diff --git a/sdcard/Android.mk b/sdcard/Android.mk
index ac5faa7..b12f3ee 100644
--- a/sdcard/Android.mk
+++ b/sdcard/Android.mk
@@ -2,7 +2,7 @@
 
 include $(CLEAR_VARS)
 
-LOCAL_SRC_FILES := sdcard.c
+LOCAL_SRC_FILES := sdcard.cpp fuse.c
 LOCAL_MODULE := sdcard
 LOCAL_CFLAGS := -Wall -Wno-unused-parameter -Werror
 LOCAL_SHARED_LIBRARIES := liblog libcutils libpackagelistparser
diff --git a/sdcard/sdcard.c b/sdcard/fuse.c
similarity index 73%
rename from sdcard/sdcard.c
rename to sdcard/fuse.c
index f08c9d8..bbf7284 100644
--- a/sdcard/sdcard.c
+++ b/sdcard/fuse.c
@@ -16,238 +16,14 @@
 
 #define LOG_TAG "sdcard"
 
-#include <ctype.h>
-#include <dirent.h>
-#include <errno.h>
-#include <fcntl.h>
-#include <inttypes.h>
-#include <limits.h>
-#include <linux/fuse.h>
-#include <pthread.h>
-#include <stdbool.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <sys/inotify.h>
-#include <sys/mount.h>
-#include <sys/param.h>
-#include <sys/resource.h>
-#include <sys/stat.h>
-#include <sys/statfs.h>
-#include <sys/time.h>
-#include <sys/types.h>
-#include <sys/uio.h>
-#include <unistd.h>
-
-#include <cutils/fs.h>
-#include <cutils/hashmap.h>
-#include <cutils/log.h>
-#include <cutils/multiuser.h>
-#include <packagelistparser/packagelistparser.h>
-
-#include <private/android_filesystem_config.h>
-
-/* README
- *
- * What is this?
- *
- * sdcard is a program that uses FUSE to emulate FAT-on-sdcard style
- * directory permissions (all files are given fixed owner, group, and
- * permissions at creation, owner, group, and permissions are not
- * changeable, symlinks and hardlinks are not createable, etc.
- *
- * See usage() for command line options.
- *
- * It must be run as root, but will drop to requested UID/GID as soon as it
- * mounts a filesystem.  It will refuse to run if requested UID/GID are zero.
- *
- * Things I believe to be true:
- *
- * - ops that return a fuse_entry (LOOKUP, MKNOD, MKDIR, LINK, SYMLINK,
- * CREAT) must bump that node's refcount
- * - don't forget that FORGET can forget multiple references (req->nlookup)
- * - if an op that returns a fuse_entry fails writing the reply to the
- * kernel, you must rollback the refcount to reflect the reference the
- * kernel did not actually acquire
- *
- * This daemon can also derive custom filesystem permissions based on directory
- * structure when requested. These custom permissions support several features:
- *
- * - Apps can access their own files in /Android/data/com.example/ without
- * requiring any additional GIDs.
- * - Separate permissions for protecting directories like Pictures and Music.
- * - Multi-user separation on the same physical device.
- */
-
-#define FUSE_TRACE 0
-
-#if FUSE_TRACE
-#define TRACE(x...) ALOGD(x)
-#else
-#define TRACE(x...) do {} while (0)
-#endif
-
-#define ERROR(x...) ALOGE(x)
+#include "fuse.h"
 
 #define FUSE_UNKNOWN_INO 0xffffffff
 
-/* Maximum number of bytes to write in one request. */
-#define MAX_WRITE (256 * 1024)
-
-/* Maximum number of bytes to read in one request. */
-#define MAX_READ (128 * 1024)
-
-/* Largest possible request.
- * The request size is bounded by the maximum size of a FUSE_WRITE request because it has
- * the largest possible data payload. */
-#define MAX_REQUEST_SIZE (sizeof(struct fuse_in_header) + sizeof(struct fuse_write_in) + MAX_WRITE)
-
 /* Pseudo-error constant used to indicate that no fuse status is needed
  * or that a reply has already been written. */
 #define NO_STATUS 1
 
-/* Supplementary groups to execute with */
-static const gid_t kGroups[1] = { AID_PACKAGE_INFO };
-
-/* Permission mode for a specific node. Controls how file permissions
- * are derived for children nodes. */
-typedef enum {
-    /* Nothing special; this node should just inherit from its parent. */
-    PERM_INHERIT,
-    /* This node is one level above a normal root; used for legacy layouts
-     * which use the first level to represent user_id. */
-    PERM_PRE_ROOT,
-    /* This node is "/" */
-    PERM_ROOT,
-    /* This node is "/Android" */
-    PERM_ANDROID,
-    /* This node is "/Android/data" */
-    PERM_ANDROID_DATA,
-    /* This node is "/Android/obb" */
-    PERM_ANDROID_OBB,
-    /* This node is "/Android/media" */
-    PERM_ANDROID_MEDIA,
-} perm_t;
-
-struct handle {
-    int fd;
-};
-
-struct dirhandle {
-    DIR *d;
-};
-
-struct node {
-    __u32 refcount;
-    __u64 nid;
-    __u64 gen;
-    /*
-     * The inode number for this FUSE node. Note that this isn't stable across
-     * multiple invocations of the FUSE daemon.
