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review.blissroms.org / platform_packages_modules_adb / f4e82284d3486a342d129ddd73efe9a4f8398392
commitf4e82284d3486a342d129ddd73efe9a4f8398392[log] [tgz]
authorShaju Mathew <shaju@google.com>Wed Aug 30 18:35:46 2023 -0700
committerShaju Mathew <shaju@google.com>Wed Aug 30 18:35:46 2023 -0700
treea6588878028ec1631185d3f82511a4031b846e33
parent888a54dcbf954fdffacc8283a793290abcc589cd [diff]
Hoisting ambiguous transport handling outside the loop.
This is a pre-cursory CL for https://android-review.git.corp.google.com/c/platform/packages/modules/adb/+/2724438

Bug: 290267160

Test: For these tests, we're constrained to using the hotspot
network (that will allow wireless adb debugging).
Alternatively, a non-corp wireless network (with less stringent
security config) would also work out (tested with both these setups).
Due to these limitations, an integrated test (e.g test_device.py)
does not apply because the test environment is too specialized for
the production environment. It is likely feasible to automate the
hotspot connection (using MH for e.g), however it does not seem
realistic at this time.

aosp-master-with-phones$adb kill-server
aosp-master-with-phones$adb tcpip 5555
restarting in TCP mode port: 5555
aosp-master-with-phones$adb connect 192.168.208.183:5555
connected to 192.168.208.183:5555
aosp-master-with-phones$adb devices
List of devices attached
6L4X895PYXTC7DR8	device
192.168.208.183:5555	device
Disconnect the USB (both point to the same device) and connect another Android device.
aosp-master-with-phones$adb devices
List of devices attached
17071FDEE0027Y	device
192.168.208.183:5555	device

Test ambiguity:
aosp-master-with-phones$adb wait-for-disconnect
error: more than one device/emulator
List of devices attached
17071FDEE0027Y	device
192.168.208.183:5555	device

aosp-master-with-phones$adb -s 17071FDEE0027Y wait-for-disconnect
Disconnect USB physically.
aosp-master-with-phones$adb devices
List of devices attached
192.168.208.183:5555	device

Reconnect USB:
aosp-master-with-phones$adb devices
List of devices attached
17071FDEE0027Y	device
192.168.208.183:5555	device

Test disconnect of wireless transport (use a secondary terminal to disconnect):
aosp-master-with-phones$adb devices
List of devices attached
17071FDEE0027Y	device
192.168.208.183:5555	device

aosp-master-with-phones$adb -s 192.168.208.183:5555 wait-for-disconnect

Run `adb disconnect 192.168.208.183:5555` from a secondary terminal.

aosp-master-with-phones$adb devices
List of devices attached
17071FDEE0027Y	device

Change-Id: I3521d993a32962d72f59e8f8ac172f39bc2f02d8
1 file changed
tree: a6588878028ec1631185d3f82511a4031b846e33
  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. tls/
  15. tools/
  16. .clang-format
  17. adb.bash
  18. adb.cpp
  19. adb.h
  20. adb_auth.h
  21. adb_integration_test_adb.xml
  22. adb_integration_test_device.xml
  23. adb_io.cpp
  24. adb_io.h
  25. adb_io_test.cpp
  26. adb_listeners.cpp
  27. adb_listeners.h
  28. adb_listeners_test.cpp
  29. adb_mdns.cpp
  30. adb_mdns.h
  31. adb_trace.cpp
  32. adb_trace.h
  33. adb_unique_fd.cpp
  34. adb_unique_fd.h
  35. adb_utils.cpp
  36. adb_utils.h
  37. adb_utils_test.cpp
  38. adb_wifi.h
  39. adbd_test.xml
  40. Android.bp
  41. benchmark_device.py
  42. bugreport_test.cpp
  43. compression_utils.h
  44. file_sync_protocol.h
  45. mdns_test.cpp
  46. MODULE_LICENSE_APACHE2
  47. NOTICE
  48. OVERVIEW.TXT
  49. OWNERS
  50. PREUPLOAD.cfg
  51. protocol.txt
  52. README.md
  53. security_log_tags.h
  54. services.cpp
  55. services.h
  56. SERVICES.TXT
  57. shell_protocol.h
  58. shell_service_protocol.cpp
  59. shell_service_protocol_test.cpp
  60. SOCKET-ACTIVATION.txt
  61. socket.h
  62. socket_spec.cpp
  63. socket_spec.h
  64. socket_spec_test.cpp
  65. socket_test.cpp
  66. sockets.cpp
  67. sockets.dia
  68. SYNC.TXT
  69. sysdeps.h
  70. sysdeps_test.cpp
  71. sysdeps_unix.cpp
  72. sysdeps_win32.cpp
  73. sysdeps_win32_test.cpp
  74. test_adb.py
  75. test_device.py
  76. TEST_MAPPING
  77. trace.sh
  78. transfer_id.h
  79. transport.cpp
  80. transport.h
  81. transport_benchmark.cpp
  82. transport_fd.cpp
  83. transport_test.cpp
  84. types.cpp
  85. types.h
  86. 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/+/master/docs/debugmon.html
  • platform/dalvik/+/master/docs/debugger.html