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[netbsd-mini2440.git] / sys / kern / vfs_lockf.c

/*      $NetBSD: vfs_lockf.c,v 1.71 2009/06/10 22:34:35 yamt Exp $      */

/*
 * Copyright (c) 1982, 1986, 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Scooter Morris at Genentech Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)ufs_lockf.c 8.4 (Berkeley) 10/26/94
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: vfs_lockf.c,v 1.71 2009/06/10 22:34:35 yamt Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/file.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/pool.h>
#include <sys/fcntl.h>
#include <sys/lockf.h>
#include <sys/atomic.h>
#include <sys/kauth.h>
#include <sys/uidinfo.h>

/*
 * The lockf structure is a kernel structure which contains the information
 * associated with a byte range lock.  The lockf structures are linked into
 * the vnode structure.  Locks are sorted by the starting byte of the lock for
 * efficiency.
 *
 * lf_next is used for two purposes, depending on whether the lock is
 * being held, or is in conflict with an existing lock.  If this lock
 * is held, it indicates the next lock on the same vnode.
 * For pending locks, if lock->lf_next is non-NULL, then lock->lf_block
 * must be queued on the lf_blkhd TAILQ of lock->lf_next.
 */

TAILQ_HEAD(locklist, lockf);

struct lockf {
        kcondvar_t lf_cv;        /* Signalling */
        short   lf_flags;        /* Lock semantics: F_POSIX, F_FLOCK, F_WAIT */
        short   lf_type;         /* Lock type: F_RDLCK, F_WRLCK */
        off_t   lf_start;        /* The byte # of the start of the lock */
        off_t   lf_end;          /* The byte # of the end of the lock (-1=EOF)*/
        void    *lf_id;          /* process or file description holding lock */
        struct  lockf **lf_head; /* Back pointer to the head of lockf list */
        struct  lockf *lf_next;  /* Next lock on this vnode, or blocking lock */
        struct  locklist lf_blkhd; /* List of requests blocked on this lock */
        TAILQ_ENTRY(lockf) lf_block;/* A request waiting for a lock */
        uid_t   lf_uid;          /* User ID responsible */
};

/* Maximum length of sleep chains to traverse to try and detect deadlock. */
#define MAXDEPTH 50

static pool_cache_t lockf_cache;
static kmutex_t *lockf_lock;
static char lockstr[] = "lockf";

/*
 * This variable controls the maximum number of processes that will
 * be checked in doing deadlock detection.
 */
int maxlockdepth = MAXDEPTH;

#ifdef LOCKF_DEBUG
int     lockf_debug = 0;
#endif

#define SELF    0x1
#define OTHERS  0x2

/*
 * XXX TODO
 * Misc cleanups: "void *id" should be visible in the API as a
 * "struct proc *".
 * (This requires rototilling all VFS's which support advisory locking).
 */

/*
 * If there's a lot of lock contention on a single vnode, locking
 * schemes which allow for more paralleism would be needed.  Given how
 * infrequently byte-range locks are actually used in typical BSD
 * code, a more complex approach probably isn't worth it.
 */

/*
 * We enforce a limit on locks by uid, so that a single user cannot
 * run the kernel out of memory.  For now, the limit is pretty coarse.
 * There is no limit on root.
 *
 * Splitting a lock will always succeed, regardless of current allocations.
 * If you're slightly above the limit, we still have to permit an allocation
 * so that the unlock can succeed.  If the unlocking causes too many splits,
 * however, you're totally cutoff.
 */
int maxlocksperuid = 1024;

#ifdef LOCKF_DEBUG
/*
 * Print out a lock.
 */
static void
lf_print(const char *tag, struct lockf *lock)
{

        printf("%s: lock %p for ", tag, lock);
        if (lock->lf_flags & F_POSIX)
                printf("proc %d", ((struct proc *)lock->lf_id)->p_pid);
        else
                printf("file %p", (struct file *)lock->lf_id);
        printf(" %s, start %qx, end %qx",
                lock->lf_type == F_RDLCK ? "shared" :
                lock->lf_type == F_WRLCK ? "exclusive" :
                lock->lf_type == F_UNLCK ? "unlock" :
                "unknown", lock->lf_start, lock->lf_end);
        if (TAILQ_FIRST(&lock->lf_blkhd))
                printf(" block %p\n", TAILQ_FIRST(&lock->lf_blkhd));
        else
                printf("\n");
}

