8322 nl: misleading-indentation

[unleashed/tickless.git] / usr / src / cmd / fm / fmd / common / fmd_module.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 (c) 2004, 2010, Oracle and/or its affiliates. All rights reserved.
 */

#include <signal.h>
#include <dirent.h>
#include <limits.h>
#include <alloca.h>
#include <unistd.h>
#include <stdio.h>

#include <fmd_string.h>
#include <fmd_alloc.h>
#include <fmd_module.h>
#include <fmd_error.h>
#include <fmd_conf.h>
#include <fmd_dispq.h>
#include <fmd_eventq.h>
#include <fmd_timerq.h>
#include <fmd_subr.h>
#include <fmd_thread.h>
#include <fmd_ustat.h>
#include <fmd_case.h>
#include <fmd_protocol.h>
#include <fmd_buf.h>
#include <fmd_ckpt.h>
#include <fmd_xprt.h>
#include <fmd_topo.h>

#include <fmd.h>

/*
 * Template for per-module statistics installed by fmd on behalf of each active
 * module.  These are used to initialize the per-module mp->mod_stats below.
 * NOTE: FMD_TYPE_STRING statistics should not be used here.  If they are
 * required in the future, the FMD_ADM_MODDSTAT service routine must change.
 */
static const fmd_modstat_t _fmd_modstat_tmpl = {
{
{ "fmd.dispatched", FMD_TYPE_UINT64, "total events dispatched to module" },
{ "fmd.dequeued", FMD_TYPE_UINT64, "total events dequeued by module" },
{ "fmd.prdequeued", FMD_TYPE_UINT64, "protocol events dequeued by module" },
{ "fmd.dropped", FMD_TYPE_UINT64, "total events dropped on queue overflow" },
{ "fmd.wcnt", FMD_TYPE_UINT32, "count of events waiting on queue" },
{ "fmd.wtime", FMD_TYPE_TIME, "total wait time on queue" },
{ "fmd.wlentime", FMD_TYPE_TIME, "total wait length * time product" },
{ "fmd.wlastupdate", FMD_TYPE_TIME, "hrtime of last wait queue update" },
{ "fmd.dtime", FMD_TYPE_TIME, "total processing time after dequeue" },
{ "fmd.dlastupdate", FMD_TYPE_TIME, "hrtime of last event dequeue completion" },
},
{ "fmd.loadtime", FMD_TYPE_TIME, "hrtime at which module was loaded" },
{ "fmd.snaptime", FMD_TYPE_TIME, "hrtime of last statistics snapshot" },
{ "fmd.accepted", FMD_TYPE_UINT64, "total events accepted by module" },
{ "fmd.debugdrop", FMD_TYPE_UINT64, "dropped debug messages" },
{ "fmd.memtotal", FMD_TYPE_SIZE, "total memory allocated by module" },
{ "fmd.memlimit", FMD_TYPE_SIZE, "limit on total memory allocated" },
{ "fmd.buftotal", FMD_TYPE_SIZE, "total buffer space used by module" },
{ "fmd.buflimit", FMD_TYPE_SIZE, "limit on total buffer space" },
{ "fmd.thrtotal", FMD_TYPE_UINT32, "total number of auxiliary threads" },
{ "fmd.thrlimit", FMD_TYPE_UINT32, "limit on number of auxiliary threads" },
{ "fmd.doorthrtotal", FMD_TYPE_UINT32, "total number of door server threads" },
{ "fmd.doorthrlimit", FMD_TYPE_UINT32, "limit on door server threads" },
{ "fmd.caseopen", FMD_TYPE_UINT64, "cases currently open by module" },
{ "fmd.casesolved", FMD_TYPE_UINT64, "total cases solved by module" },
{ "fmd.caseclosed", FMD_TYPE_UINT64, "total cases closed by module" },
{ "fmd.ckptsave", FMD_TYPE_BOOL, "save checkpoints for module" },
{ "fmd.ckptrestore", FMD_TYPE_BOOL, "restore checkpoints for module" },
{ "fmd.ckptzero", FMD_TYPE_BOOL, "zeroed checkpoint at startup" },
{ "fmd.ckptcnt", FMD_TYPE_UINT64, "number of checkpoints taken" },
{ "fmd.ckpttime", FMD_TYPE_TIME, "total checkpoint time" },
{ "fmd.xprtopen", FMD_TYPE_UINT32, "total number of open transports" },
{ "fmd.xprtlimit", FMD_TYPE_UINT32, "limit on number of open transports" },
{ "fmd.xprtqlimit", FMD_TYPE_UINT32, "limit on transport event queue length" },
};

static void
fmd_module_start(void *arg)
{
        fmd_module_t *mp = arg;
        fmd_event_t *ep;
        fmd_xprt_t *xp;

        (void) pthread_mutex_lock(&mp->mod_lock);

        if (mp->mod_ops->mop_init(mp) != 0 || mp->mod_error != 0) {
                if (mp->mod_error == 0)
                        mp->mod_error = errno ? errno : EFMD_MOD_INIT;
                goto out;
        }

        if (fmd.d_mod_event != NULL)
                fmd_eventq_insert_at_head(mp->mod_queue, fmd.d_mod_event);

        ASSERT(MUTEX_HELD(&mp->mod_lock));
        mp->mod_flags |= FMD_MOD_INIT;

        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);

        /*
         * If the module opened any transports while executing _fmd_init(),
         * they are suspended. Now that _fmd_init() is done, wake them up.
         */
        for (xp = fmd_list_next(&mp->mod_transports);
            xp != NULL; xp = fmd_list_next(xp))
                fmd_xprt_xresume(xp, FMD_XPRT_ISUSPENDED);

        /*
         * Wait for events to arrive by checking mod_error and then sleeping in
         * fmd_eventq_delete().  If a NULL event is returned, the eventq has
         * been aborted and we continue on to call fini and exit the thread.
         */
        while ((ep = fmd_eventq_delete(mp->mod_queue)) != NULL) {
                /*
                 * If the module has failed, discard the event without ever
                 * passing it to the module and go back to sleep.
                 */
                if (mp->mod_error != 0) {
                        fmd_eventq_done(mp->mod_queue);
                        fmd_event_rele(ep);
                        continue;
                }

                mp->mod_ops->mop_dispatch(mp, ep);
                fmd_eventq_done(mp->mod_queue);

