- Copy stable/10 (r259064) to releng/10.0 as part of the

[FreeBSD/releng/10.0.git] / sys / geom / journal / g_journal.c

/*-
 * Copyright (c) 2005-2006 Pawel Jakub Dawidek <pjd@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/module.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/bio.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/eventhandler.h>
#include <sys/proc.h>
#include <sys/kthread.h>
#include <sys/sched.h>
#include <sys/taskqueue.h>
#include <sys/vnode.h>
#include <sys/sbuf.h>
#ifdef GJ_MEMDEBUG
#include <sys/stack.h>
#include <sys/kdb.h>
#endif
#include <vm/vm.h>
#include <vm/vm_kern.h>
#include <geom/geom.h>

#include <geom/journal/g_journal.h>

FEATURE(geom_journal, "GEOM journaling support");

/*
 * On-disk journal format:
 *
 * JH - Journal header
 * RH - Record header
 *
 * %%%%%% ****** +------+ +------+     ****** +------+     %%%%%%
 * % JH % * RH * | Data | | Data | ... * RH * | Data | ... % JH % ...
 * %%%%%% ****** +------+ +------+     ****** +------+     %%%%%%
 *
 */

CTASSERT(sizeof(struct g_journal_header) <= 512);
CTASSERT(sizeof(struct g_journal_record_header) <= 512);

static MALLOC_DEFINE(M_JOURNAL, "journal_data", "GEOM_JOURNAL Data");
static struct mtx g_journal_cache_mtx;
MTX_SYSINIT(g_journal_cache, &g_journal_cache_mtx, "cache usage", MTX_DEF);

const struct g_journal_desc *g_journal_filesystems[] = {
        &g_journal_ufs,
        NULL
};

SYSCTL_DECL(_kern_geom);

int g_journal_debug = 0;
TUNABLE_INT("kern.geom.journal.debug", &g_journal_debug);
static u_int g_journal_switch_time = 10;
static u_int g_journal_force_switch = 70;
static u_int g_journal_parallel_flushes = 16;
static u_int g_journal_parallel_copies = 16;
static u_int g_journal_accept_immediately = 64;
static u_int g_journal_record_entries = GJ_RECORD_HEADER_NENTRIES;
static u_int g_journal_do_optimize = 1;

static SYSCTL_NODE(_kern_geom, OID_AUTO, journal, CTLFLAG_RW, 0,
    "GEOM_JOURNAL stuff");
SYSCTL_INT(_kern_geom_journal, OID_AUTO, debug, CTLFLAG_RW, &g_journal_debug, 0,
    "Debug level");
SYSCTL_UINT(_kern_geom_journal, OID_AUTO, switch_time, CTLFLAG_RW,
    &g_journal_switch_time, 0, "Switch journals every N seconds");
SYSCTL_UINT(_kern_geom_journal, OID_AUTO, force_switch, CTLFLAG_RW,
    &g_journal_force_switch, 0, "Force switch when journal is N% full");
SYSCTL_UINT(_kern_geom_journal, OID_AUTO, parallel_flushes, CTLFLAG_RW,
    &g_journal_parallel_flushes, 0,
    "Number of flush I/O requests to send in parallel");
SYSCTL_UINT(_kern_geom_journal, OID_AUTO, accept_immediately, CTLFLAG_RW,
    &g_journal_accept_immediately, 0,
    "Number of I/O requests accepted immediately");
SYSCTL_UINT(_kern_geom_journal, OID_AUTO, parallel_copies, CTLFLAG_RW,
    &g_journal_parallel_copies, 0,
    "Number of copy I/O requests to send in parallel");
static int
g_journal_record_entries_sysctl(SYSCTL_HANDLER_ARGS)
{
        u_int entries;
        int error;

        entries = g_journal_record_entries;
        error = sysctl_handle_int(oidp, &entries, 0, req);
        if (error != 0 || req->newptr == NULL)
                return (error);
        if (entries < 1 || entries > GJ_RECORD_HEADER_NENTRIES)
                return (EINVAL);
        g_journal_record_entries = entries;
        return (0);
}
SYSCTL_PROC(_kern_geom_journal, OID_AUTO, record_entries,
    CTLTYPE_UINT | CTLFLAG_RW, NULL, 0, g_journal_record_entries_sysctl, "I",
    "Maximum number of entires in one journal record");
SYSCTL_UINT(_kern_geom_journal, OID_AUTO, optimize, CTLFLAG_RW,
    &g_journal_do_optimize, 0, "Try to combine bios on flush and copy");

static u_int g_journal_cache_used = 0;
static u_int g_journal_cache_limit = 64 * 1024 * 1024;
TUNABLE_INT("kern.geom.journal.cache.limit", &g_journal_cache_limit);
static u_int g_journal_cache_divisor = 2;
TUNABLE_INT("kern.geom.journal.cache.divisor", &g_journal_cache_divisor);
static u_int g_journal_cache_switch = 90;
static u_int g_journal_cache_misses = 0;
static u_int g_journal_cache_alloc_failures = 0;
static u_int g_journal_cache_low = 0;

static SYSCTL_NODE(_kern_geom_journal, OID_AUTO, cache, CTLFLAG_RW, 0,
    "GEOM_JOURNAL cache");
SYSCTL_UINT(_kern_geom_journal_cache, OID_AUTO, used, CTLFLAG_RD,
    &g_journal_cache_used, 0, "Number of allocated bytes");
static int
g_journal_cache_limit_sysctl(SYSCTL_HANDLER_ARGS)
{
        u_int limit;
        int error;

        limit = g_journal_cache_limit;
        error = sysctl_handle_int(oidp, &limit, 0, req);
        if (error != 0 || req->newptr == NULL)
                return (error);
        g_journal_cache_limit = limit;
        g_journal_cache_low = (limit / 100) * g_journal_cache_switch;
        return (0);
}
SYSCTL_PROC(_kern_geom_journal_cache, OID_AUTO, limit,
    CTLTYPE_UINT | CTLFLAG_RW, NULL, 0, g_journal_cache_limit_sysctl, "I",
    "Maximum number of allocated bytes");
SYSCTL_UINT(_kern_geom_journal_cache, OID_AUTO, divisor, CTLFLAG_RDTUN,
    &g_journal_cache_divisor, 0,
    "(kmem_size / kern.geom.journal.cache.divisor) == cache size");
static int
g_journal_cache_switch_sysctl(SYSCTL_HANDLER_ARGS)
{
        u_int cswitch;
        int error;

        cswitch = g_journal_cache_switch;
        error = sysctl_handle_int(oidp, &cswitch, 0, req);
        if (error != 0 || req->newptr == NULL)
                return (error);
        if (cswitch < 0 || cswitch > 100)
                return (EINVAL);
        g_journal_cache_switch = cswitch;
        g_journal_cache_low = (g_journal_cache_limit / 100) * cswitch;
        return (0);
}
SYSCTL_PROC(_kern_geom_journal_cache, OID_AUTO, switch,
    CTLTYPE_UINT | CTLFLAG_RW, NULL, 0, g_journal_cache_switch_sysctl, "I",
    "Force switch when we hit this percent of cache use");
SYSCTL_UINT(_kern_geom_journal_cache, OID_AUTO, misses, CTLFLAG_RW,
    &g_journal_cache_misses, 0, "Number of cache misses");
SYSCTL_UINT(_kern_geom_journal_cache, OID_AUTO, alloc_failures, CTLFLAG_RW,
    &g_journal_cache_alloc_failures, 0, "Memory allocation failures");

static u_long g_journal_stats_bytes_skipped = 0;
static u_long g_journal_stats_combined_ios = 0;
static u_long g_journal_stats_switches = 0;
static u_long g_journal_stats_wait_for_copy = 0;
static u_long g_journal_stats_journal_full = 0;
static u_long g_journal_stats_low_mem = 0;

static SYSCTL_NODE(_kern_geom_journal, OID_AUTO, stats, CTLFLAG_RW, 0,
    "GEOM_JOURNAL statistics");
SYSCTL_ULONG(_kern_geom_journal_stats, OID_AUTO, skipped_bytes, CTLFLAG_RW,
    &g_journal_stats_bytes_skipped, 0, "Number of skipped bytes");
SYSCTL_ULONG(_kern_geom_journal_stats, OID_AUTO, combined_ios, CTLFLAG_RW,
    &g_journal_stats_combined_ios, 0, "Number of combined I/O requests");
SYSCTL_ULONG(_kern_geom_journal_stats, OID_AUTO, switches, CTLFLAG_RW,
    &g_journal_stats_switches, 0, "Number of journal switches");
SYSCTL_ULONG(_kern_geom_journal_stats, OID_AUTO, wait_for_copy, CTLFLAG_RW,
    &g_journal_stats_wait_for_copy, 0, "Wait for journal copy on switch");
SYSCTL_ULONG(_kern_geom_journal_stats, OID_AUTO, journal_full, CTLFLAG_RW,
    &g_journal_stats_journal_full, 0,
    "Number of times journal was almost full.");
SYSCTL_ULONG(_kern_geom_journal_stats, OID_AUTO, low_mem, CTLFLAG_RW,
    &g_journal_stats_low_mem, 0, "Number of times low_mem hook was called.");

static g_taste_t g_journal_taste;
static g_ctl_req_t g_journal_config;
static g_dumpconf_t g_journal_dumpconf;
static g_init_t g_journal_init;
static g_fini_t g_journal_fini;

struct g_class g_journal_class = {
        .name = G_JOURNAL_CLASS_NAME,
        .version = G_VERSION,
        .taste = g_journal_taste,
        .ctlreq = g_journal_config,
        .dumpconf = g_journal_dumpconf,
        .init = g_journal_init,
        .fini = g_journal_fini
};

static int g_journal_destroy(struct g_journal_softc *sc);
static void g_journal_metadata_update(struct g_journal_softc *sc);
static void g_journal_switch_wait(struct g_journal_softc *sc);

#define GJ_SWITCHER_WORKING     0
#define GJ_SWITCHER_DIE         1
#define GJ_SWITCHER_DIED        2
static int g_journal_switcher_state = GJ_SWITCHER_WORKING;
static int g_journal_switcher_wokenup = 0;
static int g_journal_sync_requested = 0;

#ifdef GJ_MEMDEBUG
struct meminfo {
        size_t          mi_size;
        struct stack    mi_stack;
};
#endif

/*
 * We use our own malloc/realloc/free funtions, so we can collect statistics
 * and force journal switch when we're running out of cache.
 */
static void *
gj_malloc(size_t size, int flags)
{
        void *p;
#ifdef GJ_MEMDEBUG
        struct meminfo *mi;
#endif

        mtx_lock(&g_journal_cache_mtx);
        if (g_journal_cache_limit > 0 && !g_journal_switcher_wokenup &&
            g_journal_cache_used + size > g_journal_cache_low) {
                GJ_DEBUG(1, "No cache, waking up the switcher.");
                g_journal_switcher_wokenup = 1;
                wakeup(&g_journal_switcher_state);
        }
        if ((flags & M_NOWAIT) && g_journal_cache_limit > 0 &&
            g_journal_cache_used + size > g_journal_cache_limit) {
                mtx_unlock(&g_journal_cache_mtx);
                g_journal_cache_alloc_failures++;
                return (NULL);
        }
        g_journal_cache_used += size;
        mtx_unlock(&g_journal_cache_mtx);
        flags &= ~M_NOWAIT;
#ifndef GJ_MEMDEBUG
        p = malloc(size, M_JOURNAL, flags | M_WAITOK);
#else
        mi = malloc(sizeof(*mi) + size, M_JOURNAL, flags | M_WAITOK);
        p = (u_char *)mi + sizeof(*mi);
        mi->mi_size = size;
        stack_save(&mi->mi_stack);
#endif
        return (p);
}

static void
gj_free(void *p, size_t size)
{
#ifdef GJ_MEMDEBUG
        struct meminfo *mi;
#endif

        KASSERT(p != NULL, ("p=NULL"));
        KASSERT(size > 0, ("size=0"));
        mtx_lock(&g_journal_cache_mtx);
        KASSERT(g_journal_cache_used >= size, ("Freeing too much?"));
        g_journal_cache_used -= size;
        mtx_unlock(&g_journal_cache_mtx);
#ifdef GJ_MEMDEBUG
        mi = p = (void *)((u_char *)p - sizeof(*mi));
        if (mi->mi_size != size) {
                printf("GJOURNAL: Size mismatch! %zu != %zu\n", size,
                    mi->mi_size);
                printf("GJOURNAL: Alloc backtrace:\n");
                stack_print(&mi->mi_stack);
                printf("GJOURNAL: Free backtrace:\n");
                kdb_backtrace();
        }
#endif
        free(p, M_JOURNAL);
}

static void *
gj_realloc(void *p, size_t size, size_t oldsize)
{
        void *np;