static void
lf_printlist(const char *tag, struct lockf *lock)
{
        struct lockf *lf, *blk;

        printf("%s: Lock list:\n", tag);
        for (lf = *lock->lf_head; lf; lf = lf->lf_next) {
                printf("\tlock %p for ", lf);
                if (lf->lf_flags & F_POSIX)
                        printf("proc %d", ((struct proc *)lf->lf_id)->p_pid);
                else
                        printf("file %p", (struct file *)lf->lf_id);
                printf(", %s, start %qx, end %qx",
                        lf->lf_type == F_RDLCK ? "shared" :
                        lf->lf_type == F_WRLCK ? "exclusive" :
                        lf->lf_type == F_UNLCK ? "unlock" :
                        "unknown", lf->lf_start, lf->lf_end);
                TAILQ_FOREACH(blk, &lf->lf_blkhd, lf_block) {
                        if (blk->lf_flags & F_POSIX)
                                printf("; proc %d",
                                    ((struct proc *)blk->lf_id)->p_pid);
                        else
                                printf("; file %p", (struct file *)blk->lf_id);
                        printf(", %s, start %qx, end %qx",
                                blk->lf_type == F_RDLCK ? "shared" :
                                blk->lf_type == F_WRLCK ? "exclusive" :
                                blk->lf_type == F_UNLCK ? "unlock" :
                                "unknown", blk->lf_start, blk->lf_end);
                        if (TAILQ_FIRST(&blk->lf_blkhd))
                                 panic("lf_printlist: bad list");
                }
                printf("\n");
        }
}
#endif /* LOCKF_DEBUG */

/*
 * 3 options for allowfail.
 * 0 - always allocate.  1 - cutoff at limit.  2 - cutoff at double limit.
 */
static struct lockf *
lf_alloc(int allowfail)
{
        struct uidinfo *uip;
        struct lockf *lock;
        u_long lcnt;
        const uid_t uid = kauth_cred_geteuid(kauth_cred_get());

        uip = uid_find(uid);
        lcnt = atomic_inc_ulong_nv(&uip->ui_lockcnt);
        if (uid && allowfail && lcnt >
            (allowfail == 1 ? maxlocksperuid : (maxlocksperuid * 2))) {
                atomic_dec_ulong(&uip->ui_lockcnt);
                return NULL;
        }

        lock = pool_cache_get(lockf_cache, PR_WAITOK);
        lock->lf_uid = uid;
        return lock;
}

static void
lf_free(struct lockf *lock)
{
        struct uidinfo *uip;

        uip = uid_find(lock->lf_uid);
        atomic_dec_ulong(&uip->ui_lockcnt);
        pool_cache_put(lockf_cache, lock);
}

static int
lf_ctor(void *arg, void *obj, int flag)
{
        struct lockf *lock;

        lock = obj;
        cv_init(&lock->lf_cv, lockstr);

        return 0;
}

static void
lf_dtor(void *arg, void *obj)
{
        struct lockf *lock;

        lock = obj;
        cv_destroy(&lock->lf_cv);
}

/*
 * Walk the list of locks for an inode to
 * find an overlapping lock (if any).
 *
 * NOTE: this returns only the FIRST overlapping lock.  There
 *       may be more than one.
 */
static int
lf_findoverlap(struct lockf *lf, struct lockf *lock, int type,
    struct lockf ***prev, struct lockf **overlap)
{
        off_t start, end;

