[libvirt PATCH 1/6] conf: add support for <acpi index='NNN'/> for PCI devices

[Peter Krempa]

On Wed, Apr 07, 2021 at 09:17:36 +0200, Peter Krempa wrote:
> On Tue, Apr 06, 2021 at 16:31:32 +0100, Daniel Berrange wrote:
> > PCI devices can be associated with a unique integer index that is
> > exposed via ACPI. In Linux OS with systemd, this value is used for
> > provide a NIC device naming scheme that is stable across changes
> > in PCI slot configuration.
> > 
> > Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
> > ---
> >  docs/formatdomain.rst         |  6 +++
> >  docs/schemas/domaincommon.rng | 73 +++++++++++++++++++++++++++++++++++
> >  src/conf/device_conf.h        |  3 ++
> >  src/conf/domain_conf.c        | 12 ++++++
> >  4 files changed, 94 insertions(+)
> > 
> > diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
> > index 7ba32ea9c1..5db0aac77a 100644
> > --- a/docs/formatdomain.rst
> > +++ b/docs/formatdomain.rst
> > @@ -4363,6 +4363,7 @@ Network interfaces
> >         <mac address='52:54:00:5d:c7:9e'/>
> >         <boot order='1'/>
> >         <rom bar='off'/>
> > +       <acpi index='4'/>
> >       </interface>
> >     </devices>
> >     ...
> > @@ -4389,6 +4390,11 @@ when it's in the reserved VMware range by adding a ``type="static"`` attribute
> >  to the ``<mac/>`` element. Note that this attribute is useless if the provided
> >  MAC address is outside of the reserved VMWare ranges.
> >  
> > +:since:`Since 7.3.0`, one can set the ACPI index against network interfaces.
> > +With some operating systems (eg Linux with systemd), the ACPI index is used
> > +to provide network interface device naming, that is stable across changes
> > +in PCI addresses assigned to the device.
> 
> Any range limits or uniqueness requirements worth mentioning?

QEMU / ACPI spec seems to be enforcing unique indexes:

commit 4fd7da4c0336c8fd822cd808d62f7ff8c9936aef
Author: Igor Mammedov <imammedo at redhat.com>
Date:   Mon Mar 15 14:00:59 2021 -0400

    pci: acpi: ensure that acpi-index is unique

    it helps to avoid device naming conflicts when guest OS is
    configured to use acpi-index for naming.
    Spec ialso says so:

    PCI Firmware Specification Revision 3.2
    4.6.7.  _DSM for Naming a PCI or PCI Express Device Under Operating Systems
    "
    Instance number must be unique under \_SB scope. This instance number does not have to
    be sequential in a given system configuration.
    "


The code isn't checking whether they are declared as unique.