diff --git a/adb/Android.mk b/adb/Android.mk
index c38cf93..fe3c9cc 100644
--- a/adb/Android.mk
+++ b/adb/Android.mk
@@ -160,6 +160,19 @@
 LOCAL_SHARED_LIBRARIES := libbase libcutils
 include $(BUILD_NATIVE_TEST)
 
+# libdiagnose_usb
+# =========================================================
+
+include $(CLEAR_VARS)
+LOCAL_MODULE := libdiagnose_usb
+LOCAL_MODULE_HOST_OS := darwin linux windows
+LOCAL_CFLAGS := $(LIBADB_CFLAGS)
+LOCAL_SRC_FILES := diagnose_usb.cpp
+# Even though we're building a static library (and thus there's no link step for
+# this to take effect), this adds the includes to our path.
+LOCAL_STATIC_LIBRARIES := libbase
+include $(BUILD_HOST_STATIC_LIBRARY)
+
 # adb_test
 # =========================================================
 
@@ -185,6 +198,7 @@
     libadb \
     libcrypto_static \
     libcutils \
+    libdiagnose_usb \
 
 # Set entrypoint to wmain from sysdeps_win32.cpp instead of main
 LOCAL_LDFLAGS_windows := -municode
@@ -261,6 +275,7 @@
     libadb \
     libbase \
     libcrypto_static \
+    libdiagnose_usb \
     liblog \
 
 # Don't use libcutils on Windows.
diff --git a/adb/adb.h b/adb/adb.h
index 774215e..9020fc3 100644
--- a/adb/adb.h
+++ b/adb/adb.h
@@ -226,11 +226,6 @@
 int is_adb_interface(int vid, int pid, int usb_class, int usb_subclass, int usb_protocol);
 #endif
 
-// USB permission error help text. The short version will be one line, long may be multi-line.
-// Returns a string message to print, or an empty string if no problems could be found.
-std::string UsbNoPermissionsShortHelpText();
-std::string UsbNoPermissionsLongHelpText();
-
 int adb_commandline(int argc, const char **argv);
 
 ConnectionState connection_state(atransport *t);
diff --git a/adb/diagnose_usb.cpp b/adb/diagnose_usb.cpp
new file mode 100644
index 0000000..0f067b0
--- /dev/null
+++ b/adb/diagnose_usb.cpp
@@ -0,0 +1,83 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "diagnose_usb.h"
+
+#include <errno.h>
+#include <unistd.h>
+
+#include <string>
+
+#include <android-base/stringprintf.h>
+
+#if defined(__linux__)
+#include <grp.h>
+#endif
+
+static const char kPermissionsHelpUrl[] = "http://developer.android.com/tools/device.html";
+
+// Returns a message describing any potential problems we find with udev, or nullptr if we can't
+// find plugdev information (i.e. udev is not installed).
+static const char* GetUdevProblem() {
+#if defined(__linux__)
+    errno = 0;
+    group* plugdev_group = getgrnam("plugdev");
+
+    if (plugdev_group == nullptr) {
+        if (errno != 0) {
+            perror("failed to read plugdev group info");
+        }
+        // We can't give any generally useful advice here, just let the caller print the help URL.
+        return nullptr;
+    }
+
+    // getgroups(2) indicates that the group_member() may not check the egid so we check it
+    // additionally just to be sure.
+    if (group_member(plugdev_group->gr_gid) || getegid() == plugdev_group->gr_gid) {
+        // The user is in plugdev so the problem is likely with the udev rules.
+        return "verify udev rules";
+    }
+    return "udev requires plugdev group membership";
+#else
+    return nullptr;
+#endif
+}
+
+// Short help text must be a single line, and will look something like:
+//   no permissions (reason); see <URL>
+std::string UsbNoPermissionsShortHelpText() {
+    std::string help_text = "no permissions";
+
+    const char* problem = GetUdevProblem();
+    if (problem != nullptr) {
+        help_text += android::base::StringPrintf(" (%s)", problem);
+    }
+
+    return android::base::StringPrintf("%s; see [%s]", help_text.c_str(), kPermissionsHelpUrl);
+}
+
+// Long help text can span multiple lines and should provide more detailed information.
+std::string UsbNoPermissionsLongHelpText() {
+    std::string header = "insufficient permissions for device";
+
+    const char* problem = GetUdevProblem();
+    if (problem != nullptr) {
+        header += android::base::StringPrintf(": %s", problem);
+    }
+
+    return android::base::StringPrintf("%s.\nSee [%s] for more information.",
+                                       header.c_str(), kPermissionsHelpUrl);
+}
diff --git a/adb/diagnose_usb.h b/adb/diagnose_usb.h
new file mode 100644
index 0000000..325b2e3
--- /dev/null
+++ b/adb/diagnose_usb.h
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __DIAGNOSE_LINUX_USB_H
+#define __DIAGNOSE_LINUX_USB_H
+
+#include <string>
+
+// USB permission error help text. The short version will be one line, long may be multi-line.
+// Returns a string message to print, or an empty string if no problems could be found.
+std::string UsbNoPermissionsShortHelpText();
+std::string UsbNoPermissionsLongHelpText();
+
+#endif
diff --git a/adb/transport.cpp b/adb/transport.cpp
index d4f60ec..6020ad5 100644
--- a/adb/transport.cpp
+++ b/adb/transport.cpp
@@ -35,6 +35,7 @@
 
