core: Bring back support for legacy FunctionFS

Change-Id: Ibaaf031c167d66e1f08957763b5353d71134b4e0

8 files changed, 688 insertions, 7 deletions

diff --git a/adb/Android.bp b/adb/Android.bp
index 91882673e..67810272e 100644
--- a/adb/Android.bp
+++ b/adb/Android.bp
@@ -79,7 +79,7 @@ cc_defaults {
     name: "adbd_defaults",
     defaults: ["adb_defaults"],
 
-    cflags: ["-UADB_HOST", "-DADB_HOST=0"],
+    cflags: ["-UADB_HOST", "-DADB_HOST=0", "-DLEGACY_FFS=1"],
 }
 
 cc_defaults {
@@ -159,6 +159,7 @@ libadb_srcs = [
     "sysdeps/errno.cpp",
     "transport.cpp",
     "transport_fd.cpp",
+    "transport_legacy.cpp",
     "transport_local.cpp",
     "types.cpp",
 ]
@@ -405,8 +406,14 @@ cc_library_static {
                 "daemon/transport_qemu.cpp",
                 "daemon/usb.cpp",
                 "daemon/usb_ffs.cpp",
+                "daemon/usb_legacy.cpp",
             ]
         },
+        linux_glibc: {
+            srcs: [
+                "daemon/usb_dummy.cpp",
+             ]
+        },
         recovery: {
             exclude_shared_libs: [
                 "libadb_pairing_auth",
diff --git a/adb/daemon/usb.cpp b/adb/daemon/usb.cpp
index 50d73644d..5561b168d 100644
--- a/adb/daemon/usb.cpp
+++ b/adb/daemon/usb.cpp
@@ -54,6 +54,9 @@
 
 using android::base::StringPrintf;
 
+// We can't find out whether we have support for AIO on ffs endpoints until we submit a read.
+static std::optional<bool> gFfsAioSupported;
+
 // Not all USB controllers support operations larger than 16k, so don't go above that.
 // Also, each submitted operation does an allocation in the kernel of that size, so we want to
 // minimize our queue depth while still maintaining a deep enough queue to keep the USB stack fed.
@@ -617,10 +620,17 @@ struct UsbFfsConnection : public Connection {
         block->pending = true;
         struct iocb* iocb = &block->control;
         if (io_submit(aio_context_.get(), 1, &iocb) != 1) {
+            if (errno == EINVAL && !gFfsAioSupported.has_value()) {
+                HandleError("failed to submit first read, AIO on FFS not supported");
+                gFfsAioSupported = false;
+                return false;
+            }
+
             HandleError(StringPrintf("failed to submit read: %s", strerror(errno)));
             return false;
         }
 
+        gFfsAioSupported = true;
         return true;
     }
 
@@ -737,10 +747,17 @@ struct UsbFfsConnection : public Connection {
     static constexpr int kInterruptionSignal = SIGUSR1;
 };
 
+void usb_init_legacy();
+
 static void usb_ffs_open_thread() {
     adb_thread_setname("usb ffs open");
 
     while (true) {
+        if (gFfsAioSupported.has_value() && !gFfsAioSupported.value()) {
+            LOG(INFO) << "failed to use nonblocking ffs, falling back to legacy";
+            return usb_init_legacy();
+        }
+
         unique_fd control;
         unique_fd bulk_out;
         unique_fd bulk_in;
@@ -762,5 +779,13 @@ static void usb_ffs_open_thread() {
 }
 
