debuggerd/tombstoned/tombstoned.cpp - LeafOS-Project/android_system_core - Gitiles

 /*
  * Copyright 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 specific language governing permissions and
  * limitations under the License.
  */

 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>

 #include <array>
 #include <deque>
 #include <string>
 #include <unordered_map>
 #include <utility>

 #include <event2/event.h>
 #include <event2/listener.h>
 #include <event2/thread.h>

 #include <android-base/cmsg.h>
 #include <android-base/logging.h>
 #include <android-base/properties.h>
 #include <android-base/stringprintf.h>
 #include <android-base/unique_fd.h>
 #include <cutils/sockets.h>

 #include "debuggerd/handler.h"
 #include "dump_type.h"
 #include "protocol.h"
 #include "util.h"

 #include "intercept_manager.h"

 using android::base::GetIntProperty;
 using android::base::SendFileDescriptors;
 using android::base::StringPrintf;

 using android::base::borrowed_fd;
 using android::base::unique_fd;

 static InterceptManager* intercept_manager;

 enum CrashStatus {
   kCrashStatusRunning,
   kCrashStatusQueued,
 };

 struct CrashArtifact {
   unique_fd fd;
   std::optional<std::string> temporary_path;

   static CrashArtifact devnull() {
     CrashArtifact result;
     result.fd.reset(open("/dev/null", O_WRONLY | O_CLOEXEC));
     return result;
   }
 };

 struct CrashArtifactPaths {
   std::string text;
   std::optional<std::string> proto;
 };

 struct CrashOutput {
   CrashArtifact text;
   std::optional<CrashArtifact> proto;
 };

 // Ownership of Crash is a bit messy.
 // It's either owned by an active event that must have a timeout, or owned by
 // queued_requests, in the case that multiple crashes come in at the same time.
 struct Crash {
   ~Crash() { event_free(crash_event); }

   CrashOutput output;
   unique_fd crash_socket_fd;
   pid_t crash_pid;
   event* crash_event = nullptr;

   DebuggerdDumpType crash_type;
 };

 class CrashQueue {
  public:
   CrashQueue(const std::string& dir_path, const std::string& file_name_prefix, size_t max_artifacts,
              size_t max_concurrent_dumps, bool supports_proto)
       : file_name_prefix_(file_name_prefix),
         dir_path_(dir_path),
         dir_fd_(open(dir_path.c_str(), O_DIRECTORY | O_RDONLY | O_CLOEXEC)),
         max_artifacts_(max_artifacts),
         next_artifact_(0),
         max_concurrent_dumps_(max_concurrent_dumps),
         num_concurrent_dumps_(0),
         supports_proto_(supports_proto) {
     if (dir_fd_ == -1) {
       PLOG(FATAL) << "failed to open directory: " << dir_path;
     }

     // NOTE: If max_artifacts_ <= max_concurrent_dumps_, then theoretically the
     // same filename could be handed out to multiple processes.
     CHECK(max_artifacts_ > max_concurrent_dumps_);

     find_oldest_artifact();
   }

   static CrashQueue* for_crash(const Crash* crash) {
     return (crash->crash_type == kDebuggerdJavaBacktrace) ? for_anrs() : for_tombstones();
   }

   static CrashQueue* for_crash(const std::unique_ptr<Crash>& crash) {
     return for_crash(crash.get());
   }

   static CrashQueue* for_tombstones() {
     static CrashQueue queue("/data/tombstones", "tombstone_" /* file_name_prefix */,
                             GetIntProperty("tombstoned.max_tombstone_count", 32),
                             1 /* max_concurrent_dumps */, true /* supports_proto */);
     return &queue;
   }

   static CrashQueue* for_anrs() {
     static CrashQueue queue("/data/anr", "trace_" /* file_name_prefix */,
                             GetIntProperty("tombstoned.max_anr_count", 64),
                             4 /* max_concurrent_dumps */, false /* supports_proto */);
     return &queue;
   }

   CrashArtifact create_temporary_file() const {
     CrashArtifact result;

     std::optional<std::string> path;
     result.fd.reset(openat(dir_fd_, ".", O_WRONLY | O_APPEND | O_TMPFILE | O_CLOEXEC, 0660));
     if (result.fd == -1) {
       // We might not have O_TMPFILE. Try creating with an arbitrary filename instead.
       static size_t counter = 0;
       std::string tmp_filename = StringPrintf(".temporary%zu", counter++);
       result.fd.reset(openat(dir_fd_, tmp_filename.c_str(),
                              O_WRONLY | O_APPEND | O_CREAT | O_TRUNC | O_CLOEXEC, 0660));
       if (result.fd == -1) {
         PLOG(FATAL) << "failed to create temporary tombstone in " << dir_path_;
       }

       result.temporary_path = std::move(tmp_filename);
     }

     return std::move(result);
   }

   std::optional<CrashOutput> get_output(DebuggerdDumpType dump_type) {
     CrashOutput result;

