/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2006-2007 Ivan Voras <ivoras@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.
 */

/* Implementation notes:
 * - "Components" are wrappers around providers that make up the
 *   virtual storage (i.e. a virstor has "physical" components)
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/module.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/sx.h>
#include <sys/bio.h>
#include <sys/sbuf.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/time.h>
#include <sys/proc.h>
#include <sys/kthread.h>
#include <sys/mutex.h>
#include <vm/uma.h>
#include <geom/geom.h>
#include <geom/geom_dbg.h>

#include <geom/virstor/g_virstor.h>
#include <geom/virstor/g_virstor_md.h>

FEATURE(g_virstor, "GEOM virtual storage support");

/* Declare malloc(9) label */
static MALLOC_DEFINE(M_GVIRSTOR, "gvirstor", "GEOM_VIRSTOR Data");

/* GEOM class methods */
static g_init_t g_virstor_init;
static g_fini_t g_virstor_fini;
static g_taste_t g_virstor_taste;
static g_ctl_req_t g_virstor_config;
static g_ctl_destroy_geom_t g_virstor_destroy_geom;

/* Declare & initialize class structure ("geom class") */
struct g_class g_virstor_class = {
        .name =         G_VIRSTOR_CLASS_NAME,
        .version =      G_VERSION,
        .init =         g_virstor_init,
        .fini =         g_virstor_fini,
        .taste =        g_virstor_taste,
        .ctlreq =       g_virstor_config,
        .destroy_geom = g_virstor_destroy_geom
        /* The .dumpconf and the rest are only usable for a geom instance, so
         * they will be set when such instance is created. */
};

/* Declare sysctl's and loader tunables */
SYSCTL_DECL(_kern_geom);
static SYSCTL_NODE(_kern_geom, OID_AUTO, virstor,
    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "GEOM_GVIRSTOR information");

static u_int g_virstor_debug = 2; /* XXX: lower to 2 when released to public */
SYSCTL_UINT(_kern_geom_virstor, OID_AUTO, debug, CTLFLAG_RWTUN, &g_virstor_debug,
    0, "Debug level (2=production, 5=normal, 15=excessive)");

static u_int g_virstor_chunk_watermark = 100;
SYSCTL_UINT(_kern_geom_virstor, OID_AUTO, chunk_watermark, CTLFLAG_RWTUN,
    &g_virstor_chunk_watermark, 0,
    "Minimum number of free chunks before issuing administrative warning");

static u_int g_virstor_component_watermark = 1;
SYSCTL_UINT(_kern_geom_virstor, OID_AUTO, component_watermark, CTLFLAG_RWTUN,
    &g_virstor_component_watermark, 0,
    "Minimum number of free components before issuing administrative warning");

static int read_metadata(struct g_consumer *, struct g_virstor_metadata *);
static void write_metadata(struct g_consumer *, struct g_virstor_metadata *);
static int clear_metadata(struct g_virstor_component *);
static int add_provider_to_geom(struct g_virstor_softc *, struct g_provider *,
    struct g_virstor_metadata *);
static struct g_geom *create_virstor_geom(struct g_class *,
    struct g_virstor_metadata *);
static void virstor_check_and_run(struct g_virstor_softc *);
static u_int virstor_valid_components(struct g_virstor_softc *);
static int virstor_geom_destroy(struct g_virstor_softc *, boolean_t,
    boolean_t);
static void remove_component(struct g_virstor_softc *,
    struct g_virstor_component *, boolean_t);
static void bioq_dismantle(struct bio_queue_head *);
static int allocate_chunk(struct g_virstor_softc *,
    struct g_virstor_component **, u_int *, u_int *);
static void delay_destroy_consumer(void *, int);
static void dump_component(struct g_virstor_component *comp);
#if 0
static void dump_me(struct virstor_map_entry *me, unsigned int nr);
#endif

static void virstor_ctl_stop(struct gctl_req *, struct g_class *);
static void virstor_ctl_add(struct gctl_req *, struct g_class *);
static void virstor_ctl_remove(struct gctl_req *, struct g_class *);
static struct g_virstor_softc * virstor_find_geom(const struct g_class *,
    const char *);
static void update_metadata(struct g_virstor_softc *);
static void fill_metadata(struct g_virstor_softc *, struct g_virstor_metadata *,
    u_int, u_int);

static void g_virstor_orphan(struct g_consumer *);
static int g_virstor_access(struct g_provider *, int, int, int);
static void g_virstor_start(struct bio *);
static void g_virstor_dumpconf(struct sbuf *, const char *, struct g_geom *,
    struct g_consumer *, struct g_provider *);
static void g_virstor_done(struct bio *);

static void invalid_call(void);
/*
 * Initialise GEOM class (per-class callback)
 */
static void
g_virstor_init(struct g_class *mp __unused)
{

        /* Catch map struct size mismatch at compile time; Map entries must
         * fit into maxphys exactly, with no wasted space. */
        MPASS(VIRSTOR_MAP_BLOCK_ENTRIES * VIRSTOR_MAP_ENTRY_SIZE == maxphys);

        /* Init UMA zones, TAILQ's, other global vars */
}

/*
 * Finalise GEOM class (per-class callback)
 */
static void
g_virstor_fini(struct g_class *mp __unused)
{

        /* Deinit UMA zones & global vars */
}

/*
 * Config (per-class callback)
 */
static void
g_virstor_config(struct gctl_req *req, struct g_class *cp, char const *verb)
{
        uint32_t *version;

        g_topology_assert();

        version = gctl_get_paraml(req, "version", sizeof(*version));
        if (version == NULL) {
                gctl_error(req, "Failed to get 'version' argument");
                return;
        }
        if (*version != G_VIRSTOR_VERSION) {
                gctl_error(req, "Userland and kernel versions out of sync");
                return;
        }

        g_topology_unlock();
        if (strcmp(verb, "add") == 0)
                virstor_ctl_add(req, cp);
        else if (strcmp(verb, "stop") == 0 || strcmp(verb, "destroy") == 0)
                virstor_ctl_stop(req, cp);
        else if (strcmp(verb, "remove") == 0)
                virstor_ctl_remove(req, cp);
        else
                gctl_error(req, "unknown verb: '%s'", verb);
        g_topology_lock();
}

/*
 * "stop" verb from userland
 */
static void
virstor_ctl_stop(struct gctl_req *req, struct g_class *cp)
{
        int *force, *nargs;
        int i;

        nargs = gctl_get_paraml(req, "nargs", sizeof(*nargs));
        if (nargs == NULL) {
                gctl_error(req, "Error fetching argument '%s'", "nargs");
                return;
        }
        if (*nargs < 1) {
                gctl_error(req, "Invalid number of arguments");
                return;
        }
        force = gctl_get_paraml(req, "force", sizeof(*force));
        if (force == NULL) {
                gctl_error(req, "Error fetching argument '%s'", "force");
                return;
        }

        g_topology_lock();
        for (i = 0; i < *nargs; i++) {
                char param[8];
                const char *name;
                struct g_virstor_softc *sc;
                int error;

                snprintf(param, sizeof(param), "arg%d", i);
                name = gctl_get_asciiparam(req, param);
                if (name == NULL) {
                        gctl_error(req, "No 'arg%d' argument", i);
                        g_topology_unlock();
                        return;
                }
                sc = virstor_find_geom(cp, name);
                if (sc == NULL) {
                        gctl_error(req, "Don't know anything about '%s'", name);
                        g_topology_unlock();
                        return;
                }

                LOG_MSG(LVL_INFO, "Stopping %s by the userland command",
                    sc->geom->name);
                update_metadata(sc);
                if ((error = virstor_geom_destroy(sc, TRUE, TRUE)) != 0) {
                        LOG_MSG(LVL_ERROR, "Cannot destroy %s: %d",
                            sc->geom->name, error);
                }
        }
        g_topology_unlock();
}