        *overlap = lf;
        if (lf == NULL)
                return 0;
#ifdef LOCKF_DEBUG
        if (lockf_debug & 2)
                lf_print("lf_findoverlap: looking for overlap in", lock);
#endif /* LOCKF_DEBUG */
        start = lock->lf_start;
        end = lock->lf_end;
        while (lf != NULL) {
                if (((type == SELF) && lf->lf_id != lock->lf_id) ||
                    ((type == OTHERS) && lf->lf_id == lock->lf_id)) {
                        *prev = &lf->lf_next;
                        *overlap = lf = lf->lf_next;
                        continue;
                }
#ifdef LOCKF_DEBUG
                if (lockf_debug & 2)
                        lf_print("\tchecking", lf);
#endif /* LOCKF_DEBUG */
                /*
                 * OK, check for overlap
                 *
                 * Six cases:
                 *      0) no overlap
                 *      1) overlap == lock
                 *      2) overlap contains lock
                 *      3) lock contains overlap
                 *      4) overlap starts before lock
                 *      5) overlap ends after lock
                 */
                if ((lf->lf_end != -1 && start > lf->lf_end) ||
                    (end != -1 && lf->lf_start > end)) {
                        /* Case 0 */
#ifdef LOCKF_DEBUG
                        if (lockf_debug & 2)
                                printf("no overlap\n");
#endif /* LOCKF_DEBUG */
                        if ((type & SELF) && end != -1 && lf->lf_start > end)
                                return 0;
                        *prev = &lf->lf_next;
                        *overlap = lf = lf->lf_next;
                        continue;
                }
                if ((lf->lf_start == start) && (lf->lf_end == end)) {
                        /* Case 1 */
#ifdef LOCKF_DEBUG
                        if (lockf_debug & 2)
                                printf("overlap == lock\n");
#endif /* LOCKF_DEBUG */
                        return 1;
                }
                if ((lf->lf_start <= start) &&
                    (end != -1) &&
                    ((lf->lf_end >= end) || (lf->lf_end == -1))) {
                        /* Case 2 */
#ifdef LOCKF_DEBUG
                        if (lockf_debug & 2)
                                printf("overlap contains lock\n");
#endif /* LOCKF_DEBUG */
                        return 2;
                }
                if (start <= lf->lf_start &&
                           (end == -1 ||
                           (lf->lf_end != -1 && end >= lf->lf_end))) {
                        /* Case 3 */
#ifdef LOCKF_DEBUG
                        if (lockf_debug & 2)
                                printf("lock contains overlap\n");
#endif /* LOCKF_DEBUG */
                        return 3;
                }
                if ((lf->lf_start < start) &&
                        ((lf->lf_end >= start) || (lf->lf_end == -1))) {
                        /* Case 4 */
#ifdef LOCKF_DEBUG
                        if (lockf_debug & 2)
                                printf("overlap starts before lock\n");
#endif /* LOCKF_DEBUG */
                        return 4;
                }
                if ((lf->lf_start > start) &&
                        (end != -1) &&
                        ((lf->lf_end > end) || (lf->lf_end == -1))) {
                        /* Case 5 */
#ifdef LOCKF_DEBUG
                        if (lockf_debug & 2)
                                printf("overlap ends after lock\n");
#endif /* LOCKF_DEBUG */
                        return 5;
                }
                panic("lf_findoverlap: default");
        }
        return 0;
}

/*
 * Split a lock and a contained region into
 * two or three locks as necessary.
 */
static void
lf_split(struct lockf *lock1, struct lockf *lock2, struct lockf **sparelock)
{
        struct lockf *splitlock;

#ifdef LOCKF_DEBUG
        if (lockf_debug & 2) {
                lf_print("lf_split", lock1);
                lf_print("splitting from", lock2);
        }
#endif /* LOCKF_DEBUG */
        /*
         * Check to see if spliting into only two pieces.
         */
        if (lock1->lf_start == lock2->lf_start) {
                lock1->lf_start = lock2->lf_end + 1;
                lock2->lf_next = lock1;
                return;
        }
        if (lock1->lf_end == lock2->lf_end) {
                lock1->lf_end = lock2->lf_start - 1;
                lock2->lf_next = lock1->lf_next;
                lock1->lf_next = lock2;
                return;
        }
        /*
         * Make a new lock consisting of the last part of
         * the encompassing lock
         */
        splitlock = *sparelock;
        *sparelock = NULL;
        cv_destroy(&splitlock->lf_cv);
        memcpy(splitlock, lock1, sizeof(*splitlock));
        cv_init(&splitlock->lf_cv, lockstr);

        splitlock->lf_start = lock2->lf_end + 1;
        TAILQ_INIT(&splitlock->lf_blkhd);
        lock1->lf_end = lock2->lf_start - 1;
        /*
         * OK, now link it in
         */
        splitlock->lf_next = lock1->lf_next;
        lock2->lf_next = splitlock;
        lock1->lf_next = lock2;
}