     switch (dump_type) {
       case kDebuggerdNativeBacktrace:
         // Don't generate tombstones for native backtrace requests.
         return {};

       case kDebuggerdTombstoneProto:
         if (!supports_proto_) {
           LOG(ERROR) << "received kDebuggerdTombstoneProto on a queue that doesn't support proto";
           return {};
         }
         result.proto = create_temporary_file();
         result.text = create_temporary_file();
         break;

       case kDebuggerdJavaBacktrace:
       case kDebuggerdTombstone:
         result.text = create_temporary_file();
         break;

       default:
         LOG(ERROR) << "unexpected dump type: " << dump_type;
         return {};
     }

     return result;
   }

   borrowed_fd dir_fd() { return dir_fd_; }

   CrashArtifactPaths get_next_artifact_paths() {
     CrashArtifactPaths result;
     result.text = StringPrintf("%s%02d", file_name_prefix_.c_str(), next_artifact_);

     if (supports_proto_) {
       result.proto = StringPrintf("%s%02d.pb", file_name_prefix_.c_str(), next_artifact_);
     }

     next_artifact_ = (next_artifact_ + 1) % max_artifacts_;
     return result;
   }

   // Consumes crash if it returns true, otherwise leaves it untouched.
   bool maybe_enqueue_crash(std::unique_ptr<Crash>&& crash) {
     if (num_concurrent_dumps_ == max_concurrent_dumps_) {
       queued_requests_.emplace_back(std::move(crash));
       return true;
     }

     return false;
   }

   void maybe_dequeue_crashes(void (*handler)(std::unique_ptr<Crash> crash)) {
     while (!queued_requests_.empty() && num_concurrent_dumps_ < max_concurrent_dumps_) {
       std::unique_ptr<Crash> next_crash = std::move(queued_requests_.front());
       queued_requests_.pop_front();
       handler(std::move(next_crash));
     }
   }

   void on_crash_started() { ++num_concurrent_dumps_; }

   void on_crash_completed() { --num_concurrent_dumps_; }

  private:
   void find_oldest_artifact() {
     size_t oldest_tombstone = 0;
     time_t oldest_time = std::numeric_limits<time_t>::max();

     for (size_t i = 0; i < max_artifacts_; ++i) {
       std::string path =
           StringPrintf("%s/%s%02zu", dir_path_.c_str(), file_name_prefix_.c_str(), i);
       struct stat st;
       if (stat(path.c_str(), &st) != 0) {
         if (errno == ENOENT) {
           oldest_tombstone = i;
           break;
         } else {
           PLOG(ERROR) << "failed to stat " << path;
           continue;
         }
       }

       if (st.st_mtime < oldest_time) {
         oldest_tombstone = i;
         oldest_time = st.st_mtime;
       }
     }

     next_artifact_ = oldest_tombstone;
   }

   const std::string file_name_prefix_;

   const std::string dir_path_;
   const int dir_fd_;

   const size_t max_artifacts_;
   int next_artifact_;

   const size_t max_concurrent_dumps_;
   size_t num_concurrent_dumps_;

   bool supports_proto_;

   std::deque<std::unique_ptr<Crash>> queued_requests_;

   DISALLOW_COPY_AND_ASSIGN(CrashQueue);
 };

 // Whether java trace dumps are produced via tombstoned.
 static constexpr bool kJavaTraceDumpsEnabled = true;

 // Forward declare the callbacks so they can be placed in a sensible order.
 static void crash_accept_cb(evconnlistener* listener, evutil_socket_t sockfd, sockaddr*, int,
                             void*);
 static void crash_request_cb(evutil_socket_t sockfd, short ev, void* arg);
 static void crash_completed_cb(evutil_socket_t sockfd, short ev, void* arg);

 static void perform_request(std::unique_ptr<Crash> crash) {
   unique_fd output_fd;
   if (intercept_manager->FindIntercept(crash->crash_pid, crash->crash_type, &output_fd)) {
     if (crash->crash_type == kDebuggerdTombstoneProto) {
       crash->output.proto = CrashArtifact::devnull();
     }
   } else {
     if (auto o = CrashQueue::for_crash(crash.get())->get_output(crash->crash_type); o) {
       crash->output = std::move(*o);
       output_fd.reset(dup(crash->output.text.fd));
     } else {
       LOG(ERROR) << "failed to get crash output for type " << crash->crash_type;
       return;
     }
   }

   TombstonedCrashPacket response = {.packet_type = CrashPacketType::kPerformDump};

   ssize_t rc = -1;
   if (crash->output.proto) {
     rc = SendFileDescriptors(crash->crash_socket_fd, &response, sizeof(response), output_fd.get(),
                              crash->output.proto->fd.get());
   } else {
     rc = SendFileDescriptors(crash->crash_socket_fd, &response, sizeof(response), output_fd.get());
   }

   output_fd.reset();

   if (rc == -1) {
     PLOG(WARNING) << "failed to send response to CrashRequest";
     return;
   } else if (rc != sizeof(response)) {
     PLOG(WARNING) << "crash socket write returned short";
     return;
   }

