don't bother resolving onbld python module deps

[unleashed.git] / kernel / syscall / poll.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*      Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T     */
/*        All Rights Reserved   */

/*
 * Copyright (c) 2012, 2016 by Delphix. All rights reserved.
 * Copyright 2015, Joyent, Inc.
 */

/*
 * Portions of this source code were derived from Berkeley 4.3 BSD
 * under license from the Regents of the University of California.
 */

#include <sys/param.h>
#include <sys/isa_defs.h>
#include <sys/types.h>
#include <sys/sysmacros.h>
#include <sys/user.h>
#include <sys/systm.h>
#include <sys/errno.h>
#include <sys/time.h>
#include <sys/vnode.h>
#include <sys/file.h>
#include <sys/mode.h>
#include <sys/proc.h>
#include <sys/uio.h>
#include <sys/poll_impl.h>
#include <sys/kmem.h>
#include <sys/cmn_err.h>
#include <sys/debug.h>
#include <sys/bitmap.h>
#include <sys/kstat.h>
#include <sys/rctl.h>
#include <sys/port_impl.h>
#include <sys/schedctl.h>
#include <sys/cpu.h>

#define NPHLOCKS        64      /* Number of locks; must be power of 2 */
#define PHLOCKADDR(php) &plocks[(((uintptr_t)(php)) >> 8) & (NPHLOCKS - 1)]
#define PHLOCK(php)     PHLOCKADDR(php).pp_lock
#define PH_ENTER(php)   mutex_enter(PHLOCK(php))
#define PH_EXIT(php)    mutex_exit(PHLOCK(php))
#define VALID_POLL_EVENTS       (POLLIN | POLLPRI | POLLOUT | POLLRDNORM \
        | POLLRDBAND | POLLWRBAND | POLLHUP | POLLERR | POLLNVAL)

/*
 * global counters to collect some stats
 */
static struct {
        kstat_named_t   polllistmiss;   /* failed to find a cached poll list */
        kstat_named_t   pollcachehit;   /* list matched 100% w/ cached one */
        kstat_named_t   pollcachephit;  /* list matched < 100% w/ cached one */
        kstat_named_t   pollcachemiss;  /* every list entry is dif from cache */
        kstat_named_t   pollunlockfail; /* failed to perform pollunlock */
} pollstats = {
        { "polllistmiss",       KSTAT_DATA_UINT64 },
        { "pollcachehit",       KSTAT_DATA_UINT64 },
        { "pollcachephit",      KSTAT_DATA_UINT64 },
        { "pollcachemiss",      KSTAT_DATA_UINT64 },
        { "pollunlockfail",     KSTAT_DATA_UINT64 }
};

kstat_named_t *pollstats_ptr = (kstat_named_t *)&pollstats;
uint_t pollstats_ndata = sizeof (pollstats) / sizeof (kstat_named_t);

struct pplock   {
        kmutex_t        pp_lock;
        short           pp_flag;
        kcondvar_t      pp_wait_cv;
        int32_t         pp_pad;         /* to a nice round 16 bytes */
};

static struct pplock plocks[NPHLOCKS];  /* Hash array of pollhead locks */

/* Contention lock & list for preventing deadlocks in recursive /dev/poll. */
static  kmutex_t        pollstate_contenders_lock;
static  pollstate_t     *pollstate_contenders = NULL;

#ifdef DEBUG
static int pollchecksanity(pollstate_t *, nfds_t);
static int pollcheckxref(pollstate_t *, int);
static void pollcheckphlist(void);
static int pollcheckrevents(pollstate_t *, int, int, int);
static void checkpolldat(pollstate_t *);
#endif  /* DEBUG */
static int plist_chkdupfd(file_t *, polldat_t *, pollstate_t *, pollfd_t *, int,
    int *);

/*
 * Data structure overview:
 * The per-thread poll state consists of
 *      one pollstate_t
 *      one pollcache_t
 *      one bitmap with one event bit per fd
 *      a (two-dimensional) hashed array of polldat_t structures - one entry
 *      per fd
 *
 * This conglomerate of data structures interact with
 *      the pollhead which is used by fop_poll and pollwakeup
 *      (protected by the PHLOCK, cached array of plocks), and
 *      the fpollinfo list hanging off the fi_list which is used to notify
 *      poll when a cached fd is closed. This is protected by uf_lock.
 *
 * Invariants:
 *      pd_php (pollhead pointer) is set iff (if and only if) the polldat
 *      is on that pollhead. This is modified atomically under pc_lock.
 *
 *      pd_fp (file_t pointer) is set iff the thread is on the fpollinfo
 *      list for that open file.
 *      This is modified atomically under pc_lock.
 *
 *      pd_count is the sum (over all values of i) of pd_ref[i].xf_refcnt.
 *      Iff pd_ref[i].xf_refcnt >= 1 then
 *              ps_pcacheset[i].pcs_pollfd[pd_ref[i].xf_position].fd == pd_fd
 *      Iff pd_ref[i].xf_refcnt > 1 then
 *              In ps_pcacheset[i].pcs_pollfd between index
 *              pd_ref[i].xf_position] and the end of the list
 *              there are xf_refcnt entries with .fd == pd_fd
 *
 * Locking design:
 * Whenever possible the design relies on the fact that the poll cache state
 * is per thread thus for both poll and exit it is self-synchronizing.
 * Thus the key interactions where other threads access the state are:
 *      pollwakeup (and polltime), and
 *      close cleaning up the cached references to an open file
 *
 * The two key locks in poll proper is ps_lock and pc_lock.
 *
 * The ps_lock is used for synchronization between poll, (lwp_)exit and close
 * to ensure that modifications to pollcacheset structure are serialized.
 * This lock is held through most of poll() except where poll sleeps
 * since there is little need to handle closes concurrently with the execution
 * of poll.
 * The pc_lock protects most of the fields in pollcache structure and polldat
 * structures (which are accessed by poll, pollwakeup, and polltime)
 * with the exception of fields that are only modified when only one thread
 * can access this per-thread state.
 * Those exceptions occur in poll when first allocating the per-thread state,
 * when poll grows the number of polldat (never shrinks), and when
 * exit/pollcleanup has ensured that there are no references from either
 * pollheads or fpollinfo to the threads poll state.
 *
 * Poll(2) system call is the only path which ps_lock and pc_lock are both
 * held, in that order. It needs ps_lock to synchronize with close and
 * lwp_exit; and pc_lock with pollwakeup.
 *
 * The locking interaction between pc_lock and PHLOCK take into account
 * that poll acquires these locks in the order of pc_lock and then PHLOCK
 * while pollwakeup does it in the reverse order. Thus pollwakeup implements
 * deadlock avoidance by dropping the locks and reacquiring them in the
 * reverse order. For this to work pollwakeup needs to prevent the thread
 * from exiting and freeing all of the poll related state. Thus is done
 * using
 *      the pc_no_exit lock
 *      the pc_busy counter
 *      the pc_busy_cv condition variable
 *
 * The locking interaction between pc_lock and uf_lock has similar
 * issues. Poll holds ps_lock and/or pc_lock across calls to getf/releasef
 * which acquire uf_lock. The poll cleanup in close needs to hold uf_lock
 * to prevent poll or exit from doing a delfpollinfo after which the thread
 * might exit. But the cleanup needs to acquire pc_lock when modifying
 * the poll cache state. The solution is to use pc_busy and do the close
 * cleanup in two phases:
 *      First close calls pollblockexit which increments pc_busy.
 *      This prevents the per-thread poll related state from being freed.
 *      Then close drops uf_lock and calls pollcacheclean.
 *      This routine can then acquire pc_lock and remove any references
 *      to the closing fd (as well as recording that it has been closed
 *      so that a POLLNVAL can be generated even if the fd is reused before
 *      poll has been woken up and checked getf() again).
 *
 * When removing a polled fd from poll cache, the fd is always removed
 * from pollhead list first and then from fpollinfo list, i.e.,
 * pollhead_delete() is called before delfpollinfo().
 *
 *
 * Locking hierarchy:
 *      pc_no_exit is a leaf level lock.
 *      ps_lock is held when acquiring pc_lock (except when pollwakeup
 *      acquires pc_lock).
 *      pc_lock might be held when acquiring PHLOCK (pollhead_insert/
 *      pollhead_delete)
 *      pc_lock is always held (but this is not required)
 *      when acquiring PHLOCK (in polladd/pollhead_delete and pollwakeup called
 *      from pcache_clean_entry).
 *      pc_lock is held across addfpollinfo/delfpollinfo which acquire
 *      uf_lock.
 *      pc_lock is held across getf/releasef which acquire uf_lock.
 *      ps_lock might be held across getf/releasef which acquire uf_lock.
 *      pollwakeup tries to acquire pc_lock while holding PHLOCK
 *      but drops the locks and reacquire them in reverse order to avoid
 *      deadlock.
 *
 * Note also that there is deadlock avoidance support for fop_poll routines
 * and pollwakeup involving a file system or driver lock.
 * See below.
 */

/*
 * Deadlock avoidance support for fop_poll() routines.  This is
 * sometimes necessary to prevent deadlock between polling threads
 * (which hold poll locks on entry to xx_poll(), then acquire foo)
 * and pollwakeup() threads (which hold foo, then acquire poll locks).
 *
 * pollunlock(*cookie) releases whatever poll locks the current thread holds,
 *      setting a cookie for use by pollrelock();
 *
 * pollrelock(cookie) reacquires previously dropped poll locks;
 *
 * polllock(php, mutex) does the common case: pollunlock(),
 *      acquire the problematic mutex, pollrelock().
 *
 * If polllock() or pollunlock() return non-zero, it indicates that a recursive
 * /dev/poll is in progress and pollcache locks cannot be dropped.  Callers
 * must handle this by indicating a POLLNVAL in the revents of the fop_poll.
 */
int
pollunlock(int *lockstate)
{
        pollstate_t *ps = curthread->t_pollstate;
        pollcache_t *pcp;

        ASSERT(lockstate != NULL);

        /*
         * There is no way to safely perform a pollunlock() while in the depths
         * of a recursive /dev/poll operation.
         */
        if (ps != NULL && ps->ps_depth > 1) {
                ps->ps_flags |= POLLSTATE_ULFAIL;
                pollstats.pollunlockfail.value.ui64++;
                return (-1);
        }

        /*
         * t_pollcache is set by /dev/poll and event ports (port_fd.c).
         * If the pollrelock/pollunlock is called as a result of poll(2),
         * the t_pollcache should be NULL.
         */
        if (curthread->t_pollcache == NULL)
                pcp = ps->ps_pcache;
        else
                pcp = curthread->t_pollcache;

        if (!mutex_owned(&pcp->pc_lock)) {
                *lockstate = 0;
        } else {
                *lockstate = 1;
                mutex_exit(&pcp->pc_lock);
        }
        return (0);
}

void
pollrelock(int lockstate)
{
        pollstate_t *ps = curthread->t_pollstate;
        pollcache_t *pcp;

        /* Skip this whole ordeal if the pollcache was not locked to begin */
        if (lockstate == 0)
                return;

        /*
         * t_pollcache is set by /dev/poll and event ports (port_fd.c).
         * If the pollrelock/pollunlock is called as a result of poll(2),
         * the t_pollcache should be NULL.
         */
        if (curthread->t_pollcache == NULL)
                pcp = ps->ps_pcache;
        else
                pcp = curthread->t_pollcache;

        mutex_enter(&pcp->pc_lock);
}

/* ARGSUSED */
int
polllock(pollhead_t *php, kmutex_t *lp)
{
        if (mutex_tryenter(lp) == 0) {
                int state;

                if (pollunlock(&state) != 0) {
                        return (-1);
                }
                mutex_enter(lp);
                pollrelock(state);
        }
        return (0);
}

static int
poll_common(pollfd_t *fds, nfds_t nfds, timespec_t *tsp, k_sigset_t *ksetp)
{
        kthread_t *t = curthread;
        klwp_t *lwp = ttolwp(t);
        proc_t *p = ttoproc(t);
        int fdcnt = 0;
        int i;
        hrtime_t deadline; /* hrtime value when we want to return */
        pollfd_t *pollfdp;
        pollstate_t *ps;
        pollcache_t *pcp;
        int error = 0;
        nfds_t old_nfds;
        int cacheindex = 0;     /* which cache set is used */

        /*
         * Determine the precise future time of the requested timeout, if any.
         */
        if (tsp == NULL) {
                deadline = -1;
        } else if (tsp->tv_sec == 0 && tsp->tv_nsec == 0) {
                deadline = 0;
        } else {
                /* They must wait at least a tick. */
                deadline = ((hrtime_t)tsp->tv_sec * NANOSEC) + tsp->tv_nsec;
                deadline = MAX(deadline, nsec_per_tick);
                deadline += gethrtime();
        }