                /*
                 * Once mop_dispatch() is complete, grab the lock and perform
                 * any event-specific post-processing.  Finally, if necessary,
                 * checkpoint the state of the module after this event.
                 */
                fmd_module_lock(mp);

                if (FMD_EVENT_TYPE(ep) == FMD_EVT_CLOSE)
                        fmd_case_delete(FMD_EVENT_DATA(ep));

                fmd_ckpt_save(mp);
                fmd_module_unlock(mp);
                fmd_event_rele(ep);
        }

        if (mp->mod_ops->mop_fini(mp) != 0 && mp->mod_error == 0)
                mp->mod_error = errno ? errno : EFMD_MOD_FINI;

        (void) pthread_mutex_lock(&mp->mod_lock);
        mp->mod_flags |= FMD_MOD_FINI;

out:
        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);
}

fmd_module_t *
fmd_module_create(const char *path, const fmd_modops_t *ops)
{
        fmd_module_t *mp = fmd_zalloc(sizeof (fmd_module_t), FMD_SLEEP);

        char buf[PATH_MAX], *p;
        const char *dir;
        uint32_t limit;
        int err;

        (void) strlcpy(buf, fmd_strbasename(path), sizeof (buf));
        if ((p = strrchr(buf, '.')) != NULL && strcmp(p, ".so") == 0)
                *p = '\0'; /* strip trailing .so from any module name */

        (void) pthread_mutex_init(&mp->mod_lock, NULL);
        (void) pthread_cond_init(&mp->mod_cv, NULL);
        (void) pthread_mutex_init(&mp->mod_stats_lock, NULL);

        mp->mod_name = fmd_strdup(buf, FMD_SLEEP);
        mp->mod_path = fmd_strdup(path, FMD_SLEEP);
        mp->mod_ops = ops;
        mp->mod_ustat = fmd_ustat_create();

        (void) fmd_conf_getprop(fmd.d_conf, "ckpt.dir", &dir);
        (void) snprintf(buf, sizeof (buf),
            "%s/%s/%s", fmd.d_rootdir, dir, mp->mod_name);

        mp->mod_ckpt = fmd_strdup(buf, FMD_SLEEP);

        (void) fmd_conf_getprop(fmd.d_conf, "client.tmrlim", &limit);
        mp->mod_timerids = fmd_idspace_create(mp->mod_name, 1, limit + 1);
        mp->mod_threads = fmd_idspace_create(mp->mod_name, 0, INT_MAX);

        fmd_buf_hash_create(&mp->mod_bufs);
        fmd_serd_hash_create(&mp->mod_serds);

        mp->mod_topo_current = fmd_topo_hold();

        (void) pthread_mutex_lock(&fmd.d_mod_lock);
        fmd_list_append(&fmd.d_mod_list, mp);
        (void) pthread_mutex_unlock(&fmd.d_mod_lock);

        /*
         * Initialize the module statistics that are kept on its behalf by fmd.
         * These are set up using a template defined at the top of this file.
         */
        if ((mp->mod_stats = (fmd_modstat_t *)fmd_ustat_insert(mp->mod_ustat,
            FMD_USTAT_ALLOC, sizeof (_fmd_modstat_tmpl) / sizeof (fmd_stat_t),
            (fmd_stat_t *)&_fmd_modstat_tmpl, NULL)) == NULL) {
                fmd_error(EFMD_MOD_INIT, "failed to initialize per-mod stats");
                fmd_module_destroy(mp);
                return (NULL);
        }

        if (nv_alloc_init(&mp->mod_nva_sleep,
            &fmd_module_nva_ops_sleep, mp) != 0 ||
            nv_alloc_init(&mp->mod_nva_nosleep,
            &fmd_module_nva_ops_nosleep, mp) != 0) {
                fmd_error(EFMD_MOD_INIT, "failed to initialize nvlist "
                    "allocation routines");
                fmd_module_destroy(mp);
                return (NULL);
        }

        (void) fmd_conf_getprop(fmd.d_conf, "client.evqlim", &limit);

        mp->mod_queue = fmd_eventq_create(mp,
            &mp->mod_stats->ms_evqstat, &mp->mod_stats_lock, limit);

        (void) fmd_conf_getprop(fmd.d_conf, "client.memlim",
            &mp->mod_stats->ms_memlimit.fmds_value.ui64);

        (void) fmd_conf_getprop(fmd.d_conf, "client.buflim",
            &mp->mod_stats->ms_buflimit.fmds_value.ui64);

        (void) fmd_conf_getprop(fmd.d_conf, "client.thrlim",
            &mp->mod_stats->ms_thrlimit.fmds_value.ui32);

        (void) fmd_conf_getprop(fmd.d_conf, "client.doorthrlim",
            &mp->mod_stats->ms_doorthrlimit.fmds_value.ui32);

        (void) fmd_conf_getprop(fmd.d_conf, "client.xprtlim",
            &mp->mod_stats->ms_xprtlimit.fmds_value.ui32);

        (void) fmd_conf_getprop(fmd.d_conf, "client.xprtqlim",
            &mp->mod_stats->ms_xprtqlimit.fmds_value.ui32);

        (void) fmd_conf_getprop(fmd.d_conf, "ckpt.save",
            &mp->mod_stats->ms_ckpt_save.fmds_value.bool);

        (void) fmd_conf_getprop(fmd.d_conf, "ckpt.restore",
            &mp->mod_stats->ms_ckpt_restore.fmds_value.bool);

        (void) fmd_conf_getprop(fmd.d_conf, "ckpt.zero",
            &mp->mod_stats->ms_ckpt_zeroed.fmds_value.bool);

        if (mp->mod_stats->ms_ckpt_zeroed.fmds_value.bool)
                fmd_ckpt_delete(mp); /* blow away any pre-existing checkpoint */

        /*
         * Place a hold on the module and grab the module lock before creating
         * the module's thread to ensure that it cannot destroy the module and
         * that it cannot call ops->mop_init() before we're done setting up.
         * NOTE: from now on, we must use fmd_module_rele() for error paths.
         */
        fmd_module_hold(mp);
        (void) pthread_mutex_lock(&mp->mod_lock);
        mp->mod_stats->ms_loadtime.fmds_value.ui64 = gethrtime();
        mp->mod_thread = fmd_thread_create(mp, fmd_module_start, mp);

        if (mp->mod_thread == NULL) {
                fmd_error(EFMD_MOD_THR, "failed to create thread for %s", path);
                (void) pthread_mutex_unlock(&mp->mod_lock);
                fmd_module_rele(mp);
                return (NULL);
        }

        /*
         * At this point our module structure is nearly finished and its thread
         * is starting execution in fmd_module_start() above, which will begin
         * by blocking for mod_lock.  We now drop mod_lock and wait for either
         * FMD_MOD_INIT or mod_error to be set before proceeding.
         */
        while (!(mp->mod_flags & FMD_MOD_INIT) && mp->mod_error == 0)
                (void) pthread_cond_wait(&mp->mod_cv, &mp->mod_lock);