/*
 * "add" verb from userland - add new component(s) to the structure.
 * This will be done all at once in here, without going through the
 * .taste function for new components.
 */
static void
virstor_ctl_add(struct gctl_req *req, struct g_class *cp)
{
        /* Note: while this is going on, I/O is being done on
         * the g_up and g_down threads. The idea is to make changes
         * to softc members in a way that can atomically activate
         * them all at once. */
        struct g_virstor_softc *sc;
        int *hardcode, *nargs;
        const char *geom_name;  /* geom to add a component to */
        struct g_consumer *fcp;
        struct g_virstor_bio_q *bq;
        u_int added;
        int error;
        int i;

        nargs = gctl_get_paraml(req, "nargs", sizeof(*nargs));
        if (nargs == NULL) {
                gctl_error(req, "Error fetching argument '%s'", "nargs");
                return;
        }
        if (*nargs < 2) {
                gctl_error(req, "Invalid number of arguments");
                return;
        }
        hardcode = gctl_get_paraml(req, "hardcode", sizeof(*hardcode));
        if (hardcode == NULL) {
                gctl_error(req, "Error fetching argument '%s'", "hardcode");
                return;
        }

        /* Find "our" geom */
        geom_name = gctl_get_asciiparam(req, "arg0");
        if (geom_name == NULL) {
                gctl_error(req, "Error fetching argument '%s'", "geom_name (arg0)");
                return;
        }
        sc = virstor_find_geom(cp, geom_name);
        if (sc == NULL) {
                gctl_error(req, "Don't know anything about '%s'", geom_name);
                return;
        }

        if (virstor_valid_components(sc) != sc->n_components) {
                LOG_MSG(LVL_ERROR, "Cannot add components to incomplete "
                    "virstor %s", sc->geom->name);
                gctl_error(req, "Virstor %s is incomplete", sc->geom->name);
                return;
        }

        fcp = sc->components[0].gcons;
        added = 0;
        g_topology_lock();
        for (i = 1; i < *nargs; i++) {
                struct g_virstor_metadata md;
                char aname[8];
                struct g_provider *pp;
                struct g_consumer *cp;
                u_int nc;
                u_int j;

                snprintf(aname, sizeof(aname), "arg%d", i);
                pp = gctl_get_provider(req, aname);
                if (pp == NULL) {
                        /* This is the most common error so be verbose about it */
                        if (added != 0) {
                                gctl_error(req, "Invalid provider. (added"
                                    " %u components)", added);
                                update_metadata(sc);
                        }
                        g_topology_unlock();
                        return;
                }
                cp = g_new_consumer(sc->geom);
                if (cp == NULL) {
                        gctl_error(req, "Cannot create consumer");
                        g_topology_unlock();
                        return;
                }
                error = g_attach(cp, pp);
                if (error != 0) {
                        gctl_error(req, "Cannot attach a consumer to %s",
                            pp->name);
                        g_destroy_consumer(cp);
                        g_topology_unlock();
                        return;
                }
                if (fcp->acr != 0 || fcp->acw != 0 || fcp->ace != 0) {
                        error = g_access(cp, fcp->acr, fcp->acw, fcp->ace);
                        if (error != 0) {
                                gctl_error(req, "Access request failed for %s",
                                    pp->name);
                                g_destroy_consumer(cp);
                                g_topology_unlock();
                                return;
                        }
                }
                if (fcp->provider->sectorsize != pp->sectorsize) {
                        gctl_error(req, "Sector size doesn't fit for %s",
                            pp->name);
                        g_destroy_consumer(cp);
                        g_topology_unlock();
                        return;
                }
                for (j = 0; j < sc->n_components; j++) {
                        if (strcmp(sc->components[j].gcons->provider->name,
                            pp->name) == 0) {
                                gctl_error(req, "Component %s already in %s",
                                    pp->name, sc->geom->name);
                                g_destroy_consumer(cp);
                                g_topology_unlock();
                                return;
                        }
                }
                sc->components = realloc(sc->components,
                    sizeof(*sc->components) * (sc->n_components + 1),
                    M_GVIRSTOR, M_WAITOK);

                nc = sc->n_components;
                sc->components[nc].gcons = cp;
                sc->components[nc].sc = sc;
                sc->components[nc].index = nc;
                sc->components[nc].chunk_count = cp->provider->mediasize /
                    sc->chunk_size;
                sc->components[nc].chunk_next = 0;
                sc->components[nc].chunk_reserved = 0;

                if (sc->components[nc].chunk_count < 4) {
                        gctl_error(req, "Provider too small: %s",
                            cp->provider->name);
                        g_destroy_consumer(cp);
                        g_topology_unlock();
                        return;
                }
                fill_metadata(sc, &md, nc, *hardcode);
                write_metadata(cp, &md);
                /* The new component becomes visible when n_components is
                 * incremented */
                sc->n_components++;
                added++;
        }
        /* This call to update_metadata() is critical. In case there's a
         * power failure in the middle of it and some components are updated
         * while others are not, there will be trouble on next .taste() iff
         * a non-updated component is detected first */
        update_metadata(sc);
        g_topology_unlock();
        LOG_MSG(LVL_INFO, "Added %d component(s) to %s", added,
            sc->geom->name);
        /* Fire off BIOs previously queued because there wasn't any
         * physical space left. If the BIOs still can't be satisfied
         * they will again be added to the end of the queue (during
         * which the mutex will be recursed) */
        bq = malloc(sizeof(*bq), M_GVIRSTOR, M_WAITOK);
        bq->bio = NULL;
        mtx_lock(&sc->delayed_bio_q_mtx);
        /* First, insert a sentinel to the queue end, so we don't
         * end up in an infinite loop if there's still no free
         * space available. */
        STAILQ_INSERT_TAIL(&sc->delayed_bio_q, bq, linkage);
        while (!STAILQ_EMPTY(&sc->delayed_bio_q)) {
                bq = STAILQ_FIRST(&sc->delayed_bio_q);
                if (bq->bio != NULL) {
                        g_virstor_start(bq->bio);
                        STAILQ_REMOVE_HEAD(&sc->delayed_bio_q, linkage);
                        free(bq, M_GVIRSTOR);
                } else {
                        STAILQ_REMOVE_HEAD(&sc->delayed_bio_q, linkage);
                        free(bq, M_GVIRSTOR);
                        break;
                }
        }
        mtx_unlock(&sc->delayed_bio_q_mtx);

}

/*
 * Find a geom handled by the class
 */
static struct g_virstor_softc *
virstor_find_geom(const struct g_class *cp, const char *name)
{
        struct g_geom *gp;

        LIST_FOREACH(gp, &cp->geom, geom) {
                if (strcmp(name, gp->name) == 0)
                        return (gp->softc);
        }
        return (NULL);
}

/*
 * Update metadata on all components to reflect the current state
 * of these fields:
 *    - chunk_next
 *    - flags
 *    - md_count
 * Expects things to be set up so write_metadata() can work, i.e.
 * the topology lock must be held.
 */
static void
update_metadata(struct g_virstor_softc *sc)
{
        struct g_virstor_metadata md;
        u_int n;

        if (virstor_valid_components(sc) != sc->n_components)
                return; /* Incomplete device */
        LOG_MSG(LVL_DEBUG, "Updating metadata on components for %s",
            sc->geom->name);
        /* Update metadata on components */
        g_trace(G_T_TOPOLOGY, "%s(%s, %s)", __func__,
            sc->geom->class->name, sc->geom->name);
        g_topology_assert();
        for (n = 0; n < sc->n_components; n++) {
                read_metadata(sc->components[n].gcons, &md);
                md.chunk_next = sc->components[n].chunk_next;
                md.flags = sc->components[n].flags;
                md.md_count = sc->n_components;
                write_metadata(sc->components[n].gcons, &md);
        }
}

/*
 * Fills metadata (struct md) from information stored in softc and the nc'th
 * component of virstor
 */
static void
fill_metadata(struct g_virstor_softc *sc, struct g_virstor_metadata *md,
    u_int nc, u_int hardcode)
{
        struct g_virstor_component *c;

        bzero(md, sizeof(*md));
        c = &sc->components[nc];

        strncpy(md->md_magic, G_VIRSTOR_MAGIC, sizeof(md->md_magic));
        md->md_version = G_VIRSTOR_VERSION;
        strncpy(md->md_name, sc->geom->name, sizeof(md->md_name));
        md->md_id = sc->id;
        md->md_virsize = sc->virsize;
        md->md_chunk_size = sc->chunk_size;
        md->md_count = sc->n_components;

        if (hardcode) {
                strncpy(md->provider, c->gcons->provider->name,
                    sizeof(md->provider));
        }
        md->no = nc;
        md->provsize = c->gcons->provider->mediasize;
        md->chunk_count = c->chunk_count;
        md->chunk_next = c->chunk_next;
        md->chunk_reserved = c->chunk_reserved;
        md->flags = c->flags;
}

