xnu-1228.tar.gz

[apple/xnu.git] / bsd / kern / kern_lockf.c

/*
 * Copyright (c) 2006 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * 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.
 * 4. 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 8.3 (Berkeley) 1/6/94
 */

#include <sys/cdefs.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mount.h>
#include <sys/proc.h>
#include <sys/signalvar.h>
#include <sys/unistd.h>
#include <sys/user.h>
#include <sys/vnode.h>
#include <sys/vnode_internal.h>
#include <sys/vnode_if.h>
#include <sys/malloc.h>
#include <sys/fcntl.h>
#include <sys/lockf.h>

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

#ifdef LOCKF_DEBUGGING
#include <sys/sysctl.h>
#include <ufs/ufs/quota.h>
#include <ufs/ufs/inode.h>
void lf_print(const char *tag, struct lockf *lock);
void lf_printlist(const char *tag, struct lockf *lock);
static int      lockf_debug = 2;
SYSCTL_INT(_debug, OID_AUTO, lockf_debug, CTLFLAG_RW, &lockf_debug, 0, "");

/*
 * If there is no mask bit selector, or there is on, and the selector is
 * set, then output the debugging diagnostic.
 */
#define LOCKF_DEBUG(mask, ...)                                  \
        do {                                                    \
                if( !(mask) || ((mask) & lockf_debug)) {        \
                        printf(__VA_ARGS__);                    \
                }                                               \
        } while(0)
#else   /* !LOCKF_DEBUGGING */
#define LOCKF_DEBUG(mask, ...)          /* mask */
#endif  /* !LOCKF_DEBUGGING */

MALLOC_DEFINE(M_LOCKF, "lockf", "Byte-range locking structures");

#define NOLOCKF (struct lockf *)0
#define SELF    0x1
#define OTHERS  0x2
#define OFF_MAX 0x7fffffffffffffffULL   /* max off_t */

/*
 * Overlapping lock states
 */
typedef enum {
        OVERLAP_NONE = 0,
        OVERLAP_EQUALS_LOCK,
        OVERLAP_CONTAINS_LOCK,
        OVERLAP_CONTAINED_BY_LOCK,
        OVERLAP_STARTS_BEFORE_LOCK,
        OVERLAP_ENDS_AFTER_LOCK
} overlap_t;

static int       lf_clearlock(struct lockf *);
static overlap_t lf_findoverlap(struct lockf *,
            struct lockf *, int, struct lockf ***, struct lockf **);
static struct lockf *lf_getblock(struct lockf *);
static int       lf_getlock(struct lockf *, struct flock *);
static int       lf_setlock(struct lockf *);
static int       lf_split(struct lockf *, struct lockf *);
static void      lf_wakelock(struct lockf *);


/*
 * lf_advlock
 *
 * Description: Advisory record locking support
 *
 * Parameters:  ap                      Argument pointer to a vnop_advlock_args
 *                                      argument descriptor structure for the
 *                                      lock operation to be attempted.
 *
 * Returns:     0                       Success
 *              EOVERFLOW
 *              EINVAL
 *              ENOLCK                  Number of locked regions exceeds limit
 *      lf_setlock:EAGAIN
 *      lf_setlock:EDEADLK
 *      lf_setlock:EINTR
 *      lf_setlock:ENOLCK
 *      lf_clearlock:ENOLCK
 *      vnode_size:???
 *
 * Notes:       We return ENOLCK when we run out of memory to support locks; as
 *              such, there is no specific expectation limit other than the
 *              amount of available resources.
 */
int
lf_advlock(struct vnop_advlock_args *ap)
{
        struct vnode *vp = ap->a_vp;
        struct flock *fl = ap->a_fl;
        vfs_context_t context = ap->a_context;
        struct lockf *lock;
        off_t start, end, oadd;
        u_quad_t size;
        int error;
        struct lockf **head = &vp->v_lockf;

