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

[FreeBSD/releng/10.0.git] / sys / geom / sched / g_sched.c

/*-
 * Copyright (c) 2009-2010 Fabio Checconi
 * Copyright (c) 2009-2010 Luigi Rizzo, Universita` di Pisa
 * 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.
 */

/*
 * $Id$
 * $FreeBSD$
 *
 * Main control module for geom-based disk schedulers ('sched').
 *
 * USER VIEW
 * A 'sched' node is typically inserted transparently between
 * an existing provider pp and its original geom gp
 *
 *      [pp --> gp  ..]
 *
 * using the command "geom sched insert <provider>" and
 * resulting in the following topology
 *
 *      [pp --> sched_gp --> cp]   [new_pp --> gp ... ]
 *
 * Deletion "geom sched destroy <provider>.sched." restores the
 * original chain. The normal "geom sched create <provide>"
 * is also supported.
 *
 * INTERNALS
 * Internally, the 'sched' uses the following data structures
 *
 *   geom{}         g_sched_softc{}      g_gsched{}
 * +----------+    +---------------+   +-------------+
 * |  softc *-|--->| sc_gsched   *-|-->|  gs_init    |
 * |  ...     |    |               |   |  gs_fini    |
 * |          |    | [ hash table] |   |  gs_start   |
 * +----------+    |               |   |  ...        |
 *                 |               |   +-------------+
 *                 |               |
 *                 |               |     g_*_softc{}
 *                 |               |   +-------------+
 *                 | sc_data     *-|-->|             |
 *                 +---------------+   |  algorithm- |
 *                                     |  specific   |
 *                                     +-------------+
 *
 * A g_sched_softc{} is created with a "geom sched insert" call.
 * In turn this instantiates a specific scheduling algorithm,
 * which sets sc_gsched to point to the algorithm callbacks,
 * and calls gs_init() to create the g_*_softc{} .
 * The other callbacks (gs_start, gs_next, ...) are invoked
 * as needed 
 *
 * g_sched_softc{} is defined in g_sched.h and mostly used here;
 * g_gsched{}, and the gs_callbacks, are documented in gs_scheduler.h;
 * g_*_softc{} is defined/implemented by each algorithm (gs_*.c)
 *
 * DATA MOVING
 * When a bio is received on the provider, it goes to the
 * g_sched_start() which calls gs_start() to initially queue it;
 * then we call g_sched_dispatch() that loops around gs_next()
 * to select zero or more bio's to be sent downstream.
 *
 * g_sched_dispatch() can also be called as a result of a timeout,
 * e.g. when doing anticipation or pacing requests.
 *
 * When a bio comes back, it goes to g_sched_done() which in turn
 * calls gs_done(). The latter does any necessary housekeeping in
 * the scheduling algorithm, and may decide to call g_sched_dispatch()
 * to send more bio's downstream.
 *
 * If an algorithm needs per-flow queues, these are created
 * calling gs_init_class() and destroyed with gs_fini_class(),
 * and they are also inserted in the hash table implemented in
 * the g_sched_softc{}
 *
 * If an algorithm is replaced, or a transparently-inserted node is
 * removed with "geom sched destroy", we need to remove all references
 * to the g_*_softc{} and g_sched_softc from the bio's still in
 * the scheduler. g_sched_forced_dispatch() helps doing this.
 * XXX need to explain better.
 */

#include <sys/cdefs.h>
#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/bio.h>
#include <sys/limits.h>
#include <sys/hash.h>
#include <sys/sbuf.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/proc.h>           /* we access curthread */
#include <geom/geom.h>
#include "gs_scheduler.h"
#include "g_sched.h"            /* geom hooks */

/*
 * Size of the per-geom hash table storing traffic classes.
 * We may decide to change it at a later time, it has no ABI
 * implications as it is only used for run-time allocations.
 */
#define G_SCHED_HASH_SIZE       32

static int g_sched_destroy(struct g_geom *gp, boolean_t force);
static int g_sched_destroy_geom(struct gctl_req *req,
    struct g_class *mp, struct g_geom *gp);
static void g_sched_config(struct gctl_req *req, struct g_class *mp,
    const char *verb);
static struct g_geom *g_sched_taste(struct g_class *mp,
    struct g_provider *pp, int flags __unused);
static void g_sched_dumpconf(struct sbuf *sb, const char *indent,
    struct g_geom *gp, struct g_consumer *cp, struct g_provider *pp);
static void g_sched_init(struct g_class *mp);
static void g_sched_fini(struct g_class *mp);
static int g_sched_ioctl(struct g_provider *pp, u_long cmd, void *data,
    int fflag, struct thread *td);

struct g_class g_sched_class = {
        .name = G_SCHED_CLASS_NAME,
        .version = G_VERSION,
        .ctlreq = g_sched_config,
        .taste = g_sched_taste,
        .destroy_geom = g_sched_destroy_geom,
        .init = g_sched_init,
        .ioctl = g_sched_ioctl,
        .fini = g_sched_fini
};

MALLOC_DEFINE(M_GEOM_SCHED, "GEOM_SCHED", "Geom schedulers data structures");

/*
 * Global variables describing the state of the geom_sched module.
 * There is only one static instance of this structure.
 */
LIST_HEAD(gs_list, g_gsched);   /* type, link field */
struct geom_sched_vars {
        struct mtx      gs_mtx;
        struct gs_list  gs_scheds;      /* list of algorithms */
        u_int           gs_debug;
        u_int           gs_sched_count; /* how many algorithms ? */
        u_int           gs_patched;     /* g_io_request was patched */

        u_int           gs_initialized;
        u_int           gs_expire_secs; /* expiration of hash entries */

        struct bio_queue_head gs_pending;
        u_int           gs_npending;

        /* The following are for stats, usually protected by gs_mtx. */
        u_long          gs_requests;    /* total requests */
        u_long          gs_done;        /* total done */
        u_int           gs_in_flight;   /* requests in flight */
        u_int           gs_writes_in_flight;
        u_int           gs_bytes_in_flight;
        u_int           gs_write_bytes_in_flight;

        char            gs_names[256];  /* names of schedulers */
};

static struct geom_sched_vars me = {
        .gs_expire_secs = 10,
};

SYSCTL_DECL(_kern_geom);
SYSCTL_NODE(_kern_geom, OID_AUTO, sched, CTLFLAG_RW, 0,
    "GEOM_SCHED stuff");

SYSCTL_UINT(_kern_geom_sched, OID_AUTO, in_flight_wb, CTLFLAG_RD,
    &me.gs_write_bytes_in_flight, 0, "Write bytes in flight");

