adb/daemon/usb.cpp - third_party/android/platform/system/core - Git at Google

 /*
  * Copyright (C) 2018 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 <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/ioctl.h>
 #include <sys/types.h>
 #include <unistd.h>

 #include <linux/usb/functionfs.h>
 #include <sys/eventfd.h>

 #include <algorithm>
 #include <array>
 #include <future>
 #include <memory>
 #include <mutex>
 #include <optional>
 #include <vector>

 #include <asyncio/AsyncIO.h>

 #include <android-base/logging.h>
 #include <android-base/macros.h>
 #include <android-base/properties.h>
 #include <android-base/thread_annotations.h>

 #include <adbd/usb.h>

 #include "adb_unique_fd.h"
 #include "adb_utils.h"
 #include "sysdeps/chrono.h"
 #include "transport.h"
 #include "types.h"

 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.
 static constexpr size_t kUsbReadQueueDepth = 8;
 static constexpr size_t kUsbReadSize = 4 * PAGE_SIZE;

 static constexpr size_t kUsbWriteQueueDepth = 8;
 static constexpr size_t kUsbWriteSize = 4 * PAGE_SIZE;

 static const char* to_string(enum usb_functionfs_event_type type) {
     switch (type) {
         case FUNCTIONFS_BIND:
             return "FUNCTIONFS_BIND";
         case FUNCTIONFS_UNBIND:
             return "FUNCTIONFS_UNBIND";
         case FUNCTIONFS_ENABLE:
             return "FUNCTIONFS_ENABLE";
         case FUNCTIONFS_DISABLE:
             return "FUNCTIONFS_DISABLE";
         case FUNCTIONFS_SETUP:
             return "FUNCTIONFS_SETUP";
         case FUNCTIONFS_SUSPEND:
             return "FUNCTIONFS_SUSPEND";
         case FUNCTIONFS_RESUME:
             return "FUNCTIONFS_RESUME";
     }
 }

 enum class TransferDirection : uint64_t {
     READ = 0,
     WRITE = 1,
 };

 struct TransferId {
     TransferDirection direction : 1;
     uint64_t id : 63;

     TransferId() : TransferId(TransferDirection::READ, 0) {}

   private:
     TransferId(TransferDirection direction, uint64_t id) : direction(direction), id(id) {}

   public:
     explicit operator uint64_t() const {
         uint64_t result;
         static_assert(sizeof(*this) == sizeof(result));
         memcpy(&result, this, sizeof(*this));
         return result;
     }

     static TransferId read(uint64_t id) { return TransferId(TransferDirection::READ, id); }
     static TransferId write(uint64_t id) { return TransferId(TransferDirection::WRITE, id); }

     static TransferId from_value(uint64_t value) {
         TransferId result;
         memcpy(&result, &value, sizeof(value));
         return result;
     }
 };

 struct IoBlock {
     bool pending = false;
     struct iocb control = {};
     std::shared_ptr<Block> payload;

     TransferId id() const { return TransferId::from_value(control.aio_data); }
 };

 struct ScopedAioContext {
     ScopedAioContext() = default;
     ~ScopedAioContext() { reset(); }

     ScopedAioContext(ScopedAioContext&& move) { reset(move.release()); }
     ScopedAioContext(const ScopedAioContext& copy) = delete;

     ScopedAioContext& operator=(ScopedAioContext&& move) {
         reset(move.release());
         return *this;
     }
     ScopedAioContext& operator=(const ScopedAioContext& copy) = delete;

     static ScopedAioContext Create(size_t max_events) {
         aio_context_t ctx = 0;
         if (io_setup(max_events, &ctx) != 0) {
             PLOG(FATAL) << "failed to create aio_context_t";
         }
         ScopedAioContext result;
         result.reset(ctx);
         return result;
     }

     aio_context_t release() {
         aio_context_t result = context_;
         context_ = 0;
         return result;
     }

     void reset(aio_context_t new_context = 0) {
         if (context_ != 0) {
             io_destroy(context_);
         }

         context_ = new_context;
     }

     aio_context_t get() { return context_; }

   private:
     aio_context_t context_ = 0;
 };

 struct UsbFfsConnection : public Connection {
     UsbFfsConnection(unique_fd control, unique_fd read, unique_fd write,
                      std::promise<void> destruction_notifier)
         : worker_started_(false),
           stopped_(false),
           destruction_notifier_(std::move(destruction_notifier)),
           control_fd_(std::move(control)),
           read_fd_(std::move(read)),
           write_fd_(std::move(write)) {
         LOG(INFO) << "UsbFfsConnection constructed";
         worker_event_fd_.reset(eventfd(0, EFD_CLOEXEC));
         if (worker_event_fd_ == -1) {
             PLOG(FATAL) << "failed to create eventfd";
         }

         monitor_event_fd_.reset(eventfd(0, EFD_CLOEXEC));
         if (monitor_event_fd_ == -1) {
             PLOG(FATAL) << "failed to create eventfd";
         }

         aio_context_ = ScopedAioContext::Create(kUsbReadQueueDepth + kUsbWriteQueueDepth);
     }

     ~UsbFfsConnection() {
         LOG(INFO) << "UsbFfsConnection being destroyed";
         Stop();
         monitor_thread_.join();

