Annotation of prex-old/sys/sync/sem.c, Revision 1.1
1.1 ! nbrk 1: /*-
! 2: * Copyright (c) 2005-2007, Kohsuke Ohtani
! 3: * All rights reserved.
! 4: *
! 5: * Redistribution and use in source and binary forms, with or without
! 6: * modification, are permitted provided that the following conditions
! 7: * are met:
! 8: * 1. Redistributions of source code must retain the above copyright
! 9: * notice, this list of conditions and the following disclaimer.
! 10: * 2. Redistributions in binary form must reproduce the above copyright
! 11: * notice, this list of conditions and the following disclaimer in the
! 12: * documentation and/or other materials provided with the distribution.
! 13: * 3. Neither the name of the author nor the names of any co-contributors
! 14: * may be used to endorse or promote products derived from this software
! 15: * without specific prior written permission.
! 16: *
! 17: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
! 18: * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
! 19: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
! 20: * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
! 21: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
! 22: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
! 23: * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
! 24: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
! 25: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
! 26: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
! 27: * SUCH DAMAGE.
! 28: */
! 29:
! 30: /*
! 31: * sem.c - semaphore support
! 32: */
! 33:
! 34: /*
! 35: * All of the Prex semaphore is un-named semaphore. Instead, the
! 36: * named semaphore is implemented by a file system server.
! 37: * In order to access the other task's semaphore, the task must
! 38: * have CAP_SEMAPHORE capability.
! 39: */
! 40:
! 41: #include <kernel.h>
! 42: #include <event.h>
! 43: #include <sched.h>
! 44: #include <kmem.h>
! 45: #include <thread.h>
! 46: #include <sync.h>
! 47:
! 48: /*
! 49: * sem_init - initialize a semaphore.
! 50: * @sem: ID for new semaphore.
! 51: * @value: initial semaphore count.
! 52: *
! 53: * sem_init() creates a new semaphore if the specified semaphore does
! 54: * not exist yet. If the semaphore already exists, it is re-initialized
! 55: * only if nobody is waiting for it. The initial semaphore value is set
! 56: * to the requested value.
! 57: */
! 58: int
! 59: sem_init(sem_t *sem, u_int value)
! 60: {
! 61: struct sem *s, *sem_org;
! 62: int err = 0;
! 63:
! 64: if (value > MAXSEMVAL)
! 65: return EINVAL;
! 66: if (umem_copyin(sem, &sem_org, sizeof(sem_t)))
! 67: return EFAULT;
! 68:
! 69: /*
! 70: * An application can call sem_init() to reset the
! 71: * value of existing semaphore. So, we have to check
! 72: * the semaphore is already allocated.
! 73: */
! 74: sched_lock();
! 75: if (sem_valid(sem_org)) {
! 76: /*
! 77: * Semaphore already exists.
! 78: */
! 79: if (sem_org->task != cur_task() &&
! 80: !task_capable(CAP_SEMAPHORE))
! 81: err = EPERM;
! 82: else if (event_waiting(&sem_org->event))
! 83: err = EBUSY;
! 84: else
! 85: s->value = value;
! 86: } else {
! 87: /*
! 88: * Create new semaphore.
! 89: */
! 90: if ((s = kmem_alloc(sizeof(struct sem))) == NULL)
! 91: err = ENOSPC;
! 92: else {
! 93: event_init(&s->event, "semaphore");
! 94: s->task = cur_task();
! 95: s->value = value;
! 96: s->magic = SEM_MAGIC;
! 97: if (umem_copyout(&s, sem, sizeof(sem_t))) {
! 98: kmem_free(s);
! 99: err = EFAULT;
! 100: }
! 101: }
! 102: }
! 103: sched_unlock();
! 104: return err;
! 105: }
! 106:
! 107: /*
! 108: * sem_copyin - copy a semaphore from user space.
! 109: * @usem: pointer to semaphore in user space.
! 110: * @ksem: pointer to semaphore in kernel space.
! 111: *
! 112: * It also checks if the passed semaphore is valid.
! 113: */
! 114: static int
! 115: sem_copyin(sem_t *usem, sem_t *ksem)
! 116: {
! 117: sem_t s;
! 118:
! 119: if (umem_copyin(usem, &s, sizeof(sem_t)))
! 120: return EFAULT;
! 121: if (!sem_valid(s))
! 122: return EINVAL;
! 123: /*
! 124: * Need a capability to access semaphores created
! 125: * by another task.