/*
 * Remove a component from virstor device.
 * Can only be done if the component is unallocated.
 */
static void
virstor_ctl_remove(struct gctl_req *req, struct g_class *cp)
{
        /* As this is executed in parallel to I/O, operations on virstor
         * structures must be as atomic as possible. */
        struct g_virstor_softc *sc;
        int *nargs;
        const char *geom_name;
        u_int removed;
        int i;

        nargs = gctl_get_paraml(req, "nargs", sizeof(*nargs));
        if (nargs == NULL) {
                gctl_error(req, "Error fetching argument '%s'", "nargs");
                return;
        }
        if (*nargs < 2) {
                gctl_error(req, "Invalid number of arguments");
                return;
        }
        /* Find "our" geom */
        geom_name = gctl_get_asciiparam(req, "arg0");
        if (geom_name == NULL) {
                gctl_error(req, "Error fetching argument '%s'",
                    "geom_name (arg0)");
                return;
        }
        sc = virstor_find_geom(cp, geom_name);
        if (sc == NULL) {
                gctl_error(req, "Don't know anything about '%s'", geom_name);
                return;
        }

        if (virstor_valid_components(sc) != sc->n_components) {
                LOG_MSG(LVL_ERROR, "Cannot remove components from incomplete "
                    "virstor %s", sc->geom->name);
                gctl_error(req, "Virstor %s is incomplete", sc->geom->name);
                return;
        }

        removed = 0;
        for (i = 1; i < *nargs; i++) {
                char param[8];
                const char *prov_name;
                int j, found;
                struct g_virstor_component *newcomp, *compbak;

                snprintf(param, sizeof(param), "arg%d", i);
                prov_name = gctl_get_asciiparam(req, param);
                if (prov_name == NULL) {
                        gctl_error(req, "Error fetching argument '%s'", param);
                        return;
                }
                if (strncmp(prov_name, _PATH_DEV, sizeof(_PATH_DEV) - 1) == 0)
                        prov_name += sizeof(_PATH_DEV) - 1;

                found = -1;
                for (j = 0; j < sc->n_components; j++) {
                        if (strcmp(sc->components[j].gcons->provider->name,
                            prov_name) == 0) {
                                found = j;
                                break;
                        }
                }
                if (found == -1) {
                        LOG_MSG(LVL_ERROR, "No %s component in %s",
                            prov_name, sc->geom->name);
                        continue;
                }

                compbak = sc->components;
                newcomp = malloc(sc->n_components * sizeof(*sc->components),
                    M_GVIRSTOR, M_WAITOK | M_ZERO);
                bcopy(sc->components, newcomp, found * sizeof(*sc->components));
                bcopy(&sc->components[found + 1], newcomp + found,
                    (sc->n_components - (found + 1)) * sizeof(*sc->components));
                if ((sc->components[j].flags & VIRSTOR_PROVIDER_ALLOCATED) != 0) {
                        LOG_MSG(LVL_ERROR, "Allocated provider %s cannot be "
                            "removed from %s",
                            prov_name, sc->geom->name);
                        free(newcomp, M_GVIRSTOR);
                        /* We'll consider this non-fatal error */
                        continue;
                }
                /* Renumerate unallocated components */
                for (j = 0; j < sc->n_components-1; j++) {
                        if ((sc->components[j].flags &
                            VIRSTOR_PROVIDER_ALLOCATED) == 0) {
                                sc->components[j].index = j;
                        }
                }
                /* This is the critical section. If a component allocation
                 * event happens while both variables are not yet set,
                 * there will be trouble. Something will panic on encountering
                 * NULL sc->components[x].gcomp member.
                 * Luckily, component allocation happens very rarely and
                 * removing components is an abnormal action in any case. */
                sc->components = newcomp;
                sc->n_components--;
                /* End critical section */

                g_topology_lock();
                if (clear_metadata(&compbak[found]) != 0) {
                        LOG_MSG(LVL_WARNING, "Trouble ahead: cannot clear "
                            "metadata on %s", prov_name);
                }
                g_detach(compbak[found].gcons);
                g_destroy_consumer(compbak[found].gcons);
                g_topology_unlock();

                free(compbak, M_GVIRSTOR);

                removed++;
        }

        /* This call to update_metadata() is critical. In case there's a
         * power failure in the middle of it and some components are updated
         * while others are not, there will be trouble on next .taste() iff
         * a non-updated component is detected first */
        g_topology_lock();
        update_metadata(sc);
        g_topology_unlock();
        LOG_MSG(LVL_INFO, "Removed %d component(s) from %s", removed,
            sc->geom->name);
}

/*
 * Clear metadata sector on component
 */
static int
clear_metadata(struct g_virstor_component *comp)
{
        char *buf;
        int error;

        LOG_MSG(LVL_INFO, "Clearing metadata on %s",
            comp->gcons->provider->name);
        g_topology_assert();
        error = g_access(comp->gcons, 0, 1, 0);
        if (error != 0)
                return (error);
        buf = malloc(comp->gcons->provider->sectorsize, M_GVIRSTOR,
            M_WAITOK | M_ZERO);
        error = g_write_data(comp->gcons,
            comp->gcons->provider->mediasize -
            comp->gcons->provider->sectorsize,
            buf,
            comp->gcons->provider->sectorsize);
        free(buf, M_GVIRSTOR);
        g_access(comp->gcons, 0, -1, 0);
        return (error);
}

/*
 * Destroy geom forcibly.
 */
static int
g_virstor_destroy_geom(struct gctl_req *req __unused, struct g_class *mp,
    struct g_geom *gp)
{
        struct g_virstor_softc *sc;
        int exitval;

        sc = gp->softc;
        KASSERT(sc != NULL, ("%s: NULL sc", __func__));

        exitval = 0;
        LOG_MSG(LVL_DEBUG, "%s called for %s, sc=%p", __func__, gp->name,
            gp->softc);

        if (sc != NULL) {
#ifdef INVARIANTS
                char *buf;
                int error;
                off_t off;
                int isclean, count;
                int n;

                LOG_MSG(LVL_INFO, "INVARIANTS detected");
                LOG_MSG(LVL_INFO, "Verifying allocation "
                    "table for %s", sc->geom->name);
                count = 0;
                for (n = 0; n < sc->chunk_count; n++) {
                        if (sc->map[n].flags || VIRSTOR_MAP_ALLOCATED != 0)
                                count++;
                }
                LOG_MSG(LVL_INFO, "Device %s has %d allocated chunks",
                    sc->geom->name, count);
                n = off = count = 0;
                isclean = 1;
                if (virstor_valid_components(sc) != sc->n_components) {
                        /* This is a incomplete virstor device (not all
                         * components have been found) */
                        LOG_MSG(LVL_ERROR, "Device %s is incomplete",
                            sc->geom->name);
                        goto bailout;
                }
                error = g_access(sc->components[0].gcons, 1, 0, 0);
                KASSERT(error == 0, ("%s: g_access failed (%d)", __func__,
                    error));
                /* Compare the whole on-disk allocation table with what's
                 * currently in memory */
                while (n < sc->chunk_count) {
                        buf = g_read_data(sc->components[0].gcons, off,
                            sc->sectorsize, &error);
                        KASSERT(buf != NULL, ("g_read_data returned NULL (%d) "
                            "for read at %jd", error, off));
                        if (bcmp(buf, &sc->map[n], sc->sectorsize) != 0) {
                                LOG_MSG(LVL_ERROR, "ERROR in allocation table, "
                                    "entry %d, offset %jd", n, off);
                                isclean = 0;
                                count++;
                        }
                        n += sc->me_per_sector;
                        off += sc->sectorsize;
                        g_free(buf);
                }
                error = g_access(sc->components[0].gcons, -1, 0, 0);
                KASSERT(error == 0, ("%s: g_access failed (%d) on exit",
                    __func__, error));
                if (isclean != 1) {
                        LOG_MSG(LVL_ERROR, "ALLOCATION TABLE CORRUPTED FOR %s "
                            "(%d sectors don't match, max %zu allocations)",
                            sc->geom->name, count,
                            count * sc->me_per_sector);
                } else {
                        LOG_MSG(LVL_INFO, "Allocation table ok for %s",
                            sc->geom->name);
                }
bailout:
#endif
                update_metadata(sc);
                virstor_geom_destroy(sc, FALSE, FALSE);
                exitval = EAGAIN;
        } else
                exitval = 0;
        return (exitval);
}