         // We need to explicitly close our file descriptors before we notify our destruction,
         // because the thread listening on the future will immediately try to reopen the endpoint.
         aio_context_.reset();
         control_fd_.reset();
         read_fd_.reset();
         write_fd_.reset();

         destruction_notifier_.set_value();
     }

     virtual bool Write(std::unique_ptr<apacket> packet) override final {
         LOG(DEBUG) << "USB write: " << dump_header(&packet->msg);
         Block header(sizeof(packet->msg));
         memcpy(header.data(), &packet->msg, sizeof(packet->msg));

         std::lock_guard<std::mutex> lock(write_mutex_);
         write_requests_.push_back(CreateWriteBlock(std::move(header), next_write_id_++));
         if (!packet->payload.empty()) {
             // The kernel attempts to allocate a contiguous block of memory for each write,
             // which can fail if the write is large and the kernel heap is fragmented.
             // Split large writes into smaller chunks to avoid this.
             std::shared_ptr<Block> payload = std::make_shared<Block>(std::move(packet->payload));
             size_t offset = 0;
             size_t len = payload->size();

             while (len > 0) {
                 size_t write_size = std::min(kUsbWriteSize, len);
                 write_requests_.push_back(
                         CreateWriteBlock(payload, offset, write_size, next_write_id_++));
                 len -= write_size;
                 offset += write_size;
             }
         }
         SubmitWrites();
         return true;
     }

     virtual void Start() override final { StartMonitor(); }

     virtual void Stop() override final {
         if (stopped_.exchange(true)) {
             return;
         }
         stopped_ = true;
         uint64_t notify = 1;
         ssize_t rc = adb_write(worker_event_fd_.get(), &notify, sizeof(notify));
         if (rc < 0) {
             PLOG(FATAL) << "failed to notify worker eventfd to stop UsbFfsConnection";
         }
         CHECK_EQ(static_cast<size_t>(rc), sizeof(notify));

         rc = adb_write(monitor_event_fd_.get(), &notify, sizeof(notify));
         if (rc < 0) {
             PLOG(FATAL) << "failed to notify monitor eventfd to stop UsbFfsConnection";
         }

         CHECK_EQ(static_cast<size_t>(rc), sizeof(notify));
     }

   private:
     void StartMonitor() {
         // This is a bit of a mess.
         // It's possible for io_submit to end up blocking, if we call it as the endpoint
         // becomes disabled. Work around this by having a monitor thread to listen for functionfs
         // lifecycle events. If we notice an error condition (either we've become disabled, or we
         // were never enabled in the first place), we send interruption signals to the worker thread
         // until it dies, and then report failure to the transport via HandleError, which will
         // eventually result in the transport being destroyed, which will result in UsbFfsConnection
         // being destroyed, which unblocks the open thread and restarts this entire process.
         static std::once_flag handler_once;
         std::call_once(handler_once, []() { signal(kInterruptionSignal, [](int) {}); });

         monitor_thread_ = std::thread([this]() {
             adb_thread_setname("UsbFfs-monitor");

             bool bound = false;
             bool enabled = false;
             bool running = true;
             while (running) {
                 adb_pollfd pfd[2] = {
                   { .fd = control_fd_.get(), .events = POLLIN, .revents = 0 },
                   { .fd = monitor_event_fd_.get(), .events = POLLIN, .revents = 0 },
                 };

                 // If we don't see our first bind within a second, try again.
                 int timeout_ms = bound ? -1 : 1000;

                 int rc = TEMP_FAILURE_RETRY(adb_poll(pfd, 2, timeout_ms));
                 if (rc == -1) {
                     PLOG(FATAL) << "poll on USB control fd failed";
                 } else if (rc == 0) {
                     LOG(WARNING) << "timed out while waiting for FUNCTIONFS_BIND, trying again";
                     break;
                 }

                 if (pfd[1].revents) {
                     // We were told to die.
                     break;
                 }

                 struct usb_functionfs_event event;
                 rc = TEMP_FAILURE_RETRY(adb_read(control_fd_.get(), &event, sizeof(event)));
                 if (rc == -1) {
                     PLOG(FATAL) << "failed to read functionfs event";
                 } else if (rc == 0) {
                     LOG(WARNING) << "hit EOF on functionfs control fd";
                     break;
                 } else if (rc != sizeof(event)) {
                     LOG(FATAL) << "read functionfs event of unexpected size, expected "
                                << sizeof(event) << ", got " << rc;
                 }

                 LOG(INFO) << "USB event: "
                           << to_string(static_cast<usb_functionfs_event_type>(event.type));

                 switch (event.type) {
                     case FUNCTIONFS_BIND:
                         if (bound) {
                             LOG(WARNING) << "received FUNCTIONFS_BIND while already bound?";
                             running = false;
                             break;
                         }

                         if (enabled) {
                             LOG(WARNING) << "received FUNCTIONFS_BIND while already enabled?";
                             running = false;
                             break;
                         }

                         bound = true;
                         break;

                     case FUNCTIONFS_ENABLE:
                         if (!bound) {
                             LOG(WARNING) << "received FUNCTIONFS_ENABLE while not bound?";
                             running = false;
                             break;
                         }

                         if (enabled) {
                             LOG(WARNING) << "received FUNCTIONFS_ENABLE while already enabled?";
                             running = false;
                             break;
                         }

                         enabled = true;
                         StartWorker();
                         break;

                     case FUNCTIONFS_DISABLE:
                         if (!bound) {
                             LOG(WARNING) << "received FUNCTIONFS_DISABLE while not bound?";
                         }

                         if (!enabled) {
                             LOG(WARNING) << "received FUNCTIONFS_DISABLE while not enabled?";
                         }

                         enabled = false;
                         running = false;
                         break;

                     case FUNCTIONFS_UNBIND:
                         if (enabled) {
                             LOG(WARNING) << "received FUNCTIONFS_UNBIND while still enabled?";
                         }

                         if (!bound) {
                             LOG(WARNING) << "received FUNCTIONFS_UNBIND when not bound?";
                         }

                         bound = false;
                         running = false;
                         break;

                     case FUNCTIONFS_SETUP: {
                         LOG(INFO) << "received FUNCTIONFS_SETUP control transfer: bRequestType = "
                                   << static_cast<int>(event.u.setup.bRequestType)
                                   << ", bRequest = " << static_cast<int>(event.u.setup.bRequest)
                                   << ", wValue = " << static_cast<int>(event.u.setup.wValue)
                                   << ", wIndex = " << static_cast<int>(event.u.setup.wIndex)
                                   << ", wLength = " << static_cast<int>(event.u.setup.wLength);