        /*
         * Reset our signal mask, if requested.
         */
        if (ksetp != NULL) {
                mutex_enter(&p->p_lock);
                schedctl_finish_sigblock(t);
                lwp->lwp_sigoldmask = t->t_hold;
                t->t_hold = *ksetp;
                t->t_flag |= T_TOMASK;
                /*
                 * Call cv_reltimedwait_sig() just to check for signals.
                 * We will return immediately with either 0 or -1.
                 */
                if (!cv_reltimedwait_sig(&t->t_delay_cv, &p->p_lock, 0,
                    TR_CLOCK_TICK)) {
                        mutex_exit(&p->p_lock);
                        error = EINTR;
                        goto pollout;
                }
                mutex_exit(&p->p_lock);
        }

        /*
         * Check to see if this one just wants to use poll() as a timeout.
         * If yes then bypass all the other stuff and make it sleep.
         */
        if (nfds == 0) {
                /*
                 * Sleep until we have passed the requested future
                 * time or until interrupted by a signal.
                 * Do not check for signals if we do not want to wait.
                 */
                if (deadline != 0) {
                        mutex_enter(&t->t_delay_lock);
                        while ((error = cv_timedwait_sig_hrtime(&t->t_delay_cv,
                            &t->t_delay_lock, deadline)) > 0)
                                continue;
                        mutex_exit(&t->t_delay_lock);
                        error = (error == 0) ? EINTR : 0;
                }
                goto pollout;
        }

        if (nfds > p->p_fno_ctl) {
                mutex_enter(&p->p_lock);
                (void) rctl_action(rctlproc_legacy[RLIMIT_NOFILE],
                    p->p_rctls, p, RCA_SAFE);
                mutex_exit(&p->p_lock);
                error = EINVAL;
                goto pollout;
        }

        /*
         * Need to allocate memory for pollstate before anything because
         * the mutex and cv are created in this space
         */
        ps = pollstate_create();

        if (ps->ps_pcache == NULL)
                ps->ps_pcache = pcache_alloc();
        pcp = ps->ps_pcache;

        /*
         * NOTE: for performance, buffers are saved across poll() calls.
         * The theory is that if a process polls heavily, it tends to poll
         * on the same set of descriptors.  Therefore, we only reallocate
         * buffers when nfds changes.  There is no hysteresis control,
         * because there is no data to suggest that this is necessary;
         * the penalty of reallocating is not *that* great in any event.
         */
        old_nfds = ps->ps_nfds;
        if (nfds != old_nfds) {

                kmem_free(ps->ps_pollfd, old_nfds * sizeof (pollfd_t));
                pollfdp = kmem_alloc(nfds * sizeof (pollfd_t), KM_SLEEP);
                ps->ps_pollfd = pollfdp;
                ps->ps_nfds = nfds;
        }

        pollfdp = ps->ps_pollfd;
        if (copyin(fds, pollfdp, nfds * sizeof (pollfd_t))) {
                error = EFAULT;
                goto pollout;
        }

        if (fds == NULL) {
                /*
                 * If the process has page 0 mapped, then the copyin() above
                 * will succeed even if fds is NULL.  However, our cached
                 * poll lists are keyed by the address of the passed-in fds
                 * structure, and we use the value NULL to indicate an unused
                 * poll cache list entry.  As such, we elect not to support
                 * NULL as a valid (user) memory address and fail the poll()
                 * call.
                 */
                error = EINVAL;
                goto pollout;
        }

        /*
         * If this thread polls for the first time, allocate ALL poll
         * cache data structures and cache the poll fd list. This
         * allocation is delayed till now because lwp's polling 0 fd
         * (i.e. using poll as timeout()) don't need this memory.
         */
        mutex_enter(&ps->ps_lock);
        pcp = ps->ps_pcache;
        ASSERT(pcp != NULL);
        if (pcp->pc_bitmap == NULL) {
                pcache_create(pcp, nfds);
                /*
                 * poll and cache this poll fd list in ps_pcacheset[0].
                 */
                error = pcacheset_cache_list(ps, fds, &fdcnt, cacheindex);
                if (fdcnt || error) {
                        mutex_exit(&ps->ps_lock);
                        goto pollout;
                }
        } else {
                pollcacheset_t  *pcset = ps->ps_pcacheset;

                /*
                 * Not first time polling. Select a cached poll list by
                 * matching user pollfd list buffer address.
                 */
                for (cacheindex = 0; cacheindex < ps->ps_nsets; cacheindex++) {
                        if (pcset[cacheindex].pcs_usradr == (uintptr_t)fds) {
                                if ((++pcset[cacheindex].pcs_count) == 0) {
                                        /*
                                         * counter is wrapping around.
                                         */
                                        pcacheset_reset_count(ps, cacheindex);
                                }
                                /*
                                 * examine and resolve possible
                                 * difference of the current poll
                                 * list and previously cached one.
                                 * If there is an error during resolve(),
                                 * the callee will guarantee the consistency
                                 * of cached poll list and cache content.
                                 */
                                error = pcacheset_resolve(ps, nfds, &fdcnt,
                                    cacheindex);
                                if (error) {
                                        mutex_exit(&ps->ps_lock);
                                        goto pollout;
                                }
                                break;
                        }

                        /*
                         * Note that pcs_usradr field of an used entry won't be
                         * NULL because it stores the address of passed-in fds,
                         * and NULL fds will not be cached (Then it is either
                         * the special timeout case when nfds is 0 or it returns
                         * failure directly).
                         */
                        if (pcset[cacheindex].pcs_usradr == (uintptr_t)NULL) {
                                /*
                                 * found an unused entry. Use it to cache
                                 * this poll list.
                                 */
                                error = pcacheset_cache_list(ps, fds, &fdcnt,
                                    cacheindex);
                                if (fdcnt || error) {
                                        mutex_exit(&ps->ps_lock);
                                        goto pollout;
                                }
                                break;
                        }
                }
                if (cacheindex == ps->ps_nsets) {
                        /*
                         * We failed to find a matching cached poll fd list.
                         * replace an old list.
                         */
                        pollstats.polllistmiss.value.ui64++;
                        cacheindex = pcacheset_replace(ps);
                        ASSERT(cacheindex < ps->ps_nsets);
                        pcset[cacheindex].pcs_usradr = (uintptr_t)fds;
                        error = pcacheset_resolve(ps, nfds, &fdcnt, cacheindex);
                        if (error) {
                                mutex_exit(&ps->ps_lock);
                                goto pollout;
                        }
                }
        }

        /*
         * Always scan the bitmap with the lock on the pollcache held.
         * This is to make sure that a wakeup does not come undetected.
         * If the lock is not held, a pollwakeup could have come for an
         * fd we already checked but before this thread sleeps, in which
         * case the wakeup is missed. Now we hold the pcache lock and
         * check the bitmap again. This will prevent wakeup from happening
         * while we hold pcache lock since pollwakeup() will also lock
         * the pcache before updating poll bitmap.
         */
        mutex_enter(&pcp->pc_lock);
        for (;;) {
                pcp->pc_flag = 0;
                error = pcache_poll(pollfdp, ps, nfds, &fdcnt, cacheindex);
                if (fdcnt || error) {
                        mutex_exit(&pcp->pc_lock);
                        mutex_exit(&ps->ps_lock);
                        break;
                }

                /*
                 * If PC_POLLWAKE is set, a pollwakeup() was performed on
                 * one of the file descriptors.  This can happen only if
                 * one of the fop_poll() functions dropped pcp->pc_lock.
                 * The only current cases of this is in procfs (prpoll())
                 * and STREAMS (strpoll()).
                 */
                if (pcp->pc_flag & PC_POLLWAKE)
                        continue;

                /*
                 * If you get here, the poll of fds was unsuccessful.
                 * Wait until some fd becomes readable, writable, or gets
                 * an exception, or until a signal or a timeout occurs.
                 * Do not check for signals if we have a zero timeout.
                 */
                mutex_exit(&ps->ps_lock);
                if (deadline == 0) {
                        error = -1;
                } else {
                        error = cv_timedwait_sig_hrtime(&pcp->pc_cv,
                            &pcp->pc_lock, deadline);
                }
                mutex_exit(&pcp->pc_lock);
                /*
                 * If we have received a signal or timed out
                 * then break out and return.
                 */
                if (error <= 0) {
                        error = (error == 0) ? EINTR : 0;
                        break;
                }
                /*
                 * We have not received a signal or timed out.
                 * Continue around and poll fds again.
                 */
                mutex_enter(&ps->ps_lock);
                mutex_enter(&pcp->pc_lock);
        }

pollout:
        /*
         * If we changed the signal mask but we received
         * no signal then restore the signal mask.
         * Otherwise psig() will deal with the signal mask.
         */
        if (ksetp != NULL) {
                mutex_enter(&p->p_lock);
                if (lwp->lwp_cursig == 0) {
                        t->t_hold = lwp->lwp_sigoldmask;
                        t->t_flag &= ~T_TOMASK;
                }
                mutex_exit(&p->p_lock);
        }

        if (error)
                return (set_errno(error));

        /*
         * Copy out the events and return the fdcnt to the user.
         */
        if (nfds != 0 &&
            copyout(pollfdp, fds, nfds * sizeof (pollfd_t)))
                return (set_errno(EFAULT));

#ifdef DEBUG
        /*
         * Another sanity check:
         */
        if (fdcnt) {
                int     reventcnt = 0;

                for (i = 0; i < nfds; i++) {
                        if (pollfdp[i].fd < 0) {
                                ASSERT(pollfdp[i].revents == 0);
                                continue;
                        }
                        if (pollfdp[i].revents) {
                                reventcnt++;
                        }
                }
                ASSERT(fdcnt == reventcnt);
        } else {
                for (i = 0; i < nfds; i++) {
                        ASSERT(pollfdp[i].revents == 0);
                }
        }
#endif  /* DEBUG */

        return (fdcnt);
}

/*
 * This is the system call trap that poll(),
 * select() and pselect() are built upon.
 * It is a private interface between libc and the kernel.
 */
int
pollsys(pollfd_t *fds, nfds_t nfds, timespec_t *timeoutp, sigset_t *setp)
{
        timespec_t ts;
        timespec_t *tsp;
        sigset_t set;
        k_sigset_t kset;
        k_sigset_t *ksetp;
        model_t datamodel = get_udatamodel();

        if (timeoutp == NULL)
                tsp = NULL;
        else {
                if (datamodel == DATAMODEL_NATIVE) {
                        if (copyin(timeoutp, &ts, sizeof (ts)))
                                return (set_errno(EFAULT));
                } else {
                        timespec32_t ts32;

                        if (copyin(timeoutp, &ts32, sizeof (ts32)))
                                return (set_errno(EFAULT));
                        TIMESPEC32_TO_TIMESPEC(&ts, &ts32)
                }

                if (itimerspecfix(&ts))
                        return (set_errno(EINVAL));
                tsp = &ts;
        }

        if (setp == NULL)
                ksetp = NULL;
        else {
                if (copyin(setp, &set, sizeof (set)))
                        return (set_errno(EFAULT));
                sigutok(&set, &kset);
                ksetp = &kset;
        }

        return (poll_common(fds, nfds, tsp, ksetp));
}

/*
 * Clean up any state left around by poll(2). Called when a thread exits.
 */
void
pollcleanup()
{
        pollstate_t *ps = curthread->t_pollstate;
        pollcache_t *pcp;

        if (ps == NULL)
                return;
        pcp = ps->ps_pcache;
        /*
         * free up all cached poll fds
         */
        if (pcp == NULL) {
                /* this pollstate is used by /dev/poll */
                goto pollcleanout;
        }

        if (pcp->pc_bitmap != NULL) {
                ASSERT(MUTEX_NOT_HELD(&ps->ps_lock));
                /*
                 * a close lwp can race with us when cleaning up a polldat
                 * entry. We hold the ps_lock when cleaning hash table.
                 * Since this pollcache is going away anyway, there is no
                 * need to hold the pc_lock.
                 */
                mutex_enter(&ps->ps_lock);
                pcache_clean(pcp);
                mutex_exit(&ps->ps_lock);
#ifdef DEBUG
                /*
                 * At this point, all fds cached by this lwp should be
                 * cleaned up. There should be no fd in fi_list still
                 * reference this thread.
                 */
                checkfpollinfo();       /* sanity check */
                pollcheckphlist();      /* sanity check */
#endif  /* DEBUG */
        }
        /*
         * Be sure no one is referencing thread before exiting
         */
        mutex_enter(&pcp->pc_no_exit);
        ASSERT(pcp->pc_busy >= 0);
        while (pcp->pc_busy > 0)
                cv_wait(&pcp->pc_busy_cv, &pcp->pc_no_exit);
        mutex_exit(&pcp->pc_no_exit);
pollcleanout:
        pollstate_destroy(ps);
        curthread->t_pollstate = NULL;
}

