Move system_properties over to C++.

This change constitutes the minimum amount of
work required to move the code over to C++, address
compiler warnings, and to make it const correct and
idiomatic (within the constraints of being called
from C code).

bug: 13058886

Change-Id: Ic78cf91b7c8e8f07b4ab0781333a9e243763298c

3 files changed, 376 insertions, 319 deletions

diff --git a/libc/Android.mk b/libc/Android.mk
index 4e140f0..c060ff6 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -79,7 +79,6 @@ libc_common_src_files := \
     bionic/strntoimax.c \
     bionic/strntoumax.c \
     bionic/strtotimeval.c \
-    bionic/system_properties.c \
     bionic/system_properties_compat.c \
     bionic/tcgetpgrp.c \
     bionic/tcsetpgrp.c \
@@ -223,6 +222,7 @@ libc_bionic_src_files := \
     bionic/stubs.cpp \
     bionic/symlink.cpp \
     bionic/sysconf.cpp \
+    bionic/system_properties.cpp \
     bionic/sys_siglist.c \
     bionic/sys_signame.c \
     bionic/tdestroy.cpp \
diff --git a/libc/bionic/system_properties.c b/libc/bionic/system_properties.cpp
index 825894f..7c2f8dc 100644
--- a/libc/bionic/system_properties.c
+++ b/libc/bionic/system_properties.cpp
@@ -25,6 +25,7 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
+#include <new>
 #include <stdio.h>
 #include <stdint.h>
 #include <stdlib.h>
@@ -48,6 +49,7 @@
 
 #define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
 #include <sys/_system_properties.h>
+#include <sys/system_properties.h>
 
 #include <sys/atomics.h>
 
@@ -55,24 +57,9 @@
 
 #define ALIGN(x, a) (((x) + (a - 1)) & ~(a - 1))
 
-struct prop_area {
-    unsigned bytes_used;
-    unsigned volatile serial;
-    unsigned magic;
-    unsigned version;
-    unsigned reserved[28];
-    char data[0];
-};
 
-typedef struct prop_area prop_area;
-
-struct prop_info {
-    unsigned volatile serial;
-    char value[PROP_VALUE_MAX];
-    char name[0];
-};
+static const char property_service_socket[] = "/dev/socket/" PROP_SERVICE_NAME;
 
-typedef struct prop_info prop_info;
 
 /*
  * Properties are stored in a hybrid trie/binary tree structure.
@@ -91,34 +78,98 @@ typedef struct prop_info prop_info;
  *                  +-----+   +-----+     +-----+            +===========+
  */
 
-typedef volatile uint32_t prop_off_t;
+// Represents a node in the trie.
 struct prop_bt {
     uint8_t namelen;
     uint8_t reserved[3];
 
-    prop_off_t prop;
+    volatile uint32_t prop;
 
-    prop_off_t left;
-    prop_off_t right;
+    volatile uint32_t left;
+    volatile uint32_t right;
 
-    prop_off_t children;
+    volatile uint32_t children;
 
     char name[0];
+
+    prop_bt(const char *name, const uint8_t name_length) {
+        this->namelen = name_length;
+        memcpy(this->name, name, name_length);
+        this->name[name_length] = '\0';
+        ANDROID_MEMBAR_FULL();
+    }
+
+private:
+    // Disallow copy and assign.
+    prop_bt(const prop_bt&);
+    prop_bt& operator=(const prop_bt&);
 };
 
