| # Microdroid Payload |
| |
| Payload disk is a composite disk image referencing host APEXes and an APK so that microdroid |
| mounts/activates APK/APEXes and executes a binary within the APK. |
| |
| Payload disk is created by [VirtualizationService](../../virtualizationservice) Service when |
| starting a VM. |
| |
| ## Partitions |
| |
| Payload disk has 1 + N(number of APEX/APK payloads) partitions. |
| |
| The first partition is a "payload-metadata" partition which describes other partitions. |
| And APEXes and an APK are following as separate partitions. |
| |
| For now, the order of partitions are important. |
| |
| * partition 1: Metadata partition |
| * partition 2 ~ n: APEX payloads |
| * partition n+1, n+2: APK payload and its idsig |
| |
| It's subject to change in the future, though. |
| |
| ### Metadata partition |
| |
| Metadata partition provides description of the other partitions and the location for VM payload |
| configuration. |
| |
| The partition is a protobuf message prefixed with the size of the message. |
| |
| | offset | size | description | |
| | ------ | ---- | ---------------------------------------------------- | |
| | 0 | 4 | Header. unsigned int32: body length(L) in big endian | |
| | 4 | L | Body. A protobuf message. [schema](metadata.proto) | |
| |
| ### Payload partitions |
| |
| Each payload partition presents APEX or APK passed from the host. |
| |
| The size of a payload partition must be a multiple of 4096 bytes. |
