[apple/xnu.git] / bsd / nfs / nfs_lock.c

/*
 * Copyright (c) 2002-2005 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_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. 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_LICENSE_HEADER_END@
 */
/*-
 * Copyright (c) 1997 Berkeley Software Design, Inc. All rights reserved.
 *
 * 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. Berkeley Software Design Inc's name may not be used to endorse or
 *    promote products derived from this software without specific prior
 *    written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``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 BERKELEY SOFTWARE DESIGN INC 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.
 *
 *      from BSDI nfs_lock.c,v 2.4 1998/12/14 23:49:56 jch Exp
 */

#include <sys/cdefs.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/fcntl.h>
#include <sys/kernel.h>         /* for hz */
#include <sys/file_internal.h>
#include <sys/malloc.h>
#include <sys/lockf.h>          /* for hz */ /* Must come after sys/malloc.h */
#include <sys/kpi_mbuf.h>
#include <sys/mount_internal.h>
#include <sys/proc_internal.h>  /* for p_start */
#include <sys/kauth.h>
#include <sys/resourcevar.h>
#include <sys/socket.h>
#include <sys/unistd.h>
#include <sys/user.h>
#include <sys/vnode_internal.h>

#include <kern/thread.h>

#include <machine/limits.h>

#include <net/if.h>

#include <nfs/rpcv2.h>
#include <nfs/nfsproto.h>
#include <nfs/nfs.h>
#include <nfs/nfsmount.h>
#include <nfs/nfsnode.h>
#include <nfs/nfs_lock.h>

#define OFF_MAX QUAD_MAX

/*
 * globals for managing the lockd fifo
 */
vnode_t nfslockdvnode = 0;
int nfslockdwaiting = 0;
time_t nfslockdstarttimeout = 0;
int nfslockdfifolock = 0;
#define NFSLOCKDFIFOLOCK_LOCKED 1
#define NFSLOCKDFIFOLOCK_WANT   2

/*
 * pending lock request messages are kept in this queue which is
 * kept sorted by transaction ID (xid).
 */
uint64_t nfs_lockxid = 0;
LOCKD_MSG_QUEUE nfs_pendlockq;

/*
 * This structure is used to identify processes which have acquired NFS locks.
 * Knowing which processes have ever acquired locks allows us to short-circuit
 * unlock requests for processes that have never had an NFS file lock.  Thus
 * avoiding a costly and unnecessary lockd request.
 */
struct nfs_lock_pid {
        TAILQ_ENTRY(nfs_lock_pid)       lp_lru;         /* LRU list */
        LIST_ENTRY(nfs_lock_pid)        lp_hash;        /* hash chain */
        int                             lp_valid;       /* valid entry? */
        int                             lp_time;        /* last time seen valid */
        pid_t                           lp_pid;         /* The process ID. */
        struct timeval                  lp_pid_start;   /* Start time of process id */
};

#define NFS_LOCK_PID_HASH_SIZE          64      // XXX tune me
#define NFS_LOCK_PID_HASH(pid)  \
        (&nfs_lock_pid_hash_tbl[(pid) & nfs_lock_pid_hash])
LIST_HEAD(, nfs_lock_pid) *nfs_lock_pid_hash_tbl;
TAILQ_HEAD(, nfs_lock_pid) nfs_lock_pid_lru;
u_long nfs_lock_pid_hash;
int nfs_lock_pid_lock;


/*
 * initialize global nfs lock state
 */
void
nfs_lockinit(void)
{
        TAILQ_INIT(&nfs_pendlockq);
        nfs_lock_pid_lock = 0;
        nfs_lock_pid_hash_tbl = hashinit(NFS_LOCK_PID_HASH_SIZE,
                                         M_TEMP, &nfs_lock_pid_hash);
        TAILQ_INIT(&nfs_lock_pid_lru);
}

/*
 * insert a lock request message into the pending queue
 */
static inline void
nfs_lockdmsg_enqueue(LOCKD_MSG_REQUEST *msgreq)
{
        LOCKD_MSG_REQUEST *mr;

        mr = TAILQ_LAST(&nfs_pendlockq, nfs_lock_msg_queue);
        if (!mr || (msgreq->lmr_msg.lm_xid > mr->lmr_msg.lm_xid)) {
                /* fast path: empty queue or new largest xid */
                TAILQ_INSERT_TAIL(&nfs_pendlockq, msgreq, lmr_next);
                return;
        }
        /* slow path: need to walk list to find insertion point */
        while (mr && (msgreq->lmr_msg.lm_xid > mr->lmr_msg.lm_xid)) {
                mr = TAILQ_PREV(mr, nfs_lock_msg_queue, lmr_next);
        }
        if (mr) {
                TAILQ_INSERT_AFTER(&nfs_pendlockq, mr, msgreq, lmr_next);
        } else {
                TAILQ_INSERT_HEAD(&nfs_pendlockq, msgreq, lmr_next);
        }
}

