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LeafOS / LeafOS-Project / android_packages_modules_adb / e31085c67dbf99dde35c8300c271a72400fc3f63
commite31085c67dbf99dde35c8300c271a72400fc3f63[log] [tgz]
authorShaju Mathew <shaju@google.com>Thu Feb 29 17:19:43 2024 +0000
committerAutomerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>Thu Feb 29 17:19:43 2024 +0000
tree1b3d590c67e0ef8568162e84c96d6cfbba6e9691
parent752be326d1b833cfe3efc9209eaa84288066d671 [diff]
parent5e80f31967e4fee8a84f91470237cc0c85e9cdeb [diff]
Merge "Revert "Defaulting to libusb for all hosts, including Windows"" into main am: 7f5b268560 am: 5e80f31967

Original change: https://android-review.googlesource.com/c/platform/packages/modules/adb/+/2983196

Change-Id: Iffadf584529efea85605ee01e3a38113fc3c3667
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
tree: 1b3d590c67e0ef8568162e84c96d6cfbba6e9691
  1. apex/
  2. client/
  3. coverage/
  4. crypto/
  5. daemon/
  6. docs/
  7. fastdeploy/
  8. fdevent/
  9. libs/
  10. pairing_auth/
  11. pairing_connection/
  12. proto/
  13. sysdeps/
  14. test_utils/
  15. tls/
  16. tools/
  17. .clang-format
  18. adb.bash
  19. adb.cpp
  20. adb.h
  21. adb_auth.h
  22. adb_integration_test_adb.xml
  23. adb_integration_test_device.xml
  24. adb_io.cpp
  25. adb_io.h
  26. adb_io_test.cpp
  27. adb_listeners.cpp
  28. adb_listeners.h
  29. adb_listeners_test.cpp
  30. adb_mdns.cpp
  31. adb_mdns.h
  32. adb_trace.cpp
  33. adb_trace.h
  34. adb_unique_fd.cpp
  35. adb_unique_fd.h
  36. adb_utils.cpp
  37. adb_utils.h
  38. adb_utils_test.cpp
  39. adb_wifi.h
  40. adbd_test.xml
  41. Android.bp
  42. benchmark_device.py
  43. bugreport_test.cpp
  44. compression_utils.h
  45. file_sync_protocol.h
  46. mdns_test.cpp
  47. MODULE_LICENSE_APACHE2
  48. NOTICE
  49. OVERVIEW.TXT
  50. OWNERS
  51. PREUPLOAD.cfg
  52. protocol.txt
  53. README.md
  54. security_log_tags.h
  55. services.cpp
  56. services.h
  57. SERVICES.TXT
  58. shell_protocol.h
  59. shell_service_protocol.cpp
  60. shell_service_protocol_test.cpp
  61. SOCKET-ACTIVATION.txt
  62. socket.h
  63. socket_spec.cpp
  64. socket_spec.h
  65. socket_spec_test.cpp
  66. socket_test.cpp
  67. sockets.cpp
  68. sockets.dia
  69. SYNC.TXT
  70. sysdeps.h
  71. sysdeps_test.cpp
  72. sysdeps_unix.cpp
  73. sysdeps_win32.cpp
  74. sysdeps_win32_test.cpp
  75. test_adb.py
  76. test_device.py
  77. TEST_MAPPING
  78. trace.sh
  79. transfer_id.h
  80. transport.cpp
  81. transport.h
  82. transport_benchmark.cpp
  83. transport_fd.cpp
  84. transport_test.cpp
  85. types.cpp
  86. types.h
  87. types_test.cpp
README.md

ADB Internals

If you are new to adb source code, you should start by reading OVERVIEW.TXT which describes the three components of adb pipeline.

This document is here to boost what can be achieved within a "window of naive interest". You will not find function or class documentation here but rather the "big picture" which should allow you to build a mental map to help navigate the code.

Three components of adb pipeline

As outlined in the overview, this codebase generates three components (Client, Server (a.k.a Host), and Daemon (a.k.a adbd)). The central part is the Server which runs on the Host computer. On one side the Server exposes a "Smart Socket" to Clients such as adb or DDMLIB. On the other side, the Server continuously monitors for connecting Daemons (as USB devices or TCP emulator). Communication with a device is done with a Transport.

+----------+              +------------------------+
|   ADB    +----------+   |      ADB SERVER        |                   +----------+
|  CLIENT  |          |   |                        |              (USB)|   ADBD   |
+----------+          |   |                     Transport+-------------+ (DEVICE) |
                      |   |                        |                   +----------+
+-----------          |   |                        |
|   ADB    |          v   +                        |                   +----------+
|  CLIENT  +--------->SmartSocket                  |              (USB)|   ADBD   |
+----------+          ^   | (TCP/IP)            Transport+-------------+ (DEVICE) |
                      |   |                        |                   +----------+
+----------+          |   |                        |
|  DDMLIB  |          |   |                     Transport+--+          +----------+
|  CLIENT  +----------+   |                        |        |  (TCP/IP)|   ADBD   |
+----------+              +------------------------+        +----------|(EMULATOR)|
                                                                       +----------+

The Client and the Server are contained in the same executable and both run on the Host machine. Code sections specific to the Host is enclosed within ADB_HOST guard. adbd runs on the Android Device. Daemon specific code is enclosed in !ADB_HOST but also sometimes with-in __ANDROID__ guard.