        /* XXX HFS may need a !vnode_isreg(vp) EISDIR error here */

        /*
         * 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;
                        LOCKF_DEBUG(0, "lf_advlock: '%s' unlock without lock\n", vfs_context_proc(context)->p_comm);
                        return (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:

                /*
                 * It's OK to cast the u_quad_t to and off_t here, since they
                 * are the same storage size, and the value of the returned
                 * contents will never overflow into the sign bit.  We need to
                 * do this because we will use size to force range checks.
                 */
                if ((error = vnode_size(vp, (off_t *)&size, context))) {
                        LOCKF_DEBUG(0, "lf_advlock: vnode_getattr failed: %d\n", error);
                        return (error);
                }

                if (size > OFF_MAX ||
                    (fl->l_start > 0 &&
                     size > (u_quad_t)(OFF_MAX - fl->l_start)))
                        return (EOVERFLOW);
                start = size + fl->l_start;
                break;

        default:
                LOCKF_DEBUG(0, "lf_advlock: unknown whence %d\n", fl->l_whence);
                return (EINVAL);
        }
        if (start < 0) {
                LOCKF_DEBUG(0, "lf_advlock: start < 0 (%qd)\n", start);
                return (EINVAL);
        }
        if (fl->l_len < 0) {
                if (start == 0) {
                        LOCKF_DEBUG(0, "lf_advlock: len < 0 & start == 0\n");
                        return (EINVAL);
                }
                end = start - 1;
                start += fl->l_len;
                if (start < 0) {
                        LOCKF_DEBUG(0, "lf_advlock: start < 0 (%qd)\n", start);
                        return (EINVAL);
                }
        } else if (fl->l_len == 0)
                end = -1;
        else {
                oadd = fl->l_len - 1;
                if (oadd > (off_t)(OFF_MAX - start)) {
                        LOCKF_DEBUG(0, "lf_advlock: overflow\n");
                        return (EOVERFLOW);
                }
                end = start + oadd;
        }
        /*
         * Create the lockf structure
         */
        MALLOC(lock, struct lockf *, sizeof *lock, M_LOCKF, M_WAITOK);
        if (lock == NULL)
                return (ENOLCK);
        lock->lf_start = start;
        lock->lf_end = end;
        lock->lf_id = ap->a_id;
        lock->lf_vnode = vp;
        lock->lf_type = fl->l_type;
        lock->lf_head = head;
        lock->lf_next = (struct lockf *)0;
        TAILQ_INIT(&lock->lf_blkhd);
        lock->lf_flags = ap->a_flags;

        lck_mtx_lock(&vp->v_lock);      /* protect the lockf list */
        /*
         * Do the requested operation.
         */
        switch(ap->a_op) {
        case F_SETLK:
                error = lf_setlock(lock);
                break;

        case F_UNLCK:
                error = lf_clearlock(lock);
                FREE(lock, M_LOCKF);
                break;

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

        default:
                FREE(lock, M_LOCKF);
                error = EINVAL;
                break;
        }
        lck_mtx_unlock(&vp->v_lock);    /* done maniplulating the list */

        LOCKF_DEBUG(0, "lf_advlock: normal exit: %d\n\n", error);
        return (error);
}


/*
 * lf_coelesce_adjacent
 *
 * Description: Helper function: when setting a lock, coelesce adjacent
 *              locks.  Needed because adjacent locks are not overlapping,
 *              but POSIX requires that they be coelesced.
 *
 * Parameters:  lock                    The new lock which may be adjacent
 *                                      to already locked reagions, and which
 *                                      should therefore be coelesced with them
 *
 * Returns:     <void>
 */
static void
lf_coelesce_adjacent(struct lockf *lock)
{
        struct lockf **lf = lock->lf_head;

        while (*lf != NOLOCKF) {
                /* reject locks that obviously could not be coelesced */
                if ((*lf == lock) ||
                    ((*lf)->lf_id != lock->lf_id) ||
                    ((*lf)->lf_type != lock->lf_type)) {
                        lf = &(*lf)->lf_next;
                        continue;
                }

