libappfuse/FuseBridgeLoop.cc - android_system_core - Gitiles

 /*
  * Copyright (C) 2016 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 specic language governing permissions and
  * limitations under the License.
  */

 #include "libappfuse/FuseBridgeLoop.h"

 #include <sys/epoll.h>
 #include <sys/socket.h>

 #include <unordered_map>

 #include <android-base/logging.h>
 #include <android-base/unique_fd.h>

 #include "libappfuse/EpollController.h"

 namespace android {
 namespace fuse {
 namespace {

 enum class FuseBridgeState { kWaitToReadEither, kWaitToReadProxy, kWaitToWriteProxy, kClosing };

 struct FuseBridgeEntryEvent {
     FuseBridgeEntry* entry;
     int events;
 };

 void GetObservedEvents(FuseBridgeState state, int* device_events, int* proxy_events) {
     switch (state) {
         case FuseBridgeState::kWaitToReadEither:
             *device_events = EPOLLIN;
             *proxy_events = EPOLLIN;
             return;
         case FuseBridgeState::kWaitToReadProxy:
             *device_events = 0;
             *proxy_events = EPOLLIN;
             return;
         case FuseBridgeState::kWaitToWriteProxy:
             *device_events = 0;
             *proxy_events = EPOLLOUT;
             return;
         case FuseBridgeState::kClosing:
             *device_events = 0;
             *proxy_events = 0;
             return;
     }
 }

 void LogResponseError(const std::string& message, const FuseResponse& response) {
     LOG(ERROR) << message << ": header.len=" << response.header.len
                << " header.error=" << response.header.error
                << " header.unique=" << response.header.unique;
 }
 }

 class FuseBridgeEntry {
   public:
     FuseBridgeEntry(int mount_id, base::unique_fd&& dev_fd, base::unique_fd&& proxy_fd)
         : mount_id_(mount_id),
           device_fd_(std::move(dev_fd)),
           proxy_fd_(std::move(proxy_fd)),
           state_(FuseBridgeState::kWaitToReadEither),
           last_state_(FuseBridgeState::kWaitToReadEither),
           last_device_events_({this, 0}),
           last_proxy_events_({this, 0}),
           open_count_(0) {}

     // Transfer bytes depends on availability of FDs and the internal |state_|.
     void Transfer(FuseBridgeLoopCallback* callback) {
         constexpr int kUnexpectedEventMask = ~(EPOLLIN | EPOLLOUT);
         const bool unexpected_event = (last_device_events_.events & kUnexpectedEventMask) ||
                                       (last_proxy_events_.events & kUnexpectedEventMask);
         const bool device_read_ready = last_device_events_.events & EPOLLIN;
         const bool proxy_read_ready = last_proxy_events_.events & EPOLLIN;
         const bool proxy_write_ready = last_proxy_events_.events & EPOLLOUT;

         last_device_events_.events = 0;
         last_proxy_events_.events = 0;

         LOG(VERBOSE) << "Transfer device_read_ready=" << device_read_ready
                      << " proxy_read_ready=" << proxy_read_ready
                      << " proxy_write_ready=" << proxy_write_ready;

         if (unexpected_event) {
             LOG(ERROR) << "Invalid epoll event is observed";
             state_ = FuseBridgeState::kClosing;
             return;
         }

         switch (state_) {
             case FuseBridgeState::kWaitToReadEither:
                 if (proxy_read_ready) {
                     state_ = ReadFromProxy();
                 } else if (device_read_ready) {
                     state_ = ReadFromDevice(callback);
                 }
                 return;

             case FuseBridgeState::kWaitToReadProxy:
                 CHECK(proxy_read_ready);
                 state_ = ReadFromProxy();
                 return;

             case FuseBridgeState::kWaitToWriteProxy:
                 CHECK(proxy_write_ready);
                 state_ = WriteToProxy();
                 return;

             case FuseBridgeState::kClosing:
                 return;
         }
     }

     bool IsClosing() const { return state_ == FuseBridgeState::kClosing; }

     int mount_id() const { return mount_id_; }

   private:
     friend class BridgeEpollController;