SYSCTL_UINT(_kern_geom_sched, OID_AUTO, in_flight_b, CTLFLAG_RD,
    &me.gs_bytes_in_flight, 0, "Bytes in flight");

SYSCTL_UINT(_kern_geom_sched, OID_AUTO, in_flight_w, CTLFLAG_RD,
    &me.gs_writes_in_flight, 0, "Write Requests in flight");

SYSCTL_UINT(_kern_geom_sched, OID_AUTO, in_flight, CTLFLAG_RD,
    &me.gs_in_flight, 0, "Requests in flight");

SYSCTL_ULONG(_kern_geom_sched, OID_AUTO, done, CTLFLAG_RD,
    &me.gs_done, 0, "Total done");

SYSCTL_ULONG(_kern_geom_sched, OID_AUTO, requests, CTLFLAG_RD,
    &me.gs_requests, 0, "Total requests");

SYSCTL_STRING(_kern_geom_sched, OID_AUTO, algorithms, CTLFLAG_RD,
    &me.gs_names, 0, "Algorithm names");

SYSCTL_UINT(_kern_geom_sched, OID_AUTO, alg_count, CTLFLAG_RD,
    &me.gs_sched_count, 0, "Number of algorithms");

SYSCTL_UINT(_kern_geom_sched, OID_AUTO, debug, CTLFLAG_RW,
    &me.gs_debug, 0, "Debug level");

SYSCTL_UINT(_kern_geom_sched, OID_AUTO, expire_secs, CTLFLAG_RW,
    &me.gs_expire_secs, 0, "Expire time in seconds");

/*
 * g_sched calls the scheduler algorithms with this lock held.
 * The locking functions are exposed so the scheduler algorithms can also
 * protect themselves e.g. when running a callout handler.
 */
void
g_sched_lock(struct g_geom *gp)
{
        struct g_sched_softc *sc = gp->softc;

        mtx_lock(&sc->sc_mtx);
}

void
g_sched_unlock(struct g_geom *gp)
{
        struct g_sched_softc *sc = gp->softc;

        mtx_unlock(&sc->sc_mtx);
}

/*
 * Support functions to handle references to the module,
 * which are coming from devices using this scheduler.
 */
static inline void
g_gsched_ref(struct g_gsched *gsp)
{

        atomic_add_int(&gsp->gs_refs, 1);
}

static inline void
g_gsched_unref(struct g_gsched *gsp)
{

        atomic_add_int(&gsp->gs_refs, -1);
}

/*
 * Update the stats when this request is done.
 */
static void
g_sched_update_stats(struct bio *bio)
{

        me.gs_done++;
        me.gs_in_flight--;
        me.gs_bytes_in_flight -= bio->bio_length;
        if (bio->bio_cmd & BIO_WRITE) {
                me.gs_writes_in_flight--;
                me.gs_write_bytes_in_flight -= bio->bio_length;
        }
}

/*
 * Dispatch any pending request.
 */
static void
g_sched_forced_dispatch(struct g_geom *gp)
{
        struct g_sched_softc *sc = gp->softc;
        struct g_gsched *gsp = sc->sc_gsched;
        struct bio *bp;

        KASSERT(mtx_owned(&sc->sc_mtx),
            ("sc_mtx not owned during forced dispatch"));

        while ((bp = gsp->gs_next(sc->sc_data, 1)) != NULL)
                g_io_request(bp, LIST_FIRST(&gp->consumer));
}

/*
 * The main dispatch loop, called either here after the start
 * routine, or by scheduling algorithms when they receive a timeout
 * or a 'done' notification.  Does not share code with the forced
 * dispatch path, since the gs_done() callback can call us.
 */
void
g_sched_dispatch(struct g_geom *gp)
{
        struct g_sched_softc *sc = gp->softc;
        struct g_gsched *gsp = sc->sc_gsched;
        struct bio *bp;

        KASSERT(mtx_owned(&sc->sc_mtx), ("sc_mtx not owned during dispatch"));

        if ((sc->sc_flags & G_SCHED_FLUSHING))
                return;

        while ((bp = gsp->gs_next(sc->sc_data, 0)) != NULL)
                g_io_request(bp, LIST_FIRST(&gp->consumer));
}

/*
 * Recent (8.0 and above) versions of FreeBSD have support to
 * register classifiers of disk requests. The classifier is
 * invoked by g_io_request(), and stores the information into
 * bp->bio_classifier1.
 *
 * Support for older versions, which is left here only for
 * documentation purposes, relies on two hacks:
 * 1. classification info is written into the bio_caller1
 *    field of the topmost node in the bio chain. This field
 *    is rarely used, but this module is incompatible with
 *    those that use bio_caller1 for other purposes,
 *    such as ZFS and gjournal;
 * 2. g_io_request() is patched in-memory when the module is
 *    loaded, so that the function calls a classifier as its
 *    first thing. g_io_request() is restored when the module
 *    is unloaded. This functionality is only supported for
 *    x86 and amd64, other architectures need source code changes.
 */

/*
 * Lookup the identity of the issuer of the original request.
 * In the current implementation we use the curthread of the
 * issuer, but different mechanisms may be implemented later
 * so we do not make assumptions on the return value which for
 * us is just an opaque identifier.
 */

static inline u_long
g_sched_classify(struct bio *bp)
{

#if __FreeBSD_version > 800098
        /* we have classifier fields in the struct bio */
#define HAVE_BIO_CLASSIFIER
        return ((u_long)bp->bio_classifier1);
#else
#warning old version!!!
        while (bp->bio_parent != NULL)
                bp = bp->bio_parent;

        return ((u_long)bp->bio_caller1);
#endif
}

/* Return the hash chain for the given key. */
static inline struct g_hash *
g_sched_hash(struct g_sched_softc *sc, u_long key)
{

        return (&sc->sc_hash[key & sc->sc_mask]);
}

/*
 * Helper function for the children classes, which takes
 * a geom and a bio and returns the private descriptor
 * associated to the request.  This involves fetching
 * the classification field and [al]locating the
 * corresponding entry in the hash table.
 */
void *
g_sched_get_class(struct g_geom *gp, struct bio *bp)
{
        struct g_sched_softc *sc;
        struct g_sched_class *gsc;
        struct g_gsched *gsp;
        struct g_hash *bucket;
        u_long key;

        sc = gp->softc;
        key = g_sched_classify(bp);
        bucket = g_sched_hash(sc, key);
        LIST_FOREACH(gsc, bucket, gsc_clist) {
                if (key == gsc->gsc_key) {
                        gsc->gsc_refs++;
                        return (gsc->gsc_priv);
                }
        }

        gsp = sc->sc_gsched;
        gsc = malloc(sizeof(*gsc) + gsp->gs_priv_size,
            M_GEOM_SCHED, M_NOWAIT | M_ZERO);
        if (!gsc)
                return (NULL);