   // TODO: Make this configurable by the interceptor?
   struct timeval timeout = {10 * android::base::HwTimeoutMultiplier(), 0};

   event_base* base = event_get_base(crash->crash_event);

   event_assign(crash->crash_event, base, crash->crash_socket_fd, EV_TIMEOUT | EV_READ,
                crash_completed_cb, crash.get());
   event_add(crash->crash_event, &timeout);
   CrashQueue::for_crash(crash)->on_crash_started();

   // The crash is now owned by the event loop.
   crash.release();
 }

 static void crash_accept_cb(evconnlistener* listener, evutil_socket_t sockfd, sockaddr*, int,
                             void*) {
   event_base* base = evconnlistener_get_base(listener);
   Crash* crash = new Crash();

   // TODO: Make sure that only java crashes come in on the java socket
   // and only native crashes on the native socket.
   struct timeval timeout = {1 * android::base::HwTimeoutMultiplier(), 0};
   event* crash_event = event_new(base, sockfd, EV_TIMEOUT | EV_READ, crash_request_cb, crash);
   crash->crash_socket_fd.reset(sockfd);
   crash->crash_event = crash_event;
   event_add(crash_event, &timeout);
 }

 static void crash_request_cb(evutil_socket_t sockfd, short ev, void* arg) {
   std::unique_ptr<Crash> crash(static_cast<Crash*>(arg));
   TombstonedCrashPacket request = {};

   if ((ev & EV_TIMEOUT) != 0) {
     LOG(WARNING) << "crash request timed out";
     return;
   } else if ((ev & EV_READ) == 0) {
     LOG(WARNING) << "tombstoned received unexpected event from crash socket";
     return;
   }

   ssize_t rc = TEMP_FAILURE_RETRY(read(sockfd, &request, sizeof(request)));
   if (rc == -1) {
     PLOG(WARNING) << "failed to read from crash socket";
     return;
   } else if (rc != sizeof(request)) {
     LOG(WARNING) << "crash socket received short read of length " << rc << " (expected "
                  << sizeof(request) << ")";
     return;
   }

   if (request.packet_type != CrashPacketType::kDumpRequest) {
     LOG(WARNING) << "unexpected crash packet type, expected kDumpRequest, received  "
                  << StringPrintf("%#2hhX", request.packet_type);
     return;
   }

   crash->crash_type = request.packet.dump_request.dump_type;
   if (crash->crash_type < 0 || crash->crash_type > kDebuggerdTombstoneProto) {
     LOG(WARNING) << "unexpected crash dump type: " << crash->crash_type;
     return;
   }

   if (crash->crash_type != kDebuggerdJavaBacktrace) {
     crash->crash_pid = request.packet.dump_request.pid;
   } else {
     // Requests for java traces are sent from untrusted processes, so we
     // must not trust the PID sent down with the request. Instead, we ask the
     // kernel.
     ucred cr = {};
     socklen_t len = sizeof(cr);
     int ret = getsockopt(sockfd, SOL_SOCKET, SO_PEERCRED, &cr, &len);
     if (ret != 0) {
       PLOG(ERROR) << "Failed to getsockopt(..SO_PEERCRED)";
       return;
     }

     crash->crash_pid = cr.pid;
   }

   pid_t crash_pid = crash->crash_pid;
   LOG(INFO) << "received crash request for pid " << crash_pid;

   if (CrashQueue::for_crash(crash)->maybe_enqueue_crash(std::move(crash))) {
     LOG(INFO) << "enqueueing crash request for pid " << crash_pid;
   } else {
     perform_request(std::move(crash));
   }
 }

 static bool rename_tombstone_fd(borrowed_fd fd, borrowed_fd dirfd, const std::string& path) {
   // Always try to unlink the tombstone file.
   // linkat doesn't let us replace a file, so we need to unlink before linking
   // our results onto disk, and if we fail for some reason, we should delete
   // stale tombstones to avoid confusing inconsistency.
   int rc = unlinkat(dirfd.get(), path.c_str(), 0);
   if (rc != 0 && errno != ENOENT) {
     PLOG(ERROR) << "failed to unlink tombstone at " << path;
     return false;
   }