     FuseBridgeState ReadFromProxy() {
         switch (buffer_.response.ReadOrAgain(proxy_fd_)) {
             case ResultOrAgain::kSuccess:
                 break;
             case ResultOrAgain::kFailure:
                 return FuseBridgeState::kClosing;
             case ResultOrAgain::kAgain:
                 return FuseBridgeState::kWaitToReadProxy;
         }

         if (!buffer_.response.Write(device_fd_)) {
             LogResponseError("Failed to write a reply from proxy to device", buffer_.response);
             return FuseBridgeState::kClosing;
         }

         auto it = opcode_map_.find(buffer_.response.header.unique);
         if (it != opcode_map_.end()) {
             switch (it->second) {
                 case FUSE_OPEN:
                     if (buffer_.response.header.error == fuse::kFuseSuccess) {
                         open_count_++;
                     }
                     break;

                 case FUSE_RELEASE:
                     if (open_count_ > 0) {
                         open_count_--;
                     } else {
                         LOG(WARNING) << "Unexpected FUSE_RELEASE before opening a file.";
                         break;
                     }
                     if (open_count_ == 0) {
                         return FuseBridgeState::kClosing;
                     }
                     break;
             }
             opcode_map_.erase(it);
         }

         return FuseBridgeState::kWaitToReadEither;
     }

     FuseBridgeState ReadFromDevice(FuseBridgeLoopCallback* callback) {
         LOG(VERBOSE) << "ReadFromDevice";
         if (!buffer_.request.Read(device_fd_)) {
             return FuseBridgeState::kClosing;
         }

         const uint32_t opcode = buffer_.request.header.opcode;
         const uint64_t unique = buffer_.request.header.unique;
         LOG(VERBOSE) << "Read a fuse packet, opcode=" << opcode << " unique=" << unique;
         if (unique == 0) {
             return FuseBridgeState::kWaitToReadEither;
         }
         switch (opcode) {
             case FUSE_FORGET:
                 // Do not reply to FUSE_FORGET.
                 return FuseBridgeState::kWaitToReadEither;

             case FUSE_LOOKUP:
             case FUSE_GETATTR:
             case FUSE_OPEN:
             case FUSE_READ:
             case FUSE_WRITE:
             case FUSE_RELEASE:
             case FUSE_FSYNC:
                 if (opcode == FUSE_OPEN || opcode == FUSE_RELEASE) {
                     opcode_map_.emplace(buffer_.request.header.unique, opcode);
                 }
                 return WriteToProxy();

             case FUSE_INIT:
                 buffer_.HandleInit();
                 break;

             default:
                 buffer_.HandleNotImpl();
                 break;
         }

         if (!buffer_.response.Write(device_fd_)) {
             LogResponseError("Failed to write a response to device", buffer_.response);
             return FuseBridgeState::kClosing;
         }

         if (opcode == FUSE_INIT) {
             callback->OnMount(mount_id_);
         }

         return FuseBridgeState::kWaitToReadEither;
     }

     FuseBridgeState WriteToProxy() {
         switch (buffer_.request.WriteOrAgain(proxy_fd_)) {
             case ResultOrAgain::kSuccess:
                 return FuseBridgeState::kWaitToReadEither;
             case ResultOrAgain::kFailure:
                 LOG(ERROR) << "Failed to write a request to proxy:"
                            << " header.len=" << buffer_.request.header.len
                            << " header.opcode=" << buffer_.request.header.opcode
                            << " header.unique=" << buffer_.request.header.unique
                            << " header.nodeid=" << buffer_.request.header.nodeid;
                 return FuseBridgeState::kClosing;
             case ResultOrAgain::kAgain:
                 return FuseBridgeState::kWaitToWriteProxy;
         }
     }

     const int mount_id_;
     base::unique_fd device_fd_;
     base::unique_fd proxy_fd_;
     FuseBuffer buffer_;
     FuseBridgeState state_;
     FuseBridgeState last_state_;
     FuseBridgeEntryEvent last_device_events_;
     FuseBridgeEntryEvent last_proxy_events_;

     // Remember map between unique and opcode in fuse_in_header so that we can
     // refer the opcode later.
     std::unordered_map<uint64_t, uint32_t> opcode_map_;

     int open_count_;

