diff --git a/include/private/android_filesystem_config.h b/include/private/android_filesystem_config.h
index 4a7d377..0ed0d78 100644
--- a/include/private/android_filesystem_config.h
+++ b/include/private/android_filesystem_config.h
@@ -34,8 +34,8 @@
 #endif
 
 /* This is the master Users and Groups config for the platform.
-** DO NOT EVER RENUMBER.
-*/
+ * DO NOT EVER RENUMBER
+ */
 
 #define AID_ROOT             0  /* traditional unix root user */
 
@@ -72,6 +72,10 @@
 #define AID_CLAT          1029  /* clat part of nat464 */
 #define AID_LOOP_RADIO    1030  /* loop radio devices */
 #define AID_MEDIA_DRM     1031  /* MediaDrm plugins */
+#define AID_PACKAGE_INFO  1032  /* access to installed package details */
+#define AID_SDCARD_PICS   1033  /* external storage photos access */
+#define AID_SDCARD_AV     1034  /* external storage audio/video access */
+#define AID_SDCARD_ALL    1035  /* access all users external storage */
 
 #define AID_SHELL         2000  /* adb and debug shell user */
 #define AID_CACHE         2001  /* cache access */
@@ -108,50 +112,61 @@
 };
 
 static const struct android_id_info android_ids[] = {
-    { "root",      AID_ROOT, },
-    { "system",    AID_SYSTEM, },
-    { "radio",     AID_RADIO, },
-    { "bluetooth", AID_BLUETOOTH, },
-    { "graphics",  AID_GRAPHICS, },
-    { "input",     AID_INPUT, },
-    { "audio",     AID_AUDIO, },
-    { "camera",    AID_CAMERA, },
-    { "log",       AID_LOG, },
-    { "compass",   AID_COMPASS, },
-    { "mount",     AID_MOUNT, },
-    { "wifi",      AID_WIFI, },
-    { "dhcp",      AID_DHCP, },
-    { "adb",       AID_ADB, },
-    { "install",   AID_INSTALL, },
-    { "media",     AID_MEDIA, },
-    { "drm",       AID_DRM, },
-    { "mdnsr",     AID_MDNSR, },
-    { "nfc",       AID_NFC, },
-    { "drmrpc",    AID_DRMRPC, },
-    { "shell",     AID_SHELL, },
-    { "cache",     AID_CACHE, },
-    { "diag",      AID_DIAG, },
-    { "net_bt_admin", AID_NET_BT_ADMIN, },
-    { "net_bt",    AID_NET_BT, },
-    { "net_bt_stack",    AID_NET_BT_STACK, },
-    { "sdcard_r",  AID_SDCARD_R, },
-    { "sdcard_rw", AID_SDCARD_RW, },
-    { "media_rw",  AID_MEDIA_RW, },
-    { "vpn",       AID_VPN, },
-    { "keystore",  AID_KEYSTORE, },
-    { "usb",       AID_USB, },
-    { "mtp",       AID_MTP, },
-    { "gps",       AID_GPS, },
-    { "inet",      AID_INET, },
-    { "net_raw",   AID_NET_RAW, },
-    { "net_admin", AID_NET_ADMIN, },
-    { "net_bw_stats", AID_NET_BW_STATS, },
-    { "net_bw_acct", AID_NET_BW_ACCT, },
-    { "loop_radio", AID_LOOP_RADIO, },
-    { "misc",      AID_MISC, },
-    { "nobody",    AID_NOBODY, },
-    { "clat",      AID_CLAT, },
-    { "mediadrm",  AID_MEDIA_DRM, },
+    { "root",          AID_ROOT, },
+
+    { "system",        AID_SYSTEM, },
+
+    { "radio",         AID_RADIO, },
+    { "bluetooth",     AID_BLUETOOTH, },
+    { "graphics",      AID_GRAPHICS, },
+    { "input",         AID_INPUT, },
+    { "audio",         AID_AUDIO, },
+    { "camera",        AID_CAMERA, },
+    { "log",           AID_LOG, },
+    { "compass",       AID_COMPASS, },
+    { "mount",         AID_MOUNT, },
+    { "wifi",          AID_WIFI, },
+    { "adb",           AID_ADB, },
+    { "install",       AID_INSTALL, },
+    { "media",         AID_MEDIA, },
+    { "dhcp",          AID_DHCP, },
+    { "sdcard_rw",     AID_SDCARD_RW, },
+    { "vpn",           AID_VPN, },
+    { "keystore",      AID_KEYSTORE, },
+    { "usb",           AID_USB, },
+    { "drm",           AID_DRM, },
+    { "mdnsr",         AID_MDNSR, },
+    { "gps",           AID_GPS, },
+    // AID_UNUSED1
+    { "media_rw",      AID_MEDIA_RW, },
+    { "mtp",           AID_MTP, },
+    // AID_UNUSED2
+    { "drmrpc",        AID_DRMRPC, },
+    { "nfc",           AID_NFC, },
+    { "sdcard_r",      AID_SDCARD_R, },
+    { "clat",          AID_CLAT, },
+    { "loop_radio",    AID_LOOP_RADIO, },
+    { "mediadrm",      AID_MEDIA_DRM, },
+    { "package_info",  AID_PACKAGE_INFO, },
+    { "sdcard_pics",   AID_SDCARD_PICS, },
+    { "sdcard_av",     AID_SDCARD_AV, },
+    { "sdcard_all",    AID_SDCARD_ALL, },
+
+    { "shell",         AID_SHELL, },
+    { "cache",         AID_CACHE, },
+    { "diag",          AID_DIAG, },
+
+    { "net_bt_admin",  AID_NET_BT_ADMIN, },
+    { "net_bt",        AID_NET_BT, },
+    { "inet",          AID_INET, },
+    { "net_raw",       AID_NET_RAW, },
+    { "net_admin",     AID_NET_ADMIN, },
+    { "net_bw_stats",  AID_NET_BW_STATS, },
+    { "net_bw_acct",   AID_NET_BW_ACCT, },
+    { "net_bt_stack",  AID_NET_BT_STACK, },
+
+    { "misc",          AID_MISC, },
+    { "nobody",        AID_NOBODY, },
 };
 