                         if ((event.u.setup.bRequestType & USB_DIR_IN)) {
                             LOG(INFO) << "acking device-to-host control transfer";
                             ssize_t rc = adb_write(control_fd_.get(), "", 0);
                             if (rc != 0) {
                                 PLOG(ERROR) << "failed to write empty packet to host";
                                 break;
                             }
                         } else {
                             std::string buf;
                             buf.resize(event.u.setup.wLength + 1);

                             ssize_t rc = adb_read(control_fd_.get(), buf.data(), buf.size());
                             if (rc != event.u.setup.wLength) {
                                 LOG(ERROR)
                                         << "read " << rc
                                         << " bytes when trying to read control request, expected "
                                         << event.u.setup.wLength;
                             }

                             LOG(INFO) << "control request contents: " << buf;
                             break;
                         }
                     }
                 }
             }

             StopWorker();
             HandleError("monitor thread finished");
         });
     }

     void StartWorker() {
         CHECK(!worker_started_);
         worker_started_ = true;
         worker_thread_ = std::thread([this]() {
             adb_thread_setname("UsbFfs-worker");
             for (size_t i = 0; i < kUsbReadQueueDepth; ++i) {
                 read_requests_[i] = CreateReadBlock(next_read_id_++);
                 if (!SubmitRead(&read_requests_[i])) {
                     return;
                 }
             }

             while (!stopped_) {
                 uint64_t dummy;
                 ssize_t rc = adb_read(worker_event_fd_.get(), &dummy, sizeof(dummy));
                 if (rc == -1) {
                     PLOG(FATAL) << "failed to read from eventfd";
                 } else if (rc == 0) {
                     LOG(FATAL) << "hit EOF on eventfd";
                 }

                 ReadEvents();
             }
         });
     }

     void StopWorker() {
         if (!worker_started_) {
             return;
         }

         pthread_t worker_thread_handle = worker_thread_.native_handle();
         while (true) {
             int rc = pthread_kill(worker_thread_handle, kInterruptionSignal);
             if (rc != 0) {
                 LOG(ERROR) << "failed to send interruption signal to worker: " << strerror(rc);
                 break;
             }

             std::this_thread::sleep_for(100ms);

             rc = pthread_kill(worker_thread_handle, 0);
             if (rc == 0) {
                 continue;
             } else if (rc == ESRCH) {
                 break;
             } else {
                 LOG(ERROR) << "failed to send interruption signal to worker: " << strerror(rc);
             }
         }

         worker_thread_.join();
     }

     void PrepareReadBlock(IoBlock* block, uint64_t id) {
         block->pending = false;
         block->payload = std::make_shared<Block>(kUsbReadSize);
         block->control.aio_data = static_cast<uint64_t>(TransferId::read(id));
         block->control.aio_buf = reinterpret_cast<uintptr_t>(block->payload->data());
         block->control.aio_nbytes = block->payload->size();
     }

     IoBlock CreateReadBlock(uint64_t id) {
         IoBlock block;
         PrepareReadBlock(&block, id);
         block.control.aio_rw_flags = 0;
         block.control.aio_lio_opcode = IOCB_CMD_PREAD;
         block.control.aio_reqprio = 0;
         block.control.aio_fildes = read_fd_.get();
         block.control.aio_offset = 0;
         block.control.aio_flags = IOCB_FLAG_RESFD;
         block.control.aio_resfd = worker_event_fd_.get();
         return block;
     }

     void ReadEvents() {
         static constexpr size_t kMaxEvents = kUsbReadQueueDepth + kUsbWriteQueueDepth;
         struct io_event events[kMaxEvents];
         struct timespec timeout = {.tv_sec = 0, .tv_nsec = 0};
         int rc = io_getevents(aio_context_.get(), 0, kMaxEvents, events, &timeout);
         if (rc == -1) {
             HandleError(StringPrintf("io_getevents failed while reading: %s", strerror(errno)));
             return;
         }

         for (int event_idx = 0; event_idx < rc; ++event_idx) {
             auto& event = events[event_idx];
             TransferId id = TransferId::from_value(event.data);

             if (event.res < 0) {
                 std::string error =
                         StringPrintf("%s %" PRIu64 " failed with error %s",
                                      id.direction == TransferDirection::READ ? "read" : "write",
                                      id.id, strerror(-event.res));
                 HandleError(error);
                 return;
             }

             if (id.direction == TransferDirection::READ) {
                 if (!HandleRead(id, event.res)) {
                     return;
                 }
             } else {
                 HandleWrite(id);
             }
         }
     }

     bool HandleRead(TransferId id, int64_t size) {
         uint64_t read_idx = id.id % kUsbReadQueueDepth;
         IoBlock* block = &read_requests_[read_idx];
         block->pending = false;
         block->payload->resize(size);

         // Notification for completed reads can be received out of order.
         if (block->id().id != needed_read_id_) {
             LOG(VERBOSE) << "read " << block->id().id << " completed while waiting for "
                          << needed_read_id_;
             return true;
         }

         for (uint64_t id = needed_read_id_;; ++id) {
             size_t read_idx = id % kUsbReadQueueDepth;
             IoBlock* current_block = &read_requests_[read_idx];
             if (current_block->pending) {
                 break;
             }
             if (!ProcessRead(current_block)) {
                 return false;
             }
             ++needed_read_id_;
         }

         return true;
     }

     bool ProcessRead(IoBlock* block) {
         if (!block->payload->empty()) {
             if (!incoming_header_.has_value()) {
                 if (block->payload->size() != sizeof(amessage)) {
                     HandleError("received packet of unexpected length while reading header");
                     return false;
                 }
                 amessage msg;
                 memcpy(&msg, block->payload->data(), sizeof(amessage));
                 LOG(DEBUG) << "USB read:" << dump_header(&msg);
                 incoming_header_ = msg;
             } else {
                 size_t bytes_left = incoming_header_->data_length - incoming_payload_.size();
                 Block payload = std::move(*block->payload);
                 if (block->payload->size() > bytes_left) {
                     HandleError("received too many bytes while waiting for payload");
                     return false;
                 }
                 incoming_payload_.append(std::make_unique<Block>(std::move(payload)));
             }

             if (incoming_header_->data_length == incoming_payload_.size()) {
                 auto packet = std::make_unique<apacket>();
                 packet->msg = *incoming_header_;