/*
 * remove a lock request message from the pending queue
 */
static inline void
nfs_lockdmsg_dequeue(LOCKD_MSG_REQUEST *msgreq)
{
        TAILQ_REMOVE(&nfs_pendlockq, msgreq, lmr_next);
}

/*
 * find a pending lock request message by xid
 *
 * We search from the head of the list assuming that the message we're
 * looking for is for an older request (because we have an answer to it).
 * This assumes that lock request will be answered primarily in FIFO order.
 * However, this may not be the case if there are blocked requests.  We may
 * want to move blocked requests to a separate queue (but that'll complicate
 * duplicate xid checking).
 */
static inline LOCKD_MSG_REQUEST *
nfs_lockdmsg_find_by_xid(uint64_t lockxid)
{
        LOCKD_MSG_REQUEST *mr;

        TAILQ_FOREACH(mr, &nfs_pendlockq, lmr_next) {
                if (mr->lmr_msg.lm_xid == lockxid)
                        return mr;
                if (mr->lmr_msg.lm_xid > lockxid)
                        return NULL;
        }
        return mr;
}

/*
 * Because we can't depend on nlm_granted messages containing the same
 * cookie we sent with the original lock request, we need code test if
 * an nlm_granted answer matches the lock request.  We also need code
 * that can find a lockd message based solely on the nlm_granted answer.
 */

/*
 * compare lockd message to answer
 *
 * returns 0 on equality and 1 if different
 */
static inline int
nfs_lockdmsg_compare_to_answer(LOCKD_MSG_REQUEST *msgreq, struct lockd_ans *ansp)
{
        if (!(ansp->la_flags & LOCKD_ANS_LOCK_INFO))
                return 1;
        if (msgreq->lmr_msg.lm_fl.l_pid != ansp->la_pid)
                return 1;
        if (msgreq->lmr_msg.lm_fl.l_start != ansp->la_start)
                return 1;
        if (msgreq->lmr_msg.lm_fl.l_len != ansp->la_len)
                return 1;
        if (msgreq->lmr_msg.lm_fh_len != ansp->la_fh_len)
                return 1;
        if (bcmp(msgreq->lmr_msg.lm_fh, ansp->la_fh, ansp->la_fh_len))
                return 1;
        return 0;
}

/*
 * find a pending lock request message based on the lock info provided
 * in the lockd_ans/nlm_granted data.  We need this because we can't
 * depend on nlm_granted messages containing the same cookie we sent
 * with the original lock request.
 *
 * We search from the head of the list assuming that the message we're
 * looking for is for an older request (because we have an answer to it).
 * This assumes that lock request will be answered primarily in FIFO order.
 * However, this may not be the case if there are blocked requests.  We may
 * want to move blocked requests to a separate queue (but that'll complicate
 * duplicate xid checking).
 */
static inline LOCKD_MSG_REQUEST *
nfs_lockdmsg_find_by_answer(struct lockd_ans *ansp)
{
        LOCKD_MSG_REQUEST *mr;

        if (!(ansp->la_flags & LOCKD_ANS_LOCK_INFO))
                return NULL;
        TAILQ_FOREACH(mr, &nfs_pendlockq, lmr_next) {
                if (!nfs_lockdmsg_compare_to_answer(mr, ansp))
                        break;
        }
        return mr;
}

/*
 * return the next unique lock request transaction ID
 */
static inline uint64_t
nfs_lockxid_get(void)
{
        LOCKD_MSG_REQUEST *mr;

        /* derive initial lock xid from system time */
        if (!nfs_lockxid) {
                /*
                 * Note: it's OK if this code inits nfs_lockxid to 0 (for example,
                 * due to a broken clock) because we immediately increment it
                 * and we guarantee to never use xid 0.  So, nfs_lockxid should only
                 * ever be 0 the first time this function is called.
                 */
                struct timeval tv;
                microtime(&tv);
                nfs_lockxid = (uint64_t)tv.tv_sec << 12;
        }

        /* make sure we get a unique xid */
        do {
                /* Skip zero xid if it should ever happen.  */
                if (++nfs_lockxid == 0)
                        nfs_lockxid++;
                if (!(mr = TAILQ_LAST(&nfs_pendlockq, nfs_lock_msg_queue)) ||
                     (mr->lmr_msg.lm_xid < nfs_lockxid)) {
                        /* fast path: empty queue or new largest xid */
                        break;
                }
                /* check if xid is already in use */
        } while (nfs_lockdmsg_find_by_xid(nfs_lockxid));

        return nfs_lockxid;
}


/*
 * Check the nfs_lock_pid hash table for an entry and, if requested,
 * add the entry if it is not found.
 *
 * (Also, if adding, try to clean up some stale entries.)
 */
static int
nfs_lock_pid_check(proc_t p, int addflag, vnode_t vp)
{
        struct nfs_lock_pid *lp, *lplru, *lplru_next;
        proc_t plru;
        int error = 0;
        struct timeval now;