/*
 * Taste event (per-class callback)
 * Examines a provider and creates geom instances if needed
 */
static struct g_geom *
g_virstor_taste(struct g_class *mp, struct g_provider *pp, int flags)
{
        struct g_virstor_metadata md;
        struct g_geom *gp;
        struct g_consumer *cp;
        struct g_virstor_softc *sc;
        int error;

        g_trace(G_T_TOPOLOGY, "%s(%s, %s)", __func__, mp->name, pp->name);
        g_topology_assert();
        LOG_MSG(LVL_DEBUG, "Tasting %s", pp->name);

        /* We need a dummy geom to attach a consumer to the given provider */
        gp = g_new_geom(mp, "virstor:taste.helper");
        gp->start = (void *)invalid_call;       /* XXX: hacked up so the        */
        gp->access = (void *)invalid_call;      /* compiler doesn't complain.   */
        gp->orphan = (void *)invalid_call;      /* I really want these to fail. */

        cp = g_new_consumer(gp);
        cp->flags |= G_CF_DIRECT_SEND | G_CF_DIRECT_RECEIVE;
        error = g_attach(cp, pp);
        if (error == 0) {
                error = read_metadata(cp, &md);
                g_detach(cp);
        }
        g_destroy_consumer(cp);
        g_destroy_geom(gp);

        if (error != 0)
                return (NULL);

        if (strcmp(md.md_magic, G_VIRSTOR_MAGIC) != 0)
                return (NULL);
        if (md.md_version != G_VIRSTOR_VERSION) {
                LOG_MSG(LVL_ERROR, "Kernel module version invalid "
                    "to handle %s (%s) : %d should be %d",
                    md.md_name, pp->name, md.md_version, G_VIRSTOR_VERSION);
                return (NULL);
        }
        if (md.provsize != pp->mediasize)
                return (NULL);

        /* If the provider name is hardcoded, use the offered provider only
         * if it's been offered with its proper name (the one used in
         * the label command). */
        if (md.provider[0] != '\0' &&
            !g_compare_names(md.provider, pp->name))
                return (NULL);

        /* Iterate all geoms this class already knows about to see if a new
         * geom instance of this class needs to be created (in case the provider
         * is first from a (possibly) multi-consumer geom) or it just needs
         * to be added to an existing instance. */
        sc = NULL;
        gp = NULL;
        LIST_FOREACH(gp, &mp->geom, geom) {
                sc = gp->softc;
                if (sc == NULL)
                        continue;
                if (strcmp(md.md_name, sc->geom->name) != 0)
                        continue;
                if (md.md_id != sc->id)
                        continue;
                break;
        }
        if (gp != NULL) { /* We found an existing geom instance; add to it */
                LOG_MSG(LVL_INFO, "Adding %s to %s", pp->name, md.md_name);
                error = add_provider_to_geom(sc, pp, &md);
                if (error != 0) {
                        LOG_MSG(LVL_ERROR, "Error adding %s to %s (error %d)",
                            pp->name, md.md_name, error);
                        return (NULL);
                }
        } else { /* New geom instance needs to be created */
                gp = create_virstor_geom(mp, &md);
                if (gp == NULL) {
                        LOG_MSG(LVL_ERROR, "Error creating new instance of "
                            "class %s: %s", mp->name, md.md_name);
                        LOG_MSG(LVL_DEBUG, "Error creating %s at %s",
                            md.md_name, pp->name);
                        return (NULL);
                }
                sc = gp->softc;
                LOG_MSG(LVL_INFO, "Adding %s to %s (first found)", pp->name,
                    md.md_name);
                error = add_provider_to_geom(sc, pp, &md);
                if (error != 0) {
                        LOG_MSG(LVL_ERROR, "Error adding %s to %s (error %d)",
                            pp->name, md.md_name, error);
                        virstor_geom_destroy(sc, TRUE, FALSE);
                        return (NULL);
                }
        }

        return (gp);
}

/*
 * Destroyes consumer passed to it in arguments. Used as a callback
 * on g_event queue.
 */
static void
delay_destroy_consumer(void *arg, int flags __unused)
{
        struct g_consumer *c = arg;
        KASSERT(c != NULL, ("%s: invalid consumer", __func__));
        LOG_MSG(LVL_DEBUG, "Consumer %s destroyed with delay",
            c->provider->name);
        g_detach(c);
        g_destroy_consumer(c);
}

/*
 * Remove a component (consumer) from geom instance; If it's the first
 * component being removed, orphan the provider to announce geom's being
 * dismantled
 */
static void
remove_component(struct g_virstor_softc *sc, struct g_virstor_component *comp,
    boolean_t delay)
{
        struct g_consumer *c;

        KASSERT(comp->gcons != NULL, ("Component with no consumer in %s",
            sc->geom->name));
        c = comp->gcons;

        comp->gcons = NULL;
        KASSERT(c->provider != NULL, ("%s: no provider", __func__));
        LOG_MSG(LVL_DEBUG, "Component %s removed from %s", c->provider->name,
            sc->geom->name);
        if (sc->provider != NULL) {
                LOG_MSG(LVL_INFO, "Removing provider %s", sc->provider->name);
                g_wither_provider(sc->provider, ENXIO);
                sc->provider = NULL;
        }

        if (c->acr > 0 || c->acw > 0 || c->ace > 0)
                return;
        if (delay) {
                /* Destroy consumer after it's tasted */
                g_post_event(delay_destroy_consumer, c, M_WAITOK, NULL);
        } else {
                g_detach(c);
                g_destroy_consumer(c);
        }
}

/*
 * Destroy geom - called internally
 * See g_virstor_destroy_geom for the other one
 */
static int
virstor_geom_destroy(struct g_virstor_softc *sc, boolean_t force,
    boolean_t delay)
{
        struct g_provider *pp;
        struct g_geom *gp;
        u_int n;

        g_topology_assert();

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

        pp = sc->provider;
        if (pp != NULL && (pp->acr != 0 || pp->acw != 0 || pp->ace != 0)) {
                LOG_MSG(force ? LVL_WARNING : LVL_ERROR,
                    "Device %s is still open.", pp->name);
                if (!force)
                        return (EBUSY);
        }

        for (n = 0; n < sc->n_components; n++) {
                if (sc->components[n].gcons != NULL)
                        remove_component(sc, &sc->components[n], delay);
        }

        gp = sc->geom;
        gp->softc = NULL;

        KASSERT(sc->provider == NULL, ("Provider still exists for %s",
            gp->name));