-     */
-    __u32 ino;
-
-    /* State derived based on current position in hierarchy. */
-    perm_t perm;
-    userid_t userid;
-    uid_t uid;
-    bool under_android;
-
-    struct node *next;          /* per-dir sibling list */
-    struct node *child;         /* first contained file by this dir */
-    struct node *parent;        /* containing directory */
-
-    size_t namelen;
-    char *name;
-    /* If non-null, this is the real name of the file in the underlying storage.
-     * This may differ from the field "name" only by case.
-     * strlen(actual_name) will always equal strlen(name), so it is safe to use
-     * namelen for both fields.
-     */
-    char *actual_name;
-
-    /* If non-null, an exact underlying path that should be grafted into this
-     * position. Used to support things like OBB. */
-    char* graft_path;
-    size_t graft_pathlen;
-
-    bool deleted;
-};
-
-static int str_hash(void *key) {
-    return hashmapHash(key, strlen(key));
-}
-
-/** Test if two string keys are equal ignoring case */
-static bool str_icase_equals(void *keyA, void *keyB) {
-    return strcasecmp(keyA, keyB) == 0;
-}
-
-/* Global data for all FUSE mounts */
-struct fuse_global {
-    pthread_mutex_t lock;
-
-    uid_t uid;
-    gid_t gid;
-    bool multi_user;
-
-    char source_path[PATH_MAX];
-    char obb_path[PATH_MAX];
-
-    Hashmap* package_to_appid;
-
-    __u64 next_generation;
-    struct node root;
-
-    /* Used to allocate unique inode numbers for fuse nodes. We use
-     * a simple counter based scheme where inode numbers from deleted
-     * nodes aren't reused. Note that inode allocations are not stable
-     * across multiple invocation of the sdcard daemon, but that shouldn't
-     * be a huge problem in practice.
-     *
-     * Note that we restrict inodes to 32 bit unsigned integers to prevent
-     * truncation on 32 bit processes when unsigned long long stat.st_ino is
-     * assigned to an unsigned long ino_t type in an LP32 process.
-     *
-     * Also note that fuse_attr and fuse_dirent inode values are 64 bits wide
-     * on both LP32 and LP64, but the fuse kernel code doesn't squash 64 bit
-     * inode numbers into 32 bit values on 64 bit kernels (see fuse_squash_ino
-     * in fs/fuse/inode.c).
-     *
-     * Accesses must be guarded by |lock|.
-     */
-    __u32 inode_ctr;
-
-    struct fuse* fuse_default;
-    struct fuse* fuse_read;
-    struct fuse* fuse_write;
-};
-
-/* Single FUSE mount */
-struct fuse {
-    struct fuse_global* global;
-
-    char dest_path[PATH_MAX];
-
-    int fd;
-
-    gid_t gid;
-    mode_t mask;
-};
-
-/* Private data used by a single FUSE handler */
-struct fuse_handler {
-    struct fuse* fuse;
-    int token;
-
-    /* To save memory, we never use the contents of the request buffer and the read
-     * buffer at the same time.  This allows us to share the underlying storage. */
-    union {
-        __u8 request_buffer[MAX_REQUEST_SIZE];
-        __u8 read_buffer[MAX_READ + PAGE_SIZE];
-    };
-};
-
 static inline void *id_to_ptr(__u64 nid)
 {
     return (void *) (uintptr_t) nid;
@@ -507,7 +283,7 @@
     }
 }
 
-static void derive_permissions_recursive_locked(struct fuse* fuse, struct node *parent) {
+void derive_permissions_recursive_locked(struct fuse* fuse, struct node *parent) {
     struct node *node;
     for (node = parent->child; node; node = node->next) {
         derive_permissions_locked(fuse, parent, node);
@@ -1608,7 +1384,7 @@
     }
 }
 
-static void handle_fuse_requests(struct fuse_handler* handler)
+void handle_fuse_requests(struct fuse_handler* handler)
 {
     struct fuse* fuse = handler->fuse;
     for (;;) {
@@ -1651,339 +1427,3 @@
         }
     }
 }
-
-static void* start_handler(void* data)
-{
-    struct fuse_handler* handler = data;
-    handle_fuse_requests(handler);
-    return NULL;
-}
-
-static bool remove_str_to_int(void *key, void *value, void *context) {
-    Hashmap* map = context;
-    hashmapRemove(map, key);
-    free(key);
-    return true;
-}
-
-static bool package_parse_callback(pkg_info *info, void *userdata) {
-    struct fuse_global *global = (struct fuse_global *)userdata;
-
-    char* name = strdup(info->name);
-    hashmapPut(global->package_to_appid, name, (void*) (uintptr_t) info->uid);
-    packagelist_free(info);
-    return true;
-}
-
-static bool read_package_list(struct fuse_global* global) {
-    pthread_mutex_lock(&global->lock);
-
-    hashmapForEach(global->package_to_appid, remove_str_to_int, global->package_to_appid);
-
-    bool rc = packagelist_parse(package_parse_callback, global);
-    TRACE("read_package_list: found %zu packages\n",
-            hashmapSize(global->package_to_appid));
-
