_system_properties.h revision 1dc9e472e19acfe6dc7f41e429236e7eef7ceda1 
1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#ifndef _INCLUDE_SYS__SYSTEM_PROPERTIES_H
30#define _INCLUDE_SYS__SYSTEM_PROPERTIES_H
31
32#ifndef _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
33#error you should #include <sys/system_properties.h> instead
34#else
35#include <sys/system_properties.h>
36
37typedef struct prop_area prop_area;
38typedef struct prop_msg prop_msg;
39
40#define PROP_AREA_MAGIC   0x504f5250
41#define PROP_AREA_VERSION 0x45434f76
42
43#define PROP_SERVICE_NAME "property_service"
44
45/* #define PROP_MAX_ENTRIES 247 */
46/* 247 -> 32620 bytes (<32768) */
47
48#define TOC_NAME_LEN(toc)       ((toc) >> 24)
49#define TOC_TO_INFO(area, toc)  ((prop_info*) (((char*) area) + ((toc) & 0xFFFFFF)))
50
51struct prop_area {
52    unsigned volatile count;
53    unsigned volatile serial;
54    unsigned magic;
55    unsigned version;
56    unsigned reserved[4];
57    unsigned toc[1];
58};
59
60#define SERIAL_VALUE_LEN(serial) ((serial) >> 24)
61#define SERIAL_DIRTY(serial) ((serial) & 1)
62
63struct prop_info {
64    char name[PROP_NAME_MAX];
65    unsigned volatile serial;
66    char value[PROP_VALUE_MAX];
67};
68
69struct prop_msg
70{
71    unsigned cmd;
72    char name[PROP_NAME_MAX];
73    char value[PROP_VALUE_MAX];
74};
75
76#define PROP_MSG_SETPROP 1
77
78/*
79** Rules:
80**
81** - there is only one writer, but many readers
82** - prop_area.count will never decrease in value
83** - once allocated, a prop_info's name will not change
84** - once allocated, a prop_info's offset will not change
85** - reading a value requires the following steps
86**   1. serial = pi->serial
87**   2. if SERIAL_DIRTY(serial), wait*, then goto 1
88**   3. memcpy(local, pi->value, SERIAL_VALUE_LEN(serial) + 1)
89**   4. if pi->serial != serial, goto 2
90**
91** - writing a value requires the following steps
92**   1. pi->serial = pi->serial | 1
93**   2. memcpy(pi->value, local_value, value_len)
94**   3. pi->serial = (value_len << 24) | ((pi->serial + 1) & 0xffffff)
95**
96** Improvements:
97** - maintain the toc sorted by pi->name to allow lookup
98**   by binary search
99**
100*/
101
102#define PROP_PATH_RAMDISK_DEFAULT  "/default.prop"
103#define PROP_PATH_SYSTEM_BUILD     "/system/build.prop"
104#define PROP_PATH_SYSTEM_DEFAULT   "/system/default.prop"
105#define PROP_PATH_LOCAL_OVERRIDE   "/data/local.prop"
106
107#endif
108#endif
109