        if (gsp->gs_init_class(sc->sc_data, gsc->gsc_priv)) {
                free(gsc, M_GEOM_SCHED);
                return (NULL);
        }

        gsc->gsc_refs = 2;      /* 1 for the hash table, 1 for the caller. */
        gsc->gsc_key = key;
        LIST_INSERT_HEAD(bucket, gsc, gsc_clist);

        gsc->gsc_expire = ticks + me.gs_expire_secs * hz;

        return (gsc->gsc_priv);
}

/*
 * Release a reference to the per-client descriptor,
 */
void
g_sched_put_class(struct g_geom *gp, void *priv)
{
        struct g_sched_class *gsc;
        struct g_sched_softc *sc;

        gsc = g_sched_priv2class(priv);
        gsc->gsc_expire = ticks + me.gs_expire_secs * hz;

        if (--gsc->gsc_refs > 0)
                return;

        sc = gp->softc;
        sc->sc_gsched->gs_fini_class(sc->sc_data, priv);

        LIST_REMOVE(gsc, gsc_clist);
        free(gsc, M_GEOM_SCHED);
}

static void
g_sched_hash_fini(struct g_geom *gp, struct g_hash *hp, u_long mask,
    struct g_gsched *gsp, void *data)
{
        struct g_sched_class *cp, *cp2;
        int i;

        if (!hp)
                return;

        if (data && gsp->gs_hash_unref)
                gsp->gs_hash_unref(data);

        for (i = 0; i < G_SCHED_HASH_SIZE; i++) {
                LIST_FOREACH_SAFE(cp, &hp[i], gsc_clist, cp2)
                        g_sched_put_class(gp, cp->gsc_priv);
        }

        hashdestroy(hp, M_GEOM_SCHED, mask);
}

static struct g_hash *
g_sched_hash_init(struct g_gsched *gsp, u_long *mask, int flags)
{
        struct g_hash *hash;

        if (gsp->gs_priv_size == 0)
                return (NULL);

        hash = hashinit_flags(G_SCHED_HASH_SIZE, M_GEOM_SCHED, mask, flags);

        return (hash);
}

static void
g_sched_flush_classes(struct g_geom *gp)
{
        struct g_sched_softc *sc;
        struct g_sched_class *cp, *cp2;
        int i;

        sc = gp->softc;

        if (!sc->sc_hash || ticks - sc->sc_flush_ticks <= 0)
                return;

        for (i = 0; i < G_SCHED_HASH_SIZE; i++) {
                LIST_FOREACH_SAFE(cp, &sc->sc_hash[i], gsc_clist, cp2) {
                        if (cp->gsc_refs == 1 && ticks - cp->gsc_expire > 0)
                                g_sched_put_class(gp, cp->gsc_priv);
                }
        }

        sc->sc_flush_ticks = ticks + me.gs_expire_secs * hz;
}

/*
 * Wait for the completion of any outstanding request.  To ensure
 * that this does not take forever the caller has to make sure that
 * no new request enter the scehduler before calling us.
 *
 * Must be called with the gp mutex held and topology locked.
 */
static int
g_sched_wait_pending(struct g_geom *gp)
{
        struct g_sched_softc *sc = gp->softc;
        int endticks = ticks + hz;

        g_topology_assert();

        while (sc->sc_pending && endticks - ticks >= 0)
                msleep(gp, &sc->sc_mtx, 0, "sched_wait_pending", hz / 4);

        return (sc->sc_pending ? ETIMEDOUT : 0);
}

static int
g_sched_remove_locked(struct g_geom *gp, struct g_gsched *gsp)
{
        struct g_sched_softc *sc = gp->softc;
        int error;

        /* Set the flushing flag: new bios will not enter the scheduler. */
        sc->sc_flags |= G_SCHED_FLUSHING;

        g_sched_forced_dispatch(gp);
        error = g_sched_wait_pending(gp);
        if (error)
                goto failed;
        
        /* No more requests pending or in flight from the old gsp. */

        g_sched_hash_fini(gp, sc->sc_hash, sc->sc_mask, gsp, sc->sc_data);
        sc->sc_hash = NULL;

        /*
         * Avoid deadlock here by releasing the gp mutex and reacquiring
         * it once done.  It should be safe, since no reconfiguration or
         * destruction can take place due to the geom topology lock; no
         * new request can use the current sc_data since we flagged the
         * geom as being flushed.
         */
        g_sched_unlock(gp);
        gsp->gs_fini(sc->sc_data);
        g_sched_lock(gp);

        sc->sc_gsched = NULL;
        sc->sc_data = NULL;
        g_gsched_unref(gsp);

failed:
        sc->sc_flags &= ~G_SCHED_FLUSHING;

        return (error);
}

static int
g_sched_remove(struct g_geom *gp, struct g_gsched *gsp)
{
        int error;

        g_sched_lock(gp);
        error = g_sched_remove_locked(gp, gsp); /* gsp is surely non-null */
        g_sched_unlock(gp);

        return (error);
}

/*
 * Support function for create/taste -- locate the desired
 * algorithm and grab a reference to it.
 */
static struct g_gsched *
g_gsched_find(const char *name)
{
        struct g_gsched *gsp = NULL;

        mtx_lock(&me.gs_mtx);
        LIST_FOREACH(gsp, &me.gs_scheds, glist) {
                if (strcmp(name, gsp->gs_name) == 0) {
                        g_gsched_ref(gsp);
                        break;
                }
        }
        mtx_unlock(&me.gs_mtx);

        return (gsp);
}

/*
 * Rebuild the list of scheduler names.
 * To be called with me.gs_mtx lock held.
 */
static void
g_gsched_build_names(struct g_gsched *gsp)
{
        int pos, l;
        struct g_gsched *cur;

        pos = 0;
        LIST_FOREACH(cur, &me.gs_scheds, glist) {
                l = strlen(cur->gs_name);
                if (l + pos + 1 + 1 < sizeof(me.gs_names)) {
                        if (pos != 0)
                                me.gs_names[pos++] = ' ';
                        strcpy(me.gs_names + pos, cur->gs_name);
                        pos += l;
                }
        }
        me.gs_names[pos] = '\0';
}