        /*
         * If the module has failed to initialize, copy its errno to the errno
         * of the caller, wait for it to unload, and then destroy it.
         */
        if (!(mp->mod_flags & FMD_MOD_INIT)) {
                err = mp->mod_error;
                (void) pthread_mutex_unlock(&mp->mod_lock);

                if (err == EFMD_CKPT_INVAL)
                        fmd_ckpt_rename(mp); /* move aside bad checkpoint */

                /*
                 * If we're in the background, keep quiet about failure to
                 * load because a handle wasn't registered: this is a module's
                 * way of telling us it didn't want to be loaded for some
                 * reason related to system configuration.  If we're in the
                 * foreground we log this too in order to inform developers.
                 */
                if (fmd.d_fg || err != EFMD_HDL_INIT) {
                        fmd_error(EFMD_MOD_INIT, "failed to load %s: %s\n",
                            path, fmd_strerror(err));
                }

                fmd_module_unload(mp);
                fmd_module_rele(mp);

                (void) fmd_set_errno(err);
                return (NULL);
        }

        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);

        fmd_dprintf(FMD_DBG_MOD, "loaded module %s\n", mp->mod_name);
        return (mp);
}

static void
fmd_module_untimeout(fmd_idspace_t *ids, id_t id, fmd_module_t *mp)
{
        void *arg = fmd_timerq_remove(fmd.d_timers, ids, id);

        /*
         * The root module calls fmd_timerq_install() directly and must take
         * responsibility for any cleanup of timer arguments that is required.
         * All other modules use fmd_modtimer_t's as the arg data; free them.
         */
        if (arg != NULL && mp != fmd.d_rmod)
                fmd_free(arg, sizeof (fmd_modtimer_t));
}

void
fmd_module_unload(fmd_module_t *mp)
{
        fmd_modtopo_t *mtp;

        (void) pthread_mutex_lock(&mp->mod_lock);

        if (mp->mod_flags & FMD_MOD_QUIT) {
                (void) pthread_mutex_unlock(&mp->mod_lock);
                return; /* module is already unloading */
        }

        ASSERT(mp->mod_thread != NULL);
        mp->mod_flags |= FMD_MOD_QUIT;

        if (mp->mod_queue != NULL)
                fmd_eventq_abort(mp->mod_queue);

        /*
         * Wait for the module's thread to stop processing events and call
         * _fmd_fini() and exit.  We do this by waiting for FMD_MOD_FINI to be
         * set if INIT was set, and then attempting to join with the thread.
         */
        while ((mp->mod_flags & (FMD_MOD_INIT | FMD_MOD_FINI)) == FMD_MOD_INIT)
                (void) pthread_cond_wait(&mp->mod_cv, &mp->mod_lock);

        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);

        fmd_thread_destroy(mp->mod_thread, FMD_THREAD_JOIN);
        mp->mod_thread = NULL;

        /*
         * Once the module is no longer active, clean up any data structures
         * that are only required when the module is loaded.
         */
        fmd_module_lock(mp);

        if (mp->mod_timerids != NULL) {
                fmd_idspace_apply(mp->mod_timerids,
                    (void (*)())fmd_module_untimeout, mp);

                fmd_idspace_destroy(mp->mod_timerids);
                mp->mod_timerids = NULL;
        }

        if (mp->mod_threads != NULL) {
                fmd_idspace_destroy(mp->mod_threads);
                mp->mod_threads = NULL;
        }

        (void) fmd_buf_hash_destroy(&mp->mod_bufs);
        fmd_serd_hash_destroy(&mp->mod_serds);

        while ((mtp = fmd_list_next(&mp->mod_topolist)) != NULL) {
                fmd_list_delete(&mp->mod_topolist, mtp);
                fmd_topo_rele(mtp->mt_topo);
                fmd_free(mtp, sizeof (fmd_modtopo_t));
        }

        fmd_module_unlock(mp);
        fmd_dprintf(FMD_DBG_MOD, "unloaded module %s\n", mp->mod_name);
}

void
fmd_module_destroy(fmd_module_t *mp)
{
        fmd_conf_formal_t *cfp = mp->mod_argv;
        int i;

        ASSERT(MUTEX_HELD(&mp->mod_lock));

        if (mp->mod_thread != NULL) {
                (void) pthread_mutex_unlock(&mp->mod_lock);
                fmd_module_unload(mp);
                (void) pthread_mutex_lock(&mp->mod_lock);
        }

        ASSERT(mp->mod_thread == NULL);
        ASSERT(mp->mod_refs == 0);

        /*
         * Once the module's thread is dead, we can safely remove the module
         * from global visibility and by removing it from d_mod_list.  Any
         * modhash pointers are already gone by virtue of mod_refs being zero.
         */
        (void) pthread_mutex_lock(&fmd.d_mod_lock);
        fmd_list_delete(&fmd.d_mod_list, mp);
        (void) pthread_mutex_unlock(&fmd.d_mod_lock);

        if (mp->mod_topo_current != NULL)
                fmd_topo_rele(mp->mod_topo_current);

        if (mp->mod_nva_sleep.nva_ops != NULL)
                nv_alloc_fini(&mp->mod_nva_sleep);
        if (mp->mod_nva_nosleep.nva_ops != NULL)
                nv_alloc_fini(&mp->mod_nva_nosleep);

        /*
         * Once the module is no longer processing events and no longer visible
         * through any program data structures, we can free all of its content.
         */
        if (mp->mod_queue != NULL) {
                fmd_eventq_destroy(mp->mod_queue);
                mp->mod_queue = NULL;
        }

        if (mp->mod_ustat != NULL) {
                (void) pthread_mutex_lock(&mp->mod_stats_lock);
                fmd_ustat_destroy(mp->mod_ustat);
                mp->mod_ustat = NULL;
                mp->mod_stats = NULL;
                (void) pthread_mutex_unlock(&mp->mod_stats_lock);
        }

        for (i = 0; i < mp->mod_dictc; i++)
                fm_dc_closedict(mp->mod_dictv[i]);

        fmd_free(mp->mod_dictv, sizeof (struct fm_dc_handle *) * mp->mod_dictc);

        if (mp->mod_conf != NULL)
                fmd_conf_close(mp->mod_conf);

        for (i = 0; i < mp->mod_argc; i++, cfp++) {
                fmd_strfree((char *)cfp->cf_name);
                fmd_strfree((char *)cfp->cf_default);
        }

        fmd_free(mp->mod_argv, sizeof (fmd_conf_formal_t) * mp->mod_argc);

        fmd_strfree(mp->mod_name);
        fmd_strfree(mp->mod_path);
        fmd_strfree(mp->mod_ckpt);
        nvlist_free(mp->mod_fmri);
        fmd_strfree(mp->mod_vers);

        fmd_free(mp, sizeof (fmd_module_t));
}

/*
 * fmd_module_error() is called after the stack is unwound from a call to
 * fmd_module_abort() to indicate that the module has failed.  The mod_error
 * field is used to hold the error code of the first fatal error to the module.
 * An EFMD_MOD_FAIL event is then created and sent to fmd-self-diagnosis.
 */
static void
fmd_module_error(fmd_module_t *mp, int err)
{
        fmd_event_t *e;
        nvlist_t *nvl;
        char *class;