   // This fd is created inside of dirfd in CrashQueue::create_temporary_file.
   std::string fd_path = StringPrintf("/proc/self/fd/%d", fd.get());
   rc = linkat(AT_FDCWD, fd_path.c_str(), dirfd.get(), path.c_str(), AT_SYMLINK_FOLLOW);
   if (rc != 0) {
     PLOG(ERROR) << "failed to link tombstone at " << path;
     return false;
   }
   return true;
 }

 static void crash_completed(borrowed_fd sockfd, std::unique_ptr<Crash> crash) {
   TombstonedCrashPacket request = {};
   CrashQueue* queue = CrashQueue::for_crash(crash);

   ssize_t rc = TEMP_FAILURE_RETRY(read(sockfd.get(), &request, sizeof(request)));
   if (rc == -1) {
     PLOG(WARNING) << "failed to read from crash socket";
     return;
   } else if (rc != sizeof(request)) {
     LOG(WARNING) << "crash socket received short read of length " << rc << " (expected "
                  << sizeof(request) << ")";
     return;
   }

   if (request.packet_type != CrashPacketType::kCompletedDump) {
     LOG(WARNING) << "unexpected crash packet type, expected kCompletedDump, received "
                  << uint32_t(request.packet_type);
     return;
   }

   if (crash->output.text.fd == -1) {
     LOG(WARNING) << "skipping tombstone file creation due to intercept";
     return;
   }

   CrashArtifactPaths paths = queue->get_next_artifact_paths();

   if (rename_tombstone_fd(crash->output.text.fd, queue->dir_fd(), paths.text)) {
     if (crash->crash_type == kDebuggerdJavaBacktrace) {
       LOG(ERROR) << "Traces for pid " << crash->crash_pid << " written to: " << paths.text;
     } else {
       // NOTE: Several tools parse this log message to figure out where the
       // tombstone associated with a given native crash was written. Any changes
       // to this message must be carefully considered.
       LOG(ERROR) << "Tombstone written to: " << paths.text;
     }
   }

   if (crash->output.proto && crash->output.proto->fd != -1) {
     if (!paths.proto) {
       LOG(ERROR) << "missing path for proto tombstone";
     } else {
       rename_tombstone_fd(crash->output.proto->fd, queue->dir_fd(), *paths.proto);
     }
   }

   // If we don't have O_TMPFILE, we need to clean up after ourselves.
   if (crash->output.text.temporary_path) {
     rc = unlinkat(queue->dir_fd().get(), crash->output.text.temporary_path->c_str(), 0);
     if (rc != 0) {
       PLOG(ERROR) << "failed to unlink temporary tombstone at " << paths.text;
     }
   }
   if (crash->output.proto && crash->output.proto->temporary_path) {
     rc = unlinkat(queue->dir_fd().get(), crash->output.proto->temporary_path->c_str(), 0);
     if (rc != 0) {
       PLOG(ERROR) << "failed to unlink temporary proto tombstone";
     }
   }
 }

 static void crash_completed_cb(evutil_socket_t sockfd, short ev, void* arg) {
   std::unique_ptr<Crash> crash(static_cast<Crash*>(arg));
   CrashQueue* queue = CrashQueue::for_crash(crash);

   queue->on_crash_completed();

   if ((ev & EV_READ) == EV_READ) {
     crash_completed(sockfd, std::move(crash));
   }

   // If there's something queued up, let them proceed.
   queue->maybe_dequeue_crashes(perform_request);
 }

 int main(int, char* []) {
   umask(0117);

   // Don't try to connect to ourselves if we crash.
   struct sigaction action = {};
   action.sa_handler = [](int signal) {
     LOG(ERROR) << "received fatal signal " << signal;
     _exit(1);
   };
   debuggerd_register_handlers(&action);

   int intercept_socket = android_get_control_socket(kTombstonedInterceptSocketName);
   int crash_socket = android_get_control_socket(kTombstonedCrashSocketName);

   if (intercept_socket == -1 || crash_socket == -1) {
     PLOG(FATAL) << "failed to get socket from init";
   }

   evutil_make_socket_nonblocking(intercept_socket);
   evutil_make_socket_nonblocking(crash_socket);

   event_base* base = event_base_new();
   if (!base) {
     LOG(FATAL) << "failed to create event_base";
   }

   intercept_manager = new InterceptManager(base, intercept_socket);

   evconnlistener* tombstone_listener =
       evconnlistener_new(base, crash_accept_cb, CrashQueue::for_tombstones(), LEV_OPT_CLOSE_ON_FREE,
                          -1 /* backlog */, crash_socket);
   if (!tombstone_listener) {
     LOG(FATAL) << "failed to create evconnlistener for tombstones.";
   }

   if (kJavaTraceDumpsEnabled) {
     const int java_trace_socket = android_get_control_socket(kTombstonedJavaTraceSocketName);
     if (java_trace_socket == -1) {
       PLOG(FATAL) << "failed to get socket from init";
     }

     evutil_make_socket_nonblocking(java_trace_socket);
     evconnlistener* java_trace_listener =
         evconnlistener_new(base, crash_accept_cb, CrashQueue::for_anrs(), LEV_OPT_CLOSE_ON_FREE,
                            -1 /* backlog */, java_trace_socket);
     if (!java_trace_listener) {
       LOG(FATAL) << "failed to create evconnlistener for java traces.";
     }
   }

   LOG(INFO) << "tombstoned successfully initialized";
   event_base_dispatch(base);
 }
	/*
	* Copyright 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 specific language governing permissions and
	* limitations under the License.
	*/

