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

1 files changed, 763 insertions, 0 deletions

diff --git a/libc/bionic/system_properties.cpp b/libc/bionic/system_properties.cpp
new file mode 100644
index 000000000..7c2f8dc4f
--- /dev/null
+++ b/libc/bionic/system_properties.cpp
@@ -0,0 +1,763 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * 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>
+#include <unistd.h>
+#include <stddef.h>
+#include <errno.h>
+#include <poll.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <string.h>
+
+#include <sys/mman.h>
+
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <sys/select.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <netinet/in.h>
+#include <unistd.h>
+
+#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
+#include <sys/_system_properties.h>
+#include <sys/system_properties.h>
+
+#include <sys/atomics.h>
+
+#include "private/bionic_atomic_inline.h"
+
+#define ALIGN(x, a) (((x) + (a - 1)) & ~(a - 1))
+
+
+static const char property_service_socket[] = "/dev/socket/" PROP_SERVICE_NAME;
+
+
+/*
+ * Properties are stored in a hybrid trie/binary tree structure.
+ * Each property's name is delimited at '.' characters, and the tokens are put
+ * into a trie structure.  Siblings at each level of the trie are stored in a
+ * binary tree.  For instance, "ro.secure"="1" could be stored as follows:
+ *
+ * +-----+   children    +----+   children    +--------+
+ * |     |-------------->| ro |-------------->| secure |
+ * +-----+               +----+               +--------+
+ *                       /    \                /   |
+ *                 left /      \ right   left /    |  prop   +===========+
+ *                     v        v            v     +-------->| ro.secure |
+ *                  +-----+   +-----+     +-----+            +-----------+
+ *                  | net |   | sys |     | com |            |     1     |
+ *                  +-----+   +-----+     +-----+            +===========+
+ */
+
+// Represents a node in the trie.
+struct prop_bt {
+    uint8_t namelen;
+    uint8_t reserved[3];
+
+    volatile uint32_t prop;
+
+    volatile uint32_t left;
+    volatile uint32_t right;
+
+    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&);
+};
+
+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 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;
+
+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) {
+        return -1;
+    }
+
+    return atoi(env);
+}
+
+static int map_prop_area_rw()
+{
+    /* dev is a tmpfs that we can use to carve a shared workspace
+     * out of, so let's do that...
+     */
+    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
+             * mapped the page in and segfaults when trying to write to it
+             */
+            abort();
+        }
+        return -1;
+    }
+
+    // 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) {
+        close(fd);
+        return -1;
+    }
+
+    pa_size = PA_SIZE;
+    pa_data_size = pa_size - sizeof(prop_area);
+    compat_mode = false;
+
+    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;
+    }
+
+    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;
+}
+
+static int map_fd_ro(const int fd) {
+    struct stat fd_stat;
+    if (fstat(fd, &fd_stat) < 0) {
+        return -1;
+    }
+
+    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;
+    }
+
+    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()
+{
+    int fd(open(property_filename, O_RDONLY | O_NOFOLLOW | O_CLOEXEC));
+    if (fd >= 0) {
+        /* For old kernels that don't support O_CLOEXEC */
+        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
+         * exist, we use the environment to get the file descriptor.
+         * For security reasons, we only use this backup if the kernel
+         * returns ENOENT. We don't want to use the backup if the kernel
+         * returns other errors such as ENOMEM or ENFILE, since it
+         * might be possible for an external program to trigger this
+         * condition.
+         */
+        fd = get_fd_from_env();
+        close_fd = false;
+    }
+
+    if (fd < 0) {
+        return -1;
+    }
+
+    const int map_result = map_fd_ro(fd);
+    if (close_fd) {
+        close(fd);
+    }
+
+    return map_result;
+}
+
+static void *allocate_obj(const size_t size, uint32_t *const off)
+{
+    prop_area *pa = __system_property_area__;
+    const size_t aligned = ALIGN(size, sizeof(uint32_t));
+    if (pa->bytes_used + aligned > pa_data_size) {
+        return NULL;
+    }
+
+    *off = pa->bytes_used;
+    pa->bytes_used += aligned;
+    return pa->data + *off;
+}
+
+static prop_bt *new_prop_bt(const char *name, uint8_t namelen, uint32_t *const off)
+{
+    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 NULL;
+}
+
+static prop_info *new_prop_info(const char *name, uint8_t namelen,
+        const char *value, uint8_t valuelen, uint32_t *const off)
+{
+    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 NULL;
+}
+
+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);
+}
+
+static prop_bt *root_node()
+{
+    return reinterpret_cast<prop_bt*>(to_prop_obj(0));
+}
+
+static int cmp_prop_name(const char *one, uint8_t one_len, const char *two,
+        uint8_t two_len)
+{
+    if (one_len < two_len)
+        return -1;
+    else if (one_len > two_len)
+        return 1;
+    else
+        return strncmp(one, two, one_len);
+}
+
+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) {
+        if (!current) {
+            return NULL;
+        }
+
