Implement runtime-generated, human-readable hostnames derived from
permanent hardware properties (DMI serial/UUID, MAC address, or
machine-id). The hostname format is 'ghaf-NNNNNNNNNN' where N is a
10-digit number deterministically generated from hardware properties.

Key features:

• Host generates and shares hostname via /persist/common/ghaf/hostname
• NetVM sets its actual hostname for DHCP client identification
• All VMs have access to the hostname via environment variable
• NetworkManager configured to preserve the dynamic hostname
• 10 billion possible hostnames for excellent uniqueness
• Replaces random device-id with deterministic hardware-based ID
• Consolidates device-id and machine-id generation into single script
• All machine-ids are deterministic and hardware-based (not random UUIDs)

Implementation:

• dynamic-hostname.nix: Single script generates hostname, device-id, and all VM machine-ids
• vm-hostname-export.nix: Exports hostname as environment variable
• vm-hostname-setter.nix: Sets actual VM hostname from shared file
• Virtiofs share (/persist/common -> /etc/common) propagates to VMs
• NetworkManager hostname-mode set to 'none' to prevent override
• Replaces generate-device-id service from microvm-host.nix with single atomic operation

Technical details:

• Hostname: ghaf-NNNNNNNNNN (10-digit CRC32-based hardware ID)
• Device-id: Hardware ID formatted as hex string (e.g., 00-01-23-45-67)
• Machine-ids: MD5 hash of hardware key + VM name (deterministic, not random)
• Service runs before network-online.target for DHCP client identification
• All identity files generated atomically in single service execution
• Same hardware always produces same hostname, device-id, and machine-ids
• Each VM gets unique but deterministic machine-id

Use cases:

• DHCP client identification with unique device names
• Network troubleshooting and device tracking
• Logging and monitoring across host and VMs
• User visibility of hardware instance identity
• Deterministic device identification across reboots
• Reproducible VM identities for testing and automation

Documentation added at docs/src/content/docs/ghaf/dev/ref/dynamic-hostname.mdx

Description of Changes

Type of Change

• New Feature
• Bug Fix
• Improvement / Refactor

Related Issues / Tickets

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:

Testing Instructions: Dynamic Hostname Generation

Overview

This commit adds hardware-based dynamic hostname generation for Ghaf hosts and VMs. Test the following scenarios to ensure proper functionality.

Test 1: Basic Hostname Generation (Hardware Mode)

Setup

Build and deploy a Ghaf system with default configuration.

Steps

1. Boot the system
2. On the host, check hostname generation:

   cat /run/ghaf-hostname
   cat /var/lib/ghaf/identity/hostname
   cat /var/lib/ghaf/identity/id
   echo $GHAF_HOSTNAME

3. Verify format: ghaf-NNNNNNNNNN (10 digits)
4. Check host's actual hostname remains unchanged:

   hostname  # Should show "ghaf-host"

Expected Results

• /run/ghaf-hostname contains hostname like ghaf-1234567890
• $GHAF_HOSTNAME environment variable is set
• Host's actual hostname is still ghaf-host (not changed)
• Files are created in /persist/common/ghaf/

Test 2: VM Hostname Propagation

Steps

1. Access NetVM:

   microvm-console net-vm

2. Check hostname in NetVM:

   cat /etc/common/ghaf/hostname
   echo $GHAF_HOSTNAME
   hostname  # Should match the dynamic hostname

3. Access GUIVM and repeat:

   cat /etc/common/ghaf/hostname
   echo $GHAF_HOSTNAME
   hostname  # Should show "gui-vm" (static)

Expected Results

• NetVM: actual hostname matches dynamic hostname (for DHCP)
• GUIVM: $GHAF_HOSTNAME set, but actual hostname remains gui-vm
• Both VMs can read /etc/common/ghaf/hostname

Test 3: Deterministic Behavior

Steps

1. Note the generated hostname: cat /run/ghaf-hostname
2. Reboot the system
3. After reboot, verify hostname is identical:

   cat /run/ghaf-hostname

Expected Results

• Same hardware produces identical hostname across reboots
• Hostname is deterministic, not random

Test 4: Device ID Generation

Steps

1. Check device-id file:

   cat /persist/common/device-id

2. Verify format is hex with dashes: XX-XX-XX-XX-XX

Expected Results

• Device ID exists and has correct format
• Device ID is derived from same hardware key as hostname

Test 5: VM Machine IDs

Steps

1. Check machine-ids for each VM:

   cat /persist/storagevm/net-vm/etc/machine-id
   cat /persist/storagevm/gui-vm/etc/machine-id

2. Verify they are unique but deterministic
3. Reboot and verify machine-ids remain the same

Expected Results

• Each VM has a unique machine-id
• Machine-ids are deterministic (not random UUIDs)
• Same across reboots

Test 6: DHCP Client Identification

Steps

1. Access NetVM
2. Check NetworkManager configuration:

   nmcli general hostname

3. Request DHCP lease and verify hostname is sent:

   journalctl -u NetworkManager | grep -i hostname

4. On DHCP server, verify client hostname appears as ghaf-NNNNNNNNNN

Expected Results

• NetVM uses dynamic hostname for DHCP identification
• DHCP server sees the hardware-based hostname
• NetworkManager does not override the hostname (hostname-mode = "none")

Test 7: Static Mode Configuration

Setup

Configure system with static hardware ID:

ghaf.identity.dynamicHostName = {
  enable = true;
  source = "static";
  staticValue = "my-test-device";
};

Steps

1. Rebuild and deploy
2. Check generated hostname:

   cat /run/ghaf-hostname

Expected Results

• Hostname is deterministically derived from "my-test-device"
• Format is still ghaf-NNNNNNNNNN
• Same static value produces same hostname

Test 8: Random Mode Configuration

Setup

Configure with random ID generation:

ghaf.identity.dynamicHostName = {
  enable = true;
  source = "random";
};

Steps

1. Rebuild and deploy
2. Note the generated hostname
3. Reboot and verify hostname persists
4. Check random seed file:

   cat /var/lib/ghaf/identity/random-seed

Expected Results

• Random hostname generated on first boot
• Hostname persists across reboots (not regenerated)
• Random seed file exists and doesn't change

Test 9: Custom Prefix and Digits

Setup

Configure with custom parameters:

ghaf.identity.dynamicHostName = {
  enable = true;
  prefix = "test";
  digits = 6;
};

Steps

1. Rebuild and check hostname format

Expected Results

• Hostname format: test-NNNNNN (6 digits)
• All functionality works with custom parameters

Test 10: Hardware Detection Priority

Steps

1. Check which hardware source is being used:

   cat /sys/class/dmi/id/product_serial  # Priority 1
   cat /sys/class/dmi/id/product_uuid    # Priority 2
   ls /dev/disk/by-uuid/                 # Priority 3
   cat /sys/class/net/*/address          # Priority 4 (non-loopback)
   cat /etc/machine-id                   # Priority 5 (fallback)

2. Test on different hardware (if available)

Expected Results

• System uses highest-priority available hardware identifier
• Different hardware produces different hostnames
• Fallback chain works correctly

Test 11: Cross-VM Communication

Steps

1. From host, log all VMs' environment variables:

   # In each VM
   echo $GHAF_HOSTNAME

2. Verify all VMs see the same hostname

Expected Results

• All VMs share the same $GHAF_HOSTNAME value
• Hostname is consistent across the entire system