-    /* Regenerate ownership details using newly loaded mapping */
-    derive_permissions_recursive_locked(global->fuse_default, &global->root);
-
-    pthread_mutex_unlock(&global->lock);
-
-    return rc;
-}
-
-static void watch_package_list(struct fuse_global* global) {
-    struct inotify_event *event;
-    char event_buf[512];
-
-    int nfd = inotify_init();
-    if (nfd < 0) {
-        ERROR("inotify_init failed: %s\n", strerror(errno));
-        return;
-    }
-
-    bool active = false;
-    while (1) {
-        if (!active) {
-            int res = inotify_add_watch(nfd, PACKAGES_LIST_FILE, IN_DELETE_SELF);
-            if (res == -1) {
-                if (errno == ENOENT || errno == EACCES) {
-                    /* Framework may not have created yet, sleep and retry */
-                    ERROR("missing \"%s\"; retrying\n", PACKAGES_LIST_FILE);
-                    sleep(3);
-                    continue;
-                } else {
-                    ERROR("inotify_add_watch failed: %s\n", strerror(errno));
-                    return;
-                }
-            }
-
-            /* Watch above will tell us about any future changes, so
-             * read the current state. */
-            if (read_package_list(global) == false) {
-                ERROR("read_package_list failed\n");
-                return;
-            }
-            active = true;
-        }
-
-        int event_pos = 0;
-        int res = read(nfd, event_buf, sizeof(event_buf));
-        if (res < (int) sizeof(*event)) {
-            if (errno == EINTR)
-                continue;
-            ERROR("failed to read inotify event: %s\n", strerror(errno));
-            return;
-        }
-
-        while (res >= (int) sizeof(*event)) {
-            int event_size;
-            event = (struct inotify_event *) (event_buf + event_pos);
-
-            TRACE("inotify event: %08x\n", event->mask);
-            if ((event->mask & IN_IGNORED) == IN_IGNORED) {
-                /* Previously watched file was deleted, probably due to move
-                 * that swapped in new data; re-arm the watch and read. */
-                active = false;
-            }
-
-            event_size = sizeof(*event) + event->len;
-            res -= event_size;
-            event_pos += event_size;
-        }
-    }
-}
-
-static int usage() {
-    ERROR("usage: sdcard [OPTIONS] <source_path> <label>\n"
-            "    -u: specify UID to run as\n"
-            "    -g: specify GID to run as\n"
-            "    -U: specify user ID that owns device\n"
-            "    -m: source_path is multi-user\n"
-            "    -w: runtime write mount has full write access\n"
-            "\n");
-    return 1;
-}
-
-static int fuse_setup(struct fuse* fuse, gid_t gid, mode_t mask) {
-    char opts[256];
-
-    fuse->fd = open("/dev/fuse", O_RDWR);
-    if (fuse->fd == -1) {
-        ERROR("failed to open fuse device: %s\n", strerror(errno));
-        return -1;
-    }
-
-    umount2(fuse->dest_path, MNT_DETACH);
-
-    snprintf(opts, sizeof(opts),
-            "fd=%i,rootmode=40000,default_permissions,allow_other,user_id=%d,group_id=%d",
-            fuse->fd, fuse->global->uid, fuse->global->gid);
-    if (mount("/dev/fuse", fuse->dest_path, "fuse", MS_NOSUID | MS_NODEV | MS_NOEXEC |
-            MS_NOATIME, opts) != 0) {
-        ERROR("failed to mount fuse filesystem: %s\n", strerror(errno));
-        return -1;
-    }
-
-    fuse->gid = gid;
-    fuse->mask = mask;
-
-    return 0;
-}
-
-static void run(const char* source_path, const char* label, uid_t uid,
-        gid_t gid, userid_t userid, bool multi_user, bool full_write) {
-    struct fuse_global global;
-    struct fuse fuse_default;
-    struct fuse fuse_read;
-    struct fuse fuse_write;
-    struct fuse_handler handler_default;
-    struct fuse_handler handler_read;
-    struct fuse_handler handler_write;
-    pthread_t thread_default;
-    pthread_t thread_read;
-    pthread_t thread_write;
-
-    memset(&global, 0, sizeof(global));
-    memset(&fuse_default, 0, sizeof(fuse_default));
-    memset(&fuse_read, 0, sizeof(fuse_read));
-    memset(&fuse_write, 0, sizeof(fuse_write));
-    memset(&handler_default, 0, sizeof(handler_default));
-    memset(&handler_read, 0, sizeof(handler_read));
-    memset(&handler_write, 0, sizeof(handler_write));
-
-    pthread_mutex_init(&global.lock, NULL);
-    global.package_to_appid = hashmapCreate(256, str_hash, str_icase_equals);
-    global.uid = uid;
-    global.gid = gid;
-    global.multi_user = multi_user;
-    global.next_generation = 0;
-    global.inode_ctr = 1;
-
-    memset(&global.root, 0, sizeof(global.root));
-    global.root.nid = FUSE_ROOT_ID; /* 1 */
-    global.root.refcount = 2;
-    global.root.namelen = strlen(source_path);
