diff --git a/adb/adb.cpp b/adb/adb.cpp
index 45d26f8..be390d9 100644
--- a/adb/adb.cpp
+++ b/adb/adb.cpp
@@ -360,7 +360,7 @@
                 adb_auth_verified(t);
                 t->failed_auth_attempts = 0;
             } else {
-                if (t->failed_auth_attempts++ > 10) adb_sleep_ms(1000);
+                if (t->failed_auth_attempts++ > 256) adb_sleep_ms(1000);
                 send_auth_request(t);
             }
         } else if (p->msg.arg0 == ADB_AUTH_RSAPUBLICKEY) {
diff --git a/adb/adb_auth.cpp b/adb/adb_auth.cpp
index 446c3df..0b07158 100644
--- a/adb/adb_auth.cpp
+++ b/adb/adb_auth.cpp
@@ -64,12 +64,14 @@
 
     p->msg.command = A_AUTH;
     p->msg.arg0 = ADB_AUTH_RSAPUBLICKEY;
-    p->msg.data_length = key.size();
+
+    // adbd expects a null-terminated string.
+    p->msg.data_length = key.size() + 1;
     send_packet(p, t);
 }
 
 void send_auth_response(uint8_t* token, size_t token_size, atransport* t) {
-    RSA* key = t->NextKey();
+    std::shared_ptr<RSA> key = t->NextKey();
     if (key == nullptr) {
         // No more private keys to try, send the public key.
         send_auth_publickey(t);
@@ -79,12 +81,7 @@
     LOG(INFO) << "Calling send_auth_response";
     apacket* p = get_apacket();
 
-    int ret = adb_auth_sign(key, token, token_size, p->data);
-
-    // Stop sharing this key.
-    RSA_free(key);
-    key = nullptr;
-
+    int ret = adb_auth_sign(key.get(), token, token_size, p->data);
     if (!ret) {
         D("Error signing the token");
         put_apacket(p);
diff --git a/adb/adb_auth.h b/adb/adb_auth.h
index 723ded5..59b80d8 100644
--- a/adb/adb_auth.h
+++ b/adb/adb_auth.h
@@ -20,6 +20,7 @@
 #include "adb.h"
 
 #include <deque>
+#include <memory>
 
 #include <openssl/rsa.h>
 
@@ -43,7 +44,7 @@
 void adb_auth_init();
 int adb_auth_sign(RSA* key, const unsigned char* token, size_t token_size, unsigned char* sig);
 std::string adb_auth_get_userkey();
-std::deque<RSA*> adb_auth_get_private_keys();
+std::deque<std::shared_ptr<RSA>> adb_auth_get_private_keys();
 
 static inline bool adb_auth_generate_token(void*, size_t) { abort(); }
 static inline bool adb_auth_verify(void*, size_t, void*, int) { abort(); }
@@ -53,7 +54,7 @@
 
 static inline int adb_auth_sign(void*, const unsigned char*, size_t, unsigned char*) { abort(); }
 static inline std::string adb_auth_get_userkey() { abort(); }
-static inline std::deque<RSA*> adb_auth_get_private_keys() { abort(); }
+static inline std::deque<std::shared_ptr<RSA>> adb_auth_get_private_keys() { abort(); }
 
 void adbd_auth_init(void);
 void adbd_cloexec_auth_socket();
diff --git a/adb/adb_auth_host.cpp b/adb/adb_auth_host.cpp
index ce269cc..4f4f382 100644
--- a/adb/adb_auth_host.cpp
+++ b/adb/adb_auth_host.cpp
@@ -16,16 +16,18 @@
 
 #define TRACE_TAG AUTH
 
-#include "adb_auth.h"
-#include "adb.h"
-#include "adb_utils.h"
-#include "sysdeps.h"
-
+#include <dirent.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#if defined(__linux__)
+#include <sys/inotify.h>
+#endif
 
+#include <map>
 #include <mutex>
+#include <set>
+#include <string>
 
 #include <android-base/errors.h>
 #include <android-base/file.h>
@@ -39,10 +41,16 @@
 #include <openssl/rsa.h>
 #include <openssl/sha.h>
 
+#include "adb.h"
+#include "adb_auth.h"
+#include "adb_utils.h"
+#include "sysdeps.h"
 #include "sysdeps/mutex.h"
 
-static std::mutex& g_key_list_mutex = *new std::mutex;
-static std::deque<RSA*>& g_key_list = *new std::deque<RSA*>;
+static std::mutex& g_keys_mutex = *new std::mutex;
+static std::map<std::string, std::shared_ptr<RSA>>& g_keys =
+    *new std::map<std::string, std::shared_ptr<RSA>>;
+static std::map<int, std::string>& g_monitored_paths = *new std::map<int, std::string>;
 
 static std::string get_user_info() {
     LOG(INFO) << "get_user_info...";
@@ -146,8 +154,23 @@
     return ret;
 }
 