                 // TODO: Make apacket contain an IOVector so we don't have to coalesce.
                 packet->payload = incoming_payload_.coalesce();
                 read_callback_(this, std::move(packet));

                 incoming_header_.reset();
                 incoming_payload_.clear();
             }
         }

         PrepareReadBlock(block, block->id().id + kUsbReadQueueDepth);
         SubmitRead(block);
         return true;
     }

     bool SubmitRead(IoBlock* block) {
         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;
     }

     void HandleWrite(TransferId id) {
         std::lock_guard<std::mutex> lock(write_mutex_);
         auto it =
                 std::find_if(write_requests_.begin(), write_requests_.end(), [id](const auto& req) {
                     return static_cast<uint64_t>(req->id()) == static_cast<uint64_t>(id);
                 });
         CHECK(it != write_requests_.end());

         write_requests_.erase(it);
         size_t outstanding_writes = --writes_submitted_;
         LOG(DEBUG) << "USB write: reaped, down to " << outstanding_writes;

         SubmitWrites();
     }

     std::unique_ptr<IoBlock> CreateWriteBlock(std::shared_ptr<Block> payload, size_t offset,
                                               size_t len, uint64_t id) {
         auto block = std::make_unique<IoBlock>();
         block->payload = std::move(payload);
         block->control.aio_data = static_cast<uint64_t>(TransferId::write(id));
         block->control.aio_rw_flags = 0;
         block->control.aio_lio_opcode = IOCB_CMD_PWRITE;
         block->control.aio_reqprio = 0;
         block->control.aio_fildes = write_fd_.get();
         block->control.aio_buf = reinterpret_cast<uintptr_t>(block->payload->data() + offset);
         block->control.aio_nbytes = len;
         block->control.aio_offset = 0;
         block->control.aio_flags = IOCB_FLAG_RESFD;
         block->control.aio_resfd = worker_event_fd_.get();
         return block;
     }

     std::unique_ptr<IoBlock> CreateWriteBlock(Block payload, uint64_t id) {
         std::shared_ptr<Block> block = std::make_shared<Block>(std::move(payload));
         size_t len = block->size();
         return CreateWriteBlock(std::move(block), 0, len, id);
     }

     void SubmitWrites() REQUIRES(write_mutex_) {
         if (writes_submitted_ == kUsbWriteQueueDepth) {
             return;
         }

         ssize_t writes_to_submit = std::min(kUsbWriteQueueDepth - writes_submitted_,
                                             write_requests_.size() - writes_submitted_);
         CHECK_GE(writes_to_submit, 0);
         if (writes_to_submit == 0) {
             return;
         }

         struct iocb* iocbs[kUsbWriteQueueDepth];
         for (int i = 0; i < writes_to_submit; ++i) {
             CHECK(!write_requests_[writes_submitted_ + i]->pending);
             write_requests_[writes_submitted_ + i]->pending = true;
             iocbs[i] = &write_requests_[writes_submitted_ + i]->control;
             LOG(VERBOSE) << "submitting write_request " << static_cast<void*>(iocbs[i]);
         }

         writes_submitted_ += writes_to_submit;

         int rc = io_submit(aio_context_.get(), writes_to_submit, iocbs);
         if (rc == -1) {
             HandleError(StringPrintf("failed to submit write requests: %s", strerror(errno)));
             return;
         } else if (rc != writes_to_submit) {
             LOG(FATAL) << "failed to submit all writes: wanted to submit " << writes_to_submit
                        << ", actually submitted " << rc;
         }
     }

     void HandleError(const std::string& error) {
         std::call_once(error_flag_, [&]() {
             error_callback_(this, error);
             if (!stopped_) {
                 Stop();
             }
         });
     }

     std::thread monitor_thread_;

     bool worker_started_;
     std::thread worker_thread_;

     std::atomic<bool> stopped_;
     std::promise<void> destruction_notifier_;
     std::once_flag error_flag_;

     unique_fd worker_event_fd_;
     unique_fd monitor_event_fd_;

     ScopedAioContext aio_context_;
     unique_fd control_fd_;
     unique_fd read_fd_;
     unique_fd write_fd_;

     std::optional<amessage> incoming_header_;
     IOVector incoming_payload_;

     std::array<IoBlock, kUsbReadQueueDepth> read_requests_;
     IOVector read_data_;

     // ID of the next request that we're going to send out.
     size_t next_read_id_ = 0;

     // ID of the next packet we're waiting for.
     size_t needed_read_id_ = 0;

     std::mutex write_mutex_;
     std::deque<std::unique_ptr<IoBlock>> write_requests_ GUARDED_BY(write_mutex_);
     size_t next_write_id_ GUARDED_BY(write_mutex_) = 0;
     size_t writes_submitted_ GUARDED_BY(write_mutex_) = 0;