	#include <fcntl.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <sys/stat.h>
	#include <sys/types.h>
	#include <unistd.h>

	#include <array>
	#include <deque>
	#include <string>
	#include <unordered_map>
	#include <utility>

	#include <event2/event.h>
	#include <event2/listener.h>
	#include <event2/thread.h>

	#include <android-base/cmsg.h>
	#include <android-base/logging.h>
	#include <android-base/properties.h>
	#include <android-base/stringprintf.h>
	#include <android-base/unique_fd.h>
	#include <cutils/sockets.h>

	#include "debuggerd/handler.h"
	#include "dump_type.h"
	#include "protocol.h"
	#include "util.h"

	#include "intercept_manager.h"

	using android::base::GetIntProperty;
	using android::base::SendFileDescriptors;
	using android::base::StringPrintf;

	using android::base::borrowed_fd;
	using android::base::unique_fd;

	static InterceptManager* intercept_manager;

	enum CrashStatus {
	kCrashStatusRunning,
	kCrashStatusQueued,
	};

	struct CrashArtifact {
	unique_fd fd;
	std::optional<std::string> temporary_path;

	static CrashArtifact devnull() {
	CrashArtifact result;
	result.fd.reset(open("/dev/null", O_WRONLY \| O_CLOEXEC));
	return result;
	}
	};

	struct CrashArtifactPaths {
	std::string text;
	std::optional<std::string> proto;
	};

	struct CrashOutput {
	CrashArtifact text;
	std::optional<CrashArtifact> proto;
	};

	// Ownership of Crash is a bit messy.
	// It's either owned by an active event that must have a timeout, or owned by
	// queued_requests, in the case that multiple crashes come in at the same time.
	struct Crash {
	~Crash() { event_free(crash_event); }

	CrashOutput output;
	unique_fd crash_socket_fd;
	pid_t crash_pid;
	event* crash_event = nullptr;

	DebuggerdDumpType crash_type;
	};

	class CrashQueue {
	public:
	CrashQueue(const std::string& dir_path, const std::string& file_name_prefix, size_t max_artifacts,
	size_t max_concurrent_dumps, bool supports_proto)
	: file_name_prefix_(file_name_prefix),
	dir_path_(dir_path),
	dir_fd_(open(dir_path.c_str(), O_DIRECTORY \| O_RDONLY \| O_CLOEXEC)),
	max_artifacts_(max_artifacts),
	next_artifact_(0),
	max_concurrent_dumps_(max_concurrent_dumps),
	num_concurrent_dumps_(0),
	supports_proto_(supports_proto) {
	if (dir_fd_ == -1) {
	PLOG(FATAL) << "failed to open directory: " << dir_path;
	}

	// NOTE: If max_artifacts_ <= max_concurrent_dumps_, then theoretically the
	// same filename could be handed out to multiple processes.
	CHECK(max_artifacts_ > max_concurrent_dumps_);

	find_oldest_artifact();
	}

	static CrashQueue* for_crash(const Crash* crash) {
	return (crash->crash_type == kDebuggerdJavaBacktrace) ? for_anrs() : for_tombstones();
	}

	static CrashQueue* for_crash(const std::unique_ptr<Crash>& crash) {
	return for_crash(crash.get());
	}

	static CrashQueue* for_tombstones() {
	static CrashQueue queue("/data/tombstones", "tombstone_" /* file_name_prefix */,
	GetIntProperty("tombstoned.max_tombstone_count", 32),
	1 /* max_concurrent_dumps /, true / supports_proto */);
	return &queue;
	}

	static CrashQueue* for_anrs() {
	static CrashQueue queue("/data/anr", "trace_" /* file_name_prefix */,
	GetIntProperty("tombstoned.max_anr_count", 64),
	4 /* max_concurrent_dumps /, false / supports_proto */);
	return &queue;
	}

	CrashArtifact create_temporary_file() const {
	CrashArtifact result;

	std::optional<std::string> path;
	result.fd.reset(openat(dir_fd_, ".", O_WRONLY \| O_APPEND \| O_TMPFILE \| O_CLOEXEC, 0660));
	if (result.fd == -1) {
	// We might not have O_TMPFILE. Try creating with an arbitrary filename instead.
	static size_t counter = 0;
	std::string tmp_filename = StringPrintf(".temporary%zu", counter++);
	result.fd.reset(openat(dir_fd_, tmp_filename.c_str(),
	O_WRONLY \| O_APPEND \| O_CREAT \| O_TRUNC \| O_CLOEXEC, 0660));
	if (result.fd == -1) {
	PLOG(FATAL) << "failed to create temporary tombstone in " << dir_path_;
	}

	result.temporary_path = std::move(tmp_filename);
	}

	return std::move(result);
	}

	std::optional<CrashOutput> get_output(DebuggerdDumpType dump_type) {
	CrashOutput result;

