/* * CDDL HEADER START * * The contents of this file are subject to the terms of the * Common Development and Distribution License (the "License"). * You may not use this file except in compliance with the License. * * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE * or http://www.opensolaris.org/os/licensing. * See the License for the specific language governing permissions * and limitations under the License. * * When distributing Covered Code, include this CDDL HEADER in each * file and include the License file at usr/src/OPENSOLARIS.LICENSE. * If applicable, add the following below this CDDL HEADER, with the * fields enclosed by brackets "[]" replaced with your own identifying * information: Portions Copyright [yyyy] [name of copyright owner] * * CDDL HEADER END */ /* * Copyright 2008 Sun Microsystems, Inc. All rights reserved. * Use is subject to license terms. * * Copyright (c) 1983,1984,1985,1986,1987,1988,1989 AT&T. * All rights reserved. */ /* * A homegrown reader/writer lock implementation. It addresses * two requirements not addressed by the system primitives. They * are that the `enter" operation is optionally interruptible and * that that they can be re`enter'ed by writers without deadlock. * * All of this was borrowed from NFS. * See: uts/common/fs/nfs/nfs_subr.c * * XXX: Could we make this serve our needs instead? * See: uts/common/os/rwstlock.c * (and then use it for NFS too) */ #include <sys/param.h> #include <sys/systm.h> #include <sys/time.h> #include <sys/vnode.h> #include <smbfs/smbfs.h> #include <smbfs/smbfs_node.h> #include <smbfs/smbfs_subr.h> /* * Only can return non-zero if intr != 0. */ int smbfs_rw_enter_sig(smbfs_rwlock_t *l, krw_t rw, int intr) { mutex_enter(&l->lock); /* * If this is a nested enter, then allow it. There * must be as many exits as enters through. */ if (l->owner == curthread) { /* lock is held for writing by current thread */ ASSERT(rw == RW_READER || rw == RW_WRITER); l->count--; } else if (rw == RW_READER) { /* * While there is a writer active or writers waiting, * then wait for them to finish up and move on. Then, * increment the count to indicate that a reader is * active. */ while (l->count < 0 || l->waiters > 0) { if (intr) { klwp_t *lwp = ttolwp(curthread); if (lwp != NULL) lwp->lwp_nostop++; if (!cv_wait_sig(&l->cv, &l->lock)) { if (lwp != NULL) lwp->lwp_nostop--; mutex_exit(&l->lock); return (EINTR); } if (lwp != NULL) lwp->lwp_nostop--; } else cv_wait(&l->cv, &l->lock); } ASSERT(l->count < INT_MAX); #ifdef SMBDEBUG if ((l->count % 10000) == 9999) cmn_err(CE_WARN, "smbfs_rw_enter_sig: count %d on" "rwlock @ %p\n", l->count, (void *)&l); #endif l->count++; } else { ASSERT(rw == RW_WRITER); /* * While there are readers active or a writer * active, then wait for all of the readers * to finish or for the writer to finish. * Then, set the owner field to curthread and * decrement count to indicate that a writer * is active. */ while (l->count > 0 || l->owner != NULL) { l->waiters++; if (intr) { klwp_t *lwp = ttolwp(curthread); if (lwp != NULL) lwp->lwp_nostop++; if (!cv_wait_sig(&l->cv, &l->lock)) { if (lwp != NULL) lwp->lwp_nostop--; l->waiters--; cv_broadcast(&l->cv); mutex_exit(&l->lock); return (EINTR); } if (lwp != NULL) lwp->lwp_nostop--; } else cv_wait(&l->cv, &l->lock); l->waiters--; } l->owner = curthread; l->count--; } mutex_exit(&l->lock); return (0); } /* * If the lock is available, obtain it and return non-zero. If there is * already a conflicting lock, return 0 immediately. */ int smbfs_rw_tryenter(smbfs_rwlock_t *l, krw_t rw) { mutex_enter(&l->lock); /* * If this is a nested enter, then allow it. There * must be as many exits as enters through. */ if (l->owner == curthread) { /* lock is held for writing by current thread */ ASSERT(rw == RW_READER || rw == RW_WRITER); l->count--; } else if (rw == RW_READER) { /* * If there is a writer active or writers waiting, deny the * lock. Otherwise, bump the count of readers. */ if (l->count < 0 || l->waiters > 0) { mutex_exit(&l->lock); return (0); } l->count++; } else { ASSERT(rw == RW_WRITER); /* * If there are readers active or a writer active, deny the * lock. Otherwise, set the owner field to curthread and * decrement count to indicate that a writer is active. */ if (l->count > 0 || l->owner != NULL) { mutex_exit(&l->lock); return (0); } l->owner = curthread; l->count--; } mutex_exit(&l->lock); return (1); } void smbfs_rw_exit(smbfs_rwlock_t *l) { mutex_enter(&l->lock); /* * If this is releasing a writer lock, then increment count to * indicate that there is one less writer active. If this was * the last of possibly nested writer locks, then clear the owner * field as well to indicate that there is no writer active * and wakeup any possible waiting writers or readers. * * If releasing a reader lock, then just decrement count to * indicate that there is one less reader active. If this was * the last active reader and there are writer(s) waiting, * then wake up the first. */ if (l->owner != NULL) { ASSERT(l->owner == curthread); l->count++; if (l->count == 0) { l->owner = NULL; cv_broadcast(&l->cv); } } else { ASSERT(l->count > 0); l->count--; if (l->count == 0 && l->waiters > 0) cv_broadcast(&l->cv); } mutex_exit(&l->lock); } int smbfs_rw_lock_held(smbfs_rwlock_t *l, krw_t rw) { if (rw == RW_READER) return (l->count > 0); ASSERT(rw == RW_WRITER); return (l->count < 0); } /* ARGSUSED */ void smbfs_rw_init(smbfs_rwlock_t *l, char *name, krw_type_t type, void *arg) { l->count = 0; l->waiters = 0; l->owner = NULL; mutex_init(&l->lock, NULL, MUTEX_DEFAULT, NULL); cv_init(&l->cv, NULL, CV_DEFAULT, NULL); } void smbfs_rw_destroy(smbfs_rwlock_t *l) { mutex_destroy(&l->lock); cv_destroy(&l->cv); }