#ifndef GJ_MEMDEBUG
        mtx_lock(&g_journal_cache_mtx);
        g_journal_cache_used -= oldsize;
        g_journal_cache_used += size;
        mtx_unlock(&g_journal_cache_mtx);
        np = realloc(p, size, M_JOURNAL, M_WAITOK);
#else
        np = gj_malloc(size, M_WAITOK);
        bcopy(p, np, MIN(oldsize, size));
        gj_free(p, oldsize);
#endif
        return (np);
}

static void
g_journal_check_overflow(struct g_journal_softc *sc)
{
        off_t length, used;

        if ((sc->sc_active.jj_offset < sc->sc_inactive.jj_offset &&
             sc->sc_journal_offset >= sc->sc_inactive.jj_offset) ||
            (sc->sc_active.jj_offset > sc->sc_inactive.jj_offset &&
             sc->sc_journal_offset >= sc->sc_inactive.jj_offset &&
             sc->sc_journal_offset < sc->sc_active.jj_offset)) {
                panic("Journal overflow "
                    "(id = %u joffset=%jd active=%jd inactive=%jd)",
                    (unsigned)sc->sc_id,
                    (intmax_t)sc->sc_journal_offset,
                    (intmax_t)sc->sc_active.jj_offset,
                    (intmax_t)sc->sc_inactive.jj_offset);
        }
        if (sc->sc_active.jj_offset < sc->sc_inactive.jj_offset) {
                length = sc->sc_inactive.jj_offset - sc->sc_active.jj_offset;
                used = sc->sc_journal_offset - sc->sc_active.jj_offset;
        } else {
                length = sc->sc_jend - sc->sc_active.jj_offset;
                length += sc->sc_inactive.jj_offset - sc->sc_jstart;
                if (sc->sc_journal_offset >= sc->sc_active.jj_offset)
                        used = sc->sc_journal_offset - sc->sc_active.jj_offset;
                else {
                        used = sc->sc_jend - sc->sc_active.jj_offset;
                        used += sc->sc_journal_offset - sc->sc_jstart;
                }
        }
        /* Already woken up? */
        if (g_journal_switcher_wokenup)
                return;
        /*
         * If the active journal takes more than g_journal_force_switch precent
         * of free journal space, we force journal switch.
         */
        KASSERT(length > 0,
            ("length=%jd used=%jd active=%jd inactive=%jd joffset=%jd",
            (intmax_t)length, (intmax_t)used,
            (intmax_t)sc->sc_active.jj_offset,
            (intmax_t)sc->sc_inactive.jj_offset,
            (intmax_t)sc->sc_journal_offset));
        if ((used * 100) / length > g_journal_force_switch) {
                g_journal_stats_journal_full++;
                GJ_DEBUG(1, "Journal %s %jd%% full, forcing journal switch.",
                    sc->sc_name, (used * 100) / length);
                mtx_lock(&g_journal_cache_mtx);
                g_journal_switcher_wokenup = 1;
                wakeup(&g_journal_switcher_state);
                mtx_unlock(&g_journal_cache_mtx);
        }
}

static void
g_journal_orphan(struct g_consumer *cp)
{
        struct g_journal_softc *sc;
        char name[256];
        int error;

        g_topology_assert();
        sc = cp->geom->softc;
        strlcpy(name, cp->provider->name, sizeof(name));
        GJ_DEBUG(0, "Lost provider %s.", name);
        if (sc == NULL)
                return;
        error = g_journal_destroy(sc);
        if (error == 0)
                GJ_DEBUG(0, "Journal %s destroyed.", name);
        else {
                GJ_DEBUG(0, "Cannot destroy journal %s (error=%d). "
                    "Destroy it manually after last close.", sc->sc_name,
                    error);
        }
}

static int
g_journal_access(struct g_provider *pp, int acr, int acw, int ace)
{
        struct g_journal_softc *sc;
        int dcr, dcw, dce;

        g_topology_assert();
        GJ_DEBUG(2, "Access request for %s: r%dw%de%d.", pp->name,
            acr, acw, ace);

        dcr = pp->acr + acr;
        dcw = pp->acw + acw;
        dce = pp->ace + ace;

        sc = pp->geom->softc;
        if (sc == NULL || (sc->sc_flags & GJF_DEVICE_DESTROY)) {
                if (acr <= 0 && acw <= 0 && ace <= 0)
                        return (0);
                else
                        return (ENXIO);
        }
        if (pp->acw == 0 && dcw > 0) {
                GJ_DEBUG(1, "Marking %s as dirty.", sc->sc_name);
                sc->sc_flags &= ~GJF_DEVICE_CLEAN;
                g_topology_unlock();
                g_journal_metadata_update(sc);
                g_topology_lock();
        } /* else if (pp->acw == 0 && dcw > 0 && JEMPTY(sc)) {
                GJ_DEBUG(1, "Marking %s as clean.", sc->sc_name);
                sc->sc_flags |= GJF_DEVICE_CLEAN;
                g_topology_unlock();
                g_journal_metadata_update(sc);
                g_topology_lock();
        } */
        return (0);
}

static void
g_journal_header_encode(struct g_journal_header *hdr, u_char *data)
{

        bcopy(GJ_HEADER_MAGIC, data, sizeof(GJ_HEADER_MAGIC));
        data += sizeof(GJ_HEADER_MAGIC);
        le32enc(data, hdr->jh_journal_id);
        data += 4;
        le32enc(data, hdr->jh_journal_next_id);
}

static int
g_journal_header_decode(const u_char *data, struct g_journal_header *hdr)
{

        bcopy(data, hdr->jh_magic, sizeof(hdr->jh_magic));
        data += sizeof(hdr->jh_magic);
        if (bcmp(hdr->jh_magic, GJ_HEADER_MAGIC, sizeof(GJ_HEADER_MAGIC)) != 0)
                return (EINVAL);
        hdr->jh_journal_id = le32dec(data);
        data += 4;
        hdr->jh_journal_next_id = le32dec(data);
        return (0);
}

static void
g_journal_flush_cache(struct g_journal_softc *sc)
{
        struct bintime bt;
        int error;

        if (sc->sc_bio_flush == 0)
                return;
        GJ_TIMER_START(1, &bt);
        if (sc->sc_bio_flush & GJ_FLUSH_JOURNAL) {
                error = g_io_flush(sc->sc_jconsumer);
                GJ_DEBUG(error == 0 ? 2 : 0, "Flush cache of %s: error=%d.",
                    sc->sc_jconsumer->provider->name, error);
        }
        if (sc->sc_bio_flush & GJ_FLUSH_DATA) {
                /*
                 * TODO: This could be called in parallel with the
                 *       previous call.
                 */
                error = g_io_flush(sc->sc_dconsumer);
                GJ_DEBUG(error == 0 ? 2 : 0, "Flush cache of %s: error=%d.",
                    sc->sc_dconsumer->provider->name, error);
        }
        GJ_TIMER_STOP(1, &bt, "Cache flush time");
}

static int
g_journal_write_header(struct g_journal_softc *sc)
{
        struct g_journal_header hdr;
        struct g_consumer *cp;
        u_char *buf;
        int error;

        cp = sc->sc_jconsumer;
        buf = gj_malloc(cp->provider->sectorsize, M_WAITOK);

        strlcpy(hdr.jh_magic, GJ_HEADER_MAGIC, sizeof(hdr.jh_magic));
        hdr.jh_journal_id = sc->sc_journal_id;
        hdr.jh_journal_next_id = sc->sc_journal_next_id;
        g_journal_header_encode(&hdr, buf);
        error = g_write_data(cp, sc->sc_journal_offset, buf,
            cp->provider->sectorsize);
        /* if (error == 0) */
        sc->sc_journal_offset += cp->provider->sectorsize;

        gj_free(buf, cp->provider->sectorsize);
        return (error);
}

/*
 * Every journal record has a header and data following it.
 * Functions below are used to decode the header before storing it to
 * little endian and to encode it after reading to system endianess.
 */
static void
g_journal_record_header_encode(struct g_journal_record_header *hdr,
    u_char *data)
{
        struct g_journal_entry *ent;
        u_int i;

        bcopy(GJ_RECORD_HEADER_MAGIC, data, sizeof(GJ_RECORD_HEADER_MAGIC));
        data += sizeof(GJ_RECORD_HEADER_MAGIC);
        le32enc(data, hdr->jrh_journal_id);
        data += 8;
        le16enc(data, hdr->jrh_nentries);
        data += 2;
        bcopy(hdr->jrh_sum, data, sizeof(hdr->jrh_sum));
        data += 8;
        for (i = 0; i < hdr->jrh_nentries; i++) {
                ent = &hdr->jrh_entries[i];
                le64enc(data, ent->je_joffset);
                data += 8;
                le64enc(data, ent->je_offset);
                data += 8;
                le64enc(data, ent->je_length);
                data += 8;
        }
}

static int
g_journal_record_header_decode(const u_char *data,
    struct g_journal_record_header *hdr)
{
        struct g_journal_entry *ent;
        u_int i;

        bcopy(data, hdr->jrh_magic, sizeof(hdr->jrh_magic));
        data += sizeof(hdr->jrh_magic);
        if (strcmp(hdr->jrh_magic, GJ_RECORD_HEADER_MAGIC) != 0)
                return (EINVAL);
        hdr->jrh_journal_id = le32dec(data);
        data += 8;
        hdr->jrh_nentries = le16dec(data);
        data += 2;
        if (hdr->jrh_nentries > GJ_RECORD_HEADER_NENTRIES)
                return (EINVAL);
        bcopy(data, hdr->jrh_sum, sizeof(hdr->jrh_sum));
        data += 8;
        for (i = 0; i < hdr->jrh_nentries; i++) {
                ent = &hdr->jrh_entries[i];
                ent->je_joffset = le64dec(data);
                data += 8;
                ent->je_offset = le64dec(data);
                data += 8;
                ent->je_length = le64dec(data);
                data += 8;
        }
        return (0);
}

/*
 * Function reads metadata from a provider (via the given consumer), decodes
 * it to system endianess and verifies its correctness.
 */
static int
g_journal_metadata_read(struct g_consumer *cp, struct g_journal_metadata *md)
{
        struct g_provider *pp;
        u_char *buf;
        int error;

        g_topology_assert();

        error = g_access(cp, 1, 0, 0);
        if (error != 0)
                return (error);
        pp = cp->provider;
        g_topology_unlock();
        /* Metadata is stored in last sector. */
        buf = g_read_data(cp, pp->mediasize - pp->sectorsize, pp->sectorsize,
            &error);
        g_topology_lock();
        g_access(cp, -1, 0, 0);
        if (buf == NULL) {
                GJ_DEBUG(1, "Cannot read metadata from %s (error=%d).",
                    cp->provider->name, error);
                return (error);
        }

        /* Decode metadata. */
        error = journal_metadata_decode(buf, md);
        g_free(buf);
        /* Is this is gjournal provider at all? */
        if (strcmp(md->md_magic, G_JOURNAL_MAGIC) != 0)
                return (EINVAL);
        /*
         * Are we able to handle this version of metadata?
         * We only maintain backward compatibility.
         */
        if (md->md_version > G_JOURNAL_VERSION) {
                GJ_DEBUG(0,
                    "Kernel module is too old to handle metadata from %s.",
                    cp->provider->name);
                return (EINVAL);
        }
        /* Is checksum correct? */
        if (error != 0) {
                GJ_DEBUG(0, "MD5 metadata hash mismatch for provider %s.",
                    cp->provider->name);
                return (error);
        }
        return (0);
}

/*
 * Two functions below are responsible for updating metadata.
 * Only metadata on the data provider is updated (we need to update
 * information about active journal in there).
 */
static void
g_journal_metadata_done(struct bio *bp)
{

        /*
         * There is not much we can do on error except informing about it.
         */
        if (bp->bio_error != 0) {
                GJ_LOGREQ(0, bp, "Cannot update metadata (error=%d).",
                    bp->bio_error);
        } else {
                GJ_LOGREQ(2, bp, "Metadata updated.");
        }
        gj_free(bp->bio_data, bp->bio_length);
        g_destroy_bio(bp);
}

static void
g_journal_metadata_update(struct g_journal_softc *sc)
{
        struct g_journal_metadata md;
        struct g_consumer *cp;
        struct bio *bp;
        u_char *sector;

        cp = sc->sc_dconsumer;
        sector = gj_malloc(cp->provider->sectorsize, M_WAITOK);
        strlcpy(md.md_magic, G_JOURNAL_MAGIC, sizeof(md.md_magic));
        md.md_version = G_JOURNAL_VERSION;
        md.md_id = sc->sc_id;
        md.md_type = sc->sc_orig_type;
        md.md_jstart = sc->sc_jstart;
        md.md_jend = sc->sc_jend;
        md.md_joffset = sc->sc_inactive.jj_offset;
        md.md_jid = sc->sc_journal_previous_id;
        md.md_flags = 0;
        if (sc->sc_flags & GJF_DEVICE_CLEAN)
                md.md_flags |= GJ_FLAG_CLEAN;

        if (sc->sc_flags & GJF_DEVICE_HARDCODED)
                strlcpy(md.md_provider, sc->sc_name, sizeof(md.md_provider));
        else
                bzero(md.md_provider, sizeof(md.md_provider));
        md.md_provsize = cp->provider->mediasize;
        journal_metadata_encode(&md, sector);

        /*
         * Flush the cache, so we know all data are on disk.
         * We write here informations like "journal is consistent", so we need
         * to be sure it is. Without BIO_FLUSH here, we can end up in situation
         * where metadata is stored on disk, but not all data.
         */
        g_journal_flush_cache(sc);

        bp = g_alloc_bio();
        bp->bio_offset = cp->provider->mediasize - cp->provider->sectorsize;
        bp->bio_length = cp->provider->sectorsize;
        bp->bio_data = sector;
        bp->bio_cmd = BIO_WRITE;
        if (!(sc->sc_flags & GJF_DEVICE_DESTROY)) {
                bp->bio_done = g_journal_metadata_done;
                g_io_request(bp, cp);
        } else {
                bp->bio_done = NULL;
                g_io_request(bp, cp);
                biowait(bp, "gjmdu");
                g_journal_metadata_done(bp);
        }