/*
 * Wakeup a blocklist
 */
static void
lf_wakelock(struct lockf *listhead)
{
        struct lockf *wakelock;

        while ((wakelock = TAILQ_FIRST(&listhead->lf_blkhd))) {
                KASSERT(wakelock->lf_next == listhead);
                TAILQ_REMOVE(&listhead->lf_blkhd, wakelock, lf_block);
                wakelock->lf_next = NULL;
#ifdef LOCKF_DEBUG
                if (lockf_debug & 2)
                        lf_print("lf_wakelock: awakening", wakelock);
#endif
                cv_broadcast(&wakelock->lf_cv);
        }
}

/*
 * Remove a byte-range lock on an inode.
 *
 * Generally, find the lock (or an overlap to that lock)
 * and remove it (or shrink it), then wakeup anyone we can.
 */
static int
lf_clearlock(struct lockf *unlock, struct lockf **sparelock)
{
        struct lockf **head = unlock->lf_head;
        struct lockf *lf = *head;
        struct lockf *overlap, **prev;
        int ovcase;

        if (lf == NULL)
                return 0;
#ifdef LOCKF_DEBUG
        if (unlock->lf_type != F_UNLCK)
                panic("lf_clearlock: bad type");
        if (lockf_debug & 1)
                lf_print("lf_clearlock", unlock);
#endif /* LOCKF_DEBUG */
        prev = head;
        while ((ovcase = lf_findoverlap(lf, unlock, SELF,
            &prev, &overlap)) != 0) {
                /*
                 * Wakeup the list of locks to be retried.
                 */
                lf_wakelock(overlap);

                switch (ovcase) {

                case 1: /* overlap == lock */
                        *prev = overlap->lf_next;
                        lf_free(overlap);
                        break;

                case 2: /* overlap contains lock: split it */
                        if (overlap->lf_start == unlock->lf_start) {
                                overlap->lf_start = unlock->lf_end + 1;
                                break;
                        }
                        lf_split(overlap, unlock, sparelock);
                        overlap->lf_next = unlock->lf_next;
                        break;

                case 3: /* lock contains overlap */
                        *prev = overlap->lf_next;
                        lf = overlap->lf_next;
                        lf_free(overlap);
                        continue;

                case 4: /* overlap starts before lock */
                        overlap->lf_end = unlock->lf_start - 1;
                        prev = &overlap->lf_next;
                        lf = overlap->lf_next;
                        continue;

                case 5: /* overlap ends after lock */
                        overlap->lf_start = unlock->lf_end + 1;
                        break;
                }
                break;
        }
#ifdef LOCKF_DEBUG
        if (lockf_debug & 1)
                lf_printlist("lf_clearlock", unlock);
#endif /* LOCKF_DEBUG */
        return 0;
}

/*
 * Walk the list of locks for an inode and
 * return the first blocking lock.
 */
static struct lockf *
lf_getblock(struct lockf *lock)
{
        struct lockf **prev, *overlap, *lf = *(lock->lf_head);

        prev = lock->lf_head;
        while (lf_findoverlap(lf, lock, OTHERS, &prev, &overlap) != 0) {
                /*
                 * We've found an overlap, see if it blocks us
                 */
                if ((lock->lf_type == F_WRLCK || overlap->lf_type == F_WRLCK))
                        return overlap;
                /*
                 * Nope, point to the next one on the list and
                 * see if it blocks us
                 */
                lf = overlap->lf_next;
        }
        return NULL;
}

/*
 * Set a byte-range lock.
 */
static int
lf_setlock(struct lockf *lock, struct lockf **sparelock,
    kmutex_t *interlock)
{
        struct lockf *block;
        struct lockf **head = lock->lf_head;
        struct lockf **prev, *overlap, *ltmp;
        int ovcase, needtolink, error;

#ifdef LOCKF_DEBUG
        if (lockf_debug & 1)
                lf_print("lf_setlock", lock);
#endif /* LOCKF_DEBUG */