-    global.root.name = strdup(source_path);
-    global.root.userid = userid;
-    global.root.uid = AID_ROOT;
-    global.root.under_android = false;
-
-    strcpy(global.source_path, source_path);
-
-    if (multi_user) {
-        global.root.perm = PERM_PRE_ROOT;
-        snprintf(global.obb_path, sizeof(global.obb_path), "%s/obb", source_path);
-    } else {
-        global.root.perm = PERM_ROOT;
-        snprintf(global.obb_path, sizeof(global.obb_path), "%s/Android/obb", source_path);
-    }
-
-    fuse_default.global = &global;
-    fuse_read.global = &global;
-    fuse_write.global = &global;
-
-    global.fuse_default = &fuse_default;
-    global.fuse_read = &fuse_read;
-    global.fuse_write = &fuse_write;
-
-    snprintf(fuse_default.dest_path, PATH_MAX, "/mnt/runtime/default/%s", label);
-    snprintf(fuse_read.dest_path, PATH_MAX, "/mnt/runtime/read/%s", label);
-    snprintf(fuse_write.dest_path, PATH_MAX, "/mnt/runtime/write/%s", label);
-
-    handler_default.fuse = &fuse_default;
-    handler_read.fuse = &fuse_read;
-    handler_write.fuse = &fuse_write;
-
-    handler_default.token = 0;
-    handler_read.token = 1;
-    handler_write.token = 2;
-
-    umask(0);
-
-    if (multi_user) {
-        /* Multi-user storage is fully isolated per user, so "other"
-         * permissions are completely masked off. */
-        if (fuse_setup(&fuse_default, AID_SDCARD_RW, 0006)
-                || fuse_setup(&fuse_read, AID_EVERYBODY, 0027)
-                || fuse_setup(&fuse_write, AID_EVERYBODY, full_write ? 0007 : 0027)) {
-            ERROR("failed to fuse_setup\n");
-            exit(1);
-        }
-    } else {
-        /* Physical storage is readable by all users on device, but
-         * the Android directories are masked off to a single user
-         * deep inside attr_from_stat(). */
-        if (fuse_setup(&fuse_default, AID_SDCARD_RW, 0006)
-                || fuse_setup(&fuse_read, AID_EVERYBODY, full_write ? 0027 : 0022)
-                || fuse_setup(&fuse_write, AID_EVERYBODY, full_write ? 0007 : 0022)) {
-            ERROR("failed to fuse_setup\n");
-            exit(1);
-        }
-    }
-
-    /* Drop privs */
-    if (setgroups(sizeof(kGroups) / sizeof(kGroups[0]), kGroups) < 0) {
-        ERROR("cannot setgroups: %s\n", strerror(errno));
-        exit(1);
-    }
-    if (setgid(gid) < 0) {
-        ERROR("cannot setgid: %s\n", strerror(errno));
-        exit(1);
-    }
-    if (setuid(uid) < 0) {
-        ERROR("cannot setuid: %s\n", strerror(errno));
-        exit(1);
-    }
-
-    if (multi_user) {
-        fs_prepare_dir(global.obb_path, 0775, uid, gid);
-    }
-
-    if (pthread_create(&thread_default, NULL, start_handler, &handler_default)
-            || pthread_create(&thread_read, NULL, start_handler, &handler_read)
-            || pthread_create(&thread_write, NULL, start_handler, &handler_write)) {
-        ERROR("failed to pthread_create\n");
-        exit(1);
-    }
-
-    watch_package_list(&global);
-    ERROR("terminated prematurely\n");
-    exit(1);
-}
-
-int main(int argc, char **argv) {
-    const char *source_path = NULL;
-    const char *label = NULL;
-    uid_t uid = 0;
-    gid_t gid = 0;
-    userid_t userid = 0;
-    bool multi_user = false;
-    bool full_write = false;
-    int i;
-    struct rlimit rlim;
-    int fs_version;
-
-    int opt;
-    while ((opt = getopt(argc, argv, "u:g:U:mw")) != -1) {
-        switch (opt) {
-            case 'u':
-                uid = strtoul(optarg, NULL, 10);
-                break;
-            case 'g':
-                gid = strtoul(optarg, NULL, 10);
-                break;
-            case 'U':
-                userid = strtoul(optarg, NULL, 10);
-                break;
-            case 'm':
-                multi_user = true;
-                break;
-            case 'w':
-                full_write = true;
-                break;
-            case '?':
-            default:
-                return usage();
-        }
-    }
-
-    for (i = optind; i < argc; i++) {
-        char* arg = argv[i];
-        if (!source_path) {
-            source_path = arg;
-        } else if (!label) {
-            label = arg;
-        } else {
-            ERROR("too many arguments\n");
-            return usage();
-        }
-    }
-
-    if (!source_path) {
-        ERROR("no source path specified\n");
-        return usage();
-    }
-    if (!label) {
-        ERROR("no label specified\n");
-        return usage();
-    }
-    if (!uid || !gid) {
-        ERROR("uid and gid must be nonzero\n");
-        return usage();
-    }
-
-    rlim.rlim_cur = 8192;
-    rlim.rlim_max = 8192;
-    if (setrlimit(RLIMIT_NOFILE, &rlim)) {
-        ERROR("Error setting RLIMIT_NOFILE, errno = %d\n", errno);