        /*
         * Be sure metadata reached the disk.
         */
        g_journal_flush_cache(sc);
}

/*
 * This is where the I/O request comes from the GEOM.
 */
static void
g_journal_start(struct bio *bp)
{
        struct g_journal_softc *sc;

        sc = bp->bio_to->geom->softc;
        GJ_LOGREQ(3, bp, "Request received.");

        switch (bp->bio_cmd) {
        case BIO_READ:
        case BIO_WRITE:
                mtx_lock(&sc->sc_mtx);
                bioq_insert_tail(&sc->sc_regular_queue, bp);
                wakeup(sc);
                mtx_unlock(&sc->sc_mtx);
                return;
        case BIO_GETATTR:
                if (strcmp(bp->bio_attribute, "GJOURNAL::provider") == 0) {
                        strlcpy(bp->bio_data, bp->bio_to->name, bp->bio_length);
                        bp->bio_completed = strlen(bp->bio_to->name) + 1;
                        g_io_deliver(bp, 0);
                        return;
                }
                /* FALLTHROUGH */
        case BIO_DELETE:
        default:
                g_io_deliver(bp, EOPNOTSUPP);
                return;
        }
}

static void
g_journal_std_done(struct bio *bp)
{
        struct g_journal_softc *sc;

        sc = bp->bio_from->geom->softc;
        mtx_lock(&sc->sc_mtx);
        bioq_insert_tail(&sc->sc_back_queue, bp);
        wakeup(sc);
        mtx_unlock(&sc->sc_mtx);
}

static struct bio *
g_journal_new_bio(off_t start, off_t end, off_t joffset, u_char *data,
    int flags)
{
        struct bio *bp;

        bp = g_alloc_bio();
        bp->bio_offset = start;
        bp->bio_joffset = joffset;
        bp->bio_length = end - start;
        bp->bio_cmd = BIO_WRITE;
        bp->bio_done = g_journal_std_done;
        if (data == NULL)
                bp->bio_data = NULL;
        else {
                bp->bio_data = gj_malloc(bp->bio_length, flags);
                if (bp->bio_data != NULL)
                        bcopy(data, bp->bio_data, bp->bio_length);
        }
        return (bp);
}

#define g_journal_insert_bio(head, bp, flags)                           \
        g_journal_insert((head), (bp)->bio_offset,                      \
                (bp)->bio_offset + (bp)->bio_length, (bp)->bio_joffset, \
                (bp)->bio_data, flags)
/*
 * The function below does a lot more than just inserting bio to the queue.
 * It keeps the queue sorted by offset and ensures that there are no doubled
 * data (it combines bios where ranges overlap).
 *
 * The function returns the number of bios inserted (as bio can be splitted).
 */
static int
g_journal_insert(struct bio **head, off_t nstart, off_t nend, off_t joffset,
    u_char *data, int flags)
{
        struct bio *nbp, *cbp, *pbp;
        off_t cstart, cend;
        u_char *tmpdata;
        int n;

        GJ_DEBUG(3, "INSERT(%p): (%jd, %jd, %jd)", *head, nstart, nend,
            joffset);
        n = 0;
        pbp = NULL;
        GJQ_FOREACH(*head, cbp) {
                cstart = cbp->bio_offset;
                cend = cbp->bio_offset + cbp->bio_length;

                if (nstart >= cend) {
                        /*
                         *  +-------------+
                         *  |             |
                         *  |   current   |  +-------------+
                         *  |     bio     |  |             |
                         *  |             |  |     new     |
                         *  +-------------+  |     bio     |
                         *                   |             |
                         *                   +-------------+
                         */
                        GJ_DEBUG(3, "INSERT(%p): 1", *head);
                } else if (nend <= cstart) {
                        /*
                         *                   +-------------+
                         *                   |             |
                         *  +-------------+  |   current   |
                         *  |             |  |     bio     |
                         *  |     new     |  |             |
                         *  |     bio     |  +-------------+
                         *  |             |
                         *  +-------------+
                         */
                        nbp = g_journal_new_bio(nstart, nend, joffset, data,
                            flags);
                        if (pbp == NULL)
                                *head = nbp;
                        else
                                pbp->bio_next = nbp;
                        nbp->bio_next = cbp;
                        n++;
                        GJ_DEBUG(3, "INSERT(%p): 2 (nbp=%p pbp=%p)", *head, nbp,
                            pbp);
                        goto end;
                } else if (nstart <= cstart && nend >= cend) {
                        /*
                         *      +-------------+      +-------------+
                         *      | current bio |      | current bio |
                         *  +---+-------------+---+  +-------------+---+
                         *  |   |             |   |  |             |   |
                         *  |   |             |   |  |             |   |
                         *  |   +-------------+   |  +-------------+   |
                         *  |       new bio       |  |     new bio     |
                         *  +---------------------+  +-----------------+
                         *
                         *      +-------------+  +-------------+
                         *      | current bio |  | current bio |
                         *  +---+-------------+  +-------------+
                         *  |   |             |  |             |
                         *  |   |             |  |             |
                         *  |   +-------------+  +-------------+
                         *  |     new bio     |  |   new bio   |
                         *  +-----------------+  +-------------+
                         */
                        g_journal_stats_bytes_skipped += cbp->bio_length;
                        cbp->bio_offset = nstart;
                        cbp->bio_joffset = joffset;
                        cbp->bio_length = cend - nstart;
                        if (cbp->bio_data != NULL) {
                                gj_free(cbp->bio_data, cend - cstart);
                                cbp->bio_data = NULL;
                        }
                        if (data != NULL) {
                                cbp->bio_data = gj_malloc(cbp->bio_length,
                                    flags);
                                if (cbp->bio_data != NULL) {
                                        bcopy(data, cbp->bio_data,
                                            cbp->bio_length);
                                }
                                data += cend - nstart;
                        }
                        joffset += cend - nstart;
                        nstart = cend;
                        GJ_DEBUG(3, "INSERT(%p): 3 (cbp=%p)", *head, cbp);
                } else if (nstart > cstart && nend >= cend) {
                        /*
                         *  +-----------------+  +-------------+
                         *  |   current bio   |  | current bio |
                         *  |   +-------------+  |   +---------+---+
                         *  |   |             |  |   |         |   |
                         *  |   |             |  |   |         |   |
                         *  +---+-------------+  +---+---------+   |
                         *      |   new bio   |      |   new bio   |
                         *      +-------------+      +-------------+
                         */
                        g_journal_stats_bytes_skipped += cend - nstart;
                        nbp = g_journal_new_bio(nstart, cend, joffset, data,
                            flags);
                        nbp->bio_next = cbp->bio_next;
                        cbp->bio_next = nbp;
                        cbp->bio_length = nstart - cstart;
                        if (cbp->bio_data != NULL) {
                                cbp->bio_data = gj_realloc(cbp->bio_data,
                                    cbp->bio_length, cend - cstart);
                        }
                        if (data != NULL)
                                data += cend - nstart;
                        joffset += cend - nstart;
                        nstart = cend;
                        n++;
                        GJ_DEBUG(3, "INSERT(%p): 4 (cbp=%p)", *head, cbp);
                } else if (nstart > cstart && nend < cend) {
                        /*
                         *  +---------------------+
                         *  |     current bio     |
                         *  |   +-------------+   |
                         *  |   |             |   |
                         *  |   |             |   |
                         *  +---+-------------+---+
                         *      |   new bio   |
                         *      +-------------+
                         */
                        g_journal_stats_bytes_skipped += nend - nstart;
                        nbp = g_journal_new_bio(nstart, nend, joffset, data,
                            flags);
                        nbp->bio_next = cbp->bio_next;
                        cbp->bio_next = nbp;
                        if (cbp->bio_data == NULL)
                                tmpdata = NULL;
                        else
                                tmpdata = cbp->bio_data + nend - cstart;
                        nbp = g_journal_new_bio(nend, cend,
                            cbp->bio_joffset + nend - cstart, tmpdata, flags);
                        nbp->bio_next = ((struct bio *)cbp->bio_next)->bio_next;
                        ((struct bio *)cbp->bio_next)->bio_next = nbp;
                        cbp->bio_length = nstart - cstart;
                        if (cbp->bio_data != NULL) {
                                cbp->bio_data = gj_realloc(cbp->bio_data,
                                    cbp->bio_length, cend - cstart);
                        }
                        n += 2;
                        GJ_DEBUG(3, "INSERT(%p): 5 (cbp=%p)", *head, cbp);
                        goto end;
                } else if (nstart <= cstart && nend < cend) {
                        /*
                         *  +-----------------+      +-------------+
                         *  |   current bio   |      | current bio |
                         *  +-------------+   |  +---+---------+   |
                         *  |             |   |  |   |         |   |
                         *  |             |   |  |   |         |   |
                         *  +-------------+---+  |   +---------+---+
                         *  |   new bio   |      |   new bio   |
                         *  +-------------+      +-------------+
                         */
                        g_journal_stats_bytes_skipped += nend - nstart;
                        nbp = g_journal_new_bio(nstart, nend, joffset, data,
                            flags);
                        if (pbp == NULL)
                                *head = nbp;
                        else
                                pbp->bio_next = nbp;
                        nbp->bio_next = cbp;
                        cbp->bio_offset = nend;
                        cbp->bio_length = cend - nend;
                        cbp->bio_joffset += nend - cstart;
                        tmpdata = cbp->bio_data;
                        if (tmpdata != NULL) {
                                cbp->bio_data = gj_malloc(cbp->bio_length,
                                    flags);
                                if (cbp->bio_data != NULL) {
                                        bcopy(tmpdata + nend - cstart,
                                            cbp->bio_data, cbp->bio_length);
                                }
                                gj_free(tmpdata, cend - cstart);
                        }
                        n++;
                        GJ_DEBUG(3, "INSERT(%p): 6 (cbp=%p)", *head, cbp);
                        goto end;
                }
                if (nstart == nend)
                        goto end;
                pbp = cbp;
        }
        nbp = g_journal_new_bio(nstart, nend, joffset, data, flags);
        if (pbp == NULL)
                *head = nbp;
        else
                pbp->bio_next = nbp;
        nbp->bio_next = NULL;
        n++;
        GJ_DEBUG(3, "INSERT(%p): 8 (nbp=%p pbp=%p)", *head, nbp, pbp);
end:
        if (g_journal_debug >= 3) {
                GJQ_FOREACH(*head, cbp) {
                        GJ_DEBUG(3, "ELEMENT: %p (%jd, %jd, %jd, %p)", cbp,
                            (intmax_t)cbp->bio_offset,
                            (intmax_t)cbp->bio_length,
                            (intmax_t)cbp->bio_joffset, cbp->bio_data);
                }
                GJ_DEBUG(3, "INSERT(%p): DONE %d", *head, n);
        }
        return (n);
}

/*
 * The function combines neighbour bios trying to squeeze as much data as
 * possible into one bio.
 *
 * The function returns the number of bios combined (negative value).
 */
static int
g_journal_optimize(struct bio *head)
{
        struct bio *cbp, *pbp;
        int n;

        n = 0;
        pbp = NULL;
        GJQ_FOREACH(head, cbp) {
                /* Skip bios which has to be read first. */
                if (cbp->bio_data == NULL) {
                        pbp = NULL;
                        continue;
                }
                /* There is no previous bio yet. */
                if (pbp == NULL) {
                        pbp = cbp;
                        continue;
                }
                /* Is this a neighbour bio? */
                if (pbp->bio_offset + pbp->bio_length != cbp->bio_offset) {
                        /* Be sure that bios queue is sorted. */
                        KASSERT(pbp->bio_offset + pbp->bio_length < cbp->bio_offset,
                            ("poffset=%jd plength=%jd coffset=%jd",
                            (intmax_t)pbp->bio_offset,
                            (intmax_t)pbp->bio_length,
                            (intmax_t)cbp->bio_offset));
                        pbp = cbp;
                        continue;
                }
                /* Be sure we don't end up with too big bio. */
                if (pbp->bio_length + cbp->bio_length > MAXPHYS) {
                        pbp = cbp;
                        continue;
                }
                /* Ok, we can join bios. */
                GJ_LOGREQ(4, pbp, "Join: ");
                GJ_LOGREQ(4, cbp, "and: ");
                pbp->bio_data = gj_realloc(pbp->bio_data,
                    pbp->bio_length + cbp->bio_length, pbp->bio_length);
                bcopy(cbp->bio_data, pbp->bio_data + pbp->bio_length,
                    cbp->bio_length);
                gj_free(cbp->bio_data, cbp->bio_length);
                pbp->bio_length += cbp->bio_length;
                pbp->bio_next = cbp->bio_next;
                g_destroy_bio(cbp);
                cbp = pbp;
                g_journal_stats_combined_ios++;
                n--;
                GJ_LOGREQ(4, pbp, "Got: ");
        }
        return (n);
}

/*
 * TODO: Update comment.
 * These are functions responsible for copying one portion of data from journal
 * to the destination provider.
 * The order goes like this:
 * 1. Read the header, which contains informations about data blocks
 *    following it.
 * 2. Read the data blocks from the journal.
 * 3. Write the data blocks on the data provider.
 *
 * g_journal_copy_start()
 * g_journal_copy_done() - got finished write request, logs potential errors.
 */

/*
 * When there is no data in cache, this function is used to read it.
 */
static void
g_journal_read_first(struct g_journal_softc *sc, struct bio *bp)
{
        struct bio *cbp;