        /* lock hash */
loop:
        if (nfs_lock_pid_lock) {
                struct nfsmount *nmp = VFSTONFS(vnode_mount(vp));
                while (nfs_lock_pid_lock) {
                        nfs_lock_pid_lock = -1;
                        tsleep(&nfs_lock_pid_lock, PCATCH, "nfslockpid", 0);
                        if ((error = nfs_sigintr(nmp, NULL, p)))
                                return (error);
                }
                goto loop;
        }
        nfs_lock_pid_lock = 1;

        /* Search hash chain */
        error = ENOENT;
        lp = NFS_LOCK_PID_HASH(proc_pid(p))->lh_first;
        for (; lp != NULL; lp = lp->lp_hash.le_next)
                if (lp->lp_pid == proc_pid(p)) {
                        /* found pid... */
                        if (timevalcmp(&lp->lp_pid_start, &p->p_stats->p_start, ==)) {
                                /* ...and it's valid */
                                /* move to tail of LRU */
                                TAILQ_REMOVE(&nfs_lock_pid_lru, lp, lp_lru);
                                microuptime(&now);
                                lp->lp_time = now.tv_sec;
                                TAILQ_INSERT_TAIL(&nfs_lock_pid_lru, lp, lp_lru);
                                error = 0;
                                break;
                        }
                        /* ...but it's no longer valid */
                        /* remove from hash, invalidate, and move to lru head */
                        LIST_REMOVE(lp, lp_hash);
                        lp->lp_valid = 0;
                        TAILQ_REMOVE(&nfs_lock_pid_lru, lp, lp_lru);
                        TAILQ_INSERT_HEAD(&nfs_lock_pid_lru, lp, lp_lru);
                        lp = NULL;
                        break;
                }

        /* if we didn't find it (valid) and we've been asked to add it */
        if ((error == ENOENT) && addflag) {
                /* scan lru list for invalid, stale entries to reuse/free */
                int lrucnt = 0;
                microuptime(&now);
                for (lplru = TAILQ_FIRST(&nfs_lock_pid_lru); lplru; lplru = lplru_next) {
                        lplru_next = TAILQ_NEXT(lplru, lp_lru);
                        if (lplru->lp_valid && (lplru->lp_time >= (now.tv_sec - 2))) {
                                /*
                                 * If the oldest LRU entry is relatively new, then don't
                                 * bother scanning any further.
                                 */
                                break;
                        }
                        /* remove entry from LRU, and check if it's still in use */
                        TAILQ_REMOVE(&nfs_lock_pid_lru, lplru, lp_lru);
                        if (!lplru->lp_valid || !(plru = pfind(lplru->lp_pid)) ||
                            timevalcmp(&lplru->lp_pid_start, &plru->p_stats->p_start, !=)) {
                                /* no longer in use */
                                LIST_REMOVE(lplru, lp_hash);
                                if (!lp) {
                                        /* we'll reuse this one */
                                        lp = lplru;
                                } else {
                                        /* we can free this one */
                                        FREE(lplru, M_TEMP);
                                }
                        } else {
                                /* still in use */
                                lplru->lp_time = now.tv_sec;
                                TAILQ_INSERT_TAIL(&nfs_lock_pid_lru, lplru, lp_lru);
                        }
                        /* don't check too many entries at once */
                        if (++lrucnt > 8)
                                break;
                }
                if (!lp) {
                        /* we need to allocate a new one */
                        MALLOC(lp, struct nfs_lock_pid *, sizeof(struct nfs_lock_pid),
                                M_TEMP, M_WAITOK | M_ZERO);
                }
                if (!lp) {
                        error = ENOMEM;
                } else {
                        /* (re)initialize nfs_lock_pid info */
                        lp->lp_pid = proc_pid(p);
                        lp->lp_pid_start = p->p_stats->p_start;
                        /* insert pid in hash */
                        LIST_INSERT_HEAD(NFS_LOCK_PID_HASH(lp->lp_pid), lp, lp_hash);
                        lp->lp_valid = 1;
                        lp->lp_time = now.tv_sec;
                        TAILQ_INSERT_TAIL(&nfs_lock_pid_lru, lp, lp_lru);
                        error = 0;
                }
        }

