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 #pragma once 30 31 /** 32 * @file system_properties.h 33 * @brief System properties. 34 */ 35 36 #include <sys/cdefs.h> 37 #include <stdbool.h> 38 #include <stddef.h> 39 #include <stdint.h> 40 41 __BEGIN_DECLS 42 43 /** An opaque structure representing a system property. */ 44 typedef struct prop_info prop_info; 45 46 /** 47 * The limit on the length of a property value. 48 * (See PROP_NAME_MAX for property names.) 49 */ 50 #define PROP_VALUE_MAX 92 51 52 /** 53 * Sets system property `name` to `value`, creating the system property if it doesn't already exist. 54 * 55 * Returns 0 on success, or -1 on failure. 56 */ 57 int __system_property_set(const char* _Nonnull __name, const char* _Nonnull __value); 58 59 /** 60 * Returns a `prop_info` corresponding system property `name`, or nullptr if it doesn't exist. 61 * Use __system_property_read_callback() to query the current value. 62 * 63 * Property lookup is expensive, so it can be useful to cache the result of this 64 * function rather than using __system_property_get(). 65 */ 66 const prop_info* _Nullable __system_property_find(const char* _Nonnull __name); 67 68 /** 69 * Calls `callback` with a consistent trio of name, value, and serial number 70 * for property `pi`. 71 * 72 * Available since API level 26. 73 */ 74 75 #if __BIONIC_AVAILABILITY_GUARD(26) 76 void __system_property_read_callback(const prop_info* _Nonnull __pi, 77 void (* _Nonnull __callback)(void* _Nullable __cookie, const char* _Nonnull __name, const char* _Nonnull __value, uint32_t __serial), 78 void* _Nullable __cookie) __INTRODUCED_IN(26); 79 #endif /* __BIONIC_AVAILABILITY_GUARD(26) */ 80 81 82 /** 83 * Passes a `prop_info` for each system property to the provided 84 * callback. Use __system_property_read_callback() to read the value of 85 * any of the properties. 86 * 87 * This method is for inspecting and debugging the property system, and not generally useful. 88 * 89 * Returns 0 on success, or -1 on failure. 90 */ 91 int __system_property_foreach(void (* _Nonnull __callback)(const prop_info* _Nonnull __pi, void* _Nullable __cookie), void* _Nullable __cookie); 92 93 /** 94 * Waits for the specific system property identified by `pi` to be updated 95 * past `old_serial`. Waits no longer than `relative_timeout`, or forever 96 * if `relative_timeout` is null. 97 * 98 * If `pi` is null, waits for the global serial number instead. 99 * 100 * If you don't know the current serial, use 0. 101 * 102 * Returns true and updates `*new_serial_ptr` on success, or false if the call 103 * timed out. 104 * 105 * Available since API level 26. 106 */ 107 struct timespec; 108 109 #if __BIONIC_AVAILABILITY_GUARD(26) 110 bool __system_property_wait(const prop_info* _Nullable __pi, uint32_t __old_serial, uint32_t* _Nonnull __new_serial_ptr, const struct timespec* _Nullable __relative_timeout) 111 __INTRODUCED_IN(26); 112 #endif /* __BIONIC_AVAILABILITY_GUARD(26) */ 113 114 115 /** 116 * Deprecated: there's no limit on the length of a property name since 117 * API level 26, though the limit on property values (PROP_VALUE_MAX) remains. 118 */ 119 #define PROP_NAME_MAX 32 120 121 /** Deprecated. Use __system_property_foreach() instead. */ 122 const prop_info* _Nullable __system_property_find_nth(unsigned __n); 123 /** Deprecated. Use __system_property_read_callback() instead. */ 124 int __system_property_read(const prop_info* _Nonnull __pi, char* _Nullable __name, char* _Nonnull __value); 125 /** Deprecated. Use __system_property_read_callback() instead. */ 126 int __system_property_get(const char* _Nonnull __name, char* _Nonnull __value); 127 /** Deprecated: use __system_property_wait() instead. */ 128 uint32_t __system_property_wait_any(uint32_t __old_serial); 129 130 /** 131 * Reads the global serial number of the system properties _area_. 132 * 133 * Called to predict if a series of cached __system_property_find() 134 * objects will have seen __system_property_serial() values change. 135 * Also aids the converse, as changes in the global serial can 136 * also be used to predict if a failed __system_property_find() 137 * could in turn now find a new object; thus preventing the 138 * cycles of effort to poll __system_property_find(). 