        /*
         * Scan lock list for this file looking for locks that would block us.
         */
        while ((block = lf_getblock(lock)) != NULL) {
                /*
                 * Free the structure and return if nonblocking.
                 */
                if ((lock->lf_flags & F_WAIT) == 0) {
                        lf_free(lock);
                        return EAGAIN;
                }
                /*
                 * We are blocked. Since flock style locks cover
                 * the whole file, there is no chance for deadlock.
                 * For byte-range locks we must check for deadlock.
                 *
                 * Deadlock detection is done by looking through the
                 * wait channels to see if there are any cycles that
                 * involve us. MAXDEPTH is set just to make sure we
                 * do not go off into neverneverland.
                 */
                if ((lock->lf_flags & F_POSIX) &&
                    (block->lf_flags & F_POSIX)) {
                        struct lwp *wlwp;
                        volatile const struct lockf *waitblock;
                        int i = 0;
                        struct proc *p;

                        p = (struct proc *)block->lf_id;
                        KASSERT(p != NULL);
                        while (i++ < maxlockdepth) {
                                mutex_enter(p->p_lock);
                                if (p->p_nlwps > 1) {
                                        mutex_exit(p->p_lock);
                                        break;
                                }
                                wlwp = LIST_FIRST(&p->p_lwps);
                                lwp_lock(wlwp);
                                if (wlwp->l_wchan == NULL ||
                                    wlwp->l_wmesg != lockstr) {
                                        lwp_unlock(wlwp);
                                        mutex_exit(p->p_lock);
                                        break;
                                }
                                waitblock = wlwp->l_wchan;
                                lwp_unlock(wlwp);
                                mutex_exit(p->p_lock);
                                /* Get the owner of the blocking lock */
                                waitblock = waitblock->lf_next;
                                if ((waitblock->lf_flags & F_POSIX) == 0)
                                        break;
                                p = (struct proc *)waitblock->lf_id;
                                if (p == curproc) {
                                        lf_free(lock);
                                        return EDEADLK;
                                }
                        }
                        /*
                         * If we're still following a dependency chain
                         * after maxlockdepth iterations, assume we're in
                         * a cycle to be safe.
                         */
                        if (i >= maxlockdepth) {
                                lf_free(lock);
                                return EDEADLK;
                        }
                }
                /*
                 * For flock type locks, we must first remove
                 * any shared locks that we hold before we sleep
                 * waiting for an exclusive lock.
                 */
                if ((lock->lf_flags & F_FLOCK) &&
                    lock->lf_type == F_WRLCK) {
                        lock->lf_type = F_UNLCK;
                        (void) lf_clearlock(lock, NULL);
                        lock->lf_type = F_WRLCK;
                }
                /*
                 * Add our lock to the blocked list and sleep until we're free.
                 * Remember who blocked us (for deadlock detection).
                 */
                lock->lf_next = block;
                TAILQ_INSERT_TAIL(&block->lf_blkhd, lock, lf_block);
#ifdef LOCKF_DEBUG
                if (lockf_debug & 1) {
                        lf_print("lf_setlock: blocking on", block);
                        lf_printlist("lf_setlock", block);
                }
#endif /* LOCKF_DEBUG */
                error = cv_wait_sig(&lock->lf_cv, interlock);

                /*
                 * We may have been awoken by a signal (in
                 * which case we must remove ourselves from the
                 * blocked list) and/or by another process
                 * releasing a lock (in which case we have already
                 * been removed from the blocked list and our
                 * lf_next field set to NULL).
                 */
                if (lock->lf_next != NULL) {
                        TAILQ_REMOVE(&lock->lf_next->lf_blkhd, lock, lf_block);
                        lock->lf_next = NULL;
                }
                if (error) {
                        lf_free(lock);
                        return error;
                }
        }
        /*
         * No blocks!!  Add the lock.  Note that we will
         * downgrade or upgrade any overlapping locks this
         * process already owns.
         *
         * Skip over locks owned by other processes.
         * Handle any locks that overlap and are owned by ourselves.
         */
        prev = head;
        block = *head;
        needtolink = 1;
        for (;;) {
                ovcase = lf_findoverlap(block, lock, SELF, &prev, &overlap);
                if (ovcase)
                        block = overlap->lf_next;
                /*
                 * Six cases:
                 *      0) no overlap
                 *      1) overlap == lock
                 *      2) overlap contains lock
                 *      3) lock contains overlap
                 *      4) overlap starts before lock
                 *      5) overlap ends after lock
                 */
                switch (ovcase) {
                case 0: /* no overlap */
                        if (needtolink) {
                                *prev = lock;
                                lock->lf_next = overlap;
                        }
                        break;