     DISALLOW_COPY_AND_ASSIGN(FuseBridgeEntry);
 };

 class BridgeEpollController : private EpollController {
   public:
     BridgeEpollController(base::unique_fd&& poll_fd) : EpollController(std::move(poll_fd)) {}

     bool AddBridgePoll(FuseBridgeEntry* bridge) const {
         return InvokeControl(EPOLL_CTL_ADD, bridge);
     }

     bool UpdateOrDeleteBridgePoll(FuseBridgeEntry* bridge) const {
         return InvokeControl(
             bridge->state_ != FuseBridgeState::kClosing ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, bridge);
     }

     bool Wait(size_t bridge_count, std::unordered_set<FuseBridgeEntry*>* entries_out) {
         CHECK(entries_out);
         const size_t event_count = std::max<size_t>(bridge_count * 2, 1);
         if (!EpollController::Wait(event_count)) {
             return false;
         }
         entries_out->clear();
         for (const auto& event : events()) {
             FuseBridgeEntryEvent* const entry_event =
                 reinterpret_cast<FuseBridgeEntryEvent*>(event.data.ptr);
             entry_event->events = event.events;
             entries_out->insert(entry_event->entry);
         }
         return true;
     }

   private:
     bool InvokeControl(int op, FuseBridgeEntry* bridge) const {
         LOG(VERBOSE) << "InvokeControl op=" << op << " bridge=" << bridge->mount_id_
                      << " state=" << static_cast<int>(bridge->state_)
                      << " last_state=" << static_cast<int>(bridge->last_state_);

         int last_device_events;
         int last_proxy_events;
         int device_events;
         int proxy_events;
         GetObservedEvents(bridge->last_state_, &last_device_events, &last_proxy_events);
         GetObservedEvents(bridge->state_, &device_events, &proxy_events);
         bool result = true;
         if (op != EPOLL_CTL_MOD || last_device_events != device_events) {
             result &= EpollController::InvokeControl(op, bridge->device_fd_, device_events,
                                                      &bridge->last_device_events_);
         }
         if (op != EPOLL_CTL_MOD || last_proxy_events != proxy_events) {
             result &= EpollController::InvokeControl(op, bridge->proxy_fd_, proxy_events,
                                                      &bridge->last_proxy_events_);
         }
         return result;
     }
 };

 FuseBridgeLoop::FuseBridgeLoop() : opened_(true) {
     base::unique_fd epoll_fd(epoll_create1(/* no flag */ 0));
     if (epoll_fd.get() == -1) {
         PLOG(ERROR) << "Failed to open FD for epoll";
         opened_ = false;
         return;
     }
     epoll_controller_.reset(new BridgeEpollController(std::move(epoll_fd)));
 }

 FuseBridgeLoop::~FuseBridgeLoop() { CHECK(bridges_.empty()); }

 bool FuseBridgeLoop::AddBridge(int mount_id, base::unique_fd dev_fd, base::unique_fd proxy_fd) {
     LOG(VERBOSE) << "Adding bridge " << mount_id;

     std::unique_ptr<FuseBridgeEntry> bridge(
         new FuseBridgeEntry(mount_id, std::move(dev_fd), std::move(proxy_fd)));
     std::lock_guard<std::mutex> lock(mutex_);
     if (!opened_) {
         LOG(ERROR) << "Tried to add a mount to a closed bridge";
         return false;
     }
     if (bridges_.count(mount_id)) {
         LOG(ERROR) << "Tried to add a mount point that has already been added";
         return false;
     }
     if (!epoll_controller_->AddBridgePoll(bridge.get())) {
         return false;
     }

     bridges_.emplace(mount_id, std::move(bridge));
     return true;
 }

 bool FuseBridgeLoop::ProcessEventLocked(const std::unordered_set<FuseBridgeEntry*>& entries,
                                         FuseBridgeLoopCallback* callback) {
     for (auto entry : entries) {
         entry->Transfer(callback);
         if (!epoll_controller_->UpdateOrDeleteBridgePoll(entry)) {
             return false;
         }
         if (entry->IsClosing()) {
             const int mount_id = entry->mount_id();
             callback->OnClosed(mount_id);
             bridges_.erase(mount_id);
             if (bridges_.size() == 0) {
                 // All bridges are now closed.
                 return false;
             }
         }
     }
     return true;
 }

 void FuseBridgeLoop::Start(FuseBridgeLoopCallback* callback) {
     LOG(DEBUG) << "Start fuse bridge loop";
     std::unordered_set<FuseBridgeEntry*> entries;
     while (true) {
         const bool wait_result = epoll_controller_->Wait(bridges_.size(), &entries);
         LOG(VERBOSE) << "Receive epoll events";
         {
             std::lock_guard<std::mutex> lock(mutex_);
             if (!(wait_result && ProcessEventLocked(entries, callback))) {
                 for (auto it = bridges_.begin(); it != bridges_.end();) {
                     callback->OnClosed(it->second->mount_id());
                     it = bridges_.erase(it);
                 }
                 opened_ = false;
                 return;
             }
         }
     }
 }