        ASSERT(MUTEX_HELD(&mp->mod_lock));
        ASSERT(err != 0);

        TRACE((FMD_DBG_MOD, "module aborted: err=%d", err));

        if (mp->mod_error == 0)
                mp->mod_error = err;

        if (mp == fmd.d_self)
                return; /* do not post event if fmd.d_self itself fails */

        /*
         * Send an error indicating the module has now failed to fmd.d_self.
         * Since the error causing the failure has already been logged by
         * fmd_api_xerror(), we do not need to bother logging this event.
         * It only exists for the purpose of notifying fmd.d_self that it can
         * close the case associated with this module because mod_error is set.
         */
        nvl = fmd_protocol_moderror(mp, EFMD_MOD_FAIL, fmd_strerror(err));
        (void) nvlist_lookup_string(nvl, FM_CLASS, &class);
        e = fmd_event_create(FMD_EVT_PROTOCOL, FMD_HRT_NOW, nvl, class);
        fmd_dispq_dispatch(fmd.d_disp, e, class);
}

void
fmd_module_dispatch(fmd_module_t *mp, fmd_event_t *e)
{
        const fmd_hdl_ops_t *ops = mp->mod_info->fmdi_ops;
        fmd_event_impl_t *ep = (fmd_event_impl_t *)e;
        fmd_hdl_t *hdl = (fmd_hdl_t *)mp;
        fmd_modtimer_t *t;
        fmd_topo_t *old_topo;
        volatile int err;

        /*
         * Before calling the appropriate module callback, enter the module as
         * if by fmd_module_enter() and establish mod_jmpbuf for any aborts.
         */
        (void) pthread_mutex_lock(&mp->mod_lock);

        ASSERT(!(mp->mod_flags & FMD_MOD_BUSY));
        mp->mod_flags |= FMD_MOD_BUSY;

        if ((err = setjmp(mp->mod_jmpbuf)) != 0) {
                (void) pthread_mutex_lock(&mp->mod_lock);
                fmd_module_error(mp, err);
        }

        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);

        /*
         * If it's the first time through fmd_module_dispatch(), call the
         * appropriate module callback based on the event type.  If the call
         * triggers an fmd_module_abort(), we'll return to setjmp() above with
         * err set to a non-zero value and then bypass this before exiting.
         */
        if (err == 0) {
                switch (ep->ev_type) {
                case FMD_EVT_PROTOCOL:
                        ops->fmdo_recv(hdl, e, ep->ev_nvl, ep->ev_data);
                        break;
                case FMD_EVT_TIMEOUT:
                        t = ep->ev_data;
                        ASSERT(t->mt_mod == mp);
                        ops->fmdo_timeout(hdl, t->mt_id, t->mt_arg);
                        break;
                case FMD_EVT_CLOSE:
                        ops->fmdo_close(hdl, ep->ev_data);
                        break;
                case FMD_EVT_STATS:
                        ops->fmdo_stats(hdl);
                        fmd_modstat_publish(mp);
                        break;
                case FMD_EVT_GC:
                        ops->fmdo_gc(hdl);
                        break;
                case FMD_EVT_PUBLISH:
                        fmd_case_publish(ep->ev_data, FMD_CASE_CURRENT);
                        break;
                case FMD_EVT_TOPO:
                        /*
                         * Save the pointer to the old topology and update
                         * the pointer with the updated topology.
                         * With this approach, other threads that reference the
                         * topology either
                         *  - finishes with old topology since
                         *      it is released after updating
                         *      mod_topo_current.
                         *  - or is blocked while mod_topo_current is updated.
                         */
                        old_topo = mp->mod_topo_current;
                        fmd_module_lock(mp);
                        mp->mod_topo_current = (fmd_topo_t *)ep->ev_data;
                        fmd_topo_addref(mp->mod_topo_current);
                        fmd_module_unlock(mp);
                        fmd_topo_rele(old_topo);
                        ops->fmdo_topo(hdl, mp->mod_topo_current->ft_hdl);
                        break;
                }
        }

        fmd_module_exit(mp);
}

int
fmd_module_transport(fmd_module_t *mp, fmd_xprt_t *xp, fmd_event_t *e)
{
        fmd_event_impl_t *ep = (fmd_event_impl_t *)e;
        fmd_hdl_t *hdl = (fmd_hdl_t *)mp;

        ASSERT(ep->ev_type == FMD_EVT_PROTOCOL);
        return (mp->mod_info->fmdi_ops->fmdo_send(hdl, xp, e, ep->ev_nvl));
}

void
fmd_module_timeout(fmd_modtimer_t *t, id_t id, hrtime_t hrt)
{
        fmd_event_t *e;

        t->mt_id = id; /* save id in case we need to delete from eventq */
        e = fmd_event_create(FMD_EVT_TIMEOUT, hrt, NULL, t);
        fmd_eventq_insert_at_time(t->mt_mod->mod_queue, e);
}