        /* XXX: This might or might not work, since we're called with
         * the topology lock held. Also, it might panic the kernel if
         * the error'd BIO is in softupdates code. */
        mtx_lock(&sc->delayed_bio_q_mtx);
        while (!STAILQ_EMPTY(&sc->delayed_bio_q)) {
                struct g_virstor_bio_q *bq;
                bq = STAILQ_FIRST(&sc->delayed_bio_q);
                bq->bio->bio_error = ENOSPC;
                g_io_deliver(bq->bio, EIO);
                STAILQ_REMOVE_HEAD(&sc->delayed_bio_q, linkage);
                free(bq, M_GVIRSTOR);
        }
        mtx_unlock(&sc->delayed_bio_q_mtx);
        mtx_destroy(&sc->delayed_bio_q_mtx);

        free(sc->map, M_GVIRSTOR);
        free(sc->components, M_GVIRSTOR);
        bzero(sc, sizeof(*sc));
        free(sc, M_GVIRSTOR);

        pp = LIST_FIRST(&gp->provider); /* We only offer one provider */
        if (pp == NULL || (pp->acr == 0 && pp->acw == 0 && pp->ace == 0))
                LOG_MSG(LVL_DEBUG, "Device %s destroyed", gp->name);

        g_wither_geom(gp, ENXIO);

        return (0);
}

/*
 * Utility function: read metadata & decode. Wants topology lock to be
 * held.
 */
static int
read_metadata(struct g_consumer *cp, struct g_virstor_metadata *md)
{
        struct g_provider *pp;
        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();
        buf = g_read_data(cp, pp->mediasize - pp->sectorsize, pp->sectorsize,
            &error);
        g_topology_lock();
        g_access(cp, -1, 0, 0);
        if (buf == NULL)
                return (error);

        virstor_metadata_decode(buf, md);
        g_free(buf);

        return (0);
}

/**
 * Utility function: encode & write metadata. Assumes topology lock is
 * held.
 *
 * There is no useful way of recovering from errors in this function,
 * not involving panicking the kernel. If the metadata cannot be written
 * the most we can do is notify the operator and hope he spots it and
 * replaces the broken drive.
 */
static void
write_metadata(struct g_consumer *cp, struct g_virstor_metadata *md)
{
        struct g_provider *pp;
        char *buf;
        int error;

        KASSERT(cp != NULL && md != NULL && cp->provider != NULL,
            ("Something's fishy in %s", __func__));
        LOG_MSG(LVL_DEBUG, "Writing metadata on %s", cp->provider->name);
        g_topology_assert();
        error = g_access(cp, 0, 1, 0);
        if (error != 0) {
                LOG_MSG(LVL_ERROR, "g_access(0,1,0) failed for %s: %d",
                    cp->provider->name, error);
                return;
        }
        pp = cp->provider;

        buf = malloc(pp->sectorsize, M_GVIRSTOR, M_WAITOK);
        bzero(buf, pp->sectorsize);
        virstor_metadata_encode(md, buf);
        g_topology_unlock();
        error = g_write_data(cp, pp->mediasize - pp->sectorsize, buf,
            pp->sectorsize);
        g_topology_lock();
        g_access(cp, 0, -1, 0);
        free(buf, M_GVIRSTOR);

        if (error != 0)
                LOG_MSG(LVL_ERROR, "Error %d writing metadata to %s",
                    error, cp->provider->name);
}

/*
 * Creates a new instance of this GEOM class, initialise softc
 */
static struct g_geom *
create_virstor_geom(struct g_class *mp, struct g_virstor_metadata *md)
{
        struct g_geom *gp;
        struct g_virstor_softc *sc;

        LOG_MSG(LVL_DEBUG, "Creating geom instance for %s (id=%u)",
            md->md_name, md->md_id);

        if (md->md_count < 1 || md->md_chunk_size < 1 ||
            md->md_virsize < md->md_chunk_size) {
                /* This is bogus configuration, and probably means data is
                 * somehow corrupted. Panic, maybe? */
                LOG_MSG(LVL_ERROR, "Nonsensical metadata information for %s",
                    md->md_name);
                return (NULL);
        }

        /* Check if it's already created */
        LIST_FOREACH(gp, &mp->geom, geom) {
                sc = gp->softc;
                if (sc != NULL && strcmp(sc->geom->name, md->md_name) == 0) {
                        LOG_MSG(LVL_WARNING, "Geom %s already exists",
                            md->md_name);
                        if (sc->id != md->md_id) {
                                LOG_MSG(LVL_ERROR,
                                    "Some stale or invalid components "
                                    "exist for virstor device named %s. "
                                    "You will need to <CLEAR> all stale "
                                    "components and maybe reconfigure "
                                    "the virstor device. Tune "
                                    "kern.geom.virstor.debug sysctl up "
                                    "for more information.",
                                    sc->geom->name);
                        }
                        return (NULL);
                }
        }
        gp = g_new_geom(mp, md->md_name);
        gp->softc = NULL; /* to circumevent races that test softc */

        gp->start = g_virstor_start;
        gp->spoiled = g_virstor_orphan;
        gp->orphan = g_virstor_orphan;
        gp->access = g_virstor_access;
        gp->dumpconf = g_virstor_dumpconf;

        sc = malloc(sizeof(*sc), M_GVIRSTOR, M_WAITOK | M_ZERO);
        sc->id = md->md_id;
        sc->n_components = md->md_count;
        sc->components = malloc(sizeof(struct g_virstor_component) * md->md_count,
            M_GVIRSTOR, M_WAITOK | M_ZERO);
        sc->chunk_size = md->md_chunk_size;
        sc->virsize = md->md_virsize;
        STAILQ_INIT(&sc->delayed_bio_q);
        mtx_init(&sc->delayed_bio_q_mtx, "gvirstor_delayed_bio_q_mtx",
            "gvirstor", MTX_DEF | MTX_RECURSE);

        sc->geom = gp;
        sc->provider = NULL; /* virstor_check_and_run will create it */
        gp->softc = sc;

        LOG_MSG(LVL_ANNOUNCE, "Device %s created", sc->geom->name);

        return (gp);
}

/*
 * Add provider to a GEOM class instance
 */
static int
add_provider_to_geom(struct g_virstor_softc *sc, struct g_provider *pp,
    struct g_virstor_metadata *md)
{
        struct g_virstor_component *component;
        struct g_consumer *cp, *fcp;
        struct g_geom *gp;
        int error;

        if (md->no >= sc->n_components)
                return (EINVAL);

        /* "Current" compontent */
        component = &(sc->components[md->no]);
        if (component->gcons != NULL)
                return (EEXIST);

        gp = sc->geom;
        fcp = LIST_FIRST(&gp->consumer);

        cp = g_new_consumer(gp);
        error = g_attach(cp, pp);

        if (error != 0) {
                g_destroy_consumer(cp);
                return (error);
        }

        if (fcp != NULL) {
                if (fcp->provider->sectorsize != pp->sectorsize) {
                        /* TODO: this can be made to work */
                        LOG_MSG(LVL_ERROR, "Provider %s of %s has invalid "
                            "sector size (%d)", pp->name, sc->geom->name,
                            pp->sectorsize);
                        return (EINVAL);
                }
                if (fcp->acr > 0 || fcp->acw || fcp->ace > 0) {
                        /* Replicate access permissions from first "live" consumer
                         * to the new one */
                        error = g_access(cp, fcp->acr, fcp->acw, fcp->ace);
                        if (error != 0) {
                                g_detach(cp);
                                g_destroy_consumer(cp);
                                return (error);
                        }
                }
        }

        /* Bring up a new component */
        cp->private = component;
        component->gcons = cp;
        component->sc = sc;
        component->index = md->no;
        component->chunk_count = md->chunk_count;
        component->chunk_next = md->chunk_next;
        component->chunk_reserved = md->chunk_reserved;
        component->flags = md->flags;

        LOG_MSG(LVL_DEBUG, "%s attached to %s", pp->name, sc->geom->name);

        virstor_check_and_run(sc);
        return (0);
}

/*
 * Check if everything's ready to create the geom provider & device entry,
 * create and start provider.
 * Called ultimately by .taste, from g_event thread
 */
static void
virstor_check_and_run(struct g_virstor_softc *sc)
{
        off_t off;
        size_t n, count;
        int index;
        int error;

        if (virstor_valid_components(sc) != sc->n_components)
                return;

        if (virstor_valid_components(sc) == 0) {
                /* This is actually a candidate for panic() */
                LOG_MSG(LVL_ERROR, "No valid components for %s?",
                    sc->provider->name);
                return;
        }

        sc->sectorsize = sc->components[0].gcons->provider->sectorsize;