! 126: */
! 127: if (s->task != cur_task() && !task_capable(CAP_SEMAPHORE))
! 128: return EPERM;
! 129: *ksem = s;
! 130: return 0;
! 131: }
! 132:
! 133: /*
! 134: * Destroy a semaphore.
! 135: * If some thread is waiting for the specified semaphore,
! 136: * this routine fails with EBUSY.
! 137: */
! 138: int
! 139: sem_destroy(sem_t *sem)
! 140: {
! 141: sem_t s;
! 142: int err;
! 143:
! 144: sched_lock();
! 145: if ((err = sem_copyin(sem, &s))) {
! 146: sched_unlock();
! 147: return err;
! 148: }
! 149: if (event_waiting(&s->event) || s->value <= 0) {
! 150: sched_unlock();
! 151: return EBUSY;
! 152: }
! 153: s->magic = 0;
! 154: kmem_free(s);
! 155: sched_unlock();
! 156: return 0;
! 157: }
! 158:
! 159: /*
! 160: * sem_wait - lock a semaphore.
! 161: * @sem: semaphore ID
! 162: * @timeout: time out value in msec. 0 for no timeout.
! 163: *
! 164: * sem_wait() locks the semaphore referred by sem only if the
! 165: * semaphore value is currently positive. The thread will sleep
! 166: * while the semaphore value is zero. It decrements the semaphore
! 167: * value in return.
! 168: *
! 169: * If waiting thread receives any exception, this routine returns
! 170: * with EINTR in order to invoke exception handler. But, an
! 171: * application assumes this call does NOT return with error. So,
! 172: * system call stub routine must re-call automatically if it gets
! 173: * EINTR.
! 174: */
! 175: int
! 176: sem_wait(sem_t *sem, u_long timeout)
! 177: {
! 178: sem_t s;
! 179: int err, rc;
! 180:
! 181: sched_lock();
! 182: if ((err = sem_copyin(sem, &s)))
! 183: goto out;
! 184:
! 185: while (s->value <= 0) {
! 186: rc = sched_tsleep(&s->event, timeout);
! 187: if (rc == SLP_TIMEOUT) {
! 188: err = ETIMEDOUT;
! 189: goto out;
! 190: } else if (rc == SLP_INTR) {
! 191: err = EINTR;
! 192: goto out;
! 193: }
! 194: /* Kick scheduler */
! 195: sched_unlock();
! 196: sched_lock();
! 197: }
! 198: s->value--;
! 199: out:
! 200: sched_unlock();
! 201: return err;
! 202: }
! 203:
! 204: /*
! 205: * Try to lock a semaphore.
! 206: * If the semaphore is already locked, it just returns EAGAIN.
! 207: */
! 208: int
! 209: sem_trywait(sem_t *sem)
! 210: {
! 211: sem_t s;
! 212: int err;
! 213:
! 214: sched_lock();
! 215: if ((err = sem_copyin(sem, &s))) {
! 216: sched_unlock();
! 217: return err;
! 218: }
! 219: if (s->value > 0)
! 220: s->value--;
! 221: else
! 222: err = EAGAIN;
! 223: sched_unlock();
! 224: return err;
! 225: }
! 226:
! 227: /*
! 228: * Unlock a semaphore.
! 229: *
! 230: * If the semaphore value becomes non zero, then one of the threads
! 231: * blocked waiting for the semaphore will be unblocked.
! 232: * This is non-blocking operation.
! 233: */
! 234: int
! 235: sem_post(sem_t *sem)
! 236: {
! 237: sem_t s;
! 238: int err;
! 239:
! 240: sched_lock();
! 241: if ((err = sem_copyin(sem, &s))) {
! 242: sched_unlock();
! 243: return err;
! 244: }
! 245: if (s->value >= MAXSEMVAL) {
! 246: sched_unlock();
! 247: return ERANGE;
! 248: }
! 249: s->value++;
! 250: if (s->value > 0)
! 251: sched_wakeone(&s->event);
! 252: sched_unlock();
! 253: return 0;
! 254: }
! 255:
! 256: /*
! 257: * Get the semaphore value.
! 258: */
! 259: int
! 260: sem_getvalue(sem_t *sem, u_int *value)
! 261: {
! 262: sem_t s;
! 263: int err;
! 264:
! 265: sched_lock();
! 266: if ((err = sem_copyin(sem, &s))) {
! 267: sched_unlock();
! 268: return err;
! 269: }
! 270: if (umem_copyout(&s->value, value, sizeof(int)))
! 271: err = EFAULT;
! 272: sched_unlock();
! 273: return err;
! 274: }
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