-typedef struct prop_bt prop_bt;
+struct prop_area {
+    uint32_t bytes_used;
+    volatile uint32_t serial;
+    uint32_t magic;
+    uint32_t version;
+    uint32_t reserved[28];
+    char data[0];
+
+    prop_area(const uint32_t magic, const uint32_t version) :
+        serial(0), magic(magic), version(version) {
+        memset(reserved, 0, sizeof(reserved));
+        // Allocate enough space for the root node.
+        bytes_used = sizeof(prop_bt);
+    }
+
+private:
+    // Disallow copy and assign.
+    prop_area(const prop_area&);
+    prop_area& operator=(const prop_area&);
+};
+
+struct prop_info {
+    volatile uint32_t serial;
+    char value[PROP_VALUE_MAX];
+    char name[0];
+
+    prop_info(const char *name, const uint8_t namelen, const char *value,
+              const uint8_t valuelen) {
+        memcpy(this->name, name, namelen);
+        this->name[namelen] = '\0';
+        this->serial = (valuelen << 24);
+        memcpy(this->value, value, valuelen);
+        this->value[valuelen] = '\0';
+        ANDROID_MEMBAR_FULL();
+    }
+private:
+    // Disallow copy and assign.
+    prop_info(const prop_info&);
+    prop_info& operator=(const prop_info&);
+};
+
+struct find_nth_cookie {
+    uint32_t count;
+    const uint32_t n;
+    const prop_info *pi;
+
+    find_nth_cookie(uint32_t n) : count(0), n(n), pi(NULL) {
+    }
+};
 
-static const char property_service_socket[] = "/dev/socket/" PROP_SERVICE_NAME;
 static char property_filename[PATH_MAX] = PROP_FILENAME;
 static bool compat_mode = false;
+static size_t pa_data_size;
+static size_t pa_size;
 
+// NOTE: This isn't static because system_properties_compat.c
+// requires it.
 prop_area *__system_property_area__ = NULL;
 
-size_t pa_data_size;
-size_t pa_size;
-
 static int get_fd_from_env(void)
 {
+    // This environment variable consistes of two decimal integer
+    // values separated by a ",". The first value is a file descriptor
+    // and the second is the size of the system properties area. The
+    // size is currently unused.
     char *env = getenv("ANDROID_PROPERTY_WORKSPACE");
 
     if (!env) {
@@ -130,15 +181,12 @@ static int get_fd_from_env(void)
 
 static int map_prop_area_rw()
 {
-    prop_area *pa;
-    int fd;
-    int ret;
-
     /* dev is a tmpfs that we can use to carve a shared workspace
      * out of, so let's do that...
      */
-    fd = open(property_filename, O_RDWR | O_CREAT | O_NOFOLLOW | O_CLOEXEC |
-            O_EXCL, 0444);
+    const int fd = open(property_filename,
+                        O_RDWR | O_CREAT | O_NOFOLLOW | O_CLOEXEC | O_EXCL, 0444);
+
     if (fd < 0) {
         if (errno == EACCES) {
             /* for consistency with the case where the process has already
@@ -149,68 +197,87 @@ static int map_prop_area_rw()
         return -1;
     }
 
-    ret = fcntl(fd, F_SETFD, FD_CLOEXEC);
-    if (ret < 0)
-        goto out;
+    // TODO: Is this really required ? Does android run on any kernels that
+    // don't support O_CLOEXEC ?
+    const int ret = fcntl(fd, F_SETFD, FD_CLOEXEC);
+    if (ret < 0) {
+        close(fd);
+        return -1;
+    }
 
-    if (ftruncate(fd, PA_SIZE) < 0)
-        goto out;
+    if (ftruncate(fd, PA_SIZE) < 0) {
+        close(fd);
+        return -1;
+    }
 
     pa_size = PA_SIZE;
     pa_data_size = pa_size - sizeof(prop_area);
     compat_mode = false;
 
-    pa = mmap(NULL, pa_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
-    if(pa == MAP_FAILED)
-        goto out;
+    void *const memory_area = mmap(NULL, pa_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+    if (memory_area == MAP_FAILED) {
+        close(fd);
+        return -1;
+    }
 
-    memset(pa, 0, pa_size);
-    pa->magic = PROP_AREA_MAGIC;
-    pa->version = PROP_AREA_VERSION;
-    /* reserve root node */
-    pa->bytes_used = sizeof(prop_bt);
+    prop_area *pa = new(memory_area) prop_area(PROP_AREA_MAGIC, PROP_AREA_VERSION);
 