 #define android_id_count \
diff --git a/sdcard/Android.mk b/sdcard/Android.mk
index fb04d6d..4630db9 100644
--- a/sdcard/Android.mk
+++ b/sdcard/Android.mk
@@ -6,6 +6,6 @@
 LOCAL_MODULE:= sdcard
 LOCAL_CFLAGS := -Wall -Wno-unused-parameter
 
-LOCAL_SHARED_LIBRARIES := libc
+LOCAL_SHARED_LIBRARIES := libc libcutils
 
 include $(BUILD_EXECUTABLE)
diff --git a/sdcard/sdcard.c b/sdcard/sdcard.c
index bff6e67..377c008 100644
--- a/sdcard/sdcard.c
+++ b/sdcard/sdcard.c
@@ -30,6 +30,10 @@
 #include <pthread.h>
 #include <sys/time.h>
 #include <sys/resource.h>
+#include <sys/inotify.h>
+
+#include <cutils/hashmap.h>
+#include <cutils/multiuser.h>
 
 #include <private/android_filesystem_config.h>
 
@@ -57,6 +61,30 @@
  * - 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.
+ *
+ * The derived permissions look like this:
+ *
+ * rwxrwx--x root:sdcard_rw     /
+ * rwxrwx--- root:sdcard_pics   /Pictures
+ * rwxrwx--- root:sdcard_av     /Music
+ *
+ * rwxrwx--x root:sdcard_rw     /Android
+ * rwxrwx--x root:sdcard_rw     /Android/data
+ * rwxrwx--- u0_a12:sdcard_rw   /Android/data/com.example
+ * rwxrwx--x root:sdcard_rw     /Android/obb/
+ * rwxrwx--- u0_a12:sdcard_rw   /Android/obb/com.example
+ *
+ * rwxrwx--- root:sdcard_all    /Android/user
+ * rwxrwx--x root:sdcard_rw     /Android/user/10
+ * rwxrwx--- u10_a12:sdcard_rw  /Android/user/10/Android/data/com.example
  */
 
