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Commit 4af349b0 authored by Tom Cherry's avatar Tom Cherry
Browse files

liblog: use a blocking socket for sending messages to logd 

liblog uses a non-blocking socket for sending messages to logd as a
performance/reliability trade-off, favoring not blocking processes
when they log over reliably tracking all logs.

This change asserts that the above is the wrong trade-off: that log
relability is more important than slight delays when logging. Further
points to consider:

1) The new logd implementation without chatty has lower latency and
less variance in its ::Log() function.
2) liblog also writes to /dev/pmsg0 and this call is already blocking.
3) Logging is already expensive and excess spam must be eliminated
regardless.

Bug: 151654749
Bug: 155922578
Bug: 160314220
Test: No messages are dropped by this socket
Change-Id: I163b7d51aa73a10978850f1868cb9fc4bf9ead1b
parent 2cfea97b

liblog/logd_writer.cpp

+3 −55
Original line number Original line Diff line number Diff line
@@ -59,8 +59,7 @@ static void GetSocket() { 
    return;

    return;

  }

  }





  int new_socket =

  int new_socket = TEMP_FAILURE_RETRY(socket(PF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0));

      TEMP_FAILURE_RETRY(socket(PF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0));

  if (new_socket <= 0) {

  if (new_socket <= 0) {

    return;

    return;

  }

  }
@@ -91,8 +90,6 @@ int LogdWrite(log_id_t logId, struct timespec* ts, struct iovec* vec, size_t nr) 
  struct iovec newVec[nr + headerLength];

  struct iovec newVec[nr + headerLength];

  android_log_header_t header;

  android_log_header_t header;

  size_t i, payloadSize;

  size_t i, payloadSize;

  static atomic_int dropped;

  static atomic_int droppedSecurity;





  GetSocket();

  GetSocket();
@@ -110,6 +107,7 @@ int LogdWrite(log_id_t logId, struct timespec* ts, struct iovec* vec, size_t nr) 
    return 0;

    return 0;

  }

  }





  header.id = logId;

  header.tid = gettid();

  header.tid = gettid();

  header.realtime.tv_sec = ts->tv_sec;

  header.realtime.tv_sec = ts->tv_sec;

  header.realtime.tv_nsec = ts->tv_nsec;

  header.realtime.tv_nsec = ts->tv_nsec;
@@ -117,44 +115,6 @@ int LogdWrite(log_id_t logId, struct timespec* ts, struct iovec* vec, size_t nr) 
  newVec[0].iov_base = (unsigned char*)&header;

  newVec[0].iov_base = (unsigned char*)&header;

  newVec[0].iov_len = sizeof(header);

  newVec[0].iov_len = sizeof(header);





  int32_t snapshot = atomic_exchange_explicit(&droppedSecurity, 0, memory_order_relaxed);

  if (snapshot) {

    android_log_event_int_t buffer;



    header.id = LOG_ID_SECURITY;

    buffer.header.tag = LIBLOG_LOG_TAG;

    buffer.payload.type = EVENT_TYPE_INT;

    buffer.payload.data = snapshot;



    newVec[headerLength].iov_base = &buffer;

    newVec[headerLength].iov_len = sizeof(buffer);



    ret = TEMP_FAILURE_RETRY(writev(logd_socket, newVec, 2));

    if (ret != (ssize_t)(sizeof(header) + sizeof(buffer))) {

      atomic_fetch_add_explicit(&droppedSecurity, snapshot, memory_order_relaxed);

    }

  }

  snapshot = atomic_exchange_explicit(&dropped, 0, memory_order_relaxed);

  if (snapshot && __android_log_is_loggable_len(ANDROID_LOG_INFO, "liblog", strlen("liblog"),

                                                ANDROID_LOG_VERBOSE)) {

    android_log_event_int_t buffer;



    header.id = LOG_ID_EVENTS;

    buffer.header.tag = LIBLOG_LOG_TAG;

    buffer.payload.type = EVENT_TYPE_INT;

    buffer.payload.data = snapshot;



    newVec[headerLength].iov_base = &buffer;

    newVec[headerLength].iov_len = sizeof(buffer);



    ret = TEMP_FAILURE_RETRY(writev(logd_socket, newVec, 2));

    if (ret != (ssize_t)(sizeof(header) + sizeof(buffer))) {

      atomic_fetch_add_explicit(&dropped, snapshot, memory_order_relaxed);

    }

  }



  header.id = logId;



  for (payloadSize = 0, i = headerLength; i < nr + headerLength; i++) {

  for (payloadSize = 0, i = headerLength; i < nr + headerLength; i++) {

    newVec[i].iov_base = vec[i - headerLength].iov_base;

    newVec[i].iov_base = vec[i - headerLength].iov_base;

    payloadSize += newVec[i].iov_len = vec[i - headerLength].iov_len;

    payloadSize += newVec[i].iov_len = vec[i - headerLength].iov_len;
@@ -168,11 +128,8 @@ int LogdWrite(log_id_t logId, struct timespec* ts, struct iovec* vec, size_t nr) 
    }

    }

  }

  }





  // The write below could be lost, but will never block.

  // EAGAIN occurs if logd is overloaded, other errors indicate that something went wrong with

  // the connection, so we reset it and try again.

  ret = TEMP_FAILURE_RETRY(writev(logd_socket, newVec, i));

  ret = TEMP_FAILURE_RETRY(writev(logd_socket, newVec, i));

  if (ret < 0 && errno != EAGAIN) {

  if (ret < 0) {

    LogdConnect();

    LogdConnect();





    ret = TEMP_FAILURE_RETRY(writev(logd_socket, newVec, i));

    ret = TEMP_FAILURE_RETRY(writev(logd_socket, newVec, i));
@@ -182,14 +139,5 @@ int LogdWrite(log_id_t logId, struct timespec* ts, struct iovec* vec, size_t nr) 
    ret = -errno;

    ret = -errno;

  }

  }





  if (ret > (ssize_t)sizeof(header)) {

    ret -= sizeof(header);

  } else if (ret < 0) {

    atomic_fetch_add_explicit(&dropped, 1, memory_order_relaxed);

    if (logId == LOG_ID_SECURITY) {

      atomic_fetch_add_explicit(&droppedSecurity, 1, memory_order_relaxed);

    }

  }



  return ret;

  return ret;

}
 
}