                case 1: /* overlap == lock */
                        /*
                         * If downgrading lock, others may be
                         * able to acquire it.
                         */
                        if (lock->lf_type == F_RDLCK &&
                            overlap->lf_type == F_WRLCK)
                                lf_wakelock(overlap);
                        overlap->lf_type = lock->lf_type;
                        lf_free(lock);
                        lock = overlap; /* for debug output below */
                        break;

                case 2: /* overlap contains lock */
                        /*
                         * Check for common starting point and different types.
                         */
                        if (overlap->lf_type == lock->lf_type) {
                                lf_free(lock);
                                lock = overlap; /* for debug output below */
                                break;
                        }
                        if (overlap->lf_start == lock->lf_start) {
                                *prev = lock;
                                lock->lf_next = overlap;
                                overlap->lf_start = lock->lf_end + 1;
                        } else
                                lf_split(overlap, lock, sparelock);
                        lf_wakelock(overlap);
                        break;

                case 3: /* lock contains overlap */
                        /*
                         * If downgrading lock, others may be able to
                         * acquire it, otherwise take the list.
                         */
                        if (lock->lf_type == F_RDLCK &&
                            overlap->lf_type == F_WRLCK) {
                                lf_wakelock(overlap);
                        } else {
                                while ((ltmp = TAILQ_FIRST(&overlap->lf_blkhd))) {
                                        KASSERT(ltmp->lf_next == overlap);
                                        TAILQ_REMOVE(&overlap->lf_blkhd, ltmp,
                                            lf_block);
                                        ltmp->lf_next = lock;
                                        TAILQ_INSERT_TAIL(&lock->lf_blkhd,
                                            ltmp, lf_block);
                                }
                        }
                        /*
                         * Add the new lock if necessary and delete the overlap.
                         */
                        if (needtolink) {
                                *prev = lock;
                                lock->lf_next = overlap->lf_next;
                                prev = &lock->lf_next;
                                needtolink = 0;
                        } else
                                *prev = overlap->lf_next;
                        lf_free(overlap);
                        continue;

                case 4: /* overlap starts before lock */
                        /*
                         * Add lock after overlap on the list.
                         */
                        lock->lf_next = overlap->lf_next;
                        overlap->lf_next = lock;
                        overlap->lf_end = lock->lf_start - 1;
                        prev = &lock->lf_next;
                        lf_wakelock(overlap);
                        needtolink = 0;
                        continue;

                case 5: /* overlap ends after lock */
                        /*
                         * Add the new lock before overlap.
                         */
                        if (needtolink) {
                                *prev = lock;
                                lock->lf_next = overlap;
                        }
                        overlap->lf_start = lock->lf_end + 1;
                        lf_wakelock(overlap);
                        break;
                }
                break;
        }
#ifdef LOCKF_DEBUG
        if (lockf_debug & 1) {
                lf_print("lf_setlock: got the lock", lock);
                lf_printlist("lf_setlock", lock);
        }
#endif /* LOCKF_DEBUG */
        return 0;
}

/*
 * Check whether there is a blocking lock,
 * and if so return its process identifier.
 */
static int
lf_getlock(struct lockf *lock, struct flock *fl)
{
        struct lockf *block;

#ifdef LOCKF_DEBUG
        if (lockf_debug & 1)
                lf_print("lf_getlock", lock);
#endif /* LOCKF_DEBUG */

        if ((block = lf_getblock(lock)) != NULL) {
                fl->l_type = block->lf_type;
                fl->l_whence = SEEK_SET;
                fl->l_start = block->lf_start;
                if (block->lf_end == -1)
                        fl->l_len = 0;
                else
                        fl->l_len = block->lf_end - block->lf_start + 1;
                if (block->lf_flags & F_POSIX)
                        fl->l_pid = ((struct proc *)block->lf_id)->p_pid;
                else
                        fl->l_pid = -1;
        } else {
                fl->l_type = F_UNLCK;
        }
        return 0;
}