        /*
         * We were short in memory, so data was freed.
         * In that case we need to read it back from journal.
         */
        cbp = g_alloc_bio();
        cbp->bio_cflags = bp->bio_cflags;
        cbp->bio_parent = bp;
        cbp->bio_offset = bp->bio_joffset;
        cbp->bio_length = bp->bio_length;
        cbp->bio_data = gj_malloc(bp->bio_length, M_WAITOK);
        cbp->bio_cmd = BIO_READ;
        cbp->bio_done = g_journal_std_done;
        GJ_LOGREQ(4, cbp, "READ FIRST");
        g_io_request(cbp, sc->sc_jconsumer);
        g_journal_cache_misses++;
}

static void
g_journal_copy_send(struct g_journal_softc *sc)
{
        struct bio *bioq, *bp, *lbp;

        bioq = lbp = NULL;
        mtx_lock(&sc->sc_mtx);
        for (; sc->sc_copy_in_progress < g_journal_parallel_copies;) {
                bp = GJQ_FIRST(sc->sc_inactive.jj_queue);
                if (bp == NULL)
                        break;
                GJQ_REMOVE(sc->sc_inactive.jj_queue, bp);
                sc->sc_copy_in_progress++;
                GJQ_INSERT_AFTER(bioq, bp, lbp);
                lbp = bp;
        }
        mtx_unlock(&sc->sc_mtx);
        if (g_journal_do_optimize)
                sc->sc_copy_in_progress += g_journal_optimize(bioq);
        while ((bp = GJQ_FIRST(bioq)) != NULL) {
                GJQ_REMOVE(bioq, bp);
                GJQ_INSERT_HEAD(sc->sc_copy_queue, bp);
                bp->bio_cflags = GJ_BIO_COPY;
                if (bp->bio_data == NULL)
                        g_journal_read_first(sc, bp);
                else {
                        bp->bio_joffset = 0;
                        GJ_LOGREQ(4, bp, "SEND");
                        g_io_request(bp, sc->sc_dconsumer);
                }
        }
}

static void
g_journal_copy_start(struct g_journal_softc *sc)
{

        /*
         * Remember in metadata that we're starting to copy journaled data
         * to the data provider.
         * In case of power failure, we will copy these data once again on boot.
         */
        if (!sc->sc_journal_copying) {
                sc->sc_journal_copying = 1;
                GJ_DEBUG(1, "Starting copy of journal.");
                g_journal_metadata_update(sc);
        }
        g_journal_copy_send(sc);
}

/*
 * Data block has been read from the journal provider.
 */
static int
g_journal_copy_read_done(struct bio *bp)
{
        struct g_journal_softc *sc;
        struct g_consumer *cp;
        struct bio *pbp;

        KASSERT(bp->bio_cflags == GJ_BIO_COPY,
            ("Invalid bio (%d != %d).", bp->bio_cflags, GJ_BIO_COPY));

        sc = bp->bio_from->geom->softc;
        pbp = bp->bio_parent;

        if (bp->bio_error != 0) {
                GJ_DEBUG(0, "Error while reading data from %s (error=%d).",
                    bp->bio_to->name, bp->bio_error);
                /*
                 * We will not be able to deliver WRITE request as well.
                 */
                gj_free(bp->bio_data, bp->bio_length);
                g_destroy_bio(pbp);
                g_destroy_bio(bp);
                sc->sc_copy_in_progress--;
                return (1);
        }
        pbp->bio_data = bp->bio_data;
        cp = sc->sc_dconsumer;
        g_io_request(pbp, cp);
        GJ_LOGREQ(4, bp, "READ DONE");
        g_destroy_bio(bp);
        return (0);
}

/*
 * Data block has been written to the data provider.
 */
static void
g_journal_copy_write_done(struct bio *bp)
{
        struct g_journal_softc *sc;

        KASSERT(bp->bio_cflags == GJ_BIO_COPY,
            ("Invalid bio (%d != %d).", bp->bio_cflags, GJ_BIO_COPY));

        sc = bp->bio_from->geom->softc;
        sc->sc_copy_in_progress--;

        if (bp->bio_error != 0) {
                GJ_LOGREQ(0, bp, "[copy] Error while writing data (error=%d)",
                    bp->bio_error);
        }
        GJQ_REMOVE(sc->sc_copy_queue, bp);
        gj_free(bp->bio_data, bp->bio_length);
        GJ_LOGREQ(4, bp, "DONE");
        g_destroy_bio(bp);

        if (sc->sc_copy_in_progress == 0) {
                /*
                 * This was the last write request for this journal.
                 */
                GJ_DEBUG(1, "Data has been copied.");
                sc->sc_journal_copying = 0;
        }
}

static void g_journal_flush_done(struct bio *bp);

/*
 * Flush one record onto active journal provider.
 */
static void
g_journal_flush(struct g_journal_softc *sc)
{
        struct g_journal_record_header hdr;
        struct g_journal_entry *ent;
        struct g_provider *pp;
        struct bio **bioq;
        struct bio *bp, *fbp, *pbp;
        off_t joffset, size;
        u_char *data, hash[16];
        MD5_CTX ctx;
        u_int i;

        if (sc->sc_current_count == 0)
                return;

        size = 0;
        pp = sc->sc_jprovider;
        GJ_VALIDATE_OFFSET(sc->sc_journal_offset, sc);
        joffset = sc->sc_journal_offset;

        GJ_DEBUG(2, "Storing %d journal entries on %s at %jd.",
            sc->sc_current_count, pp->name, (intmax_t)joffset);

        /*
         * Store 'journal id', so we know to which journal this record belongs.
         */
        hdr.jrh_journal_id = sc->sc_journal_id;
        /* Could be less than g_journal_record_entries if called due timeout. */
        hdr.jrh_nentries = MIN(sc->sc_current_count, g_journal_record_entries);
        strlcpy(hdr.jrh_magic, GJ_RECORD_HEADER_MAGIC, sizeof(hdr.jrh_magic));

        bioq = &sc->sc_active.jj_queue;
        pbp = sc->sc_flush_queue;

        fbp = g_alloc_bio();
        fbp->bio_parent = NULL;
        fbp->bio_cflags = GJ_BIO_JOURNAL;
        fbp->bio_offset = -1;
        fbp->bio_joffset = joffset;
        fbp->bio_length = pp->sectorsize;
        fbp->bio_cmd = BIO_WRITE;
        fbp->bio_done = g_journal_std_done;
        GJQ_INSERT_AFTER(sc->sc_flush_queue, fbp, pbp);
        pbp = fbp;
        fbp->bio_to = pp;
        GJ_LOGREQ(4, fbp, "FLUSH_OUT");
        joffset += pp->sectorsize;
        sc->sc_flush_count++;
        if (sc->sc_flags & GJF_DEVICE_CHECKSUM)
                MD5Init(&ctx);

        for (i = 0; i < hdr.jrh_nentries; i++) {
                bp = sc->sc_current_queue;
                KASSERT(bp != NULL, ("NULL bp"));
                bp->bio_to = pp;
                GJ_LOGREQ(4, bp, "FLUSHED");
                sc->sc_current_queue = bp->bio_next;
                bp->bio_next = NULL;
                sc->sc_current_count--;

                /* Add to the header. */
                ent = &hdr.jrh_entries[i];
                ent->je_offset = bp->bio_offset;
                ent->je_joffset = joffset;
                ent->je_length = bp->bio_length;
                size += ent->je_length;

                data = bp->bio_data;
                if (sc->sc_flags & GJF_DEVICE_CHECKSUM)
                        MD5Update(&ctx, data, ent->je_length);
                bzero(bp, sizeof(*bp));
                bp->bio_cflags = GJ_BIO_JOURNAL;
                bp->bio_offset = ent->je_offset;
                bp->bio_joffset = ent->je_joffset;
                bp->bio_length = ent->je_length;
                bp->bio_data = data;
                bp->bio_cmd = BIO_WRITE;
                bp->bio_done = g_journal_std_done;
                GJQ_INSERT_AFTER(sc->sc_flush_queue, bp, pbp);
                pbp = bp;
                bp->bio_to = pp;
                GJ_LOGREQ(4, bp, "FLUSH_OUT");
                joffset += bp->bio_length;
                sc->sc_flush_count++;

                /*
                 * Add request to the active sc_journal_queue queue.
                 * This is our cache. After journal switch we don't have to
                 * read the data from the inactive journal, because we keep
                 * it in memory.
                 */
                g_journal_insert(bioq, ent->je_offset,
                    ent->je_offset + ent->je_length, ent->je_joffset, data,
                    M_NOWAIT);
        }

        /*
         * After all requests, store valid header.
         */
        data = gj_malloc(pp->sectorsize, M_WAITOK);
        if (sc->sc_flags & GJF_DEVICE_CHECKSUM) {
                MD5Final(hash, &ctx);
                bcopy(hash, hdr.jrh_sum, sizeof(hdr.jrh_sum));
        }
        g_journal_record_header_encode(&hdr, data);
        fbp->bio_data = data;

        sc->sc_journal_offset = joffset;

        g_journal_check_overflow(sc);
}

/*
 * Flush request finished.
 */
static void
g_journal_flush_done(struct bio *bp)
{
        struct g_journal_softc *sc;
        struct g_consumer *cp;

        KASSERT((bp->bio_cflags & GJ_BIO_MASK) == GJ_BIO_JOURNAL,
            ("Invalid bio (%d != %d).", bp->bio_cflags, GJ_BIO_JOURNAL));

        cp = bp->bio_from;
        sc = cp->geom->softc;
        sc->sc_flush_in_progress--;

        if (bp->bio_error != 0) {
                GJ_LOGREQ(0, bp, "[flush] Error while writing data (error=%d)",
                    bp->bio_error);
        }
        gj_free(bp->bio_data, bp->bio_length);
        GJ_LOGREQ(4, bp, "DONE");
        g_destroy_bio(bp);
}

static void g_journal_release_delayed(struct g_journal_softc *sc);

static void
g_journal_flush_send(struct g_journal_softc *sc)
{
        struct g_consumer *cp;
        struct bio *bioq, *bp, *lbp;

        cp = sc->sc_jconsumer;
        bioq = lbp = NULL;
        while (sc->sc_flush_in_progress < g_journal_parallel_flushes) {
                /* Send one flush requests to the active journal. */
                bp = GJQ_FIRST(sc->sc_flush_queue);
                if (bp != NULL) {
                        GJQ_REMOVE(sc->sc_flush_queue, bp);
                        sc->sc_flush_count--;
                        bp->bio_offset = bp->bio_joffset;
                        bp->bio_joffset = 0;
                        sc->sc_flush_in_progress++;
                        GJQ_INSERT_AFTER(bioq, bp, lbp);
                        lbp = bp;
                }
                /* Try to release delayed requests. */
                g_journal_release_delayed(sc);
                /* If there are no requests to flush, leave. */
                if (GJQ_FIRST(sc->sc_flush_queue) == NULL)
                        break;
        }
        if (g_journal_do_optimize)
                sc->sc_flush_in_progress += g_journal_optimize(bioq);
        while ((bp = GJQ_FIRST(bioq)) != NULL) {
                GJQ_REMOVE(bioq, bp);
                GJ_LOGREQ(3, bp, "Flush request send");
                g_io_request(bp, cp);
        }
}

static void
g_journal_add_current(struct g_journal_softc *sc, struct bio *bp)
{
        int n;

        GJ_LOGREQ(4, bp, "CURRENT %d", sc->sc_current_count);
        n = g_journal_insert_bio(&sc->sc_current_queue, bp, M_WAITOK);
        sc->sc_current_count += n;
        n = g_journal_optimize(sc->sc_current_queue);
        sc->sc_current_count += n;
        /*
         * For requests which are added to the current queue we deliver
         * response immediately.
         */
        bp->bio_completed = bp->bio_length;
        g_io_deliver(bp, 0);
        if (sc->sc_current_count >= g_journal_record_entries) {
                /*
                 * Let's flush one record onto active journal provider.
                 */
                g_journal_flush(sc);
        }
}

static void
g_journal_release_delayed(struct g_journal_softc *sc)
{
        struct bio *bp;

        for (;;) {
                /* The flush queue is full, exit. */
                if (sc->sc_flush_count >= g_journal_accept_immediately)
                        return;
                bp = bioq_takefirst(&sc->sc_delayed_queue);
                if (bp == NULL)
                        return;
                sc->sc_delayed_count--;
                g_journal_add_current(sc, bp);
        }
}

/*
 * Add I/O request to the current queue. If we have enough requests for one
 * journal record we flush them onto active journal provider.
 */
static void
g_journal_add_request(struct g_journal_softc *sc, struct bio *bp)
{

        /*
         * The flush queue is full, we need to delay the request.
         */
        if (sc->sc_delayed_count > 0 ||
            sc->sc_flush_count >= g_journal_accept_immediately) {
                GJ_LOGREQ(4, bp, "DELAYED");
                bioq_insert_tail(&sc->sc_delayed_queue, bp);
                sc->sc_delayed_count++;
                return;
        }

        KASSERT(TAILQ_EMPTY(&sc->sc_delayed_queue.queue),
            ("DELAYED queue not empty."));
        g_journal_add_current(sc, bp);
}

static void g_journal_read_done(struct bio *bp);

/*
 * Try to find requested data in cache.
 */
static struct bio *
g_journal_read_find(struct bio *head, int sorted, struct bio *pbp, off_t ostart,
    off_t oend)
{
        off_t cstart, cend;
        struct bio *bp;