/*
 * Garbage collection is initiated by a timer callback once per day or at the
 * request of fmadm.  Purge old SERD entries and send the module a GC event.
 */
void
fmd_module_gc(fmd_module_t *mp)
{
        fmd_hdl_info_t *info;
        fmd_event_t *e;

        if (mp->mod_error != 0)
                return; /* do not do anything if the module has failed */

        fmd_module_lock(mp);

        if ((info = mp->mod_info) != NULL) {
                fmd_serd_hash_apply(&mp->mod_serds,
                    (fmd_serd_eng_f *)fmd_serd_eng_gc, NULL);
        }

        fmd_module_unlock(mp);

        if (info != NULL) {
                e = fmd_event_create(FMD_EVT_GC, FMD_HRT_NOW, NULL, NULL);
                fmd_eventq_insert_at_head(mp->mod_queue, e);
        }
}

void
fmd_module_trygc(fmd_module_t *mp)
{
        if (fmd_module_trylock(mp)) {
                fmd_serd_hash_apply(&mp->mod_serds,
                    (fmd_serd_eng_f *)fmd_serd_eng_gc, NULL);
                fmd_module_unlock(mp);
        }
}

int
fmd_module_contains(fmd_module_t *mp, fmd_event_t *ep)
{
        fmd_case_t *cp;
        int rv = 0;

        fmd_module_lock(mp);

        for (cp = fmd_list_next(&mp->mod_cases);
            cp != NULL; cp = fmd_list_next(cp)) {
                if ((rv = fmd_case_contains(cp, ep)) != 0)
                        break;
        }

        if (rv == 0)
                rv = fmd_serd_hash_contains(&mp->mod_serds, ep);

        fmd_module_unlock(mp);
        return (rv);
}

void
fmd_module_setdirty(fmd_module_t *mp)
{
        (void) pthread_mutex_lock(&mp->mod_lock);
        mp->mod_flags |= FMD_MOD_MDIRTY;
        (void) pthread_mutex_unlock(&mp->mod_lock);
}

void
fmd_module_setcdirty(fmd_module_t *mp)
{
        (void) pthread_mutex_lock(&mp->mod_lock);
        mp->mod_flags |= FMD_MOD_CDIRTY;
        (void) pthread_mutex_unlock(&mp->mod_lock);
}

void
fmd_module_clrdirty(fmd_module_t *mp)
{
        fmd_case_t *cp;

        fmd_module_lock(mp);

        if (mp->mod_flags & FMD_MOD_CDIRTY) {
                for (cp = fmd_list_next(&mp->mod_cases);
                    cp != NULL; cp = fmd_list_next(cp))
                        fmd_case_clrdirty(cp);
        }

        if (mp->mod_flags & FMD_MOD_MDIRTY) {
                fmd_serd_hash_apply(&mp->mod_serds,
                    (fmd_serd_eng_f *)fmd_serd_eng_clrdirty, NULL);
                fmd_buf_hash_commit(&mp->mod_bufs);
        }

        (void) pthread_mutex_lock(&mp->mod_lock);
        mp->mod_flags &= ~(FMD_MOD_MDIRTY | FMD_MOD_CDIRTY);
        (void) pthread_mutex_unlock(&mp->mod_lock);

        fmd_module_unlock(mp);
}

void
fmd_module_commit(fmd_module_t *mp)
{
        fmd_case_t *cp;

        ASSERT(fmd_module_locked(mp));

        if (mp->mod_flags & FMD_MOD_CDIRTY) {
                for (cp = fmd_list_next(&mp->mod_cases);
                    cp != NULL; cp = fmd_list_next(cp))
                        fmd_case_commit(cp);
        }

        if (mp->mod_flags & FMD_MOD_MDIRTY) {
                fmd_serd_hash_apply(&mp->mod_serds,
                    (fmd_serd_eng_f *)fmd_serd_eng_commit, NULL);
                fmd_buf_hash_commit(&mp->mod_bufs);
        }

        (void) pthread_mutex_lock(&mp->mod_lock);
        mp->mod_flags &= ~(FMD_MOD_MDIRTY | FMD_MOD_CDIRTY);
        (void) pthread_mutex_unlock(&mp->mod_lock);

        mp->mod_gen++;
}

void
fmd_module_lock(fmd_module_t *mp)
{
        pthread_t self = pthread_self();

        (void) pthread_mutex_lock(&mp->mod_lock);

        while (mp->mod_flags & FMD_MOD_LOCK) {
                if (mp->mod_owner != self)
                        (void) pthread_cond_wait(&mp->mod_cv, &mp->mod_lock);
                else
                        fmd_panic("recursive module lock of %p\n", (void *)mp);
        }

        mp->mod_owner = self;
        mp->mod_flags |= FMD_MOD_LOCK;

        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);
}

void
fmd_module_unlock(fmd_module_t *mp)
{
        (void) pthread_mutex_lock(&mp->mod_lock);

        ASSERT(mp->mod_owner == pthread_self());
        ASSERT(mp->mod_flags & FMD_MOD_LOCK);

        mp->mod_owner = 0;
        mp->mod_flags &= ~FMD_MOD_LOCK;

        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);
}

int
fmd_module_trylock(fmd_module_t *mp)
{
        (void) pthread_mutex_lock(&mp->mod_lock);

        if (mp->mod_flags & FMD_MOD_LOCK) {
                (void) pthread_mutex_unlock(&mp->mod_lock);
                return (0);
        }

        mp->mod_owner = pthread_self();
        mp->mod_flags |= FMD_MOD_LOCK;

        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);

        return (1);
}

int
fmd_module_locked(fmd_module_t *mp)
{
        return ((mp->mod_flags & FMD_MOD_LOCK) &&
            mp->mod_owner == pthread_self());
}

int
fmd_module_enter(fmd_module_t *mp, void (*func)(fmd_hdl_t *))
{
        volatile int err;

        (void) pthread_mutex_lock(&mp->mod_lock);

        ASSERT(!(mp->mod_flags & FMD_MOD_BUSY));
        mp->mod_flags |= FMD_MOD_BUSY;

        if ((err = setjmp(mp->mod_jmpbuf)) != 0) {
                (void) pthread_mutex_lock(&mp->mod_lock);
                fmd_module_error(mp, err);
        }

        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);

        /*
         * If it's the first time through fmd_module_enter(), call the provided
         * function on the module.  If no fmd_module_abort() results, we will
         * fall through and return zero.  Otherwise we'll longjmp with an err,
         * return to the setjmp() above, and return the error to our caller.
         */
        if (err == 0 && func != NULL)
                (*func)((fmd_hdl_t *)mp);

        return (err);
}

void
fmd_module_exit(fmd_module_t *mp)
{
        (void) pthread_mutex_lock(&mp->mod_lock);

        ASSERT(mp->mod_flags & FMD_MOD_BUSY);
        mp->mod_flags &= ~FMD_MOD_BUSY;

        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);
}

/*
 * If the client.error policy has been set by a developer, stop or dump core
 * based on the policy; if we stop and are resumed we'll continue and execute
 * the default behavior to discard events in fmd_module_start().  If the caller
 * is the primary module thread, we reach this state by longjmp'ing back to
 * fmd_module_enter(), above.  If the caller is an auxiliary thread, we cancel
 * ourself and arrange for the primary thread to call fmd_module_abort().
 */
void
fmd_module_abort(fmd_module_t *mp, int err)
{
        uint_t policy = FMD_CERROR_UNLOAD;
        pthread_t tid = pthread_self();