     /* plug into the lib property services */
     __system_property_area__ = pa;
 
     close(fd);
     return 0;
-
-out:
-    close(fd);
-    return -1;
 }
 
-int __system_property_set_filename(const char *filename)
-{
-    size_t len = strlen(filename);
-    if (len >= sizeof(property_filename))
+static int map_fd_ro(const int fd) {
+    struct stat fd_stat;
+    if (fstat(fd, &fd_stat) < 0) {
         return -1;
+    }
 
-    strcpy(property_filename, filename);
-    return 0;
-}
+    if ((fd_stat.st_uid != 0)
+            || (fd_stat.st_gid != 0)
+            || ((fd_stat.st_mode & (S_IWGRP | S_IWOTH)) != 0)
+            || (fd_stat.st_size < sizeof(prop_area)) ) {
+        return -1;
+    }
 
-int __system_property_area_init()
-{
-    return map_prop_area_rw();
+    pa_size = fd_stat.st_size;
+    pa_data_size = pa_size - sizeof(prop_area);
+
+    void* const map_result = mmap(NULL, pa_size, PROT_READ, MAP_SHARED, fd, 0);
+    if (map_result == MAP_FAILED) {
+        return -1;
+    }
+
+    prop_area* pa = reinterpret_cast<prop_area*>(map_result);
+    if ((pa->magic != PROP_AREA_MAGIC) || (pa->version != PROP_AREA_VERSION &&
+                pa->version != PROP_AREA_VERSION_COMPAT)) {
+        munmap(pa, pa_size);
+        return -1;
+    }
+
+    if (pa->version == PROP_AREA_VERSION_COMPAT) {
+        compat_mode = true;
+    }
+
+    __system_property_area__ = pa;
+    return 0;
 }
 
 static int map_prop_area()
 {
-    bool fromFile = true;
-    int result = -1;
-    int fd;
-    int ret;
-
-    fd = open(property_filename, O_RDONLY | O_NOFOLLOW | O_CLOEXEC);
+    int fd(open(property_filename, O_RDONLY | O_NOFOLLOW | O_CLOEXEC));
     if (fd >= 0) {
         /* For old kernels that don't support O_CLOEXEC */
-        ret = fcntl(fd, F_SETFD, FD_CLOEXEC);
-        if (ret < 0)
-            goto cleanup;
+        const int ret = fcntl(fd, F_SETFD, FD_CLOEXEC);
+        if (ret < 0) {
+            close(fd);
+            return -1;
+        }
     }
 
+    bool close_fd = true;
     if ((fd < 0) && (errno == ENOENT)) {
         /*
          * For backwards compatibility, if the file doesn't
@@ -222,119 +289,74 @@ static int map_prop_area()
          * condition.
          */
         fd = get_fd_from_env();
-        fromFile = false;
+        close_fd = false;
     }
 
     if (fd < 0) {
         return -1;
     }
 
-    struct stat fd_stat;
-    if (fstat(fd, &fd_stat) < 0) {
-        goto cleanup;
-    }
-
-    if ((fd_stat.st_uid != 0)
-            || (fd_stat.st_gid != 0)
-            || ((fd_stat.st_mode & (S_IWGRP | S_IWOTH)) != 0)
-            || (fd_stat.st_size < sizeof(prop_area)) ) {
-        goto cleanup;
-    }
-
-    pa_size = fd_stat.st_size;
-    pa_data_size = pa_size - sizeof(prop_area);
-    prop_area *pa = mmap(NULL, pa_size, PROT_READ, MAP_SHARED, fd, 0);
-
-    if (pa == MAP_FAILED) {
-        goto cleanup;
-    }
-
-    if((pa->magic != PROP_AREA_MAGIC) || (pa->version != PROP_AREA_VERSION &&
-                pa->version != PROP_AREA_VERSION_COMPAT)) {
-        munmap(pa, pa_size);
-        goto cleanup;
-    }
-
-    if (pa->version == PROP_AREA_VERSION_COMPAT) {
-        compat_mode = true;
-    }
-
-    result = 0;
-
-    __system_property_area__ = pa;
-
-cleanup:
-    if (fromFile) {
+    const int map_result = map_fd_ro(fd);
+    if (close_fd) {
         close(fd);
     }
 
