Re: [PATCH 2/6] pci: introduce apci-index property for PCI device

[Daniel P . Berrangé]

On Mon, Mar 15, 2021 at 02:00:58PM -0400, Igor Mammedov wrote:
> In x86/ACPI world, linux distros are using predictable
> network interface naming since systemd v197. Which on
> QEMU based VMs results into path based naming scheme,
> that names network interfaces based on PCI topology.
> 
> With itm on has to plug NIC in exactly the same bus/slot,
> which was used when disk image was first provisioned/configured
> or one risks to loose network configuration due to NIC being
> renamed to actually used topology.
> That also restricts freedom to reshape PCI configuration of
> VM without need to reconfigure used guest image.
> 
> systemd also offers "onboard" naming scheme which is
> preferred over PCI slot/topology one, provided that
> firmware implements:
>     "
>     PCI Firmware Specification 3.1
>     4.6.7.  DSM for Naming a PCI or PCI Express Device Under
>             Operating Systems
>     "
> that allows to assign user defined index to PCI device,
> which systemd will use to name NIC. For example, using
>   -device e1000,acpi-index=100
> guest will rename NIC to 'eno100', where 'eno' is default
> prefix for "onboard" naming scheme. This doesn't require
> any advance configuration on guest side to com in effect
> at 'onboard' scheme takes priority over path based naming.
> 
> Hope is that 'acpi-index' it will be easier to consume by
> management layer, compared to forcing specific PCI topology
> and/or having several disk image templates for different
> topologies and will help to simplify process of spawning
> VM from the same template without need to reconfigure
> guest NIC.
> 
> This patch adds, 'acpi-index'* property and wires up
> a 32bit register on top of pci hotplug register block
> to pass index value to AML code at runtime.
> Following patch will add corresponding _DSM code and
> wire it up to PCI devices described in ACPI.

You've illustrated usage & benefits with NICs, but IIUC, this
feature is wired up for any PCI device. Are you aware of any
usage of this feature for non-NIC devices ?

Regards,
Daniel
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