[CentOS-virt] Are xen and centos incompatible?

Tue Jun 10 17:36:11 UTC 2014
Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>

On Tue, Jun 10, 2014 at 06:47:20PM +0200, lee wrote:
> 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.

That is a surprise. If you do 'lspci' in your dom0 do you see 
the device (06:00.0)? 

> 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.

Function Level Reset.

You pass the device to a guest so it can load the drivers and the initial
domain (dom0) won't use it.
> >> > But irrespective of that - the steps mentioned there are out of date.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  But it seems I'm using an outdated version of xen, which is what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 outdated and contribute to confusion more than do any good.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.
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