                /* If the lock ends adjacent to us, we can coelesce it */
                if ((*lf)->lf_end != -1 &&
                    ((*lf)->lf_end + 1) == lock->lf_start) {
                        struct lockf *adjacent = *lf;

                        LOCKF_DEBUG(0, "lf_coelesce_adjacent: coelesce adjacent previous\n");
                        lock->lf_start = (*lf)->lf_start;
                        *lf = lock;
                        lf = &(*lf)->lf_next;
                        FREE(adjacent, M_LOCKF);
                        continue;
                }
                /* If the lock starts adjacent to us, we can coelesce it */
                if (lock->lf_end != -1 &&
                    (lock->lf_end + 1) == (*lf)->lf_start) {
                        struct lockf *adjacent = *lf;

                        LOCKF_DEBUG(0, "lf_coelesce_adjacent: coelesce adjacent following\n");
                        lock->lf_end = (*lf)->lf_end;
                        lock->lf_next = (*lf)->lf_next;
                        lf = &lock->lf_next;
                        FREE(adjacent, M_LOCKF);
                        continue;
                }

                /* no matching conditions; go on to next lock */
                lf = &(*lf)->lf_next;
        }
}


/*
 * lf_setlock
 *
 * Description: Set a byte-range lock.
 *
 * Parameters:  lock                    The lock structure describing the lock
 *                                      to be set; allocated by the caller, it
 *                                      will be linked into the lock list if
 *                                      the set is successful, and freed if the
 *                                      set is unsuccessful.
 *
 * Returns:     0                       Success
 *              EAGAIN
 *              EDEADLK
 *      lf_split:ENOLCK
 *      lf_clearlock:ENOLCK
 *      msleep:EINTR
 *
 * Notes:       We add the lock to the provisional lock list.  We do not
 *              coelesce at this time; this has implications for other lock
 *              requestors in the blocker search mechanism.
 */
static int
lf_setlock(struct lockf *lock)
{
        struct lockf *block;
        struct lockf **head = lock->lf_head;
        struct lockf **prev, *overlap, *ltmp;
        static char lockstr[] = "lockf";
        int priority, needtolink, error;
        struct vnode *vp = lock->lf_vnode;
        overlap_t ovcase;

#ifdef LOCKF_DEBUGGING
        if (lockf_debug & 1) {
                lf_print("lf_setlock", lock);
                lf_printlist("lf_setlock(in)", lock);
        }
#endif /* LOCKF_DEBUGGING */

        /*
         * Set the priority
         */
        priority = PLOCK;
        if (lock->lf_type == F_WRLCK)
                priority += 4;
        priority |= PCATCH;
        /*
         * Scan lock list for this file looking for locks that would block us.
         */
        while ((block = lf_getblock(lock))) {
                /*
                 * Free the structure and return if nonblocking.
                 */
                if ((lock->lf_flags & F_WAIT) == 0) {
                        FREE(lock, M_LOCKF);
                        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 neverland.
                 */
                if ((lock->lf_flags & F_POSIX) &&
                    (block->lf_flags & F_POSIX)) {
                        struct proc *wproc, *bproc;
                        struct uthread *ut;
                        struct lockf *waitblock;
                        int i = 0;

                        /* The block is waiting on something */
                        wproc = (struct proc *)block->lf_id;
                        proc_lock(wproc);
                        TAILQ_FOREACH(ut, &wproc->p_uthlist, uu_list) {
                                /*
                                 * While the thread is asleep (uu_wchan != 0)
                                 * in this code (uu_wmesg == lockstr)
                                 * and we have not exceeded the maximum cycle
                                 * depth (i < maxlockdepth), then check for a
                                 * cycle to see if the lock is blocked behind
                                 * someone blocked behind us.
                                 */
                                while (((waitblock = (struct lockf *)ut->uu_wchan) != NULL) &&
                                    ut->uu_wmesg == lockstr &&
                                    (i++ < maxlockdepth)) {
                                        waitblock = (struct lockf *)ut->uu_wchan;
                                        /*
                                         * Get the lock blocking the lock
                                         * which would block us, and make
                                         * certain it hasn't come unblocked
                                         * (been granted, e.g. between the time
                                         * we called lf_getblock, and the time
                                         * we successfully acquired the
                                         * proc_lock).
                                         */
                                        waitblock = waitblock->lf_next;
                                        if (waitblock == NULL)
                                                break;