        /* unlock hash */
        if (nfs_lock_pid_lock < 0) {
                nfs_lock_pid_lock = 0;
                wakeup(&nfs_lock_pid_lock);
        } else
                nfs_lock_pid_lock = 0;

        return (error);
}


/*
 * nfs_advlock --
 *      NFS advisory byte-level locks.
 */
int
nfs_dolock(struct vnop_advlock_args *ap)
/* struct vnop_advlock_args {
        struct vnodeop_desc *a_desc;
        vnode_t a_vp;
        caddr_t a_id;
        int a_op;
        struct flock *a_fl;
        int a_flags;
        vfs_context_t a_context;
}; */
{
        LOCKD_MSG_REQUEST msgreq;
        LOCKD_MSG *msg;
        vnode_t vp, wvp;
        struct nfsnode *np;
        int error, error1;
        struct flock *fl;
        int fmode, ioflg;
        struct nfsmount *nmp;
        struct nfs_vattr nvattr;
        off_t start, end;
        struct timeval now;
        int timeo, endtime, lastmsg, wentdown = 0;
        int lockpidcheck;
        kauth_cred_t cred;
        proc_t p;
        struct sockaddr *saddr;

        p = vfs_context_proc(ap->a_context);
        cred = vfs_context_ucred(ap->a_context);

        vp = ap->a_vp;
        fl = ap->a_fl;
        np = VTONFS(vp);

        nmp = VFSTONFS(vnode_mount(vp));
        if (!nmp)
                return (ENXIO);
        if (nmp->nm_flag & NFSMNT_NOLOCKS)
                return (ENOTSUP);

        /*
         * The NLM protocol doesn't allow the server to return an error
         * on ranges, so we do it.  Pre LFS (Large File Summit)
         * standards required EINVAL for the range errors.  More recent
         * standards use EOVERFLOW, but their EINVAL wording still
         * encompasses these errors.
         * Any code sensitive to this is either:
         *  1) written pre-LFS and so can handle only EINVAL, or
         *  2) written post-LFS and thus ought to be tolerant of pre-LFS
         *     implementations.
         * Since returning EOVERFLOW certainly breaks 1), we return EINVAL.
         */
        if (fl->l_whence != SEEK_END) {
                if ((fl->l_whence != SEEK_CUR && fl->l_whence != SEEK_SET) ||
                    fl->l_start < 0 ||
                    (fl->l_len > 0 && fl->l_len - 1 > OFF_MAX - fl->l_start) ||
                    (fl->l_len < 0 && fl->l_start + fl->l_len < 0))
                        return (EINVAL);
        }
        /*
         * If daemon is running take a ref on its fifo vnode
         */
        if (!(wvp = nfslockdvnode)) {
                if (!nfslockdwaiting && !nfslockdstarttimeout)
                        return (ENOTSUP);
                /*
                 * Don't wake lock daemon if it hasn't been started yet and
                 * this is an unlock request (since we couldn't possibly
                 * actually have a lock on the file).  This could be an
                 * uninformed unlock request due to closef()'s behavior of doing
                 * unlocks on all files if a process has had a lock on ANY file.
                 */
                if (!nfslockdvnode && (fl->l_type == F_UNLCK))
                        return (EINVAL);
                microuptime(&now);
                if (nfslockdwaiting) {
                        /* wake up lock daemon */
                        nfslockdstarttimeout = now.tv_sec + 60;
                        (void)wakeup((void *)&nfslockdwaiting);
                }
                /* wait on nfslockdvnode for a while to allow daemon to start */
                while (!nfslockdvnode && (now.tv_sec < nfslockdstarttimeout)) {
                        error = tsleep((void *)&nfslockdvnode, PCATCH | PUSER, "lockdstart", 2*hz);
                        if (error && (error != EWOULDBLOCK))
                                return (error);
                        /* check that we still have our mount... */
                        /* ...and that we still support locks */
                        nmp = VFSTONFS(vnode_mount(vp));
                        if (!nmp)
                                return (ENXIO);
                        if (nmp->nm_flag & NFSMNT_NOLOCKS)
                                return (ENOTSUP);
                        if (!error)
                                break;
                        microuptime(&now);
                }
                /*
                 * check for nfslockdvnode
                 * If it hasn't started by now, there's a problem.
                 */
                if (!(wvp = nfslockdvnode))
                        return (ENOTSUP);
        }
        error = vnode_getwithref(wvp);
        if (error)
                return (ENOTSUP);
        error = vnode_ref(wvp);
        if (error) {
                vnode_put(wvp);
                return (ENOTSUP);
        }