/*
 * pollwakeup() - poke threads waiting in poll() for some event
 * on a particular object.
 *
 * The threads hanging off of the specified pollhead structure are scanned.
 * If their event mask matches the specified event(s), then pollnotify() is
 * called to poke the thread.
 *
 * Multiple events may be specified.  When POLLHUP or POLLERR are specified,
 * all waiting threads are poked.
 *
 * It is important that pollnotify() not drop the lock protecting the list
 * of threads.
 */
void
pollwakeup(pollhead_t *php, short events_arg)
{
        polldat_t       *pdp;
        int             events = (ushort_t)events_arg;
        struct plist {
                port_t *pp;
                int     pevents;
                struct plist *next;
                };
        struct plist *plhead = NULL, *pltail = NULL;

retry:
        PH_ENTER(php);

        for (pdp = php->ph_list; pdp; pdp = pdp->pd_next) {
                if ((pdp->pd_events & events) ||
                    (events & (POLLHUP | POLLERR))) {

                        pollcache_t     *pcp;

                        if (pdp->pd_portev != NULL) {
                                port_kevent_t   *pkevp = pdp->pd_portev;
                                /*
                                 * Object (fd) is associated with an event port,
                                 * => send event notification to the port.
                                 */
                                ASSERT(pkevp->portkev_source == PORT_SOURCE_FD);
                                mutex_enter(&pkevp->portkev_lock);
                                if (pkevp->portkev_flags & PORT_KEV_VALID) {
                                        int pevents;

                                        pkevp->portkev_flags &= ~PORT_KEV_VALID;
                                        pkevp->portkev_events |= events &
                                            (pdp->pd_events | POLLHUP |
                                            POLLERR);
                                        /*
                                         * portkev_lock mutex will be released
                                         * by port_send_event().
                                         */
                                        port_send_event(pkevp);

                                        /*
                                         * If we have some thread polling the
                                         * port's fd, add it to the list. They
                                         * will be notified later.
                                         * The port_pollwkup() will flag the
                                         * port_t so that it will not disappear
                                         * till port_pollwkdone() is called.
                                         */
                                        pevents =
                                            port_pollwkup(pkevp->portkev_port);
                                        if (pevents) {
                                                struct plist *t;
                                                t = kmem_zalloc(
                                                    sizeof (struct plist),
                                                    KM_SLEEP);
                                                t->pp = pkevp->portkev_port;
                                                t->pevents = pevents;
                                                if (plhead == NULL) {
                                                        plhead = t;
                                                } else {
                                                        pltail->next = t;
                                                }
                                                pltail = t;
                                        }
                                } else {
                                        mutex_exit(&pkevp->portkev_lock);
                                }
                                continue;
                        }

                        pcp = pdp->pd_pcache;

                        /*
                         * Try to grab the lock for this thread. If
                         * we don't get it then we may deadlock so
                         * back out and restart all over again. Note
                         * that the failure rate is very very low.
                         */
                        if (mutex_tryenter(&pcp->pc_lock)) {
                                pollnotify(pcp, pdp->pd_fd);
                                mutex_exit(&pcp->pc_lock);
                        } else {
                                /*
                                 * We are here because:
                                 *      1) This thread has been woke up
                                 *         and is trying to get out of poll().
                                 *      2) Some other thread is also here
                                 *         but with a different pollhead lock.
                                 *
                                 * So, we need to drop the lock on pollhead
                                 * because of (1) but we want to prevent
                                 * that thread from doing lwp_exit() or
                                 * devpoll close. We want to ensure that
                                 * the pollcache pointer is still invalid.
                                 *
                                 * Solution: Grab the pcp->pc_no_exit lock,
                                 * increment the pc_busy counter, drop every
                                 * lock in sight. Get out of the way and wait
                                 * for type (2) threads to finish.
                                 */

                                mutex_enter(&pcp->pc_no_exit);
                                pcp->pc_busy++; /* prevents exit()'s */
                                mutex_exit(&pcp->pc_no_exit);

                                PH_EXIT(php);
                                mutex_enter(&pcp->pc_lock);
                                mutex_exit(&pcp->pc_lock);
                                mutex_enter(&pcp->pc_no_exit);
                                pcp->pc_busy--;
                                if (pcp->pc_busy == 0) {
                                        /*
                                         * Wakeup the thread waiting in
                                         * thread_exit().
                                         */
                                        cv_signal(&pcp->pc_busy_cv);
                                }
                                mutex_exit(&pcp->pc_no_exit);
                                goto retry;
                        }
                }
        }


        /*
         * Event ports - If this php is of the port on the list,
         * call port_pollwkdone() to release it. The port_pollwkdone()
         * needs to be called before dropping the PH lock so that any new
         * thread attempting to poll this port are blocked. There can be
         * only one thread here in pollwakeup notifying this port's fd.
         */
        if (plhead != NULL && &plhead->pp->port_pollhd == php) {
                struct plist *t;
                port_pollwkdone(plhead->pp);
                t = plhead;
                plhead = plhead->next;
                kmem_free(t, sizeof (struct plist));
        }
        PH_EXIT(php);

        /*
         * Event ports - Notify threads polling the event port's fd.
         * This is normally done in port_send_event() where it calls
         * pollwakeup() on the port. But, for PORT_SOURCE_FD source alone,
         * we do it here in pollwakeup() to avoid a recursive call.
         */
        if (plhead != NULL) {
                php = &plhead->pp->port_pollhd;
                events = plhead->pevents;
                goto retry;
        }
}

/*
 * This function is called to inform a thread (or threads) that an event being
 * polled on has occurred.  The pollstate lock on the thread should be held
 * on entry.
 */
void
pollnotify(pollcache_t *pcp, int fd)
{
        ASSERT(fd < pcp->pc_mapsize);
        ASSERT(MUTEX_HELD(&pcp->pc_lock));
        BT_SET(pcp->pc_bitmap, fd);
        pcp->pc_flag |= PC_POLLWAKE;
        cv_broadcast(&pcp->pc_cv);
        pcache_wake_parents(pcp);
}

/*
 * add a polldat entry to pollhead ph_list. The polldat struct is used
 * by pollwakeup to wake sleeping pollers when polled events has happened.
 */
void
pollhead_insert(pollhead_t *php, polldat_t *pdp)
{
        PH_ENTER(php);
        ASSERT(pdp->pd_next == NULL);
#ifdef DEBUG
        {
                /*
                 * the polldat should not be already on the list
                 */
                polldat_t *wp;
                for (wp = php->ph_list; wp; wp = wp->pd_next) {
                        ASSERT(wp != pdp);
                }
        }
#endif  /* DEBUG */
        pdp->pd_next = php->ph_list;
        php->ph_list = pdp;
        PH_EXIT(php);
}

/*
 * Delete the polldat entry from ph_list.
 */
void
pollhead_delete(pollhead_t *php, polldat_t *pdp)
{
        polldat_t *wp;
        polldat_t **wpp;

        PH_ENTER(php);
        for (wpp = &php->ph_list; (wp = *wpp) != NULL; wpp = &wp->pd_next) {
                if (wp == pdp) {
                        *wpp = pdp->pd_next;
                        pdp->pd_next = NULL;
                        break;
                }
        }
#ifdef DEBUG
        /* assert that pdp is no longer in the list */
        for (wp = *wpp; wp; wp = wp->pd_next) {
                ASSERT(wp != pdp);
        }
#endif  /* DEBUG */
        PH_EXIT(php);
}

/*
 * walk through the poll fd lists to see if they are identical. This is an
 * expensive operation and should not be done more than once for each poll()
 * call.
 *
 * As an optimization (i.e., not having to go through the lists more than
 * once), this routine also clear the revents field of pollfd in 'current'.
 * Zeroing out the revents field of each entry in current poll list is
 * required by poll man page.
 *
 * Since the events field of cached list has illegal poll events filtered
 * out, the current list applies the same filtering before comparison.
 *
 * The routine stops when it detects a meaningful difference, or when it
 * exhausts the lists.
 */
int
pcacheset_cmp(pollfd_t *current, pollfd_t *cached, pollfd_t *newlist, int n)
{
        int    ix;

        for (ix = 0; ix < n; ix++) {
                /* Prefetch 64 bytes worth of 8-byte elements */
                if ((ix & 0x7) == 0) {
                        prefetch_write_many((caddr_t)&current[ix + 8]);
                        prefetch_write_many((caddr_t)&cached[ix + 8]);
                }
                if (current[ix].fd == cached[ix].fd) {
                        /*
                         * Filter out invalid poll events while we are in
                         * inside the loop.
                         */
                        if (current[ix].events & ~VALID_POLL_EVENTS) {
                                current[ix].events &= VALID_POLL_EVENTS;
                                if (newlist != NULL)
                                        newlist[ix].events = current[ix].events;
                        }
                        if (current[ix].events == cached[ix].events) {
                                current[ix].revents = 0;
                                continue;
                        }
                }
                if ((current[ix].fd < 0) && (cached[ix].fd < 0)) {
                        current[ix].revents = 0;
                        continue;
                }
                return (ix);
        }
        return (ix);
}

/*
 * This routine returns a pointer to a cached poll fd entry, or NULL if it
 * does not find it in the hash table.
 */
polldat_t *
pcache_lookup_fd(pollcache_t *pcp, int fd)
{
        int hashindex;
        polldat_t *pdp;

        hashindex = POLLHASH(pcp->pc_hashsize, fd);
        pdp = pcp->pc_hash[hashindex];
        while (pdp != NULL) {
                if (pdp->pd_fd == fd)
                        break;
                pdp = pdp->pd_hashnext;
        }
        return (pdp);
}

polldat_t *
pcache_alloc_fd(int nsets)
{
        polldat_t *pdp;

        pdp = kmem_zalloc(sizeof (polldat_t), KM_SLEEP);
        if (nsets > 0) {
                pdp->pd_ref = kmem_zalloc(sizeof (xref_t) * nsets, KM_SLEEP);
                pdp->pd_nsets = nsets;
        }
        return (pdp);
}

/*
 * This routine  inserts a polldat into the pollcache's hash table. It
 * may be necessary to grow the size of the hash table.
 */
void
pcache_insert_fd(pollcache_t *pcp, polldat_t *pdp, nfds_t nfds)
{
        int hashindex;
        int fd;

        if ((pcp->pc_fdcount > pcp->pc_hashsize * POLLHASHTHRESHOLD) ||
            (nfds > pcp->pc_hashsize * POLLHASHTHRESHOLD)) {
                pcache_grow_hashtbl(pcp, nfds);
        }
        fd = pdp->pd_fd;
        hashindex = POLLHASH(pcp->pc_hashsize, fd);
        pdp->pd_hashnext = pcp->pc_hash[hashindex];
        pcp->pc_hash[hashindex] = pdp;
        pcp->pc_fdcount++;

#ifdef DEBUG
        {
                /*
                 * same fd should not appear on a hash list twice
                 */
                polldat_t *pdp1;
                for (pdp1 = pdp->pd_hashnext; pdp1; pdp1 = pdp1->pd_hashnext) {
                        ASSERT(pdp->pd_fd != pdp1->pd_fd);
                }
        }
#endif  /* DEBUG */
}

/*
 * Grow the hash table -- either double the table size or round it to the
 * nearest multiples of POLLHASHCHUNKSZ, whichever is bigger. Rehash all the
 * elements on the hash table.
 */
void
pcache_grow_hashtbl(pollcache_t *pcp, nfds_t nfds)
{
        int     oldsize;
        polldat_t **oldtbl;
        polldat_t *pdp, *pdp1;
        int     i;
#ifdef DEBUG
        int     count = 0;
#endif

        ASSERT(pcp->pc_hashsize % POLLHASHCHUNKSZ == 0);
        oldsize = pcp->pc_hashsize;
        oldtbl = pcp->pc_hash;
        if (nfds > pcp->pc_hashsize * POLLHASHINC) {
                pcp->pc_hashsize = (nfds + POLLHASHCHUNKSZ - 1) &
                    ~(POLLHASHCHUNKSZ - 1);
        } else {
                pcp->pc_hashsize = pcp->pc_hashsize * POLLHASHINC;
        }
        pcp->pc_hash = kmem_zalloc(pcp->pc_hashsize * sizeof (polldat_t *),
            KM_SLEEP);
        /*
         * rehash existing elements
         */
        pcp->pc_fdcount = 0;
        for (i = 0; i < oldsize; i++) {
                pdp = oldtbl[i];
                while (pdp != NULL) {
                        pdp1 = pdp->pd_hashnext;
                        pcache_insert_fd(pcp, pdp, nfds);
                        pdp = pdp1;
#ifdef DEBUG
                        count++;
#endif
                }
        }
        kmem_free(oldtbl, oldsize * sizeof (polldat_t *));
        ASSERT(pcp->pc_fdcount == count);
}

void
pcache_grow_map(pollcache_t *pcp, int fd)
{
        int     newsize;
        ulong_t *newmap;