 #define FUSE_TRACE 0
@@ -89,6 +117,23 @@
  * or that a reply has already been written. */
 #define NO_STATUS 1
 
+/* Path to system-provided mapping of package name to appIds */
+static const char* const kPackagesListFile = "/data/system/packages.list";
+
+/* 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 {
+    PERM_INHERIT,
+    PERM_ROOT,
+    PERM_ANDROID,
+    PERM_ANDROID_DATA,
+    PERM_ANDROID_OBB,
+    PERM_ANDROID_USER,
+} perm_t;
+
 struct handle {
     int fd;
 };
@@ -97,11 +142,22 @@
     DIR *d;
 };
 
+struct package {
+    appid_t appid;
+};
+
 struct node {
     __u32 refcount;
     __u64 nid;
     __u64 gen;
 
+    /* State derived based on current position in hierarchy. */
+    perm_t perm;
+    userid_t userid;
+    uid_t uid;
+    gid_t gid;
+    mode_t mode;
+
     struct node *next;          /* per-dir sibling list */
     struct node *child;         /* first contained file by this dir */
     struct node *parent;        /* containing directory */
@@ -116,14 +172,25 @@
     char *actual_name;
 };
 
+static int str_hash(void *key) {
+    return hashmapHash(key, strlen(key));
+}
+
+static bool str_equals(void *keyA, void *keyB) {
+    return strcmp(keyA, keyB) == 0;
+}
+
 /* Global data structure shared by all fuse handlers. */
 struct fuse {
     pthread_mutex_t lock;
 
     __u64 next_generation;
     int fd;
+    bool derive_perms;
     struct node root;
     char rootpath[PATH_MAX];
+
+    Hashmap *package_to_appid;
 };
 
 /* Private data used by a single fuse handler. */
@@ -258,7 +325,7 @@
         struct dirent* entry;
         DIR* dir = opendir(path);
         if (!dir) {
-            ERROR("opendir %s failed: %s", path, strerror(errno));
+            ERROR("opendir %s failed: %s\n", path, strerror(errno));
             return actual;
         }
         while ((entry = readdir(dir))) {
@@ -273,9 +340,9 @@
     return actual;
 }
 
-static void attr_from_stat(struct fuse_attr *attr, const struct stat *s, __u64 nid)
+static void attr_from_stat(struct fuse_attr *attr, const struct stat *s, const struct node* node)
 {
-    attr->ino = nid;
+    attr->ino = node->nid;
     attr->size = s->st_size;
     attr->blocks = s->st_blocks;
     attr->atime = s->st_atime;
@@ -287,19 +354,89 @@
     attr->mode = s->st_mode;
     attr->nlink = s->st_nlink;
 
-        /* force permissions to something reasonable:
-         * world readable
-         * writable by the sdcard group
-         */
-    if (attr->mode & 0100) {
-        attr->mode = (attr->mode & (~0777)) | 0775;
-    } else {
-        attr->mode = (attr->mode & (~0777)) | 0664;
+    attr->uid = node->uid;
+    attr->gid = node->gid;
+
+    /* Filter requested mode based on underlying file, and
+     * pass through file type. */
+    int owner_mode = s->st_mode & 0700;
+    int filtered_mode = node->mode & (owner_mode | (owner_mode >> 3) | (owner_mode >> 6));
+    attr->mode = (attr->mode & S_IFMT) | filtered_mode;
+}
+
+static void derive_permissions_locked(struct fuse* fuse, struct node *parent,
+        struct node *node) {
+    struct package* package;
+
+    /* By default, each node inherits from its parent */
+    node->perm = PERM_INHERIT;
+    node->userid = parent->userid;
+    node->uid = parent->uid;
+    node->gid = parent->gid;
+    node->mode = parent->mode;
+
+    if (!fuse->derive_perms) {
+        return;
     }
 