        /*
         * Need to check if this process has successfully acquired an NFS lock before.
         * If not, and this is an unlock request we can simply return success here.
         */
        lockpidcheck = nfs_lock_pid_check(p, 0, vp);
        if (lockpidcheck) {
                if (lockpidcheck != ENOENT) {
                        vnode_rele(wvp);
                        vnode_put(wvp);
                        return (lockpidcheck);
                }
                if (ap->a_op == F_UNLCK) {
                        vnode_rele(wvp);
                        vnode_put(wvp);
                        return (0);
                }
        }

        /*
         * The NFS Lock Manager protocol doesn't directly handle
         * negative lengths or SEEK_END, so we need to normalize
         * things here where we have all the info.
         * (Note: SEEK_CUR is already adjusted for at this point)
         */
        /* 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
                 * to fl->l_start when SEEK_CUR is used.
                 */
                start = fl->l_start;
                break;
        case SEEK_END:
                /* need to flush, and refetch attributes to make */
                /* sure we have the correct end of file offset   */
                if (np->n_flag & NMODIFIED) {
                        NATTRINVALIDATE(np);
                        error = nfs_vinvalbuf(vp, V_SAVE, cred, p, 1);
                        if (error) {
                                vnode_rele(wvp);
                                vnode_put(wvp);
                                return (error);
                        }
                }
                NATTRINVALIDATE(np);

                error = nfs_getattr(vp, &nvattr, cred, p);
                if (error) {
                        vnode_rele(wvp);
                        vnode_put(wvp);
                        return (error);
                }
                start = np->n_size + fl->l_start;
                break;
        default:
                vnode_rele(wvp);
                vnode_put(wvp);
                return (EINVAL);
        }
        if (fl->l_len == 0)
                end = -1;
        else if (fl->l_len > 0)
                end = start + fl->l_len - 1;
        else { /* l_len is negative */
                end = start - 1;
                start += fl->l_len;
        }
        if (start < 0) {
                vnode_rele(wvp);
                vnode_put(wvp);
                return (EINVAL);
        }
        if (!NFS_ISV3(vp) &&
            ((start >= 0x80000000) || (end >= 0x80000000))) {
                vnode_rele(wvp);
                vnode_put(wvp);
                return (EINVAL);
        }

        /*
         * Fill in the information structure.
         */
        msgreq.lmr_answered = 0;
        msgreq.lmr_errno = 0;
        msgreq.lmr_saved_errno = 0;
        msg = &msgreq.lmr_msg;
        msg->lm_version = LOCKD_MSG_VERSION;
        msg->lm_flags = 0;

        msg->lm_fl = *fl;
        msg->lm_fl.l_start = start;
        if (end != -1)
                msg->lm_fl.l_len = end - start + 1;
        msg->lm_fl.l_pid = proc_pid(p);

        if (ap->a_flags & F_WAIT)
                msg->lm_flags |= LOCKD_MSG_BLOCK;
        if (ap->a_op == F_GETLK)
                msg->lm_flags |= LOCKD_MSG_TEST;

        nmp = VFSTONFS(vnode_mount(vp));
        if (!nmp) {
                vnode_rele(wvp);
                vnode_put(wvp);
                return (ENXIO);
        }

        saddr = mbuf_data(nmp->nm_nam);
        bcopy(saddr, &msg->lm_addr, min(sizeof msg->lm_addr, saddr->sa_len));
        msg->lm_fh_len = NFS_ISV3(vp) ? VTONFS(vp)->n_fhsize : NFSX_V2FH;
        bcopy(VTONFS(vp)->n_fhp, msg->lm_fh, msg->lm_fh_len);
        if (NFS_ISV3(vp))
                msg->lm_flags |= LOCKD_MSG_NFSV3;
        cru2x(cred, &msg->lm_cred);

        microuptime(&now);
        lastmsg = now.tv_sec - ((nmp->nm_tprintf_delay) - (nmp->nm_tprintf_initial_delay));

        fmode = FFLAGS(O_WRONLY);
        if ((error = VNOP_OPEN(wvp, fmode, ap->a_context))) {
                vnode_rele(wvp);
                vnode_put(wvp);
                return (error);
        }
        vnode_lock(wvp);
        ++wvp->v_writecount;
        vnode_unlock(wvp);

