aos/ftrace.cc

#include "aos/ftrace.h"

#include <cstdarg>
#include <cstdio>

#include "absl/flags/flag.h"
#include "absl/log/check.h"
#include "absl/strings/str_cat.h"

ABSL_FLAG(bool, enable_ftrace, false,
          "If false, disable logging to /sys/kernel/tracing/trace_marker");

namespace aos {

namespace {
int MaybeCheckOpen(const char *file) {
  if (!absl::GetFlag(FLAGS_enable_ftrace)) return -1;
  int result =
      open(absl::StrCat("/sys/kernel/tracing/", file).c_str(), O_WRONLY);
  if (result == -1) {
    result = open(absl::StrCat("/sys/kernel/debug/tracing/", file).c_str(),
                  O_WRONLY);
  }

  // New kernels prefer /sys/kernel/tracing, and old kernels prefer
  // /sys/kernel/debug/tracing...  When Ubuntu 18.04 and the 4.9 kernel
  // disappear finally, we can switch fully to /sys/kernel/tracing.
  PCHECK(result >= 0) << ": Failed to open /sys/kernel/tracing/" << file
                      << " or legacy /sys/kernel/debug/tracing/" << file;
  return result;
}
}  // namespace

Ftrace::Ftrace()
    : message_fd_(MaybeCheckOpen("trace_marker")),
      on_fd_(MaybeCheckOpen("tracing_on")) {}

Ftrace::~Ftrace() {
  if (message_fd_ != -1) {
    PCHECK(close(message_fd_) == 0);
  }
  if (message_fd_ != -1) {
    PCHECK(close(on_fd_) == 0);
  }
}

void Ftrace::TurnOffOrDie() {
  CHECK(on_fd_ != -1)
      << ": Failed to open tracing_on earlier, cannot turn off tracing";
  char zero = '0';
  CHECK_EQ(write(on_fd_, &zero, 1), 1) << ": Failed to turn tracing off";
}

void Ftrace::FormatMessage(const char *format, ...) {
  if (message_fd_ == -1) {
    return;
  }
  char buffer[512];
  va_list ap;
  va_start(ap, format);
  const int result = vsnprintf(buffer, sizeof(buffer), format, ap);
  va_end(ap);
  CHECK_LE(static_cast<size_t>(result), sizeof(buffer))
      << ": Format string ended up too long: " << format;
  WriteMessage(std::string_view(buffer, result));
}

void Ftrace::WriteMessage(std::string_view content) {
  if (message_fd_ == -1) {
    return;
  }
  const int result = write(message_fd_, content.data(), content.size());
  if (result == -1 && errno == EBADF) {
    // This just means tracing is turned off. Ignore it.
    return;
  }
  PCHECK(result >= 0) << ": Failed to write ftrace message: " << content;
  CHECK_EQ(static_cast<size_t>(result), content.size())
      << ": Failed to write complete ftrace message: " << content;
}

}  // namespace aos