        (void) fmd_conf_getprop(fmd.d_conf, "client.error", &policy);

        if (policy == FMD_CERROR_STOP) {
                fmd_error(err, "stopping after %s in client %s (%p)\n",
                    fmd_errclass(err), mp->mod_name, (void *)mp);
                (void) raise(SIGSTOP);
        } else if (policy == FMD_CERROR_ABORT) {
                fmd_panic("aborting due to %s in client %s (%p)\n",
                    fmd_errclass(err), mp->mod_name, (void *)mp);
        }

        /*
         * If the caller is an auxiliary thread, cancel the current thread.  We
         * prefer to cancel because it affords developers the option of using
         * the pthread_cleanup* APIs.  If cancellations have been disabled,
         * fall through to forcing the current thread to exit.  In either case
         * we update mod_error (if zero) to enter the failed state.  Once that
         * is set, further events received by the module will be discarded.
         *
         * We also set the FMD_MOD_FAIL bit, indicating an unrecoverable error.
         * When an auxiliary thread fails, the module is left in a delicate
         * state where it is likely not able to continue execution (even to
         * execute its _fmd_fini() routine) because our caller may hold locks
         * that are private to the module and can no longer be released.  The
         * FMD_MOD_FAIL bit forces fmd_api_module_lock() to abort if any other
         * module threads reach an API call, in an attempt to get them to exit.
         */
        if (tid != mp->mod_thread->thr_tid) {
                (void) pthread_mutex_lock(&mp->mod_lock);

                if (mp->mod_error == 0)
                        mp->mod_error = err;

                mp->mod_flags |= FMD_MOD_FAIL;
                (void) pthread_mutex_unlock(&mp->mod_lock);

                (void) pthread_cancel(tid);
                pthread_exit(NULL);
        }

        ASSERT(mp->mod_flags & FMD_MOD_BUSY);
        longjmp(mp->mod_jmpbuf, err);
}

void
fmd_module_hold(fmd_module_t *mp)
{
        (void) pthread_mutex_lock(&mp->mod_lock);

        TRACE((FMD_DBG_MOD, "hold %p (%s/%u)\n",
            (void *)mp, mp->mod_name, mp->mod_refs));

        mp->mod_refs++;
        ASSERT(mp->mod_refs != 0);

        (void) pthread_mutex_unlock(&mp->mod_lock);
}

void
fmd_module_rele(fmd_module_t *mp)
{
        (void) pthread_mutex_lock(&mp->mod_lock);

        TRACE((FMD_DBG_MOD, "rele %p (%s/%u)\n",
            (void *)mp, mp->mod_name, mp->mod_refs));

        ASSERT(mp->mod_refs != 0);

        if (--mp->mod_refs == 0)
                fmd_module_destroy(mp);
        else
                (void) pthread_mutex_unlock(&mp->mod_lock);
}

/*
 * Wrapper around libdiagcode's fm_dc_opendict() to load module dictionaries.
 * If the dictionary open is successful, the new dictionary is added to the
 * mod_dictv[] array and mod_codelen is updated with the new maximum length.
 */
int
fmd_module_dc_opendict(fmd_module_t *mp, const char *dict)
{
        struct fm_dc_handle *dcp, **dcv;
        char *dictdir, *dictnam, *p;
        size_t len;

        ASSERT(fmd_module_locked(mp));

        dictnam = strdupa(fmd_strbasename(dict));

        if ((p = strrchr(dictnam, '.')) != NULL &&
            strcmp(p, ".dict") == 0)
                *p = '\0'; /* eliminate any trailing .dict suffix */

        /*
         * If 'dict' is an absolute path, dictdir = $rootdir/`dirname dict`
         * If 'dict' is not an absolute path, dictdir = $dictdir/`dirname dict`
         */
        if (dict[0] == '/') {
                len = strlen(fmd.d_rootdir) + strlen(dict) + 1;
                dictdir = alloca(len);
                (void) snprintf(dictdir, len, "%s%s", fmd.d_rootdir, dict);
                (void) fmd_strdirname(dictdir);
        } else {
                (void) fmd_conf_getprop(fmd.d_conf, "dictdir", &p);
                len = strlen(fmd.d_rootdir) + strlen(p) + strlen(dict) + 3;
                dictdir = alloca(len);
                (void) snprintf(dictdir, len,
                    "%s/%s/%s", fmd.d_rootdir, p, dict);
                (void) fmd_strdirname(dictdir);
        }

        fmd_dprintf(FMD_DBG_MOD, "module %s opening %s -> %s/%s.dict\n",
            mp->mod_name, dict, dictdir, dictnam);

        if ((dcp = fm_dc_opendict(FM_DC_VERSION, dictdir, dictnam)) == NULL)
                return (-1); /* errno is set for us */

        dcv = fmd_alloc(sizeof (dcp) * (mp->mod_dictc + 1), FMD_SLEEP);
        bcopy(mp->mod_dictv, dcv, sizeof (dcp) * mp->mod_dictc);
        fmd_free(mp->mod_dictv, sizeof (dcp) * mp->mod_dictc);
        mp->mod_dictv = dcv;
        mp->mod_dictv[mp->mod_dictc++] = dcp;

        len = fm_dc_codelen(dcp);
        mp->mod_codelen = MAX(mp->mod_codelen, len);

        return (0);
}

/*
 * Wrapper around libdiagcode's fm_dc_key2code() that examines all the module's
 * dictionaries.  We adhere to the libdiagcode return values and semantics.
 */
int
fmd_module_dc_key2code(fmd_module_t *mp,
    char *const keys[], char *code, size_t codelen)
{
        int i, err;

        for (i = 0; i < mp->mod_dictc; i++) {
                if ((err = fm_dc_key2code(mp->mod_dictv[i], (const char **)keys,
                    code, codelen)) == 0 || errno != ENOMSG)
                        return (err);
        }

        return (fmd_set_errno(ENOMSG));
}

fmd_modhash_t *
fmd_modhash_create(void)
{
        fmd_modhash_t *mhp = fmd_alloc(sizeof (fmd_modhash_t), FMD_SLEEP);