/*
 * Register or unregister individual scheduling algorithms.
 */
static int
g_gsched_register(struct g_gsched *gsp)
{
        struct g_gsched *cur;
        int error = 0;

        mtx_lock(&me.gs_mtx);
        LIST_FOREACH(cur, &me.gs_scheds, glist) {
                if (strcmp(gsp->gs_name, cur->gs_name) == 0)
                        break;
        }
        if (cur != NULL) {
                G_SCHED_DEBUG(0, "A scheduler named %s already"
                    "exists.", gsp->gs_name);
                error = EEXIST;
        } else {
                LIST_INSERT_HEAD(&me.gs_scheds, gsp, glist);
                gsp->gs_refs = 1;
                me.gs_sched_count++;
                g_gsched_build_names(gsp);
        }
        mtx_unlock(&me.gs_mtx);

        return (error);
}

struct g_gsched_unregparm {
        struct g_gsched *gup_gsp;
        int             gup_error;
};

static void
g_gsched_unregister(void *arg, int flag)
{
        struct g_gsched_unregparm *parm = arg;
        struct g_gsched *gsp = parm->gup_gsp, *cur, *tmp;
        struct g_sched_softc *sc;
        struct g_geom *gp, *gp_tmp;
        int error;

        parm->gup_error = 0;

        g_topology_assert();

        if (flag == EV_CANCEL)
                return;

        mtx_lock(&me.gs_mtx);

        LIST_FOREACH_SAFE(gp, &g_sched_class.geom, geom, gp_tmp) {
                if (gp->class != &g_sched_class)
                        continue;       /* Should not happen. */

                sc = gp->softc;
                if (sc->sc_gsched == gsp) {
                        error = g_sched_remove(gp, gsp);
                        if (error)
                                goto failed;
                }
        }
                
        LIST_FOREACH_SAFE(cur, &me.gs_scheds, glist, tmp) {
                if (cur != gsp)
                        continue;

                if (gsp->gs_refs != 1) {
                        G_SCHED_DEBUG(0, "%s still in use.",
                            gsp->gs_name);
                        parm->gup_error = EBUSY;
                } else {
                        LIST_REMOVE(gsp, glist);
                        me.gs_sched_count--;
                        g_gsched_build_names(gsp);
                }
                break;
        }

        if (cur == NULL) {
                G_SCHED_DEBUG(0, "%s not registered.", gsp->gs_name);
                parm->gup_error = ENOENT;
        }

failed:
        mtx_unlock(&me.gs_mtx);
}

static inline void
g_gsched_global_init(void)
{

        if (!me.gs_initialized) {
                G_SCHED_DEBUG(0, "Initializing global data.");
                mtx_init(&me.gs_mtx, "gsched", NULL, MTX_DEF);
                LIST_INIT(&me.gs_scheds);
                gs_bioq_init(&me.gs_pending);
                me.gs_initialized = 1;
        }
}

/*
 * Module event called when a scheduling algorithm module is loaded or
 * unloaded.
 */
int
g_gsched_modevent(module_t mod, int cmd, void *arg)
{
        struct g_gsched *gsp = arg;
        struct g_gsched_unregparm parm;
        int error;

        G_SCHED_DEBUG(0, "Modevent %d.", cmd);

        /*
         * If the module is loaded at boot, the geom thread that calls
         * g_sched_init() might actually run after g_gsched_modevent(),
         * so make sure that the module is properly initialized.
         */
        g_gsched_global_init();

        error = EOPNOTSUPP;
        switch (cmd) {
        case MOD_LOAD:
                error = g_gsched_register(gsp);
                G_SCHED_DEBUG(0, "Loaded module %s error %d.",
                    gsp->gs_name, error);
                if (error == 0)
                        g_retaste(&g_sched_class);
                break;

        case MOD_UNLOAD:
                parm.gup_gsp = gsp;
                parm.gup_error = 0;

                error = g_waitfor_event(g_gsched_unregister,
                    &parm, M_WAITOK, NULL);
                if (error == 0)
                        error = parm.gup_error;
                G_SCHED_DEBUG(0, "Unloaded module %s error %d.",
                    gsp->gs_name, error);
                break;
        };

        return (error);
}

#ifdef KTR
#define TRC_BIO_EVENT(e, bp)    g_sched_trace_bio_ ## e (bp)

static inline char
g_sched_type(struct bio *bp)
{

        if (0 != (bp->bio_cmd & BIO_READ))
                return ('R');
        else if (0 != (bp->bio_cmd & BIO_WRITE))
                return ('W');
        return ('U');
}

static inline void
g_sched_trace_bio_START(struct bio *bp)
{

        CTR5(KTR_GSCHED, "S %lu %c %lu/%lu %lu", g_sched_classify(bp),
            g_sched_type(bp), bp->bio_offset / ULONG_MAX,
            bp->bio_offset, bp->bio_length);
}

static inline void
g_sched_trace_bio_DONE(struct bio *bp)
{

        CTR5(KTR_GSCHED, "D %lu %c %lu/%lu %lu", g_sched_classify(bp),
            g_sched_type(bp), bp->bio_offset / ULONG_MAX,
            bp->bio_offset, bp->bio_length);
}
#else /* !KTR */
#define TRC_BIO_EVENT(e, bp)
#endif /* !KTR */

/*
 * g_sched_done() and g_sched_start() dispatch the geom requests to
 * the scheduling algorithm in use.
 */
static void
g_sched_done(struct bio *bio)
{
        struct g_geom *gp = bio->bio_caller2;
        struct g_sched_softc *sc = gp->softc;

        TRC_BIO_EVENT(DONE, bio);

        KASSERT(bio->bio_caller1, ("null bio_caller1 in g_sched_done"));

        g_sched_lock(gp);

        g_sched_update_stats(bio);
        sc->sc_gsched->gs_done(sc->sc_data, bio);
        if (!--sc->sc_pending)
                wakeup(gp);

        g_sched_flush_classes(gp);
        g_sched_unlock(gp);

        g_std_done(bio);
}

static void
g_sched_start(struct bio *bp)
{
        struct g_geom *gp = bp->bio_to->geom;
        struct g_sched_softc *sc = gp->softc;
        struct bio *cbp;

        TRC_BIO_EVENT(START, bp);
        G_SCHED_LOGREQ(bp, "Request received.");

        cbp = g_clone_bio(bp);
        if (cbp == NULL) {
                g_io_deliver(bp, ENOMEM);
                return;
        }
        cbp->bio_done = g_sched_done;
        cbp->bio_to = LIST_FIRST(&gp->provider);
        KASSERT(cbp->bio_to != NULL, ("NULL provider"));

        /* We only schedule reads and writes. */
        if (0 == (bp->bio_cmd & (BIO_READ | BIO_WRITE)))
                goto bypass;

