[CentOS-virt] Are xen and centos incompatible?

Thu Jun 12 03:24:20 UTC 2014
lee <lee at yun.yagibdah.de>

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

> 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)? 

Lspci still shows it, and the device (eth1) is invisible.

>> 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.

Hm, xen kinda makes the cpus and their power management invisible, too:

root at heimdall:~# xenpm get-cpufreq-para
[CPU0] failed to get cpufreq parameter
root at heimdall:~# xenpm  get-cpufreq-states
root at heimdall:~# 

So I guess it could as well make it so that lspci doesn't show
passed-out devices.

BTW, getting some info in dmesg might be nice, like a message saying
"xen-pciback: device 06:00.0 can be passed through to guests".  We could
actually see right away if it did work or not.  That a device disappears
isn't too great as indication, especially not when lspci still lists it.

Of course, you could use the command (which I don't remember) to show
devices that can be passed through.  But that may just work as well as
'xenpm get-cpufreq-states':  Apparently, there aren't any CPUs ...

Knowledge is volatile and fluid.  Software is power.