Description of Changes

Introduces a service for passing hardware information from host systems to guest VMs using QEMU's fw_cfg interface. Detects NVMe serial numbers and MAC addresses on the host and makes them available to guest VMs.

The implementation is cross-platform and integrates with Ghaf's microvm infrastructure.

Implementation Details

• Adds ghaf.services.hwinfo module for host systems that automatically detects and exports hardware information
• Adds ghaf.services.hwinfo-guest module for guest VMs to read the hardware information
• Uses QEMU's fw_cfg mechanism which is supported across all architectures (x86_64, ARM)
• Hardware information is passed as JSON via the -fw_cfg QEMU argument
• Currently enabled only for net-vm on the Jetson AGX target
• Qemu documentation for fw_cfg mechanism

Technical Considerations

Initially attempted to use ACPI table injection via -acpitable for this feature, but discovered it is not supported on ARM architectures in QEMU. The error "Option not supported for this target" occurs even with ACPI enabled on the virt machine. Implementing ACPI table injection for ARM would require upstream changes to both QEMU and potentially the microvm framework. The fw_cfg approach was chosen as it provides a clean, cross-platform solution that works on all supported architectures.

Type of Change

• New Feature
• Bug Fix
• Improvement / Refactor

Related Issues / Tickets

None

Checklist

• Clear summary in PR description
• Detailed and meaningful commit message(s)
• Commits are logically organized and squashed if appropriate
• Contribution guidelines followed
• Ghaf documentation updated with the commit - https://tiiuae.github.io/ghaf/
• Author has run make-checks and it passes
• All automatic GitHub Action checks pass - see actions
• Author has added reviewers and removed PR draft status

Testing Instructions

Applicable Targets

• Orin AGX aarch64
• Orin NX aarch64
• Lenovo X1 x86_64
• Dell Latitude x86_64
• System 76 x86_64

Installation Method

• Requires full re-installation
• Can be updated with nixos-rebuild ... switch
• Other:

Test Steps To Verify:

1. Build and flash the Orin AGX target with this change
2. Boot the device and SSH into it
3. Verify hardware info generation on host:

   sudo systemctl status ghaf-hwinfo-generate
   ls -la /var/lib/ghaf-hwinfo/
   cat /var/lib/ghaf-hwinfo/hwinfo.json

4. Check that net-vm is running:

   systemctl status microvm@net-vm.service

5. Access net-vm and verify hardware information is available:

   # In net-vm
   sudo read-hwinfo

6. Expected output should show NVMe serial, MAC address, hostname, and timestamp

Notes

• Hostname detection requires the service to run after network initialization
• Timestamp accuracy depends on system time synchronization
• The fw_cfg kernel module (qemu_fw_cfg) must be loaded in the guest
• Currently only enabled for net-vm on Jetson AGX target

Enabling for Other Targets and VMs

To enable this service on other targets or guest VMs:

1. Enable host service in the target hardware configuration:

   ghaf.services.hwinfo = {
     enable = true;
     outputDir = "/var/lib/ghaf-hwinfo";
   };

2. For each guest VM, add to the VM's extraModules:

   {
     imports = [ <path-to>/modules/common/services/hwinfo ];
     ghaf.services.hwinfo-guest.enable = true;
   }
   {
     # Ensure hwinfo is generated before VM starts
     systemd.services."microvm@<vm-name>" = {
       wants = [ "ghaf-hwinfo-generate.service" ];
       after = [ "ghaf-hwinfo-generate.service" ];
     };
   }
   {
     # Pass hardware info via fw_cfg
     microvm.qemu.extraArgs = [
       "-fw_cfg" "name=opt/com.ghaf.hwinfo,file=/var/lib/ghaf-hwinfo/hwinfo.json"
     ];
   }

This approach works identically on both ARM and x86_64 targets.