1 | /** |
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2 | * @file rtems/bdbuf.h |
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3 | * |
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4 | * Block Device Buffer Management |
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5 | */ |
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6 | |
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7 | /* |
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8 | * Copyright (C) 2001 OKTET Ltd., St.-Petersburg, Russia |
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9 | * Author: Victor V. Vengerov <vvv@oktet.ru> |
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10 | * |
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11 | * Copyright (C) 2008 Chris Johns <chrisj@rtems.org> |
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12 | * Rewritten to remove score mutex access. Fixes many performance |
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13 | * issues. |
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14 | * |
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15 | * @(#) bdbuf.h,v 1.9 2005/02/02 00:06:18 joel Exp |
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16 | */ |
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17 | |
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18 | #ifndef _RTEMS_BDBUF_H |
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19 | #define _RTEMS_BDBUF_H |
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20 | |
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21 | #include <rtems.h> |
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22 | #include <rtems/libio.h> |
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23 | #include <rtems/chain.h> |
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24 | |
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25 | #include "rtems/blkdev.h" |
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26 | #include "rtems/diskdevs.h" |
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27 | |
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28 | #ifdef __cplusplus |
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29 | extern "C" { |
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30 | #endif |
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31 | |
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32 | |
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33 | /** |
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34 | * State of a buffer in the cache. |
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35 | */ |
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36 | typedef enum |
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37 | { |
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38 | RTEMS_BDBUF_STATE_EMPTY = 0, /*< Not in use. */ |
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39 | RTEMS_BDBUF_STATE_READ_AHEAD = 1, /*< Holds read ahead data only */ |
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40 | RTEMS_BDBUF_STATE_CACHED = 2, /*< In the cache and available */ |
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41 | RTEMS_BDBUF_STATE_ACCESS = 3, /*< The user has the buffer */ |
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42 | RTEMS_BDBUF_STATE_MODIFIED = 4, /*< In the cache but modified */ |
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43 | RTEMS_BDBUF_STATE_ACCESS_MODIFIED = 5, /*< With the user but modified */ |
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44 | RTEMS_BDBUF_STATE_SYNC = 6, /*< Requested to be sync'ed */ |
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45 | RTEMS_BDBUF_STATE_TRANSFER = 7 /*< Being transferred to or from disk */ |
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46 | } rtems_bdbuf_buf_state; |
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47 | |
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48 | /** |
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49 | * To manage buffers we using buffer descriptors (BD). A BD holds a buffer plus |
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50 | * a range of other information related to managing the buffer in the cache. To |
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51 | * speed-up buffer lookup descriptors are organized in AVL-Tree. The fields |
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52 | * 'dev' and 'block' are search keys. |
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53 | */ |
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54 | typedef struct rtems_bdbuf_buffer |
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55 | { |
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56 | rtems_chain_node link; /* Link in the BD onto a number of lists. */ |
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57 | |
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58 | struct rtems_bdbuf_avl_node |
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59 | { |
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60 | signed char cache; /*< Cache */ |
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61 | struct rtems_bdbuf_buffer* left; /*< Left Child */ |
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62 | struct rtems_bdbuf_buffer* right; /*< Right Child */ |
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63 | signed char bal; /*< The balance of the sub-tree */ |
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64 | } avl; |
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65 | |
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66 | dev_t dev; /*< device number */ |
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67 | rtems_blkdev_bnum block; /*< block number on the device */ |
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68 | |
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69 | unsigned char* buffer; /*< Pointer to the buffer memory area */ |
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70 | int error; /*< If not 0 indicate an error value (errno) |
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71 | * which can be used by user later */ |
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72 | |
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73 | volatile rtems_bdbuf_buf_state state; /*< State of the buffer. */ |
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74 | |
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75 | volatile uint32_t waiters; /*< The number of threads waiting on this |
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76 | * buffer. */ |
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77 | rtems_bdpool_id pool; /*< Identifier of buffer pool to which this buffer |
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78 | belongs */ |
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79 | |
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80 | volatile uint32_t hold_timer; /*< Timer to indicate how long a buffer |
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81 | * has been held in the cache modified. */ |
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82 | } rtems_bdbuf_buffer; |
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83 | |
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84 | /** |
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85 | * The groups of the blocks with the same size are collected in a pool. Note |
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86 | * that a several of the buffer's groups with the same size can exists. |
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87 | */ |
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88 | typedef struct rtems_bdbuf_pool |
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89 | { |
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90 | uint32_t blksize; /*< The size of the blocks (in bytes) */ |
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91 | uint32_t nblks; /*< Number of blocks in this pool */ |
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92 | |
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93 | uint32_t flags; /*< Configuration flags */ |
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94 | |
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95 | rtems_id lock; /*< The pool lock. Lock this data and |
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96 | * all BDs. */ |