	switch (dump_type) {
	case kDebuggerdNativeBacktrace:
	// Don't generate tombstones for native backtrace requests.
	return {};

	case kDebuggerdTombstoneProto:
	if (!supports_proto_) {
	LOG(ERROR) << "received kDebuggerdTombstoneProto on a queue that doesn't support proto";
	return {};
	}
	result.proto = create_temporary_file();
	result.text = create_temporary_file();
	break;

	case kDebuggerdJavaBacktrace:
	case kDebuggerdTombstone:
	result.text = create_temporary_file();
	break;

	default:
	LOG(ERROR) << "unexpected dump type: " << dump_type;
	return {};
	}

	return result;
	}

	borrowed_fd dir_fd() { return dir_fd_; }

	CrashArtifactPaths get_next_artifact_paths() {
	CrashArtifactPaths result;
	result.text = StringPrintf("%s%02d", file_name_prefix_.c_str(), next_artifact_);

	if (supports_proto_) {
	result.proto = StringPrintf("%s%02d.pb", file_name_prefix_.c_str(), next_artifact_);
	}

	next_artifact_ = (next_artifact_ + 1) % max_artifacts_;
	return result;
	}

	// Consumes crash if it returns true, otherwise leaves it untouched.
	bool maybe_enqueue_crash(std::unique_ptr<Crash>&& crash) {
	if (num_concurrent_dumps_ == max_concurrent_dumps_) {
	queued_requests_.emplace_back(std::move(crash));
	return true;
	}

	return false;
	}

	void maybe_dequeue_crashes(void (*handler)(std::unique_ptr<Crash> crash)) {
	while (!queued_requests_.empty() && num_concurrent_dumps_ < max_concurrent_dumps_) {
	std::unique_ptr<Crash> next_crash = std::move(queued_requests_.front());
	queued_requests_.pop_front();
	handler(std::move(next_crash));
	}
	}

	void on_crash_started() { ++num_concurrent_dumps_; }

	void on_crash_completed() { --num_concurrent_dumps_; }

	private:
	void find_oldest_artifact() {
	size_t oldest_tombstone = 0;
	time_t oldest_time = std::numeric_limits<time_t>::max();

	for (size_t i = 0; i < max_artifacts_; ++i) {
	std::string path =
	StringPrintf("%s/%s%02zu", dir_path_.c_str(), file_name_prefix_.c_str(), i);
	struct stat st;
	if (stat(path.c_str(), &st) != 0) {
	if (errno == ENOENT) {
	oldest_tombstone = i;
	break;
	} else {
	PLOG(ERROR) << "failed to stat " << path;
	continue;
	}
	}

	if (st.st_mtime < oldest_time) {
	oldest_tombstone = i;
	oldest_time = st.st_mtime;
	}
	}

	next_artifact_ = oldest_tombstone;
	}

	const std::string file_name_prefix_;

	const std::string dir_path_;
	const int dir_fd_;

	const size_t max_artifacts_;
	int next_artifact_;

	const size_t max_concurrent_dumps_;
	size_t num_concurrent_dumps_;

	bool supports_proto_;

	std::deque<std::unique_ptr<Crash>> queued_requests_;

	DISALLOW_COPY_AND_ASSIGN(CrashQueue);
	};

	// Whether java trace dumps are produced via tombstoned.
	static constexpr bool kJavaTraceDumpsEnabled = true;

	// Forward declare the callbacks so they can be placed in a sensible order.
	static void crash_accept_cb(evconnlistener* listener, evutil_socket_t sockfd, sockaddr*, int,
	void*);
	static void crash_request_cb(evutil_socket_t sockfd, short ev, void* arg);
	static void crash_completed_cb(evutil_socket_t sockfd, short ev, void* arg);

	static void perform_request(std::unique_ptr<Crash> crash) {
	unique_fd output_fd;
	if (intercept_manager->FindIntercept(crash->crash_pid, crash->crash_type, &output_fd)) {
	if (crash->crash_type == kDebuggerdTombstoneProto) {
	crash->output.proto = CrashArtifact::devnull();
	}
	} else {
	if (auto o = CrashQueue::for_crash(crash.get())->get_output(crash->crash_type); o) {
	crash->output = std::move(*o);
	output_fd.reset(dup(crash->output.text.fd));
	} else {
	LOG(ERROR) << "failed to get crash output for type " << crash->crash_type;
	return;
	}
	}

	TombstonedCrashPacket response = {.packet_type = CrashPacketType::kPerformDump};

	ssize_t rc = -1;
	if (crash->output.proto) {
	rc = SendFileDescriptors(crash->crash_socket_fd, &response, sizeof(response), output_fd.get(),
	crash->output.proto->fd.get());
	} else {
	rc = SendFileDescriptors(crash->crash_socket_fd, &response, sizeof(response), output_fd.get());
	}

	output_fd.reset();

	if (rc == -1) {
	PLOG(WARNING) << "failed to send response to CrashRequest";
	return;
	} else if (rc != sizeof(response)) {
	PLOG(WARNING) << "crash socket write returned short";
	return;
	}