+        const int ret = cmp_prop_name(name, namelen, current->name, current->namelen);
+        if (ret == 0) {
+            return current;
+        }
+
+        if (ret < 0) {
+            if (current->left) {
+                current = reinterpret_cast<prop_bt*>(to_prop_obj(current->left));
+            } else {
+                if (!alloc_if_needed) {
+                   return NULL;
+                }
+
+                // 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 (current->right) {
+                current = reinterpret_cast<prop_bt*>(to_prop_obj(current->right));
+            } else {
+                if (!alloc_if_needed) {
+                   return NULL;
+                }
+
+                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 *const trie, const char *name,
+        uint8_t namelen, const char *value, uint8_t valuelen,
+        bool alloc_if_needed)
+{
+    if (!trie) return NULL;
+
+    const char *remaining_name = name;
+    prop_bt* current = trie;
+    while (true) {
+        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);
+
+        if (!substr_size) {
+            return NULL;
+        }
+
+        prop_bt* root = NULL;
+        if (current->children) {
+            root = reinterpret_cast<prop_bt*>(to_prop_obj(current->children));
+        } else if (alloc_if_needed) {
+            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) {
+            return NULL;
+        }
+
+        current = find_prop_bt(root, remaining_name, substr_size, alloc_if_needed);
+        if (!current) {
+            return NULL;
+        }
+
+        if (!want_subtree)
+            break;
+
+        remaining_name = sep + 1;
+    }
+
+    if (current->prop) {
+        return reinterpret_cast<prop_info*>(to_prop_obj(current->prop));
+    } else if (alloc_if_needed) {
+        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)) {
+        return __system_property_find_compat(name);
+    }
+    return find_property(root_node(), name, strlen(name), NULL, 0, false);
+}
+
+int __system_property_read(const prop_info *pi, char *name, char *value)
+{
+    unsigned serial, len;
+
+    if (__predict_false(compat_mode)) {
+        return __system_property_read_compat(pi, name, value);
+    }
+
+    for(;;) {
+        serial = pi->serial;
+        while(SERIAL_DIRTY(serial)) {
+            __futex_wait((volatile void *)&pi->serial, serial, NULL);
+            serial = pi->serial;
+        }
+        len = SERIAL_VALUE_LEN(serial);
+        memcpy(value, pi->value, len + 1);
+        ANDROID_MEMBAR_FULL();
+        if(serial == pi->serial) {
+            if(name != 0) {
+                strcpy(name, pi->name);
+            }
+            return len;
+        }
+    }
+}
+
+int __system_property_get(const char *name, char *value)
+{
+    const prop_info *pi = __system_property_find(name);
+
+    if (pi != 0) {
+        return __system_property_read(pi, 0, value);
+    } else {
+        value[0] = 0;
+        return 0;
+    }
+}
+
+int __system_property_set(const char *key, const char *value)
+{
+    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);
+
+    const int err = send_prop_msg(&msg);
+    if (err < 0) {
+        return err;
+    }
+
+    return 0;
+}
+
+int __system_property_wait(const prop_info *pi)
+{
+    if (pi == 0) {
+        prop_area *pa = __system_property_area__;
+        const uint32_t n = pa->serial;
+        do {
+            __futex_wait(&pa->serial, n, NULL);
+        } while (n == pa->serial);
+    } else {
+        const uint32_t n = pi->serial;
+        do {
+            __futex_wait((volatile void *)&pi->serial, n, NULL);
+        } while(n == pi->serial);
+    }
+    return 0;
+}
+
+int __system_property_update(prop_info *pi, const char *value, unsigned int len)
+{
+    prop_area *pa = __system_property_area__;
+
+    if (len >= PROP_VALUE_MAX)
+        return -1;
+
+    pi->serial = pi->serial | 1;
+    ANDROID_MEMBAR_FULL();
+    memcpy(pi->value, value, len + 1);
+    ANDROID_MEMBAR_FULL();
+    pi->serial = (len << 24) | ((pi->serial + 1) & 0xffffff);
+    __futex_wake(&pi->serial, INT32_MAX);
+
+    pa->serial++;
+    __futex_wake(&pa->serial, INT32_MAX);
+
+    return 0;
+}
+int __system_property_add(const char *name, unsigned int namelen,
+            const char *value, unsigned int valuelen)
+{
+    prop_area *pa = __system_property_area__;
+    const prop_info *pi;
+
+    if (namelen >= PROP_NAME_MAX)
+        return -1;
+    if (valuelen >= PROP_VALUE_MAX)
+        return -1;
+    if (namelen < 1)
+        return -1;
+
+    pi = find_property(root_node(), name, namelen, value, valuelen, true);
+    if (!pi)
+        return -1;
+
+    pa->serial++;
+    __futex_wake(&pa->serial, INT32_MAX);
+    return 0;
+}
+
+unsigned int __system_property_serial(const prop_info *pi)
+{
+    return pi->serial;
+}
+
+unsigned int __system_property_wait_any(unsigned int serial)
+{
+    prop_area *pa = __system_property_area__;
+
+    do {
+        __futex_wait(&pa->serial, serial, NULL);
+    } while(pa->serial == serial);
+
+    return pa->serial;
+}
+
+const prop_info *__system_property_find_nth(unsigned n)
+{
+    find_nth_cookie cookie(n);
+
+    const int err = __system_property_foreach(find_nth_fn, &cookie);
+    if (err < 0) {
+        return NULL;
+    }
+
+    return cookie.pi;
+}
+
+int __system_property_foreach(void (*propfn)(const prop_info *pi, void *cookie),
+        void *cookie)
+{
+    if (__predict_false(compat_mode)) {
+        return __system_property_foreach_compat(propfn, cookie);
+    }
+
+    return foreach_property(0, propfn, cookie);
+}