diff --git a/adb/Android.mk b/adb/Android.mk
index 4ffb589..f3a4822 100644
--- a/adb/Android.mk
+++ b/adb/Android.mk
@@ -96,9 +96,6 @@
 
 ifeq ($(HOST_OS),windows)
     LOCAL_C_INCLUDES += development/host/windows/usb/api/
-    # Windows.h defines an awful ERROR macro that collides with base/logging.h.
-    # Suppress it with NOGDI.
-    LOCAL_CFLAGS += -DNOGDI
 endif
 
 include $(BUILD_HOST_STATIC_LIBRARY)
@@ -165,9 +162,6 @@
 endif
 
 ifeq ($(HOST_OS),windows)
-    # Windows.h defines an awful ERROR macro that collides with base/logging.h.
-    # Suppress it with NOGDI.
-    LOCAL_CFLAGS += -DNOGDI
     LOCAL_LDLIBS += -lws2_32 -lgdi32
     EXTRA_STATIC_LIBS := AdbWinApi
 endif
diff --git a/adb/CPPLINT.cfg b/adb/CPPLINT.cfg
index 9b906e8..f496490 100644
--- a/adb/CPPLINT.cfg
+++ b/adb/CPPLINT.cfg
@@ -1,2 +1,2 @@
 set noparent
-filter=-build/header_guard,-build/include,-readability/function
+filter=-build/header_guard,-build/include,-readability/function,-whitespace/indent
diff --git a/adb/adb.cpp b/adb/adb.cpp
index c4e3434..3d1b7b4 100644
--- a/adb/adb.cpp
+++ b/adb/adb.cpp
@@ -369,24 +369,24 @@
 
     const std::string& type = pieces[0];
     if (type == "bootloader") {
-        D("setting connection_state to CS_BOOTLOADER\n");
-        t->connection_state = CS_BOOTLOADER;
+        D("setting connection_state to kCsBootloader\n");
+        t->connection_state = kCsBootloader;
         update_transports();
     } else if (type == "device") {
-        D("setting connection_state to CS_DEVICE\n");
-        t->connection_state = CS_DEVICE;
+        D("setting connection_state to kCsDevice\n");
+        t->connection_state = kCsDevice;
         update_transports();
     } else if (type == "recovery") {
-        D("setting connection_state to CS_RECOVERY\n");
-        t->connection_state = CS_RECOVERY;
+        D("setting connection_state to kCsRecovery\n");
+        t->connection_state = kCsRecovery;
         update_transports();
     } else if (type == "sideload") {
-        D("setting connection_state to CS_SIDELOAD\n");
-        t->connection_state = CS_SIDELOAD;
+        D("setting connection_state to kCsSideload\n");
+        t->connection_state = kCsSideload;
         update_transports();
     } else {
-        D("setting connection_state to CS_HOST\n");
-        t->connection_state = CS_HOST;
+        D("setting connection_state to kCsHost\n");
+        t->connection_state = kCsHost;
     }
 }
 
@@ -406,7 +406,7 @@
             send_packet(p, t);
             if(HOST) send_connect(t);
         } else {
-            t->connection_state = CS_OFFLINE;
+            t->connection_state = kCsOffline;
             handle_offline(t);
             send_packet(p, t);
         }
@@ -414,8 +414,8 @@
 
     case A_CNXN: /* CONNECT(version, maxdata, "system-id-string") */
             /* XXX verify version, etc */
-        if(t->connection_state != CS_OFFLINE) {
-            t->connection_state = CS_OFFLINE;
+        if(t->connection_state != kCsOffline) {
+            t->connection_state = kCsOffline;
             handle_offline(t);
         }
 
@@ -431,7 +431,7 @@
 
     case A_AUTH:
         if (p->msg.arg0 == ADB_AUTH_TOKEN) {
-            t->connection_state = CS_UNAUTHORIZED;
+            t->connection_state = kCsUnauthorized;
             t->key = adb_auth_nextkey(t->key);
             if (t->key) {
                 send_auth_response(p->data, p->msg.data_length, t);
@@ -757,7 +757,7 @@
         }
 
         std::string error_msg;
-        transport = acquire_one_transport(CS_ANY, type, serial, &error_msg);
+        transport = acquire_one_transport(kCsAny, type, serial, &error_msg);
         if (!transport) {
             SendFail(reply_fd, error_msg);
             return 1;
@@ -826,7 +826,7 @@
         }
 
         std::string error_msg = "unknown failure";
-        transport = acquire_one_transport(CS_ANY, type, serial, &error_msg);
+        transport = acquire_one_transport(kCsAny, type, serial, &error_msg);
 