 void usb_init() {
-    std::thread(usb_ffs_open_thread).detach();
+    bool use_nonblocking = android::base::GetBoolProperty(
+            "persist.adb.nonblocking_ffs",
+            android::base::GetBoolProperty("ro.adb.nonblocking_ffs", true));
+
+    if (use_nonblocking) {
+        std::thread(usb_ffs_open_thread).detach();
+    } else {
+        usb_init_legacy();
+    }
 }
diff --git a/adb/daemon/usb_dummy.cpp b/adb/daemon/usb_dummy.cpp
new file mode 100644
index 000000000..9223cd491
--- /dev/null
+++ b/adb/daemon/usb_dummy.cpp
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2019 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 "usb_legacy.h"
+
+#include <android-base/logging.h>
+
+int usb_write(usb_handle*, const void*, int) {
+    LOG(FATAL) << "unimplemented";
+    return -1;
+}
+
+int usb_read(usb_handle*, void*, int) {
+    LOG(FATAL) << "unimplemented";
+    return -1;
+}
+
+int usb_close(usb_handle*) {
+    LOG(FATAL) << "unimplemented";
+    return -1;
+}
+
+void usb_reset(usb_handle*) {
+    LOG(FATAL) << "unimplemented";
+}
+
+void usb_kick(usb_handle*) {
+    LOG(FATAL) << "unimplemented";
+}
diff --git a/adb/daemon/usb_legacy.cpp b/adb/daemon/usb_legacy.cpp
new file mode 100644
index 000000000..7fd5808df
--- /dev/null
+++ b/adb/daemon/usb_legacy.cpp
@@ -0,0 +1,327 @@
+/*
+ * Copyright (C) 2007 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.
+ */
+
+#define TRACE_TAG USB
+
+#include "sysdeps.h"
+
+#include <dirent.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <linux/usb/ch9.h>
+#include <linux/usb/functionfs.h>
+
+#include <algorithm>
+#include <atomic>
+#include <chrono>
+#include <condition_variable>
+#include <mutex>
+#include <thread>
+
+#include <android-base/logging.h>
+#include <android-base/properties.h>
+
+#include "adb.h"
+#include "usb_legacy.h"
+#include "transport.h"
+
+using namespace std::chrono_literals;
+
+#define MAX_PACKET_SIZE_FS 64
+#define MAX_PACKET_SIZE_HS 512
+#define MAX_PACKET_SIZE_SS 1024
+
+#define USB_FFS_BULK_SIZE 16384
+
+// Number of buffers needed to fit MAX_PAYLOAD, with an extra for ZLPs.
+#define USB_FFS_NUM_BUFS ((4 * MAX_PAYLOAD / USB_FFS_BULK_SIZE) + 1)
+
+static unique_fd& dummy_fd = *new unique_fd();
+
+static void aio_block_init(aio_block* aiob, unsigned num_bufs) {
+    aiob->iocb.resize(num_bufs);
+    aiob->iocbs.resize(num_bufs);
+    aiob->events.resize(num_bufs);
+    aiob->num_submitted = 0;
+    for (unsigned i = 0; i < num_bufs; i++) {
+        aiob->iocbs[i] = &aiob->iocb[i];
+    }
+    memset(&aiob->ctx, 0, sizeof(aiob->ctx));
+    if (io_setup(num_bufs, &aiob->ctx)) {
+        D("[ aio: got error on io_setup (%d) ]", errno);
+    }
+}
+
+static int getMaxPacketSize(int ffs_fd) {
+    usb_endpoint_descriptor desc;
+    if (ioctl(ffs_fd, FUNCTIONFS_ENDPOINT_DESC, reinterpret_cast<unsigned long>(&desc))) {
+        D("[ could not get endpoint descriptor! (%d) ]", errno);
+        return MAX_PACKET_SIZE_HS;
+    } else {
+        return desc.wMaxPacketSize;
+    }
+}
+
+static bool init_functionfs(struct usb_handle* h) {
+    LOG(INFO) << "initializing functionfs";
+    if (!open_functionfs(&h->control, &h->bulk_out, &h->bulk_in)) {
+        return false;
+    }
+
+    h->read_aiob.fd = h->bulk_out.get();
