1 | #include <aio.h>
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2 | #include <pthread.h>
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3 | #include <semaphore.h>
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4 | #include <limits.h>
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5 | #include <errno.h>
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6 | #include <unistd.h>
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7 | #include <stdlib.h>
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8 | #include "syscall.h"
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9 | #include "atomic.h"
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10 | #include "libc.h"
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11 | #include "pthread_impl.h"
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12 |
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13 | /* The following is a threads-based implementation of AIO with minimal
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14 | * dependence on implementation details. Most synchronization is
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15 | * performed with pthread primitives, but atomics and futex operations
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16 | * are used for notification in a couple places where the pthread
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17 | * primitives would be inefficient or impractical.
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18 | *
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19 | * For each fd with outstanding aio operations, an aio_queue structure
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20 | * is maintained. These are reference-counted and destroyed by the last
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21 | * aio worker thread to exit. Accessing any member of the aio_queue
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22 | * structure requires a lock on the aio_queue. Adding and removing aio
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23 | * queues themselves requires a write lock on the global map object,
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24 | * a 4-level table mapping file descriptor numbers to aio queues. A
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25 | * read lock on the map is used to obtain locks on existing queues by
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26 | * excluding destruction of the queue by a different thread while it is
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27 | * being locked.
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28 | *
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29 | * Each aio queue has a list of active threads/operations. Presently there
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30 | * is a one to one relationship between threads and operations. The only
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31 | * members of the aio_thread structure which are accessed by other threads
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32 | * are the linked list pointers, op (which is immutable), running (which
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33 | * is updated atomically), and err (which is synchronized via running),
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34 | * so no locking is necessary. Most of the other other members are used
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35 | * for sharing data between the main flow of execution and cancellation
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36 | * cleanup handler.
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37 | *
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38 | * Taking any aio locks requires having all signals blocked. This is
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39 | * necessary because aio_cancel is needed by close, and close is required
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40 | * to be async-signal safe. All aio worker threads run with all signals
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41 | * blocked permanently.
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42 | */
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43 |
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44 | struct aio_args {
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45 | struct aiocb *cb;
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46 | int op;
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47 | int err;
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48 | sem_t sem;
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49 | };
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50 |
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51 | struct aio_thread {
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52 | pthread_t td;
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53 | struct aiocb *cb;
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54 | struct aio_thread *next, *prev;
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55 | struct aio_queue *q;
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56 | volatile int running;
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57 | int err, op;
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58 | ssize_t ret;
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59 | };
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60 |
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61 | struct aio_queue {
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62 | int fd, seekable, append, ref, init;
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63 | pthread_mutex_t lock;
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64 | pthread_cond_t cond;
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65 | struct aio_thread *head;
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66 | };
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67 |
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68 | static pthread_rwlock_t maplock = PTHREAD_RWLOCK_INITIALIZER;
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69 | static struct aio_queue *****map;
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70 | static volatile int aio_fd_cnt;
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71 | volatile int __aio_fut;
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72 |
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73 | static struct aio_queue *__aio_get_queue(int fd, int need)
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74 | {
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75 | if (fd < 0) return 0;
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76 | int a=fd>>24;
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77 | unsigned char b=fd>>16, c=fd>>8, d=fd;
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78 | struct aio_queue *q = 0;
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79 | pthread_rwlock_rdlock(&maplock);
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80 | if ((!map || !map[a] || !map[a][b] || !map[a][b][c] || !(q=map[a][b][c][d])) && need) {
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81 | pthread_rwlock_unlock(&maplock);
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82 | pthread_rwlock_wrlock(&maplock);
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83 | if (!map) map = calloc(sizeof *map, (-1U/2+1)>>24);
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84 | if (!map) goto out;
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85 | if (!map[a]) map[a] = calloc(sizeof **map, 256);
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86 | if (!map[a]) goto out;