        (void) pthread_rwlock_init(&mhp->mh_lock, NULL);
        mhp->mh_hashlen = fmd.d_str_buckets;
        mhp->mh_hash = fmd_zalloc(sizeof (void *) * mhp->mh_hashlen, FMD_SLEEP);
        mhp->mh_nelems = 0;

        return (mhp);
}

void
fmd_modhash_destroy(fmd_modhash_t *mhp)
{
        fmd_module_t *mp, *nmp;
        uint_t i;

        for (i = 0; i < mhp->mh_hashlen; i++) {
                for (mp = mhp->mh_hash[i]; mp != NULL; mp = nmp) {
                        nmp = mp->mod_next;
                        mp->mod_next = NULL;
                        fmd_module_rele(mp);
                }
        }

        fmd_free(mhp->mh_hash, sizeof (void *) * mhp->mh_hashlen);
        (void) pthread_rwlock_destroy(&mhp->mh_lock);
        fmd_free(mhp, sizeof (fmd_modhash_t));
}

static void
fmd_modhash_loaddir(fmd_modhash_t *mhp, const char *dir,
    const fmd_modops_t *ops, const char *suffix)
{
        char path[PATH_MAX];
        struct dirent *dp;
        const char *p;
        DIR *dirp;

        if ((dirp = opendir(dir)) == NULL)
                return; /* failed to open directory; just skip it */

        while ((dp = readdir(dirp)) != NULL) {
                if (dp->d_name[0] == '.')
                        continue; /* skip "." and ".." */

                p = strrchr(dp->d_name, '.');

                if (p != NULL && strcmp(p, ".conf") == 0)
                        continue; /* skip .conf files */

                if (suffix != NULL && (p == NULL || strcmp(p, suffix) != 0))
                        continue; /* skip files with the wrong suffix */

                (void) snprintf(path, sizeof (path), "%s/%s", dir, dp->d_name);
                (void) fmd_modhash_load(mhp, path, ops);
        }

        (void) closedir(dirp);
}

void
fmd_modhash_loadall(fmd_modhash_t *mhp, const fmd_conf_path_t *pap,
    const fmd_modops_t *ops, const char *suffix)
{
        int i;

        for (i = 0; i < pap->cpa_argc; i++)
                fmd_modhash_loaddir(mhp, pap->cpa_argv[i], ops, suffix);
}

void
fmd_modhash_apply(fmd_modhash_t *mhp, void (*func)(fmd_module_t *))
{
        fmd_module_t *mp, *np;
        uint_t i;

        (void) pthread_rwlock_rdlock(&mhp->mh_lock);

        for (i = 0; i < mhp->mh_hashlen; i++) {
                for (mp = mhp->mh_hash[i]; mp != NULL; mp = np) {
                        np = mp->mod_next;
                        func(mp);
                }
        }

        (void) pthread_rwlock_unlock(&mhp->mh_lock);
}

void
fmd_modhash_tryapply(fmd_modhash_t *mhp, void (*func)(fmd_module_t *))
{
        fmd_module_t *mp, *np;
        uint_t i;

        if (mhp == NULL || pthread_rwlock_tryrdlock(&mhp->mh_lock) != 0)
                return; /* not initialized or couldn't grab lock */

        for (i = 0; i < mhp->mh_hashlen; i++) {
                for (mp = mhp->mh_hash[i]; mp != NULL; mp = np) {
                        np = mp->mod_next;
                        func(mp);
                }
        }

        (void) pthread_rwlock_unlock(&mhp->mh_lock);
}

void
fmd_modhash_dispatch(fmd_modhash_t *mhp, fmd_event_t *ep)
{
        fmd_module_t *mp;
        uint_t i;

        fmd_event_hold(ep);
        (void) pthread_rwlock_rdlock(&mhp->mh_lock);

        for (i = 0; i < mhp->mh_hashlen; i++) {
                for (mp = mhp->mh_hash[i]; mp != NULL; mp = mp->mod_next) {
                        /*
                         * If FMD_MOD_INIT is set but MOD_FINI, MOD_QUIT, and
                         * mod_error are all zero, then the module is active:
                         * enqueue the event in the corresponding event queue.
                         */
                        (void) pthread_mutex_lock(&mp->mod_lock);

                        if ((mp->mod_flags & (FMD_MOD_INIT | FMD_MOD_FINI |
                            FMD_MOD_QUIT)) == FMD_MOD_INIT && !mp->mod_error) {

                                /*
                                 * If the event we're dispatching is of type
                                 * FMD_EVT_TOPO and there are already redundant
                                 * FMD_EVT_TOPO events in this module's queue,
                                 * then drop those before adding the new one.
                                 */
                                if (FMD_EVENT_TYPE(ep) == FMD_EVT_TOPO)
                                        fmd_eventq_drop_topo(mp->mod_queue);

                                fmd_eventq_insert_at_time(mp->mod_queue, ep);

                        }
                        (void) pthread_mutex_unlock(&mp->mod_lock);
                }
        }

        (void) pthread_rwlock_unlock(&mhp->mh_lock);
        fmd_event_rele(ep);
}

fmd_module_t *
fmd_modhash_lookup(fmd_modhash_t *mhp, const char *name)
{
        fmd_module_t *mp;
        uint_t h;

        (void) pthread_rwlock_rdlock(&mhp->mh_lock);
        h = fmd_strhash(name) % mhp->mh_hashlen;

        for (mp = mhp->mh_hash[h]; mp != NULL; mp = mp->mod_next) {
                if (strcmp(name, mp->mod_name) == 0)
                        break;
        }

        if (mp != NULL)
                fmd_module_hold(mp);
        else
                (void) fmd_set_errno(EFMD_MOD_NOMOD);

        (void) pthread_rwlock_unlock(&mhp->mh_lock);
        return (mp);
}

fmd_module_t *
fmd_modhash_load(fmd_modhash_t *mhp, const char *path, const fmd_modops_t *ops)
{
        char name[PATH_MAX], *p;
        fmd_module_t *mp;
        int tries = 0;
        uint_t h;

        (void) strlcpy(name, fmd_strbasename(path), sizeof (name));
        if ((p = strrchr(name, '.')) != NULL && strcmp(p, ".so") == 0)
                *p = '\0'; /* strip trailing .so from any module name */

        (void) pthread_rwlock_wrlock(&mhp->mh_lock);
        h = fmd_strhash(name) % mhp->mh_hashlen;

        /*
         * First check to see if a module is already present in the hash table
         * for this name.  If so, the module is already loaded: skip it.
         */
        for (mp = mhp->mh_hash[h]; mp != NULL; mp = mp->mod_next) {
                if (strcmp(name, mp->mod_name) == 0)
                        break;
        }

        if (mp != NULL) {
                (void) pthread_rwlock_unlock(&mhp->mh_lock);
                (void) fmd_set_errno(EFMD_MOD_LOADED);
                return (NULL);
        }