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97 | rtems_id sync_lock; /*< Sync calls lock writes. */ |
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98 | bool sync_active; /*< True if a sync is active. */ |
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99 | rtems_id sync_requester; /*< The sync requester. */ |
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100 | dev_t sync_device; /*< The device to sync */ |
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101 | |
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102 | rtems_bdbuf_buffer* tree; /*< Buffer descriptor lookup AVL tree |
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103 | * root */ |
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104 | rtems_chain_control ready; /*< Free buffers list (or read-ahead) */ |
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105 | rtems_chain_control lru; /*< Last recently used list */ |
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106 | rtems_chain_control modified; /*< Modified buffers list */ |
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107 | rtems_chain_control sync; /*< Buffers to sync list */ |
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108 | |
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109 | rtems_id access; /*< Obtain if waiting for a buffer in the |
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110 | * ACCESS state. */ |
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111 | volatile uint32_t access_waiters; /*< Count of access blockers. */ |
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112 | rtems_id transfer; /*< Obtain if waiting for a buffer in the |
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113 | * TRANSFER state. */ |
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114 | volatile uint32_t transfer_waiters; /*< Count of transfer blockers. */ |
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115 | rtems_id waiting; /*< Obtain if waiting for a buffer and the |
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116 | * none are available. */ |
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117 | volatile uint32_t wait_waiters; /*< Count of waiting blockers. */ |
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118 | |
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119 | rtems_bdbuf_buffer* bds; /*< Pointer to table of buffer descriptors |
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120 | * allocated for this buffer pool. */ |
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121 | void* buffers; /*< The buffer's memory. */ |
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122 | } rtems_bdbuf_pool; |
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123 | |
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124 | /** |
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125 | * Configuration structure describes block configuration (size, amount, memory |
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126 | * location) for buffering layer pool. |
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127 | */ |
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128 | typedef struct rtems_bdbuf_pool_config { |
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129 | int size; /*< Size of block */ |
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130 | int num; /*< Number of blocks of appropriate size */ |
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131 | unsigned char* mem_area; /*< Pointer to the blocks location or NULL, in this |
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132 | * case memory for blocks will be allocated by |
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133 | * Buffering Layer with the help of RTEMS partition |
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134 | * manager */ |
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135 | } rtems_bdbuf_pool_config; |
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136 | |
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137 | /** |
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138 | * External references provided by the user for each pool in the system. |
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139 | */ |
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140 | extern rtems_bdbuf_pool_config rtems_bdbuf_pool_configuration[]; |
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141 | extern int rtems_bdbuf_pool_configuration_size; |
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142 | |
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143 | /** |
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144 | * Buffering configuration definition. See confdefs.h for support on using this |
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145 | * structure. |
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146 | */ |
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147 | typedef struct rtems_bdbuf_config { |
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148 | uint32_t max_read_ahead_blocks; /*< Number of blocks to read ahead. */ |
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149 | uint32_t max_write_blocks; /*< Number of blocks to write at once. */ |
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150 | rtems_task_priority swapout_priority; /*< Priority of the swap out task. */ |
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151 | uint32_t swapout_period; /*< Period swapout checks buf timers. */ |
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152 | uint32_t swap_block_hold; /*< Period a buffer is held. */ |
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153 | } rtems_bdbuf_config; |
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154 | |
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155 | /** |
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156 | * External referernce to the configuration. The configuration is provided by |
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157 | * the user. |
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158 | */ |
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159 | extern rtems_bdbuf_config rtems_bdbuf_configuration; |
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160 | |
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161 | /** |
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162 | * The max_read_ahead_blocks value is altered if there are fewer buffers |
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163 | * than this defined max. This stops thrashing in the cache. |
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164 | */ |
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165 | #define RTEMS_BDBUF_MAX_READ_AHEAD_BLOCKS_DEFAULT 32 |
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166 | #define RTEMS_BDBUF_MAX_WRITE_BLOCKS_DEFAULT 16 |
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167 | #define RTEMS_BDBUF_SWAPOUT_TASK_PRIORITY_DEFAULT 15 |
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168 | #define RTEMS_BDBUF_SWAPOUT_TASK_SWAP_PERIOD_DEFAULT 250 /* milli-seconds */ |
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169 | #define RTEMS_BDBUF_SWAPOUT_TASK_BLOCK_HOLD_DEFAULT 1000 /* milli-seconds */ |
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170 | |
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171 | /** |
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172 | * Prepare buffering layer to work - initialize buffer descritors and (if it is |
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173 | * neccessary) buffers. Buffers will be allocated accoriding to the |
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174 | * configuration table, each entry describes the size of block and the size of |
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175 | * the pool. After initialization all blocks is placed into the ready state. |
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176 | * lists. |
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177 | * |
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178 | * @return RTEMS status code (RTEMS_SUCCESSFUL if operation completed |
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179 | * successfully or error code if error is occured) |
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180 | */ |
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181 | rtems_status_code |