139 * 140 * Typically called at beginning of a cache cycle to signal if _any_ possible 141 * changes have occurred since last. If there is, one may check each individual 142 * __system_property_serial() to confirm dirty, or __system_property_find() 143 * to check if the property now exists. If a call to __system_property_add() 144 * or __system_property_update() has completed between two calls to 145 * __system_property_area_serial() then the second call will return a larger 146 * value than the first call. Beware of race conditions as changes to the 147 * properties are not atomic, the main value of this call is to determine 148 * whether the expensive __system_property_find() is worth retrying to see if 149 * a property now exists. 150 * 151 * Returns the serial number on success, -1 on error. 152 */ 153 uint32_t __system_property_area_serial(void); 154 155 /** 156 * Reads the serial number of a specific system property previously returned by 157 * __system_property_find(). This is a cheap way to check whether a system 158 * property has changed or not. 159 * 160 * Returns the serial number on success, -1 on error. 161 */ 162 uint32_t __system_property_serial(const prop_info* _Nonnull __pi); 163 164 // 165 // libc implementation detail. 166 // 167 168 /** 169 * Initializes the system properties area in read-only mode. 170 * 171 * This is called automatically during libc initialization, 172 * so user code should never need to call this. 173 * 174 * Returns 0 on success, -1 otherwise. 175 */ 176 int __system_properties_init(void); 177 178 // 179 // init implementation details. 180 // 181 182 #define PROP_SERVICE_NAME "property_service" 183 #define PROP_SERVICE_FOR_SYSTEM_NAME "property_service_for_system" 184 #define PROP_DIRNAME "/dev/__properties__" 185 186 // Messages sent to init. 187 #define PROP_MSG_SETPROP 1 188 #define PROP_MSG_SETPROP2 0x00020001 189 190 // Status codes returned by init (but not passed from libc to the caller). 191 #define PROP_SUCCESS 0 192 #define PROP_ERROR_READ_CMD 0x0004 193 #define PROP_ERROR_READ_DATA 0x0008 194 #define PROP_ERROR_READ_ONLY_PROPERTY 0x000B 195 #define PROP_ERROR_INVALID_NAME 0x0010 196 #define PROP_ERROR_INVALID_VALUE 0x0014 197 #define PROP_ERROR_PERMISSION_DENIED 0x0018 198 #define PROP_ERROR_INVALID_CMD 0x001B 199 #define PROP_ERROR_HANDLE_CONTROL_MESSAGE 0x0020 200 #define PROP_ERROR_SET_FAILED 0x0024 201 202 /** 203 * Initializes the area to be used to store properties. 204 * 205 * Can only be done by the process that has write access to the property area, 206 * typically init. 207 * 208 * See __system_properties_init() for the equivalent for all other processes. 209 */ 210 int __system_property_area_init(void); 211 212 /** 213 * Adds a new system property. 214 * Can only be done by the process that has write access to the property area -- 215 * typically init -- which must handle sequencing to ensure that only one property is 216 * updated at a time. 217 * 218 * Returns 0 on success, -1 if the property area is full. 219 */ 220 int __system_property_add(const char* _Nonnull __name, unsigned int __name_length, const char* _Nonnull __value, unsigned int __value_length); 221 222 /** 223 * Updates the value of a system property returned by __system_property_find(). 224 * Can only be done by the process that has write access to the property area -- 225 * typically init -- which must handle sequencing to ensure that only one property is 226 * updated at a time. 227 * 228 * Returns 0 on success, -1 if the parameters are incorrect. 229 */ 230 int __system_property_update(prop_info* _Nonnull __pi, const char* _Nonnull __value, unsigned int __value_length); 231 232 /** 233 * Reloads the system properties from disk. 234 * Not intended for use by any apps except the Zygote. 235 * Should only be called from the main thread. 236 * 237 * Pointers received from functions such as __system_property_find() 238 * may be invalidated by calls to this function. 239 * 240 * Returns 0 on success, -1 otherwise. 241 * 242 * Available since API level 35. 243 */ 244 245 #if __BIONIC_AVAILABILITY_GUARD(35) 246 int __system_properties_zygote_reload(void) __INTRODUCED_IN(35); 247 #endif /* __BIONIC_AVAILABILITY_GUARD(35) */ 248 249 250 /** 251 * Deprecated: previously for testing, but now that SystemProperties is its own 252 * testable class, there is never a reason to call this function and its 253 * implementation simply returns -1. 254 */ 255 int __system_property_set_filename(const char* _Nullable __unused __filename); 256 257 __END_DECLS 258