libprocessgroup/processgroup.cpp - platform/system/core - Gitiles

 /*
  *  Copyright 2014 Google, Inc
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
  *  you may not use this file except in compliance with the License.
  *  You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  *  Unless required by applicable law or agreed to in writing, software
  *  distributed under the License is distributed on an "AS IS" BASIS,
  *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */

 //#define LOG_NDEBUG 0
 #define LOG_TAG "libprocessgroup"

 #include <assert.h>
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <inttypes.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/types.h>

 #include <chrono>
 #include <memory>
 #include <mutex>
 #include <thread>

 #include <android-base/logging.h>
 #include <android-base/unique_fd.h>
 #include <private/android_filesystem_config.h>

 #include <processgroup/processgroup.h>

 using namespace std::chrono_literals;

 // Uncomment line below use memory cgroups for keeping track of (forked) PIDs
 // #define USE_MEMCG 1

 #define MEM_CGROUP_PATH "/dev/memcg/apps"
 #define MEM_CGROUP_TASKS "/dev/memcg/apps/tasks"
 #define ACCT_CGROUP_PATH "/acct"

 #define PROCESSGROUP_UID_PREFIX "uid_"
 #define PROCESSGROUP_PID_PREFIX "pid_"
 #define PROCESSGROUP_CGROUP_PROCS_FILE "/cgroup.procs"
 #define PROCESSGROUP_MAX_UID_LEN 11
 #define PROCESSGROUP_MAX_PID_LEN 11
 #define PROCESSGROUP_MAX_PATH_LEN \
         ((sizeof(MEM_CGROUP_PATH) > sizeof(ACCT_CGROUP_PATH) ? \
           sizeof(MEM_CGROUP_PATH) : sizeof(ACCT_CGROUP_PATH)) + \
          sizeof(PROCESSGROUP_UID_PREFIX) + 1 + \
          PROCESSGROUP_MAX_UID_LEN + \
          sizeof(PROCESSGROUP_PID_PREFIX) + 1 + \
          PROCESSGROUP_MAX_PID_LEN + \
          sizeof(PROCESSGROUP_CGROUP_PROCS_FILE) + \
          1)

 std::once_flag init_path_flag;

 class ProcessGroup {
   public:
     ProcessGroup() : buf_ptr_(buf_), buf_len_(0) {}

     bool Open(uid_t uid, int pid);

     // Return positive number and sets *pid = next pid in process cgroup on success
     // Returns 0 if there are no pids left in the process cgroup
     // Returns -errno if an error was encountered
     int GetOneAppProcess(pid_t* pid);

   private:
     // Returns positive number of bytes filled on success
     // Returns 0 if there was nothing to read
     // Returns -errno if an error was encountered
     int RefillBuffer();

     android::base::unique_fd fd_;
     char buf_[128];
     char* buf_ptr_;
     size_t buf_len_;
 };

 static const char* getCgroupRootPath() {
 #ifdef USE_MEMCG
     static const char* cgroup_root_path = NULL;
     std::call_once(init_path_flag, [&]() {
             // Check if mem cgroup is mounted, only then check for write-access to avoid
             // SELinux denials
             cgroup_root_path = access(MEM_CGROUP_TASKS, F_OK) || access(MEM_CGROUP_PATH, W_OK) ?
                     ACCT_CGROUP_PATH : MEM_CGROUP_PATH;
             });
     return cgroup_root_path;
 #else
     return ACCT_CGROUP_PATH;
 #endif
 }

 static int convertUidToPath(char *path, size_t size, uid_t uid)
 {
     return snprintf(path, size, "%s/%s%d",
             getCgroupRootPath(),
             PROCESSGROUP_UID_PREFIX,
             uid);
 }

 static int convertUidPidToPath(char *path, size_t size, uid_t uid, int pid)
 {
     return snprintf(path, size, "%s/%s%d/%s%d",
             getCgroupRootPath(),
             PROCESSGROUP_UID_PREFIX,
             uid,
             PROCESSGROUP_PID_PREFIX,
             pid);
 }

 bool ProcessGroup::Open(uid_t uid, int pid) {
     char path[PROCESSGROUP_MAX_PATH_LEN] = {0};
     convertUidPidToPath(path, sizeof(path), uid, pid);
     strlcat(path, PROCESSGROUP_CGROUP_PROCS_FILE, sizeof(path));

     int fd = open(path, O_RDONLY);
     if (fd < 0) return false;

     fd_.reset(fd);

