Function KernelLogger

Bcore/src/main/cpp/android-base/logging.cpp:169–205

#if defined(__linux__)
void KernelLogger(android_lkchan::base::LogId, android_lkchan::base::LogSeverity severity,
                  const char* tag, const char*, unsigned int, const char* msg) {
  // clang-format off
  static constexpr int kLogSeverityToKernelLogLevel[] = {
      [android_lkchan::base::VERBOSE] = 7,              // KERN_DEBUG (there is no verbose kernel log
                                                 //             level)
      [android_lkchan::base::DEBUG] = 7,                // KERN_DEBUG
      [android_lkchan::base::INFO] = 6,                 // KERN_INFO
      [android_lkchan::base::WARNING] = 4,              // KERN_WARNING
      [android_lkchan::base::ERROR] = 3,                // KERN_ERROR
      [android_lkchan::base::FATAL_WITHOUT_ABORT] = 2,  // KERN_CRIT
      [android_lkchan::base::FATAL] = 2,                // KERN_CRIT
  };
  // clang-format on
  static_assert(arraysize(kLogSeverityToKernelLogLevel) == android_lkchan::base::FATAL + 1,
                "Mismatch in size of kLogSeverityToKernelLogLevel and values in LogSeverity");

  static int klog_fd = TEMP_FAILURE_RETRY(open("/dev/kmsg", O_WRONLY | O_CLOEXEC));
  if (klog_fd == -1) return;

  int level = kLogSeverityToKernelLogLevel[severity];

  // The kernel's printk buffer is only 1024 bytes.
  // TODO: should we automatically break up long lines into multiple lines?
  // Or we could log but with something like "..." at the end?
  char buf[1024];
  size_t size = snprintf(buf, sizeof(buf), "<%d>%s: %s\n", level, tag, msg);
  if (size > sizeof(buf)) {
    size = snprintf(buf, sizeof(buf), "<%d>%s: %zu-byte message too long for printk\n",
                    level, tag, size);
  }

  iovec iov[1];
  iov[0].iov_base = buf;
  iov[0].iov_len = size;
  TEMP_FAILURE_RETRY(writev(klog_fd, iov, 1));
}
#endif

void StderrLogger(LogId, LogSeverity severity, const char* tag, const char* file, unsigned int line,