        GJQ_FOREACH(head, bp) {
                if (bp->bio_offset == -1)
                        continue;
                cstart = MAX(ostart, bp->bio_offset);
                cend = MIN(oend, bp->bio_offset + bp->bio_length);
                if (cend <= ostart)
                        continue;
                else if (cstart >= oend) {
                        if (!sorted)
                                continue;
                        else {
                                bp = NULL;
                                break;
                        }
                }
                if (bp->bio_data == NULL)
                        break;
                GJ_DEBUG(3, "READ(%p): (%jd, %jd) (bp=%p)", head, cstart, cend,
                    bp);
                bcopy(bp->bio_data + cstart - bp->bio_offset,
                    pbp->bio_data + cstart - pbp->bio_offset, cend - cstart);
                pbp->bio_completed += cend - cstart;
                if (pbp->bio_completed == pbp->bio_length) {
                        /*
                         * Cool, the whole request was in cache, deliver happy
                         * message.
                         */
                        g_io_deliver(pbp, 0);
                        return (pbp);
                }
                break;
        }
        return (bp);
}

/*
 * Try to find requested data in cache.
 */
static struct bio *
g_journal_read_queue_find(struct bio_queue *head, struct bio *pbp, off_t ostart,
    off_t oend)
{
        off_t cstart, cend;
        struct bio *bp;

        TAILQ_FOREACH(bp, head, bio_queue) {
                cstart = MAX(ostart, bp->bio_offset);
                cend = MIN(oend, bp->bio_offset + bp->bio_length);
                if (cend <= ostart)
                        continue;
                else if (cstart >= oend)
                        continue;
                KASSERT(bp->bio_data != NULL,
                    ("%s: bio_data == NULL", __func__));
                GJ_DEBUG(3, "READ(%p): (%jd, %jd) (bp=%p)", head, cstart, cend,
                    bp);
                bcopy(bp->bio_data + cstart - bp->bio_offset,
                    pbp->bio_data + cstart - pbp->bio_offset, cend - cstart);
                pbp->bio_completed += cend - cstart;
                if (pbp->bio_completed == pbp->bio_length) {
                        /*
                         * Cool, the whole request was in cache, deliver happy
                         * message.
                         */
                        g_io_deliver(pbp, 0);
                        return (pbp);
                }
                break;
        }
        return (bp);
}

/*
 * This function is used for colecting data on read.
 * The complexity is because parts of the data can be stored in four different
 * places:
 * - in delayed requests
 * - in memory - the data not yet send to the active journal provider
 * - in requests which are going to be sent to the active journal
 * - in the active journal
 * - in the inactive journal
 * - in the data provider
 */
static void
g_journal_read(struct g_journal_softc *sc, struct bio *pbp, off_t ostart,
    off_t oend)
{
        struct bio *bp, *nbp, *head;
        off_t cstart, cend;
        u_int i, sorted = 0;

        GJ_DEBUG(3, "READ: (%jd, %jd)", ostart, oend);

        cstart = cend = -1;
        bp = NULL;
        head = NULL;
        for (i = 0; i <= 5; i++) {
                switch (i) {
                case 0: /* Delayed requests. */
                        head = NULL;
                        sorted = 0;
                        break;
                case 1: /* Not-yet-send data. */
                        head = sc->sc_current_queue;
                        sorted = 1;
                        break;
                case 2: /* In-flight to the active journal. */
                        head = sc->sc_flush_queue;
                        sorted = 0;
                        break;
                case 3: /* Active journal. */
                        head = sc->sc_active.jj_queue;
                        sorted = 1;
                        break;
                case 4: /* Inactive journal. */
                        /*
                         * XXX: Here could be a race with g_journal_lowmem().
                         */
                        head = sc->sc_inactive.jj_queue;
                        sorted = 1;
                        break;
                case 5: /* In-flight to the data provider. */
                        head = sc->sc_copy_queue;
                        sorted = 0;
                        break;
                default:
                        panic("gjournal %s: i=%d", __func__, i);
                }
                if (i == 0)
                        bp = g_journal_read_queue_find(&sc->sc_delayed_queue.queue, pbp, ostart, oend);
                else
                        bp = g_journal_read_find(head, sorted, pbp, ostart, oend);
                if (bp == pbp) { /* Got the whole request. */
                        GJ_DEBUG(2, "Got the whole request from %u.", i);
                        return;
                } else if (bp != NULL) {
                        cstart = MAX(ostart, bp->bio_offset);
                        cend = MIN(oend, bp->bio_offset + bp->bio_length);
                        GJ_DEBUG(2, "Got part of the request from %u (%jd-%jd).",
                            i, (intmax_t)cstart, (intmax_t)cend);
                        break;
                }
        }
        if (bp != NULL) {
                if (bp->bio_data == NULL) {
                        nbp = g_duplicate_bio(pbp);
                        nbp->bio_cflags = GJ_BIO_READ;
                        nbp->bio_data =
                            pbp->bio_data + cstart - pbp->bio_offset;
                        nbp->bio_offset =
                            bp->bio_joffset + cstart - bp->bio_offset;
                        nbp->bio_length = cend - cstart;
                        nbp->bio_done = g_journal_read_done;
                        g_io_request(nbp, sc->sc_jconsumer);
                }
                /*
                 * If we don't have the whole request yet, call g_journal_read()
                 * recursively.
                 */
                if (ostart < cstart)
                        g_journal_read(sc, pbp, ostart, cstart);
                if (oend > cend)
                        g_journal_read(sc, pbp, cend, oend);
        } else {
                /*
                 * No data in memory, no data in journal.
                 * Its time for asking data provider.
                 */
                GJ_DEBUG(3, "READ(data): (%jd, %jd)", ostart, oend);
                nbp = g_duplicate_bio(pbp);
                nbp->bio_cflags = GJ_BIO_READ;
                nbp->bio_data = pbp->bio_data + ostart - pbp->bio_offset;
                nbp->bio_offset = ostart;
                nbp->bio_length = oend - ostart;
                nbp->bio_done = g_journal_read_done;
                g_io_request(nbp, sc->sc_dconsumer);
                /* We have the whole request, return here. */
                return;
        }
}

/*
 * Function responsible for handling finished READ requests.
 * Actually, g_std_done() could be used here, the only difference is that we
 * log error.
 */
static void
g_journal_read_done(struct bio *bp)
{
        struct bio *pbp;

        KASSERT(bp->bio_cflags == GJ_BIO_READ,
            ("Invalid bio (%d != %d).", bp->bio_cflags, GJ_BIO_READ));

        pbp = bp->bio_parent;
        pbp->bio_inbed++;
        pbp->bio_completed += bp->bio_length;

        if (bp->bio_error != 0) {
                if (pbp->bio_error == 0)
                        pbp->bio_error = bp->bio_error;
                GJ_DEBUG(0, "Error while reading data from %s (error=%d).",
                    bp->bio_to->name, bp->bio_error);
        }
        g_destroy_bio(bp);
        if (pbp->bio_children == pbp->bio_inbed &&
            pbp->bio_completed == pbp->bio_length) {
                /* We're done. */
                g_io_deliver(pbp, 0);
        }
}

/*
 * Deactive current journal and active next one.
 */
static void
g_journal_switch(struct g_journal_softc *sc)
{
        struct g_provider *pp;

        if (JEMPTY(sc)) {
                GJ_DEBUG(3, "No need for %s switch.", sc->sc_name);
                pp = LIST_FIRST(&sc->sc_geom->provider);
                if (!(sc->sc_flags & GJF_DEVICE_CLEAN) && pp->acw == 0) {
                        sc->sc_flags |= GJF_DEVICE_CLEAN;
                        GJ_DEBUG(1, "Marking %s as clean.", sc->sc_name);
                        g_journal_metadata_update(sc);
                }
        } else {
                GJ_DEBUG(3, "Switching journal %s.", sc->sc_geom->name);

                pp = sc->sc_jprovider;

                sc->sc_journal_previous_id = sc->sc_journal_id;

                sc->sc_journal_id = sc->sc_journal_next_id;
                sc->sc_journal_next_id = arc4random();

                GJ_VALIDATE_OFFSET(sc->sc_journal_offset, sc);

                g_journal_write_header(sc);

                sc->sc_inactive.jj_offset = sc->sc_active.jj_offset;
                sc->sc_inactive.jj_queue = sc->sc_active.jj_queue;

                sc->sc_active.jj_offset =
                    sc->sc_journal_offset - pp->sectorsize;
                sc->sc_active.jj_queue = NULL;

                /*
                 * Switch is done, start copying data from the (now) inactive
                 * journal to the data provider.
                 */
                g_journal_copy_start(sc);
        }
        mtx_lock(&sc->sc_mtx);
        sc->sc_flags &= ~GJF_DEVICE_SWITCH;
        mtx_unlock(&sc->sc_mtx);
}

static void
g_journal_initialize(struct g_journal_softc *sc)
{

        sc->sc_journal_id = arc4random();
        sc->sc_journal_next_id = arc4random();
        sc->sc_journal_previous_id = sc->sc_journal_id;
        sc->sc_journal_offset = sc->sc_jstart;
        sc->sc_inactive.jj_offset = sc->sc_jstart;
        g_journal_write_header(sc);
        sc->sc_active.jj_offset = sc->sc_jstart;
}

static void
g_journal_mark_as_dirty(struct g_journal_softc *sc)
{
        const struct g_journal_desc *desc;
        int i;

        GJ_DEBUG(1, "Marking file system %s as dirty.", sc->sc_name);
        for (i = 0; (desc = g_journal_filesystems[i]) != NULL; i++)
                desc->jd_dirty(sc->sc_dconsumer);
}

/*
 * Function read record header from the given journal.
 * It is very simlar to g_read_data(9), but it doesn't allocate memory for bio
 * and data on every call.
 */
static int
g_journal_sync_read(struct g_consumer *cp, struct bio *bp, off_t offset,
    void *data)
{
        int error;

        bzero(bp, sizeof(*bp));
        bp->bio_cmd = BIO_READ;
        bp->bio_done = NULL;
        bp->bio_offset = offset;
        bp->bio_length = cp->provider->sectorsize;
        bp->bio_data = data;
        g_io_request(bp, cp);
        error = biowait(bp, "gjs_read");
        return (error);
}

#if 0
/*
 * Function is called when we start the journal device and we detect that
 * one of the journals was not fully copied.
 * The purpose of this function is to read all records headers from journal
 * and placed them in the inactive queue, so we can start journal
 * synchronization process and the journal provider itself.
 * Design decision was taken to not synchronize the whole journal here as it
 * can take too much time. Reading headers only and delaying synchronization
 * process until after journal provider is started should be the best choice.
 */
#endif

static void
g_journal_sync(struct g_journal_softc *sc)
{
        struct g_journal_record_header rhdr;
        struct g_journal_entry *ent;
        struct g_journal_header jhdr;
        struct g_consumer *cp;
        struct bio *bp, *fbp, *tbp;
        off_t joffset, offset;
        u_char *buf, sum[16];
        uint64_t id;
        MD5_CTX ctx;
        int error, found, i;

        found = 0;
        fbp = NULL;
        cp = sc->sc_jconsumer;
        bp = g_alloc_bio();
        buf = gj_malloc(cp->provider->sectorsize, M_WAITOK);
        offset = joffset = sc->sc_inactive.jj_offset = sc->sc_journal_offset;

        GJ_DEBUG(2, "Looking for termination at %jd.", (intmax_t)joffset);

        /*
         * Read and decode first journal header.
         */
        error = g_journal_sync_read(cp, bp, offset, buf);
        if (error != 0) {
                GJ_DEBUG(0, "Error while reading journal header from %s.",
                    cp->provider->name);
                goto end;
        }
        error = g_journal_header_decode(buf, &jhdr);
        if (error != 0) {
                GJ_DEBUG(0, "Cannot decode journal header from %s.",
                    cp->provider->name);
                goto end;
        }
        id = sc->sc_journal_id;
        if (jhdr.jh_journal_id != sc->sc_journal_id) {
                GJ_DEBUG(1, "Journal ID mismatch at %jd (0x%08x != 0x%08x).",
                    (intmax_t)offset, (u_int)jhdr.jh_journal_id, (u_int)id);
                goto end;
        }
        offset += cp->provider->sectorsize;
        id = sc->sc_journal_next_id = jhdr.jh_journal_next_id;

        for (;;) {
                /*
                 * If the biggest record won't fit, look for a record header or
                 * journal header from the begining.
                 */
                GJ_VALIDATE_OFFSET(offset, sc);
                error = g_journal_sync_read(cp, bp, offset, buf);
                if (error != 0) {
                        /*
                         * Not good. Having an error while reading header
                         * means, that we cannot read next headers and in
                         * consequence we cannot find termination.
                         */
                        GJ_DEBUG(0,
                            "Error while reading record header from %s.",
                            cp->provider->name);
                        break;
                }

                error = g_journal_record_header_decode(buf, &rhdr);
                if (error != 0) {
                        GJ_DEBUG(2, "Not a record header at %jd (error=%d).",
                            (intmax_t)offset, error);
                        /*
                         * This is not a record header.
                         * If we are lucky, this is next journal header.
                         */
                        error = g_journal_header_decode(buf, &jhdr);
                        if (error != 0) {
                                GJ_DEBUG(1, "Not a journal header at %jd (error=%d).",
                                    (intmax_t)offset, error);
                                /*
                                 * Nope, this is not journal header, which
                                 * bascially means that journal is not
                                 * terminated properly.
                                 */
                                error = ENOENT;
                                break;
                        }
                        /*
                         * Ok. This is header of _some_ journal. Now we need to
                         * verify if this is header of the _next_ journal.
                         */
                        if (jhdr.jh_journal_id != id) {
                                GJ_DEBUG(1, "Journal ID mismatch at %jd "
                                    "(0x%08x != 0x%08x).", (intmax_t)offset,
                                    (u_int)jhdr.jh_journal_id, (u_int)id);
                                error = ENOENT;
                                break;
                        }