     LOG(VERBOSE) << "Initialized context for " << path;

     return true;
 }

 int ProcessGroup::RefillBuffer() {
     memmove(buf_, buf_ptr_, buf_len_);
     buf_ptr_ = buf_;

     ssize_t ret = read(fd_, buf_ptr_ + buf_len_, sizeof(buf_) - buf_len_ - 1);
     if (ret < 0) {
         return -errno;
     } else if (ret == 0) {
         return 0;
     }

     buf_len_ += ret;
     buf_[buf_len_] = 0;
     LOG(VERBOSE) << "Read " << ret << " to buffer: " << buf_;

     assert(buf_len_ <= sizeof(buf_));

     return ret;
 }

 int ProcessGroup::GetOneAppProcess(pid_t* out_pid) {
     *out_pid = 0;

     char* eptr;
     while ((eptr = static_cast<char*>(memchr(buf_ptr_, '\n', buf_len_))) == nullptr) {
         int ret = RefillBuffer();
         if (ret <= 0) return ret;
     }

     *eptr = '\0';
     char* pid_eptr = nullptr;
     errno = 0;
     long pid = strtol(buf_ptr_, &pid_eptr, 10);
     if (errno != 0) {
         return -errno;
     }
     if (pid_eptr != eptr) {
         errno = EINVAL;
         return -errno;
     }

     buf_len_ -= (eptr - buf_ptr_) + 1;
     buf_ptr_ = eptr + 1;

     *out_pid = static_cast<pid_t>(pid);
     return 1;
 }

 static int removeProcessGroup(uid_t uid, int pid)
 {
     int ret;
     char path[PROCESSGROUP_MAX_PATH_LEN] = {0};

     convertUidPidToPath(path, sizeof(path), uid, pid);
     ret = rmdir(path);

     convertUidToPath(path, sizeof(path), uid);
     rmdir(path);

     return ret;
 }

 static void removeUidProcessGroups(const char *uid_path)
 {
     std::unique_ptr<DIR, decltype(&closedir)> uid(opendir(uid_path), closedir);
     if (uid != NULL) {
         dirent* dir;
         while ((dir = readdir(uid.get())) != nullptr) {
             char path[PROCESSGROUP_MAX_PATH_LEN];

             if (dir->d_type != DT_DIR) {
                 continue;
             }

             if (strncmp(dir->d_name, PROCESSGROUP_PID_PREFIX, strlen(PROCESSGROUP_PID_PREFIX))) {
                 continue;
             }

             snprintf(path, sizeof(path), "%s/%s", uid_path, dir->d_name);
             LOG(VERBOSE) << "Removing " << path;
             if (rmdir(path) == -1) PLOG(WARNING) << "Failed to remove " << path;
         }
     }
 }

 void removeAllProcessGroups()
 {
     LOG(VERBOSE) << "removeAllProcessGroups()";
     const char* cgroup_root_path = getCgroupRootPath();
     std::unique_ptr<DIR, decltype(&closedir)> root(opendir(cgroup_root_path), closedir);
     if (root == NULL) {
         PLOG(ERROR) << "Failed to open " << cgroup_root_path;
     } else {
         dirent* dir;
         while ((dir = readdir(root.get())) != nullptr) {
             char path[PROCESSGROUP_MAX_PATH_LEN];

             if (dir->d_type != DT_DIR) {
                 continue;
             }
             if (strncmp(dir->d_name, PROCESSGROUP_UID_PREFIX, strlen(PROCESSGROUP_UID_PREFIX))) {
                 continue;
             }

             snprintf(path, sizeof(path), "%s/%s", cgroup_root_path, dir->d_name);
             removeUidProcessGroups(path);
             LOG(VERBOSE) << "Removing " << path;
             if (rmdir(path) == -1) PLOG(WARNING) << "Failed to remove " << path;
         }
     }
 }