-        /* all files owned by root.sdcard */
-    attr->uid = 0;
-    attr->gid = AID_SDCARD_RW;
+    /* Derive custom permissions based on parent and current node */
+    switch (parent->perm) {
+    case PERM_INHERIT:
+        /* Already inherited above */
+        break;
+    case PERM_ROOT:
+        if (!strcmp(node->name, "Android")) {
+            /* App-specific directories inside; let anyone traverse */
+            node->perm = PERM_ANDROID;
+            node->mode = 0771;
+        } else if (!strcmp(node->name, "DCIM")
+                || !strcmp(node->name, "Pictures")) {
+            node->gid = AID_SDCARD_PICS;
+            node->mode = 0770;
+        } else if (!strcmp(node->name, "Alarms")
+                || !strcmp(node->name, "Movies")
+                || !strcmp(node->name, "Music")
+                || !strcmp(node->name, "Notifications")
+                || !strcmp(node->name, "Podcasts")
+                || !strcmp(node->name, "Ringtones")) {
+            node->gid = AID_SDCARD_AV;
+            node->mode = 0770;
+        }
+        break;
+    case PERM_ANDROID:
+        if (!strcmp(node->name, "data")) {
+            /* App-specific directories inside; let anyone traverse */
+            node->perm = PERM_ANDROID_DATA;
+            node->mode = 0771;
+        } else if (!strcmp(node->name, "obb")) {
+            /* App-specific directories inside; let anyone traverse */
+            node->perm = PERM_ANDROID_OBB;
+            node->mode = 0771;
+        } else if (!strcmp(node->name, "user")) {
+            /* User directories must only be accessible to system, protected
+             * by sdcard_all. Zygote will bind mount the appropriate user-
+             * specific path. */
+            node->perm = PERM_ANDROID_USER;
+            node->gid = AID_SDCARD_ALL;
+            node->mode = 0770;
+        }
+        break;
+    case PERM_ANDROID_DATA:
+    case PERM_ANDROID_OBB:
+        package = hashmapGet(fuse->package_to_appid, node->name);
+        if (package != NULL) {
+            node->uid = multiuser_get_uid(parent->userid, package->appid);
+        }
+        node->mode = 0770;
+        break;
+    case PERM_ANDROID_USER:
+        /* Root of a secondary user */
+        node->perm = PERM_ROOT;
+        node->userid = atoi(node->name);
+        node->gid = AID_SDCARD_RW;
+        node->mode = 0771;
+        break;
+    }
 }
 
 struct node *create_node_locked(struct fuse* fuse,
@@ -330,6 +467,8 @@
     node->namelen = namelen;
     node->nid = ptr_to_id(node);
     node->gen = fuse->next_generation++;
+
+    derive_permissions_locked(fuse, parent, node);
     acquire_node_locked(node);
     add_node_to_parent_locked(node, parent);
     return node;
@@ -422,18 +561,33 @@
     return child;
 }
 
-static void fuse_init(struct fuse *fuse, int fd, const char *source_path)
+static void fuse_init(struct fuse *fuse, int fd, const char *source_path, bool derive_perms)
 {
     pthread_mutex_init(&fuse->lock, NULL);
 
     fuse->fd = fd;
     fuse->next_generation = 0;
+    fuse->derive_perms = derive_perms;
 