+    h->write_aiob.fd = h->bulk_in.get();
+    h->reads_zero_packets = true;
+    return true;
+}
+
+static void usb_legacy_ffs_open_thread(usb_handle* usb) {
+    adb_thread_setname("usb legacy ffs open");
+
+    while (true) {
+        // wait until the USB device needs opening
+        std::unique_lock<std::mutex> lock(usb->lock);
+        while (!usb->open_new_connection) {
+            usb->notify.wait(lock);
+        }
+        usb->open_new_connection = false;
+        lock.unlock();
+
+        while (true) {
+            if (init_functionfs(usb)) {
+                LOG(INFO) << "functionfs successfully initialized";
+                break;
+            }
+            std::this_thread::sleep_for(1s);
+        }
+
+        LOG(INFO) << "registering usb transport";
+        register_usb_transport(usb, nullptr, nullptr, 1);
+    }
+
+    // never gets here
+    abort();
+}
+
+static int usb_ffs_write(usb_handle* h, const void* data, int len) {
+    D("about to write (fd=%d, len=%d)", h->bulk_in.get(), len);
+
+    const char* buf = static_cast<const char*>(data);
+    int orig_len = len;
+    while (len > 0) {
+        int write_len = std::min(USB_FFS_BULK_SIZE, len);
+        int n = adb_write(h->bulk_in, buf, write_len);
+        if (n < 0) {
+            D("ERROR: fd = %d, n = %d: %s", h->bulk_in.get(), n, strerror(errno));
+            return -1;
+        }
+        buf += n;
+        len -= n;
+    }
+
+    D("[ done fd=%d ]", h->bulk_in.get());
+    return orig_len;
+}
+
+static int usb_ffs_read(usb_handle* h, void* data, int len, bool allow_partial) {
+    D("about to read (fd=%d, len=%d)", h->bulk_out.get(), len);
+
+    char* buf = static_cast<char*>(data);
+    int orig_len = len;
+    unsigned count = 0;
+    while (len > 0) {
+        int read_len = std::min(USB_FFS_BULK_SIZE, len);
+        int n = adb_read(h->bulk_out, buf, read_len);
+        if (n < 0) {
+            D("ERROR: fd = %d, n = %d: %s", h->bulk_out.get(), n, strerror(errno));
+            return -1;
+        }
+        buf += n;
+        len -= n;
+        count += n;
+
+        // For fastbootd command such as "getvar all", len parameter is always set 64.
+        // But what we read is actually less than 64.
+        // For example, length 10 for "getvar all" command.
+        // If we get less data than expected, this means there should be no more data.
+        if (allow_partial && n < read_len) {
+            orig_len = count;
+            break;
+        }
+    }
+
+    D("[ done fd=%d ]", h->bulk_out.get());
+    return orig_len;
+}
+
+static int usb_ffs_do_aio(usb_handle* h, const void* data, int len, bool read) {
+    aio_block* aiob = read ? &h->read_aiob : &h->write_aiob;
+    bool zero_packet = false;
+
+    int num_bufs = len / h->io_size + (len % h->io_size == 0 ? 0 : 1);
+    const char* cur_data = reinterpret_cast<const char*>(data);
+    int packet_size = getMaxPacketSize(aiob->fd);
+
+    if (posix_madvise(const_cast<void*>(data), len, POSIX_MADV_SEQUENTIAL | POSIX_MADV_WILLNEED) <
+        0) {
+        D("[ Failed to madvise: %d ]", errno);
+    }
+
+    for (int i = 0; i < num_bufs; i++) {
+        int buf_len = std::min(len, static_cast<int>(h->io_size));
