adb: add `adb host-features`, report libusb status.

Add a 'host-features' command to get the features of the currently
running host adb server. Abuse it to report libusb status.

Bug: http://b/34983123
Test: adb host-features; adb kill-server; ADB_LIBUSB=1 adb start-server; adb host-features
Change-Id: I0e8d503a2dbdff9002ebb6ce8a298498a9421422

adb/adb.cpp

@@ -1129,6 +1129,18 @@ int handle_host_request(const char* service, TransportType type,
         return 0;
     }
 
+#if ADB_HOST
+    if (!strcmp(service, "host-features")) {
+        FeatureSet features = supported_features();
+        // Abuse features to report libusb status.
+        if (should_use_libusb()) {
+            features.insert(kFeatureLibusb);
+        }
+        SendOkay(reply_fd, FeatureSetToString(features));
+        return 0;
+    }
+#endif
+
     // remove TCP transport
     if (!strncmp(service, "disconnect:", 11)) {
         const std::string address(service + 11);

adb/adb.h

@@ -54,7 +54,7 @@ constexpr size_t LINUX_MAX_SOCKET_SIZE = 4194304;
 std::string adb_version();
 
 // Increment this when we want to force users to start a new adb server.
-#define ADB_SERVER_VERSION 38
+#define ADB_SERVER_VERSION 39
 
 class atransport;
 

adb/client/usb_dispatch.cpp

@@ -17,11 +17,6 @@
 #include <android-base/logging.h>
 #include "usb.h"
 
-static bool should_use_libusb() {
-    static bool enable = getenv("ADB_LIBUSB") && strcmp(getenv("ADB_LIBUSB"), "1") == 0;
-    return enable;
-}
-
 void usb_init() {
     if (should_use_libusb()) {
         LOG(DEBUG) << "using libusb backend";

adb/commandline.cpp

@@ -1929,8 +1929,7 @@ int adb_commandline(int argc, const char** argv) {
     else if (!strcmp(argv[0], "--version") || !strcmp(argv[0], "version")) {
         fprintf(stdout, "%s", adb_version().c_str());
         return 0;
-    }
-    else if (!strcmp(argv[0], "features")) {
+    } else if (!strcmp(argv[0], "features")) {
         // Only list the features common to both the adb client and the device.
         FeatureSet features;
         std::string error;
@@ -1945,6 +1944,8 @@ int adb_commandline(int argc, const char** argv) {
             }
         }
         return 0;
+    } else if (!strcmp(argv[0], "host-features")) {
+        return adb_query_command("host:host-features");
     } else if (!strcmp(argv[0], "reconnect")) {
         if (argc == 1) {
             return adb_query_command("host:reconnect");

adb/transport.cpp

@@ -51,6 +51,7 @@ static std::mutex& transport_lock = *new std::mutex();
 const char* const kFeatureShell2 = "shell_v2";
 const char* const kFeatureCmd = "cmd";
 const char* const kFeatureStat2 = "stat_v2";
+const char* const kFeatureLibusb = "libusb";
 
 static std::string dump_packet(const char* name, const char* func, apacket* p) {
     unsigned command = p->msg.command;

adb/transport.h

@@ -47,6 +47,8 @@ extern const char* const kFeatureShell2;
 // The 'cmd' command is available
 extern const char* const kFeatureCmd;
 extern const char* const kFeatureStat2;
+// The server is running with libusb enabled.
+extern const char* const kFeatureLibusb;
 
 class atransport {
 public:

adb/transport_usb.cpp

@@ -97,3 +97,12 @@ int is_adb_interface(int usb_class, int usb_subclass, int usb_protocol)
 {
     return (usb_class == ADB_CLASS && usb_subclass == ADB_SUBCLASS && usb_protocol == ADB_PROTOCOL);
 }
+
+bool should_use_libusb() {
+#if defined(_WIN32) || !ADB_HOST
+    return false;
+#else
+    static bool enable = getenv("ADB_LIBUSB") && strcmp(getenv("ADB_LIBUSB"), "1") == 0;
+    return enable;
+#endif
+}

adb/usb.h

@@ -55,3 +55,5 @@ ADB_USB_INTERFACE(::usb_handle*);
 
 // USB device detection.
 int is_adb_interface(int usb_class, int usb_subclass, int usb_protocol);
+
+bool should_use_libusb();