 }  // namespace fuse
 }  // namespace android
	/*
	* Copyright (C) 2016 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 specic language governing permissions and
	* limitations under the License.
	*/

	#include "libappfuse/FuseBridgeLoop.h"

	#include <sys/epoll.h>
	#include <sys/socket.h>

	#include <unordered_map>

	#include <android-base/logging.h>
	#include <android-base/unique_fd.h>

	#include "libappfuse/EpollController.h"

	namespace android {
	namespace fuse {
	namespace {

	enum class FuseBridgeState { kWaitToReadEither, kWaitToReadProxy, kWaitToWriteProxy, kClosing };

	struct FuseBridgeEntryEvent {
	FuseBridgeEntry* entry;
	int events;
	};

	void GetObservedEvents(FuseBridgeState state, int* device_events, int* proxy_events) {
	switch (state) {
	case FuseBridgeState::kWaitToReadEither:
	*device_events = EPOLLIN;
	*proxy_events = EPOLLIN;
	return;
	case FuseBridgeState::kWaitToReadProxy:
	*device_events = 0;
	*proxy_events = EPOLLIN;
	return;
	case FuseBridgeState::kWaitToWriteProxy:
	*device_events = 0;
	*proxy_events = EPOLLOUT;
	return;
	case FuseBridgeState::kClosing:
	*device_events = 0;
	*proxy_events = 0;
	return;
	}
	}

	void LogResponseError(const std::string& message, const FuseResponse& response) {
	LOG(ERROR) << message << ": header.len=" << response.header.len
	<< " header.error=" << response.header.error
	<< " header.unique=" << response.header.unique;
	}
	}

	class FuseBridgeEntry {
	public:
	FuseBridgeEntry(int mount_id, base::unique_fd&& dev_fd, base::unique_fd&& proxy_fd)
	: mount_id_(mount_id),
	device_fd_(std::move(dev_fd)),
	proxy_fd_(std::move(proxy_fd)),
	state_(FuseBridgeState::kWaitToReadEither),
	last_state_(FuseBridgeState::kWaitToReadEither),
	last_device_events_({this, 0}),
	last_proxy_events_({this, 0}),
	open_count_(0) {}

	// Transfer bytes depends on availability of FDs and the internal \|state_\|.
	void Transfer(FuseBridgeLoopCallback* callback) {
	constexpr int kUnexpectedEventMask = ~(EPOLLIN \| EPOLLOUT);
	const bool unexpected_event = (last_device_events_.events & kUnexpectedEventMask) \|\|
	(last_proxy_events_.events & kUnexpectedEventMask);
	const bool device_read_ready = last_device_events_.events & EPOLLIN;
	const bool proxy_read_ready = last_proxy_events_.events & EPOLLIN;
	const bool proxy_write_ready = last_proxy_events_.events & EPOLLOUT;

	last_device_events_.events = 0;
	last_proxy_events_.events = 0;

	LOG(VERBOSE) << "Transfer device_read_ready=" << device_read_ready
	<< " proxy_read_ready=" << proxy_read_ready
	<< " proxy_write_ready=" << proxy_write_ready;

	if (unexpected_event) {
	LOG(ERROR) << "Invalid epoll event is observed";
	state_ = FuseBridgeState::kClosing;
	return;
	}

	switch (state_) {
	case FuseBridgeState::kWaitToReadEither:
	if (proxy_read_ready) {
	state_ = ReadFromProxy();
	} else if (device_read_ready) {
	state_ = ReadFromDevice(callback);
	}
	return;

	case FuseBridgeState::kWaitToReadProxy:
	CHECK(proxy_read_ready);
	state_ = ReadFromProxy();
	return;

	case FuseBridgeState::kWaitToWriteProxy:
	CHECK(proxy_write_ready);
	state_ = WriteToProxy();
	return;

	case FuseBridgeState::kClosing:
	return;
	}
	}

	bool IsClosing() const { return state_ == FuseBridgeState::kClosing; }

	int mount_id() const { return mount_id_; }

	private:
	friend class BridgeEpollController;