	// TODO: Make this configurable by the interceptor?
	struct timeval timeout = {10 * android::base::HwTimeoutMultiplier(), 0};

	event_base* base = event_get_base(crash->crash_event);

	event_assign(crash->crash_event, base, crash->crash_socket_fd, EV_TIMEOUT \| EV_READ,
	crash_completed_cb, crash.get());
	event_add(crash->crash_event, &timeout);
	CrashQueue::for_crash(crash)->on_crash_started();

	// The crash is now owned by the event loop.
	crash.release();
	}

	static void crash_accept_cb(evconnlistener* listener, evutil_socket_t sockfd, sockaddr*, int,
	void*) {
	event_base* base = evconnlistener_get_base(listener);
	Crash* crash = new Crash();

	// TODO: Make sure that only java crashes come in on the java socket
	// and only native crashes on the native socket.
	struct timeval timeout = {1 * android::base::HwTimeoutMultiplier(), 0};
	event* crash_event = event_new(base, sockfd, EV_TIMEOUT \| EV_READ, crash_request_cb, crash);
	crash->crash_socket_fd.reset(sockfd);
	crash->crash_event = crash_event;
	event_add(crash_event, &timeout);
	}

	static void crash_request_cb(evutil_socket_t sockfd, short ev, void* arg) {
	std::unique_ptr<Crash> crash(static_cast<Crash*>(arg));
	TombstonedCrashPacket request = {};

	if ((ev & EV_TIMEOUT) != 0) {
	LOG(WARNING) << "crash request timed out";
	return;
	} else if ((ev & EV_READ) == 0) {
	LOG(WARNING) << "tombstoned received unexpected event from crash socket";
	return;
	}

	ssize_t rc = TEMP_FAILURE_RETRY(read(sockfd, &request, sizeof(request)));
	if (rc == -1) {
	PLOG(WARNING) << "failed to read from crash socket";
	return;
	} else if (rc != sizeof(request)) {
	LOG(WARNING) << "crash socket received short read of length " << rc << " (expected "
	<< sizeof(request) << ")";
	return;
	}

	if (request.packet_type != CrashPacketType::kDumpRequest) {
	LOG(WARNING) << "unexpected crash packet type, expected kDumpRequest, received "
	<< StringPrintf("%#2hhX", request.packet_type);
	return;
	}

	crash->crash_type = request.packet.dump_request.dump_type;
	if (crash->crash_type < 0 \|\| crash->crash_type > kDebuggerdTombstoneProto) {
	LOG(WARNING) << "unexpected crash dump type: " << crash->crash_type;
	return;
	}

	if (crash->crash_type != kDebuggerdJavaBacktrace) {
	crash->crash_pid = request.packet.dump_request.pid;
	} else {
	// Requests for java traces are sent from untrusted processes, so we
	// must not trust the PID sent down with the request. Instead, we ask the
	// kernel.
	ucred cr = {};
	socklen_t len = sizeof(cr);
	int ret = getsockopt(sockfd, SOL_SOCKET, SO_PEERCRED, &cr, &len);
	if (ret != 0) {
	PLOG(ERROR) << "Failed to getsockopt(..SO_PEERCRED)";
	return;
	}

	crash->crash_pid = cr.pid;
	}

	pid_t crash_pid = crash->crash_pid;
	LOG(INFO) << "received crash request for pid " << crash_pid;

	if (CrashQueue::for_crash(crash)->maybe_enqueue_crash(std::move(crash))) {
	LOG(INFO) << "enqueueing crash request for pid " << crash_pid;
	} else {
	perform_request(std::move(crash));
	}
	}

	static bool rename_tombstone_fd(borrowed_fd fd, borrowed_fd dirfd, const std::string& path) {
	// Always try to unlink the tombstone file.
	// linkat doesn't let us replace a file, so we need to unlink before linking
	// our results onto disk, and if we fail for some reason, we should delete
	// stale tombstones to avoid confusing inconsistency.
	int rc = unlinkat(dirfd.get(), path.c_str(), 0);
	if (rc != 0 && errno != ENOENT) {
	PLOG(ERROR) << "failed to unlink tombstone at " << path;
	return false;
	}