         if (transport) {
             s->transport = transport;
@@ -889,7 +889,7 @@
 
     if(!strncmp(service,"get-serialno",strlen("get-serialno"))) {
         const char *out = "unknown";
-        transport = acquire_one_transport(CS_ANY, type, serial, NULL);
+        transport = acquire_one_transport(kCsAny, type, serial, NULL);
         if (transport && transport->serial) {
             out = transport->serial;
         }
@@ -899,7 +899,7 @@
     }
     if(!strncmp(service,"get-devpath",strlen("get-devpath"))) {
         const char *out = "unknown";
-        transport = acquire_one_transport(CS_ANY, type, serial, NULL);
+        transport = acquire_one_transport(kCsAny, type, serial, NULL);
         if (transport && transport->devpath) {
             out = transport->devpath;
         }
@@ -916,7 +916,7 @@
     }
 
     if(!strncmp(service,"get-state",strlen("get-state"))) {
-        transport = acquire_one_transport(CS_ANY, type, serial, NULL);
+        transport = acquire_one_transport(kCsAny, type, serial, NULL);
         SendOkay(reply_fd);
         SendProtocolString(reply_fd, transport->connection_state_name());
         return 0;
diff --git a/adb/adb.h b/adb/adb.h
index 7942a86..e8960e3 100644
--- a/adb/adb.h
+++ b/adb/adb.h
@@ -170,6 +170,18 @@
 
 #define TOKEN_SIZE 20
 
+enum ConnectionState {
+    kCsAny = -1,
+    kCsOffline = 0,
+    kCsBootloader,
+    kCsDevice,
+    kCsHost,
+    kCsRecovery,
+    kCsNoPerm,  // Insufficient permissions to communicate with the device.
+    kCsSideload,
+    kCsUnauthorized,
+};
+
 struct atransport
 {
     atransport *next;
@@ -266,7 +278,7 @@
 int get_available_local_transport_index();
 #endif
 int  init_socket_transport(atransport *t, int s, int port, int local);
-void init_usb_transport(atransport *t, usb_handle *usb, int state);
+void init_usb_transport(atransport *t, usb_handle *usb, ConnectionState state);
 
 #if ADB_HOST
 atransport* find_emulator_transport_by_adb_port(int adb_port);
@@ -336,17 +348,7 @@
 
 int adb_commandline(int argc, const char **argv);
 
-int connection_state(atransport *t);
-
-#define CS_ANY       -1
-#define CS_OFFLINE    0
-#define CS_BOOTLOADER 1
-#define CS_DEVICE     2
-#define CS_HOST       3
-#define CS_RECOVERY   4
-#define CS_NOPERM     5 /* Insufficient permissions to communicate with the device */
-#define CS_SIDELOAD   6
-#define CS_UNAUTHORIZED 7
+ConnectionState connection_state(atransport *t);
 
 extern const char *adb_device_banner;
 extern int HOST;
diff --git a/adb/adb_auth_host.cpp b/adb/adb_auth_host.cpp
index 5581516..61a3777 100644
--- a/adb/adb_auth_host.cpp
+++ b/adb/adb_auth_host.cpp
@@ -16,11 +16,6 @@
 
 #define TRACE_TAG TRACE_AUTH
 
-#ifdef _WIN32
-// This blocks some definitions we need on Windows.
-#undef NOGDI
-#endif
-
 #include "sysdeps.h"
 #include "adb_auth.h"
 
diff --git a/adb/services.cpp b/adb/services.cpp
index 8ce9f71..a9edbe5 100644
--- a/adb/services.cpp
+++ b/adb/services.cpp
@@ -516,7 +516,7 @@
 struct state_info {
     TransportType transport_type;
     char* serial;
-    int state;
+    ConnectionState state;
 };
 
 static void wait_for_state(int fd, void* cookie)
@@ -665,13 +665,13 @@
 
         if (!strncmp(name, "local", strlen("local"))) {
             sinfo->transport_type = kTransportLocal;
-            sinfo->state = CS_DEVICE;
+            sinfo->state = kCsDevice;
         } else if (!strncmp(name, "usb", strlen("usb"))) {
             sinfo->transport_type = kTransportUsb;
-            sinfo->state = CS_DEVICE;
+            sinfo->state = kCsDevice;
         } else if (!strncmp(name, "any", strlen("any"))) {
             sinfo->transport_type = kTransportAny;
-            sinfo->state = CS_DEVICE;
+            sinfo->state = kCsDevice;
         } else {
             if (sinfo->serial) {
                 free(sinfo->serial);
diff --git a/adb/sockets.cpp b/adb/sockets.cpp
index 62cba6d..621944e 100644
--- a/adb/sockets.cpp
+++ b/adb/sockets.cpp
@@ -815,7 +815,8 @@
 #else /* !ADB_HOST */
     if (s->transport == NULL) {
         std::string error_msg = "unknown failure";
-        s->transport = acquire_one_transport(CS_ANY, kTransportAny, NULL, &error_msg);
+        s->transport =
+            acquire_one_transport(kCsAny, kTransportAny, NULL, &error_msg);
 
         if (s->transport == NULL) {
             SendFail(s->peer->fd, error_msg);
@@ -824,7 +825,7 @@
     }
 #endif
 