        G_SCHED_LOGREQ(cbp, "Sending request.");

        g_sched_lock(gp);
        /*
         * Call the algorithm's gs_start to queue the request in the
         * scheduler. If gs_start fails then pass the request down,
         * otherwise call g_sched_dispatch() which tries to push
         * one or more requests down.
         */
        if (!sc->sc_gsched || (sc->sc_flags & G_SCHED_FLUSHING) ||
            sc->sc_gsched->gs_start(sc->sc_data, cbp)) {
                g_sched_unlock(gp);
                goto bypass;
        }
        /*
         * We use bio_caller1 to mark requests that are scheduled
         * so make sure it is not NULL.
         */
        if (cbp->bio_caller1 == NULL)
                cbp->bio_caller1 = &me; /* anything not NULL */

        cbp->bio_caller2 = gp;
        sc->sc_pending++;

        /* Update general stats. */
        me.gs_in_flight++;
        me.gs_requests++;
        me.gs_bytes_in_flight += bp->bio_length;
        if (bp->bio_cmd & BIO_WRITE) {
                me.gs_writes_in_flight++;
                me.gs_write_bytes_in_flight += bp->bio_length;
        }
        g_sched_dispatch(gp);
        g_sched_unlock(gp);
        return;

bypass:
        cbp->bio_done = g_std_done;
        cbp->bio_caller1 = NULL; /* not scheduled */
        g_io_request(cbp, LIST_FIRST(&gp->consumer));
}

/*
 * The next few functions are the geom glue.
 */
static void
g_sched_orphan(struct g_consumer *cp)
{

        g_topology_assert();
        g_sched_destroy(cp->geom, 1);
}

static int
g_sched_access(struct g_provider *pp, int dr, int dw, int de)
{
        struct g_geom *gp;
        struct g_consumer *cp;
        int error;

        gp = pp->geom;
        cp = LIST_FIRST(&gp->consumer);
        error = g_access(cp, dr, dw, de);

        return (error);
}

static void
g_sched_temporary_start(struct bio *bio)
{

        mtx_lock(&me.gs_mtx);
        me.gs_npending++;
        gs_bioq_disksort(&me.gs_pending, bio);
        mtx_unlock(&me.gs_mtx);
}

static void
g_sched_flush_pending(g_start_t *start)
{
        struct bio *bp;

        while ((bp = gs_bioq_takefirst(&me.gs_pending)))
                start(bp);
}

static int
g_insert_proxy(struct g_geom *gp, struct g_provider *newpp,
    struct g_geom *dstgp, struct g_provider *pp, struct g_consumer *cp)
{
        struct g_sched_softc *sc = gp->softc;
        g_start_t *saved_start, *flush = g_sched_start;
        int error = 0, endticks = ticks + hz;

        g_cancel_event(newpp);  /* prevent taste() */
        /* copy private fields */
        newpp->private = pp->private;
        newpp->index = pp->index;

        /* Queue all the early requests coming for us. */
        me.gs_npending = 0;
        saved_start = pp->geom->start;
        dstgp->start = g_sched_temporary_start;

        while (pp->nstart - pp->nend != me.gs_npending &&
            endticks - ticks >= 0)
                tsleep(pp, PRIBIO, "-", hz/10);

        if (pp->nstart - pp->nend != me.gs_npending) {
                flush = saved_start;
                error = ETIMEDOUT;
                goto fail;
        }

        /* link pp to this geom */
        LIST_REMOVE(pp, provider);
        pp->geom = gp;
        LIST_INSERT_HEAD(&gp->provider, pp, provider);

        /*
         * replicate the counts from the parent in the
         * new provider and consumer nodes
         */
        cp->acr = newpp->acr = pp->acr;
        cp->acw = newpp->acw = pp->acw;
        cp->ace = newpp->ace = pp->ace;
        sc->sc_flags |= G_SCHED_PROXYING;

fail:
        dstgp->start = saved_start;

        g_sched_flush_pending(flush);

        return (error);
}

/*
 * Create a geom node for the device passed as *pp.
 * If successful, add a reference to this gsp.
 */
static int
g_sched_create(struct gctl_req *req, struct g_class *mp,
    struct g_provider *pp, struct g_gsched *gsp, int proxy)
{
        struct g_sched_softc *sc = NULL;
        struct g_geom *gp, *dstgp;
        struct g_provider *newpp = NULL;
        struct g_consumer *cp = NULL;
        char name[64];
        int error;

        g_topology_assert();

        snprintf(name, sizeof(name), "%s%s", pp->name, G_SCHED_SUFFIX);
        LIST_FOREACH(gp, &mp->geom, geom) {
                if (strcmp(gp->name, name) == 0) {
                        gctl_error(req, "Geom %s already exists.",
                            name);
                        return (EEXIST);
                }
        }

        gp = g_new_geomf(mp, "%s", name);
        dstgp = proxy ? pp->geom : gp; /* where do we link the provider */

        sc = g_malloc(sizeof(*sc), M_WAITOK | M_ZERO);
        sc->sc_gsched = gsp;
        sc->sc_data = gsp->gs_init(gp);
        if (sc->sc_data == NULL) {
                error = ENOMEM;
                goto fail;
        }

        sc->sc_hash = g_sched_hash_init(gsp, &sc->sc_mask, HASH_WAITOK);

        /*
         * Do not initialize the flush mechanism, will be initialized
         * on the first insertion on the hash table.
         */

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

        gp->softc = sc;
        gp->start = g_sched_start;
        gp->orphan = g_sched_orphan;
        gp->access = g_sched_access;
        gp->dumpconf = g_sched_dumpconf;

        newpp = g_new_providerf(dstgp, "%s", gp->name);
        newpp->mediasize = pp->mediasize;
        newpp->sectorsize = pp->sectorsize;

        cp = g_new_consumer(gp);
        error = g_attach(cp, proxy ? newpp : pp);
        if (error != 0) {
                gctl_error(req, "Cannot attach to provider %s.",
                    pp->name);
                goto fail;
        }

        g_error_provider(newpp, 0);
        if (proxy) {
                error = g_insert_proxy(gp, newpp, dstgp, pp, cp);
                if (error)
                        goto fail;
        }
        G_SCHED_DEBUG(0, "Device %s created.", gp->name);

        g_gsched_ref(gsp);

        return (0);

fail:
        if (cp != NULL) {
                if (cp->provider != NULL)
                        g_detach(cp);
                g_destroy_consumer(cp);
        }
        if (newpp != NULL)
                g_destroy_provider(newpp);
        if (sc->sc_hash)
                g_sched_hash_fini(gp, sc->sc_hash, sc->sc_mask,
                    gsp, sc->sc_data);
        if (sc->sc_data)
                gsp->gs_fini(sc->sc_data);
        g_free(gp->softc);
        g_destroy_geom(gp);

        return (error);
}

/*
 * Support for dynamic switching of scheduling algorithms.
 * First initialize the data structures for the new algorithm,
 * then call g_sched_remove_locked() to flush all references
 * to the old one, finally link the new algorithm.
 */
static int
g_sched_change_algo(struct gctl_req *req, struct g_class *mp,
    struct g_provider *pp, struct g_gsched *gsp)
{
        struct g_sched_softc *sc;
        struct g_geom *gp;
        struct g_hash *newh;
        void *data;
        u_long mask;
        int error = 0;