        /* allocate unique xid */
        msg->lm_xid = nfs_lockxid_get();
        nfs_lockdmsg_enqueue(&msgreq);

        timeo = 2*hz;
#define IO_NOMACCHECK 0;
        ioflg = IO_UNIT | IO_NOMACCHECK;
        for (;;) {
                error = 0;
                while (nfslockdfifolock & NFSLOCKDFIFOLOCK_LOCKED) {
                        nfslockdfifolock |= NFSLOCKDFIFOLOCK_WANT;
                        error = tsleep((void *)&nfslockdfifolock,
                                        PCATCH | PUSER, "lockdfifo", 20*hz);
                        if (error)
                                break;
                }
                if (error)
                        break;
                nfslockdfifolock |= NFSLOCKDFIFOLOCK_LOCKED;

                error = vn_rdwr(UIO_WRITE, wvp, (caddr_t)msg, sizeof(*msg), 0,
                    UIO_SYSSPACE32, ioflg, proc_ucred(kernproc), NULL, p);

                nfslockdfifolock &= ~NFSLOCKDFIFOLOCK_LOCKED;
                if (nfslockdfifolock & NFSLOCKDFIFOLOCK_WANT) {
                        nfslockdfifolock &= ~NFSLOCKDFIFOLOCK_WANT;
                        wakeup((void *)&nfslockdfifolock);
                }

                if (error && (((ioflg & IO_NDELAY) == 0) || error != EAGAIN)) {
                        break;
                }

                /*
                 * Always wait for an answer.  Not waiting for unlocks could
                 * cause a lock to be left if the unlock request gets dropped.
                 */

                /*
                 * Retry if it takes too long to get a response.
                 *
                 * The timeout numbers were picked out of thin air... they start
                 * at 2 and double each timeout with a max of 60 seconds.
                 *
                 * In order to maintain responsiveness, we pass a small timeout
                 * to tsleep and calculate the timeouts ourselves.  This allows
                 * us to pick up on mount changes quicker.
                 */
wait_for_granted:
                error = EWOULDBLOCK;
                microuptime(&now);
                if ((timeo/hz) > 0)
                        endtime = now.tv_sec + timeo/hz;
                else
                        endtime = now.tv_sec + 1;
                while (now.tv_sec < endtime) {
                        error = tsleep((void *)&msgreq, PCATCH | PUSER, "lockd", 2*hz);
                        if (msgreq.lmr_answered) {
                                /*
                                 * Note: it's possible to have a lock granted at
                                 * essentially the same time that we get interrupted.
                                 * Since the lock may be granted, we can't return an
                                 * error from this request or we might not unlock the
                                 * lock that's been granted.
                                 */
                                error = 0;
                                break;
                        }
                        if (error != EWOULDBLOCK)
                                break;
                        /* check that we still have our mount... */
                        /* ...and that we still support locks */
                        nmp = VFSTONFS(vnode_mount(vp));
                        if (!nmp || (nmp->nm_flag & NFSMNT_NOLOCKS))
                                break;
                        /*
                         * If the mount is hung and we've requested not to hang
                         * on remote filesystems, then bail now.
                         */
                        if ((p != NULL) && ((proc_noremotehang(p)) != 0) &&
                            ((nmp->nm_state & (NFSSTA_TIMEO|NFSSTA_LOCKTIMEO)) != 0)) {
                                if (fl->l_type == F_UNLCK)
                                        printf("nfs_dolock: aborting unlock request "
                                            "due to timeout (noremotehang)\n");
                                error = EIO;
                                break;
                        }
                        microuptime(&now);
                }
                if (error) {
                        /* check that we still have our mount... */
                        nmp = VFSTONFS(vnode_mount(vp));
                        if (!nmp) {
                                if (error == EWOULDBLOCK)
                                        error = ENXIO;
                                break;
                        }
                        /* ...and that we still support locks */
                        if (nmp->nm_flag & NFSMNT_NOLOCKS) {
                                if (error == EWOULDBLOCK)
                                        error = ENOTSUP;
                                break;
                        }
                        if ((error == ENOTSUP) &&
                            (nmp->nm_state & NFSSTA_LOCKSWORK)) {
                                /*
                                 * We have evidence that locks work, yet lockd
                                 * returned ENOTSUP.  This is probably because
                                 * it was unable to contact the server's lockd to
                                 * send it the request.
                                 *
                                 * Because we know locks work, we'll consider
                                 * this failure to be a timeout.
                                 */
                                error = EWOULDBLOCK;
                        }
                        if (error != EWOULDBLOCK) {
                                /*
                                 * We're going to bail on this request.
                                 * If we were a blocked lock request, send a cancel.
                                 */
                                if ((msgreq.lmr_errno == EINPROGRESS) &&
                                    !(msg->lm_flags & LOCKD_MSG_CANCEL)) {
                                        /* set this request up as a cancel */
                                        msg->lm_flags |= LOCKD_MSG_CANCEL;
                                        nfs_lockdmsg_dequeue(&msgreq);
                                        msg->lm_xid = nfs_lockxid_get();
                                        nfs_lockdmsg_enqueue(&msgreq);
                                        msgreq.lmr_saved_errno = error;
                                        msgreq.lmr_errno = 0;
                                        msgreq.lmr_answered = 0;
                                        /* reset timeout */
                                        timeo = 2*hz;
                                        /* send cancel request */
                                        continue;
                                }
                                break;
                        }