-static bool read_key(const std::string& file) {
-    LOG(INFO) << "read_key '" << file << "'...";
+static std::string hash_key(RSA* key) {
+    unsigned char* pubkey = nullptr;
+    int len = i2d_RSA_PUBKEY(key, &pubkey);
+    if (len < 0) {
+        LOG(ERROR) << "failed to encode RSA public key";
+        return std::string();
+    }
+
+    std::string result;
+    result.resize(SHA256_DIGEST_LENGTH);
+    SHA256(pubkey, len, reinterpret_cast<unsigned char*>(&result[0]));
+    OPENSSL_free(pubkey);
+    return result;
+}
+
+static bool read_key_file(const std::string& file) {
+    LOG(INFO) << "read_key_file '" << file << "'...";
 
     std::unique_ptr<FILE, decltype(&fclose)> fp(fopen(file.c_str(), "r"), fclose);
     if (!fp) {
@@ -162,10 +185,66 @@
         return false;
     }
 
-    g_key_list.push_back(key);
+    std::lock_guard<std::mutex> lock(g_keys_mutex);
+    std::string fingerprint = hash_key(key);
+    if (g_keys.find(fingerprint) != g_keys.end()) {
+        LOG(INFO) << "ignoring already-loaded key: " << file;
+        RSA_free(key);
+    } else {
+        g_keys[fingerprint] = std::shared_ptr<RSA>(key, RSA_free);
+    }
+
     return true;
 }
 
+static bool read_keys(const std::string& path, bool allow_dir = true) {
+    LOG(INFO) << "read_keys '" << path << "'...";
+
+    struct stat st;
+    if (stat(path.c_str(), &st) != 0) {
+        PLOG(ERROR) << "failed to stat '" << path << "'";
+        return false;
+    }
+
+    if (S_ISREG(st.st_mode)) {
+        if (!android::base::EndsWith(path, ".adb_key")) {
+            LOG(INFO) << "skipping non-adb_key '" << path << "'";
+            return false;
+        }
+
+        return read_key_file(path);
+    } else if (S_ISDIR(st.st_mode)) {
+        if (!allow_dir) {
+            // inotify isn't recursive. It would break expectations to load keys in nested
+            // directories but not monitor them for new keys.
+            LOG(WARNING) << "refusing to recurse into directory '" << path << "'";
+            return false;
+        }
+
+        std::unique_ptr<DIR, decltype(&closedir)> dir(opendir(path.c_str()), closedir);
+        if (!dir) {
+            PLOG(ERROR) << "failed to open directory '" << path << "'";
+            return false;
+        }
+
+        bool result = false;
+        while (struct dirent* dent = readdir(dir.get())) {
+            std::string name = dent->d_name;
+
+            // We can't use dent->d_type here because it's not available on Windows.
+            if (name == "." || name == "..") {
+                continue;
+            }
+
+            result |= read_keys((path + OS_PATH_SEPARATOR + name).c_str(), false);
+        }
+        return result;
+    }
+
+    LOG(ERROR) << "unexpected type for '" << path << "': 0x" << std::hex << st.st_mode;
+    return false;
+}
+
 static std::string get_user_key_path() {
     const std::string home = adb_get_homedir_path(true);
     LOG(DEBUG) << "adb_get_homedir_path returned '" << home << "'";
@@ -200,31 +279,29 @@
         }
     }
 
-    return read_key(path);
+    return read_key_file(path);
 }
 
-static void get_vendor_keys() {
+static std::set<std::string> get_vendor_keys() {
     const char* adb_keys_path = getenv("ADB_VENDOR_KEYS");
     if (adb_keys_path == nullptr) {
-        return;
+        return std::set<std::string>();
     }
 
+    std::set<std::string> result;
     for (const auto& path : android::base::Split(adb_keys_path, ENV_PATH_SEPARATOR_STR)) {
-        if (!read_key(path.c_str())) {
-            PLOG(ERROR) << "Failed to read '" << path << "'";
-        }
+        result.emplace(path);
     }
+    return result;
 }
 
-std::deque<RSA*> adb_auth_get_private_keys() {
-    std::deque<RSA*> result;
+std::deque<std::shared_ptr<RSA>> adb_auth_get_private_keys() {
+    std::deque<std::shared_ptr<RSA>> result;
 
-    // Copy all the currently known keys, increasing their reference count so they're
-    // usable until both we and the caller have freed our pointers.
-    std::lock_guard<std::mutex> lock(g_key_list_mutex);
-    for (const auto& key : g_key_list) {
-        RSA_up_ref(key); // Since we're handing out another pointer to this key...
-        result.push_back(key);
+    // Copy all the currently known keys.
+    std::lock_guard<std::mutex> lock(g_keys_mutex);
+    for (const auto& it : g_keys) {
+        result.push_back(it.second);
     }
 
     // Add a sentinel to the list. Our caller uses this to mean "out of private keys,
@@ -270,6 +347,77 @@
     return (generate_key(filename) == 0);
 }
 
