qemu:///embed and isolation from global components

[Andrea Bolognani]

On Mon, 2020-03-09 at 18:04 +0000, Daniel P. Berrangé wrote:
> At a high level the embedded QEMU driver
> 
>  - Isolated from any other instance of the QEMU driver

Replying here because it looks as good a place as any.

Now that Michal has made it so that identically-name domains defined
under different qemu:///embed roots no longer clash at the machined
level (thanks!), I have immediately bumped into the next issue: if
I use either one of

  <memoryBacking>
    <hugepages/>
  </memoryBacking>

  <memoryBacking>
    <access mode='shared'/>
  </memoryBacking>

both qemu:///embed instances try to use the same paths:

  /dev/hugepages/libvirt/qemu/$domid-$domname/

  /dev/shm/libvirt/qemu/$domid-$domname/

which obviously breaks everything.

In this case, is the application expected to set

  hugetlbfs_mount = "/dev/hugepages/$random"

  memory_backing_dir = "/dev/shm/$random"

in qemu.conf beforehand (I'm not sure the former setting would even
work), or should libvirt take care of it automatically in a similar
way it now does for machine names?

-- 
Andrea Bolognani / Red Hat / Virtualization