	FuseBridgeState ReadFromProxy() {
	switch (buffer_.response.ReadOrAgain(proxy_fd_)) {
	case ResultOrAgain::kSuccess:
	break;
	case ResultOrAgain::kFailure:
	return FuseBridgeState::kClosing;
	case ResultOrAgain::kAgain:
	return FuseBridgeState::kWaitToReadProxy;
	}

	if (!buffer_.response.Write(device_fd_)) {
	LogResponseError("Failed to write a reply from proxy to device", buffer_.response);
	return FuseBridgeState::kClosing;
	}

	auto it = opcode_map_.find(buffer_.response.header.unique);
	if (it != opcode_map_.end()) {
	switch (it->second) {
	case FUSE_OPEN:
	if (buffer_.response.header.error == fuse::kFuseSuccess) {
	open_count_++;
	}
	break;

	case FUSE_RELEASE:
	if (open_count_ > 0) {
	open_count_--;
	} else {
	LOG(WARNING) << "Unexpected FUSE_RELEASE before opening a file.";
	break;
	}
	if (open_count_ == 0) {
	return FuseBridgeState::kClosing;
	}
	break;
	}
	opcode_map_.erase(it);
	}

	return FuseBridgeState::kWaitToReadEither;
	}

	FuseBridgeState ReadFromDevice(FuseBridgeLoopCallback* callback) {
	LOG(VERBOSE) << "ReadFromDevice";
	if (!buffer_.request.Read(device_fd_)) {
	return FuseBridgeState::kClosing;
	}

	const uint32_t opcode = buffer_.request.header.opcode;
	const uint64_t unique = buffer_.request.header.unique;
	LOG(VERBOSE) << "Read a fuse packet, opcode=" << opcode << " unique=" << unique;
	if (unique == 0) {
	return FuseBridgeState::kWaitToReadEither;
	}
	switch (opcode) {
	case FUSE_FORGET:
	// Do not reply to FUSE_FORGET.
	return FuseBridgeState::kWaitToReadEither;

	case FUSE_LOOKUP:
	case FUSE_GETATTR:
	case FUSE_OPEN:
	case FUSE_READ:
	case FUSE_WRITE:
	case FUSE_RELEASE:
	case FUSE_FSYNC:
	if (opcode == FUSE_OPEN \|\| opcode == FUSE_RELEASE) {
	opcode_map_.emplace(buffer_.request.header.unique, opcode);
	}
	return WriteToProxy();

	case FUSE_INIT:
	buffer_.HandleInit();
	break;

	default:
	buffer_.HandleNotImpl();
	break;
	}

	if (!buffer_.response.Write(device_fd_)) {
	LogResponseError("Failed to write a response to device", buffer_.response);
	return FuseBridgeState::kClosing;
	}

	if (opcode == FUSE_INIT) {
	callback->OnMount(mount_id_);
	}

	return FuseBridgeState::kWaitToReadEither;
	}

	FuseBridgeState WriteToProxy() {
	switch (buffer_.request.WriteOrAgain(proxy_fd_)) {
	case ResultOrAgain::kSuccess:
	return FuseBridgeState::kWaitToReadEither;
	case ResultOrAgain::kFailure:
	LOG(ERROR) << "Failed to write a request to proxy:"
	<< " header.len=" << buffer_.request.header.len
	<< " header.opcode=" << buffer_.request.header.opcode
	<< " header.unique=" << buffer_.request.header.unique
	<< " header.nodeid=" << buffer_.request.header.nodeid;
	return FuseBridgeState::kClosing;
	case ResultOrAgain::kAgain:
	return FuseBridgeState::kWaitToWriteProxy;
	}
	}

	const int mount_id_;
	base::unique_fd device_fd_;
	base::unique_fd proxy_fd_;
	FuseBuffer buffer_;
	FuseBridgeState state_;
	FuseBridgeState last_state_;
	FuseBridgeEntryEvent last_device_events_;
	FuseBridgeEntryEvent last_proxy_events_;

	// Remember map between unique and opcode in fuse_in_header so that we can
	// refer the opcode later.
	std::unordered_map<uint64_t, uint32_t> opcode_map_;

	int open_count_;