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

        data = gsp->gs_init(gp);
        if (data == NULL)
                return (ENOMEM);

        newh = g_sched_hash_init(gsp, &mask, HASH_WAITOK);
        if (gsp->gs_priv_size && !newh) {
                error = ENOMEM;
                goto fail;
        }

        g_sched_lock(gp);
        if (sc->sc_gsched) {    /* can be NULL in some cases */
                error = g_sched_remove_locked(gp, sc->sc_gsched);
                if (error)
                        goto fail;
        }

        g_gsched_ref(gsp);
        sc->sc_gsched = gsp;
        sc->sc_data = data;
        sc->sc_hash = newh;
        sc->sc_mask = mask;

        g_sched_unlock(gp);

        return (0);

fail:
        if (newh)
                g_sched_hash_fini(gp, newh, mask, gsp, data);

        if (data)
                gsp->gs_fini(data);

        g_sched_unlock(gp);

        return (error);
}

/*
 * Stop the request flow directed to the proxy, redirecting the new
 * requests to the me.gs_pending queue.
 */
static struct g_provider *
g_detach_proxy(struct g_geom *gp)
{
        struct g_consumer *cp;
        struct g_provider *pp, *newpp;

        do {
                pp = LIST_FIRST(&gp->provider);
                if (pp == NULL)
                        break;
                cp = LIST_FIRST(&gp->consumer);
                if (cp == NULL)
                        break;
                newpp = cp->provider;
                if (newpp == NULL)
                        break;

                me.gs_npending = 0;
                pp->geom->start = g_sched_temporary_start;

                return (pp);
        } while (0);
        printf("%s error detaching proxy %s\n", __FUNCTION__, gp->name);

        return (NULL);
}

static void
g_sched_blackhole(struct bio *bp)
{

        g_io_deliver(bp, ENXIO);
}

static inline void
g_reparent_provider(struct g_provider *pp, struct g_geom *gp,
    struct g_provider *newpp)
{

        LIST_REMOVE(pp, provider);
        if (newpp) {
                pp->private = newpp->private;
                pp->index = newpp->index;
        }
        pp->geom = gp;
        LIST_INSERT_HEAD(&gp->provider, pp, provider);
}

static inline void
g_unproxy_provider(struct g_provider *oldpp, struct g_provider *newpp)
{
        struct g_geom *gp = oldpp->geom;

        g_reparent_provider(oldpp, newpp->geom, newpp);

        /*
         * Hackish: let the system destroy the old provider for us, just
         * in case someone attached a consumer to it, in which case a
         * direct call to g_destroy_provider() would not work.
         */
        g_reparent_provider(newpp, gp, NULL);
}

/*
 * Complete the proxy destruction, linking the old provider to its
 * original geom, and destroying the proxy provider.  Also take care
 * of issuing the pending requests collected in me.gs_pending (if any).
 */
static int
g_destroy_proxy(struct g_geom *gp, struct g_provider *oldpp)
{
        struct g_consumer *cp;
        struct g_provider *newpp;

        do {
                cp = LIST_FIRST(&gp->consumer);
                if (cp == NULL)
                        break;
                newpp = cp->provider;
                if (newpp == NULL)
                        break;

                /* Relink the provider to its original geom. */
                g_unproxy_provider(oldpp, newpp);

                /* Detach consumer from provider, and destroy provider. */
                cp->acr = newpp->acr = 0;
                cp->acw = newpp->acw = 0;
                cp->ace = newpp->ace = 0;
                g_detach(cp);

                /* Send the pending bios through the right start function. */
                g_sched_flush_pending(oldpp->geom->start);

                return (0);
        } while (0);
        printf("%s error destroying proxy %s\n", __FUNCTION__, gp->name);

        /* We cannot send the pending bios anywhere... */
        g_sched_flush_pending(g_sched_blackhole);

        return (EINVAL);
}

static int
g_sched_destroy(struct g_geom *gp, boolean_t force)
{
        struct g_provider *pp, *oldpp = NULL;
        struct g_sched_softc *sc;
        struct g_gsched *gsp;
        int error;

        g_topology_assert();
        sc = gp->softc;
        if (sc == NULL)
                return (ENXIO);
        if (!(sc->sc_flags & G_SCHED_PROXYING)) {
                pp = LIST_FIRST(&gp->provider);
                if (pp && (pp->acr != 0 || pp->acw != 0 || pp->ace != 0)) {
                        const char *msg = force ?
                                "but we force removal" : "cannot remove";

                        G_SCHED_DEBUG(!force,
                            "Device %s is still open (r%dw%de%d), %s.",
                            pp->name, pp->acr, pp->acw, pp->ace, msg);
                        if (!force)
                                return (EBUSY);
                } else {
                        G_SCHED_DEBUG(0, "Device %s removed.", gp->name);
                }
        } else
                oldpp = g_detach_proxy(gp);

        gsp = sc->sc_gsched;
        if (gsp) {
                /*
                 * XXX bad hack here: force a dispatch to release
                 * any reference to the hash table still held by
                 * the scheduler.
                 */
                g_sched_lock(gp);
                /*
                 * We are dying here, no new requests should enter
                 * the scheduler.  This is granted by the topolgy,
                 * either in case we were proxying (new bios are
                 * being redirected) or not (see the access check
                 * above).
                 */
                g_sched_forced_dispatch(gp);
                error = g_sched_wait_pending(gp);

                if (error) {
                        /*
                         * Not all the requests came home: this might happen
                         * under heavy load, or if we were waiting for any
                         * bio which is served in the event path (see
                         * geom_slice.c for an example of how this can
                         * happen).  Try to restore a working configuration
                         * if we can fail.
                         */
                        if ((sc->sc_flags & G_SCHED_PROXYING) && oldpp) {
                                g_sched_flush_pending(force ?
                                    g_sched_blackhole : g_sched_start);
                        }

                        /*
                         * In the forced destroy case there is not so much
                         * we can do, we have pending bios that will call
                         * g_sched_done() somehow, and we don't want them
                         * to crash the system using freed memory.  We tell
                         * the user that something went wrong, and leak some
                         * memory here.
                         * Note: the callers using force = 1 ignore the
                         * return value.
                         */
                        if (force) {
                                G_SCHED_DEBUG(0, "Pending requests while "
                                    " destroying geom, some memory leaked.");
                        }