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87 | if (!map[a][b]) map[a][b] = calloc(sizeof ***map, 256);
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88 | if (!map[a][b]) goto out;
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89 | if (!map[a][b][c]) map[a][b][c] = calloc(sizeof ****map, 256);
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90 | if (!map[a][b][c]) goto out;
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91 | if (!(q = map[a][b][c][d])) {
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92 | map[a][b][c][d] = q = calloc(sizeof *****map, 1);
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93 | if (q) {
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94 | q->fd = fd;
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95 | pthread_mutex_init(&q->lock, 0);
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96 | pthread_cond_init(&q->cond, 0);
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97 | a_inc(&aio_fd_cnt);
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98 | }
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99 | }
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100 | }
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101 | if (q) pthread_mutex_lock(&q->lock);
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102 | out:
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103 | pthread_rwlock_unlock(&maplock);
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104 | return q;
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105 | }
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106 |
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107 | static void __aio_unref_queue(struct aio_queue *q)
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108 | {
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109 | if (q->ref > 1) {
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110 | q->ref--;
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111 | pthread_mutex_unlock(&q->lock);
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112 | return;
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113 | }
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114 |
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115 | /* This is potentially the last reference, but a new reference
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116 | * may arrive since we cannot free the queue object without first
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117 | * taking the maplock, which requires releasing the queue lock. */
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118 | pthread_mutex_unlock(&q->lock);
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119 | pthread_rwlock_wrlock(&maplock);
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120 | pthread_mutex_lock(&q->lock);
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121 | if (q->ref == 1) {
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122 | int fd=q->fd;
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123 | int a=fd>>24;
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124 | unsigned char b=fd>>16, c=fd>>8, d=fd;
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125 | map[a][b][c][d] = 0;
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126 | a_dec(&aio_fd_cnt);
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127 | pthread_rwlock_unlock(&maplock);
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128 | pthread_mutex_unlock(&q->lock);
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129 | free(q);
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130 | } else {
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131 | q->ref--;
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132 | pthread_rwlock_unlock(&maplock);
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133 | pthread_mutex_unlock(&q->lock);
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134 | }
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135 | }
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136 |
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137 | static void cleanup(void *ctx)
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138 | {
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139 | struct aio_thread *at = ctx;
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140 | struct aio_queue *q = at->q;
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141 | struct aiocb *cb = at->cb;
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142 | struct sigevent sev = cb->aio_sigevent;
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143 |
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144 | /* There are four potential types of waiters we could need to wake:
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145 | * 1. Callers of aio_cancel/close.
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146 | * 2. Callers of aio_suspend with a single aiocb.
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147 | * 3. Callers of aio_suspend with a list.
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148 | * 4. AIO worker threads waiting for sequenced operations.
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149 | * Types 1-3 are notified via atomics/futexes, mainly for AS-safety
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150 | * considerations. Type 4 is notified later via a cond var. */
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151 |
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152 | cb->__ret = at->ret;
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153 | if (a_swap(&at->running, 0) < 0)
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154 | __wake(&at->running, -1, 1);
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155 | if (a_swap(&cb->__err, at->err) != EINPROGRESS)
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156 | __wake(&cb->__err, -1, 1);
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157 | if (a_swap(&__aio_fut, 0))
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158 | __wake(&__aio_fut, -1, 1);
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159 |
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160 | pthread_mutex_lock(&q->lock);
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161 |
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162 | if (at->next) at->next->prev = at->prev;
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163 | if (at->prev) at->prev->next = at->next;
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164 | else q->head = at->next;
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165 |
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166 | /* Signal aio worker threads waiting for sequenced operations. */
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167 | pthread_cond_broadcast(&q->cond);
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168 |
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169 | __aio_unref_queue(q);
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170 |
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171 | if (sev.sigev_notify == SIGEV_SIGNAL) {
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172 | siginfo_t si = {
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173 | .si_signo = sev.sigev_signo,
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174 | .si_value = sev.sigev_value,
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175 | .si_code = SI_ASYNCIO,
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176 | .si_pid = getpid(),
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177 | .si_uid = getuid()
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178 | };
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179 | __syscall(SYS_rt_sigqueueinfo, si.si_pid, si.si_signo, &si);