        /*
         * grow to nearest multiple of POLLMAPCHUNK, assuming POLLMAPCHUNK is
         * power of 2.
         */
        newsize = (fd + POLLMAPCHUNK) & ~(POLLMAPCHUNK - 1);
        newmap = kmem_zalloc((newsize / BT_NBIPUL) * sizeof (ulong_t),
            KM_SLEEP);
        /*
         * don't want pollwakeup to set a bit while growing the bitmap.
         */
        ASSERT(mutex_owned(&pcp->pc_lock) == 0);
        mutex_enter(&pcp->pc_lock);
        bcopy(pcp->pc_bitmap, newmap,
            (pcp->pc_mapsize / BT_NBIPUL) * sizeof (ulong_t));
        kmem_free(pcp->pc_bitmap,
            (pcp->pc_mapsize /BT_NBIPUL) * sizeof (ulong_t));
        pcp->pc_bitmap = newmap;
        pcp->pc_mapsize = newsize;
        mutex_exit(&pcp->pc_lock);
}

/*
 * remove all the reference from pollhead list and fpollinfo lists.
 */
void
pcache_clean(pollcache_t *pcp)
{
        int i;
        polldat_t **hashtbl;
        polldat_t *pdp;

        ASSERT(MUTEX_HELD(&curthread->t_pollstate->ps_lock));
        hashtbl = pcp->pc_hash;
        for (i = 0; i < pcp->pc_hashsize; i++) {
                for (pdp = hashtbl[i]; pdp; pdp = pdp->pd_hashnext) {
                        if (pdp->pd_php != NULL) {
                                pollhead_delete(pdp->pd_php, pdp);
                                pdp->pd_php = NULL;
                        }
                        if (pdp->pd_fp != NULL) {
                                delfpollinfo(pdp->pd_fd);
                                pdp->pd_fp = NULL;
                        }
                }
        }
}

void
pcacheset_invalidate(pollstate_t *ps, polldat_t *pdp)
{
        int     i;
        int     fd = pdp->pd_fd;

        /*
         * we come here because an earlier close() on this cached poll fd.
         */
        ASSERT(pdp->pd_fp == NULL);
        ASSERT(MUTEX_HELD(&ps->ps_lock));
        pdp->pd_events = 0;
        for (i = 0; i < ps->ps_nsets; i++) {
                xref_t          *refp;
                pollcacheset_t  *pcsp;

                ASSERT(pdp->pd_ref != NULL);
                refp = &pdp->pd_ref[i];
                if (refp->xf_refcnt) {
                        ASSERT(refp->xf_position >= 0);
                        pcsp = &ps->ps_pcacheset[i];
                        if (refp->xf_refcnt == 1) {
                                pcsp->pcs_pollfd[refp->xf_position].fd = -1;
                                refp->xf_refcnt = 0;
                                pdp->pd_count--;
                        } else if (refp->xf_refcnt > 1) {
                                int     j;

                                /*
                                 * turn off every appearance in pcs_pollfd list
                                 */
                                for (j = refp->xf_position;
                                    j < pcsp->pcs_nfds; j++) {
                                        if (pcsp->pcs_pollfd[j].fd == fd) {
                                                pcsp->pcs_pollfd[j].fd = -1;
                                                refp->xf_refcnt--;
                                                pdp->pd_count--;
                                        }
                                }
                        }
                        ASSERT(refp->xf_refcnt == 0);
                        refp->xf_position = POLLPOSINVAL;
                }
        }
        ASSERT(pdp->pd_count == 0);
}

/*
 * Insert poll fd into the pollcache, and add poll registration.
 * This routine is called after getf() and before releasef(). So the vnode
 * can not disappear even if we block here.
 * If there is an error, the polled fd is not cached.
 */
int
pcache_insert(pollstate_t *ps, file_t *fp, pollfd_t *pollfdp, int *fdcntp,
    ssize_t pos, int which)
{
        pollcache_t     *pcp = ps->ps_pcache;
        polldat_t       *pdp;
        int             error;
        int             fd;
        pollhead_t      *memphp = NULL;
        xref_t          *refp;
        int             newpollfd = 0;

        ASSERT(MUTEX_HELD(&ps->ps_lock));
        /*
         * The poll caching uses the existing fop_poll interface. If there
         * is no polled events, we want the polled device to set its "some
         * one is sleeping in poll" flag. When the polled events happen
         * later, the driver will call pollwakeup(). We achieve this by
         * always passing 0 in the third parameter ("anyyet") when calling
         * fop_poll. This parameter is not looked at by drivers when the
         * polled events exist. If a driver chooses to ignore this parameter
         * and call pollwakeup whenever the polled events happen, that will
         * be OK too.
         */
        ASSERT(curthread->t_pollcache == NULL);
        error = fop_poll(fp->f_vnode, pollfdp->events, 0, &pollfdp->revents,
            &memphp, NULL);
        if (error) {
                return (error);
        }
        if (pollfdp->revents) {
                (*fdcntp)++;
        }
        /*
         * polling the underlying device succeeded. Now we can cache it.
         * A close can't come in here because we have not done a releasef()
         * yet.
         */
        fd = pollfdp->fd;
        pdp = pcache_lookup_fd(pcp, fd);
        if (pdp == NULL) {
                ASSERT(ps->ps_nsets > 0);
                pdp = pcache_alloc_fd(ps->ps_nsets);
                newpollfd = 1;
        }
        /*
         * If this entry was used to cache a poll fd which was closed, and
         * this entry has not been cleaned, do it now.
         */
        if ((pdp->pd_count > 0) && (pdp->pd_fp == NULL)) {
                pcacheset_invalidate(ps, pdp);
                ASSERT(pdp->pd_next == NULL);
        }
        if (pdp->pd_count == 0) {
                pdp->pd_fd = fd;
                pdp->pd_fp = fp;
                addfpollinfo(fd);
                pdp->pd_thread = curthread;
                pdp->pd_pcache = pcp;
                /*
                 * the entry is never used or cleared by removing a cached
                 * pollfd (pcache_delete_fd). So all the fields should be clear.
                 */
                ASSERT(pdp->pd_next == NULL);
        }

        /*
         * A polled fd is considered cached. So there should be a fpollinfo
         * entry on uf_fpollinfo list.
         */
        ASSERT(infpollinfo(fd));
        /*
         * If there is an inconsistency, we want to know it here.
         */
        ASSERT(pdp->pd_fp == fp);

        /*
         * XXX pd_events is a union of all polled events on this fd, possibly
         * by different threads. Unless this is a new first poll(), pd_events
         * never shrinks. If an event is no longer polled by a process, there
         * is no way to cancel that event. In that case, poll degrade to its
         * old form -- polling on this fd every time poll() is called. The
         * assumption is an app always polls the same type of events.
         */
        pdp->pd_events |= pollfdp->events;

        pdp->pd_count++;
        /*
         * There is not much special handling for multiple appearances of
         * same fd other than xf_position always recording the first
         * appearance in poll list. If this is called from pcacheset_cache_list,
         * a fop_poll is called on every pollfd entry; therefore each
         * revents and fdcnt should be set correctly. If this is called from
         * pcacheset_resolve, we don't care about fdcnt here. Pollreadmap will
         * pick up the right count and handle revents field of each pollfd
         * entry.
         */
        ASSERT(pdp->pd_ref != NULL);
        refp = &pdp->pd_ref[which];
        if (refp->xf_refcnt == 0) {
                refp->xf_position = pos;
        } else {
                /*
                 * xf_position records the fd's first appearance in poll list
                 */
                if (pos < refp->xf_position) {
                        refp->xf_position = pos;
                }
        }
        ASSERT(pollfdp->fd == ps->ps_pollfd[refp->xf_position].fd);
        refp->xf_refcnt++;
        if (fd >= pcp->pc_mapsize) {
                pcache_grow_map(pcp, fd);
        }
        if (fd > pcp->pc_mapend) {
                pcp->pc_mapend = fd;
        }
        if (newpollfd != 0) {
                pcache_insert_fd(ps->ps_pcache, pdp, ps->ps_nfds);
        }
        if (memphp) {
                if (pdp->pd_php == NULL) {
                        pollhead_insert(memphp, pdp);
                        pdp->pd_php = memphp;
                } else {
                        if (memphp != pdp->pd_php) {
                                /*
                                 * layered devices (e.g. console driver)
                                 * may change the vnode and thus the pollhead
                                 * pointer out from underneath us.
                                 */
                                pollhead_delete(pdp->pd_php, pdp);
                                pollhead_insert(memphp, pdp);
                                pdp->pd_php = memphp;
                        }
                }
        }
        /*
         * Since there is a considerable window between fop_poll and when
         * we actually put the polldat struct on the pollhead list, we could
         * miss a pollwakeup. In the case of polling additional events, we
         * don't update the events until after fop_poll. So we could miss
         * pollwakeup there too. So we always set the bit here just to be
         * safe. The real performance gain is in subsequent pcache_poll.
         */
        mutex_enter(&pcp->pc_lock);
        BT_SET(pcp->pc_bitmap, fd);
        mutex_exit(&pcp->pc_lock);
        return (0);
}

/*
 * The entry is not really deleted. The fields are cleared so that the
 * entry is no longer useful, but it will remain in the hash table for reuse
 * later. It will be freed when the polling lwp exits.
 */
int
pcache_delete_fd(pollstate_t *ps, int fd, size_t pos, int which, uint_t cevent)
{
        pollcache_t     *pcp = ps->ps_pcache;
        polldat_t       *pdp;
        xref_t          *refp;

        ASSERT(fd < pcp->pc_mapsize);
        ASSERT(MUTEX_HELD(&ps->ps_lock));

        pdp = pcache_lookup_fd(pcp, fd);
        ASSERT(pdp != NULL);
        ASSERT(pdp->pd_count > 0);
        ASSERT(pdp->pd_ref != NULL);
        refp = &pdp->pd_ref[which];
        if (pdp->pd_count == 1) {
                pdp->pd_events = 0;
                refp->xf_position = POLLPOSINVAL;
                ASSERT(refp->xf_refcnt == 1);
                refp->xf_refcnt = 0;
                if (pdp->pd_php) {
                        /*
                         * It is possible for a wakeup thread to get ahead
                         * of the following pollhead_delete and set the bit in
                         * bitmap.  It is OK because the bit will be cleared
                         * here anyway.
                         */
                        pollhead_delete(pdp->pd_php, pdp);
                        pdp->pd_php = NULL;
                }
                pdp->pd_count = 0;
                if (pdp->pd_fp != NULL) {
                        pdp->pd_fp = NULL;
                        delfpollinfo(fd);
                }
                mutex_enter(&pcp->pc_lock);
                BT_CLEAR(pcp->pc_bitmap, fd);
                mutex_exit(&pcp->pc_lock);
                return (0);
        }
        if ((cevent & POLLCLOSED) == POLLCLOSED) {
                /*
                 * fd cached here has been closed. This is the first
                 * pcache_delete_fd called after the close. Clean up the
                 * entire entry.
                 */
                pcacheset_invalidate(ps, pdp);
                ASSERT(pdp->pd_php == NULL);
                mutex_enter(&pcp->pc_lock);
                BT_CLEAR(pcp->pc_bitmap, fd);
                mutex_exit(&pcp->pc_lock);
                return (0);
        }
#ifdef DEBUG
        if (getf(fd) != NULL) {
                ASSERT(infpollinfo(fd));
                releasef(fd);
        }
#endif  /* DEBUG */
        pdp->pd_count--;
        ASSERT(refp->xf_refcnt > 0);
        if (--refp->xf_refcnt == 0) {
                refp->xf_position = POLLPOSINVAL;
        } else {
                ASSERT(pos >= refp->xf_position);
                if (pos == refp->xf_position) {
                        /*
                         * The xref position is no longer valid.
                         * Reset it to a special value and let
                         * caller know it needs to updatexref()
                         * with a new xf_position value.
                         */
                        refp->xf_position = POLLPOSTRANS;
                        return (1);
                }
        }
        return (0);
}

void
pcache_update_xref(pollcache_t *pcp, int fd, ssize_t pos, int which)
{
        polldat_t       *pdp;

        pdp = pcache_lookup_fd(pcp, fd);
        ASSERT(pdp != NULL);
        ASSERT(pdp->pd_ref != NULL);
        pdp->pd_ref[which].xf_position = pos;
}