     memset(&fuse->root, 0, sizeof(fuse->root));
     fuse->root.nid = FUSE_ROOT_ID; /* 1 */
     fuse->root.refcount = 2;
     fuse->root.namelen = strlen(source_path);
     fuse->root.name = strdup(source_path);
+
+    fuse->root.perm = PERM_ROOT;
+    fuse->root.userid = 0;
+    fuse->root.uid = AID_ROOT;
+    fuse->root.gid = AID_SDCARD_RW;
+    if (derive_perms) {
+        fuse->root.mode = 0771;
+    } else {
+        fuse->root.mode = 0775;
+    }
+
+    if (derive_perms) {
+        fuse->package_to_appid = hashmapCreate(256, str_hash, str_equals);
+    }
 }
 
 static void fuse_status(struct fuse *fuse, __u64 unique, int err)
@@ -475,7 +629,36 @@
     struct stat s;
 
     if (lstat(path, &s) < 0) {
-        return -errno;
+        /* But wait! We'll automatically create a directory if its
+         * a valid package name under data or obb, since apps may not
+         * have enough permissions to create for themselves. */
+        if (errno == ENOENT && (parent->perm == PERM_ANDROID_DATA
+                || parent->perm == PERM_ANDROID_OBB)) {
+            TRACE("automatically creating %s\n", path);
+
+            pthread_mutex_lock(&fuse->lock);
+            bool validPackage = hashmapContainsKey(fuse->package_to_appid, name);
+            pthread_mutex_unlock(&fuse->lock);
+
+            if (!validPackage) {
+                return -ENOENT;
+            }
+            if (mkdir(path, 0775) == -1) {
+                /* We might have raced with ourselves and already created */
+                if (errno != EEXIST) {
+                    ERROR("failed to mkdir(%s): %s\n", name, strerror(errno));
+                    return -ENOENT;
+                }
+            }
+
+            /* It should exist this time around! */
+            if (lstat(path, &s) < 0) {
+                ERROR("failed to lstat(%s): %s\n", name, strerror(errno));
+                return -errno;
+            }
+        } else {
+            return -errno;
+        }
     }
 
     pthread_mutex_lock(&fuse->lock);
@@ -485,7 +668,7 @@
         return -ENOMEM;
     }
     memset(&out, 0, sizeof(out));
-    attr_from_stat(&out.attr, &s, node->nid);
+    attr_from_stat(&out.attr, &s, node);
     out.attr_valid = 10;
     out.entry_valid = 10;
     out.nodeid = node->nid;
@@ -495,7 +678,7 @@
     return NO_STATUS;
 }
 
-static int fuse_reply_attr(struct fuse* fuse, __u64 unique, __u64 nid,
+static int fuse_reply_attr(struct fuse* fuse, __u64 unique, const struct node* node,
         const char* path)
 {
     struct fuse_attr_out out;
@@ -505,7 +688,7 @@
         return -errno;
     }
     memset(&out, 0, sizeof(out));
-    attr_from_stat(&out.attr, &s, nid);
+    attr_from_stat(&out.attr, &s, node);
     out.attr_valid = 10;
     fuse_reply(fuse, unique, &out, sizeof(out));
     return NO_STATUS;
@@ -567,7 +750,7 @@
     if (!node) {
         return -ENOENT;
     }
-    return fuse_reply_attr(fuse, hdr->unique, hdr->nodeid, path);
+    return fuse_reply_attr(fuse, hdr->unique, node, path);
 }
 
 static int handle_setattr(struct fuse* fuse, struct fuse_handler* handler,
@@ -625,7 +808,7 @@
             return -errno;
         }
     }
-    return fuse_reply_attr(fuse, hdr->unique, hdr->nodeid, path);
+    return fuse_reply_attr(fuse, hdr->unique, node, path);
 }
 
 static int handle_mknod(struct fuse* fuse, struct fuse_handler* handler,
@@ -1206,6 +1389,111 @@
     return NULL;
 }
 