-    return result;
+    return map_result;
 }
 
-int __system_properties_init()
-{
-    return map_prop_area();
-}
-
-static void *new_prop_obj(size_t size, prop_off_t *off)
+static void *allocate_obj(const size_t size, uint32_t *const off)
 {
     prop_area *pa = __system_property_area__;
-    size = ALIGN(size, sizeof(uint32_t));
-
-    if (pa->bytes_used + size > pa_data_size)
+    const size_t aligned = ALIGN(size, sizeof(uint32_t));
+    if (pa->bytes_used + aligned > pa_data_size) {
         return NULL;
+    }
 
     *off = pa->bytes_used;
-    __system_property_area__->bytes_used += size;
-    return __system_property_area__->data + *off;
+    pa->bytes_used += aligned;
+    return pa->data + *off;
 }
 
-static prop_bt *new_prop_bt(const char *name, uint8_t namelen, prop_off_t *off)
+static prop_bt *new_prop_bt(const char *name, uint8_t namelen, uint32_t *const off)
 {
-    prop_off_t off_tmp;
-    prop_bt *bt = new_prop_obj(sizeof(prop_bt) + namelen + 1, &off_tmp);
-    if (bt) {
-        memcpy(bt->name, name, namelen);
-        bt->name[namelen] = '\0';
-        bt->namelen = namelen;
-        ANDROID_MEMBAR_FULL();
-        *off = off_tmp;
+    uint32_t new_offset;
+    void *const offset = allocate_obj(sizeof(prop_bt) + namelen + 1, &new_offset);
+    if (offset) {
+        prop_bt* bt = new(offset) prop_bt(name, namelen);
+        *off = new_offset;
+        return bt;
     }
 
-    return bt;
+    return NULL;
 }
 
 static prop_info *new_prop_info(const char *name, uint8_t namelen,
-        const char *value, uint8_t valuelen, prop_off_t *off)
+        const char *value, uint8_t valuelen, uint32_t *const off)
 {
-    prop_off_t off_tmp;
-    prop_info *info = new_prop_obj(sizeof(prop_info) + namelen + 1, &off_tmp);
-    if (info) {
-        memcpy(info->name, name, namelen);
-        info->name[namelen] = '\0';
-        info->serial = (valuelen << 24);
-        memcpy(info->value, value, valuelen);
-        info->value[valuelen] = '\0';
-        ANDROID_MEMBAR_FULL();
+    uint32_t off_tmp;
+    void* const offset = allocate_obj(sizeof(prop_info) + namelen + 1, &off_tmp);
+    if (offset) {
+        prop_info* info = new(offset) prop_info(name, namelen, value, valuelen);
         *off = off_tmp;
+        return info;
     }
 
-    return info;
+    return NULL;
 }
 
-static void *to_prop_obj(prop_off_t off)
+static void *to_prop_obj(const uint32_t off)
 {
     if (off > pa_data_size)
         return NULL;
     if (!__system_property_area__)
         return NULL;
 
-    return __system_property_area__->data + off;
+    return (__system_property_area__->data + off);
 }
 
 static prop_bt *root_node()
 {
-    return to_prop_obj(0);
+    return reinterpret_cast<prop_bt*>(to_prop_obj(0));
 }
 
 static int cmp_prop_name(const char *one, uint8_t one_len, const char *two,
@@ -348,77 +370,96 @@ static int cmp_prop_name(const char *one, uint8_t one_len, const char *two,
         return strncmp(one, two, one_len);
 }
 
-static prop_bt *find_prop_bt(prop_bt *bt, const char *name, uint8_t namelen,
-        bool alloc_if_needed)
+static prop_bt *find_prop_bt(prop_bt *const bt, const char *name,
+                             uint8_t namelen, bool alloc_if_needed)
 {
+
+    prop_bt* current = bt;
     while (true) {
-        int ret;
-        if (!bt)
-            return bt;
-        ret = cmp_prop_name(name, namelen, bt->name, bt->namelen);
+        if (!current) {
+            return NULL;
+        }
 