        /* Initialise allocation map from the first consumer */
        sc->chunk_count = sc->virsize / sc->chunk_size;
        if (sc->chunk_count * (off_t)sc->chunk_size != sc->virsize) {
                LOG_MSG(LVL_WARNING, "Device %s truncated to %ju bytes",
                    sc->provider->name,
                    sc->chunk_count * (off_t)sc->chunk_size);
        }
        sc->map_size = sc->chunk_count * sizeof(*(sc->map));
        /* The following allocation is in order of 4MB - 8MB */
        sc->map = malloc(sc->map_size, M_GVIRSTOR, M_WAITOK);
        KASSERT(sc->map != NULL, ("%s: Memory allocation error (%zu bytes) for %s",
            __func__, sc->map_size, sc->provider->name));
        sc->map_sectors = sc->map_size / sc->sectorsize;

        count = 0;
        for (n = 0; n < sc->n_components; n++)
                count += sc->components[n].chunk_count;
        LOG_MSG(LVL_INFO, "Device %s has %zu physical chunks and %zu virtual "
            "(%zu KB chunks)",
            sc->geom->name, count, sc->chunk_count, sc->chunk_size / 1024);

        error = g_access(sc->components[0].gcons, 1, 0, 0);
        if (error != 0) {
                LOG_MSG(LVL_ERROR, "Cannot acquire read access for %s to "
                    "read allocation map for %s",
                    sc->components[0].gcons->provider->name,
                    sc->geom->name);
                return;
        }
        /* Read in the allocation map */
        LOG_MSG(LVL_DEBUG, "Reading map for %s from %s", sc->geom->name,
            sc->components[0].gcons->provider->name);
        off = count = n = 0;
        while (count < sc->map_size) {
                struct g_virstor_map_entry *mapbuf;
                size_t bs;

                bs = MIN(maxphys, sc->map_size - count);
                if (bs % sc->sectorsize != 0) {
                        /* Check for alignment errors */
                        bs = rounddown(bs, sc->sectorsize);
                        if (bs == 0)
                                break;
                        LOG_MSG(LVL_ERROR, "Trouble: map is not sector-aligned "
                            "for %s on %s", sc->geom->name,
                            sc->components[0].gcons->provider->name);
                }
                mapbuf = g_read_data(sc->components[0].gcons, off, bs, &error);
                if (mapbuf == NULL) {
                        free(sc->map, M_GVIRSTOR);
                        LOG_MSG(LVL_ERROR, "Error reading allocation map "
                            "for %s from %s (offset %ju) (error %d)",
                            sc->geom->name,
                            sc->components[0].gcons->provider->name,
                            off, error);
                        return;
                }

                bcopy(mapbuf, &sc->map[n], bs);
                off += bs;
                count += bs;
                n += bs / sizeof(*(sc->map));
                g_free(mapbuf);
        }
        g_access(sc->components[0].gcons, -1, 0, 0);
        LOG_MSG(LVL_DEBUG, "Read map for %s", sc->geom->name);

        /* find first component with allocatable chunks */
        index = -1;
        for (n = 0; n < sc->n_components; n++) {
                if (sc->components[n].chunk_next <
                    sc->components[n].chunk_count) {
                        index = n;
                        break;
                }
        }
        if (index == -1)
                /* not found? set it to the last component and handle it
                 * later */
                index = sc->n_components - 1;

        if (index >= sc->n_components - g_virstor_component_watermark - 1) {
                LOG_MSG(LVL_WARNING, "Device %s running out of components "
                    "(%d/%u: %s)", sc->geom->name,
                    index+1,
                    sc->n_components,
                    sc->components[index].gcons->provider->name);
        }
        sc->curr_component = index;

        if (sc->components[index].chunk_next >=
            sc->components[index].chunk_count - g_virstor_chunk_watermark) {
                LOG_MSG(LVL_WARNING,
                    "Component %s of %s is running out of free space "
                    "(%u chunks left)",
                    sc->components[index].gcons->provider->name,
                    sc->geom->name, sc->components[index].chunk_count -
                    sc->components[index].chunk_next);
        }

        sc->me_per_sector = sc->sectorsize / sizeof(*(sc->map));
        if (sc->sectorsize % sizeof(*(sc->map)) != 0) {
                LOG_MSG(LVL_ERROR,
                    "%s: Map entries don't fit exactly in a sector (%s)",
                    __func__, sc->geom->name);
                return;
        }

        /* Recalculate allocated chunks in components & at the same time
         * verify map data is sane. We could trust metadata on this, but
         * we want to make sure. */
        for (n = 0; n < sc->n_components; n++)
                sc->components[n].chunk_next = sc->components[n].chunk_reserved;

        for (n = 0; n < sc->chunk_count; n++) {
                if (sc->map[n].provider_no >= sc->n_components ||
                        sc->map[n].provider_chunk >=
                        sc->components[sc->map[n].provider_no].chunk_count) {
                        LOG_MSG(LVL_ERROR, "%s: Invalid entry %u in map for %s",
                            __func__, (u_int)n, sc->geom->name);
                        LOG_MSG(LVL_ERROR, "%s: provider_no: %u, n_components: %u"
                            " provider_chunk: %u, chunk_count: %u", __func__,
                            sc->map[n].provider_no, sc->n_components,
                            sc->map[n].provider_chunk,
                            sc->components[sc->map[n].provider_no].chunk_count);
                        return;
                }
                if (sc->map[n].flags & VIRSTOR_MAP_ALLOCATED)
                        sc->components[sc->map[n].provider_no].chunk_next++;
        }

        sc->provider = g_new_providerf(sc->geom, "virstor/%s",
            sc->geom->name);

        sc->provider->sectorsize = sc->sectorsize;
        sc->provider->mediasize = sc->virsize;
        g_error_provider(sc->provider, 0);

        LOG_MSG(LVL_INFO, "%s activated", sc->provider->name);
        LOG_MSG(LVL_DEBUG, "%s starting with current component %u, starting "
            "chunk %u", sc->provider->name, sc->curr_component,
            sc->components[sc->curr_component].chunk_next);
}

/*
 * Returns count of active providers in this geom instance
 */
static u_int
virstor_valid_components(struct g_virstor_softc *sc)
{
        unsigned int nc, i;

        nc = 0;
        KASSERT(sc != NULL, ("%s: softc is NULL", __func__));
        KASSERT(sc->components != NULL, ("%s: sc->components is NULL", __func__));
        for (i = 0; i < sc->n_components; i++)
                if (sc->components[i].gcons != NULL)
                        nc++;
        return (nc);
}

/*
 * Called when the consumer gets orphaned (?)
 */
static void
g_virstor_orphan(struct g_consumer *cp)
{
        struct g_virstor_softc *sc;
        struct g_virstor_component *comp;
        struct g_geom *gp;

        g_topology_assert();
        gp = cp->geom;
        sc = gp->softc;
        if (sc == NULL)
                return;

        comp = cp->private;
        KASSERT(comp != NULL, ("%s: No component in private part of consumer",
            __func__));
        remove_component(sc, comp, FALSE);
        if (LIST_EMPTY(&gp->consumer))
                virstor_geom_destroy(sc, TRUE, FALSE);
}

/*
 * Called to notify geom when it's been opened, and for what intent
 */
static int
g_virstor_access(struct g_provider *pp, int dr, int dw, int de)
{
        struct g_consumer *c, *c2, *tmp;
        struct g_virstor_softc *sc;
        struct g_geom *gp;
        int error;

        KASSERT(pp != NULL, ("%s: NULL provider", __func__));
        gp = pp->geom;
        KASSERT(gp != NULL, ("%s: NULL geom", __func__));
        sc = gp->softc;

        /* Grab an exclusive bit to propagate on our consumers on first open */
        if (pp->acr == 0 && pp->acw == 0 && pp->ace == 0)
                de++;
        /* ... drop it on close */
        if (pp->acr + dr == 0 && pp->acw + dw == 0 && pp->ace + de == 0) {
                de--;
                if (sc != NULL)
                        update_metadata(sc);
        }

        error = ENXIO;
        LIST_FOREACH_SAFE(c, &gp->consumer, consumer, tmp) {
                error = g_access(c, dr, dw, de);
                if (error != 0)
                        goto fail;
                if (c->acr == 0 && c->acw == 0 && c->ace == 0 &&
                    c->flags & G_CF_ORPHAN) {
                        g_detach(c);
                        g_destroy_consumer(c);
                }
        }

        if (sc != NULL && LIST_EMPTY(&gp->consumer))
                virstor_geom_destroy(sc, TRUE, FALSE);

        return (error);

fail:
        /* Backout earlier changes */
        LIST_FOREACH(c2, &gp->consumer, consumer) {
                if (c2 == c)
                        break;
                g_access(c2, -dr, -dw, -de);
        }
        return (error);
}