        /*
         * fmd_module_create() will return a held (as if by fmd_module_hold())
         * module.  We leave this hold in place to correspond to the hash-in.
         */
        while ((mp = fmd_module_create(path, ops)) == NULL) {
                if (tries++ != 0 || errno != EFMD_CKPT_INVAL) {
                        (void) pthread_rwlock_unlock(&mhp->mh_lock);
                        return (NULL); /* errno is set for us */
                }
        }

        mp->mod_hash = mhp;
        mp->mod_next = mhp->mh_hash[h];

        mhp->mh_hash[h] = mp;
        mhp->mh_nelems++;

        (void) pthread_rwlock_unlock(&mhp->mh_lock);
        return (mp);
}

int
fmd_modhash_unload(fmd_modhash_t *mhp, const char *name)
{
        fmd_module_t *mp, **pp;
        uint_t h;

        (void) pthread_rwlock_wrlock(&mhp->mh_lock);
        h = fmd_strhash(name) % mhp->mh_hashlen;
        pp = &mhp->mh_hash[h];

        for (mp = *pp; mp != NULL; mp = mp->mod_next) {
                if (strcmp(name, mp->mod_name) == 0)
                        break;
                else
                        pp = &mp->mod_next;
        }

        if (mp == NULL) {
                (void) pthread_rwlock_unlock(&mhp->mh_lock);
                return (fmd_set_errno(EFMD_MOD_NOMOD));
        }

        *pp = mp->mod_next;
        mp->mod_next = NULL;

        ASSERT(mhp->mh_nelems != 0);
        mhp->mh_nelems--;

        (void) pthread_rwlock_unlock(&mhp->mh_lock);

        fmd_module_unload(mp);
        fmd_module_rele(mp);

        return (0);
}

void
fmd_modstat_publish(fmd_module_t *mp)
{
        (void) pthread_mutex_lock(&mp->mod_lock);

        ASSERT(mp->mod_flags & FMD_MOD_STSUB);
        mp->mod_flags |= FMD_MOD_STPUB;
        (void) pthread_cond_broadcast(&mp->mod_cv);

        while (mp->mod_flags & FMD_MOD_STPUB)
                (void) pthread_cond_wait(&mp->mod_cv, &mp->mod_lock);

        (void) pthread_mutex_unlock(&mp->mod_lock);
}

int
fmd_modstat_snapshot(fmd_module_t *mp, fmd_ustat_snap_t *uss)
{
        fmd_event_t *e;
        int err;

        /*
         * Grab the module lock and wait for the STSUB bit to be clear.  Then
         * set it to indicate we are a subscriber and everyone else must wait.
         */
        (void) pthread_mutex_lock(&mp->mod_lock);

        while (mp->mod_error == 0 && (mp->mod_flags & FMD_MOD_STSUB))
                (void) pthread_cond_wait(&mp->mod_cv, &mp->mod_lock);

        if (mp->mod_error != 0) {
                (void) pthread_mutex_unlock(&mp->mod_lock);
                return (fmd_set_errno(EFMD_HDL_ABORT));
        }

        mp->mod_flags |= FMD_MOD_STSUB;
        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);

        /*
         * Create a stats pseudo-event and dispatch it to the module, forcing
         * it to next execute its custom snapshot routine (or the empty one).
         */
        e = fmd_event_create(FMD_EVT_STATS, FMD_HRT_NOW, NULL, NULL);
        fmd_eventq_insert_at_head(mp->mod_queue, e);

        /*
         * Grab the module lock and then wait on mod_cv for STPUB to be set,
         * indicating the snapshot routine is completed and the module is idle.
         */
        (void) pthread_mutex_lock(&mp->mod_lock);

        while (mp->mod_error == 0 && !(mp->mod_flags & FMD_MOD_STPUB)) {
                struct timespec tms;

                (void) pthread_cond_wait(&mp->mod_cv, &mp->mod_lock);
                (void) pthread_mutex_unlock(&mp->mod_lock);
                tms.tv_sec = 0;
                tms.tv_nsec = 10000000;
                (void) nanosleep(&tms, NULL);
                (void) pthread_mutex_lock(&mp->mod_lock);
        }

        if (mp->mod_error != 0) {
                (void) pthread_mutex_unlock(&mp->mod_lock);
                return (fmd_set_errno(EFMD_HDL_ABORT));
        }

        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);

        /*
         * Update ms_snaptime and take the actual snapshot of the various
         * statistics while the module is quiescent and waiting for us.
         */
        (void) pthread_mutex_lock(&mp->mod_stats_lock);

        if (mp->mod_stats != NULL) {
                mp->mod_stats->ms_snaptime.fmds_value.ui64 = gethrtime();
                err = fmd_ustat_snapshot(mp->mod_ustat, uss);
        } else
                err = fmd_set_errno(EFMD_HDL_ABORT);

        (void) pthread_mutex_unlock(&mp->mod_stats_lock);

        /*
         * With the snapshot complete, grab the module lock and clear both
         * STSUB and STPUB, permitting everyone to wake up and continue.
         */
        (void) pthread_mutex_lock(&mp->mod_lock);

        ASSERT(mp->mod_flags & FMD_MOD_STSUB);
        ASSERT(mp->mod_flags & FMD_MOD_STPUB);
        mp->mod_flags &= ~(FMD_MOD_STSUB | FMD_MOD_STPUB);

        (void) pthread_cond_broadcast(&mp->mod_cv);
        (void) pthread_mutex_unlock(&mp->mod_lock);

        return (err);
}

struct topo_hdl *
fmd_module_topo_hold(fmd_module_t *mp)
{
        fmd_modtopo_t *mtp;

        ASSERT(fmd_module_locked(mp));

        mtp = fmd_zalloc(sizeof (fmd_modtopo_t), FMD_SLEEP);
        mtp->mt_topo = mp->mod_topo_current;
        fmd_topo_addref(mtp->mt_topo);
        fmd_list_prepend(&mp->mod_topolist, mtp);

        return (mtp->mt_topo->ft_hdl);
}

int
fmd_module_topo_rele(fmd_module_t *mp, struct topo_hdl *hdl)
{
        fmd_modtopo_t *mtp;

        ASSERT(fmd_module_locked(mp));

        for (mtp = fmd_list_next(&mp->mod_topolist); mtp != NULL;
            mtp = fmd_list_next(mtp)) {
                if (mtp->mt_topo->ft_hdl == hdl)
                        break;
        }

        if (mtp == NULL)
                return (-1);

        fmd_list_delete(&mp->mod_topolist, mtp);
        fmd_topo_rele(mtp->mt_topo);
        fmd_free(mtp, sizeof (fmd_modtopo_t));
        return (0);
}