#ifdef DEBUG
/*
 * For each polled fd, it's either in the bitmap or cached in
 * pcache hash table. If this routine returns 0, something is wrong.
 */
static int
pollchecksanity(pollstate_t *ps, nfds_t nfds)
{
        int             i;
        int             fd;
        pollcache_t     *pcp = ps->ps_pcache;
        polldat_t       *pdp;
        pollfd_t        *pollfdp = ps->ps_pollfd;
        file_t          *fp;

        ASSERT(MUTEX_HELD(&ps->ps_lock));
        for (i = 0; i < nfds; i++) {
                fd = pollfdp[i].fd;
                if (fd < 0) {
                        ASSERT(pollfdp[i].revents == 0);
                        continue;
                }
                if (pollfdp[i].revents == POLLNVAL)
                        continue;
                if ((fp = getf(fd)) == NULL)
                        continue;
                pdp = pcache_lookup_fd(pcp, fd);
                ASSERT(pdp != NULL);
                ASSERT(infpollinfo(fd));
                ASSERT(pdp->pd_fp == fp);
                releasef(fd);
                if (BT_TEST(pcp->pc_bitmap, fd))
                        continue;
                if (pdp->pd_php == NULL)
                        return (0);
        }
        return (1);
}
#endif  /* DEBUG */

/*
 * resolve the difference between the current poll list and a cached one.
 */
int
pcacheset_resolve(pollstate_t *ps, nfds_t nfds, int *fdcntp, int which)
{
        int             i;
        pollcache_t     *pcp = ps->ps_pcache;
        pollfd_t        *newlist = NULL;
        pollfd_t        *current = ps->ps_pollfd;
        pollfd_t        *cached;
        pollcacheset_t  *pcsp;
        int             common;
        int             count = 0;
        int             offset;
        int             remain;
        int             fd;
        file_t          *fp;
        int             fdcnt = 0;
        int             cnt = 0;
        nfds_t          old_nfds;
        int             error = 0;
        int             mismatch = 0;

        ASSERT(MUTEX_HELD(&ps->ps_lock));
#ifdef DEBUG
        checkpolldat(ps);
#endif
        pcsp = &ps->ps_pcacheset[which];
        old_nfds = pcsp->pcs_nfds;
        common = (nfds > old_nfds) ? old_nfds : nfds;
        if (nfds != old_nfds) {
                /*
                 * the length of poll list has changed. allocate a new
                 * pollfd list.
                 */
                newlist = kmem_alloc(nfds * sizeof (pollfd_t), KM_SLEEP);
                bcopy(current, newlist, sizeof (pollfd_t) * nfds);
        }
        /*
         * Compare the overlapping part of the current fd list with the
         * cached one. Whenever a difference is found, resolve it.
         * The comparison is done on the current poll list and the
         * cached list. But we may be setting up the newlist to be the
         * cached list for next poll.
         */
        cached = pcsp->pcs_pollfd;
        remain = common;

        while (count < common) {
                int     tmpfd;
                pollfd_t *np;

                np = (newlist != NULL) ? &newlist[count] : NULL;
                offset = pcacheset_cmp(&current[count], &cached[count], np,
                    remain);
                /*
                 * Collect stats. If lists are completed the first time,
                 * it's a hit. Otherwise, it's a partial hit or miss.
                 */
                if ((count == 0) && (offset == common)) {
                        pollstats.pollcachehit.value.ui64++;
                } else {
                        mismatch++;
                }
                count += offset;
                if (offset < remain) {
                        ASSERT(count < common);
                        ASSERT((current[count].fd != cached[count].fd) ||
                            (current[count].events != cached[count].events));
                        /*
                         * Filter out invalid events.
                         */
                        if (current[count].events & ~VALID_POLL_EVENTS) {
                                if (newlist != NULL) {
                                        newlist[count].events =
                                            current[count].events &=
                                            VALID_POLL_EVENTS;
                                } else {
                                        current[count].events &=
                                            VALID_POLL_EVENTS;
                                }
                        }
                        /*
                         * when resolving a difference, we always remove the
                         * fd from cache before inserting one into cache.
                         */
                        if (cached[count].fd >= 0) {
                                tmpfd = cached[count].fd;
                                if (pcache_delete_fd(ps, tmpfd, count, which,
                                    (uint_t)cached[count].events)) {
                                        /*
                                         * This should be rare but needed for
                                         * correctness.
                                         *
                                         * The first appearance in cached list
                                         * is being "turned off". The same fd
                                         * appear more than once in the cached
                                         * poll list. Find the next one on the
                                         * list and update the cached
                                         * xf_position field.
                                         */
                                        for (i = count + 1; i < old_nfds; i++) {
                                                if (cached[i].fd == tmpfd) {
                                                        pcache_update_xref(pcp,
                                                            tmpfd, (ssize_t)i,
                                                            which);
                                                        break;
                                                }
                                        }
                                        ASSERT(i <= old_nfds);
                                }
                                /*
                                 * In case a new cache list is allocated,
                                 * need to keep both cache lists in sync
                                 * b/c the new one can be freed if we have
                                 * an error later.
                                 */
                                cached[count].fd = -1;
                                if (newlist != NULL) {
                                        newlist[count].fd = -1;
                                }
                        }
                        if ((tmpfd = current[count].fd) >= 0) {
                                /*
                                 * add to the cached fd tbl and bitmap.
                                 */
                                if ((fp = getf(tmpfd)) == NULL) {
                                        current[count].revents = POLLNVAL;
                                        if (newlist != NULL) {
                                                newlist[count].fd = -1;
                                        }
                                        cached[count].fd = -1;
                                        fdcnt++;
                                } else {
                                        /*
                                         * Here we don't care about the
                                         * fdcnt. We will examine the bitmap
                                         * later and pick up the correct
                                         * fdcnt there. So we never bother
                                         * to check value of 'cnt'.
                                         */
                                        error = pcache_insert(ps, fp,
                                            &current[count], &cnt,
                                            (ssize_t)count, which);
                                        /*
                                         * if no error, we want to do releasef
                                         * after we updated cache poll list
                                         * entry so that close() won't race
                                         * us.
                                         */
                                        if (error) {
                                                /*
                                                 * If we encountered an error,
                                                 * we have invalidated an
                                                 * entry in cached poll list
                                                 * (in pcache_delete_fd() above)
                                                 * but failed to add one here.
                                                 * This is OK b/c what's in the
                                                 * cached list is consistent
                                                 * with content of cache.
                                                 * It will not have any ill
                                                 * effect on next poll().
                                                 */
                                                releasef(tmpfd);
                                                if (newlist != NULL) {
                                                        kmem_free(newlist,
                                                            nfds *
                                                            sizeof (pollfd_t));
                                                }
                                                return (error);
                                        }
                                        /*
                                         * If we have allocated a new(temp)
                                         * cache list, we need to keep both
                                         * in sync b/c the new one can be freed
                                         * if we have an error later.
                                         */
                                        if (newlist != NULL) {
                                                newlist[count].fd =
                                                    current[count].fd;
                                                newlist[count].events =
                                                    current[count].events;
                                        }
                                        cached[count].fd = current[count].fd;
                                        cached[count].events =
                                            current[count].events;
                                        releasef(tmpfd);
                                }
                        } else {
                                current[count].revents = 0;
                        }
                        count++;
                        remain = common - count;
                }
        }
        if (mismatch != 0) {
                if (mismatch == common) {
                        pollstats.pollcachemiss.value.ui64++;
                } else {
                        pollstats.pollcachephit.value.ui64++;
                }
        }
        /*
         * take care of the non overlapping part of a list
         */
        if (nfds > old_nfds) {
                ASSERT(newlist != NULL);
                for (i = old_nfds; i < nfds; i++) {
                        /* filter out invalid events */
                        if (current[i].events & ~VALID_POLL_EVENTS) {
                                newlist[i].events = current[i].events =
                                    current[i].events & VALID_POLL_EVENTS;
                        }
                        if ((fd = current[i].fd) < 0) {
                                current[i].revents = 0;
                                continue;
                        }
                        /*
                         * add to the cached fd tbl and bitmap.
                         */
                        if ((fp = getf(fd)) == NULL) {
                                current[i].revents = POLLNVAL;
                                newlist[i].fd = -1;
                                fdcnt++;
                                continue;
                        }
                        /*
                         * Here we don't care about the
                         * fdcnt. We will examine the bitmap
                         * later and pick up the correct
                         * fdcnt there. So we never bother to
                         * check 'cnt'.
                         */
                        error = pcache_insert(ps, fp, &current[i], &cnt,
                            (ssize_t)i, which);
                        releasef(fd);
                        if (error) {
                                /*
                                 * Here we are half way through adding newly
                                 * polled fd. Undo enough to keep the cache
                                 * list consistent with the cache content.
                                 */
                                pcacheset_remove_list(ps, current, old_nfds,
                                    i, which, 0);
                                kmem_free(newlist, nfds * sizeof (pollfd_t));
                                return (error);
                        }
                }
        }
        if (old_nfds > nfds) {
                /*
                 * remove the fd's which are no longer polled.
                 */
                pcacheset_remove_list(ps, pcsp->pcs_pollfd, nfds, old_nfds,
                    which, 1);
        }
        /*
         * set difference resolved. update nfds and cachedlist
         * in pollstate struct.
         */
        if (newlist != NULL) {
                kmem_free(pcsp->pcs_pollfd, old_nfds * sizeof (pollfd_t));
                /*
                 * By now, the pollfd.revents field should
                 * all be zeroed.
                 */
                pcsp->pcs_pollfd = newlist;
                pcsp->pcs_nfds = nfds;
        }
        ASSERT(*fdcntp == 0);
        *fdcntp = fdcnt;
        /*
         * By now for every fd in pollfdp, one of the following should be
         * true. Otherwise we will miss a polled event.
         *
         * 1. the bit corresponding to the fd in bitmap is set. So fop_poll
         *    will be called on this fd in next poll.
         * 2. the fd is cached in the pcache (i.e. pd_php is set). So
         *    pollnotify will happen.
         */
        ASSERT(pollchecksanity(ps, nfds));
        /*
         * make sure cross reference between cached poll lists and cached
         * poll fds are correct.
         */
        ASSERT(pollcheckxref(ps, which));
        /*
         * ensure each polldat in pollcache reference a polled fd in
         * pollcacheset.
         */
#ifdef DEBUG
        checkpolldat(ps);
#endif
        return (0);
}

#ifdef DEBUG
static int
pollscanrevents(pollcache_t *pcp, pollfd_t *pollfdp, nfds_t nfds)
{
        int i;
        int reventcnt = 0;

        for (i = 0; i < nfds; i++) {
                if (pollfdp[i].fd < 0) {
                        ASSERT(pollfdp[i].revents == 0);
                        continue;
                }
                if (pollfdp[i].revents) {
                        reventcnt++;
                }
                if (pollfdp[i].revents && (pollfdp[i].revents != POLLNVAL)) {
                        ASSERT(BT_TEST(pcp->pc_bitmap, pollfdp[i].fd));
                }
        }
        return (reventcnt);
}
#endif  /* DEBUG */

