platform_bootable_recovery/minadbd/README.md

minadbd

minadbd is analogous to the regular adbd, but providing the minimal services to support recovery-specific use cases. Generally speaking, adbd = libadbd + libadbd_services, whereas minadbd = libadbd + libminadbd_services.

Although both modules may be installed into the recovery image, only one of them, or none, can be active at any given time.

• The start / stop of adbd is managed via system property sys.usb.config, when setting to adb or none respectively. Upon starting recovery mode, adbd is started in debuggable builds by default; otherwise adbd will stay off at all times in user builds. See the triggers in bootable/recovery/etc/init.rc.

• minadbd is started by recovery as needed.

  • When requested to start minadbd, recovery stops adbd first, if it's running; it then forks and execs minadbd in a separate process.
  • minadbd talks to host-side adb server to get user requests.
    • minadbd handles some requests directly, e.g. querying device properties for rescue service.
    • minadbd communicates with recovery to fulfill requests regarding package installation. See the comments in bootable/recovery/install/adb_install.cpp for the IPC protocol between recovery and minadbd.
  • Upon exiting minadbd, recovery restarts adbd if it was previously running.