                        /*
                         * If the mount is hung and we've requested not to hang
                         * on remote filesystems, then bail now.
                         */
                        if ((p != NULL) && ((proc_noremotehang(p)) != 0) &&
                            ((nmp->nm_state & (NFSSTA_TIMEO|NFSSTA_LOCKTIMEO)) != 0)) {
                                if (fl->l_type == F_UNLCK)
                                        printf("nfs_dolock: aborting unlock request "
                                            "due to timeout (noremotehang)\n");
                                error = EIO;
                                break;
                        }
                        /* warn if we're not getting any response */
                        microuptime(&now);
                        if ((msgreq.lmr_errno != EINPROGRESS) &&
                            (nmp->nm_tprintf_initial_delay != 0) &&
                            ((lastmsg + nmp->nm_tprintf_delay) < now.tv_sec)) {
                                lastmsg = now.tv_sec;
                                nfs_down(nmp, p, 0, NFSSTA_LOCKTIMEO, "lockd not responding");
                                wentdown = 1;
                        }
                        if (msgreq.lmr_errno == EINPROGRESS) {
                                /*
                                 * We've got a blocked lock request that we are
                                 * going to retry.  First, we'll want to try to
                                 * send a cancel for the previous request.
                                 *
                                 * Clear errno so if we don't get a response
                                 * to the resend we'll call nfs_down().
                                 * Also reset timeout because we'll expect a
                                 * quick response to the cancel/resend (even if
                                 * it is NLM_BLOCKED).
                                 */
                                msg->lm_flags |= LOCKD_MSG_CANCEL;
                                nfs_lockdmsg_dequeue(&msgreq);
                                msg->lm_xid = nfs_lockxid_get();
                                nfs_lockdmsg_enqueue(&msgreq);
                                msgreq.lmr_saved_errno = msgreq.lmr_errno;
                                msgreq.lmr_errno = 0;
                                msgreq.lmr_answered = 0;
                                timeo = 2*hz;
                                /* send cancel then resend request */
                                continue;
                        }
                        /*
                         * We timed out, so we will rewrite the request
                         * to the fifo, but only if it isn't already full.
                         */
                        ioflg |= IO_NDELAY;
                        timeo *= 2;
                        if (timeo > 60*hz)
                                timeo = 60*hz;
                        /* resend request */
                        continue;
                }

                /* we got a reponse, so the server's lockd is OK */
                nfs_up(VFSTONFS(vnode_mount(vp)), p, NFSSTA_LOCKTIMEO,
                        wentdown ? "lockd alive again" : NULL);
                wentdown = 0;

                if (msgreq.lmr_errno == EINPROGRESS) {
                        /* got NLM_BLOCKED response */
                        /* need to wait for NLM_GRANTED */
                        timeo = 60*hz;
                        msgreq.lmr_answered = 0;
                        goto wait_for_granted;
                }

                if ((msg->lm_flags & LOCKD_MSG_CANCEL) &&
                    (msgreq.lmr_saved_errno == EINPROGRESS)) {
                        /*
                         * We just got a successful reply to the
                         * cancel of the previous blocked lock request.
                         * Now, go ahead and resend the request.
                         */
                        msg->lm_flags &= ~LOCKD_MSG_CANCEL;
                        nfs_lockdmsg_dequeue(&msgreq);
                        msg->lm_xid = nfs_lockxid_get();
                        nfs_lockdmsg_enqueue(&msgreq);
                        msgreq.lmr_saved_errno = 0;
                        msgreq.lmr_errno = 0;
                        msgreq.lmr_answered = 0;
                        timeo = 2*hz;
                        /* resend request */
                        continue;
                }

                if ((msg->lm_flags & LOCKD_MSG_TEST) && msgreq.lmr_errno == 0) {
                        if (msg->lm_fl.l_type != F_UNLCK) {
                                fl->l_type = msg->lm_fl.l_type;
                                fl->l_pid = msg->lm_fl.l_pid;
                                fl->l_start = msg->lm_fl.l_start;
                                fl->l_len = msg->lm_fl.l_len;
                                fl->l_whence = SEEK_SET;
                        } else {
                                fl->l_type = F_UNLCK;
                        }
                }

