Re: [RFC v1] hw/smbios: support for type 41 (onboard devices extended information)

["Daniel P. Berrangé" <berrange@redhat.com>]

On Sun, Mar 28, 2021 at 10:57:26PM +0200, Vincent Bernat wrote:
> Type 41 defines the attributes of devices that are onboard. The
> original intent was to imply the BIOS had some level of control over
> the enablement of the associated devices.
> 
> If network devices are present in this table, by default, udev will
> name the corresponding interfaces enoX, X being the instance number.
> Without such information, udev will fallback to using the PCI ID and
> this usually gives ens3 or ens4. This can be a bit annoying as the
> name of the network card may depend on the order of options and may
> change if a new PCI device is added earlier on the commande line.
> Being able to provide SMBIOS type 41 entry ensure the name of the
> interface won't change and helps the user guess the right name without
> booting a first time.
> 
> This can be invoked with:
> 
>     $QEMU -netdev user,id=internet
>           -device virtio-net-pci,mac=50:54:00:00:00:42,netdev=internet \
>           -smbios type=41,designation=Onboard LAN,instance=1,kind=ethernet,pci=0000:00:09.0
> 
> Which results in the guest seeing dmidecode data and the interface
> exposed as "eno1":
> 
>     $ dmidecode -t 41
>     # dmidecode 3.3
>     Getting SMBIOS data from sysfs.
>     SMBIOS 2.8 present.Handle 0x2900, DMI type 41, 11 bytes
>     Onboard Device
>             Reference Designation: Onboard LAN
>             Type: Ethernet
>             Status: Enabled
>             Type Instance: 1
>             Bus Address: 0000:00:09.0
>     $ udevadm info -p /sys/class/net/eno1 | grep ONBOARD
>     E: ID_NET_NAME_ONBOARD=eno1
>     E: ID_NET_LABEL_ONBOARD=Onboard LAN
> 
> The original plan was to directly provide a device and populate "kind"
> and "pci" from the device. However, since the SMIBIOS tables are built
> during argument evaluation, the information is not yet available.
> I would welcome some guidance on how to implement this.

I'm not sure I see the problem you're describing here, could
you elaborate ?

I see SMBIOS tables are built by  smbios_get_tables() method.
This is called from qemu_init(), after all arguents have been
processed and devices have been created.

It seems like this should allow SMBIOS tables to be auto-populated
from the NICs listed in -device args previously.


Note, if we're going to auto-populate the SMBIOS type 41 tabes
from -device args, then we'll need to make this behaviour
configurable via a property, so that we can ensure this only
applies to new machine types.

Regards,
Daniel
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