+        const int ret = cmp_prop_name(name, namelen, current->name, current->namelen);
         if (ret == 0) {
-            return bt;
-        } else if (ret < 0) {
-            if (bt->left) {
-                bt = to_prop_obj(bt->left);
+            return current;
+        }
+
+        if (ret < 0) {
+            if (current->left) {
+                current = reinterpret_cast<prop_bt*>(to_prop_obj(current->left));
             } else {
-                if (!alloc_if_needed)
+                if (!alloc_if_needed) {
                    return NULL;
-
-                bt = new_prop_bt(name, namelen, &bt->left);
+                }
+
+                // Note that there isn't a race condition here. "clients" never
+                // reach this code-path since It's only the (single threaded) server
+                // that allocates new nodes. Though "bt->left" is volatile, it can't
+                // have changed since the last value was last read.
+                uint32_t new_offset = 0;
+                prop_bt* new_bt = new_prop_bt(name, namelen, &new_offset);
+                if (new_bt) {
+                    current->left = new_offset;
+                }
+                return new_bt;
             }
         } else {
-            if (bt->right) {
-                bt = to_prop_obj(bt->right);
+            if (current->right) {
+                current = reinterpret_cast<prop_bt*>(to_prop_obj(current->right));
             } else {
-                if (!alloc_if_needed)
+                if (!alloc_if_needed) {
                    return NULL;
-
-                bt = new_prop_bt(name, namelen, &bt->right);
+                }
+
+                uint32_t new_offset;
+                prop_bt* new_bt = new_prop_bt(name, namelen, &new_offset);
+                if (new_bt) {
+                    current->right = new_offset;
+                }
+                return new_bt;
             }
         }
     }
 }
 
-static const prop_info *find_property(prop_bt *trie, const char *name,
+static const prop_info *find_property(prop_bt *const trie, const char *name,
         uint8_t namelen, const char *value, uint8_t valuelen,
         bool alloc_if_needed)
 {
-    const char *remaining_name = name;
-
     if (!trie) return NULL;
 
+    const char *remaining_name = name;
+    prop_bt* current = trie;
     while (true) {
-        char *sep = strchr(remaining_name, '.');
-        bool want_subtree = (sep != NULL);
-        uint8_t substr_size;
+        const char *sep = strchr(remaining_name, '.');
+        const bool want_subtree = (sep != NULL);
+        const uint8_t substr_size = (want_subtree) ?
+            sep - remaining_name : strlen(remaining_name);
 
-        prop_bt *root;
-
-        if (want_subtree) {
-            substr_size = sep - remaining_name;
-        } else {
-            substr_size = strlen(remaining_name);
-        }
-
-        if (!substr_size)
+        if (!substr_size) {
             return NULL;
+        }
 
-        if (trie->children) {
-            root = to_prop_obj(trie->children);
+        prop_bt* root = NULL;
+        if (current->children) {
+            root = reinterpret_cast<prop_bt*>(to_prop_obj(current->children));
         } else if (alloc_if_needed) {
-            root = new_prop_bt(remaining_name, substr_size, &trie->children);
-        } else {
-            root = NULL;
+            uint32_t new_bt_offset;
+            root = new_prop_bt(remaining_name, substr_size, &new_bt_offset);
+            if (root) {
+                current->children = new_bt_offset;
+            }
         }
 
-        if (!root)
+        if (!root) {
             return NULL;
+        }
 
-        trie = find_prop_bt(root, remaining_name, substr_size, alloc_if_needed);
-        if (!trie)
+        current = find_prop_bt(root, remaining_name, substr_size, alloc_if_needed);
+        if (!current) {
             return NULL;
+        }
 
         if (!want_subtree)
             break;
@@ -426,15 +467,138 @@ static const prop_info *find_property(prop_bt *trie, const char *name,
         remaining_name = sep + 1;
     }
 