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182 | rtems_bdbuf_init (void); |
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183 | |
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184 | /** |
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185 | * Get block buffer for data to be written into. The buffers is set to the |
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186 | * access or modifed access state. If the buffer is in the cache and modified |
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187 | * the state is access modified else the state is access. This buffer contents |
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188 | * are not initialised if the buffer is not already in the cache. If the block |
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189 | * is already resident in memory it is returned how-ever if not in memory the |
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190 | * buffer is not read from disk. This call is used when writing the whole block |
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191 | * on a disk rather than just changing a part of it. If there is no buffers |
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192 | * available this call will block. A buffer obtained with this call will not be |
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193 | * involved in a transfer request and will not be returned to another user |
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194 | * until released. If the buffer is already with a user when this call is made |
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195 | * the call is blocked until the buffer is returned. The highest priority |
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196 | * waiter will obtain the buffer first. |
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197 | * |
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198 | * The block number is the linear block number. This is relative to the start |
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199 | * of the partition on the media. |
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200 | * |
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201 | * @param device Device number (constructed of major and minor device number) |
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202 | * @param block Linear media block number |
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203 | * @param bd Reference to the buffer descriptor pointer. |
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204 | * |
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205 | * @return RTEMS status code (RTEMS_SUCCESSFUL if operation completed |
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206 | * successfully or error code if error is occured) |
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207 | */ |
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208 | rtems_status_code |
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209 | rtems_bdbuf_get (dev_t device, rtems_blkdev_bnum block, rtems_bdbuf_buffer** bd); |
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210 | |
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211 | /** |
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212 | * Get the block buffer and if not already in the cache read from the disk. If |
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213 | * specified block already cached return. The buffer is set to the access or |
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214 | * modifed access state. If the buffer is in the cache and modified the state |
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215 | * is access modified else the state is access. If block is already being read |
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216 | * from disk for being written to disk this call blocks. If the buffer is |
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217 | * waiting to be written it is removed from modified queue and returned to the |
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218 | * user. If the buffer is not in the cache a new buffer is obtained and the |
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219 | * data read from disk. The call may block until these operations complete. A |
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220 | * buffer obtained with this call will not be involved in a transfer request |
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221 | * and will not be returned to another user until released. If the buffer is |
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222 | * already with a user when this call is made the call is blocked until the |
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223 | * buffer is returned. The highest priority waiter will obtain the buffer |
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224 | * first. |
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225 | * |
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226 | * @param device Device number (constructed of major and minor device number) |
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227 | * @param block Linear media block number |
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228 | * @param bd Reference to the buffer descriptor pointer. |
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229 | * |
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230 | * @return RTEMS status code (RTEMS_SUCCESSFUL if operation completed |
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231 | * successfully or error code if error is occured) |
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232 | */ |
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233 | rtems_status_code |
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234 | rtems_bdbuf_read (dev_t device, rtems_blkdev_bnum block, rtems_bdbuf_buffer** bd); |
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235 | |
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236 | /** |
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237 | * Release the buffer obtained by a read call back to the cache. If the buffer |
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238 | * was obtained by a get call and was not already in the cache the release |
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239 | * modified call should be used. A buffer released with this call obtained by a |
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240 | * get call may not be in sync with the contents on disk. If the buffer was in |
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241 | * the cache and modified before this call it will be returned to the modified |
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242 | * queue. The buffers is returned to the end of the LRU list. |
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243 | * |
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244 | * @param bd Reference to the buffer descriptor. |
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245 | * |
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246 | * @return RTEMS status code (RTEMS_SUCCESSFUL if operation completed |
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247 | * successfully or error code if error is occured) |
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248 | */ |
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249 | rtems_status_code |
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250 | rtems_bdbuf_release (rtems_bdbuf_buffer* bd); |
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251 | |
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252 | /** |
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253 | * Release the buffer allocated with a get or read call placing it on the |
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254 | * modidied list. If the buffer was not released modified before the hold |
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255 | * timer is set to the configuration value. If the buffer had been released |
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256 | * modified before but not written to disk the hold timer is not updated. The |
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257 | * buffer will be written to disk when the hold timer has expired, there are |