                                        /*
                                         * Make sure it's an advisory range
                                         * lock and not an overall file lock;
                                         * if we mix lock types, it's our own
                                         * fault.
                                         */
                                        if ((waitblock->lf_flags & F_POSIX) == 0)
                                                break;

                                        /*
                                         * If the owner of the lock that's
                                         * blocking a lock that's blocking us
                                         * getting the requested lock, then we
                                         * would deadlock, so error out.
                                         */
                                        bproc = (struct proc *)waitblock->lf_id;
                                        if (bproc == (struct proc *)lock->lf_id) {
                                                proc_unlock(wproc);
                                                FREE(lock, M_LOCKF);
                                                return (EDEADLK);
                                        }
                                }
                        }
                        proc_unlock(wproc);
                }

                /*
                 * 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;
                        if ((error = lf_clearlock(lock)) != 0) {
                                FREE(lock, M_LOCKF);
                                return (error);
                        }
                        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_DEBUGGING
                if (lockf_debug & 1) {
                        lf_print("lf_setlock: blocking on", block);
                        lf_printlist("lf_setlock(block)", block);
                }
#endif /* LOCKF_DEBUGGING */
                error = msleep(lock, &vp->v_lock, priority, lockstr, 0);
                if (error) {    /* XXX */
                        /*
                         * We may have been awakened by a signal and/or by a
                         * debugger continuing us (in which cases 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 NOLOCKF).
                         */
                        if (lock->lf_next) {
                                TAILQ_REMOVE(&lock->lf_next->lf_blkhd, lock, lf_block);
                                lock->lf_next = NOLOCKF;
                        }
                        FREE(lock, M_LOCKF);
                        return (error);
                }       /* XXX */
        }
        /*
         * 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 OVERLAP_NONE:
                        if (needtolink) {
                                *prev = lock;
                                lock->lf_next = overlap;
                        }
                        break;

                case OVERLAP_EQUALS_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;
                        FREE(lock, M_LOCKF);
                        lock = overlap; /* for lf_coelesce_adjacent() */
                        break;

                case OVERLAP_CONTAINS_LOCK:
                        /*
                         * Check for common starting point and different types.
                         */
                        if (overlap->lf_type == lock->lf_type) {
                                FREE(lock, M_LOCKF);
                                lock = overlap; /* for lf_coelesce_adjacent() */
                                break;
                        }
                        if (overlap->lf_start == lock->lf_start) {
                                *prev = lock;
                                lock->lf_next = overlap;
                                overlap->lf_start = lock->lf_end + 1;
                        } else {
                                /*
                                 * If we can't split the lock, we can't
                                 * grant it.  Claim a system limit for the
                                 * resource shortage.
                                 */
                                if (lf_split(overlap, lock)) {
                                        FREE(lock, M_LOCKF);
                                        return (ENOLCK);
                                }
                        }
                        lf_wakelock(overlap);
                        break;

                case OVERLAP_CONTAINED_BY_LOCK:
                        /*
                         * 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 (!TAILQ_EMPTY(&overlap->lf_blkhd)) {
                                        ltmp = TAILQ_FIRST(&overlap->lf_blkhd);
                                        TAILQ_REMOVE(&overlap->lf_blkhd, ltmp,
                                            lf_block);
                                        TAILQ_INSERT_TAIL(&lock->lf_blkhd,
                                            ltmp, lf_block);
                                        ltmp->lf_next = lock;
                                }
                        }
                        /*
                         * 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;
                        FREE(overlap, M_LOCKF);
                        continue;

                case 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 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;
        }
        /* Coelesce adjacent locks with identical attributes */
        lf_coelesce_adjacent(lock);
#ifdef LOCKF_DEBUGGING
        if (lockf_debug & 1) {
                lf_print("lf_setlock: got the lock", lock);
                lf_printlist("lf_setlock(out)", lock);
        }
#endif /* LOCKF_DEBUGGING */
        return (0);
}