-    if (trie->prop) {
-        return to_prop_obj(trie->prop);
+    if (current->prop) {
+        return reinterpret_cast<prop_info*>(to_prop_obj(current->prop));
     } else if (alloc_if_needed) {
-        return new_prop_info(name, namelen, value, valuelen, &trie->prop);
+        uint32_t new_info_offset;
+        prop_info* new_info = new_prop_info(name, namelen, value, valuelen, &new_info_offset);
+        if (new_info) {
+            current->prop = new_info_offset;
+        }
+
+        return new_info;
     } else {
         return NULL;
     }
 }
 
+static int send_prop_msg(const prop_msg *msg)
+{
+    const int fd = socket(AF_LOCAL, SOCK_STREAM, 0);
+    if (fd < 0) {
+        return -1;
+    }
+
+    const size_t namelen = strlen(property_service_socket);
+
+    sockaddr_un addr;
+    memset(&addr, 0, sizeof(addr));
+    strlcpy(addr.sun_path, property_service_socket, sizeof(addr.sun_path));
+    addr.sun_family = AF_LOCAL;
+    socklen_t alen = namelen + offsetof(sockaddr_un, sun_path) + 1;
+    if (TEMP_FAILURE_RETRY(connect(fd, reinterpret_cast<sockaddr*>(&addr), alen)) < 0) {
+        close(fd);
+        return -1;
+    }
+
+    const int num_bytes = TEMP_FAILURE_RETRY(send(fd, msg, sizeof(prop_msg), 0));
+
+    int result = -1;
+    if (num_bytes == sizeof(prop_msg)) {
+        // We successfully wrote to the property server but now we
+        // wait for the property server to finish its work.  It
+        // acknowledges its completion by closing the socket so we
+        // poll here (on nothing), waiting for the socket to close.
+        // If you 'adb shell setprop foo bar' you'll see the POLLHUP
+        // once the socket closes.  Out of paranoia we cap our poll
+        // at 250 ms.
+        pollfd pollfds[1];
+        pollfds[0].fd = fd;
+        pollfds[0].events = 0;
+        const int poll_result = TEMP_FAILURE_RETRY(poll(pollfds, 1, 250 /* ms */));
+        if (poll_result == 1 && (pollfds[0].revents & POLLHUP) != 0) {
+            result = 0;
+        } else {
+            // Ignore the timeout and treat it like a success anyway.
+            // The init process is single-threaded and its property
+            // service is sometimes slow to respond (perhaps it's off
+            // starting a child process or something) and thus this
+            // times out and the caller thinks it failed, even though
+            // it's still getting around to it.  So we fake it here,
+            // mostly for ctl.* properties, but we do try and wait 250
+            // ms so callers who do read-after-write can reliably see
+            // what they've written.  Most of the time.
+            // TODO: fix the system properties design.
+            result = 0;
+        }
+    }
+
+    close(fd);
+    return result;
+}
+
+static void find_nth_fn(const prop_info *pi, void *ptr)
+{
+    find_nth_cookie *cookie = reinterpret_cast<find_nth_cookie*>(ptr);
+
+    if (cookie->n == cookie->count)
+        cookie->pi = pi;
+
+    cookie->count++;
+}
+
+static int foreach_property(const uint32_t off,
+        void (*propfn)(const prop_info *pi, void *cookie), void *cookie)
+{
+    prop_bt *trie = reinterpret_cast<prop_bt*>(to_prop_obj(off));
+    if (!trie)
+        return -1;
+
+    if (trie->left) {
+        const int err = foreach_property(trie->left, propfn, cookie);
+        if (err < 0)
+            return -1;
+    }
+    if (trie->prop) {
+        prop_info *info = reinterpret_cast<prop_info*>(to_prop_obj(trie->prop));
+        if (!info)
+            return -1;
+        propfn(info, cookie);
+    }
+    if (trie->children) {
+        const int err = foreach_property(trie->children, propfn, cookie);
+        if (err < 0)
+            return -1;
+    }
+    if (trie->right) {
+        const int err = foreach_property(trie->right, propfn, cookie);
+        if (err < 0)
+            return -1;
+    }
+
+    return 0;
+}
+
+int __system_properties_init()
+{
+    return map_prop_area();
+}
+
+int __system_property_set_filename(const char *filename)
+{
+    size_t len = strlen(filename);
+    if (len >= sizeof(property_filename))
+        return -1;
+
+    strcpy(property_filename, filename);
+    return 0;
+}
+
+int __system_property_area_init()
+{
+    return map_prop_area_rw();
+}
+
 const prop_info *__system_property_find(const char *name)
 {
     if (__predict_false(compat_mode)) {
@@ -473,7 +637,7 @@ int __system_property_get(const char *name, char *value)
 {
     const prop_info *pi = __system_property_find(name);
 