                        /* Found termination. */
                        found++;
                        GJ_DEBUG(1, "Found termination at %jd (id=0x%08x).",
                            (intmax_t)offset, (u_int)id);
                        sc->sc_active.jj_offset = offset;
                        sc->sc_journal_offset =
                            offset + cp->provider->sectorsize;
                        sc->sc_journal_id = id;
                        id = sc->sc_journal_next_id = jhdr.jh_journal_next_id;

                        while ((tbp = fbp) != NULL) {
                                fbp = tbp->bio_next;
                                GJ_LOGREQ(3, tbp, "Adding request.");
                                g_journal_insert_bio(&sc->sc_inactive.jj_queue,
                                    tbp, M_WAITOK);
                        }

                        /* Skip journal's header. */
                        offset += cp->provider->sectorsize;
                        continue;
                }

                /* Skip record's header. */
                offset += cp->provider->sectorsize;

                /*
                 * Add information about every record entry to the inactive
                 * queue.
                 */
                if (sc->sc_flags & GJF_DEVICE_CHECKSUM)
                        MD5Init(&ctx);
                for (i = 0; i < rhdr.jrh_nentries; i++) {
                        ent = &rhdr.jrh_entries[i];
                        GJ_DEBUG(3, "Insert entry: %jd %jd.",
                            (intmax_t)ent->je_offset, (intmax_t)ent->je_length);
                        g_journal_insert(&fbp, ent->je_offset,
                            ent->je_offset + ent->je_length, ent->je_joffset,
                            NULL, M_WAITOK);
                        if (sc->sc_flags & GJF_DEVICE_CHECKSUM) {
                                u_char *buf2;

                                /*
                                 * TODO: Should use faster function (like
                                 *       g_journal_sync_read()).
                                 */
                                buf2 = g_read_data(cp, offset, ent->je_length,
                                    NULL);
                                if (buf2 == NULL)
                                        GJ_DEBUG(0, "Cannot read data at %jd.",
                                            (intmax_t)offset);
                                else {
                                        MD5Update(&ctx, buf2, ent->je_length);
                                        g_free(buf2);
                                }
                        }
                        /* Skip entry's data. */
                        offset += ent->je_length;
                }
                if (sc->sc_flags & GJF_DEVICE_CHECKSUM) {
                        MD5Final(sum, &ctx);
                        if (bcmp(sum, rhdr.jrh_sum, sizeof(rhdr.jrh_sum)) != 0) {
                                GJ_DEBUG(0, "MD5 hash mismatch at %jd!",
                                    (intmax_t)offset);
                        }
                }
        }
end:
        gj_free(bp->bio_data, cp->provider->sectorsize);
        g_destroy_bio(bp);

        /* Remove bios from unterminated journal. */
        while ((tbp = fbp) != NULL) {
                fbp = tbp->bio_next;
                g_destroy_bio(tbp);
        }

        if (found < 1 && joffset > 0) {
                GJ_DEBUG(0, "Journal on %s is broken/corrupted. Initializing.",
                    sc->sc_name);
                while ((tbp = sc->sc_inactive.jj_queue) != NULL) {
                        sc->sc_inactive.jj_queue = tbp->bio_next;
                        g_destroy_bio(tbp);
                }
                g_journal_initialize(sc);
                g_journal_mark_as_dirty(sc);
        } else {
                GJ_DEBUG(0, "Journal %s consistent.", sc->sc_name);
                g_journal_copy_start(sc);
        }
}

/*
 * Wait for requests.
 * If we have requests in the current queue, flush them after 3 seconds from the
 * last flush. In this way we don't wait forever (or for journal switch) with
 * storing not full records on journal.
 */
static void
g_journal_wait(struct g_journal_softc *sc, time_t last_write)
{
        int error, timeout;

        GJ_DEBUG(3, "%s: enter", __func__);
        if (sc->sc_current_count == 0) {
                if (g_journal_debug < 2)
                        msleep(sc, &sc->sc_mtx, PRIBIO | PDROP, "gj:work", 0);
                else {
                        /*
                         * If we have debug turned on, show number of elements
                         * in various queues.
                         */
                        for (;;) {
                                error = msleep(sc, &sc->sc_mtx, PRIBIO,
                                    "gj:work", hz * 3);
                                if (error == 0) {
                                        mtx_unlock(&sc->sc_mtx);
                                        break;
                                }
                                GJ_DEBUG(3, "Report: current count=%d",
                                    sc->sc_current_count);
                                GJ_DEBUG(3, "Report: flush count=%d",
                                    sc->sc_flush_count);
                                GJ_DEBUG(3, "Report: flush in progress=%d",
                                    sc->sc_flush_in_progress);
                                GJ_DEBUG(3, "Report: copy in progress=%d",
                                    sc->sc_copy_in_progress);
                                GJ_DEBUG(3, "Report: delayed=%d",
                                    sc->sc_delayed_count);
                        }
                }
                GJ_DEBUG(3, "%s: exit 1", __func__);
                return;
        }

        /*
         * Flush even not full records every 3 seconds.
         */
        timeout = (last_write + 3 - time_second) * hz;
        if (timeout <= 0) {
                mtx_unlock(&sc->sc_mtx);
                g_journal_flush(sc);
                g_journal_flush_send(sc);
                GJ_DEBUG(3, "%s: exit 2", __func__);
                return;
        }
        error = msleep(sc, &sc->sc_mtx, PRIBIO | PDROP, "gj:work", timeout);
        if (error == EWOULDBLOCK)
                g_journal_flush_send(sc);
        GJ_DEBUG(3, "%s: exit 3", __func__);
}

/*
 * Worker thread.
 */
static void
g_journal_worker(void *arg)
{
        struct g_journal_softc *sc;
        struct g_geom *gp;
        struct g_provider *pp;
        struct bio *bp;
        time_t last_write;
        int type;

        thread_lock(curthread);
        sched_prio(curthread, PRIBIO);
        thread_unlock(curthread);

        sc = arg;
        type = 0;       /* gcc */

        if (sc->sc_flags & GJF_DEVICE_CLEAN) {
                GJ_DEBUG(0, "Journal %s clean.", sc->sc_name);
                g_journal_initialize(sc);
        } else {
                g_journal_sync(sc);
        }
        /*
         * Check if we can use BIO_FLUSH.
         */
        sc->sc_bio_flush = 0;
        if (g_io_flush(sc->sc_jconsumer) == 0) {
                sc->sc_bio_flush |= GJ_FLUSH_JOURNAL;
                GJ_DEBUG(1, "BIO_FLUSH supported by %s.",
                    sc->sc_jconsumer->provider->name);
        } else {
                GJ_DEBUG(0, "BIO_FLUSH not supported by %s.",
                    sc->sc_jconsumer->provider->name);
        }
        if (sc->sc_jconsumer != sc->sc_dconsumer) {
                if (g_io_flush(sc->sc_dconsumer) == 0) {
                        sc->sc_bio_flush |= GJ_FLUSH_DATA;
                        GJ_DEBUG(1, "BIO_FLUSH supported by %s.",
                            sc->sc_dconsumer->provider->name);
                } else {
                        GJ_DEBUG(0, "BIO_FLUSH not supported by %s.",
                            sc->sc_dconsumer->provider->name);
                }
        }

        gp = sc->sc_geom;
        g_topology_lock();
        pp = g_new_providerf(gp, "%s.journal", sc->sc_name);
        pp->mediasize = sc->sc_mediasize;
        /*
         * There could be a problem when data provider and journal providers
         * have different sectorsize, but such scenario is prevented on journal
         * creation.
         */
        pp->sectorsize = sc->sc_sectorsize;
        g_error_provider(pp, 0);
        g_topology_unlock();
        last_write = time_second;

        if (sc->sc_rootmount != NULL) {
                GJ_DEBUG(1, "root_mount_rel %p", sc->sc_rootmount);
                root_mount_rel(sc->sc_rootmount);
                sc->sc_rootmount = NULL;
        }

        for (;;) {
                /* Get first request from the queue. */
                mtx_lock(&sc->sc_mtx);
                bp = bioq_first(&sc->sc_back_queue);
                if (bp != NULL)
                        type = (bp->bio_cflags & GJ_BIO_MASK);
                if (bp == NULL) {
                        bp = bioq_first(&sc->sc_regular_queue);
                        if (bp != NULL)
                                type = GJ_BIO_REGULAR;
                }
                if (bp == NULL) {
try_switch:
                        if ((sc->sc_flags & GJF_DEVICE_SWITCH) ||
                            (sc->sc_flags & GJF_DEVICE_DESTROY)) {
                                if (sc->sc_current_count > 0) {
                                        mtx_unlock(&sc->sc_mtx);
                                        g_journal_flush(sc);
                                        g_journal_flush_send(sc);
                                        continue;
                                }
                                if (sc->sc_flush_in_progress > 0)
                                        goto sleep;
                                if (sc->sc_copy_in_progress > 0)
                                        goto sleep;
                        }
                        if (sc->sc_flags & GJF_DEVICE_SWITCH) {
                                mtx_unlock(&sc->sc_mtx);
                                g_journal_switch(sc);
                                wakeup(&sc->sc_journal_copying);
                                continue;
                        }
                        if (sc->sc_flags & GJF_DEVICE_DESTROY) {
                                GJ_DEBUG(1, "Shutting down worker "
                                    "thread for %s.", gp->name);
                                sc->sc_worker = NULL;
                                wakeup(&sc->sc_worker);
                                mtx_unlock(&sc->sc_mtx);
                                kproc_exit(0);
                        }
sleep:
                        g_journal_wait(sc, last_write);
                        continue;
                }
                /*
                 * If we're in switch process, we need to delay all new
                 * write requests until its done.
                 */
                if ((sc->sc_flags & GJF_DEVICE_SWITCH) &&
                    type == GJ_BIO_REGULAR && bp->bio_cmd == BIO_WRITE) {
                        GJ_LOGREQ(2, bp, "WRITE on SWITCH");
                        goto try_switch;
                }
                if (type == GJ_BIO_REGULAR)
                        bioq_remove(&sc->sc_regular_queue, bp);
                else
                        bioq_remove(&sc->sc_back_queue, bp);
                mtx_unlock(&sc->sc_mtx);
                switch (type) {
                case GJ_BIO_REGULAR:
                        /* Regular request. */
                        switch (bp->bio_cmd) {
                        case BIO_READ:
                                g_journal_read(sc, bp, bp->bio_offset,
                                    bp->bio_offset + bp->bio_length);
                                break;
                        case BIO_WRITE:
                                last_write = time_second;
                                g_journal_add_request(sc, bp);
                                g_journal_flush_send(sc);
                                break;
                        default:
                                panic("Invalid bio_cmd (%d).", bp->bio_cmd);
                        }
                        break;
                case GJ_BIO_COPY:
                        switch (bp->bio_cmd) {
                        case BIO_READ:
                                if (g_journal_copy_read_done(bp))
                                        g_journal_copy_send(sc);
                                break;
                        case BIO_WRITE:
                                g_journal_copy_write_done(bp);
                                g_journal_copy_send(sc);
                                break;
                        default:
                                panic("Invalid bio_cmd (%d).", bp->bio_cmd);
                        }
                        break;
                case GJ_BIO_JOURNAL:
                        g_journal_flush_done(bp);
                        g_journal_flush_send(sc);
                        break;
                case GJ_BIO_READ:
                default:
                        panic("Invalid bio (%d).", type);
                }
        }
}

static void
g_journal_destroy_event(void *arg, int flags __unused)
{
        struct g_journal_softc *sc;

        g_topology_assert();
        sc = arg;
        g_journal_destroy(sc);
}

static void
g_journal_timeout(void *arg)
{
        struct g_journal_softc *sc;

        sc = arg;
        GJ_DEBUG(0, "Timeout. Journal %s cannot be completed.",
            sc->sc_geom->name);
        g_post_event(g_journal_destroy_event, sc, M_NOWAIT, NULL);
}

static struct g_geom *
g_journal_create(struct g_class *mp, struct g_provider *pp,
    const struct g_journal_metadata *md)
{
        struct g_journal_softc *sc;
        struct g_geom *gp;
        struct g_consumer *cp;
        int error;

        sc = NULL;      /* gcc */

        g_topology_assert();
        /*
         * There are two possibilities:
         * 1. Data and both journals are on the same provider.
         * 2. Data and journals are all on separated providers.
         */
        /* Look for journal device with the same ID. */
        LIST_FOREACH(gp, &mp->geom, geom) {
                sc = gp->softc;
                if (sc == NULL)
                        continue;
                if (sc->sc_id == md->md_id)
                        break;
        }
        if (gp == NULL)
                sc = NULL;
        else if (sc != NULL && (sc->sc_type & md->md_type) != 0) {
                GJ_DEBUG(1, "Journal device %u already configured.", sc->sc_id);
                return (NULL);
        }
        if (md->md_type == 0 || (md->md_type & ~GJ_TYPE_COMPLETE) != 0) {
                GJ_DEBUG(0, "Invalid type on %s.", pp->name);
                return (NULL);
        }
        if (md->md_type & GJ_TYPE_DATA) {
                GJ_DEBUG(0, "Journal %u: %s contains data.", md->md_id,
                    pp->name);
        }
        if (md->md_type & GJ_TYPE_JOURNAL) {
                GJ_DEBUG(0, "Journal %u: %s contains journal.", md->md_id,
                    pp->name);
        }