/*
 * lf_clearlock
 *
 * Description: Remove a byte-range lock on an vnode.  Generally, find the
 *              lock (or an overlap to that lock) and remove it (or shrink
 *              it), then wakeup anyone we can.
 *
 * Parameters:  unlock                  The lock to clear
 *
 * Returns:     0                       Success
 *      lf_split:ENOLCK
 *
 * Notes:       A caller may unlock all the locks owned by the caller by
 *              specifying the entire file range; locks owned by other
 *              callers are not effected by this operation.
 */
static int
lf_clearlock(struct lockf *unlock)
{
        struct lockf **head = unlock->lf_head;
        struct lockf *lf = *head;
        struct lockf *overlap, **prev;
        overlap_t ovcase;

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

                switch (ovcase) {
                case OVERLAP_NONE:      /* satisfy compiler enum/switch */
                        break;

                case OVERLAP_EQUALS_LOCK:
                        *prev = overlap->lf_next;
                        FREE(overlap, M_LOCKF);
                        break;

                case OVERLAP_CONTAINS_LOCK: /* split it */
                        if (overlap->lf_start == unlock->lf_start) {
                                overlap->lf_start = unlock->lf_end + 1;
                                break;
                        }
                        /*
                         * If we can't split the lock, we can't grant it.
                         * Claim a system limit for the resource shortage.
                         */
                        if (lf_split(overlap, unlock))
                                return (ENOLCK);
                        overlap->lf_next = unlock->lf_next;
                        break;

                case OVERLAP_CONTAINED_BY_LOCK:
                        *prev = overlap->lf_next;
                        lf = overlap->lf_next;
                        FREE(overlap, M_LOCKF);
                        continue;

                case OVERLAP_STARTS_BEFORE_LOCK:
                        overlap->lf_end = unlock->lf_start - 1;
                        prev = &overlap->lf_next;
                        lf = overlap->lf_next;
                        continue;

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


/*
 * lf_getlock
 *
 * Description: Check whether there is a blocking lock, and if so return
 *              its process identifier into the lock being requested.
 *
 * Parameters:  lock                    Pointer to lock to test for blocks
 *              fl                      Pointer to flock structure to receive
 *                                      the blocking lock information, if a
 *                                      blocking lock is found.
 *
 * Returns:     0                       Success
 *
 * Implicit Returns:
 *              *fl                     Contents modified to reflect the
 *                                      blocking lock, if one is found; not
 *                                      modified otherwise
 *
 * Notes:       fl->l_pid will be (-1) for file locks and will only be set to
 *              the blocking process ID for advisory record locks.
 */
static int
lf_getlock(struct lockf *lock, struct flock *fl)
{
        struct lockf *block;

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

        if ((block = lf_getblock(lock))) {
                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 = proc_pid((struct proc *)(block->lf_id));
                else
                        fl->l_pid = -1;
        } else {
                fl->l_type = F_UNLCK;
        }
        return (0);
}


