look at /proc/mounts output inside VE. The information about bind mount can be obtained from it, so you can umount this directory from inside the VE and init scripts actually do this.

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Re: mount --bind Bug in OpenVZ? [message #35801 is a reply to message #35800]

Thu, 23 April 2009 09:29

divB
Messages: 79
Registered: April 2009

Member

CORRECTION!!! This was a copy & paste error. Sorry.

I certainly meant:

umount /var/lib/vz/root/${VEID}/home

Sorry.

Now it is really a bug, isn't it? Smile

However, you say I should just leave the umount-scripts empty? It is unmounted automatically? Is this really the "right way"?

(I always try to avoid using things without cleanup code - it seems to me like using malloc without free or like creating a service with "start" but without "stop"...)

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