/*
 * Generate XML dump of current state
 */
static void
g_virstor_dumpconf(struct sbuf *sb, const char *indent, struct g_geom *gp,
    struct g_consumer *cp, struct g_provider *pp)
{
        struct g_virstor_softc *sc;

        g_topology_assert();
        sc = gp->softc;

        if (sc == NULL || pp != NULL)
                return;

        if (cp != NULL) {
                /* For each component */
                struct g_virstor_component *comp;

                comp = cp->private;
                if (comp == NULL)
                        return;
                sbuf_printf(sb, "%s<ComponentIndex>%u</ComponentIndex>\n",
                    indent, comp->index);
                sbuf_printf(sb, "%s<ChunkCount>%u</ChunkCount>\n",
                    indent, comp->chunk_count);
                sbuf_printf(sb, "%s<ChunksUsed>%u</ChunksUsed>\n",
                    indent, comp->chunk_next);
                sbuf_printf(sb, "%s<ChunksReserved>%u</ChunksReserved>\n",
                    indent, comp->chunk_reserved);
                sbuf_printf(sb, "%s<StorageFree>%u%%</StorageFree>\n",
                    indent,
                    comp->chunk_next > 0 ? 100 -
                    ((comp->chunk_next + comp->chunk_reserved) * 100) /
                    comp->chunk_count : 100);
        } else {
                /* For the whole thing */
                u_int count, used, i;
                off_t size;

                count = used = size = 0;
                for (i = 0; i < sc->n_components; i++) {
                        if (sc->components[i].gcons != NULL) {
                                count += sc->components[i].chunk_count;
                                used += sc->components[i].chunk_next +
                                    sc->components[i].chunk_reserved;
                                size += sc->components[i].gcons->
                                    provider->mediasize;
                        }
                }

                sbuf_printf(sb, "%s<Status>"
                    "Components=%u, Online=%u</Status>\n", indent,
                    sc->n_components, virstor_valid_components(sc));
                sbuf_printf(sb, "%s<State>%u%% physical free</State>\n",
                    indent, 100-(used * 100) / count);
                sbuf_printf(sb, "%s<ChunkSize>%zu</ChunkSize>\n", indent,
                    sc->chunk_size);
                sbuf_printf(sb, "%s<PhysicalFree>%u%%</PhysicalFree>\n",
                    indent, used > 0 ? 100 - (used * 100) / count : 100);
                sbuf_printf(sb, "%s<ChunkPhysicalCount>%u</ChunkPhysicalCount>\n",
                    indent, count);
                sbuf_printf(sb, "%s<ChunkVirtualCount>%zu</ChunkVirtualCount>\n",
                    indent, sc->chunk_count);
                sbuf_printf(sb, "%s<PhysicalBacking>%zu%%</PhysicalBacking>\n",
                    indent,
                    (count * 100) / sc->chunk_count);
                sbuf_printf(sb, "%s<PhysicalBackingSize>%jd</PhysicalBackingSize>\n",
                    indent, size);
                sbuf_printf(sb, "%s<VirtualSize>%jd</VirtualSize>\n", indent,
                    sc->virsize);
        }
}

/*
 * GEOM .done handler
 * Can't use standard handler because one requested IO may
 * fork into additional data IOs
 */
static void
g_virstor_done(struct bio *b)
{
        struct bio *parent_b;

        parent_b = b->bio_parent;

        if (b->bio_error != 0) {
                LOG_MSG(LVL_ERROR, "Error %d for offset=%ju, length=%ju, %s",
                    b->bio_error, b->bio_offset, b->bio_length,
                    b->bio_to->name);
                if (parent_b->bio_error == 0)
                        parent_b->bio_error = b->bio_error;
        }

        parent_b->bio_inbed++;
        parent_b->bio_completed += b->bio_completed;

        if (parent_b->bio_children == parent_b->bio_inbed) {
                parent_b->bio_completed = parent_b->bio_length;
                g_io_deliver(parent_b, parent_b->bio_error);
        }
        g_destroy_bio(b);
}

/*
 * I/O starts here
 * Called in g_down thread
 */
static void
g_virstor_start(struct bio *b)
{
        struct g_virstor_softc *sc;
        struct g_virstor_component *comp;
        struct bio *cb;
        struct g_provider *pp;
        char *addr;
        off_t offset, length;
        struct bio_queue_head bq;
        size_t chunk_size;      /* cached for convenience */
        u_int count;

        pp = b->bio_to;
        sc = pp->geom->softc;
        KASSERT(sc != NULL, ("%s: no softc (error=%d, device=%s)", __func__,
            b->bio_to->error, b->bio_to->name));

        LOG_REQ(LVL_MOREDEBUG, b, "%s", __func__);

        switch (b->bio_cmd) {
        case BIO_READ:
        case BIO_WRITE:
        case BIO_DELETE:
                break;
        default:
                g_io_deliver(b, EOPNOTSUPP);
                return;
        }

        LOG_MSG(LVL_DEBUG2, "BIO arrived, size=%ju", b->bio_length);
        bioq_init(&bq);

        chunk_size = sc->chunk_size;
        addr = b->bio_data;
        offset = b->bio_offset; /* virtual offset and length */
        length = b->bio_length;

        while (length > 0) {
                size_t chunk_index, in_chunk_offset, in_chunk_length;
                struct virstor_map_entry *me;

                chunk_index = offset / chunk_size; /* round downwards */
                in_chunk_offset = offset % chunk_size;
                in_chunk_length = min(length, chunk_size - in_chunk_offset);
                LOG_MSG(LVL_DEBUG, "Mapped %s(%ju, %ju) to (%zu,%zu,%zu)",
                    b->bio_cmd == BIO_READ ? "R" : "W",
                    offset, length,
                    chunk_index, in_chunk_offset, in_chunk_length);
                me = &sc->map[chunk_index];

                if (b->bio_cmd == BIO_READ || b->bio_cmd == BIO_DELETE) {
                        if ((me->flags & VIRSTOR_MAP_ALLOCATED) == 0) {
                                /* Reads from unallocated chunks return zeroed
                                 * buffers */
                                if (b->bio_cmd == BIO_READ)
                                        bzero(addr, in_chunk_length);
                        } else {
                                comp = &sc->components[me->provider_no];

                                cb = g_clone_bio(b);
                                if (cb == NULL) {
                                        bioq_dismantle(&bq);
                                        if (b->bio_error == 0)
                                                b->bio_error = ENOMEM;
                                        g_io_deliver(b, b->bio_error);
                                        return;
                                }
                                cb->bio_to = comp->gcons->provider;
                                cb->bio_done = g_virstor_done;
                                cb->bio_offset =
                                    (off_t)me->provider_chunk * (off_t)chunk_size
                                    + in_chunk_offset;
                                cb->bio_length = in_chunk_length;
                                cb->bio_data = addr;
                                cb->bio_caller1 = comp;
                                bioq_disksort(&bq, cb);
                        }
                } else { /* handle BIO_WRITE */
                        KASSERT(b->bio_cmd == BIO_WRITE,
                            ("%s: Unknown command %d", __func__,
                            b->bio_cmd));

                        if ((me->flags & VIRSTOR_MAP_ALLOCATED) == 0) {
                                /* We have a virtual chunk, represented by
                                 * the "me" entry, but it's not yet allocated
                                 * (tied to) a physical chunk. So do it now. */
                                struct virstor_map_entry *data_me;
                                u_int phys_chunk, comp_no;
                                off_t s_offset;
                                int error;