                        return (error);
                }

                g_sched_unlock(gp);
                g_sched_hash_fini(gp, sc->sc_hash, sc->sc_mask,
                    gsp, sc->sc_data);
                sc->sc_hash = NULL;
                gsp->gs_fini(sc->sc_data);
                g_gsched_unref(gsp);
                sc->sc_gsched = NULL;
        }

        if ((sc->sc_flags & G_SCHED_PROXYING) && oldpp) {
                error = g_destroy_proxy(gp, oldpp);

                if (error) {
                        if (force) {
                                G_SCHED_DEBUG(0, "Unrecoverable error while "
                                    "destroying a proxy geom, leaking some "
                                    " memory.");
                        }

                        return (error);
                }
        }

        mtx_destroy(&sc->sc_mtx);

        g_free(gp->softc);
        gp->softc = NULL;
        g_wither_geom(gp, ENXIO);

        return (error);
}

static int
g_sched_destroy_geom(struct gctl_req *req, struct g_class *mp,
    struct g_geom *gp)
{

        return (g_sched_destroy(gp, 0));
}

/*
 * Functions related to the classification of requests.
 *
 * On recent FreeBSD versions (8.0 and above), we store a reference
 * to the issuer of a request in bp->bio_classifier1 as soon
 * as the bio is posted to the geom queue (and not later, because
 * requests are managed by the g_down thread afterwards).
 *
 * On older versions of the system (but this code is not used
 * in any existing release), we [ab]use the caller1 field in the
 * root element of the bio tree to store the classification info.
 * The marking is done at the beginning of g_io_request()
 * and only if we find that the field is NULL.
 *
 * To avoid rebuilding the kernel, this module will patch the
 * initial part of g_io_request() so it jumps to some hand-coded
 * assembly that does the marking and then executes the original
 * body of g_io_request().
 *
 * fake_ioreq[] is architecture-specific machine code
 * that implements the above. CODE_SIZE, STORE_SIZE etc.
 * are constants used in the patching routine. Look at the
 * code in g_ioreq_patch() for the details.
 */

#ifndef HAVE_BIO_CLASSIFIER
/*
 * Support for old FreeBSD versions
 */
#if defined(__i386__)
#define CODE_SIZE       29
#define STORE_SIZE      5
#define EPILOGUE        5
#define SIZE            (CODE_SIZE + STORE_SIZE + EPILOGUE)

static u_char fake_ioreq[SIZE] = {
        0x8b, 0x44, 0x24, 0x04,         /* mov bp, %eax */
        /* 1: */
        0x89, 0xc2,                     /* mov %eax, %edx # edx = bp */
        0x8b, 0x40, 0x64,               /* mov bp->bio_parent, %eax */
        0x85, 0xc0,                     /* test %eax, %eax */
        0x75, 0xf7,                     /* jne 1b */
        0x8b, 0x42, 0x30,               /* mov bp->bp_caller1, %eax */
        0x85, 0xc0,                     /* test %eax, %eax */
        0x75, 0x09,                     /* jne 2f */
        0x64, 0xa1, 0x00, 0x00,         /* mov %fs:0, %eax */
        0x00, 0x00,
        0x89, 0x42, 0x30,               /* mov %eax, bp->bio_caller1 */
        /* 2: */
        0x55, 0x89, 0xe5, 0x57, 0x56,
        0xe9, 0x00, 0x00, 0x00, 0x00,   /* jmp back... */
};
#elif defined(__amd64)
#define CODE_SIZE       38
#define STORE_SIZE      6
#define EPILOGUE        5
#define SIZE            (CODE_SIZE + STORE_SIZE + EPILOGUE)

static u_char fake_ioreq[SIZE] = {
        0x48, 0x89, 0xf8,               /* mov bp, %rax */
        /* 1: */
        0x48, 0x89, 0xc2,               /* mov %rax, %rdx # rdx = bp */
        0x48, 0x8b, 0x82, 0xa8,         /* mov bp->bio_parent, %rax */
        0x00, 0x00, 0x00,
        0x48, 0x85, 0xc0,               /* test %rax, %rax */
        0x75, 0xf1,                     /* jne 1b */
        0x48, 0x83, 0x7a, 0x58,         /* cmp $0, bp->bp_caller1 */
        0x00,
        0x75, 0x0d,                     /* jne 2f */
        0x65, 0x48, 0x8b, 0x04,         /* mov %gs:0, %rax */
        0x25, 0x00, 0x00, 0x00,
        0x00,
        0x48, 0x89, 0x42, 0x58,         /* mov %rax, bp->bio_caller1 */
        /* 2: */
        0x55, 0x48, 0x89, 0xe5, 0x41, 0x56,
        0xe9, 0x00, 0x00, 0x00, 0x00,   /* jmp back... */
};
#else /* neither x86 nor amd64 */
static void
g_new_io_request(struct bio *bp, struct g_consumer *cp)
{
        struct bio *top = bp;

        /*
         * bio classification: if bio_caller1 is available in the
         * root of the 'struct bio' tree, store there the thread id
         * of the thread that originated the request.
         * More sophisticated classification schemes can be used.
         */
        while (top->bio_parent)
                top = top->bio_parent;

        if (top->bio_caller1 == NULL)
                top->bio_caller1 = curthread;
}

#error please add the code above in g_new_io_request() to the beginning of \
        /sys/geom/geom_io.c::g_io_request(), and remove this line.
#endif /* end of arch-specific code */

static int
g_ioreq_patch(void)
{
        u_char *original;
        u_long ofs;
        int found;

        if (me.gs_patched)
                return (-1);

        original = (u_char *)g_io_request;

        found = !bcmp(original, fake_ioreq + CODE_SIZE, STORE_SIZE);
        if (!found)
                return (-1);

        /* Jump back to the original + STORE_SIZE. */
        ofs = (original + STORE_SIZE) - (fake_ioreq + SIZE);
        bcopy(&ofs, fake_ioreq + CODE_SIZE + STORE_SIZE + 1, 4);