/*
 * Do an advisory lock operation.
 */
int
lf_advlock(struct vop_advlock_args *ap, struct lockf **head, off_t size)
{
        struct flock *fl = ap->a_fl;
        struct lockf *lock = NULL;
        struct lockf *sparelock;
        kmutex_t *interlock = lockf_lock;
        off_t start, end;
        int error = 0;

        /*
         * Convert the flock structure into a start and end.
         */
        switch (fl->l_whence) {
        case SEEK_SET:
        case SEEK_CUR:
                /*
                 * Caller is responsible for adding any necessary offset
                 * when SEEK_CUR is used.
                 */
                start = fl->l_start;
                break;

        case SEEK_END:
                start = size + fl->l_start;
                break;

        default:
                return EINVAL;
        }

        if (fl->l_len == 0)
                end = -1;
        else {
                if (fl->l_len > 0)
                        end = start + fl->l_len - 1;
                else {
                        /* lockf() allows -ve lengths */
                        end = start - 1;
                        start += fl->l_len;
                }
        }
        if (start < 0)
                return EINVAL;

        /*
         * Allocate locks before acquiring the interlock.  We need two
         * locks in the worst case.
         */
        switch (ap->a_op) {
        case F_SETLK:
        case F_UNLCK:
                /*
                 * XXX For F_UNLCK case, we can re-use the lock.
                 */
                if ((ap->a_flags & F_FLOCK) == 0) {
                        /*
                         * Byte-range lock might need one more lock.
                         */
                        sparelock = lf_alloc(0);
                        if (sparelock == NULL) {
                                error = ENOMEM;
                                goto quit;
                        }
                        break;
                }
                /* FALLTHROUGH */

        case F_GETLK:
                sparelock = NULL;
                break;

        default:
                return EINVAL;
        }

        switch (ap->a_op) {
        case F_SETLK:
                lock = lf_alloc(1);
                break;
        case F_UNLCK:
                if (start == 0 || end == -1) {
                        /* never split */
                        lock = lf_alloc(0);
                } else {
                        /* might split */
                        lock = lf_alloc(2);
                }
                break;
        case F_GETLK:
                lock = lf_alloc(0);
                break;
        }
        if (lock == NULL) {
                error = ENOMEM;
                goto quit;
        }

        mutex_enter(interlock);

        /*
         * Avoid the common case of unlocking when inode has no locks.
         */
        if (*head == (struct lockf *)0) {
                if (ap->a_op != F_SETLK) {
                        fl->l_type = F_UNLCK;
                        error = 0;
                        goto quit_unlock;
                }
        }

        /*
         * Create the lockf structure.
         */
        lock->lf_start = start;
        lock->lf_end = end;
        lock->lf_head = head;
        lock->lf_type = fl->l_type;
        lock->lf_next = (struct lockf *)0;
        TAILQ_INIT(&lock->lf_blkhd);
        lock->lf_flags = ap->a_flags;
        if (lock->lf_flags & F_POSIX) {
                KASSERT(curproc == (struct proc *)ap->a_id);
        }
        lock->lf_id = ap->a_id;

        /*
         * Do the requested operation.
         */
        switch (ap->a_op) {

        case F_SETLK:
                error = lf_setlock(lock, &sparelock, interlock);
                lock = NULL; /* lf_setlock freed it */
                break;

        case F_UNLCK:
                error = lf_clearlock(lock, &sparelock);
                break;

        case F_GETLK:
                error = lf_getlock(lock, fl);
                break;

        default:
                break;
                /* NOTREACHED */
        }

quit_unlock:
        mutex_exit(interlock);
quit:
        if (lock)
                lf_free(lock);
        if (sparelock)
                lf_free(sparelock);

        return error;
}

/*
 * Initialize subsystem.   XXX We use a global lock.  This could be the
 * vnode interlock, but the deadlock detection code may need to inspect
 * locks belonging to other files.
 */
void
lf_init(void)
{

        lockf_cache = pool_cache_init(sizeof(struct lockf), 0, 0, 0, "lockf",
            NULL, IPL_NONE, lf_ctor, lf_dtor, NULL);
        lockf_lock = mutex_obj_alloc(MUTEX_DEFAULT, IPL_NONE);
}