 // Returns number of processes killed on success
 // Returns 0 if there are no processes in the process cgroup left to kill
 // Returns -errno on error
 static int doKillProcessGroupOnce(uid_t uid, int initialPid, int signal) {
     ProcessGroup process_group;
     if (!process_group.Open(uid, initialPid)) {
         PLOG(WARNING) << "Failed to open process cgroup uid " << uid << " pid " << initialPid;
         return -errno;
     }

     int ret;
     pid_t pid;
     int processes = 0;
     while ((ret = process_group.GetOneAppProcess(&pid)) > 0 && pid >= 0) {
         processes++;
         if (pid == 0) {
             // Should never happen...  but if it does, trying to kill this
             // will boomerang right back and kill us!  Let's not let that happen.
             LOG(WARNING) << "Yikes, we've been told to kill pid 0!  How about we don't do that?";
             continue;
         }
         LOG(VERBOSE) << "Killing pid " << pid << " in uid " << uid << " as part of process cgroup "
                      << initialPid;
         if (kill(pid, signal) == -1) {
             PLOG(WARNING) << "kill(" << pid << ", " << signal << ") failed";
         }
     }

     return ret >= 0 ? processes : ret;
 }

 static int killProcessGroup(uid_t uid, int initialPid, int signal, int retries) {
     std::chrono::steady_clock::time_point start = std::chrono::steady_clock::now();

     int retry = retries;
     int processes;
     while ((processes = doKillProcessGroupOnce(uid, initialPid, signal)) > 0) {
         LOG(VERBOSE) << "Killed " << processes << " processes for processgroup " << initialPid;
         if (retry > 0) {
             std::this_thread::sleep_for(5ms);
             --retry;
         } else {
             break;
         }
     }

     if (processes < 0) {
         PLOG(ERROR) << "Error encountered killing process cgroup uid " << uid << " pid "
                     << initialPid;
         return -1;
     }

     std::chrono::steady_clock::time_point end = std::chrono::steady_clock::now();
     auto ms = std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count();

     // We only calculate the number of 'processes' when killing the processes.
     // In the retries == 0 case, we only kill the processes once and therefore
     // will not have waited then recalculated how many processes are remaining
     // after the first signals have been sent.
     // Logging anything regarding the number of 'processes' here does not make sense.

     if (processes == 0) {
         if (retries > 0) {
             LOG(INFO) << "Successfully killed process cgroup uid " << uid << " pid " << initialPid
                       << " in " << static_cast<int>(ms) << "ms";
         }
         return removeProcessGroup(uid, initialPid);
     } else {
         if (retries > 0) {
             LOG(ERROR) << "Failed to kill process cgroup uid " << uid << " pid " << initialPid
                        << " in " << static_cast<int>(ms) << "ms, " << processes
                        << " processes remain";
         }
         return -1;
     }
 }

 int killProcessGroup(uid_t uid, int initialPid, int signal) {
     return killProcessGroup(uid, initialPid, signal, 40 /*retries*/);
 }

 int killProcessGroupOnce(uid_t uid, int initialPid, int signal) {
     return killProcessGroup(uid, initialPid, signal, 0 /*retries*/);
 }

 static bool mkdirAndChown(const char *path, mode_t mode, uid_t uid, gid_t gid)
 {
     if (mkdir(path, mode) == -1 && errno != EEXIST) {
         return false;
     }

     if (chown(path, uid, gid) == -1) {
         int saved_errno = errno;
         rmdir(path);
         errno = saved_errno;
         return false;
     }

     return true;
 }

 int createProcessGroup(uid_t uid, int initialPid)
 {
     char path[PROCESSGROUP_MAX_PATH_LEN] = {0};

     convertUidToPath(path, sizeof(path), uid);

     if (!mkdirAndChown(path, 0750, AID_SYSTEM, AID_SYSTEM)) {
         PLOG(ERROR) << "Failed to make and chown " << path;
         return -errno;
     }

     convertUidPidToPath(path, sizeof(path), uid, initialPid);

     if (!mkdirAndChown(path, 0750, AID_SYSTEM, AID_SYSTEM)) {
         PLOG(ERROR) << "Failed to make and chown " << path;
         return -errno;
     }

     strlcat(path, PROCESSGROUP_CGROUP_PROCS_FILE, sizeof(path));

     int fd = open(path, O_WRONLY);
     if (fd == -1) {
         int ret = -errno;
         PLOG(ERROR) << "Failed to open " << path;
         return ret;
     }

     char pid[PROCESSGROUP_MAX_PID_LEN + 1] = {0};
     int len = snprintf(pid, sizeof(pid), "%d", initialPid);

     int ret = 0;
     if (write(fd, pid, len) < 0) {
         ret = -errno;
         PLOG(ERROR) << "Failed to write '" << pid << "' to " << path;
     }

     close(fd);
     return ret;
 }
	/*
	* Copyright 2014 Google, Inc
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	//#define LOG_NDEBUG 0
	#define LOG_TAG "libprocessgroup"