-    if(!(s->transport) || (s->transport->connection_state == CS_OFFLINE)) {
+    if(!(s->transport) || (s->transport->connection_state == kCsOffline)) {
            /* if there's no remote we fail the connection
             ** right here and terminate it
             */
diff --git a/adb/sysdeps_win32.cpp b/adb/sysdeps_win32.cpp
index b7962b9..a21272f 100644
--- a/adb/sysdeps_win32.cpp
+++ b/adb/sysdeps_win32.cpp
@@ -16,9 +16,6 @@
 
 #define TRACE_TAG TRACE_SYSDEPS
 
-// For whatever reason this blocks the definition of ToAscii...
-#undef NOGDI
-
 #include "sysdeps.h"
 
 #include <winsock2.h> /* winsock.h *must* be included before windows.h. */
diff --git a/adb/transport.cpp b/adb/transport.cpp
index 29cf580..818ed97 100644
--- a/adb/transport.cpp
+++ b/adb/transport.cpp
@@ -578,7 +578,7 @@
     }
 
     /* don't create transport threads for inaccessible devices */
-    if (t->connection_state != CS_NOPERM) {
+    if (t->connection_state != kCsNoPerm) {
         /* initial references are the two threads */
         t->ref_count = 2;
 
@@ -738,9 +738,8 @@
     return !*to_test;
 }
 
-atransport* acquire_one_transport(int state, TransportType type,
-                                  const char* serial, std::string* error_out)
-{
+atransport* acquire_one_transport(ConnectionState state, TransportType type,
+                                  const char* serial, std::string* error_out) {
     atransport *t;
     atransport *result = NULL;
     int ambiguous = 0;
@@ -750,7 +749,7 @@
 
     adb_mutex_lock(&transport_lock);
     for (t = transport_list.next; t != &transport_list; t = t->next) {
-        if (t->connection_state == CS_NOPERM) {
+        if (t->connection_state == kCsNoPerm) {
             if (error_out) *error_out = "insufficient permissions for device";
             continue;
         }
@@ -801,7 +800,7 @@
     adb_mutex_unlock(&transport_lock);
 
     if (result) {
-        if (result->connection_state == CS_UNAUTHORIZED) {
+        if (result->connection_state == kCsUnauthorized) {
             if (error_out) {
                 *error_out = "device unauthorized.\n";
                 char* ADB_VENDOR_KEYS = getenv("ADB_VENDOR_KEYS");
@@ -814,13 +813,13 @@
         }
 
         /* offline devices are ignored -- they are either being born or dying */
-        if (result && result->connection_state == CS_OFFLINE) {
+        if (result && result->connection_state == kCsOffline) {
             if (error_out) *error_out = "device offline";
             result = NULL;
         }
 
         /* check for required connection state */
-        if (result && state != CS_ANY && result->connection_state != state) {
+        if (result && state != kCsAny && result->connection_state != state) {
             if (error_out) *error_out = "invalid device state";
             result = NULL;
         }
@@ -829,7 +828,7 @@
     if (result) {
         /* found one that we can take */
         if (error_out) *error_out = "success";
-    } else if (state != CS_ANY && (serial || !ambiguous)) {
+    } else if (state != kCsAny && (serial || !ambiguous)) {
         adb_sleep_ms(1000);
         goto retry;
     }
@@ -839,14 +838,14 @@
 
 const char* atransport::connection_state_name() const {
     switch (connection_state) {
-    case CS_OFFLINE: return "offline";
-    case CS_BOOTLOADER: return "bootloader";
-    case CS_DEVICE: return "device";
-    case CS_HOST: return "host";
-    case CS_RECOVERY: return "recovery";
-    case CS_NOPERM: return "no permissions";
-    case CS_SIDELOAD: return "sideload";
-    case CS_UNAUTHORIZED: return "unauthorized";
+    case kCsOffline: return "offline";
+    case kCsBootloader: return "bootloader";
+    case kCsDevice: return "device";
+    case kCsHost: return "host";
+    case kCsRecovery: return "recovery";
+    case kCsNoPerm: return "no permissions";
+    case kCsSideload: return "sideload";
+    case kCsUnauthorized: return "unauthorized";
     default: return "unknown";
     }
 }
@@ -1021,7 +1020,7 @@
     if (t == nullptr) fatal("cannot allocate USB atransport");
     D("transport: %p init'ing for usb_handle %p (sn='%s')\n", t, usb,
       serial ? serial : "");
-    init_usb_transport(t, usb, (writeable ? CS_OFFLINE : CS_NOPERM));
+    init_usb_transport(t, usb, (writeable ? kCsOffline : kCsNoPerm));
     if(serial) {
         t->serial = strdup(serial);
     }
@@ -1039,18 +1038,17 @@
     register_transport(t);
 }
 
