On 08/27/2018 04:33 AM, Cornelia Huck wrote:
On Thu, 23 Aug 2018 10:16:59 -0400
Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
On 08/23/2018 06:25 AM, Cornelia Huck wrote:
On Wed, 22 Aug 2018 15:16:19 -0400
Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
One of the things I suggested in a private conversation with Christian
earlier
today was to provide an additional rw sysfs attribute - a boolean - that
indicates
whether all usage domains should also be control domains. The default
could be
true. This would allow one to configure guests with usage-only domains
as well
as satisfy the convention.
Would this additional attribute then control "add usage domains to the
list of control domains automatically", or "don't allow to add a usage
domain if it has not already been added as a control domain"?
It was just a proposal that wasn't really discussed at all, but this
attribute would add usage domains to the list of control domains
automatically if set to one. That would be the default behavior which
would be turned off by manually setting it to zero.
If we want to do something like that, having it add the usage domains
automatically sounds like the more workable alternative. What I like
about this is that we make it explicit that we change the masks beyond
what the admin explicitly configured, and provide a knob to turn off
that behaviour.
So, are you saying I should go ahead and implement this?
One thing I'm still unsure about is how libvirt comes into the picture
here. Will it consume the setting, or actively manipulate it?
libvirt is not in the picture. The only thing libvirt does is identify
which mediated matrix device (i.e., UUID) is to be used by the guest.
[In general, I'm not very clear about how libvirt will interact with the
whole infrastructure...]
The libvirt domain XML will only specify the UUID of the matrix device
to be used by the guest. Consequently, libvirt will insert the device
statement for the vfio-ap device into the QEMU command line:
-device vfio-ap,syfsdev={path-to-mdev}
All configuration of the mediated device, including the proposed attribute
above, is handled via sysfs attributes.
So, basically, libvirt will only consume what the admin has already
configured?
Yes.