-    }
-
-    while ((fs_read_atomic_int("/data/.layout_version", &fs_version) == -1) || (fs_version < 3)) {
-        ERROR("installd fs upgrade not yet complete. Waiting...\n");
-        sleep(1);
-    }
-
-    run(source_path, label, uid, gid, userid, multi_user, full_write);
-    return 1;
-}
diff --git a/sdcard/fuse.h b/sdcard/fuse.h
new file mode 100644
index 0000000..e1347f9
--- /dev/null
+++ b/sdcard/fuse.h
@@ -0,0 +1,203 @@
+/*
+ * Copyright (C) 2016 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 FUSE_H_
+#define FUSE_H_
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <linux/fuse.h>
+#include <pthread.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <sys/param.h>
+#include <sys/stat.h>
+#include <sys/statfs.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+#include <unistd.h>
+
+#include <cutils/fs.h>
+#include <cutils/hashmap.h>
+#include <cutils/log.h>
+#include <cutils/multiuser.h>
+#include <packagelistparser/packagelistparser.h>
+
+#include <private/android_filesystem_config.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define FUSE_TRACE 0
+
+#if FUSE_TRACE
+#define TRACE(x...) ALOGD(x)
+#else
+#define TRACE(x...) do {} while (0)
+#endif
+
+#define ERROR(x...) ALOGE(x)
+
+/* Maximum number of bytes to write in one request. */
+#define MAX_WRITE (256 * 1024)
+
+/* Maximum number of bytes to read in one request. */
+#define MAX_READ (128 * 1024)
+
+/* Largest possible request.
+ * The request size is bounded by the maximum size of a FUSE_WRITE request because it has
+ * the largest possible data payload. */
+#define MAX_REQUEST_SIZE (sizeof(struct fuse_in_header) + sizeof(struct fuse_write_in) + MAX_WRITE)
+
+/* Permission mode for a specific node. Controls how file permissions
+ * are derived for children nodes. */
+typedef enum {
+    /* Nothing special; this node should just inherit from its parent. */
+    PERM_INHERIT,
+    /* This node is one level above a normal root; used for legacy layouts
+     * which use the first level to represent user_id. */
+    PERM_PRE_ROOT,
+    /* This node is "/" */
+    PERM_ROOT,
+    /* This node is "/Android" */
+    PERM_ANDROID,
+    /* This node is "/Android/data" */
+    PERM_ANDROID_DATA,
+    /* This node is "/Android/obb" */
+    PERM_ANDROID_OBB,
+    /* This node is "/Android/media" */
+    PERM_ANDROID_MEDIA,
+} perm_t;
+
+struct handle {
+    int fd;
+};
+
+struct dirhandle {
+    DIR *d;
+};
+
+struct node {
+    __u32 refcount;
+    __u64 nid;
+    __u64 gen;
+    /*
+     * The inode number for this FUSE node. Note that this isn't stable across
+     * multiple invocations of the FUSE daemon.
+     */
+    __u32 ino;
+
+    /* State derived based on current position in hierarchy. */
+    perm_t perm;
+    userid_t userid;
+    uid_t uid;
+    bool under_android;
+
+    struct node *next;          /* per-dir sibling list */
+    struct node *child;         /* first contained file by this dir */
+    struct node *parent;        /* containing directory */
+
+    size_t namelen;
+    char *name;
+    /* If non-null, this is the real name of the file in the underlying storage.
+     * This may differ from the field "name" only by case.
+     * strlen(actual_name) will always equal strlen(name), so it is safe to use
+     * namelen for both fields.
+     */
+    char *actual_name;
+
+    /* If non-null, an exact underlying path that should be grafted into this
+     * position. Used to support things like OBB. */
+    char* graft_path;
+    size_t graft_pathlen;
+
+    bool deleted;
+};
+
+/* Global data for all FUSE mounts */
+struct fuse_global {
+    pthread_mutex_t lock;
+
+    uid_t uid;
+    gid_t gid;
+    bool multi_user;
+
+    char source_path[PATH_MAX];
+    char obb_path[PATH_MAX];
+
+    Hashmap* package_to_appid;
+
+    __u64 next_generation;
+    struct node root;
+
+    /* Used to allocate unique inode numbers for fuse nodes. We use
+     * a simple counter based scheme where inode numbers from deleted
+     * nodes aren't reused. Note that inode allocations are not stable
+     * across multiple invocation of the sdcard daemon, but that shouldn't
+     * be a huge problem in practice.
+     *
+     * Note that we restrict inodes to 32 bit unsigned integers to prevent
+     * truncation on 32 bit processes when unsigned long long stat.st_ino is
+     * assigned to an unsigned long ino_t type in an LP32 process.
+     *
+     * Also note that fuse_attr and fuse_dirent inode values are 64 bits wide
+     * on both LP32 and LP64, but the fuse kernel code doesn't squash 64 bit
+     * inode numbers into 32 bit values on 64 bit kernels (see fuse_squash_ino
+     * in fs/fuse/inode.c).
+     *
+     * Accesses must be guarded by |lock|.