     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;
         if (!open_functionfs(&control, &bulk_out, &bulk_in)) {
             std::this_thread::sleep_for(1s);
             continue;
         }

         atransport* transport = new atransport();
         transport->serial = "UsbFfs";
         std::promise<void> destruction_notifier;
         std::future<void> future = destruction_notifier.get_future();
         transport->SetConnection(std::make_unique<UsbFfsConnection>(
                 std::move(control), std::move(bulk_out), std::move(bulk_in),
                 std::move(destruction_notifier)));
         register_transport(transport);
         future.wait();
     }
 }

 void usb_init() {
     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();
     }
 }
	/*
	* Copyright (C) 2018 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 <errno.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>
	#include <sys/ioctl.h>
	#include <sys/types.h>
	#include <unistd.h>

	#include <linux/usb/functionfs.h>
	#include <sys/eventfd.h>

	#include <algorithm>
	#include <array>
	#include <future>
	#include <memory>
	#include <mutex>
	#include <optional>
	#include <vector>

	#include <asyncio/AsyncIO.h>

	#include <android-base/logging.h>
	#include <android-base/macros.h>
	#include <android-base/properties.h>
	#include <android-base/thread_annotations.h>

	#include <adbd/usb.h>

	#include "adb_unique_fd.h"
	#include "adb_utils.h"
	#include "sysdeps/chrono.h"
	#include "transport.h"
	#include "types.h"

	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.
	static constexpr size_t kUsbReadQueueDepth = 8;
	static constexpr size_t kUsbReadSize = 4 * PAGE_SIZE;

	static constexpr size_t kUsbWriteQueueDepth = 8;
	static constexpr size_t kUsbWriteSize = 4 * PAGE_SIZE;

	static const char* to_string(enum usb_functionfs_event_type type) {
	switch (type) {
	case FUNCTIONFS_BIND:
	return "FUNCTIONFS_BIND";
	case FUNCTIONFS_UNBIND:
	return "FUNCTIONFS_UNBIND";
	case FUNCTIONFS_ENABLE:
	return "FUNCTIONFS_ENABLE";
	case FUNCTIONFS_DISABLE:
	return "FUNCTIONFS_DISABLE";
	case FUNCTIONFS_SETUP:
	return "FUNCTIONFS_SETUP";
	case FUNCTIONFS_SUSPEND:
	return "FUNCTIONFS_SUSPEND";
	case FUNCTIONFS_RESUME:
	return "FUNCTIONFS_RESUME";
	}
	}

	enum class TransferDirection : uint64_t {
	READ = 0,
	WRITE = 1,
	};

	struct TransferId {
	TransferDirection direction : 1;
	uint64_t id : 63;

	TransferId() : TransferId(TransferDirection::READ, 0) {}

	private:
	TransferId(TransferDirection direction, uint64_t id) : direction(direction), id(id) {}

	public:
	explicit operator uint64_t() const {
	uint64_t result;
	static_assert(sizeof(*this) == sizeof(result));
	memcpy(&result, this, sizeof(*this));
	return result;
	}

	static TransferId read(uint64_t id) { return TransferId(TransferDirection::READ, id); }
	static TransferId write(uint64_t id) { return TransferId(TransferDirection::WRITE, id); }

	static TransferId from_value(uint64_t value) {
	TransferId result;
	memcpy(&result, &value, sizeof(value));
	return result;
	}
	};

	struct IoBlock {
	bool pending = false;
	struct iocb control = {};
	std::shared_ptr<Block> payload;

	TransferId id() const { return TransferId::from_value(control.aio_data); }
	};

	struct ScopedAioContext {
	ScopedAioContext() = default;
	~ScopedAioContext() { reset(); }

	ScopedAioContext(ScopedAioContext&& move) { reset(move.release()); }
	ScopedAioContext(const ScopedAioContext& copy) = delete;

	ScopedAioContext& operator=(ScopedAioContext&& move) {
	reset(move.release());
	return *this;
	}
	ScopedAioContext& operator=(const ScopedAioContext& copy) = delete;

	static ScopedAioContext Create(size_t max_events) {
	aio_context_t ctx = 0;
	if (io_setup(max_events, &ctx) != 0) {
	PLOG(FATAL) << "failed to create aio_context_t";
	}
	ScopedAioContext result;
	result.reset(ctx);
	return result;
	}

	aio_context_t release() {
	aio_context_t result = context_;
	context_ = 0;
	return result;
	}

	void reset(aio_context_t new_context = 0) {
	if (context_ != 0) {
	io_destroy(context_);
	}

	context_ = new_context;
	}

	aio_context_t get() { return context_; }

	private:
	aio_context_t context_ = 0;
	};

	struct UsbFfsConnection : public Connection {
	UsbFfsConnection(unique_fd control, unique_fd read, unique_fd write,
	std::promise<void> destruction_notifier)
	: worker_started_(false),
	stopped_(false),
	destruction_notifier_(std::move(destruction_notifier)),
	control_fd_(std::move(control)),
	read_fd_(std::move(read)),
	write_fd_(std::move(write)) {
	LOG(INFO) << "UsbFfsConnection constructed";
	worker_event_fd_.reset(eventfd(0, EFD_CLOEXEC));
	if (worker_event_fd_ == -1) {
	PLOG(FATAL) << "failed to create eventfd";
	}

	monitor_event_fd_.reset(eventfd(0, EFD_CLOEXEC));
	if (monitor_event_fd_ == -1) {
	PLOG(FATAL) << "failed to create eventfd";
	}

	aio_context_ = ScopedAioContext::Create(kUsbReadQueueDepth + kUsbWriteQueueDepth);
	}

	~UsbFfsConnection() {
	LOG(INFO) << "UsbFfsConnection being destroyed";
	Stop();
	monitor_thread_.join();

