Annotation of prex/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,
! 36: * the named semaphore is implemented by a file system server.
! 37: * In order to access the other task's semaphore, the task
! 38: * must 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: *
! 51: * sem_init() creates a new semaphore if the specified
! 52: * semaphore does not exist yet. If the semaphore already
! 53: * exists, it is re-initialized only if nobody is waiting for
! 54: * it. The initial semaphore value is set to the requested
! 55: * value.
! 56: */
! 57: int
! 58: sem_init(sem_t *sem, u_int value)
! 59: {
! 60: struct sem *s;
! 61: int err = 0;
! 62:
! 63: if (value > MAXSEMVAL)
! 64: return EINVAL;
! 65: if (umem_copyin(sem, &s, sizeof(sem_t)))
! 66: return EFAULT;
! 67:
! 68: /*
! 69: * An application can call sem_init() to reset the
! 70: * value of existing semaphore. So, we have to check
! 71: * whether the semaphore is already allocated.
! 72: */
! 73: sched_lock();
! 74: if (sem_valid(s)) {
! 75: /*
! 76: * Semaphore already exists.
! 77: */
! 78: if (s->task != cur_task() &&
! 79: !task_capable(CAP_SEMAPHORE))
! 80: err = EPERM;
! 81: else if (event_waiting(&s->event))
! 82: err = EBUSY;
! 83: else
! 84: s->value = value;
! 85: } else {
! 86: /*
! 87: * Create new semaphore.
! 88: */
! 89: if ((s = kmem_alloc(sizeof(struct sem))) == NULL)
! 90: err = ENOSPC;
! 91: else {
! 92: event_init(&s->event, "semaphore");
! 93: s->task = cur_task();
! 94: s->value = value;
! 95: s->magic = SEM_MAGIC;
! 96: if (umem_copyout(&s, sem, sizeof(sem_t))) {
! 97: kmem_free(s);
! 98: err = EFAULT;
! 99: }
! 100: }
! 101: }
! 102: sched_unlock();
! 103: return err;
! 104: }
! 105:
! 106: /*
! 107: * sem_copyin - copy a semaphore from user space.
! 108: *
! 109: * It also checks whether the passed semaphore is valid.
! 110: */
! 111: static int
! 112: sem_copyin(sem_t *usem, sem_t *ksem)
! 113: {
! 114: sem_t s;
! 115:
! 116: if (umem_copyin(usem, &s, sizeof(sem_t)))
! 117: return EFAULT;
! 118: if (!sem_valid(s))
! 119: return EINVAL;
! 120: /*
! 121: * Need a capability to access semaphores created
! 122: * by another task.
! 123: */
! 124: if (s->task != cur_task() && !task_capable(CAP_SEMAPHORE))
! 125: return EPERM;
! 126: *ksem = s;
! 127: return 0;
! 128: }
! 129:
! 130: /*
! 131: * Destroy a semaphore.
! 132: * If some thread is waiting for the specified semaphore,
! 133: * this routine fails with EBUSY.
! 134: */
! 135: int
! 136: sem_destroy(sem_t *sem)
! 137: {
! 138: sem_t s;
! 139: int err;
! 140:
! 141: sched_lock();
! 142: if ((err = sem_copyin(sem, &s))) {
! 143: sched_unlock();
! 144: return err;
! 145: }
! 146: if (event_waiting(&s->event) || s->value == 0) {
! 147: sched_unlock();
! 148: return EBUSY;
! 149: }
! 150: s->magic = 0;
! 151: kmem_free(s);
! 152: sched_unlock();
! 153: return 0;
! 154: }
! 155:
! 156: /*
! 157: * sem_wait - lock a semaphore.
! 158: *
! 159: * The value of timeout is msec unit. 0 for no timeout.
! 160: *
! 161: * sem_wait() locks the semaphore referred by sem only if the
! 162: * semaphore value is currently positive. The thread will
! 163: * sleep while the semaphore value is zero. It decrements the
! 164: * semaphore value in return.
! 165: *
! 166: * If waiting thread receives any exception, this routine
! 167: * returns with EINTR in order to invoke exception
! 168: * handler. But, an application assumes this call does NOT
! 169: * return with error. So, system call stub routine must
! 170: * re-call automatically if it gets EINTR.
! 171: */
! 172: int
! 173: sem_wait(sem_t *sem, u_long timeout)
! 174: {
! 175: sem_t s;
! 176: int err, rc;
! 177:
! 178: sched_lock();
! 179: if ((err = sem_copyin(sem, &s)))
! 180: goto out;
! 181:
! 182: while (s->value == 0) {
! 183: rc = sched_tsleep(&s->event, timeout);
! 184: if (rc == SLP_TIMEOUT) {
! 185: err = ETIMEDOUT;
! 186: goto out;
! 187: }
! 188: if (rc == SLP_INTR) {
! 189: err = EINTR;
! 190: goto out;
! 191: }
! 192: /* Kick scheduler */
! 193: sched_unlock();
! 194: sched_lock();
! 195: }
! 196: s->value--;
! 197: out:
! 198: sched_unlock();
! 199: return err;
! 200: }
! 201:
! 202: /*
! 203: * Try to lock a semaphore.
! 204: * If the semaphore is already locked, it just returns EAGAIN.
! 205: */
! 206: int
! 207: sem_trywait(sem_t *sem)
! 208: {
! 209: sem_t s;
! 210: int err;
! 211:
! 212: sched_lock();
! 213: if ((err = sem_copyin(sem, &s))) {
! 214: sched_unlock();
! 215: return err;
! 216: }
! 217: if (s->value > 0)
! 218: s->value--;
! 219: else
! 220: err = EAGAIN;
! 221: sched_unlock();
! 222: return err;
! 223: }
! 224:
! 225: /*
! 226: * Unlock a semaphore.
! 227: *
! 228: * If the semaphore value becomes non zero, then one of
! 229: * the threads blocked waiting for the semaphore will be
! 230: * unblocked. This is non-blocking operation.
! 231: */
! 232: int
! 233: sem_post(sem_t *sem)
! 234: {
! 235: sem_t s;
! 236: int err;
! 237:
! 238: sched_lock();
! 239: if ((err = sem_copyin(sem, &s))) {
! 240: sched_unlock();
! 241: return err;
! 242: }
! 243: if (s->value >= MAXSEMVAL) {
! 244: sched_unlock();
! 245: return ERANGE;
! 246: }
! 247: s->value++;
! 248: if (s->value > 0)
! 249: sched_wakeone(&s->event);
! 250: sched_unlock();
! 251: return 0;
! 252: }
! 253:
! 254: /*
! 255: * Get the semaphore value.
! 256: */
! 257: int
! 258: sem_getvalue(sem_t *sem, u_int *value)
! 259: {
! 260: sem_t s;
! 261: int err;
! 262:
! 263: sched_lock();
! 264: if ((err = sem_copyin(sem, &s))) {
! 265: sched_unlock();
! 266: return err;
! 267: }
! 268: if (umem_copyout(&s->value, value, sizeof(int)))
! 269: err = EFAULT;
! 270: sched_unlock();
! 271: return err;
! 272: }
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