Revert "Revert "Support socket activation of adb server""
Test: actually build both device and client adb this time
This reverts commit c77904e3c5b71e005e70ce0b1022501ac47b5677.
Change-Id: I8c2b8f24884ff36ff2460dab2500bad777100dfd
diff --git a/adb/SOCKET-ACTIVATION.txt b/adb/SOCKET-ACTIVATION.txt
new file mode 100644
index 0000000..4ef62ac
--- /dev/null
+++ b/adb/SOCKET-ACTIVATION.txt
@@ -0,0 +1,42 @@
+adb can be configured to work with systemd-style socket activation,
+allowing the daemon to start automatically when the adb control port
+is forwarded across a network. You need two files, placed in the usual
+systemd service directories (e.g., ~/.config/systemd/user for a user
+service).
+
+adb.service:
+
+--- START adb.service CUT HERE ---
+[Unit]
+Description=adb
+After=adb.socket
+Requires=adb.socket
+[Service]
+Type=simple
+# FD 3 is part of the systemd interface
+ExecStart=/path/to/adb server nodaemon -L acceptfd:3
+--- END adb.service CUT HERE ---
+
+--- START adb.socket CUT HERE ---
+[Unit]
+Description=adb
+PartOf=adb.service
+[Socket]
+ListenStream=127.0.0.1:5037
+Accept=no
+[Install]
+WantedBy=sockets.target
+--- END adb.socket CUT HERE ---
+
+After installing the adb service, the adb server will be started
+automatically on any connection to 127.0.0.1:5037 (the default adb
+control port), even after adb kill-server kills the server.
+
+Other "superserver" launcher systems (like macOS launchd) can be
+configured analogously. The important part is that adb be started with
+"server" and "nodaemon" command line arguments and that the listen
+address (passed to -L) name a file descriptor that's ready to
+accept(2) connections and that's already bound to the desired address
+and listening. inetd-style pre-accepted sockets do _not_ work in this
+configuration: the file descriptor passed to acceptfd must be the
+serve socket, not the accepted connection socket.