	#include <assert.h>
	#include <dirent.h>
	#include <errno.h>
	#include <fcntl.h>
	#include <inttypes.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>
	#include <sys/stat.h>
	#include <sys/types.h>

	#include <chrono>
	#include <memory>
	#include <mutex>
	#include <thread>

	#include <android-base/logging.h>
	#include <android-base/unique_fd.h>
	#include <private/android_filesystem_config.h>

	#include <processgroup/processgroup.h>

	using namespace std::chrono_literals;

	// Uncomment line below use memory cgroups for keeping track of (forked) PIDs
	// #define USE_MEMCG 1

	#define MEM_CGROUP_PATH "/dev/memcg/apps"
	#define MEM_CGROUP_TASKS "/dev/memcg/apps/tasks"
	#define ACCT_CGROUP_PATH "/acct"

	#define PROCESSGROUP_UID_PREFIX "uid_"
	#define PROCESSGROUP_PID_PREFIX "pid_"
	#define PROCESSGROUP_CGROUP_PROCS_FILE "/cgroup.procs"
	#define PROCESSGROUP_MAX_UID_LEN 11
	#define PROCESSGROUP_MAX_PID_LEN 11
	#define PROCESSGROUP_MAX_PATH_LEN \
	((sizeof(MEM_CGROUP_PATH) > sizeof(ACCT_CGROUP_PATH) ? \
	sizeof(MEM_CGROUP_PATH) : sizeof(ACCT_CGROUP_PATH)) + \
	sizeof(PROCESSGROUP_UID_PREFIX) + 1 + \
	PROCESSGROUP_MAX_UID_LEN + \
	sizeof(PROCESSGROUP_PID_PREFIX) + 1 + \
	PROCESSGROUP_MAX_PID_LEN + \
	sizeof(PROCESSGROUP_CGROUP_PROCS_FILE) + \
	1)

	std::once_flag init_path_flag;

	class ProcessGroup {
	public:
	ProcessGroup() : buf_ptr_(buf_), buf_len_(0) {}

	bool Open(uid_t uid, int pid);

	// Return positive number and sets *pid = next pid in process cgroup on success
	// Returns 0 if there are no pids left in the process cgroup
	// Returns -errno if an error was encountered
	int GetOneAppProcess(pid_t* pid);

	private:
	// Returns positive number of bytes filled on success
	// Returns 0 if there was nothing to read
	// Returns -errno if an error was encountered
	int RefillBuffer();

	android::base::unique_fd fd_;
	char buf_[128];
	char* buf_ptr_;
	size_t buf_len_;
	};

	static const char* getCgroupRootPath() {
	#ifdef USE_MEMCG
	static const char* cgroup_root_path = NULL;
	std::call_once(init_path_flag, [&]() {
	// Check if mem cgroup is mounted, only then check for write-access to avoid
	// SELinux denials
	cgroup_root_path = access(MEM_CGROUP_TASKS, F_OK) \|\| access(MEM_CGROUP_PATH, W_OK) ?
	ACCT_CGROUP_PATH : MEM_CGROUP_PATH;
	});
	return cgroup_root_path;
	#else
	return ACCT_CGROUP_PATH;
	#endif
	}

	static int convertUidToPath(char *path, size_t size, uid_t uid)
	{
	return snprintf(path, size, "%s/%s%d",
	getCgroupRootPath(),
	PROCESSGROUP_UID_PREFIX,
	uid);
	}

	static int convertUidPidToPath(char *path, size_t size, uid_t uid, int pid)
	{
	return snprintf(path, size, "%s/%s%d/%s%d",
	getCgroupRootPath(),
	PROCESSGROUP_UID_PREFIX,
	uid,
	PROCESSGROUP_PID_PREFIX,
	pid);
	}

	bool ProcessGroup::Open(uid_t uid, int pid) {
	char path[PROCESSGROUP_MAX_PATH_LEN] = {0};
	convertUidPidToPath(path, sizeof(path), uid, pid);
	strlcat(path, PROCESSGROUP_CGROUP_PROCS_FILE, sizeof(path));

	int fd = open(path, O_RDONLY);
	if (fd < 0) return false;

	fd_.reset(fd);