	DISALLOW_COPY_AND_ASSIGN(FuseBridgeEntry);
	};

	class BridgeEpollController : private EpollController {
	public:
	BridgeEpollController(base::unique_fd&& poll_fd) : EpollController(std::move(poll_fd)) {}

	bool AddBridgePoll(FuseBridgeEntry* bridge) const {
	return InvokeControl(EPOLL_CTL_ADD, bridge);
	}

	bool UpdateOrDeleteBridgePoll(FuseBridgeEntry* bridge) const {
	return InvokeControl(
	bridge->state_ != FuseBridgeState::kClosing ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, bridge);
	}

	bool Wait(size_t bridge_count, std::unordered_set<FuseBridgeEntry> entries_out) {
	CHECK(entries_out);
	const size_t event_count = std::max<size_t>(bridge_count * 2, 1);
	if (!EpollController::Wait(event_count)) {
	return false;
	}
	entries_out->clear();
	for (const auto& event : events()) {
	FuseBridgeEntryEvent* const entry_event =
	reinterpret_cast<FuseBridgeEntryEvent*>(event.data.ptr);
	entry_event->events = event.events;
	entries_out->insert(entry_event->entry);
	}
	return true;
	}

	private:
	bool InvokeControl(int op, FuseBridgeEntry* bridge) const {
	LOG(VERBOSE) << "InvokeControl op=" << op << " bridge=" << bridge->mount_id_
	<< " state=" << static_cast<int>(bridge->state_)
	<< " last_state=" << static_cast<int>(bridge->last_state_);

	int last_device_events;
	int last_proxy_events;
	int device_events;
	int proxy_events;
	GetObservedEvents(bridge->last_state_, &last_device_events, &last_proxy_events);
	GetObservedEvents(bridge->state_, &device_events, &proxy_events);
	bool result = true;
	if (op != EPOLL_CTL_MOD \|\| last_device_events != device_events) {
	result &= EpollController::InvokeControl(op, bridge->device_fd_, device_events,
	&bridge->last_device_events_);
	}
	if (op != EPOLL_CTL_MOD \|\| last_proxy_events != proxy_events) {
	result &= EpollController::InvokeControl(op, bridge->proxy_fd_, proxy_events,
	&bridge->last_proxy_events_);
	}
	return result;
	}
	};

	FuseBridgeLoop::FuseBridgeLoop() : opened_(true) {
	base::unique_fd epoll_fd(epoll_create1(/* no flag */ 0));
	if (epoll_fd.get() == -1) {
	PLOG(ERROR) << "Failed to open FD for epoll";
	opened_ = false;
	return;
	}
	epoll_controller_.reset(new BridgeEpollController(std::move(epoll_fd)));
	}

	FuseBridgeLoop::~FuseBridgeLoop() { CHECK(bridges_.empty()); }

	bool FuseBridgeLoop::AddBridge(int mount_id, base::unique_fd dev_fd, base::unique_fd proxy_fd) {
	LOG(VERBOSE) << "Adding bridge " << mount_id;

	std::unique_ptr<FuseBridgeEntry> bridge(
	new FuseBridgeEntry(mount_id, std::move(dev_fd), std::move(proxy_fd)));
	std::lock_guard<std::mutex> lock(mutex_);
	if (!opened_) {
	LOG(ERROR) << "Tried to add a mount to a closed bridge";
	return false;
	}
	if (bridges_.count(mount_id)) {
	LOG(ERROR) << "Tried to add a mount point that has already been added";
	return false;
	}
	if (!epoll_controller_->AddBridgePoll(bridge.get())) {
	return false;
	}

	bridges_.emplace(mount_id, std::move(bridge));
	return true;
	}

	bool FuseBridgeLoop::ProcessEventLocked(const std::unordered_set<FuseBridgeEntry*>& entries,
	FuseBridgeLoopCallback* callback) {
	for (auto entry : entries) {
	entry->Transfer(callback);
	if (!epoll_controller_->UpdateOrDeleteBridgePoll(entry)) {
	return false;
	}
	if (entry->IsClosing()) {
	const int mount_id = entry->mount_id();
	callback->OnClosed(mount_id);
	bridges_.erase(mount_id);
	if (bridges_.size() == 0) {
	// All bridges are now closed.
	return false;
	}
	}
	}
	return true;
	}

	void FuseBridgeLoop::Start(FuseBridgeLoopCallback* callback) {
	LOG(DEBUG) << "Start fuse bridge loop";
	std::unordered_set<FuseBridgeEntry*> entries;
	while (true) {
	const bool wait_result = epoll_controller_->Wait(bridges_.size(), &entries);
	LOG(VERBOSE) << "Receive epoll events";
	{
	std::lock_guard<std::mutex> lock(mutex_);
	if (!(wait_result && ProcessEventLocked(entries, callback))) {
	for (auto it = bridges_.begin(); it != bridges_.end();) {
	callback->OnClosed(it->second->mount_id());
	it = bridges_.erase(it);
	}
	opened_ = false;
	return;
	}
	}
	}
	}

	} // namespace fuse
	} // namespace android