android - 无法从 ART 创建磁盘文件

Question

我希望 Android 运行时 (ART) 写入文件。因此，我将以下代码添加到 WORKING_DIRECTORY/art/runtime/runtime.cc。

  std::string pid_str = std::to_string(getpid());
  time_t n = time(nullptr);
  struct tm* local = localtime(&n);
  char strTime[80];
  strftime(strTime, 80, "%Y-%m-%d %H-%M-%S", local);
  std::string perf_filename = std::string("/storage/self/primary") + "/" + strTime + "-" + pid_str + ".log";

  auto log = std::ofstream(perf_filename.c_str());
  struct passwd *pwd = getpwuid(getuid());
  if (log.is_open())
    LOG(INFO) << "User " << pwd->pw_name << "(" << pwd->pw_uid << ") created field log is created at " << perf_filename;
  else {
    LOG(WARNING) << "User " << pwd->pw_name << "(" << pwd->pw_uid << ") cannot opening field log at " << perf_filename << ". Error: " << strerror(errno);
  }

$ adb logcat | grep -F "field log"
04-23 15:28:34.390  3521  3521 W zygote64: User u0_a44(10044) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-34-3521.log. Error: Permission denied
04-23 15:28:34.517  3581  3581 I zygote64: User nfc(1027) created field log is created at /storage/self/primary/nvm-1970-04-23 15-28-34-3581.log
04-23 15:28:34.539  3597  3597 W zygote64: User u0_a57(10057) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-34-3597.log. Error: Permission denied
04-23 15:28:34.620  3641  3641 W zygote64: User u0_a15(10015) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-34-3641.log. Error: Permission denied
04-23 15:28:34.656  3660  3660 W zygote64: User u0_a19(10019) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-34-3660.log. Error: Permission denied
04-23 15:28:34.743  3718  3718 I zygote64: User system(1000) created field log is created at /storage/self/primary/nvm-1970-04-23 15-28-34-3718.log
04-23 15:28:35.728  3841  3841 W zygote64: User u0_a16(10016) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-35-3841.log. Error: Permission denied
04-23 15:28:35.817  3860  3860 W zygote64: User u0_a58(10058) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-35-3860.log. Error: Permission denied
04-23 15:28:35.928  3886  3886 I zygote64: User u0_a3(10003) created field log is created at /storage/self/primary/nvm-1970-04-23 15-28-35-3886.log
04-23 15:28:36.217  3906  3906 W zygote64: User u0_a2(10002) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-36-3906.log. Error: Permission denied
04-23 15:28:36.392  3968  3968 W zygote64: User u0_a59(10059) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-36-3968.log. Error: Permission denied
04-23 15:28:37.892  4189  4189 W zygote64: User u0_a13(10013) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-37-4189.log. Error: Permission denied
04-23 15:28:38.359  4233  4233 W zygote64: User u0_a36(10036) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-38-4233.log. Error: Permission denied
04-23 15:28:38.549  4289  4289 I zygote64: User u0_a39(10039) created field log is created at /storage/self/primary/nvm-1970-04-23 15-28-38-4289.log
04-23 15:28:38.738  4309  4309 W zygote64: User u0_a8(10008) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-38-4309.log. Error: Permission denied
04-23 15:28:38.881  4328  4328 W zygote64: User u0_a7(10007) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-38-4328.log. Error: Permission denied
04-23 15:28:39.194  4373  4373 I zygote64: User u0_a45(10045) created field log is created at /storage/self/primary/nvm-1970-04-23 15-28-39-4373.log
04-23 15:28:39.797  4425  4425 I zygote64: User u0_a48(10048) created field log is created at /storage/self/primary/nvm-1970-04-23 15-28-39-4425.log
04-23 15:28:40.014  4441  4441 I zygote64: User u0_a62(10062) created field log is created at /storage/self/primary/nvm-1970-04-23 15-28-40-4441.log
04-23 15:28:40.320  4460  4460 W zygote64: User u0_a17(10017) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-40-4460.log. Error: Permission denied
04-23 15:28:40.551  4505  4505 W zygote64: User u0_a21(10021) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-28-40-4505.log. Error: Permission denied
04-23 15:29:02.961  4821  4821 I zygote64: User system(1000) created field log is created at /storage/self/primary/nvm-1970-04-23 15-29-02-4821.log
04-23 15:29:29.317  4891  4891 W zygote64: User u0_a47(10047) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-29-29-4891.log. Error: Permission denied
04-23 15:29:55.592  5012  5012 W zygote64: User u0_a2(10002) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-29-55-5012.log. Error: Permission denied
04-23 15:31:29.829  5084  5084 I zygote64: User u0_a5(10005) created field log is created at /storage/self/primary/nvm-1970-04-23 15-31-29-5084.log
04-23 15:32:07.743  5144  5144 W zygote64: User u0_a23(10023) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-32-07-5144.log. Error: Permission denied
04-23 15:32:16.602  5217  5217 W zygote  : User u0_a63(10063) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-32-16-5217.log. Error: Permission denied
04-23 15:32:23.596  5405  5405 W zygote  : User u0_a54(10054) cannot opening field log at /storage/self/primary/nvm-1970-04-23 15-32-23-5405.log. Error: Permission denied

adb logcat 显示一些用户 u0_a39、u0_a3、u0_a5 能够创建文件，而其他用户则不能。有谁知道为什么吗？

Answer 1

这是因为权限。如果 ART 托管的应用请求并且用户授予 android.permission.WRITE_EXTERNAL_STORAGE，则代码有效。

目前还不清楚为什么 Java 级别的权限会影响运行时代码。