-/* this should only be used for transports with connection_state == CS_NOPERM */
-void unregister_usb_transport(usb_handle *usb)
-{
-    atransport *t;
+// This should only be used for transports with connection_state == kCsNoPerm.
+void unregister_usb_transport(usb_handle* usb) {
     adb_mutex_lock(&transport_lock);
-    for(t = transport_list.next; t != &transport_list; t = t->next) {
-        if (t->usb == usb && t->connection_state == CS_NOPERM) {
+    for (atransport* t = transport_list.next; t != &transport_list;
+         t = t->next) {
+        if (t->usb == usb && t->connection_state == kCsNoPerm) {
             t->next->prev = t->prev;
             t->prev->next = t->next;
             break;
         }
-     }
+    }
     adb_mutex_unlock(&transport_lock);
 }
 
diff --git a/adb/transport.h b/adb/transport.h
index 7b799b9..538f63e 100644
--- a/adb/transport.h
+++ b/adb/transport.h
@@ -25,11 +25,11 @@
 
 /*
  * Obtain a transport from the available transports.
- * If state is != CS_ANY, only transports in that state are considered.
+ * If state is != kCsAny, only transports in that state are considered.
  * If serial is non-NULL then only the device with that serial will be chosen.
  * If no suitable transport is found, error is set.
  */
-atransport* acquire_one_transport(int state, TransportType type,
+atransport* acquire_one_transport(ConnectionState state, TransportType type,
                                   const char* serial, std::string* error_out);
 void add_transport_disconnect(atransport* t, adisconnect* dis);
 void remove_transport_disconnect(atransport* t, adisconnect* dis);
@@ -50,7 +50,7 @@
 /* cause new transports to be init'd and added to the list */
 int register_socket_transport(int s, const char* serial, int port, int local);
 
-/* this should only be used for transports with connection_state == CS_NOPERM */
+// This should only be used for transports with connection_state == kCsNoPerm.
 void unregister_usb_transport(usb_handle* usb);
 
 /* these should only be used for the "adb disconnect" command */
diff --git a/adb/transport_local.cpp b/adb/transport_local.cpp
index 5f7449d..d3c4c30 100644
--- a/adb/transport_local.cpp
+++ b/adb/transport_local.cpp
@@ -387,7 +387,7 @@
     t->write_to_remote = remote_write;
     t->sfd = s;
     t->sync_token = 1;
-    t->connection_state = CS_OFFLINE;
+    t->connection_state = kCsOffline;
     t->type = kTransportLocal;
     t->adb_port = 0;
 
diff --git a/adb/transport_usb.cpp b/adb/transport_usb.cpp
index cdabffe..eb3454d 100644
--- a/adb/transport_usb.cpp
+++ b/adb/transport_usb.cpp
@@ -80,7 +80,7 @@
     usb_kick(t->usb);
 }
 
-void init_usb_transport(atransport *t, usb_handle *h, int state)
+void init_usb_transport(atransport *t, usb_handle *h, ConnectionState state)
 {
     D("transport: usb\n");
     t->close = remote_close;
diff --git a/base/file.cpp b/base/file.cpp
index 6b19818..9a340b7 100644
--- a/base/file.cpp
+++ b/base/file.cpp
@@ -51,7 +51,7 @@
     return false;
   }
   bool result = ReadFdToString(fd, content);
-  TEMP_FAILURE_RETRY(close(fd));
+  close(fd);
   return result;
 }
 
@@ -102,7 +102,7 @@
     ALOGE("android::WriteStringToFile write failed: %s", strerror(errno));
     return CleanUpAfterFailedWrite(path);
   }
-  TEMP_FAILURE_RETRY(close(fd));
+  close(fd);
   return true;
 }
 #endif
@@ -116,7 +116,7 @@
   }
 
   bool result = WriteStringToFd(content, fd);
-  TEMP_FAILURE_RETRY(close(fd));
+  close(fd);
   return result || CleanUpAfterFailedWrite(path);
 }
 
diff --git a/base/include/base/logging.h b/base/include/base/logging.h
index 4a15f43..283a7bc 100644
--- a/base/include/base/logging.h
+++ b/base/include/base/logging.h
@@ -13,18 +13,15 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 #ifndef BASE_LOGGING_H
 #define BASE_LOGGING_H
 
-#ifdef ERROR
-#error ERROR is already defined. If this is Windows code, #define NOGDI before \
-including anything.
-#endif
-
+// NOTE: For Windows, you must include logging.h after windows.h to allow the
+// following code to suppress the evil ERROR macro:
 #ifdef _WIN32
-#ifndef NOGDI
-#define NOGDI // Suppress the evil ERROR macro.
+// windows.h includes wingdi.h which defines an evil macro ERROR.
+#ifdef ERROR
+#undef ERROR
 #endif
 #endif
 
diff --git a/base/logging.cpp b/base/logging.cpp
index 7a08c39..34229a2 100644
--- a/base/logging.cpp
+++ b/base/logging.cpp
@@ -14,6 +14,10 @@
  * limitations under the License.
  */
 
+#ifdef _WIN32
+#include <windows.h>
+#endif
+
 #include "base/logging.h"
 