+     */
+    __u32 inode_ctr;
+
+    struct fuse* fuse_default;
+    struct fuse* fuse_read;
+    struct fuse* fuse_write;
+};
+
+/* Single FUSE mount */
+struct fuse {
+    struct fuse_global* global;
+
+    char dest_path[PATH_MAX];
+
+    int fd;
+
+    gid_t gid;
+    mode_t mask;
+};
+
+/* Private data used by a single FUSE handler */
+struct fuse_handler {
+    struct fuse* fuse;
+    int token;
+
+    /* To save memory, we never use the contents of the request buffer and the read
+     * buffer at the same time.  This allows us to share the underlying storage. */
+    union {
+        __u8 request_buffer[MAX_REQUEST_SIZE];
+        __u8 read_buffer[MAX_READ + PAGE_SIZE];
+    };
+};
+
+void handle_fuse_requests(struct fuse_handler* handler);
+void derive_permissions_recursive_locked(struct fuse* fuse, struct node *parent);
+
+#ifdef __cplusplus
+}; /* extern "C" */
+#endif
+
+#endif  /* FUSE_H_ */
diff --git a/sdcard/sdcard.cpp b/sdcard/sdcard.cpp
new file mode 100644
index 0000000..00dcaf9
--- /dev/null
+++ b/sdcard/sdcard.cpp
@@ -0,0 +1,418 @@
+// Copyright (C) 2016 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.
+
+#define LOG_TAG "sdcard"
+
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/fuse.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/inotify.h>
+#include <sys/mount.h>
+#include <sys/resource.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <cutils/fs.h>
+#include <cutils/hashmap.h>
+#include <cutils/log.h>
+#include <cutils/multiuser.h>
+#include <packagelistparser/packagelistparser.h>
+
+#include <private/android_filesystem_config.h>
+
+/* README
+ *
+ * What is this?
+ *
+ * sdcard is a program that uses FUSE to emulate FAT-on-sdcard style
+ * directory permissions (all files are given fixed owner, group, and
+ * permissions at creation, owner, group, and permissions are not
+ * changeable, symlinks and hardlinks are not createable, etc.
+ *
+ * See usage() for command line options.
+ *
+ * It must be run as root, but will drop to requested UID/GID as soon as it
+ * mounts a filesystem.  It will refuse to run if requested UID/GID are zero.
+ *
+ * Things I believe to be true:
+ *
+ * - ops that return a fuse_entry (LOOKUP, MKNOD, MKDIR, LINK, SYMLINK,
+ * CREAT) must bump that node's refcount
+ * - don't forget that FORGET can forget multiple references (req->nlookup)
+ * - if an op that returns a fuse_entry fails writing the reply to the
+ * kernel, you must rollback the refcount to reflect the reference the
+ * kernel did not actually acquire
+ *
+ * This daemon can also derive custom filesystem permissions based on directory
+ * structure when requested. These custom permissions support several features:
+ *
+ * - Apps can access their own files in /Android/data/com.example/ without
+ * requiring any additional GIDs.
+ * - Separate permissions for protecting directories like Pictures and Music.
+ * - Multi-user separation on the same physical device.
+ */
+
+#include "fuse.h"
+
+/* Supplementary groups to execute with. */
+static const gid_t kGroups[1] = { AID_PACKAGE_INFO };
+
+static int str_hash(void *key) {
+    return hashmapHash(key, strlen(static_cast<const char*>(key)));
+}
+
+/* Tests if two string keys are equal ignoring case. */
+static bool str_icase_equals(void *keyA, void *keyB) {
+    return strcasecmp(static_cast<const char*>(keyA), static_cast<const char*>(keyB)) == 0;
+}
+
+static bool remove_str_to_int(void *key, void *value, void *context) {
+    Hashmap* map = static_cast<Hashmap*>(context);
+    hashmapRemove(map, key);
+    free(key);
+    return true;
+}
+
+static bool package_parse_callback(pkg_info *info, void *userdata) {
+    struct fuse_global *global = (struct fuse_global *)userdata;
+
+    char* name = strdup(info->name);
+    hashmapPut(global->package_to_appid, name, (void*) (uintptr_t) info->uid);
+    packagelist_free(info);
+    return true;
+}
+
+static bool read_package_list(struct fuse_global* global) {
+    pthread_mutex_lock(&global->lock);
+
+    hashmapForEach(global->package_to_appid, remove_str_to_int, global->package_to_appid);
+
+    bool rc = packagelist_parse(package_parse_callback, global);
+    TRACE("read_package_list: found %zu packages\n",
+            hashmapSize(global->package_to_appid));
+
+    /* Regenerate ownership details using newly loaded mapping */
+    derive_permissions_recursive_locked(global->fuse_default, &global->root);
+
+    pthread_mutex_unlock(&global->lock);
+
+    return rc;
+}
+
+static void watch_package_list(struct fuse_global* global) {
+    struct inotify_event *event;
+    char event_buf[512];
+
+    int nfd = inotify_init();
+    if (nfd < 0) {
+        ERROR("inotify_init failed: %s\n", strerror(errno));
+        return;
+    }
+
+    bool active = false;