"SMART SOCKET" and TRANSPORT

A smart socket is a simple TCP socket with a smart protocol built on top of it. This is what Clients connect onto from the Host side. The Client must always initiate communication via a human readable request but the response format varies. The smart protocol is documented in SERVICES.TXT.

On the other side, the Server communicates with a device via a Transport. adb initially targeted devices connecting over USB, which is restricted to a fixed number of data streams. Therefore, adb multiplexes multiple byte streams over a single pipe via Transport. When devices connecting over other mechanisms (e.g. emulators over TCP) were introduced, the existing transport protocol was maintained.

THREADING MODEL and FDEVENT system

At the heart of both the Server and Daemon is a main thread running an fdevent loop, which is a platform-independent abstraction over poll/epoll/WSAPoll monitoring file descriptors events. Requests and services are usually served from the main thread but some service requests result in new threads being spawned.

To allow for operations to run on the Main thread, fdevent features a RunQueue combined with an interrupt fd to force polling to return.

+------------+    +-------------------------^
|  RUNQUEUE  |    |                         |
+------------+    |  POLLING (Main thread)  |
| Function<> |    |                         |
+------------+    |                         |
| Function<> |    ^-^-------^-------^------^^
+------------+      |       |       |       |
|    ...     |      |       |       |       |
+------------+      |       |       |       |
|            |      |       |       |       |
|============|      |       |       |       |
|Interrupt fd+------+  +----+  +----+  +----+
+------------+         fd      Socket  Pipe

ASOCKET, APACKET, and AMESSAGE

The asocket, apacket, and amessage constructs exist only to wrap data while it transits on a Transport. An asocket handles a stream of apackets. An apacket consists in a amessage header featuring a command (A_SYNC, A_OPEN, A_CLSE, A_WRTE, A_OKAY, ...) followed by a payload (find more documentation in protocol.txt. There is no A_READ command because an asocket is unidirectional. To model a bi-directional stream, asocket have a peer which go in the opposite direction.

An asocket features a buffer where the elemental unit is an apacket. If traffic is inbound, the buffer stores the apacket until it is consumed. If the traffic is oubound, the buffer stores apackets until they are sent down the wire (with A_WRTE commands).

+---------------------ASocket------------------------+
 |                                                   |
 | +----------------APacket Queue------------------+ |
 | |                                               | |
 | |            APacket     APacket     APacket    | |
 | |          +--------+  +--------+  +--------+   | |
 | |          |AMessage|  |AMessage|  |AMessage|   | |
 | |          +--------+  +--------+  +--------+   | |
 | |          |        |  |        |  |        |   | |
 | |  .....   |        |  |        |  |        |   | |
 | |          |  Data  |  |  Data  |  |  Data  |   | |
 | |          |        |  |        |  |        |   | |
 | |          |        |  |        |  |        |   | |
 | |          +--------+  +--------+  +--------+   | |
 | |                                               | |
 | +-----------------------------------------------+ |
 +---------------------------------------------------+

This system allows to multiplex data streams on an unique byte stream. Without entering too much into details, the amessage fields arg1 and arg2 are used alike in the TCP protocol where local and remote ports identify an unique stream. Note that unlike TCP which feature an "unacknowledged-send window", an apacket is sent only after the previous one has been confirmed to be received.

The two types of asocket (Remote and Local) differentiate between outbound and inbound traffic.

adbd <-> APPPLICATION communication

This pipeline is detailed in daemon/jdwp_service.cpp with ASCII drawings! The JDWP extension implemented by Dalvik/ART are documented in:

  • platform/dalvik/+/main/docs/debugmon.html
  • platform/dalvik/+/main/docs/debugger.html

Benchmark sample run for Pixel 8,USB

$ ./benchmark_device.py
sink 100MiB: 10 runs: median 27.00 MiB/s, mean 26.39 MiB/s, stddev: 1.11 MiB/s
source 100MiB: 10 runs: median 36.97 MiB/s, mean 37.05 MiB/s, stddev: 0.46 MiB/s
push 100MiB: 10 runs: median 331.96 MiB/s, mean 329.81 MiB/s, stddev: 14.67 MiB/s
pull 100MiB: 10 runs: median 34.55 MiB/s, mean 33.57 MiB/s, stddev: 2.54 MiB/s