+#if defined(__linux__)
+static void adb_auth_inotify_update(int fd, unsigned fd_event, void*) {
+    LOG(INFO) << "adb_auth_inotify_update called";
+    if (!(fd_event & FDE_READ)) {
+        return;
+    }
+
+    char buf[sizeof(struct inotify_event) + NAME_MAX + 1];
+    while (true) {
+        ssize_t rc = TEMP_FAILURE_RETRY(unix_read(fd, buf, sizeof(buf)));
+        if (rc == -1) {
+            if (errno == EAGAIN) {
+                LOG(INFO) << "done reading inotify fd";
+                break;
+            }
+            PLOG(FATAL) << "read of inotify event failed";
+        }
+
+        // The read potentially returned multiple events.
+        char* start = buf;
+        char* end = buf + rc;
+
+        while (start < end) {
+            inotify_event* event = reinterpret_cast<inotify_event*>(start);
+            auto root_it = g_monitored_paths.find(event->wd);
+            if (root_it == g_monitored_paths.end()) {
+                LOG(FATAL) << "observed inotify event for unmonitored path, wd = " << event->wd;
+            }
+
+            std::string path = root_it->second;
+            if (event->len > 0) {
+                path += '/';
+                path += event->name;
+            }
+
+            if (event->mask & (IN_CREATE | IN_MOVED_TO)) {
+                if (event->mask & IN_ISDIR) {
+                    LOG(INFO) << "ignoring new directory at '" << path << "'";
+                } else {
+                    LOG(INFO) << "observed new file at '" << path << "'";
+                    read_keys(path, false);
+                }
+            } else {
+                LOG(WARNING) << "unmonitored event for " << path << ": 0x" << std::hex
+                             << event->mask;
+            }
+
+            start += sizeof(struct inotify_event) + event->len;
+        }
+    }
+}
+
+static void adb_auth_inotify_init(const std::set<std::string>& paths) {
+    LOG(INFO) << "adb_auth_inotify_init...";
+    int infd = inotify_init1(IN_CLOEXEC | IN_NONBLOCK);
+    for (const std::string& path : paths) {
+        int wd = inotify_add_watch(infd, path.c_str(), IN_CREATE | IN_MOVED_TO);
+        if (wd < 0) {
+            PLOG(ERROR) << "failed to inotify_add_watch on path '" << path;
+            continue;
+        }
+
+        g_monitored_paths[wd] = path;
+        LOG(INFO) << "watch descriptor " << wd << " registered for " << path;
+    }
+
+    fdevent* event = fdevent_create(infd, adb_auth_inotify_update, nullptr);
+    fdevent_add(event, FDE_READ);
+}
+#endif
+
 void adb_auth_init() {
     LOG(INFO) << "adb_auth_init...";
 
@@ -278,6 +426,13 @@
         return;
     }
 
-    std::lock_guard<std::mutex> lock(g_key_list_mutex);
-    get_vendor_keys();
+    const auto& key_paths = get_vendor_keys();
+
+#if defined(__linux__)
+    adb_auth_inotify_init(key_paths);
+#endif
+
+    for (const std::string& path : key_paths) {
+        read_keys(path.c_str());
+    }
 }
diff --git a/adb/transport.cpp b/adb/transport.cpp
index e0216e3..f5ef174 100644
--- a/adb/transport.cpp
+++ b/adb/transport.cpp
@@ -1076,10 +1076,10 @@
     }
 }
 
-RSA* atransport::NextKey() {
+std::shared_ptr<RSA> atransport::NextKey() {
     if (keys_.empty()) keys_ = adb_auth_get_private_keys();
 
-    RSA* result = keys_[0];
+    std::shared_ptr<RSA> result = keys_[0];
     keys_.pop_front();
     return result;
 }
diff --git a/adb/transport.h b/adb/transport.h
index d41c8bd..959681f 100644
--- a/adb/transport.h
+++ b/adb/transport.h
@@ -21,6 +21,7 @@
 
 #include <deque>
 #include <list>
+#include <memory>
 #include <string>
 #include <unordered_set>
 
@@ -107,7 +108,7 @@
         return type == kTransportLocal && local_port_for_emulator_ == -1;
     }
 
-    RSA* NextKey();
+    std::shared_ptr<RSA> NextKey();
 
     unsigned char token[TOKEN_SIZE] = {};
     size_t failed_auth_attempts = 0;
@@ -160,7 +161,7 @@
     // A list of adisconnect callbacks called when the transport is kicked.
     std::list<adisconnect*> disconnects_;
 
-    std::deque<RSA*> keys_;
+    std::deque<std::shared_ptr<RSA>> keys_;
 
