I want Android Runtime (ART) to write to a file. Therefore I added the following code to 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 shows some users u0_a39, u0_a3, u0_a5 are able to create the file, while the others cannot. Does anyone know why?
It's because of permissions. If the app that ART is hosting requested and user granted android.permission.WRITE_EXTERNAL_STORAGE, the code works.
It's still unclear why Java level permission affects the runtime code.