-    if(pi != 0) {
+    if (pi != 0) {
         return __system_property_read(pi, 0, value);
     } else {
         value[0] = 0;
@@ -481,84 +645,21 @@ int __system_property_get(const char *name, char *value)
     }
 }
 
-
-static int send_prop_msg(prop_msg *msg)
-{
-    struct pollfd pollfds[1];
-    struct sockaddr_un addr;
-    socklen_t alen;
-    size_t namelen;
-    int s;
-    int r;
-    int result = -1;
-
-    s = socket(AF_LOCAL, SOCK_STREAM, 0);
-    if(s < 0) {
-        return result;
-    }
-
-    memset(&addr, 0, sizeof(addr));
-    namelen = strlen(property_service_socket);
-    strlcpy(addr.sun_path, property_service_socket, sizeof addr.sun_path);
-    addr.sun_family = AF_LOCAL;
-    alen = namelen + offsetof(struct sockaddr_un, sun_path) + 1;
-
-    if(TEMP_FAILURE_RETRY(connect(s, (struct sockaddr *) &addr, alen)) < 0) {
-        close(s);
-        return result;
-    }
-
-    r = TEMP_FAILURE_RETRY(send(s, msg, sizeof(prop_msg), 0));
-
-    if(r == sizeof(prop_msg)) {
-        // We successfully wrote to the property server but now we
-        // wait for the property server to finish its work.  It
-        // acknowledges its completion by closing the socket so we
-        // poll here (on nothing), waiting for the socket to close.
-        // If you 'adb shell setprop foo bar' you'll see the POLLHUP
-        // once the socket closes.  Out of paranoia we cap our poll
-        // at 250 ms.
-        pollfds[0].fd = s;
-        pollfds[0].events = 0;
-        r = TEMP_FAILURE_RETRY(poll(pollfds, 1, 250 /* ms */));
-        if (r == 1 && (pollfds[0].revents & POLLHUP) != 0) {
-            result = 0;
-        } else {
-            // Ignore the timeout and treat it like a success anyway.
-            // The init process is single-threaded and its property
-            // service is sometimes slow to respond (perhaps it's off
-            // starting a child process or something) and thus this
-            // times out and the caller thinks it failed, even though
-            // it's still getting around to it.  So we fake it here,
-            // mostly for ctl.* properties, but we do try and wait 250
-            // ms so callers who do read-after-write can reliably see
-            // what they've written.  Most of the time.
-            // TODO: fix the system properties design.
-            result = 0;
-        }
-    }
-
-    close(s);
-    return result;
-}
-
 int __system_property_set(const char *key, const char *value)
 {
-    int err;
-    prop_msg msg;
-
-    if(key == 0) return -1;
-    if(value == 0) value = "";
-    if(strlen(key) >= PROP_NAME_MAX) return -1;
-    if(strlen(value) >= PROP_VALUE_MAX) return -1;
+    if (key == 0) return -1;
+    if (value == 0) value = "";
+    if (strlen(key) >= PROP_NAME_MAX) return -1;
+    if (strlen(value) >= PROP_VALUE_MAX) return -1;
 
+    prop_msg msg;
     memset(&msg, 0, sizeof msg);
     msg.cmd = PROP_MSG_SETPROP;
     strlcpy(msg.name, key, sizeof msg.name);
     strlcpy(msg.value, value, sizeof msg.value);
 