     DISALLOW_COPY_AND_ASSIGN(atransport);
 };
diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index c097d04..1f2408f 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -97,19 +97,40 @@
 };
 
 static struct {
-    char img_name[13];
-    char sig_name[13];
+    char img_name[17];
+    char sig_name[17];
     char part_name[9];
     bool is_optional;
+    bool is_secondary;
 } images[] = {
-    {"boot.img", "boot.sig", "boot", false},
-    {"recovery.img", "recovery.sig", "recovery", true},
-    {"system.img", "system.sig", "system", false},
-    {"vendor.img", "vendor.sig", "vendor", true},
+    {"boot.img", "boot.sig", "boot", false, false},
+    {"boot_other.img", "boot.sig", "boot", true, true},
+    {"recovery.img", "recovery.sig", "recovery", true, false},
+    {"system.img", "system.sig", "system", false, false},
+    {"system_other.img", "system.sig", "system", true, true},
+    {"vendor.img", "vendor.sig", "vendor", true, false},
+    {"vendor_other.img", "vendor.sig", "vendor", true, true},
 };
 
-static std::string find_item(const char* item, const char* product) {
+static std::string find_item_given_name(const char* img_name, const char* product) {
+    if(product) {
+        std::string path = get_my_path();
+        path.erase(path.find_last_of('/'));
+        return android::base::StringPrintf("%s/../../../target/product/%s/%s",
+                                           path.c_str(), product, img_name);
+    }
+
+    char *dir = getenv("ANDROID_PRODUCT_OUT");
+    if (dir == nullptr || dir[0] == '\0') {
+        die("neither -p product specified nor ANDROID_PRODUCT_OUT set");
+    }
+
+    return android::base::StringPrintf("%s/%s", dir, img_name);
+}
+
+std::string find_item(const char* item, const char* product) {
     const char *fn;
+
     if (!strcmp(item,"boot")) {
         fn = "boot.img";
     } else if(!strcmp(item,"recovery")) {
@@ -129,19 +150,7 @@
         return "";
     }
 
-    if (product) {
-        std::string path = get_my_path();
-        path.erase(path.find_last_of('/'));
-        return android::base::StringPrintf("%s/../../../target/product/%s/%s",
-                                           path.c_str(), product, fn);
-    }
-
-    char* dir = getenv("ANDROID_PRODUCT_OUT");
-    if (dir == nullptr || dir[0] == '\0') {
-        die("neither -p product specified nor ANDROID_PRODUCT_OUT set");
-    }
-
-    return android::base::StringPrintf("%s/%s", dir, fn);
+    return find_item_given_name(fn, product);
 }
 
 static int64_t get_file_size(int fd) {
@@ -307,8 +316,13 @@
             "\n"
             "commands:\n"
             "  update <filename>                        Reflash device from update.zip.\n"
+            "                                           Sets the flashed slot as active.\n"
             "  flashall                                 Flash boot, system, vendor, and --\n"
-            "                                           if found -- recovery.\n"
+            "                                           if found -- recovery. If the device\n"
+            "                                           supports slots, the slot that has\n"
+            "                                           been flashed to is set as active.\n"
+            "                                           Secondary images may be flashed to\n"
+            "                                           an inactive slot.\n"
             "  flash <partition> [ <filename> ]         Write a file to a flash partition.\n"
             "  flashing lock                            Locks the device. Prevents flashing.\n"
             "  flashing unlock                          Unlocks the device. Allows flashing\n"
@@ -331,7 +345,7 @@
             "                                           override the fs type and/or size\n"
             "                                           the bootloader reports.\n"
             "  getvar <variable>                        Display a bootloader variable.\n"
-            "  set_active <suffix>                      Sets the active slot. If slots are\n"
+            "  set_active <slot>                        Sets the active slot. If slots are\n"
             "                                           not supported, this does nothing.\n"
             "  boot <kernel> [ <ramdisk> [ <second> ] ] Download and boot kernel.\n"
             "  flash:raw boot <kernel> [ <ramdisk> [ <second> ] ]\n"
@@ -368,19 +382,24 @@
             "                                           (default: 2048).\n"
             "  -S <size>[K|M|G]                         Automatically sparse files greater\n"
             "                                           than 'size'. 0 to disable.\n"
-            "  --slot <suffix>                          Specify slot suffix to be used if the\n"
-            "                                           device supports slots. This will be\n"
-            "                                           added to all partition names that use\n"
-            "                                           slots. 'all' can be given to refer\n"
-            "                                           to all slots. 'other' can be given to\n"
-            "                                           refer to a non-current slot. If this\n"
-            "                                           flag is not used, slotted partitions\n"
-            "                                           will default to the current active slot.\n"
-            "  -a, --set-active[=<suffix>]              Sets the active slot. If no suffix is\n"
+            "  --slot <slot>                            Specify slot name to be used if the\n"
+            "                                           device supports slots. All operations\n"
+            "                                           on partitions that support slots will\n"
+            "                                           be done on the slot specified.\n"
+            "                                           'all' can be given to refer to all slots.\n"
+            "                                           'other' can be given to refer to a\n"
+            "                                           non-current slot. If this flag is not\n"
+            "                                           used, slotted partitions will default\n"
+            "                                           to the current active slot.\n"
+            "  -a, --set-active[=<slot>]                Sets the active slot. If no slot is\n"
             "                                           provided, this will default to the value\n"
             "                                           given by --slot. If slots are not\n"
-            "                                           supported, this does nothing. This will\n"
-            "                                           run after all non-reboot commands.\n"
+            "                                           supported, this sets the current slot\n"
+            "                                           to be active. This will run after all\n"
+            "                                           non-reboot commands.\n"
+            "  --skip-secondary                         Will not flash secondary slots when\n"
+            "                                           performing a flashall or update. This\n"
+            "                                           will preserve data on other slots.\n"
             "  --unbuffered                             Do not buffer input or output.\n"
             "  --version                                Display version.\n"
             "  -h, --help                               show this message.\n"
@@ -782,83 +801,138 @@
     }
 }
 
