[CentOS-virt] Are xen and centos incompatible?

Tue Jun 10 16:47:20 UTC 2014
lee <lee at yun.yagibdah.de>

Konrad Rzeszutek Wilk <konrad.wilk at oracle.com> writes:

> On Tue, Jun 10, 2014 at 04:44:23AM +0200, lee wrote:
>>> Konrad Rzeszutek Wilk <konrad.wilk at oracle.com> writes:
>> >
>> > The device should be visible in the dom0 - even when it is for passthrough.
>> Why should it be visible when it's hidden?
> The 'hide' part is to hide it from the device drivers in the initial
> domain - dom0. That is so that they will not try to use it - as we
> plan to pass them to a guest. We need it in the dom0 to do admin type
> work - FLR it, etc.

With Debian, it's not visible in dom0 when the passthrough works.
That's how I found out that it does work to begin with, and it makes
sense to me.

What does FLR mean?  And how do you do something with a device for which
no drivers are loaded?  I'd find it rather unusual to have a device
without drivers and even be able to use it; such devices usually don't
show up.

>> > But irrespective of that - the steps mentioned there are out of date.
>> > The correct option should be 'xen-pciback.hide=(06:00.0) xen-pciback.permissive=1'
>> That's one of the problems: Xen is very poorly documented.
> Any help in improving the documentations would be appreciated. Every month
> we run 'Documentation days' and any work - either on Wiki, manuals, docs, etc
> would be quite appreciated.

If I have some time, I might make a writeup about how to set up what I
did.  But it seems I'm using an outdated version of xen, which is what
comes with Debian, so by the time I'd finish the writeup, it would be
outdated and contribute to confusion more than do any good.

And considering xen, I don't really know anything.  I figured out that
passthrough doesn't work out of the box on Debian because the module for
the device was loaded from the initrd.img before the xen-pciback module
and made a bug report because you're supposed to be able to use files in
/etc/modprobe.d which can specify dependencies and when you do that, you
can't have that just overridden or there's no point in doing that ---
and there doesn't seem to be any other way to specify the order in which
modules are loaded, and long ago, Debian came up with a policy that
things should work out of the box whenever possible (which they might
have forgotten by now ...).  So maybe they'll fix this problem.

Anyway, it probably goes for other distributions as well, and a hint in
the xen docs probably won't hurt.

> Please see http://wiki.xenproject.org/wiki/Xen_Project_Document_Days

I tried to make a request to become a "wiki editor".  There might be
some places in the docs I might be able to make clearer.  I don't know
if that was successful, though.  It seemed to want to redirect me to
some google website ...

Knowledge is volatile and fluid.  Software is power.