+static bool hashmap_remove(void *key, void *value, void *context) {
+    Hashmap* map = context;
+    hashmapRemove(map, key);
+    free(key);
+    free(value);
+    return true;
+}
+
+static int read_package_list(struct fuse *fuse) {
+    pthread_mutex_lock(&fuse->lock);
+
+    hashmapForEach(fuse->package_to_appid, hashmap_remove, fuse->package_to_appid);
+
+    FILE* file = fopen(kPackagesListFile, "r");
+    if (!file) {
+        ERROR("failed to open package list: %s\n", strerror(errno));
+        pthread_mutex_unlock(&fuse->lock);
+        return -1;
+    }
+
+    char buf[512];
+    while (fgets(buf, sizeof(buf), file) != NULL) {
+        char package_name[512];
+        int appid;
+        if (sscanf(buf, "%s %d", package_name, &appid) == 2) {
+            char* package_name_dup = strdup(package_name);
+            struct package* package = malloc(sizeof(struct package));
+            if (!package_name_dup || !package) {
+                ERROR("cannot allocate package details\n");
+                return -ENOMEM;
+            }
+
+            package->appid = appid;
+            hashmapPut(fuse->package_to_appid, package_name_dup, package);
+        }
+    }
+
+    TRACE("read_package_list: found %d packages\n", hashmapSize(fuse->package_to_appid));
+    fclose(file);
+    pthread_mutex_unlock(&fuse->lock);
+    return 0;
+}
+
+static void watch_package_list(struct fuse* fuse) {
+    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, kPackagesListFile, IN_DELETE_SELF);
+            if (res == -1) {
+                if (errno == ENOENT || errno == EACCES) {
+                    /* Framework may not have created yet, sleep and retry */
+                    ERROR("missing packages.list; retrying\n");
+                    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(fuse) == -1) {
+                ERROR("read_package_list failed: %s\n", strerror(errno));
+                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 ignite_fuse(struct fuse* fuse, int num_threads)
 {
     struct fuse_handler* handlers;
@@ -1213,7 +1501,7 @@
 
     handlers = malloc(num_threads * sizeof(struct fuse_handler));
     if (!handlers) {
-        ERROR("cannot allocate storage for threads");
+        ERROR("cannot allocate storage for threads\n");
         return -ENOMEM;
     }
 
@@ -1222,16 +1510,25 @@
         handlers[i].token = i;
     }
 
-    for (i = 1; i < num_threads; i++) {
+    /* When deriving permissions, this thread is used to process inotify events,
+     * otherwise it becomes one of the FUSE handlers. */
+    i = fuse->derive_perms ? 0 : 1;
+    for (; i < num_threads; i++) {
         pthread_t thread;
         int res = pthread_create(&thread, NULL, start_handler, &handlers[i]);
         if (res) {
-            ERROR("failed to start thread #%d, error=%d", i, res);
+            ERROR("failed to start thread #%d, error=%d\n", i, res);
             goto quit;
         }
     }
-    handle_fuse_requests(&handlers[0]);
-    ERROR("terminated prematurely");
+
+    if (fuse->derive_perms) {
+        watch_package_list(fuse);
+    } else {
+        handle_fuse_requests(&handlers[0]);
+    }
+
+    ERROR("terminated prematurely\n");
 
     /* don't bother killing all of the other threads or freeing anything,
      * should never get here anyhow */
@@ -1241,14 +1538,17 @@
 
 static int usage()
 {
-    ERROR("usage: sdcard [-t<threads>] <source_path> <dest_path> <uid> <gid>\n"
-            "    -t<threads>: specify number of threads to use, default -t%d\n"
+    ERROR("usage: sdcard [OPTIONS] <source_path> <dest_path>\n"
+            "    -u: specify UID to run as\n"
+            "    -g: specify GID to run as\n"
+            "    -t: specify number of threads to use (default %d)\n"
+            "    -d: derive file permissions based on path\n"
             "\n", DEFAULT_NUM_THREADS);
     return 1;
 }
 
 static int run(const char* source_path, const char* dest_path, uid_t uid, gid_t gid,
-        int num_threads) {
+        int num_threads, bool derive_perms) {
     int fd;
     char opts[256];
     int res;
@@ -1259,7 +1559,7 @@
 
     fd = open("/dev/fuse", O_RDWR);
     if (fd < 0){
-        ERROR("cannot open fuse device (error %d)\n", errno);
+        ERROR("cannot open fuse device: %s\n", strerror(errno));
         return -1;
     }
 