-static std::vector<std::string> get_suffixes(Transport* transport) {
+static std::string get_current_slot(Transport* transport)
+{
+    std::string current_slot;
+    if (fb_getvar(transport, "current-slot", &current_slot)) {
+        if (current_slot == "_a") return "a"; // Legacy support
+        if (current_slot == "_b") return "b"; // Legacy support
+        return current_slot;
+    }
+    return "";
+}
+
+// Legacy support
+static std::vector<std::string> get_suffixes_obsolete(Transport* transport) {
     std::vector<std::string> suffixes;
     std::string suffix_list;
     if (!fb_getvar(transport, "slot-suffixes", &suffix_list)) {
-        die("Could not get suffixes.\n");
+        return suffixes;
     }
-    return android::base::Split(suffix_list, ",");
+    suffixes = android::base::Split(suffix_list, ",");
+    // Unfortunately some devices will return an error message in the
+    // guise of a valid value. If we only see only one suffix, it's probably
+    // not real.
+    if (suffixes.size() == 1) {
+        suffixes.clear();
+    }
+    return suffixes;
 }
 
-static std::string verify_slot(Transport* transport, const char *slot, bool allow_all) {
-    if (strcmp(slot, "all") == 0) {
+// Legacy support
+static bool supports_AB_obsolete(Transport* transport) {
+  return !get_suffixes_obsolete(transport).empty();
+}
+
+static int get_slot_count(Transport* transport) {
+    std::string var;
+    int count;
+    if (!fb_getvar(transport, "slot-count", &var)) {
+        if (supports_AB_obsolete(transport)) return 2; // Legacy support
+    }
+    if (!android::base::ParseInt(var.c_str(), &count)) return 0;
+    return count;
+}
+
+static bool supports_AB(Transport* transport) {
+  return get_slot_count(transport) >= 2;
+}
+
+// Given a current slot, this returns what the 'other' slot is.
+static std::string get_other_slot(const std::string& current_slot, int count) {
+    if (count == 0) return "";
+
+    char next = (current_slot[0] - 'a' + 1)%count + 'a';
+    return std::string(1, next);
+}
+
+static std::string get_other_slot(Transport* transport, const std::string& current_slot) {
+    return get_other_slot(current_slot, get_slot_count(transport));
+}
+
+static std::string get_other_slot(Transport* transport, int count) {
+    return get_other_slot(get_current_slot(transport), count);
+}
+
+static std::string get_other_slot(Transport* transport) {
+    return get_other_slot(get_current_slot(transport), get_slot_count(transport));
+}
+
+static std::string verify_slot(Transport* transport, const std::string& slot_name, bool allow_all) {
+    std::string slot = slot_name;
+    if (slot == "_a") slot = "a"; // Legacy support
+    if (slot == "_b") slot = "b"; // Legacy support
+    if (slot == "all") {
         if (allow_all) {
             return "all";
         } else {
-            std::vector<std::string> suffixes = get_suffixes(transport);
-            if (!suffixes.empty()) {
-                return suffixes[0];
+            int count = get_slot_count(transport);
+            if (count > 0) {
+                return "a";
             } else {
                 die("No known slots.");
             }
         }
     }
 
-    std::vector<std::string> suffixes = get_suffixes(transport);
+    int count = get_slot_count(transport);
+    if (count == 0) die("Device does not support slots.\n");
 
-    if (strcmp(slot, "other") == 0) {
-        std::string current_slot;
-        if (!fb_getvar(transport, "current-slot", &current_slot)) {
-            die("Failed to identify current slot.");
+    if (slot == "other") {
+        std::string other = get_other_slot(transport, count);
+        if (other == "") {
+           die("No known slots.");
         }
-        if (!suffixes.empty()) {
-            for (size_t i = 0; i < suffixes.size(); i++) {
-                if (current_slot == suffixes[i])
-                    return suffixes[(i+1)%suffixes.size()];
-            }
-        } else {
-            die("No known slots.");
-        }
+        return other;
     }
 