 #include <libgen.h>
@@ -34,8 +38,6 @@
 
 #ifndef _WIN32
 #include <mutex>
-#else
-#include <windows.h>
 #endif
 
 #include "base/macros.h"
diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index e139bcd..7acfd6e 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -280,6 +280,17 @@
             "  flashall                                 flash boot, system, vendor and if found,\n"
             "                                           recovery\n"
             "  flash <partition> [ <filename> ]         write a file to a flash partition\n"
+            "  flashing lock                            locks the device. Prevents flashing"
+            "                                           partitions\n"
+            "  flashing unlock                          unlocks the device. Allows user to"
+            "                                           flash any partition except the ones"
+            "                                           that are related to bootloader\n"
+            "  flashing lock_critical                   Prevents flashing bootloader related"
+            "                                           partitions\n"
+            "  flashing unlock_critical                 Enables flashing bootloader related"
+            "                                           partitions\n"
+            "  flashing get_unlock_ability              Queries bootloader to see if the"
+            "                                           device is unlocked\n"
             "  erase <partition>                        erase a flash partition\n"
             "  format[:[<fs type>][:[<size>]] <partition> format a flash partition.\n"
             "                                           Can override the fs type and/or\n"
@@ -1201,6 +1212,16 @@
             wants_reboot = 1;
         } else if(!strcmp(*argv, "oem")) {
             argc = do_oem_command(argc, argv);
+        } else if(!strcmp(*argv, "flashing") && argc == 2) {
+            if(!strcmp(*(argv+1), "unlock") || !strcmp(*(argv+1), "lock")
+               || !strcmp(*(argv+1), "unlock_critical")
+               || !strcmp(*(argv+1), "lock_critical")
+               || !strcmp(*(argv+1), "get_unlock_ability")) {
+              argc = do_oem_command(argc, argv);
+            } else {
+              usage();
+              return 1;
+            }
         } else {
             usage();
             return 1;
diff --git a/include/nativebridge/native_bridge.h b/include/nativebridge/native_bridge.h
index 523dc49..18300bc 100644
--- a/include/nativebridge/native_bridge.h
+++ b/include/nativebridge/native_bridge.h
@@ -18,6 +18,7 @@
 #define NATIVE_BRIDGE_H_
 
 #include "jni.h"
+#include <signal.h>
 #include <stdint.h>
 #include <sys/types.h>
 
@@ -26,6 +27,12 @@
 struct NativeBridgeRuntimeCallbacks;
 struct NativeBridgeRuntimeValues;
 
+// Function pointer type for sigaction. This is mostly the signature of a signal handler, except
+// for the return type. The runtime needs to know whether the signal was handled or should be given
+// to the chain.
+typedef bool (*NativeBridgeSignalHandlerFn)(int, siginfo_t*, void*);
+
+
 // Open the native bridge, if any. Should be called by Runtime::Init(). A null library filename
 // signals that we do not want to load a native bridge.
 bool LoadNativeBridge(const char* native_bridge_library_filename,
@@ -63,6 +70,16 @@
 // True if native library is valid and is for an ABI that is supported by native bridge.
 bool NativeBridgeIsSupported(const char* libpath);
 
+// Returns the version number of the native bridge. This information is available after a
+// successful LoadNativeBridge() and before closing it, that is, as long as NativeBridgeAvailable()
+// returns true. Returns 0 otherwise.
+uint32_t NativeBridgeGetVersion();
+
+// Returns a signal handler that the bridge would like to be managed. Only valid for a native
+// bridge supporting the version 2 interface. Will return null if the bridge does not support
+// version 2, or if it doesn't have a signal handler it wants to be known.
+NativeBridgeSignalHandlerFn NativeBridgeGetSignalHandler(int signal);
+
 // Returns whether we have seen a native bridge error. This could happen because the library
 // was not found, rejected, could not be initialized and so on.
 //
@@ -127,6 +144,31 @@
   //    NULL if not supported by native bridge.
   //    Otherwise, return all environment values to be set after fork.
   const struct NativeBridgeRuntimeValues* (*getAppEnv)(const char* instruction_set);
+
+  // Added callbacks in version 2.
+
+  // Check whether the bridge is compatible with the given version. A bridge may decide not to be
+  // forwards- or backwards-compatible, and libnativebridge will then stop using it.
+  //
+  // Parameters:
+  //     bridge_version [IN] the version of libnativebridge.
+  // Returns:
+  //     true iff the native bridge supports the given version of libnativebridge.
+  bool (*isCompatibleWith)(uint32_t bridge_version);
+
+  // A callback to retrieve a native bridge's signal handler for the specified signal. The runtime
+  // will ensure that the signal handler is being called after the runtime's own handler, but before
+  // all chained handlers. The native bridge should not try to install the handler by itself, as
+  // that will potentially lead to cycles.
+  //
+  // Parameters:
+  //     signal [IN] the signal for which the handler is asked for. Currently, only SIGSEGV is
+  //                 supported by the runtime.
+  // Returns:
+  //     NULL if the native bridge doesn't use a handler or doesn't want it to be managed by the
+  //     runtime.
+  //     Otherwise, a pointer to the signal handler.
+  NativeBridgeSignalHandlerFn (*getSignalHandler)(int signal);
 };
 
