Restrict scanning port range, not emulator count

Our servers can comfortably run more than 16 emulators, and this is
much easier than messing with hypervisors or docker port allocation.

Assumes you know how to avoid clashes with Google Wear's default port.

Test: manual - still registers emulators.

Change-Id: I47cfd28725a550de0bd77fd11fcd94cdd11d2cc2

2 files changed, 25 insertions, 14 deletions

diff --git a/adb/client/commandline.cpp b/adb/client/commandline.cpp
index f70b48009..3cb10ba77 100644
--- a/adb/client/commandline.cpp
+++ b/adb/client/commandline.cpp
@@ -222,7 +222,9 @@ static void help() {
         "     all,adb,sockets,packets,rwx,usb,sync,sysdeps,transport,jdwp\n"
         " $ADB_VENDOR_KEYS         colon-separated list of keys (files or directories)\n"
         " $ANDROID_SERIAL          serial number to connect to (see -s)\n"
-        " $ANDROID_LOG_TAGS        tags to be used by logcat (see logcat --help)\n");
+        " $ANDROID_LOG_TAGS        tags to be used by logcat (see logcat --help)\n"
+        " $ADB_LOCAL_TRANSPORT_MAX_PORT max emulator scan port (default 5585, 16 emus)\n"
+    );
     // clang-format on
 }
 
diff --git a/adb/transport_local.cpp b/adb/transport_local.cpp
index 9a74fb3c3..b9f738dfc 100644
--- a/adb/transport_local.cpp
+++ b/adb/transport_local.cpp
@@ -53,12 +53,27 @@
 
 // Android Wear has been using port 5601 in all of its documentation/tooling,
 // but we search for emulators on ports [5554, 5555 + ADB_LOCAL_TRANSPORT_MAX].
-// Avoid stomping on their port by limiting the number of emulators that can be
-// connected.
-#define ADB_LOCAL_TRANSPORT_MAX 16
+// Avoid stomping on their port by restricting the active scanning range.
+// Once emulators self-(re-)register, they'll have to avoid 5601 in their own way.
+static int adb_local_transport_max_port = DEFAULT_ADB_LOCAL_TRANSPORT_PORT + 16 * 2 - 1;
 
 static std::mutex& local_transports_lock = *new std::mutex();
 
+static void adb_local_transport_max_port_env_override() {
+    const char* env_max_s = getenv("ADB_LOCAL_TRANSPORT_MAX_PORT");
+    if (env_max_s != nullptr) {
+        size_t env_max;
+        if (ParseUint(&env_max, env_max_s, nullptr) && env_max < 65536) {
+            // < DEFAULT_ADB_LOCAL_TRANSPORT_PORT harmlessly mimics ADB_EMU=0
+            adb_local_transport_max_port = env_max;
+            D("transport: ADB_LOCAL_TRANSPORT_MAX_PORT read as %d", adb_local_transport_max_port);
+        } else {
+            D("transport: ADB_LOCAL_TRANSPORT_MAX_PORT '%s' invalid or >= 65536, so ignored",
+              env_max_s);
+        }
+    }
+}
+
 // We keep a map from emulator port to transport.
 // TODO: weak_ptr?
 static auto& local_transports GUARDED_BY(local_transports_lock) =
@@ -110,7 +125,6 @@ void connect_device(const std::string& address, std::string* response) {
             D("reconnect failed: %s", response.c_str());
             return ReconnectResult::Retry;
         }
-
         // This invokes the part of register_socket_transport() that needs to be
         // invoked if the atransport* has already been setup. This eventually
         // calls atransport->SetConnection() with a newly created Connection*
@@ -168,12 +182,10 @@ int local_connect_arbitrary_ports(int console_port, int adb_port, std::string* e
 #if ADB_HOST
 
 static void PollAllLocalPortsForEmulator() {
-    int port = DEFAULT_ADB_LOCAL_TRANSPORT_PORT;
-    int count = ADB_LOCAL_TRANSPORT_MAX;
-
     // Try to connect to any number of running emulator instances.
-    for ( ; count > 0; count--, port += 2 ) {
-        local_connect(port);
+    for (int port = DEFAULT_ADB_LOCAL_TRANSPORT_PORT; port <= adb_local_transport_max_port;
+         port += 2) {
+        local_connect(port);  // Note, uses port and port-1, so '=max_port' is OK.
     }
 }
 
@@ -289,6 +301,7 @@ void local_init(int port) {
 #if ADB_HOST
     D("transport: local client init");
     std::thread(client_socket_thread, port).detach();
+    adb_local_transport_max_port_env_override();
 #elif !defined(__ANDROID__)
     // Host adbd.
     D("transport: local server init");
@@ -371,10 +384,6 @@ int init_socket_transport(atransport* t, unique_fd fd, int adb_port, int local)
         if (existing_transport != nullptr) {
             D("local transport for port %d already registered (%p)?", adb_port, existing_transport);
             fail = -1;
-        } else if (local_transports.size() >= ADB_LOCAL_TRANSPORT_MAX) {
-            // Too many emulators.
-            D("cannot register more emulators. Maximum is %d", ADB_LOCAL_TRANSPORT_MAX);
-            fail = -1;
         } else {
             local_transports[adb_port] = t;
         }