+        io_prep(&aiob->iocb[i], aiob->fd, cur_data, buf_len, 0, read);
+
+        len -= buf_len;
+        cur_data += buf_len;
+
+        if (len == 0 && buf_len % packet_size == 0 && read) {
+            // adb does not expect the device to send a zero packet after data transfer,
+            // but the host *does* send a zero packet for the device to read.
+            zero_packet = h->reads_zero_packets;
+        }
+    }
+    if (zero_packet) {
+        io_prep(&aiob->iocb[num_bufs], aiob->fd, reinterpret_cast<const void*>(cur_data),
+                packet_size, 0, read);
+        num_bufs += 1;
+    }
+
+    while (true) {
+        if (TEMP_FAILURE_RETRY(io_submit(aiob->ctx, num_bufs, aiob->iocbs.data())) < num_bufs) {
+            PLOG(ERROR) << "aio: got error submitting " << (read ? "read" : "write");
+            return -1;
+        }
+        if (TEMP_FAILURE_RETRY(io_getevents(aiob->ctx, num_bufs, num_bufs, aiob->events.data(),
+                                            nullptr)) < num_bufs) {
+            PLOG(ERROR) << "aio: got error waiting " << (read ? "read" : "write");
+            return -1;
+        }
+        if (num_bufs == 1 && aiob->events[0].res == -EINTR) {
+            continue;
+        }
+        int ret = 0;
+        for (int i = 0; i < num_bufs; i++) {
+            if (aiob->events[i].res < 0) {
+                errno = -aiob->events[i].res;
+                PLOG(ERROR) << "aio: got error event on " << (read ? "read" : "write")
+                            << " total bufs " << num_bufs;
+                return -1;
+            }
+            ret += aiob->events[i].res;
+        }
+        return ret;
+    }
+}
+
+static int usb_ffs_aio_read(usb_handle* h, void* data, int len, bool allow_partial) {
+    return usb_ffs_do_aio(h, data, len, true);
+}
+
+static int usb_ffs_aio_write(usb_handle* h, const void* data, int len) {
+    return usb_ffs_do_aio(h, data, len, false);
+}
+
+static void usb_ffs_kick(usb_handle* h) {
+    int err;
+
+    err = ioctl(h->bulk_in.get(), FUNCTIONFS_CLEAR_HALT);
+    if (err < 0) {
+        D("[ kick: source (fd=%d) clear halt failed (%d) ]", h->bulk_in.get(), errno);
+    }
+
+    err = ioctl(h->bulk_out.get(), FUNCTIONFS_CLEAR_HALT);
+    if (err < 0) {
+        D("[ kick: sink (fd=%d) clear halt failed (%d) ]", h->bulk_out.get(), errno);
+    }
+
+    // don't close ep0 here, since we may not need to reinitialize it with
+    // the same descriptors again. if however ep1/ep2 fail to re-open in
+    // init_functionfs, only then would we close and open ep0 again.
+    // Ditto the comment in usb_adb_kick.
+    h->kicked = true;
+    TEMP_FAILURE_RETRY(dup2(dummy_fd.get(), h->bulk_out.get()));
+    TEMP_FAILURE_RETRY(dup2(dummy_fd.get(), h->bulk_in.get()));
+}
+
+static void usb_ffs_close(usb_handle* h) {
+    LOG(INFO) << "closing functionfs transport";
+
+    h->kicked = false;
+    h->bulk_out.reset();
+    h->bulk_in.reset();
+
+    // Notify usb_adb_open_thread to open a new connection.
+    h->lock.lock();
+    h->open_new_connection = true;
+    h->lock.unlock();
+    h->notify.notify_one();
+}
+
+usb_handle* create_usb_handle(unsigned num_bufs, unsigned io_size) {
+    usb_handle* h = new usb_handle();
+