+    while (1) {
+        if (!active) {
+            int res = inotify_add_watch(nfd, PACKAGES_LIST_FILE, IN_DELETE_SELF);
+            if (res == -1) {
+                if (errno == ENOENT || errno == EACCES) {
+                    /* Framework may not have created yet, sleep and retry */
+                    ERROR("missing \"%s\"; retrying\n", PACKAGES_LIST_FILE);
+                    sleep(3);
+                    continue;
+                } else {
+                    ERROR("inotify_add_watch failed: %s\n", strerror(errno));
+                    return;
+                }
+            }
+
+            /* Watch above will tell us about any future changes, so
+             * read the current state. */
+            if (read_package_list(global) == false) {
+                ERROR("read_package_list failed\n");
+                return;
+            }
+            active = true;
+        }
+
+        int event_pos = 0;
+        int res = read(nfd, event_buf, sizeof(event_buf));
+        if (res < (int) sizeof(*event)) {
+            if (errno == EINTR)
+                continue;
+            ERROR("failed to read inotify event: %s\n", strerror(errno));
+            return;
+        }
+
+        while (res >= (int) sizeof(*event)) {
+            int event_size;
+            event = (struct inotify_event *) (event_buf + event_pos);
+
+            TRACE("inotify event: %08x\n", event->mask);
+            if ((event->mask & IN_IGNORED) == IN_IGNORED) {
+                /* Previously watched file was deleted, probably due to move
+                 * that swapped in new data; re-arm the watch and read. */
+                active = false;
+            }
+
+            event_size = sizeof(*event) + event->len;
+            res -= event_size;
+            event_pos += event_size;
+        }
+    }
+}
+
+static int fuse_setup(struct fuse* fuse, gid_t gid, mode_t mask) {
+    char opts[256];
+
+    fuse->fd = open("/dev/fuse", O_RDWR);
+    if (fuse->fd == -1) {
+        ERROR("failed to open fuse device: %s\n", strerror(errno));
+        return -1;
+    }
+
+    umount2(fuse->dest_path, MNT_DETACH);
+
+    snprintf(opts, sizeof(opts),
+            "fd=%i,rootmode=40000,default_permissions,allow_other,user_id=%d,group_id=%d",
+            fuse->fd, fuse->global->uid, fuse->global->gid);
+    if (mount("/dev/fuse", fuse->dest_path, "fuse", MS_NOSUID | MS_NODEV | MS_NOEXEC |
+            MS_NOATIME, opts) != 0) {
+        ERROR("failed to mount fuse filesystem: %s\n", strerror(errno));
+        return -1;
+    }
+
+    fuse->gid = gid;
+    fuse->mask = mask;
+
+    return 0;
+}
+
+static void* start_handler(void* data) {
+    struct fuse_handler* handler = static_cast<fuse_handler*>(data);
+    handle_fuse_requests(handler);
+    return NULL;
+}
+
+static void run(const char* source_path, const char* label, uid_t uid,
+        gid_t gid, userid_t userid, bool multi_user, bool full_write) {
+    struct fuse_global global;
+    struct fuse fuse_default;
+    struct fuse fuse_read;
+    struct fuse fuse_write;
+    struct fuse_handler handler_default;
+    struct fuse_handler handler_read;
+    struct fuse_handler handler_write;
+    pthread_t thread_default;
+    pthread_t thread_read;
+    pthread_t thread_write;
+
+    memset(&global, 0, sizeof(global));
+    memset(&fuse_default, 0, sizeof(fuse_default));
+    memset(&fuse_read, 0, sizeof(fuse_read));
+    memset(&fuse_write, 0, sizeof(fuse_write));
+    memset(&handler_default, 0, sizeof(handler_default));
+    memset(&handler_read, 0, sizeof(handler_read));
+    memset(&handler_write, 0, sizeof(handler_write));
+
+    pthread_mutex_init(&global.lock, NULL);
+    global.package_to_appid = hashmapCreate(256, str_hash, str_icase_equals);
+    global.uid = uid;
+    global.gid = gid;
+    global.multi_user = multi_user;
+    global.next_generation = 0;
+    global.inode_ctr = 1;
+
+    memset(&global.root, 0, sizeof(global.root));
+    global.root.nid = FUSE_ROOT_ID; /* 1 */
+    global.root.refcount = 2;
+    global.root.namelen = strlen(source_path);
+    global.root.name = strdup(source_path);
+    global.root.userid = userid;
+    global.root.uid = AID_ROOT;
+    global.root.under_android = false;
+
+    strcpy(global.source_path, source_path);
+
+    if (multi_user) {
+        global.root.perm = PERM_PRE_ROOT;
+        snprintf(global.obb_path, sizeof(global.obb_path), "%s/obb", source_path);
+    } else {
+        global.root.perm = PERM_ROOT;
+        snprintf(global.obb_path, sizeof(global.obb_path), "%s/Android/obb", source_path);
+    }
+
+    fuse_default.global = &global;
+    fuse_read.global = &global;
+    fuse_write.global = &global;
+
+    global.fuse_default = &fuse_default;
+    global.fuse_read = &fuse_read;