        if (sc == NULL) {
                /* Action geom. */
                sc = malloc(sizeof(*sc), M_JOURNAL, M_WAITOK | M_ZERO);
                sc->sc_id = md->md_id;
                sc->sc_type = 0;
                sc->sc_flags = 0;
                sc->sc_worker = NULL;

                gp = g_new_geomf(mp, "gjournal %u", sc->sc_id);
                gp->start = g_journal_start;
                gp->orphan = g_journal_orphan;
                gp->access = g_journal_access;
                gp->softc = sc;
                gp->flags |= G_GEOM_VOLATILE_BIO;
                sc->sc_geom = gp;

                mtx_init(&sc->sc_mtx, "gjournal", NULL, MTX_DEF);

                bioq_init(&sc->sc_back_queue);
                bioq_init(&sc->sc_regular_queue);
                bioq_init(&sc->sc_delayed_queue);
                sc->sc_delayed_count = 0;
                sc->sc_current_queue = NULL;
                sc->sc_current_count = 0;
                sc->sc_flush_queue = NULL;
                sc->sc_flush_count = 0;
                sc->sc_flush_in_progress = 0;
                sc->sc_copy_queue = NULL;
                sc->sc_copy_in_progress = 0;
                sc->sc_inactive.jj_queue = NULL;
                sc->sc_active.jj_queue = NULL;

                sc->sc_rootmount = root_mount_hold("GJOURNAL");
                GJ_DEBUG(1, "root_mount_hold %p", sc->sc_rootmount);

                callout_init(&sc->sc_callout, CALLOUT_MPSAFE);
                if (md->md_type != GJ_TYPE_COMPLETE) {
                        /*
                         * Journal and data are on separate providers.
                         * At this point we have only one of them.
                         * We setup a timeout in case the other part will not
                         * appear, so we won't wait forever.
                         */
                        callout_reset(&sc->sc_callout, 5 * hz,
                            g_journal_timeout, sc);
                }
        }

        /* Remember type of the data provider. */
        if (md->md_type & GJ_TYPE_DATA)
                sc->sc_orig_type = md->md_type;
        sc->sc_type |= md->md_type;
        cp = NULL;

        if (md->md_type & GJ_TYPE_DATA) {
                if (md->md_flags & GJ_FLAG_CLEAN)
                        sc->sc_flags |= GJF_DEVICE_CLEAN;
                if (md->md_flags & GJ_FLAG_CHECKSUM)
                        sc->sc_flags |= GJF_DEVICE_CHECKSUM;
                cp = g_new_consumer(gp);
                error = g_attach(cp, pp);
                KASSERT(error == 0, ("Cannot attach to %s (error=%d).",
                    pp->name, error));
                error = g_access(cp, 1, 1, 1);
                if (error != 0) {
                        GJ_DEBUG(0, "Cannot access %s (error=%d).", pp->name,
                            error);
                        g_journal_destroy(sc);
                        return (NULL);
                }
                sc->sc_dconsumer = cp;
                sc->sc_mediasize = pp->mediasize - pp->sectorsize;
                sc->sc_sectorsize = pp->sectorsize;
                sc->sc_jstart = md->md_jstart;
                sc->sc_jend = md->md_jend;
                if (md->md_provider[0] != '\0')
                        sc->sc_flags |= GJF_DEVICE_HARDCODED;
                sc->sc_journal_offset = md->md_joffset;
                sc->sc_journal_id = md->md_jid;
                sc->sc_journal_previous_id = md->md_jid;
        }
        if (md->md_type & GJ_TYPE_JOURNAL) {
                if (cp == NULL) {
                        cp = g_new_consumer(gp);
                        error = g_attach(cp, pp);
                        KASSERT(error == 0, ("Cannot attach to %s (error=%d).",
                            pp->name, error));
                        error = g_access(cp, 1, 1, 1);
                        if (error != 0) {
                                GJ_DEBUG(0, "Cannot access %s (error=%d).",
                                    pp->name, error);
                                g_journal_destroy(sc);
                                return (NULL);
                        }
                } else {
                        /*
                         * Journal is on the same provider as data, which means
                         * that data provider ends where journal starts.
                         */
                        sc->sc_mediasize = md->md_jstart;
                }
                sc->sc_jconsumer = cp;
        }

        if ((sc->sc_type & GJ_TYPE_COMPLETE) != GJ_TYPE_COMPLETE) {
                /* Journal is not complete yet. */
                return (gp);
        } else {
                /* Journal complete, cancel timeout. */
                callout_drain(&sc->sc_callout);
        }

        error = kproc_create(g_journal_worker, sc, &sc->sc_worker, 0, 0,
            "g_journal %s", sc->sc_name);
        if (error != 0) {
                GJ_DEBUG(0, "Cannot create worker thread for %s.journal.",
                    sc->sc_name);
                g_journal_destroy(sc);
                return (NULL);
        }

        return (gp);
}

static void
g_journal_destroy_consumer(void *arg, int flags __unused)
{
        struct g_consumer *cp;

        g_topology_assert();
        cp = arg;
        g_detach(cp);
        g_destroy_consumer(cp);
}

static int
g_journal_destroy(struct g_journal_softc *sc)
{
        struct g_geom *gp;
        struct g_provider *pp;
        struct g_consumer *cp;

        g_topology_assert();

        if (sc == NULL)
                return (ENXIO);

        gp = sc->sc_geom;
        pp = LIST_FIRST(&gp->provider);
        if (pp != NULL) {
                if (pp->acr != 0 || pp->acw != 0 || pp->ace != 0) {
                        GJ_DEBUG(1, "Device %s is still open (r%dw%de%d).",
                            pp->name, pp->acr, pp->acw, pp->ace);
                        return (EBUSY);
                }
                g_error_provider(pp, ENXIO);

                g_journal_flush(sc);
                g_journal_flush_send(sc);
                g_journal_switch(sc);
        }

        sc->sc_flags |= (GJF_DEVICE_DESTROY | GJF_DEVICE_CLEAN);

        g_topology_unlock();

        if (sc->sc_rootmount != NULL) {
                GJ_DEBUG(1, "root_mount_rel %p", sc->sc_rootmount);
                root_mount_rel(sc->sc_rootmount);
                sc->sc_rootmount = NULL;
        }

        callout_drain(&sc->sc_callout);
        mtx_lock(&sc->sc_mtx);
        wakeup(sc);
        while (sc->sc_worker != NULL)
                msleep(&sc->sc_worker, &sc->sc_mtx, PRIBIO, "gj:destroy", 0);
        mtx_unlock(&sc->sc_mtx);

        if (pp != NULL) {
                GJ_DEBUG(1, "Marking %s as clean.", sc->sc_name);
                g_journal_metadata_update(sc);
                g_topology_lock();
                pp->flags |= G_PF_WITHER;
                g_orphan_provider(pp, ENXIO);
        } else {
                g_topology_lock();
        }
        mtx_destroy(&sc->sc_mtx);

        if (sc->sc_current_count != 0) {
                GJ_DEBUG(0, "Warning! Number of current requests %d.",
                    sc->sc_current_count);
        }

        LIST_FOREACH(cp, &gp->consumer, consumer) {
                if (cp->acr + cp->acw + cp->ace > 0)
                        g_access(cp, -1, -1, -1);
                /*
                 * We keep all consumers open for writting, so if I'll detach
                 * and destroy consumer here, I'll get providers for taste, so
                 * journal will be started again.
                 * Sending an event here, prevents this from happening.
                 */
                g_post_event(g_journal_destroy_consumer, cp, M_WAITOK, NULL);
        }
        gp->softc = NULL;
        g_wither_geom(gp, ENXIO);
        free(sc, M_JOURNAL);
        return (0);
}

static void
g_journal_taste_orphan(struct g_consumer *cp)
{

        KASSERT(1 == 0, ("%s called while tasting %s.", __func__,
            cp->provider->name));
}

static struct g_geom *
g_journal_taste(struct g_class *mp, struct g_provider *pp, int flags __unused)
{
        struct g_journal_metadata md;
        struct g_consumer *cp;
        struct g_geom *gp;
        int error;

        g_topology_assert();
        g_trace(G_T_TOPOLOGY, "%s(%s, %s)", __func__, mp->name, pp->name);
        GJ_DEBUG(2, "Tasting %s.", pp->name);
        if (pp->geom->class == mp)
                return (NULL);

        gp = g_new_geomf(mp, "journal:taste");
        /* This orphan function should be never called. */
        gp->orphan = g_journal_taste_orphan;
        cp = g_new_consumer(gp);
        g_attach(cp, pp);
        error = g_journal_metadata_read(cp, &md);
        g_detach(cp);
        g_destroy_consumer(cp);
        g_destroy_geom(gp);
        if (error != 0)
                return (NULL);
        gp = NULL;

        if (md.md_provider[0] != '\0' &&
            !g_compare_names(md.md_provider, pp->name))
                return (NULL);
        if (md.md_provsize != 0 && md.md_provsize != pp->mediasize)
                return (NULL);
        if (g_journal_debug >= 2)
                journal_metadata_dump(&md);

        gp = g_journal_create(mp, pp, &md);
        return (gp);
}

static struct g_journal_softc *
g_journal_find_device(struct g_class *mp, const char *name)
{
        struct g_journal_softc *sc;
        struct g_geom *gp;
        struct g_provider *pp;

        if (strncmp(name, "/dev/", 5) == 0)
                name += 5;
        LIST_FOREACH(gp, &mp->geom, geom) {
                sc = gp->softc;
                if (sc == NULL)
                        continue;
                if (sc->sc_flags & GJF_DEVICE_DESTROY)
                        continue;
                if ((sc->sc_type & GJ_TYPE_COMPLETE) != GJ_TYPE_COMPLETE)
                        continue;
                pp = LIST_FIRST(&gp->provider);
                if (strcmp(sc->sc_name, name) == 0)
                        return (sc);
                if (pp != NULL && strcmp(pp->name, name) == 0)
                        return (sc);
        }
        return (NULL);
}

static void
g_journal_ctl_destroy(struct gctl_req *req, struct g_class *mp)
{
        struct g_journal_softc *sc;
        const char *name;
        char param[16];
        int *nargs;
        int error, i;

        g_topology_assert();

        nargs = gctl_get_paraml(req, "nargs", sizeof(*nargs));
        if (nargs == NULL) {
                gctl_error(req, "No '%s' argument.", "nargs");
                return;
        }
        if (*nargs <= 0) {
                gctl_error(req, "Missing device(s).");
                return;
        }

        for (i = 0; i < *nargs; i++) {
                snprintf(param, sizeof(param), "arg%d", i);
                name = gctl_get_asciiparam(req, param);
                if (name == NULL) {
                        gctl_error(req, "No 'arg%d' argument.", i);
                        return;
                }
                sc = g_journal_find_device(mp, name);
                if (sc == NULL) {
                        gctl_error(req, "No such device: %s.", name);
                        return;
                }
                error = g_journal_destroy(sc);
                if (error != 0) {
                        gctl_error(req, "Cannot destroy device %s (error=%d).",
                            LIST_FIRST(&sc->sc_geom->provider)->name, error);
                        return;
                }
        }
}

static void
g_journal_ctl_sync(struct gctl_req *req __unused, struct g_class *mp __unused)
{

        g_topology_assert();
        g_topology_unlock();
        g_journal_sync_requested++;
        wakeup(&g_journal_switcher_state);
        while (g_journal_sync_requested > 0)
                tsleep(&g_journal_sync_requested, PRIBIO, "j:sreq", hz / 2);
        g_topology_lock();
}

static void
g_journal_config(struct gctl_req *req, struct g_class *mp, const char *verb)
{
        uint32_t *version;

        g_topology_assert();

        version = gctl_get_paraml(req, "version", sizeof(*version));
        if (version == NULL) {
                gctl_error(req, "No '%s' argument.", "version");
                return;
        }
        if (*version != G_JOURNAL_VERSION) {
                gctl_error(req, "Userland and kernel parts are out of sync.");
                return;
        }

        if (strcmp(verb, "destroy") == 0 || strcmp(verb, "stop") == 0) {
                g_journal_ctl_destroy(req, mp);
                return;
        } else if (strcmp(verb, "sync") == 0) {
                g_journal_ctl_sync(req, mp);
                return;
        }

        gctl_error(req, "Unknown verb.");
}

static void
g_journal_dumpconf(struct sbuf *sb, const char *indent, struct g_geom *gp,
    struct g_consumer *cp, struct g_provider *pp)
{
        struct g_journal_softc *sc;

        g_topology_assert();

        sc = gp->softc;
        if (sc == NULL)
                return;
        if (pp != NULL) {
                /* Nothing here. */
        } else if (cp != NULL) {
                int first = 1;

                sbuf_printf(sb, "%s<Role>", indent);
                if (cp == sc->sc_dconsumer) {
                        sbuf_printf(sb, "Data");
                        first = 0;
                }
                if (cp == sc->sc_jconsumer) {
                        if (!first)
                                sbuf_printf(sb, ",");
                        sbuf_printf(sb, "Journal");
                }
                sbuf_printf(sb, "</Role>\n");
                if (cp == sc->sc_jconsumer) {
                        sbuf_printf(sb, "<Jstart>%jd</Jstart>\n",
                            (intmax_t)sc->sc_jstart);
                        sbuf_printf(sb, "<Jend>%jd</Jend>\n",
                            (intmax_t)sc->sc_jend);
                }
        } else {
                sbuf_printf(sb, "%s<ID>%u</ID>\n", indent, (u_int)sc->sc_id);
        }
}

static eventhandler_tag g_journal_event_shutdown = NULL;
static eventhandler_tag g_journal_event_lowmem = NULL;

static void
g_journal_shutdown(void *arg, int howto __unused)
{
        struct g_class *mp;
        struct g_geom *gp, *gp2;

        if (panicstr != NULL)
                return;
        mp = arg;
        DROP_GIANT();
        g_topology_lock();
        LIST_FOREACH_SAFE(gp, &mp->geom, geom, gp2) {
                if (gp->softc == NULL)
                        continue;
                GJ_DEBUG(0, "Shutting down geom %s.", gp->name);
                g_journal_destroy(gp->softc);
        }
        g_topology_unlock();
        PICKUP_GIANT();
}