+    if (android::base::GetBoolProperty("sys.usb.ffs.aio_compat", false)) {
+        // Devices on older kernels (< 3.18) will not have aio support for ffs
+        // unless backported. Fall back on the non-aio functions instead.
+        h->write = usb_ffs_write;
+        h->read = usb_ffs_read;
+    } else {
+        h->write = usb_ffs_aio_write;
+        h->read = usb_ffs_aio_read;
+        aio_block_init(&h->read_aiob, num_bufs);
+        aio_block_init(&h->write_aiob, num_bufs);
+    }
+    h->io_size = io_size;
+    h->kick = usb_ffs_kick;
+    h->close = usb_ffs_close;
+    return h;
+}
+
+void usb_init_legacy() {
+    D("[ usb_init - using legacy FunctionFS ]");
+    dummy_fd.reset(adb_open("/dev/null", O_WRONLY | O_CLOEXEC));
+    CHECK_NE(-1, dummy_fd.get());
+
+    std::thread(usb_legacy_ffs_open_thread, create_usb_handle(USB_FFS_NUM_BUFS, USB_FFS_BULK_SIZE))
+            .detach();
+}
+
+int usb_write(usb_handle* h, const void* data, int len) {
+    return h->write(h, data, len);
+}
+
+int usb_read(usb_handle* h, void* data, int len) {
+    return h->read(h, data, len, false /* allow_partial */);
+}
+
+int usb_close(usb_handle* h) {
+    h->close(h);
+    return 0;
+}
+
+void usb_reset(usb_handle* h) {
+    usb_close(h);
+}
+
+void usb_kick(usb_handle* h) {
+    h->kick(h);
+}
diff --git a/adb/daemon/usb_legacy.h b/adb/daemon/usb_legacy.h
new file mode 100644
index 000000000..2204246c1
--- /dev/null
+++ b/adb/daemon/usb_legacy.h
@@ -0,0 +1,68 @@
+#pragma once
+
+/*
+ * Copyright (C) 2017 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 <linux/usb/functionfs.h>
+
+#include <atomic>
+#include <condition_variable>
+#include <mutex>
+#include <vector>
+
+#include <android-base/unique_fd.h>
+#include <asyncio/AsyncIO.h>
+
+struct aio_block {
+    std::vector<struct iocb> iocb;
+    std::vector<struct iocb*> iocbs;
+    std::vector<struct io_event> events;
+    aio_context_t ctx;
+    int num_submitted;
+    int fd;
+};
+
+struct usb_handle {
+    usb_handle() : kicked(false) {
+    }
+
+    std::condition_variable notify;
+    std::mutex lock;
+    std::atomic<bool> kicked;
+    bool open_new_connection = true;
+
+    int (*write)(usb_handle* h, const void* data, int len);
+    int (*read)(usb_handle* h, void* data, int len, bool allow_partial);
+    void (*kick)(usb_handle* h);
+    void (*close)(usb_handle* h);
+
+    // FunctionFS
+    android::base::unique_fd control;
+    android::base::unique_fd bulk_out;  // "out" from the host's perspective => source for adbd
+    android::base::unique_fd bulk_in;   // "in" from the host's perspective => sink for adbd
+
+    // Access to these blocks is very not thread safe. Have one block for each of the
+    // read and write threads.
+    struct aio_block read_aiob;
+    struct aio_block write_aiob;
+
+    bool reads_zero_packets;
+    size_t io_size;
+};
+
+usb_handle *create_usb_handle(unsigned num_bufs, unsigned io_size);
+bool open_functionfs(android::base::unique_fd* control, android::base::unique_fd* bulk_out,
+                     android::base::unique_fd* bulk_in);
diff --git a/adb/transport.cpp b/adb/transport.cpp
index fe286dee4..ca0092b8c 100644
--- a/adb/transport.cpp
+++ b/adb/transport.cpp
@@ -1453,7 +1453,7 @@ void kick_all_tcp_devices() {
 