 // Runtime interfaces to native bridge.
diff --git a/libcutils/klog.c b/libcutils/klog.c
index f574f08..710dc66 100644
--- a/libcutils/klog.c
+++ b/libcutils/klog.c
@@ -40,6 +40,11 @@
 void klog_init(void) {
     if (klog_fd >= 0) return; /* Already initialized */
 
+    klog_fd = open("/dev/kmsg", O_WRONLY | O_CLOEXEC);
+    if (klog_fd >= 0) {
+        return;
+    }
+
     static const char* name = "/dev/__kmsg__";
     if (mknod(name, S_IFCHR | 0600, (1 << 8) | 11) == 0) {
         klog_fd = open(name, O_WRONLY | O_CLOEXEC);
diff --git a/libnativebridge/native_bridge.cc b/libnativebridge/native_bridge.cc
index 6fa4b39..f63497b 100644
--- a/libnativebridge/native_bridge.cc
+++ b/libnativebridge/native_bridge.cc
@@ -83,7 +83,7 @@
 static void* native_bridge_handle = nullptr;
 // Pointer to the callbacks. Available as soon as LoadNativeBridge succeeds, but only initialized
 // later.
-static NativeBridgeCallbacks* callbacks = nullptr;
+static const NativeBridgeCallbacks* callbacks = nullptr;
 // Callbacks provided by the environment to the bridge. Passed to LoadNativeBridge.
 static const NativeBridgeRuntimeCallbacks* runtime_callbacks = nullptr;
 
@@ -96,7 +96,7 @@
 // and hard code the directory name again here.
 static constexpr const char* kCodeCacheDir = "code_cache";
 
-static constexpr uint32_t kNativeBridgeCallbackVersion = 1;
+static constexpr uint32_t kLibNativeBridgeVersion = 2;
 
 // Characters allowed in a native bridge filename. The first character must
 // be in [a-zA-Z] (expected 'l' for "libx"). The rest must be in [a-zA-Z0-9._-].
@@ -121,7 +121,9 @@
     // First character must be [a-zA-Z].
     if (!CharacterAllowed(*ptr, true))  {
       // Found an invalid fist character, don't accept.
-      ALOGE("Native bridge library %s has been rejected for first character %c", nb_library_filename, *ptr);
+      ALOGE("Native bridge library %s has been rejected for first character %c",
+            nb_library_filename,
+            *ptr);
       return false;
     } else {
       // For the rest, be more liberal.
@@ -139,8 +141,22 @@
   }
 }
 
-static bool VersionCheck(NativeBridgeCallbacks* cb) {
-  return cb != nullptr && cb->version == kNativeBridgeCallbackVersion;
+static bool VersionCheck(const NativeBridgeCallbacks* cb) {
+  // Libnativebridge is now designed to be forward-compatible. So only "0" is an unsupported
+  // version.
+  if (cb == nullptr || cb->version == 0) {
+    return false;
+  }
+
+  // If this is a v2+ bridge, it may not be forwards- or backwards-compatible. Check.
+  if (cb->version >= 2) {
+    if (!callbacks->isCompatibleWith(kLibNativeBridgeVersion)) {
+      // TODO: Scan which version is supported, and fall back to handle it.
+      return false;
+    }
+  }
+
+  return true;
 }
 
 static void CloseNativeBridge(bool with_error) {
@@ -321,7 +337,7 @@
 }
 
 // Set up the environment for the bridged app.
-static void SetupEnvironment(NativeBridgeCallbacks* callbacks, JNIEnv* env, const char* isa) {
+static void SetupEnvironment(const NativeBridgeCallbacks* callbacks, JNIEnv* env, const char* isa) {
   // Need a JNIEnv* to do anything.
   if (env == nullptr) {
     ALOGW("No JNIEnv* to set up app environment.");
@@ -485,4 +501,18 @@
   return false;
 }
 
+uint32_t NativeBridgeGetVersion() {
+  if (NativeBridgeAvailable()) {
+    return callbacks->version;
+  }
+  return 0;
+}
+
+NativeBridgeSignalHandlerFn NativeBridgeGetSignalHandler(int signal) {
+  if (NativeBridgeInitialized() && callbacks->version >= 2) {
+    return callbacks->getSignalHandler(signal);
+  }
+  return nullptr;
+}
+
 };  // namespace android
diff --git a/libnativebridge/tests/Android.mk b/libnativebridge/tests/Android.mk
index f28c490..285e8c2 100644
--- a/libnativebridge/tests/Android.mk
+++ b/libnativebridge/tests/Android.mk
@@ -11,6 +11,8 @@
     CodeCacheExists_test.cpp \
     CompleteFlow_test.cpp \
     InvalidCharsNativeBridge_test.cpp \
+    NativeBridge2Signal_test.cpp \
+    NativeBridgeVersion_test.cpp \
     NeedsNativeBridge_test.cpp \
     PreInitializeNativeBridge_test.cpp \
     PreInitializeNativeBridgeFail1_test.cpp \
diff --git a/libnativebridge/tests/Android.nativebridge-dummy.mk b/libnativebridge/tests/Android.nativebridge-dummy.mk
index 1caf50a..2efc176 100644
--- a/libnativebridge/tests/Android.nativebridge-dummy.mk
+++ b/libnativebridge/tests/Android.nativebridge-dummy.mk
@@ -32,3 +32,39 @@
 LOCAL_MULTILIB := both
 
