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      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 
     37 typedef struct prop_msg prop_msg;
     38 
     39 #define PROP_AREA_MAGIC   0x504f5250
     40 #define PROP_AREA_VERSION 0xfc6ed0ab
     41 #define PROP_AREA_VERSION_COMPAT 0x45434f76
     42 
     43 #define PROP_SERVICE_NAME "property_service"
     44 #define PROP_FILENAME "/dev/__properties__"
     45 
     46 #define PA_SIZE         (128 * 1024)
     47 
     48 #define SERIAL_VALUE_LEN(serial) ((serial) >> 24)
     49 #define SERIAL_DIRTY(serial) ((serial) & 1)
     50 
     51 __BEGIN_DECLS
     52 
     53 struct prop_msg
     54 {
     55     unsigned cmd;
     56     char name[PROP_NAME_MAX];
     57     char value[PROP_VALUE_MAX];
     58 };
     59 
     60 #define PROP_MSG_SETPROP 1
     61 
     62 /*
     63 ** Rules:
     64 **
     65 ** - there is only one writer, but many readers
     66 ** - prop_area.count will never decrease in value
     67 ** - once allocated, a prop_info's name will not change
     68 ** - once allocated, a prop_info's offset will not change
     69 ** - reading a value requires the following steps
     70 **   1. serial = pi->serial
     71 **   2. if SERIAL_DIRTY(serial), wait*, then goto 1
     72 **   3. memcpy(local, pi->value, SERIAL_VALUE_LEN(serial) + 1)
     73 **   4. if pi->serial != serial, goto 2
     74 **
     75 ** - writing a value requires the following steps
     76 **   1. pi->serial = pi->serial | 1
     77 **   2. memcpy(pi->value, local_value, value_len)
     78 **   3. pi->serial = (value_len << 24) | ((pi->serial + 1) & 0xffffff)
     79 */
     80 
     81 #define PROP_PATH_RAMDISK_DEFAULT  "/default.prop"
     82 #define PROP_PATH_SYSTEM_BUILD     "/system/build.prop"
     83 #define PROP_PATH_VENDOR_BUILD     "/vendor/build.prop"
     84 #define PROP_PATH_LOCAL_OVERRIDE   "/data/local.prop"
     85 #define PROP_PATH_FACTORY          "/factory/factory.prop"
     86 
     87 /*
     88 ** Map the property area from the specified filename.  This
     89 ** method is for testing only.
     90 */
     91 int __system_property_set_filename(const char *filename);
     92 
     93 /*
     94 ** Initialize the area to be used to store properties.  Can
     95 ** only be done by a single process that has write access to
     96 ** the property area.
     97 */
     98 int __system_property_area_init();
     99 
    100 /* Read the global serial number of the system properties
    101 **
    102 ** Called to predict if a series of cached __system_property_find
    103 ** objects will have seen __system_property_serial values change.
    104 ** But also aids the converse, as changes in the global serial can
    105 ** also be used to predict if a failed __system_property_find
    106 ** could in-turn now find a new object; thus preventing the
    107 ** cycles of effort to poll __system_property_find.
    108 **
    109 ** Typically called at beginning of a cache cycle to signal if _any_ possible
    110 ** changes have occurred since last. If there is, one may check each individual
    111 ** __system_property_serial to confirm dirty, or __system_property_find
    112 ** to check if the property now exists. If a call to __system_property_add
    113 ** or __system_property_update has completed between two calls to
    114 ** __system_property_area_serial then the second call will return a larger
    115 ** value than the first call. Beware of race conditions as changes to the
    116 ** properties are not atomic, the main value of this call is to determine
    117 ** whether the expensive __system_property_find is worth retrying to see if
    118 ** a property now exists.
    119 **
    120 ** Returns the serial number on success, -1 on error.
    121 */
    122 unsigned int __system_property_area_serial();
    123 
    124 /* Add a new system property.  Can only be done by a single
    125 ** process that has write access to the property area, and
    126 ** that process must handle sequencing to ensure the property
    127 ** does not already exist and that only one property is added
    128 ** or updated at a time.
    129 **
    130 ** Returns 0 on success, -1 if the property area is full.
    131 */
    132 int __system_property_add(const char *name, unsigned int namelen,
    133 			const char *value, unsigned int valuelen);
    134 
    135 /* Update the value of a system property returned by
    136 ** __system_property_find.  Can only be done by a single process
    137 ** that has write access to the property area, and that process
    138 ** must handle sequencing to ensure that only one property is
    139 ** updated at a time.
    140 **
    141 ** Returns 0 on success, -1 if the parameters are incorrect.
    142 */
    143 int __system_property_update(prop_info *pi, const char *value, unsigned int len);
    144 
    145 /* Read the serial number of a system property returned by
    146 ** __system_property_find.
    147 **
    148 ** Returns the serial number on success, -1 on error.
    149 */
    150 unsigned int __system_property_serial(const prop_info *pi);
    151 
    152 /* Wait for any system property to be updated.  Caller must pass
    153 ** in 0 the first time, and the previous return value on each
    154 ** successive call. */
    155 unsigned int __system_property_wait_any(unsigned int serial);
    156 
    157 /*  Compatibility functions to support using an old init with a new libc,
    158  ** mostly for the OTA updater binary.  These can be deleted once OTAs from
    159  ** a pre-K release no longer needed to be supported. */
    160 const prop_info *__system_property_find_compat(const char *name);
    161 int __system_property_read_compat(const prop_info *pi, char *name, char *value);
    162 int __system_property_foreach_compat(
    163         void (*propfn)(const prop_info *pi, void *cookie),
    164         void *cookie);
    165 
    166 /* Initialize the system properties area in read only mode.
    167  * Should be done by all processes that need to read system
    168  * properties.
    169  *
    170  * Returns 0 on success, -1 otherwise.
    171  */
    172 int __system_properties_init();
    173 
    174 __END_DECLS
    175 
    176 #endif
    177 #endif
    178