 #include "adb.h"
 #include "adb_utils.h"
+#include "diagnose_usb.h"
 
 static void transport_unref(atransport *t);
 
@@ -674,11 +675,9 @@
     adb_mutex_lock(&transport_lock);
     for (const auto& t : transport_list) {
         if (t->connection_state == kCsNoPerm) {
+#if ADB_HOST
             *error_out = UsbNoPermissionsLongHelpText();
-            // If we couldn't figure out a reasonable help message default to something generic.
-            if (error_out->empty()) {
-                *error_out = "insufficient permissions for device";
-            }
+#endif
             continue;
         }
 
@@ -759,10 +758,7 @@
         case kCsDevice: return "device";
         case kCsHost: return "host";
         case kCsRecovery: return "recovery";
-        case kCsNoPerm: {
-            std::string message = UsbNoPermissionsShortHelpText();
-            return message.empty() ? "no permissions" : message;
-        }
+        case kCsNoPerm: return UsbNoPermissionsShortHelpText();
         case kCsSideload: return "sideload";
         case kCsUnauthorized: return "unauthorized";
         default: return "unknown";
diff --git a/adb/usb_linux.cpp b/adb/usb_linux.cpp
index e887a94..ed5d2d6 100644
--- a/adb/usb_linux.cpp
+++ b/adb/usb_linux.cpp
@@ -22,7 +22,6 @@
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
-#include <grp.h>
 #include <linux/usb/ch9.h>
 #include <linux/usbdevice_fs.h>
 #include <linux/version.h>
@@ -596,54 +595,3 @@
         fatal_errno("cannot create device_poll thread");
     }
 }
-
-static const char kPermissionsHelpUrl[] = "developer.android.com/tools/device.html";
-
-// Returns a message describing any potential problems we find with udev, or nullptr if we can't
-// find plugdev information (i.e. udev is not installed).
-static const char* GetUdevProblem() {
-    errno = 0;
-    group* plugdev_group = getgrnam("plugdev");
-
-    if (plugdev_group == nullptr) {
-        if (errno != 0) {
-            D("failed to read plugdev group info: %s", strerror(errno));
-        }
-        // We can't give any generally useful advice here, just let the caller print the help URL.
-        return nullptr;
-    }
-
-    // getgroups(2) indicates that the group_member() may not check the egid so we check it
-    // additionally just to be sure.
-    if (group_member(plugdev_group->gr_gid) || getegid() == plugdev_group->gr_gid) {
-        // The user is in plugdev so the problem is likely with the udev rules.
-        return "verify udev rules";
-    }
-    return "udev requires plugdev group membership";
-}
-
-// Short help text must be a single line, and will look something like:
-//   no permissions (reason); see <URL>
-std::string UsbNoPermissionsShortHelpText() {
-    std::string help_text = "no permissions";
-
-    const char* problem = GetUdevProblem();
-    if (problem != nullptr) {
-        help_text += android::base::StringPrintf(" (%s)", problem);
-    }
-
-    return android::base::StringPrintf("%s; see [%s]", help_text.c_str(), kPermissionsHelpUrl);
-}
-
-// Long help text can span multiple lines and should provide more detailed information.
-std::string UsbNoPermissionsLongHelpText() {
-    std::string header = "USB permission failure";
-
-    const char* problem = GetUdevProblem();
-    if (problem != nullptr) {
-        header += android::base::StringPrintf(": %s", problem);
-    }
-
-    return android::base::StringPrintf("%s.\nSee [%s] for more information.",
-                                       header.c_str(), kPermissionsHelpUrl);
-}
diff --git a/adb/usb_linux_client.cpp b/adb/usb_linux_client.cpp
index c5e7452..ceed8fa 100644
--- a/adb/usb_linux_client.cpp
+++ b/adb/usb_linux_client.cpp
@@ -571,12 +571,3 @@
 {
     h->kick(h);
 }
-
-// kCsNoPerm is a host-side issue, we can just ignore it here.
-std::string UsbNoPermissionsShortHelpText() {
-    return "";
-}
-
-std::string UsbNoPermissionsLongHelpText() {
-    return "";
-}
diff --git a/adb/usb_osx.cpp b/adb/usb_osx.cpp
index f494795..148be1d 100644
--- a/adb/usb_osx.cpp
+++ b/adb/usb_osx.cpp
@@ -552,12 +552,3 @@
         handle->interface = 0;
     }
 }
-
-// kCsNoPerm is Linux-only.
-std::string UsbNoPermissionsShortHelpText() {
-    return "";
-}
-
-std::string UsbNoPermissionsLongHelpText() {
-    return "";
-}
diff --git a/adb/usb_windows.cpp b/adb/usb_windows.cpp
index 9124685..8d3501e 100644
--- a/adb/usb_windows.cpp
+++ b/adb/usb_windows.cpp
@@ -659,12 +659,3 @@
   }
   adb_mutex_unlock(&usb_lock);
 }
-
-// kCsNoPerm is Linux-only.
-std::string UsbNoPermissionsShortHelpText() {
-    return "";
-}
-
-std::string UsbNoPermissionsLongHelpText() {
-    return "";
-}