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Re: [libvirt] [PATCH] Adding filesystem mount support for openVZ

2009/3/12 Daniel P. Berrange <berrange redhat com>

On Wed, Mar 11, 2009 at 05:42:20PM +0100, Florian Vichot wrote:
> Hi everyone,
> This patch is to allow using the "mount" type in the "filesystem" tag
> for OpenVZ domains.
> Example:
> ...
>     <filesystem type='mount'>
>       <source dir='/path/to/filesystem/directory/' />
>       <target dir='/path/to/pivot/root/' />
>     </filesystem>
> ...
> This is my first patch to an external project, so don't spare me if I
> got things wrong :)
> Also, I'm curious for suggestions as to how I could allow for the target
> not to be specified in the XML. Because in this case OpenVZ just makes a
> temporary pivot root in "/var/lib/vz/root/" and that is probably
> sufficient for most people, who might not want to have to explicitly
> create a pivot root somewhere, just for mounting the filesystem while
> it's running.

Actually the <target dir="...">  means something a little different. This
refers to the mount point *within* the container. So for the root filesystem
of the container it will be   <target dir='/' />
No, that patch does something different---it assumes that both <source dir> and <target dir>
are paths within hardware node. If we denote <source dir> and <target dir> by the VE_PRIVATE
and VE_ROOT correspondingly, we get the following picture.

In OpenVZ there are VE_ROOT and VE_PRIVATE values for each container
(they defined as VE_ROOT and VE_PRIVATE variables in container configuration file).
The VE_PRIVATE defines the actual disposition of conatainer's
root filesystem hierarchy. It can lie on it's own partition or be just a directory.
When vzctl starts a container, it mounts a VE_PRIVATE "filesystem" to VE_ROOT
mountpoint and then container starts to work in VE_ROOT chroot...
So, yes, you are right - in this case we can always assume, that "target dir within container" is "/" :)

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