/*
 * lf_getblock
 *
 * Description: Walk the list of locks for an inode and return the first
 *              blocking lock.  A lock is considered blocking if we are not
 *              the lock owner; otherwise, we are permitted to upgrade or
 *              downgrade it, and it's not considered blocking.
 *
 * Parameters:  lock                    The lock for which we are interested
 *                                      in obtaining the blocking lock, if any
 *
 * Returns:     NOLOCKF                 No blocking lock exists
 *              !NOLOCKF                The address of the blocking lock's
 *                                      struct lockf.
 */
static struct lockf *
lf_getblock(struct lockf *lock)
{
        struct lockf **prev, *overlap, *lf = *(lock->lf_head);
        int ovcase;

        prev = lock->lf_head;
        while ((ovcase = lf_findoverlap(lf, lock, OTHERS, &prev, &overlap)) != OVERLAP_NONE) {
                /*
                 * 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 (NOLOCKF);
}


/*
 * lf_findoverlap
 *
 * Description: Walk the list of locks to find an overlapping lock (if any).
 *
 * Parameters:  lf                      First lock on lock list
 *              lock                    The lock we are checking for an overlap
 *              check                   Check type
 *              prev                    pointer to pointer pointer to contain
 *                                      address of pointer to previous lock
 *                                      pointer to overlapping lock, if overlap
 *              overlap                 pointer to pointer to contain address
 *                                      of overlapping lock
 *
 * Returns:     OVERLAP_NONE
 *              OVERLAP_EQUALS_LOCK
 *              OVERLAP_CONTAINS_LOCK
 *              OVERLAP_CONTAINED_BY_LOCK
 *              OVERLAP_STARTS_BEFORE_LOCK
 *              OVERLAP_ENDS_AFTER_LOCK
 *
 * Implicit Returns:
 *              *prev                   The address of the next pointer in the
 *                                      lock previous to the overlapping lock;
 *                                      this is generally used to relink the
 *                                      lock list, avoiding a second iteration.
 *              *overlap                The pointer to the overlapping lock
 *                                      itself; this is ussed to return data in
 *                                      the check == OTHERS case, and for the
 *                                      caller to modify the overlapping lock,
 *                                      in the check == SELF case
 *
 * Note:        This returns only the FIRST overlapping lock.  There may be
 *              more than one.  lf_getlock will return the first blocking lock,
 *              while lf_setlock will iterate over all overlapping locks to
 *
 *              The check parameter can be SELF, meaning we are looking for
 *              overelapping locks owned by us, or it can be OTHERS, meaning
 *              we are looking for overlapping locks owned by someone else so
 *              we can report a blocking lock on an F_GETLK request.
 *
 *              The value of *overlap and *prev are modified, even if there is
 *              no overlapping lock found; always check the return code.
 */
static overlap_t
lf_findoverlap(struct lockf *lf, struct lockf *lock, int type,
               struct lockf ***prev, struct lockf **overlap)
{
        off_t start, end;

        *overlap = lf;
        if (lf == NOLOCKF)
                return (0);
#ifdef LOCKF_DEBUGGING
        if (lockf_debug & 2)
                lf_print("lf_findoverlap: looking for overlap in", lock);
#endif /* LOCKF_DEBUGGING */
        start = lock->lf_start;
        end = lock->lf_end;
        while (lf != NOLOCKF) {
                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_DEBUGGING
                if (lockf_debug & 2)
                        lf_print("\tchecking", lf);
#endif /* LOCKF_DEBUGGING */
                /*
                 * OK, check for overlap
                 */
                if ((lf->lf_end != -1 && start > lf->lf_end) ||
                    (end != -1 && lf->lf_start > end)) {
                        /* Case 0 */
                        LOCKF_DEBUG(2, "no overlap\n");
                        if ((type & SELF) && end != -1 && lf->lf_start > end)
                                return (OVERLAP_NONE);
                        *prev = &lf->lf_next;
                        *overlap = lf = lf->lf_next;
                        continue;
                }
                if ((lf->lf_start == start) && (lf->lf_end == end)) {
                        LOCKF_DEBUG(2, "overlap == lock\n");
                        return (OVERLAP_EQUALS_LOCK);
                }
                if ((lf->lf_start <= start) &&
                    (end != -1) &&
                    ((lf->lf_end >= end) || (lf->lf_end == -1))) {
                        LOCKF_DEBUG(2, "overlap contains lock\n");
                        return (OVERLAP_CONTAINS_LOCK);
                }
                if (start <= lf->lf_start &&
                           (end == -1 ||
                           (lf->lf_end != -1 && end >= lf->lf_end))) {
                        LOCKF_DEBUG(2, "lock contains overlap\n");
                        return (OVERLAP_CONTAINED_BY_LOCK);
                }
                if ((lf->lf_start < start) &&
                        ((lf->lf_end >= start) || (lf->lf_end == -1))) {
                        LOCKF_DEBUG(2, "overlap starts before lock\n");
                        return (OVERLAP_STARTS_BEFORE_LOCK);
                }
                if ((lf->lf_start > start) &&
                        (end != -1) &&
                        ((lf->lf_end > end) || (lf->lf_end == -1))) {
                        LOCKF_DEBUG(2, "overlap ends after lock\n");
                        return (OVERLAP_ENDS_AFTER_LOCK);
                }
                panic("lf_findoverlap: default");
        }
        return (OVERLAP_NONE);
}