-    for (const std::string &suffix : suffixes) {
-        if (suffix == slot)
-            return slot;
+    if (slot.size() == 1 && (slot[0]-'a' >= 0 && slot[0]-'a' < count)) return slot;
+
+    fprintf(stderr, "Slot %s does not exist. supported slots are:\n", slot.c_str());
+    for (int i=0; i<count; i++) {
+        fprintf(stderr, "%c\n", (char)(i + 'a'));
     }
-    fprintf(stderr, "Slot %s does not exist. supported slots are:\n", slot);
-    for (const std::string &suffix : suffixes) {
-        fprintf(stderr, "%s\n", suffix.c_str());
-    }
+
     exit(1);
 }
 
-static std::string verify_slot(Transport* transport, const char *slot) {
+static std::string verify_slot(Transport* transport, const std::string& slot) {
    return verify_slot(transport, slot, true);
 }
 
-static void do_for_partition(Transport* transport, const char *part, const char *slot,
+static void do_for_partition(Transport* transport, const std::string& part, const std::string& slot,
                              const std::function<void(const std::string&)>& func, bool force_slot) {
     std::string has_slot;
     std::string current_slot;
 
-    if (!fb_getvar(transport, std::string("has-slot:")+part, &has_slot)) {
+    if (!fb_getvar(transport, "has-slot:" + part, &has_slot)) {
         /* If has-slot is not supported, the answer is no. */
         has_slot = "no";
     }
     if (has_slot == "yes") {
-        if (!slot || slot[0] == 0) {
-            if (!fb_getvar(transport, "current-slot", &current_slot)) {
+        if (slot == "") {
+            current_slot = get_current_slot(transport);
+            if (current_slot == "") {
                 die("Failed to identify current slot.\n");
             }
-            func(std::string(part) + current_slot);
+            func(part + "_" + current_slot);
         } else {
-            func(std::string(part) + slot);
+            func(part + '_' + slot);
         }
     } else {
-        if (force_slot && slot && slot[0]) {
+        if (force_slot && slot != "") {
              fprintf(stderr, "Warning: %s does not support slots, and slot %s was requested.\n",
-                     part, slot);
+                     part.c_str(), slot.c_str());
         }
         func(part);
     }
@@ -869,18 +943,17 @@
  * partition names. If force_slot is true, it will fail if a slot is specified, and the given
  * partition does not support slots.
  */
-static void do_for_partitions(Transport* transport, const char *part, const char *slot,
+static void do_for_partitions(Transport* transport, const std::string& part, const std::string& slot,
                               const std::function<void(const std::string&)>& func, bool force_slot) {
     std::string has_slot;
 
-    if (slot && strcmp(slot, "all") == 0) {
-        if (!fb_getvar(transport, std::string("has-slot:") + part, &has_slot)) {
-            die("Could not check if partition %s has slot.", part);
+    if (slot == "all") {
+        if (!fb_getvar(transport, "has-slot:" + part, &has_slot)) {
+            die("Could not check if partition %s has slot.", part.c_str());
         }
         if (has_slot == "yes") {
-            std::vector<std::string> suffixes = get_suffixes(transport);
-            for (std::string &suffix : suffixes) {
-                do_for_partition(transport, part, suffix.c_str(), func, force_slot);
+            for (int i=0; i < get_slot_count(transport); i++) {
+                do_for_partition(transport, part, std::string(1, (char)(i + 'a')), func, force_slot);
             }
         } else {
             do_for_partition(transport, part, "", func, force_slot);
@@ -907,7 +980,28 @@
     fb_queue_command("signature", "installing signature");
 }
 
-static void do_update(Transport* transport, const char* filename, const char* slot_override, bool erase_first) {
+// Sets slot_override as the active slot. If slot_override is blank,
+// set current slot as active instead. This clears slot-unbootable.
+static void set_active(Transport* transport, const std::string& slot_override) {
+    std::string separator = "";
+    if (!supports_AB(transport)) {
+        if (supports_AB_obsolete(transport)) {
+            separator = "_"; // Legacy support
+        } else {
+            return;
+        }
+    }
+    if (slot_override != "") {
+        fb_set_active((separator + slot_override).c_str());
+    } else {
+        std::string current_slot = get_current_slot(transport);
+        if (current_slot != "") {
+            fb_set_active((separator + current_slot).c_str());
+        }
+    }
+}
+
+static void do_update(Transport* transport, const char* filename, const std::string& slot_override, bool erase_first, bool skip_secondary) {
     queue_info_dump();
 
     fb_queue_query_save("product", cur_product, sizeof(cur_product));
@@ -928,7 +1022,30 @@
 
     setup_requirements(reinterpret_cast<char*>(data), sz);
 