/*
 * read the bitmap and poll on fds corresponding to the '1' bits. The ps_lock
 * is held upon entry.
 */
int
pcache_poll(pollfd_t *pollfdp, pollstate_t *ps, nfds_t nfds, int *fdcntp,
    int which)
{
        int             i;
        pollcache_t     *pcp;
        int             fd;
        int             begin, end, done;
        pollhead_t      *php;
        int             fdcnt;
        int             error = 0;
        file_t          *fp;
        polldat_t       *pdp;
        xref_t          *refp;
        int             entry;

        pcp = ps->ps_pcache;
        ASSERT(MUTEX_HELD(&ps->ps_lock));
        ASSERT(MUTEX_HELD(&pcp->pc_lock));
retry:
        done = 0;
        begin = 0;
        fdcnt = 0;
        end = pcp->pc_mapend;
        while ((fdcnt < nfds) && !done) {
                php = NULL;
                /*
                 * only poll fds which may have events
                 */
                fd = bt_getlowbit(pcp->pc_bitmap, begin, end);
                ASSERT(fd <= end);
                if (fd >= 0) {
                        ASSERT(pollcheckrevents(ps, begin, fd, which));
                        /*
                         * adjust map pointers for next round
                         */
                        if (fd == end) {
                                done = 1;
                        } else {
                                begin = fd + 1;
                        }
                        /*
                         * A bitmap caches poll state information of
                         * multiple poll lists. Call fop_poll only if
                         * the bit corresponds to an fd in this poll
                         * list.
                         */
                        pdp = pcache_lookup_fd(pcp, fd);
                        ASSERT(pdp != NULL);
                        ASSERT(pdp->pd_ref != NULL);
                        refp = &pdp->pd_ref[which];
                        if (refp->xf_refcnt == 0)
                                continue;
                        entry = refp->xf_position;
                        ASSERT((entry >= 0) && (entry < nfds));
                        ASSERT(pollfdp[entry].fd == fd);
                        /*
                         * we are in this routine implies that we have
                         * successfully polled this fd in the past.
                         * Check to see this fd is closed while we are
                         * blocked in poll. This ensures that we don't
                         * miss a close on the fd in the case this fd is
                         * reused.
                         */
                        if (pdp->pd_fp == NULL) {
                                ASSERT(pdp->pd_count > 0);
                                pollfdp[entry].revents = POLLNVAL;
                                fdcnt++;
                                if (refp->xf_refcnt > 1) {
                                        /*
                                         * this fd appeared multiple time
                                         * in the poll list. Find all of them.
                                         */
                                        for (i = entry + 1; i < nfds; i++) {
                                                if (pollfdp[i].fd == fd) {
                                                        pollfdp[i].revents =
                                                            POLLNVAL;
                                                        fdcnt++;
                                                }
                                        }
                                }
                                pcacheset_invalidate(ps, pdp);
                                continue;
                        }
                        /*
                         * We can be here polling a device that is being
                         * closed (i.e. the file pointer is set to NULL,
                         * but pollcacheclean has not happened yet).
                         */
                        if ((fp = getf(fd)) == NULL) {
                                pollfdp[entry].revents = POLLNVAL;
                                fdcnt++;
                                if (refp->xf_refcnt > 1) {
                                        /*
                                         * this fd appeared multiple time
                                         * in the poll list. Find all of them.
                                         */
                                        for (i = entry + 1; i < nfds; i++) {
                                                if (pollfdp[i].fd == fd) {
                                                        pollfdp[i].revents =
                                                            POLLNVAL;
                                                        fdcnt++;
                                                }
                                        }
                                }
                                continue;
                        }
                        ASSERT(pdp->pd_fp == fp);
                        ASSERT(infpollinfo(fd));
                        /*
                         * Since we no longer hold poll head lock across
                         * fop_poll, pollunlock logic can be simplifed.
                         */
                        ASSERT(pdp->pd_php == NULL ||
                            MUTEX_NOT_HELD(PHLOCK(pdp->pd_php)));
                        /*
                         * underlying file systems may set a "pollpending"
                         * flag when it sees the poll may block. Pollwakeup()
                         * is called by wakeup thread if pollpending is set.
                         * Pass a 0 fdcnt so that the underlying file system
                         * will set the "pollpending" flag set when there is
                         * no polled events.
                         *
                         * Use pollfdp[].events for actual polling because
                         * the pd_events is union of all cached poll events
                         * on this fd. The events parameter also affects
                         * how the polled device sets the "poll pending"
                         * flag.
                         */
                        ASSERT(curthread->t_pollcache == NULL);
                        error = fop_poll(fp->f_vnode, pollfdp[entry].events, 0,
                            &pollfdp[entry].revents, &php, NULL);
                        /*
                         * releasef after completely done with this cached
                         * poll entry. To prevent close() coming in to clear
                         * this entry.
                         */
                        if (error) {
                                releasef(fd);
                                break;
                        }
                        /*
                         * layered devices (e.g. console driver)
                         * may change the vnode and thus the pollhead
                         * pointer out from underneath us.
                         */
                        if (php != NULL && pdp->pd_php != NULL &&
                            php != pdp->pd_php) {
                                releasef(fd);
                                pollhead_delete(pdp->pd_php, pdp);
                                pdp->pd_php = php;
                                pollhead_insert(php, pdp);
                                /*
                                 * We could have missed a wakeup on the new
                                 * target device. Make sure the new target
                                 * gets polled once.
                                 */
                                BT_SET(pcp->pc_bitmap, fd);
                                goto retry;
                        }

                        if (pollfdp[entry].revents) {
                                ASSERT(refp->xf_refcnt >= 1);
                                fdcnt++;
                                if (refp->xf_refcnt > 1) {
                                        /*
                                         * this fd appeared multiple time
                                         * in the poll list. This is rare but
                                         * we have to look at all of them for
                                         * correctness.
                                         */
                                        error = plist_chkdupfd(fp, pdp, ps,
                                            pollfdp, entry, &fdcnt);
                                        if (error > 0) {
                                                releasef(fd);
                                                break;
                                        }
                                        if (error < 0) {
                                                goto retry;
                                        }
                                }
                                releasef(fd);
                        } else {
                                /*
                                 * fop_poll didn't return any revents. We can
                                 * clear the bit in bitmap only if we have the
                                 * pollhead ptr cached and no other cached
                                 * entry is polling different events on this fd.
                                 * fop_poll may have dropped the ps_lock. Make
                                 * sure pollwakeup has not happened before clear
                                 * the bit.
                                 */
                                if ((pdp->pd_php != NULL) &&
                                    (pollfdp[entry].events == pdp->pd_events) &&
                                    ((pcp->pc_flag & PC_POLLWAKE) == 0)) {
                                        BT_CLEAR(pcp->pc_bitmap, fd);
                                }
                                /*
                                 * if the fd can be cached now but not before,
                                 * do it now.
                                 */
                                if ((pdp->pd_php == NULL) && (php != NULL)) {
                                        pdp->pd_php = php;
                                        pollhead_insert(php, pdp);
                                        /*
                                         * We are inserting a polldat struct for
                                         * the first time. We may have missed a
                                         * wakeup on this device. Re-poll once.
                                         * This should be a rare event.
                                         */
                                        releasef(fd);
                                        goto retry;
                                }
                                if (refp->xf_refcnt > 1) {
                                        /*
                                         * this fd appeared multiple time
                                         * in the poll list. This is rare but
                                         * we have to look at all of them for
                                         * correctness.
                                         */
                                        error = plist_chkdupfd(fp, pdp, ps,
                                            pollfdp, entry, &fdcnt);
                                        if (error > 0) {
                                                releasef(fd);
                                                break;
                                        }
                                        if (error < 0) {
                                                goto retry;
                                        }
                                }
                                releasef(fd);
                        }
                } else {
                        done = 1;
                        ASSERT(pollcheckrevents(ps, begin, end + 1, which));
                }
        }
        if (!error) {
                ASSERT(*fdcntp + fdcnt == pollscanrevents(pcp, pollfdp, nfds));
                *fdcntp += fdcnt;
        }
        return (error);
}

/*
 * Going through the poll list without much locking. Poll all fds and
 * cache all valid fds in the pollcache.
 */
int
pcacheset_cache_list(pollstate_t *ps, pollfd_t *fds, int *fdcntp, int which)
{
        pollfd_t        *pollfdp = ps->ps_pollfd;
        pollcacheset_t  *pcacheset = ps->ps_pcacheset;
        pollfd_t        *newfdlist;
        int             i;
        int             fd;
        file_t          *fp;
        int             error = 0;

        ASSERT(MUTEX_HELD(&ps->ps_lock));
        ASSERT(which < ps->ps_nsets);
        ASSERT(pcacheset != NULL);
        ASSERT(pcacheset[which].pcs_pollfd == NULL);
        newfdlist  = kmem_alloc(ps->ps_nfds * sizeof (pollfd_t), KM_SLEEP);
        /*
         * cache the new poll list in pollcachset.
         */
        bcopy(pollfdp, newfdlist, sizeof (pollfd_t) * ps->ps_nfds);

        pcacheset[which].pcs_pollfd = newfdlist;
        pcacheset[which].pcs_nfds = ps->ps_nfds;
        pcacheset[which].pcs_usradr = (uintptr_t)fds;

        /*
         * We have saved a copy of current poll fd list in one pollcacheset.
         * The 'revents' field of the new list is not yet set to 0. Loop
         * through the new list just to do that is expensive. We do that
         * while polling the list.
         */
        for (i = 0; i < ps->ps_nfds; i++) {
                fd = pollfdp[i].fd;
                /*
                 * We also filter out the illegal poll events in the event
                 * field for the cached poll list/set.
                 */
                if (pollfdp[i].events & ~VALID_POLL_EVENTS) {
                        newfdlist[i].events = pollfdp[i].events =
                            pollfdp[i].events & VALID_POLL_EVENTS;
                }
                if (fd < 0) {
                        pollfdp[i].revents = 0;
                        continue;
                }
                if ((fp = getf(fd)) == NULL) {
                        pollfdp[i].revents = POLLNVAL;
                        /*
                         * invalidate this cache entry in the cached poll list
                         */
                        newfdlist[i].fd = -1;
                        (*fdcntp)++;
                        continue;
                }
                /*
                 * cache this fd.
                 */
                error = pcache_insert(ps, fp, &pollfdp[i], fdcntp, (ssize_t)i,
                    which);
                releasef(fd);
                if (error) {
                        /*
                         * Here we are half way through caching a new
                         * poll list. Undo every thing.
                         */
                        pcacheset_remove_list(ps, pollfdp, 0, i, which, 0);
                        kmem_free(newfdlist, ps->ps_nfds * sizeof (pollfd_t));
                        pcacheset[which].pcs_pollfd = NULL;
                        pcacheset[which].pcs_usradr = (uintptr_t)NULL;
                        break;
                }
        }
        return (error);
}

/*
 * called by pollcacheclean() to set the fp NULL. It also sets polled events
 * in pcacheset entries to a special events 'POLLCLOSED'. Do a pollwakeup to
 * wake any sleeping poller, then remove the polldat from the driver.
 * The routine is called with ps_pcachelock held.
 */
void
pcache_clean_entry(pollstate_t *ps, int fd)
{
        pollcache_t     *pcp;
        polldat_t       *pdp;
        int             i;

        ASSERT(ps != NULL);
        ASSERT(MUTEX_HELD(&ps->ps_lock));
        pcp = ps->ps_pcache;
        ASSERT(pcp);
        pdp = pcache_lookup_fd(pcp, fd);
        ASSERT(pdp != NULL);
        /*
         * the corresponding fpollinfo in fi_list has been removed by
         * a close on this fd. Reset the cached fp ptr here.
         */
        pdp->pd_fp = NULL;
        /*
         * XXX - This routine also touches data in pcacheset struct.
         *
         * set the event in cached poll lists to POLLCLOSED. This invalidate
         * the cached poll fd entry in that poll list, which will force a
         * removal of this cached entry in next poll(). The cleanup is done
         * at the removal time.
         */
        ASSERT(pdp->pd_ref != NULL);
        for (i = 0; i < ps->ps_nsets; i++) {
                xref_t          *refp;
                pollcacheset_t  *pcsp;

                refp = &pdp->pd_ref[i];
                if (refp->xf_refcnt) {
                        ASSERT(refp->xf_position >= 0);
                        pcsp = &ps->ps_pcacheset[i];
                        if (refp->xf_refcnt == 1) {
                                pcsp->pcs_pollfd[refp->xf_position].events =
                                    (short)POLLCLOSED;
                        }
                        if (refp->xf_refcnt > 1) {
                                int     j;
                                /*
                                 * mark every matching entry in pcs_pollfd
                                 */
                                for (j = refp->xf_position;
                                    j < pcsp->pcs_nfds; j++) {
                                        if (pcsp->pcs_pollfd[j].fd == fd) {
                                                pcsp->pcs_pollfd[j].events =
                                                    (short)POLLCLOSED;
                                        }
                                }
                        }
                }
        }
        if (pdp->pd_php) {
                pollwakeup(pdp->pd_php, POLLHUP);
                pollhead_delete(pdp->pd_php, pdp);
                pdp->pd_php = NULL;
        }
}

void
pcache_wake_parents(pollcache_t *pcp)
{
        pcachelink_t *pl, *pln;

        ASSERT(MUTEX_HELD(&pcp->pc_lock));

        for (pl = pcp->pc_parents; pl != NULL; pl = pln) {
                mutex_enter(&pl->pcl_lock);
                if (pl->pcl_state == PCL_VALID) {
                        ASSERT(pl->pcl_parent_pc != NULL);
                        cv_broadcast(&pl->pcl_parent_pc->pc_cv);
                }
                pln = pl->pcl_parent_next;
                mutex_exit(&pl->pcl_lock);
        }
}