 include $(BUILD_HOST_SHARED_LIBRARY)
+
+
+# v2.
+
+NATIVE_BRIDGE2_COMMON_SRC_FILES := \
+  DummyNativeBridge2.cpp
+
+# Shared library for target
+# ========================================================
+include $(CLEAR_VARS)
+
+LOCAL_MODULE:= libnativebridge2-dummy
+
+LOCAL_SRC_FILES:= $(NATIVE_BRIDGE2_COMMON_SRC_FILES)
+LOCAL_CLANG := true
+LOCAL_CFLAGS += -Werror -Wall
+LOCAL_CPPFLAGS := -std=gnu++11 -fvisibility=protected
+LOCAL_LDFLAGS := -ldl
+LOCAL_MULTILIB := both
+
+include $(BUILD_SHARED_LIBRARY)
+
+# Shared library for host
+# ========================================================
+include $(CLEAR_VARS)
+
+LOCAL_MODULE:= libnativebridge2-dummy
+
+LOCAL_SRC_FILES:= $(NATIVE_BRIDGE2_COMMON_SRC_FILES)
+LOCAL_CLANG := true
+LOCAL_CFLAGS += -Werror -Wall
+LOCAL_CPPFLAGS := -std=gnu++11 -fvisibility=protected
+LOCAL_LDFLAGS := -ldl
+LOCAL_MULTILIB := both
+
+include $(BUILD_HOST_SHARED_LIBRARY)
diff --git a/libnativebridge/tests/DummyNativeBridge2.cpp b/libnativebridge/tests/DummyNativeBridge2.cpp
new file mode 100644
index 0000000..6920c74
--- /dev/null
+++ b/libnativebridge/tests/DummyNativeBridge2.cpp
@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2014 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.
+ */
+
+// A dummy implementation of the native-bridge interface.
+
+#include "nativebridge/native_bridge.h"
+
+#include <signal.h>
+
+// NativeBridgeCallbacks implementations
+extern "C" bool native_bridge2_initialize(const android::NativeBridgeRuntimeCallbacks* /* art_cbs */,
+                                         const char* /* app_code_cache_dir */,
+                                         const char* /* isa */) {
+  return true;
+}
+
+extern "C" void* native_bridge2_loadLibrary(const char* /* libpath */, int /* flag */) {
+  return nullptr;
+}
+
+extern "C" void* native_bridge2_getTrampoline(void* /* handle */, const char* /* name */,
+                                             const char* /* shorty */, uint32_t /* len */) {
+  return nullptr;
+}
+
+extern "C" bool native_bridge2_isSupported(const char* /* libpath */) {
+  return false;
+}
+
+extern "C" const struct android::NativeBridgeRuntimeValues* native_bridge2_getAppEnv(
+    const char* /* abi */) {
+  return nullptr;
+}
+
+extern "C" bool native_bridge2_is_compatible_compatible_with(uint32_t version) {
+  // For testing, allow 1 and 2, but disallow 3+.
+  return version <= 2;
+}
+
+static bool native_bridge2_dummy_signal_handler(int, siginfo_t*, void*) {
+  // TODO: Implement something here. We'd either have to have a death test with a log here, or
+  //       we'd have to be able to resume after the faulting instruction...
+  return true;
+}
+
+extern "C" android::NativeBridgeSignalHandlerFn native_bridge2_get_signal_handler(int signal) {
+  if (signal == SIGSEGV) {
+    return &native_bridge2_dummy_signal_handler;
+  }
+  return nullptr;
+}
+
+android::NativeBridgeCallbacks NativeBridgeItf {
+  .version = 2,
+  .initialize = &native_bridge2_initialize,
+  .loadLibrary = &native_bridge2_loadLibrary,
+  .getTrampoline = &native_bridge2_getTrampoline,
+  .isSupported = &native_bridge2_isSupported,
+  .getAppEnv = &native_bridge2_getAppEnv,
+  .isCompatibleWith = &native_bridge2_is_compatible_compatible_with,
+  .getSignalHandler = &native_bridge2_get_signal_handler
+};
+
diff --git a/libnativebridge/tests/NativeBridge2Signal_test.cpp b/libnativebridge/tests/NativeBridge2Signal_test.cpp
new file mode 100644
index 0000000..44e45e3
--- /dev/null
+++ b/libnativebridge/tests/NativeBridge2Signal_test.cpp
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2014 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 "NativeBridgeTest.h"
+
+#include <signal.h>
+#include <unistd.h>
+
+namespace android {
+
+constexpr const char* kNativeBridgeLibrary2 = "libnativebridge2-dummy.so";
+
+TEST_F(NativeBridgeTest, V2_Signal) {
+    // Init
+    ASSERT_TRUE(LoadNativeBridge(kNativeBridgeLibrary2, nullptr));
+    ASSERT_TRUE(NativeBridgeAvailable());
+    ASSERT_TRUE(PreInitializeNativeBridge(".", "isa"));
+    ASSERT_TRUE(NativeBridgeAvailable());
+    ASSERT_TRUE(InitializeNativeBridge(nullptr, nullptr));
+    ASSERT_TRUE(NativeBridgeAvailable());
+
+    ASSERT_EQ(2U, NativeBridgeGetVersion());
+    ASSERT_NE(nullptr, NativeBridgeGetSignalHandler(SIGSEGV));
+
+    // Clean-up code_cache
+    ASSERT_EQ(0, rmdir(kCodeCache));
+}
+
+}  // namespace android
diff --git a/libnativebridge/tests/NativeBridgeVersion_test.cpp b/libnativebridge/tests/NativeBridgeVersion_test.cpp
new file mode 100644
index 0000000..d3f9a80
--- /dev/null
+++ b/libnativebridge/tests/NativeBridgeVersion_test.cpp
@@ -0,0 +1,38 @@
+/*
+ * 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 "NativeBridgeTest.h"
+
+#include <unistd.h>
+
+namespace android {
+
+TEST_F(NativeBridgeTest, Version) {
+    // When a bridge isn't loaded, we expect 0.
+    EXPECT_EQ(NativeBridgeGetVersion(), 0U);
+
+    // After our dummy bridge has been loaded, we expect 1.
+    ASSERT_TRUE(LoadNativeBridge(kNativeBridgeLibrary, nullptr));
+    EXPECT_EQ(NativeBridgeGetVersion(), 1U);
+
+    // Unload
+    UnloadNativeBridge();
+
+    // Version information is gone.
+    EXPECT_EQ(NativeBridgeGetVersion(), 0U);
+}
+
+}  // namespace android
diff --git a/logd/LogBuffer.cpp b/logd/LogBuffer.cpp
index c33dca6..8c0a0be 100644
--- a/logd/LogBuffer.cpp
+++ b/logd/LogBuffer.cpp
@@ -295,7 +295,8 @@
         ssize_t index = -1;
         while((index = next(index)) >= 0) {
             LogBufferElement *l = editEntryAt(index).getLast();
-            if ((l->getDropped() >= 4) && (current > l->getRealTime().nsec())) {
+            if ((l->getDropped() >= EXPIRE_THRESHOLD)
+                    && (current > l->getRealTime().nsec())) {
                 removeAt(index);
                 index = -1;
             }
@@ -387,6 +388,7 @@
         bool kick = false;
         bool leading = true;
         LogBufferElementLast last;
+        log_time start(log_time::EPOCH);
         for(it = mLogElements.begin(); it != mLogElements.end();) {
             LogBufferElement *e = *it;
 