+    global.fuse_write = &fuse_write;
+
+    snprintf(fuse_default.dest_path, PATH_MAX, "/mnt/runtime/default/%s", label);
+    snprintf(fuse_read.dest_path, PATH_MAX, "/mnt/runtime/read/%s", label);
+    snprintf(fuse_write.dest_path, PATH_MAX, "/mnt/runtime/write/%s", label);
+
+    handler_default.fuse = &fuse_default;
+    handler_read.fuse = &fuse_read;
+    handler_write.fuse = &fuse_write;
+
+    handler_default.token = 0;
+    handler_read.token = 1;
+    handler_write.token = 2;
+
+    umask(0);
+
+    if (multi_user) {
+        /* Multi-user storage is fully isolated per user, so "other"
+         * permissions are completely masked off. */
+        if (fuse_setup(&fuse_default, AID_SDCARD_RW, 0006)
+                || fuse_setup(&fuse_read, AID_EVERYBODY, 0027)
+                || fuse_setup(&fuse_write, AID_EVERYBODY, full_write ? 0007 : 0027)) {
+            ERROR("failed to fuse_setup\n");
+            exit(1);
+        }
+    } else {
+        /* Physical storage is readable by all users on device, but
+         * the Android directories are masked off to a single user
+         * deep inside attr_from_stat(). */
+        if (fuse_setup(&fuse_default, AID_SDCARD_RW, 0006)
+                || fuse_setup(&fuse_read, AID_EVERYBODY, full_write ? 0027 : 0022)
+                || fuse_setup(&fuse_write, AID_EVERYBODY, full_write ? 0007 : 0022)) {
+            ERROR("failed to fuse_setup\n");
+            exit(1);
+        }
+    }
+
+    /* Drop privs */
+    if (setgroups(sizeof(kGroups) / sizeof(kGroups[0]), kGroups) < 0) {
+        ERROR("cannot setgroups: %s\n", strerror(errno));
+        exit(1);
+    }
+    if (setgid(gid) < 0) {
+        ERROR("cannot setgid: %s\n", strerror(errno));
+        exit(1);
+    }
+    if (setuid(uid) < 0) {
+        ERROR("cannot setuid: %s\n", strerror(errno));
+        exit(1);
+    }
+
+    if (multi_user) {
+        fs_prepare_dir(global.obb_path, 0775, uid, gid);
+    }
+
+    if (pthread_create(&thread_default, NULL, start_handler, &handler_default)
+            || pthread_create(&thread_read, NULL, start_handler, &handler_read)
+            || pthread_create(&thread_write, NULL, start_handler, &handler_write)) {
+        ERROR("failed to pthread_create\n");
+        exit(1);
+    }
+
+    watch_package_list(&global);
+    ERROR("terminated prematurely\n");
+    exit(1);
+}
+
+static int usage() {
+    ERROR("usage: sdcard [OPTIONS] <source_path> <label>\n"
+            "    -u: specify UID to run as\n"
+            "    -g: specify GID to run as\n"
+            "    -U: specify user ID that owns device\n"
+            "    -m: source_path is multi-user\n"
+            "    -w: runtime write mount has full write access\n"
+            "\n");
+    return 1;
+}
+
+int main(int argc, char **argv) {
+    const char *source_path = NULL;
+    const char *label = NULL;
+    uid_t uid = 0;
+    gid_t gid = 0;
+    userid_t userid = 0;
+    bool multi_user = false;
+    bool full_write = false;
+    int i;
+    struct rlimit rlim;
+    int fs_version;
+
+    int opt;
+    while ((opt = getopt(argc, argv, "u:g:U:mw")) != -1) {
+        switch (opt) {
+            case 'u':
+                uid = strtoul(optarg, NULL, 10);
+                break;
+            case 'g':
+                gid = strtoul(optarg, NULL, 10);
+                break;
+            case 'U':
+                userid = strtoul(optarg, NULL, 10);
+                break;
+            case 'm':
+                multi_user = true;
+                break;
+            case 'w':
+                full_write = true;
+                break;
+            case '?':
+            default:
+                return usage();
+        }
+    }
+
+    for (i = optind; i < argc; i++) {
+        char* arg = argv[i];
+        if (!source_path) {
+            source_path = arg;
+        } else if (!label) {
+            label = arg;
+        } else {
+            ERROR("too many arguments\n");
+            return usage();
+        }
+    }
+
+    if (!source_path) {
+        ERROR("no source path specified\n");
+        return usage();
+    }
+    if (!label) {
+        ERROR("no label specified\n");
+        return usage();
+    }
+    if (!uid || !gid) {
+        ERROR("uid and gid must be nonzero\n");
+        return usage();
+    }
+
+    rlim.rlim_cur = 8192;
+    rlim.rlim_max = 8192;
+    if (setrlimit(RLIMIT_NOFILE, &rlim)) {
+        ERROR("Error setting RLIMIT_NOFILE, errno = %d\n", errno);
+    }
+
+    while ((fs_read_atomic_int("/data/.layout_version", &fs_version) == -1) || (fs_version < 3)) {
+        ERROR("installd fs upgrade not yet complete. Waiting...\n");
+        sleep(1);
+    }
+
+    run(source_path, label, uid, gid, userid, multi_user, full_write);
+    return 1;
+}