/*
 * Initialize thread pollstate structure.
 * It will persist for the life of the thread, until it calls pollcleanup().
 */
pollstate_t *
pollstate_create()
{
        pollstate_t *ps = curthread->t_pollstate;

        if (ps == NULL) {
                /*
                 * This is the first time this thread has ever polled, so we
                 * have to create its pollstate structure.
                 */
                ps = kmem_zalloc(sizeof (pollstate_t), KM_SLEEP);
                ps->ps_nsets = POLLFDSETS;
                ps->ps_pcacheset = pcacheset_create(ps->ps_nsets);
                curthread->t_pollstate = ps;
        } else {
                ASSERT(ps->ps_depth == 0);
                ASSERT(ps->ps_flags == 0);
                ASSERT(ps->ps_pc_stack[0] == 0);
        }
        return (ps);
}

void
pollstate_destroy(pollstate_t *ps)
{
        if (ps->ps_pollfd != NULL) {
                kmem_free(ps->ps_pollfd, ps->ps_nfds * sizeof (pollfd_t));
                ps->ps_pollfd = NULL;
        }
        if (ps->ps_pcache != NULL) {
                pcache_destroy(ps->ps_pcache);
                ps->ps_pcache = NULL;
        }
        pcacheset_destroy(ps->ps_pcacheset, ps->ps_nsets);
        ps->ps_pcacheset = NULL;
        if (ps->ps_dpbuf != NULL) {
                kmem_free(ps->ps_dpbuf, ps->ps_dpbufsize);
                ps->ps_dpbuf = NULL;
        }
        mutex_destroy(&ps->ps_lock);
        kmem_free(ps, sizeof (pollstate_t));
}

static int
pollstate_contend(pollstate_t *ps, pollcache_t *pcp)
{
        pollstate_t *rem, *next;
        pollcache_t *desired_pc;
        int result = 0, depth_total;

        mutex_enter(&pollstate_contenders_lock);
        /*
         * There is a small chance that the pollcache of interest became
         * available while we were waiting on the contenders lock.
         */
        if (mutex_tryenter(&pcp->pc_lock) != 0) {
                goto out;
        }

        /*
         * Walk the list of contended pollstates, searching for evidence of a
         * deadlock condition.
         */
        depth_total = ps->ps_depth;
        desired_pc = pcp;
        for (rem = pollstate_contenders; rem != NULL; rem = next) {
                int i, j;
                next = rem->ps_contend_nextp;

                /* Is this pollstate holding the pollcache of interest? */
                for (i = 0; i < rem->ps_depth; i++) {
                        if (rem->ps_pc_stack[i] != desired_pc) {
                                continue;
                        }

                        /*
                         * The remote pollstate holds the pollcache lock we
                         * desire.  If it is waiting on a pollcache we hold,
                         * then we can report the obvious deadlock.
                         */
                        ASSERT(rem->ps_contend_pc != NULL);
                        for (j = 0; j < ps->ps_depth; j++) {
                                if (rem->ps_contend_pc == ps->ps_pc_stack[j]) {
                                        rem->ps_flags |= POLLSTATE_STALEMATE;
                                        result = -1;
                                        goto out;
                                }
                        }

                        /*
                         * The remote pollstate is not blocking on a pollcache
                         * which would deadlock against us.  That pollcache
                         * may, however, be held by a pollstate which would
                         * result in a deadlock.
                         *
                         * To detect such a condition, we continue walking
                         * through the list using the pollcache blocking the
                         * remote thread as our new search target.
                         *
                         * Return to the front of pollstate_contenders since it
                         * is not ordered to guarantee complete dependency
                         * traversal.  The below depth tracking places an upper
                         * bound on iterations.
                         */
                        desired_pc = rem->ps_contend_pc;
                        next = pollstate_contenders;

                        /*
                         * The recursion depth of the remote pollstate is used
                         * to calculate a final depth for the local /dev/poll
                         * recursion, since those locks will be acquired
                         * eventually.  If that value exceeds the defined
                         * limit, we can report the failure now instead of
                         * recursing to that failure depth.
                         */
                        depth_total += (rem->ps_depth - i);
                        if (depth_total >= POLLMAXDEPTH) {
                                result = -1;
                                goto out;
                        }
                }
        }

        /*
         * No deadlock partner was found.  The only course of action is to
         * record ourself as a contended pollstate and wait for the pollcache
         * mutex to become available.
         */
        ps->ps_contend_pc = pcp;
        ps->ps_contend_nextp = pollstate_contenders;
        ps->ps_contend_pnextp = &pollstate_contenders;
        if (pollstate_contenders != NULL) {
                pollstate_contenders->ps_contend_pnextp =
                    &ps->ps_contend_nextp;
        }
        pollstate_contenders = ps;

        mutex_exit(&pollstate_contenders_lock);
        mutex_enter(&pcp->pc_lock);
        mutex_enter(&pollstate_contenders_lock);

        /*
         * Our acquisition of the pollcache mutex may be due to another thread
         * giving up in the face of deadlock with us.  If that is the case,
         * we too should report the failure.
         */
        if ((ps->ps_flags & POLLSTATE_STALEMATE) != 0) {
                result = -1;
                ps->ps_flags &= ~POLLSTATE_STALEMATE;
                mutex_exit(&pcp->pc_lock);
        }

        /* Remove ourself from the contenders list. */
        if (ps->ps_contend_nextp != NULL) {
                ps->ps_contend_nextp->ps_contend_pnextp =
                    ps->ps_contend_pnextp;
        }
        *ps->ps_contend_pnextp = ps->ps_contend_nextp;
        ps->ps_contend_pc = NULL;
        ps->ps_contend_nextp = NULL;
        ps->ps_contend_pnextp = NULL;

out:
        mutex_exit(&pollstate_contenders_lock);
        return (result);
}

int
pollstate_enter(pollcache_t *pcp)
{
        pollstate_t *ps = curthread->t_pollstate;
        int i;

        if (ps == NULL) {
                /*
                 * The thread pollstate may not be initialized if fop_poll is
                 * called on a recursion-enabled /dev/poll handle from outside
                 * the poll() or /dev/poll codepaths.
                 */
                return (PSE_FAIL_POLLSTATE);
        }
        if (ps->ps_depth >= POLLMAXDEPTH) {
                return (PSE_FAIL_DEPTH);
        }
        /*
         * Check the desired pollcache against pollcaches we already have
         * locked.  Such a loop is the most simple deadlock scenario.
         */
        for (i = 0; i < ps->ps_depth; i++) {
                if (ps->ps_pc_stack[i] == pcp) {
                        return (PSE_FAIL_LOOP);
                }
        }
        ASSERT(ps->ps_pc_stack[i] == NULL);

        if (ps->ps_depth == 0) {
                /* Locking initial the pollcache requires no caution */
                mutex_enter(&pcp->pc_lock);
        } else if (mutex_tryenter(&pcp->pc_lock) == 0) {
                if (pollstate_contend(ps, pcp) != 0) {
                        /* This pollcache cannot safely be locked. */
                        return (PSE_FAIL_DEADLOCK);
                }
        }

        ps->ps_pc_stack[ps->ps_depth++] = pcp;
        return (PSE_SUCCESS);
}

void
pollstate_exit(pollcache_t *pcp)
{
        pollstate_t *ps = curthread->t_pollstate;

        VERIFY(ps != NULL);
        VERIFY(ps->ps_pc_stack[ps->ps_depth - 1] == pcp);

        mutex_exit(&pcp->pc_lock);
        ps->ps_pc_stack[--ps->ps_depth] = NULL;
        VERIFY(ps->ps_depth >= 0);
}


/*
 * We are holding the appropriate uf_lock entering this routine.
 * Bump up the ps_busy count to prevent the thread from exiting.
 */
void
pollblockexit(fpollinfo_t *fpip)
{
        for (; fpip; fpip = fpip->fp_next) {
                pollcache_t *pcp = fpip->fp_thread->t_pollstate->ps_pcache;

                mutex_enter(&pcp->pc_no_exit);
                pcp->pc_busy++;  /* prevents exit()'s */
                mutex_exit(&pcp->pc_no_exit);
        }
}

/*
 * Complete phase 2 of cached poll fd cleanup. Call pcache_clean_entry to mark
 * the pcacheset events field POLLCLOSED to force the next poll() to remove
 * this cache entry. We can't clean the polldat entry clean up here because
 * lwp block in poll() needs the info to return. Wakeup anyone blocked in
 * poll and let exiting lwp go. No lock is help upon entry. So it's OK for
 * pcache_clean_entry to call pollwakeup().
 */
void
pollcacheclean(fpollinfo_t *fip, int fd)
{
        struct fpollinfo        *fpip, *fpip2;

        fpip = fip;
        while (fpip) {
                pollstate_t *ps = fpip->fp_thread->t_pollstate;
                pollcache_t *pcp = ps->ps_pcache;

                mutex_enter(&ps->ps_lock);
                pcache_clean_entry(ps, fd);
                mutex_exit(&ps->ps_lock);
                mutex_enter(&pcp->pc_no_exit);
                pcp->pc_busy--;
                if (pcp->pc_busy == 0) {
                        /*
                         * Wakeup the thread waiting in
                         * thread_exit().
                         */
                        cv_signal(&pcp->pc_busy_cv);
                }
                mutex_exit(&pcp->pc_no_exit);

                fpip2 = fpip;
                fpip = fpip->fp_next;
                kmem_free(fpip2, sizeof (fpollinfo_t));
        }
}

/*
 * one of the cache line's counter is wrapping around. Reset all cache line
 * counters to zero except one. This is simplistic, but probably works
 * effectively.
 */
void
pcacheset_reset_count(pollstate_t *ps, int index)
{
        int     i;

        ASSERT(MUTEX_HELD(&ps->ps_lock));
        for (i = 0; i < ps->ps_nsets; i++) {
                if (ps->ps_pcacheset[i].pcs_pollfd != NULL) {
                        ps->ps_pcacheset[i].pcs_count = 0;
                }
        }
        ps->ps_pcacheset[index].pcs_count = 1;
}

/*
 * this routine implements poll cache list replacement policy.
 * It is currently choose the "least used".
 */
int
pcacheset_replace(pollstate_t *ps)
{
        int i;
        int index = 0;

        ASSERT(MUTEX_HELD(&ps->ps_lock));
        for (i = 1; i < ps->ps_nsets; i++) {
                if (ps->ps_pcacheset[index].pcs_count >
                    ps->ps_pcacheset[i].pcs_count) {
                        index = i;
                }
        }
        ps->ps_pcacheset[index].pcs_count = 0;
        return (index);
}

/*
 * this routine is called by strclose to remove remaining polldat struct on
 * the pollhead list of the device being closed. There are two reasons as why
 * the polldat structures still remain on the pollhead list:
 *
 * (1) The layered device(e.g.the console driver).
 * In this case, the existence of a polldat implies that the thread putting
 * the polldat on this list has not exited yet. Before the thread exits, it
 * will have to hold this pollhead lock to remove the polldat. So holding the
 * pollhead lock here effectively prevents the thread which put the polldat
 * on this list from exiting.
 *
 * (2) /dev/poll.
 * When a polled fd is cached in /dev/poll, its polldat will remain on the
 * pollhead list if the process has not done a POLLREMOVE before closing the
 * polled fd. We just unlink it here.
 */
void
pollhead_clean(pollhead_t *php)
{
        polldat_t       *pdp;

        /*
         * In case(1), while we must prevent the thread in question from
         * exiting, we must also obey the proper locking order, i.e.
         * (ps_lock -> phlock).
         */
        PH_ENTER(php);
        while (php->ph_list != NULL) {
                pollstate_t     *ps;
                pollcache_t     *pcp;

                pdp = php->ph_list;
                ASSERT(pdp->pd_php == php);
                if (pdp->pd_thread == NULL) {
                        /*
                         * This is case(2). Since the ph_lock is sufficient
                         * to synchronize this lwp with any other /dev/poll
                         * lwp, just unlink the polldat.
                         */
                        php->ph_list = pdp->pd_next;
                        pdp->pd_php = NULL;
                        pdp->pd_next = NULL;
                        continue;
                }
                ps = pdp->pd_thread->t_pollstate;
                ASSERT(ps != NULL);
                pcp = pdp->pd_pcache;
                ASSERT(pcp != NULL);
                mutex_enter(&pcp->pc_no_exit);
                pcp->pc_busy++;  /* prevents exit()'s */
                mutex_exit(&pcp->pc_no_exit);
                /*
                 * Now get the locks in proper order to avoid deadlock.
                 */
                PH_EXIT(php);
                mutex_enter(&ps->ps_lock);
                /*
                 * while we dropped the pollhead lock, the element could be
                 * taken off the list already.
                 */
                PH_ENTER(php);
                if (pdp->pd_php == php) {
                        ASSERT(pdp == php->ph_list);
                        php->ph_list = pdp->pd_next;
                        pdp->pd_php = NULL;
                        pdp->pd_next = NULL;
                }
                PH_EXIT(php);
                mutex_exit(&ps->ps_lock);
                mutex_enter(&pcp->pc_no_exit);
                pcp->pc_busy--;
                if (pcp->pc_busy == 0) {
                        /*
                         * Wakeup the thread waiting in
                         * thread_exit().
                         */
                        cv_signal(&pcp->pc_busy_cv);
                }
                mutex_exit(&pcp->pc_no_exit);
                PH_ENTER(php);
        }
        PH_EXIT(php);
}