@@ -446,11 +448,29 @@
             }
 
             if (e->getUid() != worst) {
+                if (start != log_time::EPOCH) {
+                    static const timespec too_old = {
+                        EXPIRE_HOUR_THRESHOLD * 60 * 60, 0
+                    };
+                    start = e->getRealTime() + too_old;
+                }
                 last.clear(e);
                 ++it;
                 continue;
             }
 
+            if ((start != log_time::EPOCH) && (e->getRealTime() > start)) {
+                // KISS. Really a heuristic rather than algorithmically strong,
+                // a crude mechanism, the following loops will move the oldest
+                // watermark possibly wiping out the extra EXPIRE_HOUR_THRESHOLD
+                // we just thought we were preserving. We count on the typical
+                // pruneRows of 10% of total not being a sledgehammer.
+                // A stronger algorithm would have us loop back to the top if
+                // we have worst-UID enabled and we start expiring messages
+                // below less than EXPIRE_HOUR_THRESHOLD old.
+                break;
+            }
+
             pruneRows--;
             if (pruneRows == 0) {
                 break;
diff --git a/logd/LogBufferElement.h b/logd/LogBufferElement.h
index 5dabaac..3dcf9d1 100644
--- a/logd/LogBufferElement.h
+++ b/logd/LogBufferElement.h
@@ -48,6 +48,11 @@
 
 class LogBuffer;
 
+#define EXPIRE_HOUR_THRESHOLD 24 // Only expire chatty UID logs to preserve
+                                 // non-chatty UIDs less than this age in hours
+#define EXPIRE_THRESHOLD 4       // A smaller expire count is considered too
+                                 // chatty for the temporal expire messages
+
 class LogBufferElement {
     const log_id_t mLogId;
     const uid_t mUid;