/*
 * lf_split
 *
 * Description: Split a lock and a contained region into two or three locks
 *              as necessary.
 *
 * Parameters:  lock1                   Lock to split
 *              lock2                   Overlapping lock region requiring the
 *                                      split (upgrade/downgrade/unlock)
 *
 * Returns:     0                       Success
 *              ENOLCK                  No memory for new lock
 *
 * Implicit Returns:
 *              *lock1                  Modified original lock
 *              *lock2                  Overlapping lock (inserted into list)
 *              (new lock)              Potential new lock inserted into list
 *                                      if split results in 3 locks
 *
 * Notes:       This operation can only fail if the split would result in three
 *              locks, and there is insufficient memory to allocate the third
 *              lock; in that case, neither of the locks will be modified.
 */
static int
lf_split(struct lockf *lock1, struct lockf *lock2)
{
        struct lockf *splitlock;

#ifdef LOCKF_DEBUGGING
        if (lockf_debug & 2) {
                lf_print("lf_split", lock1);
                lf_print("splitting from", lock2);
        }
#endif /* LOCKF_DEBUGGING */
        /*
         * 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 (0);
        }
        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 (0);
        }
        /*
         * Make a new lock consisting of the last part of
         * the encompassing lock
         */
        MALLOC(splitlock, struct lockf *, sizeof *splitlock, M_LOCKF, M_WAITOK);
        if (splitlock == NULL)
                return (ENOLCK);
        bcopy(lock1, splitlock, sizeof *splitlock);
        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;

        return (0);
}


/*
 * lf_wakelock
 *
 * Wakeup a blocklist in the case of a downgrade or unlock, since others
 * waiting on the lock may now be able to acquire it.
 *
 * Parameters:  listhead                Lock list head on which waiters may
 *                                      have pending locks
 *
 * Returns:     <void>
 *
 * Notes:       This function iterates a list of locks and wakes all waiters,
 *              rather than only waiters for the contended regions.  Because
 *              of this, for heavily contended files, this can result in a
 *              "thundering herd" situation.  Refactoring the code could make
 *              this operation more efficient, if heavy contention ever results
 *              in a real-world performance problem.
 */
static void
lf_wakelock(struct lockf *listhead)
{
        struct lockf *wakelock;

        while (!TAILQ_EMPTY(&listhead->lf_blkhd)) {
                wakelock = TAILQ_FIRST(&listhead->lf_blkhd);
                TAILQ_REMOVE(&listhead->lf_blkhd, wakelock, lf_block);
                wakelock->lf_next = NOLOCKF;
#ifdef LOCKF_DEBUGGING
                if (lockf_debug & 2)
                        lf_print("lf_wakelock: awakening", wakelock);
#endif /* LOCKF_DEBUGGING */
                wakeup(wakelock);
        }
}


