Re: Device Namespaces

[Greg Kroah-Hartman <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>]

On Mon, Sep 30, 2013 at 08:37:19AM -0700, James Bottomley wrote:
> On Thu, 2013-09-26 at 10:07 -0700, Greg Kroah-Hartman wrote:
> > On Thu, Sep 26, 2013 at 08:01:31PM +0300, Janne Karhunen wrote:
> > > That being said, our wish would be to support any combination of
> > > OS's and frankly, I'd be slightly annoyed to tell the customer that
> > > they can't do two Androids or we magically run out of bits.
> > 
> > If you want to support "any" combination of operating systems, then use
> > a hypervisor, that's what they are there for :)
> 
> No that's not quite the right way to think about it: The correct
> statement is only use a hypervisor if you need different kernels.  With
> Windows, it happens to be true that you need a different kernel for each
> different OS version.  However; with Linux, thanks to strong ABI
> backwards compatibility, you mostly don't.  The way OpenVZ works today
> is that it installs a modified kernel which can then bring up every
> Linux OS in a separate container.  Our use case is the hosters that give
> you root login to a virtual private server and allow you to upgrade it
> on your own.  The reason for using a container rather than a hypervisor
> is the old density and elasticity one:  3x the density (i.e. 1/3 the
> overhead cost to the hoster) and the boot only needs to start at init,
> not bring up of virtual hardware and booting a second kernel.

I understand that some people really like the idea of using OpenVZ for
various things like this, but to claim that because of it we need to
hack up the driver core in the kernel into unimaginable pieces is not
necessarily something that I'll agree with.

But all of this is just words, I have yet to see any patches for any of
this, so I'll just wait until that happens before worrying about it...

thanks,

greg k-h