 #endif
 
-#if ADB_HOST
+#if ADB_HOST || LEGACY_FFS
 void register_usb_transport(usb_handle* usb, const char* serial, const char* devpath,
                             unsigned writeable) {
     atransport* t = new atransport(writeable ? kCsOffline : kCsNoPerm);
diff --git a/adb/transport.h b/adb/transport.h
index 26d804b3f..ae6e9ad77 100644
--- a/adb/transport.h
+++ b/adb/transport.h
@@ -237,7 +237,7 @@ enum class ReconnectResult {
     Abort,
 };
 
-#if ADB_HOST
+#if ADB_HOST || LEGACY_FFS
 struct usb_handle;
 #endif
 
@@ -281,7 +281,7 @@ class atransport : public enable_weak_from_this<atransport> {
         return connection_;
     }
 
-#if ADB_HOST
+#if ADB_HOST || LEGACY_FFS
     void SetUsbHandle(usb_handle* h) { usb_handle_ = h; }
     usb_handle* GetUsbHandle() { return usb_handle_; }
 #endif
@@ -391,7 +391,7 @@ class atransport : public enable_weak_from_this<atransport> {
     // The underlying connection object.
     std::shared_ptr<Connection> connection_ GUARDED_BY(mutex_);
 
-#if ADB_HOST
+#if ADB_HOST || LEGACY_FFS
     // USB handle for the connection, if available.
     usb_handle* usb_handle_ = nullptr;
 #endif
@@ -436,7 +436,7 @@ void kick_all_transports_by_auth_key(std::string_view auth_key);
 
 void register_transport(atransport* transport);
 