	// We need to explicitly close our file descriptors before we notify our destruction,
	// because the thread listening on the future will immediately try to reopen the endpoint.
	aio_context_.reset();
	control_fd_.reset();
	read_fd_.reset();
	write_fd_.reset();

	destruction_notifier_.set_value();
	}

	virtual bool Write(std::unique_ptr<apacket> packet) override final {
	LOG(DEBUG) << "USB write: " << dump_header(&packet->msg);
	Block header(sizeof(packet->msg));
	memcpy(header.data(), &packet->msg, sizeof(packet->msg));

	std::lock_guard<std::mutex> lock(write_mutex_);
	write_requests_.push_back(CreateWriteBlock(std::move(header), next_write_id_++));
	if (!packet->payload.empty()) {
	// The kernel attempts to allocate a contiguous block of memory for each write,
	// which can fail if the write is large and the kernel heap is fragmented.
	// Split large writes into smaller chunks to avoid this.
	std::shared_ptr<Block> payload = std::make_shared<Block>(std::move(packet->payload));
	size_t offset = 0;
	size_t len = payload->size();

	while (len > 0) {
	size_t write_size = std::min(kUsbWriteSize, len);
	write_requests_.push_back(
	CreateWriteBlock(payload, offset, write_size, next_write_id_++));
	len -= write_size;
	offset += write_size;
	}
	}
	SubmitWrites();
	return true;
	}

	virtual void Start() override final { StartMonitor(); }

	virtual void Stop() override final {
	if (stopped_.exchange(true)) {
	return;
	}
	stopped_ = true;
	uint64_t notify = 1;
	ssize_t rc = adb_write(worker_event_fd_.get(), &notify, sizeof(notify));
	if (rc < 0) {
	PLOG(FATAL) << "failed to notify worker eventfd to stop UsbFfsConnection";
	}
	CHECK_EQ(static_cast<size_t>(rc), sizeof(notify));

	rc = adb_write(monitor_event_fd_.get(), &notify, sizeof(notify));
	if (rc < 0) {
	PLOG(FATAL) << "failed to notify monitor eventfd to stop UsbFfsConnection";
	}

	CHECK_EQ(static_cast<size_t>(rc), sizeof(notify));
	}

	private:
	void StartMonitor() {
	// This is a bit of a mess.
	// It's possible for io_submit to end up blocking, if we call it as the endpoint
	// becomes disabled. Work around this by having a monitor thread to listen for functionfs
	// lifecycle events. If we notice an error condition (either we've become disabled, or we
	// were never enabled in the first place), we send interruption signals to the worker thread
	// until it dies, and then report failure to the transport via HandleError, which will
	// eventually result in the transport being destroyed, which will result in UsbFfsConnection
	// being destroyed, which unblocks the open thread and restarts this entire process.
	static std::once_flag handler_once;
	std::call_once(handler_once, []() { signal(kInterruptionSignal, [](int) {}); });

	monitor_thread_ = std::thread([this]() {
	adb_thread_setname("UsbFfs-monitor");

	bool bound = false;
	bool enabled = false;
	bool running = true;
	while (running) {
	adb_pollfd pfd[2] = {
	{ .fd = control_fd_.get(), .events = POLLIN, .revents = 0 },
	{ .fd = monitor_event_fd_.get(), .events = POLLIN, .revents = 0 },
	};

	// If we don't see our first bind within a second, try again.
	int timeout_ms = bound ? -1 : 1000;

	int rc = TEMP_FAILURE_RETRY(adb_poll(pfd, 2, timeout_ms));
	if (rc == -1) {
	PLOG(FATAL) << "poll on USB control fd failed";
	} else if (rc == 0) {
	LOG(WARNING) << "timed out while waiting for FUNCTIONFS_BIND, trying again";
	break;
	}

	if (pfd[1].revents) {
	// We were told to die.
	break;
	}

	struct usb_functionfs_event event;
	rc = TEMP_FAILURE_RETRY(adb_read(control_fd_.get(), &event, sizeof(event)));
	if (rc == -1) {
	PLOG(FATAL) << "failed to read functionfs event";
	} else if (rc == 0) {
	LOG(WARNING) << "hit EOF on functionfs control fd";
	break;
	} else if (rc != sizeof(event)) {
	LOG(FATAL) << "read functionfs event of unexpected size, expected "
	<< sizeof(event) << ", got " << rc;
	}

	LOG(INFO) << "USB event: "
	<< to_string(static_cast<usb_functionfs_event_type>(event.type));

	switch (event.type) {
	case FUNCTIONFS_BIND:
	if (bound) {
	LOG(WARNING) << "received FUNCTIONFS_BIND while already bound?";
	running = false;
	break;
	}

	if (enabled) {
	LOG(WARNING) << "received FUNCTIONFS_BIND while already enabled?";
	running = false;
	break;
	}

	bound = true;
	break;

	case FUNCTIONFS_ENABLE:
	if (!bound) {
	LOG(WARNING) << "received FUNCTIONFS_ENABLE while not bound?";
	running = false;
	break;
	}

	if (enabled) {
	LOG(WARNING) << "received FUNCTIONFS_ENABLE while already enabled?";
	running = false;
	break;
	}

	enabled = true;
	StartWorker();
	break;

	case FUNCTIONFS_DISABLE:
	if (!bound) {
	LOG(WARNING) << "received FUNCTIONFS_DISABLE while not bound?";
	}

	if (!enabled) {
	LOG(WARNING) << "received FUNCTIONFS_DISABLE while not enabled?";
	}

	enabled = false;
	running = false;
	break;

	case FUNCTIONFS_UNBIND:
	if (enabled) {
	LOG(WARNING) << "received FUNCTIONFS_UNBIND while still enabled?";
	}

	if (!bound) {
	LOG(WARNING) << "received FUNCTIONFS_UNBIND when not bound?";
	}

	bound = false;
	running = false;
	break;

	case FUNCTIONFS_SETUP: {
	LOG(INFO) << "received FUNCTIONFS_SETUP control transfer: bRequestType = "
	<< static_cast<int>(event.u.setup.bRequestType)
	<< ", bRequest = " << static_cast<int>(event.u.setup.bRequest)
	<< ", wValue = " << static_cast<int>(event.u.setup.wValue)
	<< ", wIndex = " << static_cast<int>(event.u.setup.wIndex)
	<< ", wLength = " << static_cast<int>(event.u.setup.wLength);

	if ((event.u.setup.bRequestType & USB_DIR_IN)) {
	LOG(INFO) << "acking device-to-host control transfer";
	ssize_t rc = adb_write(control_fd_.get(), "", 0);
	if (rc != 0) {
	PLOG(ERROR) << "failed to write empty packet to host";
	break;
	}
	} else {
	std::string buf;
	buf.resize(event.u.setup.wLength + 1);

	ssize_t rc = adb_read(control_fd_.get(), buf.data(), buf.size());
	if (rc != event.u.setup.wLength) {
	LOG(ERROR)
	<< "read " << rc
	<< " bytes when trying to read control request, expected "
	<< event.u.setup.wLength;
	}