+    std::string secondary;
+    if (!skip_secondary) {
+        if (slot_override != "") {
+            secondary = get_other_slot(transport, slot_override);
+        } else {
+            secondary = get_other_slot(transport);
+        }
+        if (secondary == "") {
+            if (supports_AB(transport)) {
+                fprintf(stderr, "Warning: Could not determine slot for secondary images. Ignoring.\n");
+            }
+            skip_secondary = true;
+        }
+    }
     for (size_t i = 0; i < arraysize(images); ++i) {
+        const char* slot = slot_override.c_str();
+        if (images[i].is_secondary) {
+            if (!skip_secondary) {
+                slot = secondary.c_str();
+            } else {
+                continue;
+            }
+        }
+
         int fd = unzip_to_file(zip, images[i].img_name);
         if (fd == -1) {
             if (images[i].is_optional) {
@@ -953,49 +1070,74 @@
              * program exits.
              */
         };
-        do_for_partitions(transport, images[i].part_name, slot_override, update, false);
+        do_for_partitions(transport, images[i].part_name, slot, update, false);
     }
 
     CloseArchive(zip);
+    if (slot_override == "all") {
+        set_active(transport, "a");
+    } else {
+        set_active(transport, slot_override);
+    }
 }
 
-static void do_send_signature(const char* filename) {
-    if (android::base::EndsWith(filename, ".img") == false) {
-        return;
-    }
+static void do_send_signature(const std::string& fn) {
+    std::size_t extension_loc = fn.find(".img");
+    if (extension_loc == std::string::npos) return;
 
-    std::string sig_path = filename;
-    sig_path.erase(sig_path.size() - 4);
-    sig_path += ".sig";
+    std::string fs_sig = fn.substr(0, extension_loc) + ".sig";
 
     int64_t sz;
-    void* data = load_file(sig_path, &sz);
+    void* data = load_file(fs_sig.c_str(), &sz);
     if (data == nullptr) return;
 
     fb_queue_download("signature", data, sz);
     fb_queue_command("signature", "installing signature");
 }
 
-static void do_flashall(Transport* transport, const char* slot_override, int erase_first) {
+static void do_flashall(Transport* transport, const std::string& slot_override, int erase_first, bool skip_secondary) {
+    std::string fname;
     queue_info_dump();
 
     fb_queue_query_save("product", cur_product, sizeof(cur_product));
 
-    std::string fname = find_item("info", product);
+    fname = find_item("info", product);
     if (fname.empty()) die("cannot find android-info.txt");
 
     int64_t sz;
-    void* data = load_file(fname, &sz);
+    void* data = load_file(fname.c_str(), &sz);
     if (data == nullptr) die("could not load android-info.txt: %s", strerror(errno));
 
     setup_requirements(reinterpret_cast<char*>(data), sz);
 
+    std::string secondary;
+    if (!skip_secondary) {
+        if (slot_override != "") {
+            secondary = get_other_slot(transport, slot_override);
+        } else {
+            secondary = get_other_slot(transport);
+        }
+        if (secondary == "") {
+            if (supports_AB(transport)) {
+                fprintf(stderr, "Warning: Could not determine slot for secondary images. Ignoring.\n");
+            }
+            skip_secondary = true;
+        }
+    }
+
     for (size_t i = 0; i < arraysize(images); i++) {
-        fname = find_item(images[i].part_name, product);
+        const char* slot = NULL;
+        if (images[i].is_secondary) {
+            if (!skip_secondary) slot = secondary.c_str();
+        } else {
+            slot = slot_override.c_str();
+        }
+        if (!slot) continue;
+        fname = find_item_given_name(images[i].img_name, product);
         fastboot_buffer buf;
         if (!load_buf(transport, fname.c_str(), &buf)) {
             if (images[i].is_optional) continue;
-            die("could not load '%s': %s", images[i].img_name, strerror(errno));
+            die("could not load '%s': %s\n", images[i].img_name, strerror(errno));
         }
 
         auto flashall = [&](const std::string &partition) {
@@ -1005,7 +1147,13 @@
             }
             flash_buf(partition.c_str(), &buf);
         };
-        do_for_partitions(transport, images[i].part_name, slot_override, flashall, false);
+        do_for_partitions(transport, images[i].part_name, slot, flashall, false);
+    }
+
+    if (slot_override == "all") {
+        set_active(transport, "a");
+    } else {
+        set_active(transport, slot_override);
     }
 }
 
@@ -1184,6 +1332,7 @@
     bool wants_reboot = false;
     bool wants_reboot_bootloader = false;
     bool wants_set_active = false;
+    bool skip_secondary = false;
     bool erase_first = true;
     void *data;
     int64_t sz;
@@ -1207,6 +1356,7 @@
         {"slot", required_argument, 0, 0},
         {"set_active", optional_argument, 0, 'a'},
         {"set-active", optional_argument, 0, 'a'},
+        {"skip-secondary", no_argument, 0, 0},
         {0, 0, 0, 0}
     };
 
@@ -1288,6 +1438,12 @@
                 return 0;
             } else if (strcmp("slot", longopts[longindex].name) == 0) {
                 slot_override = std::string(optarg);
+            } else if (strcmp("skip-secondary", longopts[longindex].name) == 0 ) {
+                skip_secondary = true;
+            } else {
+                fprintf(stderr, "Internal error in options processing for %s\n",
+                    longopts[longindex].name);
+                return 1;
             }
             break;
         default:
@@ -1319,17 +1475,23 @@
         return 1;
     }
 
