Early VM

Early VMs are specialized virtual machines that can run even before the /data partition is mounted, unlike regular VMs. early_virtmgr is a binary that serves as the interface for early VMs, functioning similarly to virtmgr, which provides the IVirtualizationService aidl interface.

To run an early VM, clients must follow these steps.

1. Early VMs must be defined in XML files located at {partition}/etc/avf/early_vms*.xml. Schema for these files is defined in early_vms.xsd.

<early_vms>
    <early_vm>
        <name>vm_demo_native_early</name>
        <cid>123</cid>
        <path>/system/bin/vm_demo_native_early</path>
    </early_vm>
</early_vms>

In this example, the binary /system/bin/vm_demo_native_early can establish a connection with early_virtmgr and create a VM named vm_demo_native_early, which will be assigned the static CID 123.

Multiple XML files matching the glob pattern {partition}/etc/avf/early_vms*.xml can be used to define early VMs.

2. The client must have the following three or four capabilities.

• IPC_LOCK
• NET_BIND_SERVICE
• SYS_NICE (required if RELEASE_AVF_ENABLE_VIRT_CPUFREQ is enabled)
• SYS_RESOURCES

Typically, the client is defined as a service in an init script, where capabilities can also be specified.

service vm_demo_native_early /system/bin/vm_demo_native_early
    user system
    group system virtualmachine
    capabilities IPC_LOCK NET_BIND_SERVICE SYS_RESOURCE SYS_NICE
    oneshot
    stdio_to_kmsg
    class early_hal

3. The client forks early_virtmgr instead of virtmgr.

The remaining steps are identical to those for regular VMs: connect to early_virtmgr, obtain the IVirtualizationService interface, then create and run the VM.