legacy_property_service.c

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <fcntl.h>
#include <stdarg.h>
#include <dirent.h>
#include <limits.h>
#include <errno.h>

#include <cutils/properties.h>

#include "legacy_properties.h"

#include <sys/mman.h>
#include <sys/atomics.h>
#include "legacy_property_service.h"


static int persistent_properties_loaded = 0;
static int property_area_inited = 0;

static int property_set_fd = -1;


typedef struct {
    void *data;
    size_t size;
    int fd;
} workspace;

static int init_workspace(workspace *w, size_t size)
{
    void *data;
    int fd;

        /* dev is a tmpfs that we can use to carve a shared workspace
         * out of, so let's do that...
         */
    fd = open("/dev/__legacy_properties__", O_RDWR | O_CREAT, 0600);
    if (fd < 0)
        return -1;

    if (ftruncate(fd, size) < 0)
        goto out;

    data = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if(data == MAP_FAILED)
        goto out;

    close(fd);

    fd = open("/dev/__legacy_properties__", O_RDONLY);
    if (fd < 0)
        return -1;

    unlink("/dev/__legacy_properties__");

    w->data = data;
    w->size = size;
    w->fd = fd;
    return 0;

out:
    close(fd);
    return -1;
}

/* (8 header words + 247 toc words) = 1020 bytes */
/* 1024 bytes header and toc + 247 prop_infos @ 128 bytes = 32640 bytes */

#define PA_COUNT_MAX  247
#define PA_INFO_START 1024
#define PA_SIZE       32768

static workspace pa_workspace;
static prop_info *pa_info_array;

prop_area *__legacy_property_area__;

static int init_property_area(void)
{
    prop_area *pa;

    if(pa_info_array)
        return -1;

    if(init_workspace(&pa_workspace, PA_SIZE))
        return -1;

    fcntl(pa_workspace.fd, F_SETFD, FD_CLOEXEC);

    pa_info_array = (void*) (((char*) pa_workspace.data) + PA_INFO_START);

    pa = pa_workspace.data;
    memset(pa, 0, PA_SIZE);
    pa->magic = PROP_AREA_MAGIC;
    pa->version = PROP_AREA_VERSION;

    /* plug into the lib property services */
    __legacy_property_area__ = pa;
    property_area_inited = 1;
    return 0;
}

static void update_prop_info(prop_info *pi, const char *value, unsigned len)
{
    pi->serial = pi->serial | 1;
    memcpy(pi->value, value, len + 1);
    pi->serial = (len << 24) | ((pi->serial + 1) & 0xffffff);
    __futex_wake(&pi->serial, INT32_MAX);
}

static const prop_info *__legacy_property_find(const char *name)
{
    prop_area *pa = __legacy_property_area__;
    unsigned count = pa->count;
    unsigned *toc = pa->toc;
    unsigned len = strlen(name);
    prop_info *pi;

    while(count--) {
        unsigned entry = *toc++;
        if(TOC_NAME_LEN(entry) != len) continue;

        pi = TOC_TO_INFO(pa, entry);
        if(memcmp(name, pi->name, len)) continue;

        return pi;
    }

    return 0;
}

static int legacy_property_set(const char *name, const char *value)
{
    prop_area *pa;
    prop_info *pi;

    int namelen = strlen(name);
    int valuelen = strlen(value);

    if(namelen >= PROP_NAME_MAX) return -1;
    if(valuelen >= PROP_VALUE_MAX) return -1;
    if(namelen < 1) return -1;

    pi = (prop_info*) __legacy_property_find(name);


    if(pi != 0) {
        /* ro.* properties may NEVER be modified once set */
        if(!strncmp(name, "ro.", 3)) return -1;

        pa = __legacy_property_area__;
        update_prop_info(pi, value, valuelen);
        pa->serial++;
        __futex_wake(&pa->serial, INT32_MAX);
    } else {
        pa = __legacy_property_area__;
        if(pa->count == PA_COUNT_MAX) return -1;

        pi = pa_info_array + pa->count;
        pi->serial = (valuelen << 24);
        memcpy(pi->name, name, namelen + 1);
        memcpy(pi->value, value, valuelen + 1);

        pa->toc[pa->count] =
            (namelen << 24) | (((unsigned) pi) - ((unsigned) pa));

        pa->count++;
        pa->serial++;
        __futex_wake(&pa->serial, INT32_MAX);
    }

    return 0;
}

void legacy_get_property_workspace(int *fd, int *sz)
{
    *fd = pa_workspace.fd;
    *sz = pa_workspace.size;
}

static void copy_property_to_legacy(const char *key, const char *value, void *cookie)
{
    legacy_property_set(key, value);
}

void legacy_properties_init()
{
    init_property_area();
    property_list(copy_property_to_legacy, 0);
}