	// This fd is created inside of dirfd in CrashQueue::create_temporary_file.
	std::string fd_path = StringPrintf("/proc/self/fd/%d", fd.get());
	rc = linkat(AT_FDCWD, fd_path.c_str(), dirfd.get(), path.c_str(), AT_SYMLINK_FOLLOW);
	if (rc != 0) {
	PLOG(ERROR) << "failed to link tombstone at " << path;
	return false;
	}
	return true;
	}

	static void crash_completed(borrowed_fd sockfd, std::unique_ptr<Crash> crash) {
	TombstonedCrashPacket request = {};
	CrashQueue* queue = CrashQueue::for_crash(crash);

	ssize_t rc = TEMP_FAILURE_RETRY(read(sockfd.get(), &request, sizeof(request)));
	if (rc == -1) {
	PLOG(WARNING) << "failed to read from crash socket";
	return;
	} else if (rc != sizeof(request)) {
	LOG(WARNING) << "crash socket received short read of length " << rc << " (expected "
	<< sizeof(request) << ")";
	return;
	}

	if (request.packet_type != CrashPacketType::kCompletedDump) {
	LOG(WARNING) << "unexpected crash packet type, expected kCompletedDump, received "
	<< uint32_t(request.packet_type);
	return;
	}

	if (crash->output.text.fd == -1) {
	LOG(WARNING) << "skipping tombstone file creation due to intercept";
	return;
	}

	CrashArtifactPaths paths = queue->get_next_artifact_paths();

	if (rename_tombstone_fd(crash->output.text.fd, queue->dir_fd(), paths.text)) {
	if (crash->crash_type == kDebuggerdJavaBacktrace) {
	LOG(ERROR) << "Traces for pid " << crash->crash_pid << " written to: " << paths.text;
	} else {
	// NOTE: Several tools parse this log message to figure out where the
	// tombstone associated with a given native crash was written. Any changes
	// to this message must be carefully considered.
	LOG(ERROR) << "Tombstone written to: " << paths.text;
	}
	}

	if (crash->output.proto && crash->output.proto->fd != -1) {
	if (!paths.proto) {
	LOG(ERROR) << "missing path for proto tombstone";
	} else {
	rename_tombstone_fd(crash->output.proto->fd, queue->dir_fd(), *paths.proto);
	}
	}

	// If we don't have O_TMPFILE, we need to clean up after ourselves.
	if (crash->output.text.temporary_path) {
	rc = unlinkat(queue->dir_fd().get(), crash->output.text.temporary_path->c_str(), 0);
	if (rc != 0) {
	PLOG(ERROR) << "failed to unlink temporary tombstone at " << paths.text;
	}
	}
	if (crash->output.proto && crash->output.proto->temporary_path) {
	rc = unlinkat(queue->dir_fd().get(), crash->output.proto->temporary_path->c_str(), 0);
	if (rc != 0) {
	PLOG(ERROR) << "failed to unlink temporary proto tombstone";
	}
	}
	}

	static void crash_completed_cb(evutil_socket_t sockfd, short ev, void* arg) {
	std::unique_ptr<Crash> crash(static_cast<Crash*>(arg));
	CrashQueue* queue = CrashQueue::for_crash(crash);

	queue->on_crash_completed();

	if ((ev & EV_READ) == EV_READ) {
	crash_completed(sockfd, std::move(crash));
	}

	// If there's something queued up, let them proceed.
	queue->maybe_dequeue_crashes(perform_request);
	}

	int main(int, char* []) {
	umask(0117);

	// Don't try to connect to ourselves if we crash.
	struct sigaction action = {};
	action.sa_handler = [](int signal) {
	LOG(ERROR) << "received fatal signal " << signal;
	_exit(1);
	};
	debuggerd_register_handlers(&action);

	int intercept_socket = android_get_control_socket(kTombstonedInterceptSocketName);
	int crash_socket = android_get_control_socket(kTombstonedCrashSocketName);

	if (intercept_socket == -1 \|\| crash_socket == -1) {
	PLOG(FATAL) << "failed to get socket from init";
	}

	evutil_make_socket_nonblocking(intercept_socket);
	evutil_make_socket_nonblocking(crash_socket);

	event_base* base = event_base_new();
	if (!base) {
	LOG(FATAL) << "failed to create event_base";
	}

	intercept_manager = new InterceptManager(base, intercept_socket);

	evconnlistener* tombstone_listener =
	evconnlistener_new(base, crash_accept_cb, CrashQueue::for_tombstones(), LEV_OPT_CLOSE_ON_FREE,
	-1 /* backlog */, crash_socket);
	if (!tombstone_listener) {
	LOG(FATAL) << "failed to create evconnlistener for tombstones.";
	}

	if (kJavaTraceDumpsEnabled) {
	const int java_trace_socket = android_get_control_socket(kTombstonedJavaTraceSocketName);
	if (java_trace_socket == -1) {
	PLOG(FATAL) << "failed to get socket from init";
	}

	evutil_make_socket_nonblocking(java_trace_socket);
	evconnlistener* java_trace_listener =
	evconnlistener_new(base, crash_accept_cb, CrashQueue::for_anrs(), LEV_OPT_CLOSE_ON_FREE,
	-1 /* backlog */, java_trace_socket);
	if (!java_trace_listener) {
	LOG(FATAL) << "failed to create evconnlistener for java traces.";
	}
	}

	LOG(INFO) << "tombstoned successfully initialized";
	event_base_dispatch(base);
	}