[337] | 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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