                /*
                 * If the blocked lock request was cancelled.
                 * Restore the error condition from when we
                 * originally bailed on the request.
                 */
                if (msg->lm_flags & LOCKD_MSG_CANCEL) {
                        msg->lm_flags &= ~LOCKD_MSG_CANCEL;
                        error = msgreq.lmr_saved_errno;
                } else
                        error = msgreq.lmr_errno;

                if (!error) {
                        /* record that NFS file locking has worked on this mount */
                        nmp = VFSTONFS(vnode_mount(vp));
                        if (nmp && !(nmp->nm_state & NFSSTA_LOCKSWORK))
                                nmp->nm_state |= NFSSTA_LOCKSWORK;
                        /*
                         * If we successfully acquired a lock, make sure this pid
                         * is in the nfs_lock_pid hash table so we know we can't
                         * short-circuit unlock requests.
                         */
                        if ((lockpidcheck == ENOENT) &&
                            ((ap->a_op == F_SETLK) || (ap->a_op == F_SETLKW)))
                                nfs_lock_pid_check(p, 1, vp);
        
                }
                break;
        }

        nfs_lockdmsg_dequeue(&msgreq);

        error1 = VNOP_CLOSE(wvp, FWRITE, ap->a_context);
        vnode_rele(wvp);
        vnode_put(wvp);
        /* prefer any previous 'error' to our vn_close 'error1'. */
        return (error != 0 ? error : error1);
}

/*
 * nfslockdans --
 *      NFS advisory byte-level locks answer from the lock daemon.
 */
int
nfslockdans(proc_t p, struct lockd_ans *ansp)
{
        LOCKD_MSG_REQUEST *msgreq;
        int error;

        /* Let root make this call. */
        error = proc_suser(p);
        if (error)
                return (error);

        /* the version should match, or we're out of sync */
        if (ansp->la_version != LOCKD_ANS_VERSION)
                return (EINVAL);

        /* try to find the lockd message by transaction id (cookie) */
        msgreq = nfs_lockdmsg_find_by_xid(ansp->la_xid);
        if (ansp->la_flags & LOCKD_ANS_GRANTED) {
                /*
                 * We can't depend on the granted message having our cookie,
                 * so we check the answer against the lockd message found.
                 * If no message was found or it doesn't match the answer,
                 * we look for the lockd message by the answer's lock info.
                 */
                if (!msgreq || nfs_lockdmsg_compare_to_answer(msgreq, ansp))
                        msgreq = nfs_lockdmsg_find_by_answer(ansp);
                /*
                 * We need to make sure this request isn't being cancelled
                 * If it is, we don't want to accept the granted message.
                 */
                if (msgreq && (msgreq->lmr_msg.lm_flags & LOCKD_MSG_CANCEL))
                        msgreq = NULL;
        }
        if (!msgreq)
                return (EPIPE);

        msgreq->lmr_errno = ansp->la_errno;
        if ((msgreq->lmr_msg.lm_flags & LOCKD_MSG_TEST) && msgreq->lmr_errno == 0) {
                if (ansp->la_flags & LOCKD_ANS_LOCK_INFO) {
                        if (ansp->la_flags & LOCKD_ANS_LOCK_EXCL)
                                msgreq->lmr_msg.lm_fl.l_type = F_WRLCK;
                        else
                                msgreq->lmr_msg.lm_fl.l_type = F_RDLCK;
                        msgreq->lmr_msg.lm_fl.l_pid = ansp->la_pid;
                        msgreq->lmr_msg.lm_fl.l_start = ansp->la_start;
                        msgreq->lmr_msg.lm_fl.l_len = ansp->la_len;
                } else {
                        msgreq->lmr_msg.lm_fl.l_type = F_UNLCK;
                }
        }

        msgreq->lmr_answered = 1;
        (void)wakeup((void *)msgreq);

        return (0);
}

/*
 * nfslockdfd --
 *      NFS advisory byte-level locks: fifo file# from the lock daemon.
 */
int
nfslockdfd(proc_t p, int fd)
{
        int error;
        vnode_t vp, oldvp;

        error = proc_suser(p);
        if (error)
                return (error);
        if (fd < 0) {
                vp = NULL;
        } else {
                error = file_vnode(fd, &vp);
                if (error)
                        return (error);
                error = vnode_getwithref(vp);
                if (error)
                        return (error);
                error = vnode_ref(vp);
                if (error) {
                        vnode_put(vp);
                        return (error);
                }
        }
        oldvp = nfslockdvnode;
        nfslockdvnode = vp;
        if (oldvp) {
                vnode_rele(oldvp);
        }
        (void)wakeup((void *)&nfslockdvnode);
        if (vp) {
                vnode_put(vp);
        }
        return (0);
}

/*
 * nfslockdwait --
 *      lock daemon waiting for lock request
 */
int
nfslockdwait(proc_t p)
{
        int error;

        error = proc_suser(p);
        if (error)
                return (error);
        if (nfslockdwaiting || nfslockdvnode)
                return (EBUSY);

        nfslockdstarttimeout = 0;
        nfslockdwaiting = 1;
        tsleep((void *)&nfslockdwaiting, PCATCH | PUSER, "lockd", 0);
        nfslockdwaiting = 0;

        return (0);
}