-#if ADB_HOST
+#if ADB_HOST || LEGACY_FFS
 void init_usb_transport(atransport* t, usb_handle* usb);
 void register_usb_transport(usb_handle* h, const char* serial, const char* devpath,
                             unsigned writeable);
diff --git a/adb/transport_legacy.cpp b/adb/transport_legacy.cpp
new file mode 100644
index 000000000..777edde0b
--- /dev/null
+++ b/adb/transport_legacy.cpp
@@ -0,0 +1,212 @@
+/*
+ * Copyright (C) 2007 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.
+ */
+
+#define TRACE_TAG TRANSPORT
+
+#include "sysdeps.h"
+
+#include "client/usb.h"
+
+#include <memory>
+
+#include "sysdeps.h"
+#include "transport.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "adb.h"
+
+#if ADB_HOST
+
+#if defined(__APPLE__)
+#define CHECK_PACKET_OVERFLOW 0
+#else
+#define CHECK_PACKET_OVERFLOW 1
+#endif
+
+// Call usb_read using a buffer having a multiple of usb_get_max_packet_size() bytes
+// to avoid overflow. See http://libusb.sourceforge.net/api-1.0/packetoverflow.html.
+static int UsbReadMessage(usb_handle* h, amessage* msg) {
+    D("UsbReadMessage");
+
+#if CHECK_PACKET_OVERFLOW
+    size_t usb_packet_size = usb_get_max_packet_size(h);
+    CHECK_GE(usb_packet_size, sizeof(*msg));
+    CHECK_LT(usb_packet_size, 4096ULL);
+
+    char buffer[4096];
+    int n = usb_read(h, buffer, usb_packet_size);
+    if (n != sizeof(*msg)) {
+        D("usb_read returned unexpected length %d (expected %zu)", n, sizeof(*msg));
+        return -1;
+    }
+    memcpy(msg, buffer, sizeof(*msg));
+    return n;
+#else
+    return usb_read(h, msg, sizeof(*msg));
+#endif
+}
+
+// Call usb_read using a buffer having a multiple of usb_get_max_packet_size() bytes
+// to avoid overflow. See http://libusb.sourceforge.net/api-1.0/packetoverflow.html.
+static int UsbReadPayload(usb_handle* h, apacket* p) {
+    D("UsbReadPayload(%d)", p->msg.data_length);
+
+    if (p->msg.data_length > MAX_PAYLOAD) {
+        return -1;
+    }
+
+#if CHECK_PACKET_OVERFLOW
+    size_t usb_packet_size = usb_get_max_packet_size(h);
+
+    // Round the data length up to the nearest packet size boundary.
+    // The device won't send a zero packet for packet size aligned payloads,
+    // so don't read any more packets than needed.
+    size_t len = p->msg.data_length;
+    size_t rem_size = len % usb_packet_size;
+    if (rem_size) {
+        len += usb_packet_size - rem_size;
+    }
+
+    p->payload.resize(len);
+    int rc = usb_read(h, &p->payload[0], p->payload.size());
+    if (rc != static_cast<int>(p->msg.data_length)) {
+        return -1;
+    }
+
+    p->payload.resize(rc);
+    return rc;
+#else
+    p->payload.resize(p->msg.data_length);
+    return usb_read(h, &p->payload[0], p->payload.size());
+#endif
+}
+
+static int remote_read(apacket* p, usb_handle* usb) {
+    int n = UsbReadMessage(usb, &p->msg);
+    if (n < 0) {
+        D("remote usb: read terminated (message)");
+        return -1;
+    }
+    if (static_cast<size_t>(n) != sizeof(p->msg)) {
+        D("remote usb: read received unexpected header length %d", n);
+        return -1;
+    }
+    if (p->msg.data_length) {
+        n = UsbReadPayload(usb, p);
+        if (n < 0) {
+            D("remote usb: terminated (data)");
+            return -1;
+        }
+        if (static_cast<uint32_t>(n) != p->msg.data_length) {
+            D("remote usb: read payload failed (need %u bytes, give %d bytes), skip it",
+              p->msg.data_length, n);
+            return -1;
+        }
+    }
+    return 0;
+}
+
+#else
+
+// On Android devices, we rely on the kernel to provide buffered read.
+// So we can recover automatically from EOVERFLOW.
+static int remote_read(apacket* p, usb_handle* usb) {
+    if (usb_read(usb, &p->msg, sizeof(amessage)) != sizeof(amessage)) {
+        PLOG(ERROR) << "remote usb: read terminated (message)";
+        return -1;
+    }
+
+    if (p->msg.data_length) {
+        if (p->msg.data_length > MAX_PAYLOAD) {
+            PLOG(ERROR) << "remote usb: read overflow (data length = " << p->msg.data_length << ")";
+            return -1;
+        }
+
+        p->payload.resize(p->msg.data_length);
+        if (usb_read(usb, &p->payload[0], p->payload.size()) !=
+            static_cast<int>(p->payload.size())) {
+            PLOG(ERROR) << "remote usb: terminated (data)";
+            return -1;
+        }
+    }
+
+    return 0;
+}
+#endif
+
+UsbConnection::~UsbConnection() {
+    usb_close(handle_);
+}
+
+bool UsbConnection::Read(apacket* packet) {
+    int rc = remote_read(packet, handle_);
+    return rc == 0;
+}
+
+bool UsbConnection::Write(apacket* packet) {
+    int size = packet->msg.data_length;
+
+    if (usb_write(handle_, &packet->msg, sizeof(packet->msg)) != sizeof(packet->msg)) {
+        PLOG(ERROR) << "remote usb: 1 - write terminated";
+        return false;
+    }
+
+    if (packet->msg.data_length != 0 && usb_write(handle_, packet->payload.data(), size) != size) {
+        PLOG(ERROR) << "remote usb: 2 - write terminated";
+        return false;
+    }
+
+    return true;
+}
+
+bool UsbConnection::DoTlsHandshake(RSA* key, std::string* auth_key) {
+    // TODO: support TLS for usb connections
+    LOG(FATAL) << "Not supported yet.";
+    return false;
+}
+
+void UsbConnection::Reset() {
+    usb_reset(handle_);
+    usb_kick(handle_);
+}
+
+void UsbConnection::Close() {
+    usb_kick(handle_);
+}
+
+void init_usb_transport(atransport* t, usb_handle* h) {
+    D("transport: usb");
+    auto connection = std::make_unique<UsbConnection>(h);
+    t->SetConnection(std::make_unique<BlockingConnectionAdapter>(std::move(connection)));
+    t->type = kTransportUsb;
+    t->SetUsbHandle(h);
+}
+
+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 !ADB_HOST
+    return false;
+#else
+    static bool enable = getenv("ADB_LIBUSB") && strcmp(getenv("ADB_LIBUSB"), "1") == 0;
+    return enable;
+#endif
+}