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258 | * not more buffers available in the cache and a get or read buffer needs one |
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259 | * or a sync call has been made. If the buffer is obtained with a get or read |
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260 | * before the hold timer has expired the buffer will be returned to the user. |
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261 | * |
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262 | * @param bd Reference to the buffer descriptor. |
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263 | * |
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264 | * @return RTEMS status code (RTEMS_SUCCESSFUL if operation completed |
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265 | * successfully or error code if error is occured) |
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266 | */ |
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267 | rtems_status_code |
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268 | rtems_bdbuf_release_modified (rtems_bdbuf_buffer* bd); |
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269 | |
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270 | /** |
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271 | * Release the buffer as modified and wait until it has been synchronized with |
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272 | * the disk by writing it. This buffer will be the first to be transfer to disk |
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273 | * and other buffers may also be written if the maximum number of blocks in a |
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274 | * requests allows it. |
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275 | * |
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276 | * @note This code does not lock the sync mutex and stop additions to the |
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277 | * modified queue. |
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278 | |
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279 | * @param bd Reference to the buffer descriptor. |
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280 | * |
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281 | * @return RTEMS status code (RTEMS_SUCCESSFUL if operation completed |
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282 | * successfully or error code if error is occured) |
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283 | */ |
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284 | rtems_status_code |
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285 | rtems_bdbuf_sync (rtems_bdbuf_buffer* bd); |
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286 | |
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287 | /** |
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288 | * Synchronize all modified buffers for this device with the disk and wait |
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289 | * until the transfers have completed. The sync mutex for the pool is locked |
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290 | * stopping the addition of any further modifed buffers. It is only the |
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291 | * currently modified buffers that are written. |
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292 | * |
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293 | * @note Nesting calls to sync multiple devices attached to a single pool will |
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294 | * be handled sequentially. A nested call will be blocked until the first sync |
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295 | * request has complete. This is only true for device using the same pool. |
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296 | * |
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297 | * @param dev Block device number |
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298 | * |
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299 | * @return RTEMS status code (RTEMS_SUCCESSFUL if operation completed |
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300 | * successfully or error code if error is occured) |
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301 | */ |
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302 | rtems_status_code |
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303 | rtems_bdbuf_syncdev (dev_t dev); |
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304 | |
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305 | /** |
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306 | * Find first appropriate buffer pool. This primitive returns the index of |
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307 | * first buffer pool which block size is greater than or equal to specified |
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308 | * size. |
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309 | * |
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310 | * @param block_size Requested block size |
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311 | * @param pool The pool to use for the requested pool size. |
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312 | * |
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313 | * @return RTEMS status code (RTEMS_SUCCESSFUL if operation completed |
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314 | * successfully or error code if error is occured) |
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315 | * @retval RTEMS_INVALID_SIZE The specified block size is invalid (not a power |
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316 | * of 2) |
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317 | * @retval RTEMS_NOT_DEFINED The buffer pool for this or greater block size |
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318 | * is not configured. |
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319 | */ |
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320 | rtems_status_code |
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321 | rtems_bdbuf_find_pool (uint32_t block_size, rtems_bdpool_id *pool); |
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322 | |
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323 | /** |
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324 | * Obtain characteristics of buffer pool with specified number. |
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325 | * |
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326 | * @param pool Buffer pool number |
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327 | * @param block_size Block size for which buffer pool is configured returned |
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328 | * there |
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329 | * @param blocks Number of buffers in buffer pool. |
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330 | * |
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331 | * RETURNS: |
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332 | * @return RTEMS status code (RTEMS_SUCCESSFUL if operation completed |
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333 | * successfully or error code if error is occured) |
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334 | * @retval RTEMS_INVALID_SIZE The appropriate buffer pool is not configured. |
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335 | * |
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336 | * @note Buffer pools enumerated continuously starting from 0. |
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337 | */ |
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338 | rtems_status_code |
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339 | rtems_bdbuf_get_pool_info (rtems_bdpool_id pool, int *block_size, int *blocks); |
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340 | |
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341 | #ifdef __cplusplus |
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342 | } |
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343 | #endif |
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344 | |
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345 | #endif |
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