diff --git a/include/cutils/fs.h b/include/cutils/fs.h
new file mode 100644
index 0000000..04c8839
--- /dev/null
+++ b/include/cutils/fs.h
@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#ifndef __CUTILS_FS_H
+#define __CUTILS_FS_H
+
+#include <sys/types.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * Ensure that directory exists with given mode and owners.
+ */
+extern int fs_prepare_dir(const char* path, mode_t mode, uid_t uid, gid_t gid);
+
+/*
+ * Read single plaintext integer from given file, correctly handling files
+ * partially written with fs_write_atomic_int().
+ */
+extern int fs_read_atomic_int(const char* path, int* value);
+
+/*
+ * Write single plaintext integer to given file, creating backup while
+ * in progress.
+ */
+extern int fs_write_atomic_int(const char* path, int value);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __CUTILS_FS_H */
diff --git a/include/cutils/multiuser.h b/include/cutils/multiuser.h
index 0bf403c..635ddb1 100644
--- a/include/cutils/multiuser.h
+++ b/include/cutils/multiuser.h
@@ -30,9 +30,9 @@
 typedef uid_t userid_t;
 typedef uid_t appid_t;
 
-extern userid_t multiuser_getUserId(uid_t uid);
-extern appid_t multiuser_getAppId(uid_t uid);
-extern uid_t multiuser_getUid(userid_t userId, appid_t appId);
+extern userid_t multiuser_get_user_id(uid_t uid);
+extern appid_t multiuser_get_app_id(uid_t uid);
+extern uid_t multiuser_get_uid(userid_t userId, appid_t appId);
 
 #ifdef __cplusplus
 }
diff --git a/libcutils/Android.mk b/libcutils/Android.mk
index 9c48ad2..d9bd8d8 100644
--- a/libcutils/Android.mk
+++ b/libcutils/Android.mk
@@ -75,6 +75,7 @@
 else
     commonSources += \
         abort_socket.c \
+        fs.c \
         selector.c \
         tztime.c \
         multiuser.c \
diff --git a/libcutils/fs.c b/libcutils/fs.c
new file mode 100644
index 0000000..1788eca
--- /dev/null
+++ b/libcutils/fs.c
@@ -0,0 +1,138 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#include <cutils/fs.h>
+#include <cutils/log.h>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <limits.h>
+
+#define ALL_PERMS (S_ISUID | S_ISGID | S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO)
+#define BUF_SIZE 64
+
+int fs_prepare_dir(const char* path, mode_t mode, uid_t uid, gid_t gid) {
+    // Check if path needs to be created
+    struct stat sb;
+    if (lstat(path, &sb) == -1) {
+        if (errno == ENOENT) {
+            goto create;
+        } else {
+            ALOGE("Failed to stat(%s): %s", path, strerror(errno));
+            return -1;
+        }
+    }
+
+    // Exists, verify status
+    if (!S_ISDIR(sb.st_mode)) {
+        ALOGE("Not a directory: %s", path);
+        return -1;
+    }
+    if (((sb.st_mode & ALL_PERMS) == mode) && (sb.st_uid == uid) && (sb.st_gid == gid)) {
+        return 0;
+    } else {
+        goto fixup;
+    }
+
+create:
+    if (mkdir(path, mode) == -1) {
+        ALOGE("Failed to mkdir(%s): %s", path, strerror(errno));
+        return -1;
+    }
+
+fixup:
+    if (chmod(path, mode) == -1) {
+        ALOGE("Failed to chown(%s, %d): %s", path, mode, strerror(errno));
+        return -1;
+    }
+    if (chown(path, uid, gid) == -1) {
+        ALOGE("Failed to chown(%s, %d, %d): %s", path, uid, gid, strerror(errno));
+        return -1;
+    }
+
+    return 0;
+}
+
+int fs_read_atomic_int(const char* path, int* out_value) {
+    int fd = open(path, O_RDONLY);
+    if (fd == -1) {
+        ALOGE("Failed to read %s: %s", path, strerror(errno));
+        return -1;
+    }
+
+    char buf[BUF_SIZE];
+    if (read(fd, buf, BUF_SIZE) == -1) {
+        ALOGE("Failed to read %s: %s", path, strerror(errno));
+        goto fail;
+    }
+    if (sscanf(buf, "%d", out_value) != 1) {
+        ALOGE("Failed to parse %s: %s", path, strerror(errno));
+        goto fail;
+    }
+    close(fd);
+    return 0;
+
+fail:
+    close(fd);
+    *out_value = -1;
+    return -1;
+}
+
+int fs_write_atomic_int(const char* path, int value) {
+    char temp[PATH_MAX];
+    if (snprintf(temp, PATH_MAX, "%s.XXXXXX", path) >= PATH_MAX) {
+        ALOGE("Path too long");
+        return -1;
+    }
+
+    int fd = mkstemp(temp);
+    if (fd == -1) {
+        ALOGE("Failed to open %s: %s", temp, strerror(errno));
+        return -1;
+    }
+
+    char buf[BUF_SIZE];
+    int len = snprintf(buf, BUF_SIZE, "%d", value) + 1;
+    if (len > BUF_SIZE) {
+        ALOGE("Value %d too large: %s", value, strerror(errno));
+        goto fail;
+    }
+    if (write(fd, buf, len) < len) {
+        ALOGE("Failed to write %s: %s", temp, strerror(errno));
+        goto fail;
+    }
+    if (close(fd) == -1) {
+        ALOGE("Failed to close %s: %s", temp, strerror(errno));
+        goto fail_closed;
+    }
+
+    if (rename(temp, path) == -1) {
+        ALOGE("Failed to rename %s to %s: %s", temp, path, strerror(errno));
+        goto fail_closed;
+    }
+
+    return 0;
+
+fail:
+    close(fd);
+fail_closed:
+    unlink(temp);
+    return -1;
+}
diff --git a/libcutils/multiuser.c b/libcutils/multiuser.c
index 3c86cee..7c74bb8 100644
--- a/libcutils/multiuser.c
+++ b/libcutils/multiuser.c
@@ -16,14 +16,14 @@
 
 #include <cutils/multiuser.h>
 
-userid_t multiuser_getUserId(uid_t uid) {
+userid_t multiuser_get_user_id(uid_t uid) {
     return uid / MULTIUSER_APP_PER_USER_RANGE;
 }
 
-appid_t multiuser_getAppId(uid_t uid) {
+appid_t multiuser_get_app_id(uid_t uid) {
     return uid % MULTIUSER_APP_PER_USER_RANGE;
 }
 
-uid_t multiuser_getUid(userid_t userId, appid_t appId) {
+uid_t multiuser_get_uid(userid_t userId, appid_t appId) {
     return userId * MULTIUSER_APP_PER_USER_RANGE + (appId % MULTIUSER_APP_PER_USER_RANGE);
 }