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180 | }
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181 | if (sev.sigev_notify == SIGEV_THREAD) {
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182 | a_store(&__pthread_self()->cancel, 0);
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183 | sev.sigev_notify_function(sev.sigev_value);
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184 | }
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185 | }
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186 |
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187 | static void *io_thread_func(void *ctx)
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188 | {
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189 | struct aio_thread at, *p;
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190 |
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191 | struct aio_args *args = ctx;
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192 | struct aiocb *cb = args->cb;
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193 | int fd = cb->aio_fildes;
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194 | int op = args->op;
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195 | void *buf = (void *)cb->aio_buf;
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196 | size_t len = cb->aio_nbytes;
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197 | off_t off = cb->aio_offset;
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198 |
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199 | struct aio_queue *q = __aio_get_queue(fd, 1);
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200 | ssize_t ret;
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201 |
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202 | args->err = q ? 0 : EAGAIN;
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203 | sem_post(&args->sem);
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204 | if (!q) return 0;
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205 |
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206 | at.op = op;
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207 | at.running = 1;
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208 | at.ret = -1;
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209 | at.err = ECANCELED;
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210 | at.q = q;
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211 | at.td = __pthread_self();
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212 | at.cb = cb;
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213 | at.prev = 0;
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214 | if ((at.next = q->head)) at.next->prev = &at;
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215 | q->head = &at;
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216 | q->ref++;
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217 |
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218 | if (!q->init) {
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219 | int seekable = lseek(fd, 0, SEEK_CUR) >= 0;
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220 | q->seekable = seekable;
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221 | q->append = !seekable || (fcntl(fd, F_GETFL) & O_APPEND);
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222 | q->init = 1;
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223 | }
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224 |
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225 | pthread_cleanup_push(cleanup, &at);
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226 |
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227 | /* Wait for sequenced operations. */
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228 | if (op!=LIO_READ && (op!=LIO_WRITE || q->append)) {
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229 | for (;;) {
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230 | for (p=at.next; p && p->op!=LIO_WRITE; p=p->next);
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231 | if (!p) break;
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232 | pthread_cond_wait(&q->cond, &q->lock);
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233 | }
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234 | }
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235 |
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236 | pthread_mutex_unlock(&q->lock);
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237 |
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238 | switch (op) {
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239 | case LIO_WRITE:
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240 | ret = q->append ? write(fd, buf, len) : pwrite(fd, buf, len, off);
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241 | break;
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242 | case LIO_READ:
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243 | ret = !q->seekable ? read(fd, buf, len) : pread(fd, buf, len, off);
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244 | break;
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245 | case O_SYNC:
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246 | ret = fsync(fd);
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247 | break;
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248 | case O_DSYNC:
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249 | ret = fdatasync(fd);
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250 | break;
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251 | }
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252 | at.ret = ret;
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253 | at.err = ret<0 ? errno : 0;
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254 |
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255 | pthread_cleanup_pop(1);
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256 |
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257 | return 0;
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258 | }
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259 |
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260 | static int submit(struct aiocb *cb, int op)
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261 | {
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262 | int ret = 0;
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263 | pthread_attr_t a;
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264 | sigset_t allmask, origmask;
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265 | pthread_t td;
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266 | struct aio_args args = { .cb = cb, .op = op };
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267 | sem_init(&args.sem, 0, 0);
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268 |
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269 | if (cb->aio_sigevent.sigev_notify == SIGEV_THREAD) {
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270 | if (cb->aio_sigevent.sigev_notify_attributes)
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271 | a = *cb->aio_sigevent.sigev_notify_attributes;
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272 | else
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273 | pthread_attr_init(&a);
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274 | } else {
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275 | pthread_attr_init(&a);
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276 | pthread_attr_setstacksize(&a, PTHREAD_STACK_MIN);
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277 | pthread_attr_setguardsize(&a, 0);