/*
 * The remove_list is called to cleanup a partially cached 'current' list or
 * to remove a partial list which is no longer cached. The flag value of 1
 * indicates the second case.
 */
void
pcacheset_remove_list(pollstate_t *ps, pollfd_t *pollfdp, int start, int end,
    int cacheindex, int flag)
{
        int i;

        ASSERT(MUTEX_HELD(&ps->ps_lock));
        for (i = start; i < end; i++) {
                if ((pollfdp[i].fd >= 0) &&
                    (flag || !(pollfdp[i].revents & POLLNVAL))) {
                        if (pcache_delete_fd(ps, pollfdp[i].fd, i, cacheindex,
                            (uint_t)pollfdp[i].events)) {
                                int j;
                                int fd = pollfdp[i].fd;

                                for (j = i + 1; j < end; j++) {
                                        if (pollfdp[j].fd == fd) {
                                                pcache_update_xref(
                                                    ps->ps_pcache, fd,
                                                    (ssize_t)j, cacheindex);
                                                break;
                                        }
                                }
                                ASSERT(j <= end);
                        }
                }
        }
}

#ifdef DEBUG

#include<sys/strsubr.h>
/*
 * make sure curthread is not on anyone's pollhead list any more.
 */
static void
pollcheckphlist()
{
        int i;
        file_t *fp;
        uf_entry_t *ufp;
        uf_info_t *fip = P_FINFO(curproc);
        struct stdata *stp;
        polldat_t *pdp;

        mutex_enter(&fip->fi_lock);
        for (i = 0; i < fip->fi_nfiles; i++) {
                UF_ENTER(ufp, fip, i);
                if ((fp = ufp->uf_file) != NULL) {
                        if ((stp = fp->f_vnode->v_stream) != NULL) {
                                PH_ENTER(&stp->sd_pollist);
                                pdp = stp->sd_pollist.ph_list;
                                while (pdp) {
                                        ASSERT(pdp->pd_thread != curthread);
                                        pdp = pdp->pd_next;
                                }
                                PH_EXIT(&stp->sd_pollist);
                        }
                }
                UF_EXIT(ufp);
        }
        mutex_exit(&fip->fi_lock);
}

/*
 * for resolved set poll list, the xref info in the pcache should be
 * consistent with this poll list.
 */
static int
pollcheckxref(pollstate_t *ps, int cacheindex)
{
        pollfd_t *pollfdp = ps->ps_pcacheset[cacheindex].pcs_pollfd;
        pollcache_t *pcp = ps->ps_pcache;
        polldat_t *pdp;
        int     i;
        xref_t  *refp;

        for (i = 0; i < ps->ps_pcacheset[cacheindex].pcs_nfds; i++) {
                if (pollfdp[i].fd < 0) {
                        continue;
                }
                pdp = pcache_lookup_fd(pcp, pollfdp[i].fd);
                ASSERT(pdp != NULL);
                ASSERT(pdp->pd_ref != NULL);
                refp = &pdp->pd_ref[cacheindex];
                if (refp->xf_position >= 0) {
                        ASSERT(refp->xf_refcnt >= 1);
                        ASSERT(pollfdp[refp->xf_position].fd == pdp->pd_fd);
                        if (refp->xf_refcnt > 1) {
                                int     j;
                                int     count = 0;

                                for (j = refp->xf_position;
                                    j < ps->ps_pcacheset[cacheindex].pcs_nfds;
                                    j++) {
                                        if (pollfdp[j].fd == pdp->pd_fd) {
                                                count++;
                                        }
                                }
                                ASSERT(count == refp->xf_refcnt);
                        }
                }
        }
        return (1);
}

/*
 * For every cached pollfd, its polldat struct should be consistent with
 * what is in the pcacheset lists.
 */
static void
checkpolldat(pollstate_t *ps)
{
        pollcache_t     *pcp = ps->ps_pcache;
        polldat_t       **hashtbl;
        int             i;

        hashtbl = pcp->pc_hash;
        for (i = 0; i < pcp->pc_hashsize; i++) {
                polldat_t       *pdp;

                for (pdp = hashtbl[i]; pdp; pdp = pdp->pd_hashnext) {
                        ASSERT(pdp->pd_ref != NULL);
                        if (pdp->pd_count > 0) {
                                xref_t          *refp;
                                int             j;
                                pollcacheset_t  *pcsp;
                                pollfd_t        *pollfd;

                                for (j = 0; j < ps->ps_nsets; j++) {
                                        refp = &pdp->pd_ref[j];
                                        if (refp->xf_refcnt > 0) {
                                                pcsp = &ps->ps_pcacheset[j];
                                ASSERT(refp->xf_position < pcsp->pcs_nfds);
                                                pollfd = pcsp->pcs_pollfd;
                        ASSERT(pdp->pd_fd == pollfd[refp->xf_position].fd);
                                        }
                                }
                        }
                }
        }
}

/*
 * every wfd element on ph_list must have a corresponding fpollinfo on the
 * uf_fpollinfo list. This is a variation of infpollinfo() w/o holding locks.
 */
void
checkwfdlist(vnode_t *vp, fpollinfo_t *fpip)
{
        stdata_t *stp;
        polldat_t *pdp;
        fpollinfo_t *fpip2;

        if ((stp = vp->v_stream) == NULL) {
                return;
        }
        PH_ENTER(&stp->sd_pollist);
        for (pdp = stp->sd_pollist.ph_list; pdp; pdp = pdp->pd_next) {
                if (pdp->pd_thread != NULL &&
                    pdp->pd_thread->t_procp == curthread->t_procp) {
                        for (fpip2 = fpip; fpip2; fpip2 = fpip2->fp_next) {
                                if (pdp->pd_thread == fpip2->fp_thread) {
                                        break;
                                }
                        }
                        ASSERT(fpip2 != NULL);
                }
        }
        PH_EXIT(&stp->sd_pollist);
}

/*
 * For each cached fd whose bit is not set in bitmap, its revents field in
 * current poll list should be 0.
 */
static int
pollcheckrevents(pollstate_t *ps, int begin, int end, int cacheindex)
{
        pollcache_t     *pcp = ps->ps_pcache;
        pollfd_t        *pollfdp = ps->ps_pollfd;
        int             i;

        for (i = begin; i < end; i++) {
                polldat_t       *pdp;

                ASSERT(!BT_TEST(pcp->pc_bitmap, i));
                pdp = pcache_lookup_fd(pcp, i);
                if (pdp && pdp->pd_fp != NULL) {
                        xref_t *refp;
                        int entry;

                        ASSERT(pdp->pd_ref != NULL);
                        refp = &pdp->pd_ref[cacheindex];
                        if (refp->xf_refcnt == 0) {
                                continue;
                        }
                        entry = refp->xf_position;
                        ASSERT(entry >= 0);
                        ASSERT(pollfdp[entry].revents == 0);
                        if (refp->xf_refcnt > 1) {
                                int j;

                                for (j = entry + 1; j < ps->ps_nfds; j++) {
                                        if (pollfdp[j].fd == i) {
                                                ASSERT(pollfdp[j].revents == 0);
                                        }
                                }
                        }
                }
        }
        return (1);
}

#endif  /* DEBUG */

pollcache_t *
pcache_alloc()
{
        return (kmem_zalloc(sizeof (pollcache_t), KM_SLEEP));
}

void
pcache_create(pollcache_t *pcp, nfds_t nfds)
{
        size_t  mapsize;

        /*
         * allocate enough bits for the poll fd list
         */
        if ((mapsize = POLLMAPCHUNK) <= nfds) {
                mapsize = (nfds + POLLMAPCHUNK - 1) & ~(POLLMAPCHUNK - 1);
        }
        pcp->pc_bitmap = kmem_zalloc((mapsize / BT_NBIPUL) * sizeof (ulong_t),
            KM_SLEEP);
        pcp->pc_mapsize = mapsize;
        /*
         * The hash size is at least POLLHASHCHUNKSZ. If user polls a large
         * number of fd to start with, allocate a bigger hash table (to the
         * nearest multiple of POLLHASHCHUNKSZ) because dynamically growing a
         * hash table is expensive.
         */
        if (nfds < POLLHASHCHUNKSZ) {
                pcp->pc_hashsize = POLLHASHCHUNKSZ;
        } else {
                pcp->pc_hashsize = (nfds + POLLHASHCHUNKSZ - 1) &
                    ~(POLLHASHCHUNKSZ - 1);
        }
        pcp->pc_hash = kmem_zalloc(pcp->pc_hashsize * sizeof (polldat_t *),
            KM_SLEEP);
}

void
pcache_destroy(pollcache_t *pcp)
{
        polldat_t       **hashtbl;
        int i;

        hashtbl = pcp->pc_hash;
        for (i = 0; i < pcp->pc_hashsize; i++) {
                if (hashtbl[i] != NULL) {
                        polldat_t *pdp, *pdp2;

                        pdp = hashtbl[i];
                        while (pdp != NULL) {
                                pdp2 = pdp->pd_hashnext;
                                if (pdp->pd_ref != NULL) {
                                        kmem_free(pdp->pd_ref, sizeof (xref_t) *
                                            pdp->pd_nsets);
                                }
                                kmem_free(pdp, sizeof (polldat_t));
                                pdp = pdp2;
                                pcp->pc_fdcount--;
                        }
                }
        }
        ASSERT(pcp->pc_fdcount == 0);
        kmem_free(pcp->pc_hash, sizeof (polldat_t *) * pcp->pc_hashsize);
        kmem_free(pcp->pc_bitmap,
            sizeof (ulong_t) * (pcp->pc_mapsize/BT_NBIPUL));
        mutex_destroy(&pcp->pc_no_exit);
        mutex_destroy(&pcp->pc_lock);
        cv_destroy(&pcp->pc_cv);
        cv_destroy(&pcp->pc_busy_cv);
        kmem_free(pcp, sizeof (pollcache_t));
}

pollcacheset_t *
pcacheset_create(int nsets)
{
        return (kmem_zalloc(sizeof (pollcacheset_t) * nsets, KM_SLEEP));
}

void
pcacheset_destroy(pollcacheset_t *pcsp, int nsets)
{
        int i;

        for (i = 0; i < nsets; i++) {
                if (pcsp[i].pcs_pollfd != NULL) {
                        kmem_free(pcsp[i].pcs_pollfd, pcsp[i].pcs_nfds *
                            sizeof (pollfd_t));
                }
        }
        kmem_free(pcsp, sizeof (pollcacheset_t) * nsets);
}

/*
 * Check each duplicated poll fd in the poll list. It may be necessary to
 * fop_poll the same fd again using different poll events. getf() has been
 * done by caller. This routine returns 0 if it can sucessfully process the
 * entire poll fd list. It returns -1 if underlying vnode has changed during
 * a fop_poll, in which case the caller has to repoll. It returns a positive
 * value if fop_poll failed.
 */
static int
plist_chkdupfd(file_t *fp, polldat_t *pdp, pollstate_t *psp, pollfd_t *pollfdp,
    int entry, int *fdcntp)
{
        int     i;
        int     fd;
        nfds_t  nfds = psp->ps_nfds;

        fd = pollfdp[entry].fd;
        for (i = entry + 1; i < nfds; i++) {
                if (pollfdp[i].fd == fd) {
                        if (pollfdp[i].events == pollfdp[entry].events) {
                                if ((pollfdp[i].revents =
                                    pollfdp[entry].revents) != 0) {
                                        (*fdcntp)++;
                                }
                        } else {

                                int     error;
                                pollhead_t *php;
                                pollcache_t *pcp = psp->ps_pcache;

                                /*
                                 * the events are different. fop_poll on this
                                 * fd so that we don't miss any revents.
                                 */
                                php = NULL;
                                ASSERT(curthread->t_pollcache == NULL);
                                error = fop_poll(fp->f_vnode,
                                    pollfdp[i].events, 0,
                                    &pollfdp[i].revents, &php, NULL);
                                if (error) {
                                        return (error);
                                }
                                /*
                                 * layered devices(e.g. console driver)
                                 * may change the vnode and thus the pollhead
                                 * pointer out from underneath us.
                                 */
                                if (php != NULL && pdp->pd_php != NULL &&
                                    php != pdp->pd_php) {
                                        pollhead_delete(pdp->pd_php, pdp);
                                        pdp->pd_php = php;
                                        pollhead_insert(php, pdp);
                                        /*
                                         * We could have missed a wakeup on the
                                         * new target device. Make sure the new
                                         * target gets polled once.
                                         */
                                        BT_SET(pcp->pc_bitmap, fd);
                                        return (-1);
                                }
                                if (pollfdp[i].revents) {
                                        (*fdcntp)++;
                                }
                        }
                }
        }
        return (0);
}