	LOG(VERBOSE) << "Initialized context for " << path;

	return true;
	}

	int ProcessGroup::RefillBuffer() {
	memmove(buf_, buf_ptr_, buf_len_);
	buf_ptr_ = buf_;

	ssize_t ret = read(fd_, buf_ptr_ + buf_len_, sizeof(buf_) - buf_len_ - 1);
	if (ret < 0) {
	return -errno;
	} else if (ret == 0) {
	return 0;
	}

	buf_len_ += ret;
	buf_[buf_len_] = 0;
	LOG(VERBOSE) << "Read " << ret << " to buffer: " << buf_;

	assert(buf_len_ <= sizeof(buf_));

	return ret;
	}

	int ProcessGroup::GetOneAppProcess(pid_t* out_pid) {
	*out_pid = 0;

	char* eptr;
	while ((eptr = static_cast<char*>(memchr(buf_ptr_, '\n', buf_len_))) == nullptr) {
	int ret = RefillBuffer();
	if (ret <= 0) return ret;
	}

	*eptr = '\0';
	char* pid_eptr = nullptr;
	errno = 0;
	long pid = strtol(buf_ptr_, &pid_eptr, 10);
	if (errno != 0) {
	return -errno;
	}
	if (pid_eptr != eptr) {
	errno = EINVAL;
	return -errno;
	}

	buf_len_ -= (eptr - buf_ptr_) + 1;
	buf_ptr_ = eptr + 1;

	*out_pid = static_cast<pid_t>(pid);
	return 1;
	}

	static int removeProcessGroup(uid_t uid, int pid)
	{
	int ret;
	char path[PROCESSGROUP_MAX_PATH_LEN] = {0};

	convertUidPidToPath(path, sizeof(path), uid, pid);
	ret = rmdir(path);

	convertUidToPath(path, sizeof(path), uid);
	rmdir(path);

	return ret;
	}

	static void removeUidProcessGroups(const char *uid_path)
	{
	std::unique_ptr<DIR, decltype(&closedir)> uid(opendir(uid_path), closedir);
	if (uid != NULL) {
	dirent* dir;
	while ((dir = readdir(uid.get())) != nullptr) {
	char path[PROCESSGROUP_MAX_PATH_LEN];

	if (dir->d_type != DT_DIR) {
	continue;
	}

	if (strncmp(dir->d_name, PROCESSGROUP_PID_PREFIX, strlen(PROCESSGROUP_PID_PREFIX))) {
	continue;
	}

	snprintf(path, sizeof(path), "%s/%s", uid_path, dir->d_name);
	LOG(VERBOSE) << "Removing " << path;
	if (rmdir(path) == -1) PLOG(WARNING) << "Failed to remove " << path;
	}
	}
	}

	void removeAllProcessGroups()
	{
	LOG(VERBOSE) << "removeAllProcessGroups()";
	const char* cgroup_root_path = getCgroupRootPath();
	std::unique_ptr<DIR, decltype(&closedir)> root(opendir(cgroup_root_path), closedir);
	if (root == NULL) {
	PLOG(ERROR) << "Failed to open " << cgroup_root_path;
	} else {
	dirent* dir;
	while ((dir = readdir(root.get())) != nullptr) {
	char path[PROCESSGROUP_MAX_PATH_LEN];

	if (dir->d_type != DT_DIR) {
	continue;
	}
	if (strncmp(dir->d_name, PROCESSGROUP_UID_PREFIX, strlen(PROCESSGROUP_UID_PREFIX))) {
	continue;
	}

	snprintf(path, sizeof(path), "%s/%s", cgroup_root_path, dir->d_name);
	removeUidProcessGroups(path);
	LOG(VERBOSE) << "Removing " << path;
	if (rmdir(path) == -1) PLOG(WARNING) << "Failed to remove " << path;
	}
	}
	}