	LOG(INFO) << "control request contents: " << buf;
	break;
	}
	}
	}
	}

	StopWorker();
	HandleError("monitor thread finished");
	});
	}

	void StartWorker() {
	CHECK(!worker_started_);
	worker_started_ = true;
	worker_thread_ = std::thread([this]() {
	adb_thread_setname("UsbFfs-worker");
	for (size_t i = 0; i < kUsbReadQueueDepth; ++i) {
	read_requests_[i] = CreateReadBlock(next_read_id_++);
	if (!SubmitRead(&read_requests_[i])) {
	return;
	}
	}

	while (!stopped_) {
	uint64_t dummy;
	ssize_t rc = adb_read(worker_event_fd_.get(), &dummy, sizeof(dummy));
	if (rc == -1) {
	PLOG(FATAL) << "failed to read from eventfd";
	} else if (rc == 0) {
	LOG(FATAL) << "hit EOF on eventfd";
	}

	ReadEvents();
	}
	});
	}

	void StopWorker() {
	if (!worker_started_) {
	return;
	}

	pthread_t worker_thread_handle = worker_thread_.native_handle();
	while (true) {
	int rc = pthread_kill(worker_thread_handle, kInterruptionSignal);
	if (rc != 0) {
	LOG(ERROR) << "failed to send interruption signal to worker: " << strerror(rc);
	break;
	}

	std::this_thread::sleep_for(100ms);

	rc = pthread_kill(worker_thread_handle, 0);
	if (rc == 0) {
	continue;
	} else if (rc == ESRCH) {
	break;
	} else {
	LOG(ERROR) << "failed to send interruption signal to worker: " << strerror(rc);
	}
	}

	worker_thread_.join();
	}

	void PrepareReadBlock(IoBlock* block, uint64_t id) {
	block->pending = false;
	block->payload = std::make_shared<Block>(kUsbReadSize);
	block->control.aio_data = static_cast<uint64_t>(TransferId::read(id));
	block->control.aio_buf = reinterpret_cast<uintptr_t>(block->payload->data());
	block->control.aio_nbytes = block->payload->size();
	}

	IoBlock CreateReadBlock(uint64_t id) {
	IoBlock block;
	PrepareReadBlock(&block, id);
	block.control.aio_rw_flags = 0;
	block.control.aio_lio_opcode = IOCB_CMD_PREAD;
	block.control.aio_reqprio = 0;
	block.control.aio_fildes = read_fd_.get();
	block.control.aio_offset = 0;
	block.control.aio_flags = IOCB_FLAG_RESFD;
	block.control.aio_resfd = worker_event_fd_.get();
	return block;
	}

	void ReadEvents() {
	static constexpr size_t kMaxEvents = kUsbReadQueueDepth + kUsbWriteQueueDepth;
	struct io_event events[kMaxEvents];
	struct timespec timeout = {.tv_sec = 0, .tv_nsec = 0};
	int rc = io_getevents(aio_context_.get(), 0, kMaxEvents, events, &timeout);
	if (rc == -1) {
	HandleError(StringPrintf("io_getevents failed while reading: %s", strerror(errno)));
	return;
	}

	for (int event_idx = 0; event_idx < rc; ++event_idx) {
	auto& event = events[event_idx];
	TransferId id = TransferId::from_value(event.data);

	if (event.res < 0) {
	std::string error =
	StringPrintf("%s %" PRIu64 " failed with error %s",
	id.direction == TransferDirection::READ ? "read" : "write",
	id.id, strerror(-event.res));
	HandleError(error);
	return;
	}

	if (id.direction == TransferDirection::READ) {
	if (!HandleRead(id, event.res)) {
	return;
	}
	} else {
	HandleWrite(id);
	}
	}
	}

	bool HandleRead(TransferId id, int64_t size) {
	uint64_t read_idx = id.id % kUsbReadQueueDepth;
	IoBlock* block = &read_requests_[read_idx];
	block->pending = false;
	block->payload->resize(size);

	// Notification for completed reads can be received out of order.
	if (block->id().id != needed_read_id_) {
	LOG(VERBOSE) << "read " << block->id().id << " completed while waiting for "
	<< needed_read_id_;
	return true;
	}

	for (uint64_t id = needed_read_id_;; ++id) {
	size_t read_idx = id % kUsbReadQueueDepth;
	IoBlock* current_block = &read_requests_[read_idx];
	if (current_block->pending) {
	break;
	}
	if (!ProcessRead(current_block)) {
	return false;
	}
	++needed_read_id_;
	}

	return true;
	}

	bool ProcessRead(IoBlock* block) {
	if (!block->payload->empty()) {
	if (!incoming_header_.has_value()) {
	if (block->payload->size() != sizeof(amessage)) {
	HandleError("received packet of unexpected length while reading header");
	return false;
	}
	amessage msg;
	memcpy(&msg, block->payload->data(), sizeof(amessage));
	LOG(DEBUG) << "USB read:" << dump_header(&msg);
	incoming_header_ = msg;
	} else {
	size_t bytes_left = incoming_header_->data_length - incoming_payload_.size();
	Block payload = std::move(*block->payload);
	if (block->payload->size() > bytes_left) {
	HandleError("received too many bytes while waiting for payload");
	return false;
	}
	incoming_payload_.append(std::make_unique<Block>(std::move(payload)));
	}

	if (incoming_header_->data_length == incoming_payload_.size()) {
	auto packet = std::make_unique<apacket>();
	packet->msg = *incoming_header_;