-    err = send_prop_msg(&msg);
-    if(err < 0) {
+    const int err = send_prop_msg(&msg);
+    if (err < 0) {
         return err;
     }
 
@@ -567,15 +668,14 @@ int __system_property_set(const char *key, const char *value)
 
 int __system_property_wait(const prop_info *pi)
 {
-    unsigned n;
-    if(pi == 0) {
+    if (pi == 0) {
         prop_area *pa = __system_property_area__;
-        n = pa->serial;
+        const uint32_t n = pa->serial;
         do {
             __futex_wait(&pa->serial, n, NULL);
-        } while(n == pa->serial);
+        } while (n == pa->serial);
     } else {
-        n = pi->serial;
+        const uint32_t n = pi->serial;
         do {
             __futex_wait((volatile void *)&pi->serial, n, NULL);
         } while(n == pi->serial);
@@ -602,7 +702,6 @@ int __system_property_update(prop_info *pi, const char *value, unsigned int len)
 
     return 0;
 }
-
 int __system_property_add(const char *name, unsigned int namelen,
             const char *value, unsigned int valuelen)
 {
@@ -641,67 +740,16 @@ unsigned int __system_property_wait_any(unsigned int serial)
     return pa->serial;
 }
 
-struct find_nth_cookie {
-    unsigned count;
-    unsigned n;
-    const prop_info *pi;
-};
-
-static void find_nth_fn(const prop_info *pi, void *ptr)
-{
-    struct find_nth_cookie *cookie = ptr;
-
-    if (cookie->n == cookie->count)
-        cookie->pi = pi;
-
-    cookie->count++;
-}
-
 const prop_info *__system_property_find_nth(unsigned n)
 {
-    struct find_nth_cookie cookie;
-    int err;
+    find_nth_cookie cookie(n);
 
-    memset(&cookie, 0, sizeof(cookie));
-    cookie.n = n;
-
-    err = __system_property_foreach(find_nth_fn, &cookie);
-    if (err < 0)
+    const int err = __system_property_foreach(find_nth_fn, &cookie);
+    if (err < 0) {
         return NULL;
-
-    return cookie.pi;
-}
-
-static int foreach_property(prop_off_t off,
-        void (*propfn)(const prop_info *pi, void *cookie), void *cookie)
-{
-    prop_bt *trie = to_prop_obj(off);
-    if (!trie)
-        return -1;
-
-    if (trie->left) {
-        int err = foreach_property(trie->left, propfn, cookie);
-        if (err < 0)
-            return -1;
-    }
-    if (trie->prop) {
-        prop_info *info = to_prop_obj(trie->prop);
-        if (!info)
-            return -1;
-        propfn(info, cookie);
-    }
-    if (trie->children) {
-        int err = foreach_property(trie->children, propfn, cookie);
-        if (err < 0)
-            return -1;
-    }
-    if (trie->right) {
-        int err = foreach_property(trie->right, propfn, cookie);
-        if (err < 0)
-            return -1;
     }
 
-    return 0;
+    return cookie.pi;
 }
 
 int __system_property_foreach(void (*propfn)(const prop_info *pi, void *cookie),
@@ -709,6 +757,7 @@ int __system_property_foreach(void (*propfn)(const prop_info *pi, void *cookie),
 {
     if (__predict_false(compat_mode)) {
         return __system_property_foreach_compat(propfn, cookie);
-	}
+    }
+
     return foreach_property(0, propfn, cookie);
 }
diff --git a/libc/include/sys/_system_properties.h b/libc/include/sys/_system_properties.h
index 5eee7f0..5a681df 100644
--- a/libc/include/sys/_system_properties.h
+++ b/libc/include/sys/_system_properties.h
@@ -139,6 +139,14 @@ int __system_property_foreach_compat(
         void (*propfn)(const prop_info *pi, void *cookie),
         void *cookie);
 
+/* Initialize the system properties area in read only mode.
+ * Should be done by all processes that need to read system
+ * properties.
+ *
+ * Returns 0 on success, -1 otherwise.
+ */
+int __system_properties_init();
+
 __END_DECLS
 
 #endif