#ifdef LOCKF_DEBUGGING
/*
 * lf_print DEBUG
 *
 * Print out a lock; lock information is prefixed by the string in 'tag'
 *
 * Parameters:  tag                     A string tag for debugging
 *              lock                    The lock whose information should be
 *                                      displayed
 *
 * Returns:     <void>
 */
void
lf_print(const char *tag, struct lockf *lock)
{
        printf("%s: lock %p for ", tag, (void *)lock);
        if (lock->lf_flags & F_POSIX)
                printf("proc %ld", (long)((struct proc *)lock->lf_id)->p_pid);
        else
                printf("id %p", (void *)lock->lf_id);
        if (lock->lf_vnode != 0)
                printf(" in vno %p, %s, start 0x%016llx, end 0x%016llx",
                    lock->lf_vnode,
                    lock->lf_type == F_RDLCK ? "shared" :
                    lock->lf_type == F_WRLCK ? "exclusive" :
                    lock->lf_type == F_UNLCK ? "unlock" : "unknown",
                    (intmax_t)lock->lf_start, (intmax_t)lock->lf_end);
        else
                printf(" %s, start 0x%016llx, end 0x%016llx",
                    lock->lf_type == F_RDLCK ? "shared" :
                    lock->lf_type == F_WRLCK ? "exclusive" :
                    lock->lf_type == F_UNLCK ? "unlock" : "unknown",
                    (intmax_t)lock->lf_start, (intmax_t)lock->lf_end);
        if (!TAILQ_EMPTY(&lock->lf_blkhd))
                printf(" block %p\n", (void *)TAILQ_FIRST(&lock->lf_blkhd));
        else
                printf("\n");
}


/*
 * lf_printlist DEBUG
 *
 * Print out a lock list for the vnode associated with 'lock'; lock information
 * is prefixed by the string in 'tag'
 *
 * Parameters:  tag                     A string tag for debugging
 *              lock                    The lock whose vnode's lock list should
 *                                      be displayed
 *
 * Returns:     <void>
 */
void
lf_printlist(const char *tag, struct lockf *lock)
{
        struct lockf *lf, *blk;

        if (lock->lf_vnode == 0)
                return;

        printf("%s: Lock list for vno %p:\n",
            tag, lock->lf_vnode);
        for (lf = lock->lf_vnode->v_lockf; lf; lf = lf->lf_next) {
                printf("\tlock %p for ",(void *)lf);
                if (lf->lf_flags & F_POSIX)
                        printf("proc %ld",
                            (long)((struct proc *)lf->lf_id)->p_pid);
                else
                        printf("id %p", (void *)lf->lf_id);
                printf(", %s, start 0x%016llx, end 0x%016llx",
                    lf->lf_type == F_RDLCK ? "shared" :
                    lf->lf_type == F_WRLCK ? "exclusive" :
                    lf->lf_type == F_UNLCK ? "unlock" :
                    "unknown", (intmax_t)lf->lf_start, (intmax_t)lf->lf_end);
                TAILQ_FOREACH(blk, &lf->lf_blkhd, lf_block) {
                        printf("\n\t\tlock request %p for ", (void *)blk);
                        if (blk->lf_flags & F_POSIX)
                                printf("proc %ld",
                                    (long)((struct proc *)blk->lf_id)->p_pid);
                        else
                                printf("id %p", (void *)blk->lf_id);
                        printf(", %s, start 0x%016llx, end 0x%016llx",
                            blk->lf_type == F_RDLCK ? "shared" :
                            blk->lf_type == F_WRLCK ? "exclusive" :
                            blk->lf_type == F_UNLCK ? "unlock" :
                            "unknown", (intmax_t)blk->lf_start,
                            (intmax_t)blk->lf_end);
                        if (!TAILQ_EMPTY(&blk->lf_blkhd))
                                panic("lf_printlist: bad list");
                }
                printf("\n");
        }
}
#endif /* LOCKF_DEBUGGING */