vsock guest agent: runtime resource adjustment and network auto-configuration

[CMGS]

Background

Currently clone/restore supports increasing CPU/Memory/Storage at creation time, but the guest requires manual operations to take effect (online CPU, resize2fs, MAC/IP reconfiguration, etc.). Runtime scaling (CH vm.resize) also faces guest awareness challenges.

Proposal

Establish a host↔guest control channel via vsock (AF_VSOCK), running a lightweight agent inside the guest:

Network Auto-Configuration (Clone Scenario)

• Host notifies agent of the new MAC/IP configuration via vsock
• Agent executes ip link set dev ethN address NEW_MAC + IP reconfiguration
• Replaces current manual post-clone hints

Runtime Resource Adjustment

• CPU hotplug: Host calls CH vm.resize, then notifies agent → echo 1 > /sys/devices/system/cpu/cpuN/online
• Memory: virtio-mem kernel driver handles it automatically; balloon requires agent coordination
• Disk resize: Host resizes COW, then notifies agent → resize2fs / xfs_growfs

Vertical Scaling Loop

Monitoring → trigger scaling → CH resize API → vsock notification to agent → guest auto-adapts, no restart required.

Alternative Approaches Comparison

Approach	Applicable To	Limitations
cidata/cloud-init bootcmd	cloudimg one-time initialization	Boot-time only
kernel cmdline	OCI direct boot parameter passing	Read-only, boot-time only
virtiofs shared directory	Config file delivery	Requires polling, not real-time
vsock agent	All scenarios, runtime	Requires agent installed in guest