                                error = allocate_chunk(sc, &comp, &comp_no,
                                    &phys_chunk);
                                if (error != 0) {
                                        /* We cannot allocate a physical chunk
                                         * to satisfy this request, so we'll
                                         * delay it to when we can...
                                         * XXX: this will prevent the fs from
                                         * being umounted! */
                                        struct g_virstor_bio_q *biq;
                                        biq = malloc(sizeof(*biq), M_GVIRSTOR,
                                            M_NOWAIT);
                                        if (biq == NULL) {
                                                bioq_dismantle(&bq);
                                                if (b->bio_error == 0)
                                                        b->bio_error = ENOMEM;
                                                g_io_deliver(b, b->bio_error);
                                                return;
                                        }
                                        biq->bio = b;
                                        mtx_lock(&sc->delayed_bio_q_mtx);
                                        STAILQ_INSERT_TAIL(&sc->delayed_bio_q,
                                            biq, linkage);
                                        mtx_unlock(&sc->delayed_bio_q_mtx);
                                        LOG_MSG(LVL_WARNING, "Delaying BIO "
                                            "(size=%ju) until free physical "
                                            "space can be found on %s",
                                            b->bio_length,
                                            sc->provider->name);
                                        return;
                                }
                                LOG_MSG(LVL_DEBUG, "Allocated chunk %u on %s "
                                    "for %s",
                                    phys_chunk,
                                    comp->gcons->provider->name,
                                    sc->provider->name);

                                me->provider_no = comp_no;
                                me->provider_chunk = phys_chunk;
                                me->flags |= VIRSTOR_MAP_ALLOCATED;

                                cb = g_clone_bio(b);
                                if (cb == NULL) {
                                        me->flags &= ~VIRSTOR_MAP_ALLOCATED;
                                        me->provider_no = 0;
                                        me->provider_chunk = 0;
                                        bioq_dismantle(&bq);
                                        if (b->bio_error == 0)
                                                b->bio_error = ENOMEM;
                                        g_io_deliver(b, b->bio_error);
                                        return;
                                }

                                /* The allocation table is stored continuously
                                 * at the start of the drive. We need to
                                 * calculate the offset of the sector that holds
                                 * this map entry both on the drive and in the
                                 * map array.
                                 * sc_offset will end up pointing to the drive
                                 * sector. */
                                s_offset = chunk_index * sizeof(*me);
                                s_offset = rounddown(s_offset, sc->sectorsize);

                                /* data_me points to map entry sector
                                 * in memory (analogous to offset) */
                                data_me = &sc->map[rounddown(chunk_index,
                                    sc->me_per_sector)];

                                /* Commit sector with map entry to storage */
                                cb->bio_to = sc->components[0].gcons->provider;
                                cb->bio_done = g_virstor_done;
                                cb->bio_offset = s_offset;
                                cb->bio_data = (char *)data_me;
                                cb->bio_length = sc->sectorsize;
                                cb->bio_caller1 = &sc->components[0];
                                bioq_disksort(&bq, cb);
                        }

                        comp = &sc->components[me->provider_no];
                        cb = g_clone_bio(b);
                        if (cb == NULL) {
                                bioq_dismantle(&bq);
                                if (b->bio_error == 0)
                                        b->bio_error = ENOMEM;
                                g_io_deliver(b, b->bio_error);
                                return;
                        }
                        /* Finally, handle the data */
                        cb->bio_to = comp->gcons->provider;
                        cb->bio_done = g_virstor_done;
                        cb->bio_offset = (off_t)me->provider_chunk*(off_t)chunk_size +
                            in_chunk_offset;
                        cb->bio_length = in_chunk_length;
                        cb->bio_data = addr;
                        cb->bio_caller1 = comp;
                        bioq_disksort(&bq, cb);
                }
                addr += in_chunk_length;
                length -= in_chunk_length;
                offset += in_chunk_length;
        }

        /* Fire off bio's here */
        count = 0;
        for (cb = bioq_first(&bq); cb != NULL; cb = bioq_first(&bq)) {
                bioq_remove(&bq, cb);
                LOG_REQ(LVL_MOREDEBUG, cb, "Firing request");
                comp = cb->bio_caller1;
                cb->bio_caller1 = NULL;
                LOG_MSG(LVL_DEBUG, " firing bio, offset=%ju, length=%ju",
                    cb->bio_offset, cb->bio_length);
                g_io_request(cb, comp->gcons);
                count++;
        }
        if (count == 0) { /* We handled everything locally */
                b->bio_completed = b->bio_length;
                g_io_deliver(b, 0);
        }

}

/*
 * Allocate a chunk from a physical provider. Returns physical component,
 * chunk index relative to the component and the component's index.
 */
static int
allocate_chunk(struct g_virstor_softc *sc, struct g_virstor_component **comp,
    u_int *comp_no_p, u_int *chunk)
{
        u_int comp_no;

        KASSERT(sc->curr_component < sc->n_components,
            ("%s: Invalid curr_component: %u",  __func__, sc->curr_component));

        comp_no = sc->curr_component;
        *comp = &sc->components[comp_no];
        dump_component(*comp);
        if ((*comp)->chunk_next >= (*comp)->chunk_count) {
                /* This component is full. Allocate next component */
                if (comp_no >= sc->n_components-1) {
                        LOG_MSG(LVL_ERROR, "All physical space allocated for %s",
                            sc->geom->name);
                        return (-1);
                }
                (*comp)->flags &= ~VIRSTOR_PROVIDER_CURRENT;
                sc->curr_component = ++comp_no;

                *comp = &sc->components[comp_no];
                if (comp_no >= sc->n_components - g_virstor_component_watermark-1)
                        LOG_MSG(LVL_WARNING, "Device %s running out of components "
                            "(switching to %u/%u: %s)", sc->geom->name,
                            comp_no+1, sc->n_components,
                            (*comp)->gcons->provider->name);
                /* Take care not to overwrite reserved chunks */
                if ( (*comp)->chunk_reserved > 0 &&
                    (*comp)->chunk_next < (*comp)->chunk_reserved)
                        (*comp)->chunk_next = (*comp)->chunk_reserved;

                (*comp)->flags |=
                    VIRSTOR_PROVIDER_ALLOCATED | VIRSTOR_PROVIDER_CURRENT;
                dump_component(*comp);
                *comp_no_p = comp_no;
                *chunk = (*comp)->chunk_next++;
        } else {
                *comp_no_p = comp_no;
                *chunk = (*comp)->chunk_next++;
        }
        return (0);
}

/* Dump a component */
static void
dump_component(struct g_virstor_component *comp)
{

        if (g_virstor_debug < LVL_DEBUG2)
                return;
        printf("Component %d: %s\n", comp->index, comp->gcons->provider->name);
        printf("  chunk_count: %u\n", comp->chunk_count);
        printf("   chunk_next: %u\n", comp->chunk_next);
        printf("        flags: %u\n", comp->flags);
}

#if 0
/* Dump a map entry */
static void
dump_me(struct virstor_map_entry *me, unsigned int nr)
{
        if (g_virstor_debug < LVL_DEBUG)
                return;
        printf("VIRT. CHUNK #%d: ", nr);
        if ((me->flags & VIRSTOR_MAP_ALLOCATED) == 0)
                printf("(unallocated)\n");
        else
                printf("allocated at provider %u, provider_chunk %u\n",
                    me->provider_no, me->provider_chunk);
}
#endif

/*
 * Dismantle bio_queue and destroy its components
 */
static void
bioq_dismantle(struct bio_queue_head *bq)
{
        struct bio *b;

        for (b = bioq_first(bq); b != NULL; b = bioq_first(bq)) {
                bioq_remove(bq, b);
                g_destroy_bio(b);
        }
}

/*
 * The function that shouldn't be called.
 * When this is called, the stack is already garbled because of
 * argument mismatch. There's nothing to do now but panic, which is
 * accidentally the whole purpose of this function.
 * Motivation: to guard from accidentally calling geom methods when
 * they shouldn't be called. (see g_..._taste)
 */
static void
invalid_call(void)
{
        panic("invalid_call() has just been called. Something's fishy here.");
}

DECLARE_GEOM_CLASS(g_virstor_class, g_virstor); /* Let there be light */
MODULE_VERSION(geom_virstor, 0);