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278 | }
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279 | pthread_attr_setdetachstate(&a, PTHREAD_CREATE_DETACHED);
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280 | sigfillset(&allmask);
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281 | pthread_sigmask(SIG_BLOCK, &allmask, &origmask);
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282 | cb->__err = EINPROGRESS;
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283 | if (pthread_create(&td, &a, io_thread_func, &args)) {
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284 | errno = EAGAIN;
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285 | ret = -1;
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286 | }
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287 | pthread_sigmask(SIG_SETMASK, &origmask, 0);
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288 |
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289 | if (!ret) {
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290 | while (sem_wait(&args.sem));
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291 | if (args.err) {
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292 | errno = args.err;
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293 | ret = -1;
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294 | }
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295 | }
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296 |
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297 | return ret;
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298 | }
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299 |
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300 | int aio_read(struct aiocb *cb)
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301 | {
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302 | return submit(cb, LIO_READ);
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303 | }
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304 |
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305 | int aio_write(struct aiocb *cb)
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306 | {
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307 | return submit(cb, LIO_WRITE);
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308 | }
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309 |
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310 | int aio_fsync(int op, struct aiocb *cb)
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311 | {
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312 | if (op != O_SYNC && op != O_DSYNC) {
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313 | errno = EINVAL;
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314 | return -1;
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315 | }
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316 | return submit(cb, op);
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317 | }
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318 |
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319 | ssize_t aio_return(struct aiocb *cb)
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320 | {
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321 | return cb->__ret;
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322 | }
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323 |
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324 | int aio_error(const struct aiocb *cb)
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325 | {
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326 | a_barrier();
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327 | return cb->__err & 0x7fffffff;
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328 | }
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329 |
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330 | int aio_cancel(int fd, struct aiocb *cb)
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331 | {
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332 | sigset_t allmask, origmask;
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333 | int ret = AIO_ALLDONE;
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334 | struct aio_thread *p;
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335 | struct aio_queue *q;
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336 |
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337 | /* Unspecified behavior case. Report an error. */
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338 | if (cb && fd != cb->aio_fildes) {
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339 | errno = EINVAL;
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340 | return -1;
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341 | }
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342 |
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343 | sigfillset(&allmask);
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344 | pthread_sigmask(SIG_BLOCK, &allmask, &origmask);
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345 |
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346 | if (!(q = __aio_get_queue(fd, 0))) {
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347 | if (fcntl(fd, F_GETFD) < 0) ret = -1;
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348 | goto done;
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349 | }
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350 |
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351 | for (p = q->head; p; p = p->next) {
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352 | if (cb && cb != p->cb) continue;
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353 | /* Transition target from running to running-with-waiters */
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354 | if (a_cas(&p->running, 1, -1)) {
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355 | pthread_cancel(p->td);
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356 | __wait(&p->running, 0, -1, 1);
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357 | if (p->err == ECANCELED) ret = AIO_CANCELED;
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358 | }
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359 | }
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360 |
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361 | pthread_mutex_unlock(&q->lock);
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362 | done:
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363 | pthread_sigmask(SIG_SETMASK, &origmask, 0);
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364 | return ret;
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365 | }
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366 |
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367 | int __aio_close(int fd)
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368 | {
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369 | a_barrier();
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370 | if (aio_fd_cnt) aio_cancel(fd, 0);
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371 | return fd;
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372 | }
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373 |
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374 | LFS64(aio_cancel);
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375 | LFS64(aio_error);
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376 | LFS64(aio_fsync);
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377 | LFS64(aio_read);
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378 | LFS64(aio_write);
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379 | LFS64(aio_return);
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