	// Returns number of processes killed on success
	// Returns 0 if there are no processes in the process cgroup left to kill
	// Returns -errno on error
	static int doKillProcessGroupOnce(uid_t uid, int initialPid, int signal) {
	ProcessGroup process_group;
	if (!process_group.Open(uid, initialPid)) {
	PLOG(WARNING) << "Failed to open process cgroup uid " << uid << " pid " << initialPid;
	return -errno;
	}

	int ret;
	pid_t pid;
	int processes = 0;
	while ((ret = process_group.GetOneAppProcess(&pid)) > 0 && pid >= 0) {
	processes++;
	if (pid == 0) {
	// Should never happen... but if it does, trying to kill this
	// will boomerang right back and kill us! Let's not let that happen.
	LOG(WARNING) << "Yikes, we've been told to kill pid 0! How about we don't do that?";
	continue;
	}
	LOG(VERBOSE) << "Killing pid " << pid << " in uid " << uid << " as part of process cgroup "
	<< initialPid;
	if (kill(pid, signal) == -1) {
	PLOG(WARNING) << "kill(" << pid << ", " << signal << ") failed";
	}
	}

	return ret >= 0 ? processes : ret;
	}

	static int killProcessGroup(uid_t uid, int initialPid, int signal, int retries) {
	std::chrono::steady_clock::time_point start = std::chrono::steady_clock::now();

	int retry = retries;
	int processes;
	while ((processes = doKillProcessGroupOnce(uid, initialPid, signal)) > 0) {
	LOG(VERBOSE) << "Killed " << processes << " processes for processgroup " << initialPid;
	if (retry > 0) {
	std::this_thread::sleep_for(5ms);
	--retry;
	} else {
	break;
	}
	}

	if (processes < 0) {
	PLOG(ERROR) << "Error encountered killing process cgroup uid " << uid << " pid "
	<< initialPid;
	return -1;
	}

	std::chrono::steady_clock::time_point end = std::chrono::steady_clock::now();
	auto ms = std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count();

	// We only calculate the number of 'processes' when killing the processes.
	// In the retries == 0 case, we only kill the processes once and therefore
	// will not have waited then recalculated how many processes are remaining
	// after the first signals have been sent.
	// Logging anything regarding the number of 'processes' here does not make sense.

	if (processes == 0) {
	if (retries > 0) {
	LOG(INFO) << "Successfully killed process cgroup uid " << uid << " pid " << initialPid
	<< " in " << static_cast<int>(ms) << "ms";
	}
	return removeProcessGroup(uid, initialPid);
	} else {
	if (retries > 0) {
	LOG(ERROR) << "Failed to kill process cgroup uid " << uid << " pid " << initialPid
	<< " in " << static_cast<int>(ms) << "ms, " << processes
	<< " processes remain";
	}
	return -1;
	}
	}

	int killProcessGroup(uid_t uid, int initialPid, int signal) {
	return killProcessGroup(uid, initialPid, signal, 40 /retries/);
	}

	int killProcessGroupOnce(uid_t uid, int initialPid, int signal) {
	return killProcessGroup(uid, initialPid, signal, 0 /retries/);
	}

	static bool mkdirAndChown(const char *path, mode_t mode, uid_t uid, gid_t gid)
	{
	if (mkdir(path, mode) == -1 && errno != EEXIST) {
	return false;
	}

	if (chown(path, uid, gid) == -1) {
	int saved_errno = errno;
	rmdir(path);
	errno = saved_errno;
	return false;
	}

	return true;
	}

	int createProcessGroup(uid_t uid, int initialPid)
	{
	char path[PROCESSGROUP_MAX_PATH_LEN] = {0};

	convertUidToPath(path, sizeof(path), uid);

	if (!mkdirAndChown(path, 0750, AID_SYSTEM, AID_SYSTEM)) {
	PLOG(ERROR) << "Failed to make and chown " << path;
	return -errno;
	}

	convertUidPidToPath(path, sizeof(path), uid, initialPid);

	if (!mkdirAndChown(path, 0750, AID_SYSTEM, AID_SYSTEM)) {
	PLOG(ERROR) << "Failed to make and chown " << path;
	return -errno;
	}

	strlcat(path, PROCESSGROUP_CGROUP_PROCS_FILE, sizeof(path));

	int fd = open(path, O_WRONLY);
	if (fd == -1) {
	int ret = -errno;
	PLOG(ERROR) << "Failed to open " << path;
	return ret;
	}

	char pid[PROCESSGROUP_MAX_PID_LEN + 1] = {0};
	int len = snprintf(pid, sizeof(pid), "%d", initialPid);

	int ret = 0;
	if (write(fd, pid, len) < 0) {
	ret = -errno;
	PLOG(ERROR) << "Failed to write '" << pid << "' to " << path;
	}

	close(fd);
	return ret;
	}