@@ -1269,23 +1569,29 @@
 
     res = mount("/dev/fuse", dest_path, "fuse", MS_NOSUID | MS_NODEV, opts);
     if (res < 0) {
-        ERROR("cannot mount fuse filesystem (error %d)\n", errno);
+        ERROR("cannot mount fuse filesystem: %s\n", strerror(errno));
+        goto error;
+    }
+
+    res = setgroups(sizeof(kGroups) / sizeof(kGroups[0]), kGroups);
+    if (res < 0) {
+        ERROR("cannot setgroups: %s\n", strerror(errno));
         goto error;
     }
 
     res = setgid(gid);
     if (res < 0) {
-        ERROR("cannot setgid (error %d)\n", errno);
+        ERROR("cannot setgid: %s\n", strerror(errno));
         goto error;
     }
 
     res = setuid(uid);
     if (res < 0) {
-        ERROR("cannot setuid (error %d)\n", errno);
+        ERROR("cannot setuid: %s\n", strerror(errno));
         goto error;
     }
 
-    fuse_init(&fuse, fd, source_path);
+    fuse_init(&fuse, fd, source_path, derive_perms);
 
     umask(0);
     res = ignite_fuse(&fuse, num_threads);
@@ -1306,33 +1612,41 @@
     uid_t uid = 0;
     gid_t gid = 0;
     int num_threads = DEFAULT_NUM_THREADS;
+    bool derive_perms = false;
     int i;
     struct rlimit rlim;
 
-    for (i = 1; i < argc; i++) {
+    int opt;
+    while ((opt = getopt(argc, argv, "u:g:t:d")) != -1) {
+        switch (opt) {
+            case 'u':
+                uid = strtoul(optarg, NULL, 10);
+                break;
+            case 'g':
+                gid = strtoul(optarg, NULL, 10);
+                break;
+            case 't':
+                num_threads = strtoul(optarg, NULL, 10);
+                break;
+            case 'd':
+                derive_perms = true;
+                break;
+            case '?':
+            default:
+                return usage();
+        }
+    }
+
+    for (i = optind; i < argc; i++) {
         char* arg = argv[i];
-        if (!strncmp(arg, "-t", 2))
-            num_threads = strtoul(arg + 2, 0, 10);
-        else if (!source_path)
+        if (!source_path) {
             source_path = arg;
-        else if (!dest_path)
+        } else if (!dest_path) {
             dest_path = arg;
-        else if (!uid) {
-            char* endptr = NULL;
-            errno = 0;
-            uid = strtoul(arg, &endptr, 10);
-            if (*endptr != '\0' || errno != 0) {
-                ERROR("Invalid uid");
-                return usage();
-            }
+        } else if (!uid) {
+            uid = strtoul(arg, NULL, 10);
         } else if (!gid) {
-            char* endptr = NULL;
-            errno = 0;
-            gid = strtoul(arg, &endptr, 10);
-            if (*endptr != '\0' || errno != 0) {
-                ERROR("Invalid gid");
-                return usage();
-            }
+            gid = strtoul(arg, NULL, 10);
         } else {
             ERROR("too many arguments\n");
             return usage();
@@ -1362,6 +1676,6 @@
         ERROR("Error setting RLIMIT_NOFILE, errno = %d\n", errno);
     }
 
-    res = run(source_path, dest_path, uid, gid, num_threads);
+    res = run(source_path, dest_path, uid, gid, num_threads, derive_perms);
     return res < 0 ? 1 : 0;
 }