-    if (slot_override != "")
-        slot_override = verify_slot(transport, slot_override.c_str());
-    if (next_active != "")
-        next_active = verify_slot(transport, next_active.c_str(), false);
+    if (!supports_AB(transport) && supports_AB_obsolete(transport)) {
+        fprintf(stderr, "Warning: Device A/B support is outdated. Bootloader update required.\n");
+    }
+    if (slot_override != "") slot_override = verify_slot(transport, slot_override);
+    if (next_active != "") next_active = verify_slot(transport, next_active, false);
 
     if (wants_set_active) {
         if (next_active == "") {
             if (slot_override == "") {
-                wants_set_active = false;
+                std::string current_slot;
+                if (fb_getvar(transport, "current-slot", &current_slot)) {
+                    next_active = verify_slot(transport, current_slot, false);
+                } else {
+                    wants_set_active = false;
+                }
             } else {
-                next_active = verify_slot(transport, slot_override.c_str(), false);
+                next_active = verify_slot(transport, slot_override, false);
             }
         }
     }
@@ -1352,7 +1514,7 @@
 
                 fb_queue_erase(partition.c_str());
             };
-            do_for_partitions(transport, argv[1], slot_override.c_str(), erase, true);
+            do_for_partitions(transport, argv[1], slot_override, erase, true);
             skip(2);
         } else if(!strncmp(*argv, "format", strlen("format"))) {
             char *overrides;
@@ -1387,7 +1549,7 @@
                 }
                 fb_perform_format(transport, partition.c_str(), 0, type_override, size_override);
             };
-            do_for_partitions(transport, argv[1], slot_override.c_str(), format, true);
+            do_for_partitions(transport, argv[1], slot_override, format, true);
             skip(2);
         } else if(!strcmp(*argv, "signature")) {
             require(2);
@@ -1454,7 +1616,7 @@
                 }
                 do_flash(transport, partition.c_str(), fname.c_str());
             };
-            do_for_partitions(transport, pname, slot_override.c_str(), flash, true);
+            do_for_partitions(transport, pname, slot_override, flash, true);
         } else if(!strcmp(*argv, "flash:raw")) {
             char *kname = argv[2];
             char *rname = 0;
@@ -1474,23 +1636,32 @@
             auto flashraw = [&](const std::string &partition) {
                 fb_queue_flash(partition.c_str(), data, sz);
             };
-            do_for_partitions(transport, argv[1], slot_override.c_str(), flashraw, true);
+            do_for_partitions(transport, argv[1], slot_override, flashraw, true);
         } else if(!strcmp(*argv, "flashall")) {
             skip(1);
-            do_flashall(transport, slot_override.c_str(), erase_first);
+            if (slot_override == "all") {
+                fprintf(stderr, "Warning: slot set to 'all'. Secondary slots will not be flashed.\n");
+                do_flashall(transport, slot_override, erase_first, true);
+            } else {
+                do_flashall(transport, slot_override, erase_first, skip_secondary);
+            }
             wants_reboot = true;
         } else if(!strcmp(*argv, "update")) {
+            bool slot_all = (slot_override == "all");
+            if (slot_all) {
+                fprintf(stderr, "Warning: slot set to 'all'. Secondary slots will not be flashed.\n");
+            }
             if (argc > 1) {
-                do_update(transport, argv[1], slot_override.c_str(), erase_first);
+                do_update(transport, argv[1], slot_override, erase_first, skip_secondary || slot_all);
                 skip(2);
             } else {
-                do_update(transport, "update.zip", slot_override.c_str(), erase_first);
+                do_update(transport, "update.zip", slot_override, erase_first, skip_secondary || slot_all);
                 skip(1);
             }
             wants_reboot = 1;
         } else if(!strcmp(*argv, "set_active")) {
             require(2);
-            std::string slot = verify_slot(transport, argv[1], false);
+            std::string slot = verify_slot(transport, std::string(argv[1]), false);
             fb_set_active(slot.c_str());
             skip(2);
         } else if(!strcmp(*argv, "oem")) {
diff --git a/liblog/logd_writer.c b/liblog/logd_writer.c
index 059f170..ed82902 100644
--- a/liblog/logd_writer.c
+++ b/liblog/logd_writer.c
@@ -67,12 +67,9 @@
     int i, ret = 0;
 
     if (logdLoggerWrite.context.sock < 0) {
-        i = TEMP_FAILURE_RETRY(socket(PF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0));
+        i = TEMP_FAILURE_RETRY(socket(PF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0));
         if (i < 0) {
             ret = -errno;
-        } else if (TEMP_FAILURE_RETRY(fcntl(i, F_SETFL, O_NONBLOCK)) < 0) {
-            ret = -errno;
-            close(i);
         } else {
             struct sockaddr_un un;
             memset(&un, 0, sizeof(struct sockaddr_un));