	// TODO: Make apacket contain an IOVector so we don't have to coalesce.
	packet->payload = incoming_payload_.coalesce();
	read_callback_(this, std::move(packet));

	incoming_header_.reset();
	incoming_payload_.clear();
	}
	}

	PrepareReadBlock(block, block->id().id + kUsbReadQueueDepth);
	SubmitRead(block);
	return true;
	}

	bool SubmitRead(IoBlock* block) {
	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;
	}

	void HandleWrite(TransferId id) {
	std::lock_guard<std::mutex> lock(write_mutex_);
	auto it =
	std::find_if(write_requests_.begin(), write_requests_.end(), [id](const auto& req) {
	return static_cast<uint64_t>(req->id()) == static_cast<uint64_t>(id);
	});
	CHECK(it != write_requests_.end());

	write_requests_.erase(it);
	size_t outstanding_writes = --writes_submitted_;
	LOG(DEBUG) << "USB write: reaped, down to " << outstanding_writes;

	SubmitWrites();
	}

	std::unique_ptr<IoBlock> CreateWriteBlock(std::shared_ptr<Block> payload, size_t offset,
	size_t len, uint64_t id) {
	auto block = std::make_unique<IoBlock>();
	block->payload = std::move(payload);
	block->control.aio_data = static_cast<uint64_t>(TransferId::write(id));
	block->control.aio_rw_flags = 0;
	block->control.aio_lio_opcode = IOCB_CMD_PWRITE;
	block->control.aio_reqprio = 0;
	block->control.aio_fildes = write_fd_.get();
	block->control.aio_buf = reinterpret_cast<uintptr_t>(block->payload->data() + offset);
	block->control.aio_nbytes = len;
	block->control.aio_offset = 0;
	block->control.aio_flags = IOCB_FLAG_RESFD;
	block->control.aio_resfd = worker_event_fd_.get();
	return block;
	}

	std::unique_ptr<IoBlock> CreateWriteBlock(Block payload, uint64_t id) {
	std::shared_ptr<Block> block = std::make_shared<Block>(std::move(payload));
	size_t len = block->size();
	return CreateWriteBlock(std::move(block), 0, len, id);
	}

	void SubmitWrites() REQUIRES(write_mutex_) {
	if (writes_submitted_ == kUsbWriteQueueDepth) {
	return;
	}

	ssize_t writes_to_submit = std::min(kUsbWriteQueueDepth - writes_submitted_,
	write_requests_.size() - writes_submitted_);
	CHECK_GE(writes_to_submit, 0);
	if (writes_to_submit == 0) {
	return;
	}

	struct iocb* iocbs[kUsbWriteQueueDepth];
	for (int i = 0; i < writes_to_submit; ++i) {
	CHECK(!write_requests_[writes_submitted_ + i]->pending);
	write_requests_[writes_submitted_ + i]->pending = true;
	iocbs[i] = &write_requests_[writes_submitted_ + i]->control;
	LOG(VERBOSE) << "submitting write_request " << static_cast<void*>(iocbs[i]);
	}

	writes_submitted_ += writes_to_submit;

	int rc = io_submit(aio_context_.get(), writes_to_submit, iocbs);
	if (rc == -1) {
	HandleError(StringPrintf("failed to submit write requests: %s", strerror(errno)));
	return;
	} else if (rc != writes_to_submit) {
	LOG(FATAL) << "failed to submit all writes: wanted to submit " << writes_to_submit
	<< ", actually submitted " << rc;
	}
	}

	void HandleError(const std::string& error) {
	std::call_once(error_flag_, [&]() {
	error_callback_(this, error);
	if (!stopped_) {
	Stop();
	}
	});
	}

	std::thread monitor_thread_;

	bool worker_started_;
	std::thread worker_thread_;

	std::atomic<bool> stopped_;
	std::promise<void> destruction_notifier_;
	std::once_flag error_flag_;

	unique_fd worker_event_fd_;
	unique_fd monitor_event_fd_;

	ScopedAioContext aio_context_;
	unique_fd control_fd_;
	unique_fd read_fd_;
	unique_fd write_fd_;

	std::optional<amessage> incoming_header_;
	IOVector incoming_payload_;

	std::array<IoBlock, kUsbReadQueueDepth> read_requests_;
	IOVector read_data_;

	// ID of the next request that we're going to send out.
	size_t next_read_id_ = 0;

	// ID of the next packet we're waiting for.
	size_t needed_read_id_ = 0;

	std::mutex write_mutex_;
	std::deque<std::unique_ptr<IoBlock>> write_requests_ GUARDED_BY(write_mutex_);
	size_t next_write_id_ GUARDED_BY(write_mutex_) = 0;
	size_t writes_submitted_ GUARDED_BY(write_mutex_) = 0;

	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;
	if (!open_functionfs(&control, &bulk_out, &bulk_in)) {
	std::this_thread::sleep_for(1s);
	continue;
	}

	atransport* transport = new atransport();
	transport->serial = "UsbFfs";
	std::promise<void> destruction_notifier;
	std::future<void> future = destruction_notifier.get_future();
	transport->SetConnection(std::make_unique<UsbFfsConnection>(
	std::move(control), std::move(bulk_out), std::move(bulk_in),
	std::move(destruction_notifier)));
	register_transport(transport);
	future.wait();
	}
	}

	void usb_init() {
	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();
	}
	}