/*
 * Free cached requests from inactive queue in case of low memory.
 * We free GJ_FREE_AT_ONCE elements at once.
 */
#define GJ_FREE_AT_ONCE 4
static void
g_journal_lowmem(void *arg, int howto __unused)
{
        struct g_journal_softc *sc;
        struct g_class *mp;
        struct g_geom *gp;
        struct bio *bp;
        u_int nfree = GJ_FREE_AT_ONCE;

        g_journal_stats_low_mem++;
        mp = arg;
        DROP_GIANT();
        g_topology_lock();
        LIST_FOREACH(gp, &mp->geom, geom) {
                sc = gp->softc;
                if (sc == NULL || (sc->sc_flags & GJF_DEVICE_DESTROY))
                        continue;
                mtx_lock(&sc->sc_mtx);
                for (bp = sc->sc_inactive.jj_queue; nfree > 0 && bp != NULL;
                    nfree--, bp = bp->bio_next) {
                        /*
                         * This is safe to free the bio_data, because:
                         * 1. If bio_data is NULL it will be read from the
                         *    inactive journal.
                         * 2. If bp is sent down, it is first removed from the
                         *    inactive queue, so it's impossible to free the
                         *    data from under in-flight bio.
                         * On the other hand, freeing elements from the active
                         * queue, is not safe.
                         */
                        if (bp->bio_data != NULL) {
                                GJ_DEBUG(2, "Freeing data from %s.",
                                    sc->sc_name);
                                gj_free(bp->bio_data, bp->bio_length);
                                bp->bio_data = NULL;
                        }
                }
                mtx_unlock(&sc->sc_mtx);
                if (nfree == 0)
                        break;
        }
        g_topology_unlock();
        PICKUP_GIANT();
}

static void g_journal_switcher(void *arg);

static void
g_journal_init(struct g_class *mp)
{
        int error;

        /* Pick a conservative value if provided value sucks. */
        if (g_journal_cache_divisor <= 0 ||
            (vm_kmem_size / g_journal_cache_divisor == 0)) {
                g_journal_cache_divisor = 5;
        }
        if (g_journal_cache_limit > 0) {
                g_journal_cache_limit = vm_kmem_size / g_journal_cache_divisor;
                g_journal_cache_low =
                    (g_journal_cache_limit / 100) * g_journal_cache_switch;
        }
        g_journal_event_shutdown = EVENTHANDLER_REGISTER(shutdown_post_sync,
            g_journal_shutdown, mp, EVENTHANDLER_PRI_FIRST);
        if (g_journal_event_shutdown == NULL)
                GJ_DEBUG(0, "Warning! Cannot register shutdown event.");
        g_journal_event_lowmem = EVENTHANDLER_REGISTER(vm_lowmem,
            g_journal_lowmem, mp, EVENTHANDLER_PRI_FIRST);
        if (g_journal_event_lowmem == NULL)
                GJ_DEBUG(0, "Warning! Cannot register lowmem event.");
        error = kproc_create(g_journal_switcher, mp, NULL, 0, 0,
            "g_journal switcher");
        KASSERT(error == 0, ("Cannot create switcher thread."));
}

static void
g_journal_fini(struct g_class *mp)
{

        if (g_journal_event_shutdown != NULL) {
                EVENTHANDLER_DEREGISTER(shutdown_post_sync,
                    g_journal_event_shutdown);
        }
        if (g_journal_event_lowmem != NULL)
                EVENTHANDLER_DEREGISTER(vm_lowmem, g_journal_event_lowmem);
        g_journal_switcher_state = GJ_SWITCHER_DIE;
        wakeup(&g_journal_switcher_state);
        while (g_journal_switcher_state != GJ_SWITCHER_DIED)
                tsleep(&g_journal_switcher_state, PRIBIO, "jfini:wait", hz / 5);
        GJ_DEBUG(1, "Switcher died.");
}

DECLARE_GEOM_CLASS(g_journal_class, g_journal);

static const struct g_journal_desc *
g_journal_find_desc(const char *fstype)
{
        const struct g_journal_desc *desc;
        int i;

        for (desc = g_journal_filesystems[i = 0]; desc != NULL;
             desc = g_journal_filesystems[++i]) {
                if (strcmp(desc->jd_fstype, fstype) == 0)
                        break;
        }
        return (desc);
}

static void
g_journal_switch_wait(struct g_journal_softc *sc)
{
        struct bintime bt;

        mtx_assert(&sc->sc_mtx, MA_OWNED);
        if (g_journal_debug >= 2) {
                if (sc->sc_flush_in_progress > 0) {
                        GJ_DEBUG(2, "%d requests flushing.",
                            sc->sc_flush_in_progress);
                }
                if (sc->sc_copy_in_progress > 0) {
                        GJ_DEBUG(2, "%d requests copying.",
                            sc->sc_copy_in_progress);
                }
                if (sc->sc_flush_count > 0) {
                        GJ_DEBUG(2, "%d requests to flush.",
                            sc->sc_flush_count);
                }
                if (sc->sc_delayed_count > 0) {
                        GJ_DEBUG(2, "%d requests delayed.",
                            sc->sc_delayed_count);
                }
        }
        g_journal_stats_switches++;
        if (sc->sc_copy_in_progress > 0)
                g_journal_stats_wait_for_copy++;
        GJ_TIMER_START(1, &bt);
        sc->sc_flags &= ~GJF_DEVICE_BEFORE_SWITCH;
        sc->sc_flags |= GJF_DEVICE_SWITCH;
        wakeup(sc);
        while (sc->sc_flags & GJF_DEVICE_SWITCH) {
                msleep(&sc->sc_journal_copying, &sc->sc_mtx, PRIBIO,
                    "gj:switch", 0);
        }
        GJ_TIMER_STOP(1, &bt, "Switch time of %s", sc->sc_name);
}

static void
g_journal_do_switch(struct g_class *classp)
{
        struct g_journal_softc *sc;
        const struct g_journal_desc *desc;
        struct g_geom *gp;
        struct mount *mp;
        struct bintime bt;
        char *mountpoint;
        int error, save;

        DROP_GIANT();
        g_topology_lock();
        LIST_FOREACH(gp, &classp->geom, geom) {
                sc = gp->softc;
                if (sc == NULL)
                        continue;
                if (sc->sc_flags & GJF_DEVICE_DESTROY)
                        continue;
                if ((sc->sc_type & GJ_TYPE_COMPLETE) != GJ_TYPE_COMPLETE)
                        continue;
                mtx_lock(&sc->sc_mtx);
                sc->sc_flags |= GJF_DEVICE_BEFORE_SWITCH;
                mtx_unlock(&sc->sc_mtx);
        }
        g_topology_unlock();
        PICKUP_GIANT();

        mtx_lock(&mountlist_mtx);
        TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                if (mp->mnt_gjprovider == NULL)
                        continue;
                if (mp->mnt_flag & MNT_RDONLY)
                        continue;
                desc = g_journal_find_desc(mp->mnt_stat.f_fstypename);
                if (desc == NULL)
                        continue;
                if (vfs_busy(mp, MBF_NOWAIT | MBF_MNTLSTLOCK))
                        continue;
                /* mtx_unlock(&mountlist_mtx) was done inside vfs_busy() */

                DROP_GIANT();
                g_topology_lock();
                sc = g_journal_find_device(classp, mp->mnt_gjprovider);
                g_topology_unlock();
                PICKUP_GIANT();

                if (sc == NULL) {
                        GJ_DEBUG(0, "Cannot find journal geom for %s.",
                            mp->mnt_gjprovider);
                        goto next;
                } else if (JEMPTY(sc)) {
                        mtx_lock(&sc->sc_mtx);
                        sc->sc_flags &= ~GJF_DEVICE_BEFORE_SWITCH;
                        mtx_unlock(&sc->sc_mtx);
                        GJ_DEBUG(3, "No need for %s switch.", sc->sc_name);
                        goto next;
                }

                mountpoint = mp->mnt_stat.f_mntonname;

                error = vn_start_write(NULL, &mp, V_WAIT);
                if (error != 0) {
                        GJ_DEBUG(0, "vn_start_write(%s) failed (error=%d).",
                            mountpoint, error);
                        goto next;
                }

                save = curthread_pflags_set(TDP_SYNCIO);

                GJ_TIMER_START(1, &bt);
                vfs_msync(mp, MNT_NOWAIT);
                GJ_TIMER_STOP(1, &bt, "Msync time of %s", mountpoint);

                GJ_TIMER_START(1, &bt);
                error = VFS_SYNC(mp, MNT_NOWAIT);
                if (error == 0)
                        GJ_TIMER_STOP(1, &bt, "Sync time of %s", mountpoint);
                else {
                        GJ_DEBUG(0, "Cannot sync file system %s (error=%d).",
                            mountpoint, error);
                }

                curthread_pflags_restore(save);

                vn_finished_write(mp);

                if (error != 0)
                        goto next;

                /*
                 * Send BIO_FLUSH before freezing the file system, so it can be
                 * faster after the freeze.
                 */
                GJ_TIMER_START(1, &bt);
                g_journal_flush_cache(sc);
                GJ_TIMER_STOP(1, &bt, "BIO_FLUSH time of %s", sc->sc_name);

                GJ_TIMER_START(1, &bt);
                error = vfs_write_suspend(mp, VS_SKIP_UNMOUNT);
                GJ_TIMER_STOP(1, &bt, "Suspend time of %s", mountpoint);
                if (error != 0) {
                        GJ_DEBUG(0, "Cannot suspend file system %s (error=%d).",
                            mountpoint, error);
                        goto next;
                }

                error = desc->jd_clean(mp);
                if (error != 0)
                        goto next;

                mtx_lock(&sc->sc_mtx);
                g_journal_switch_wait(sc);
                mtx_unlock(&sc->sc_mtx);

                vfs_write_resume(mp, 0);
next:
                mtx_lock(&mountlist_mtx);
                vfs_unbusy(mp);
        }
        mtx_unlock(&mountlist_mtx);

        sc = NULL;
        for (;;) {
                DROP_GIANT();
                g_topology_lock();
                LIST_FOREACH(gp, &g_journal_class.geom, geom) {
                        sc = gp->softc;
                        if (sc == NULL)
                                continue;
                        mtx_lock(&sc->sc_mtx);
                        if ((sc->sc_type & GJ_TYPE_COMPLETE) == GJ_TYPE_COMPLETE &&
                            !(sc->sc_flags & GJF_DEVICE_DESTROY) &&
                            (sc->sc_flags & GJF_DEVICE_BEFORE_SWITCH)) {
                                break;
                        }
                        mtx_unlock(&sc->sc_mtx);
                        sc = NULL;
                }
                g_topology_unlock();
                PICKUP_GIANT();
                if (sc == NULL)
                        break;
                mtx_assert(&sc->sc_mtx, MA_OWNED);
                g_journal_switch_wait(sc);
                mtx_unlock(&sc->sc_mtx);
        }
}

/*
 * TODO: Switcher thread should be started on first geom creation and killed on
 * last geom destruction.
 */
static void
g_journal_switcher(void *arg)
{
        struct g_class *mp;
        struct bintime bt;
        int error;

        mp = arg;
        curthread->td_pflags |= TDP_NORUNNINGBUF;
        for (;;) {
                g_journal_switcher_wokenup = 0;
                error = tsleep(&g_journal_switcher_state, PRIBIO, "jsw:wait",
                    g_journal_switch_time * hz);
                if (g_journal_switcher_state == GJ_SWITCHER_DIE) {
                        g_journal_switcher_state = GJ_SWITCHER_DIED;
                        GJ_DEBUG(1, "Switcher exiting.");
                        wakeup(&g_journal_switcher_state);
                        kproc_exit(0);
                }
                if (error == 0 && g_journal_sync_requested == 0) {
                        GJ_DEBUG(1, "Out of cache, force switch (used=%u "
                            "limit=%u).", g_journal_cache_used,
                            g_journal_cache_limit);
                }
                GJ_TIMER_START(1, &bt);
                g_journal_do_switch(mp);
                GJ_TIMER_STOP(1, &bt, "Entire switch time");
                if (g_journal_sync_requested > 0) {
                        g_journal_sync_requested = 0;
                        wakeup(&g_journal_sync_requested);
                }
        }
}