        /* Patch the original address with a jump to the trampoline. */
        *original = 0xe9;     /* jump opcode */
        ofs = fake_ioreq - (original + 5);
        bcopy(&ofs, original + 1, 4);

        me.gs_patched = 1;

        return (0);
}

/*
 * Restore the original code, this is easy.
 */
static void
g_ioreq_restore(void)
{
        u_char *original;

        if (me.gs_patched) {
                original = (u_char *)g_io_request;
                bcopy(fake_ioreq + CODE_SIZE, original, STORE_SIZE);
                me.gs_patched = 0;
        }
}

static inline void
g_classifier_ini(void)
{

        g_ioreq_patch();
}

static inline void
g_classifier_fini(void)
{

        g_ioreq_restore();
}

/*--- end of support code for older FreeBSD versions */

#else /* HAVE_BIO_CLASSIFIER */

/*
 * Classifier support for recent FreeBSD versions: we use
 * a very simple classifier, only use curthread to tag a request.
 * The classifier is registered at module load, and unregistered
 * at module unload.
 */
static int
g_sched_tag(void *arg, struct bio *bp)
{

        bp->bio_classifier1 = curthread;
        return (1);
}

static struct g_classifier_hook g_sched_classifier = {
        .func = g_sched_tag,
};

static inline void
g_classifier_ini(void)
{

        g_register_classifier(&g_sched_classifier);
}

static inline void
g_classifier_fini(void)
{

        g_unregister_classifier(&g_sched_classifier);
}
#endif /* HAVE_BIO_CLASSIFIER */

static void
g_sched_init(struct g_class *mp)
{

        g_gsched_global_init();

        G_SCHED_DEBUG(0, "Loading: mp = %p, g_sched_class = %p.",
            mp, &g_sched_class);

        /* Patch g_io_request to store classification info in the bio. */
        g_classifier_ini();
}

static void
g_sched_fini(struct g_class *mp)
{

        g_classifier_fini();

        G_SCHED_DEBUG(0, "Unloading...");

        KASSERT(LIST_EMPTY(&me.gs_scheds), ("still registered schedulers"));
        mtx_destroy(&me.gs_mtx);
}

static int
g_sched_ioctl(struct g_provider *pp, u_long cmd, void *data, int fflag,
    struct thread *td)
{
        struct g_consumer *cp;
        struct g_geom *gp;

        cp = LIST_FIRST(&pp->geom->consumer);
        if (cp == NULL)
                return (ENOIOCTL);
        gp = cp->provider->geom;
        if (gp->ioctl == NULL)
                return (ENOIOCTL);
        return (gp->ioctl(cp->provider, cmd, data, fflag, td));
}

/*
 * Read the i-th argument for a request, skipping the /dev/
 * prefix if present.
 */
static const char *
g_sched_argi(struct gctl_req *req, int i)
{
        static const char *dev_prefix = "/dev/";
        const char *name;
        char param[16];
        int l = strlen(dev_prefix);

        snprintf(param, sizeof(param), "arg%d", i);
        name = gctl_get_asciiparam(req, param);
        if (name == NULL)
                gctl_error(req, "No 'arg%d' argument", i);
        else if (strncmp(name, dev_prefix, l) == 0)
                name += l;
        return (name);
}

/*
 * Fetch nargs and do appropriate checks.
 */
static int
g_sched_get_nargs(struct gctl_req *req)
{
        int *nargs;

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

/*
 * Check whether we should add the class on certain volumes when
 * this geom is created. Right now this is under control of a kenv
 * variable containing the names of all devices that we care about.
 * Probably we should only support transparent insertion as the
 * preferred mode of operation.
 */
static struct g_geom *
g_sched_taste(struct g_class *mp, struct g_provider *pp,
                int flags __unused)
{
        struct g_gsched *gsp = NULL;    /* the . algorithm we want */
        const char *s;                  /* generic string pointer */
        const char *taste_names;        /* devices we like */
        int l;
    
        g_trace(G_T_TOPOLOGY, "%s(%s, %s)", __func__,
            mp->name, pp->name);
        g_topology_assert();
 
        G_SCHED_DEBUG(2, "Tasting %s.", pp->name);

        do {
                /* do not taste on ourselves */
                if (pp->geom->class == mp)
                        break;

                taste_names = getenv("geom.sched.taste");
                if (taste_names == NULL)
                        break;

                l = strlen(pp->name);
                for (s = taste_names; *s &&
                    (s = strstr(s, pp->name)); s++) {
                        /* further checks for an exact match */
                        if ( (s == taste_names || s[-1] == ' ') &&
                             (s[l] == '\0' || s[l] == ' ') )
                                break;
                }
                if (s == NULL)
                        break;
                G_SCHED_DEBUG(0, "Attach device %s match [%s]\n",
                    pp->name, s);

                /* look up the provider name in the list */
                s = getenv("geom.sched.algo");
                if (s == NULL)
                        s = "rr";

                gsp = g_gsched_find(s); /* also get a reference */
                if (gsp == NULL) {
                        G_SCHED_DEBUG(0, "Bad '%s' algorithm.", s);
                        break;
                }

                /* XXX create with 1 as last argument ? */
                g_sched_create(NULL, mp, pp, gsp, 0);
                g_gsched_unref(gsp);
        } while (0);
        return NULL;
}

static void
g_sched_ctl_create(struct gctl_req *req, struct g_class *mp, int proxy)
{
        struct g_provider *pp;
        struct g_gsched *gsp;
        const char *name;
        int i, nargs;

        g_topology_assert();

        name = gctl_get_asciiparam(req, "algo");
        if (name == NULL) {
                gctl_error(req, "No '%s' argument", "algo");
                return;
        }

        gsp = g_gsched_find(name);      /* also get a reference */
        if (gsp == NULL) {
                gctl_error(req, "Bad algorithm '%s'", name);
                return;
        }

        nargs = g_sched_get_nargs(req);

        /*
         * Run on the arguments, and break on any error.
         * We look for a device name, but skip the /dev/ prefix if any.
         */
        for (i = 0; i < nargs; i++) {
                name = g_sched_argi(req, i);
                if (name == NULL)
                        break;
                pp = g_provider_by_name(name);
                if (pp == NULL) {
                        G_SCHED_DEBUG(1, "Provider %s is invalid.", name);
                        gctl_error(req, "Provider %s is invalid.", name);
                        break;
                }
                if (g_sched_create(req, mp, pp, gsp, proxy) != 0)
                        break;
        }

        g_gsched_unref(gsp);
}

static void
g_sched_ctl_configure(struct gctl_req *req, struct g_class *mp)
{
        struct g_provider *pp;
        struct g_gsched *gsp;
        const char *name;
        int i, nargs;

        g_topology_assert();

        name = gctl_get_asciiparam(req, "algo");
        if (name == NULL) {
                gctl_error(req, "No '%s' argument", "algo");
                return;
        }

        gsp = g_gsched_find(name);      /* also get a reference */
        if (gsp == NULL) {
                gctl_error(req, "Bad algorithm '%s'", name);
                return;
        }

        nargs = g_sched_get_nargs(req);

        /*
         * Run on the arguments, and break on any error.
         * We look for a device name, but skip the /dev/ prefix if any.
         */
        for (i = 0; i < nargs; i++) {
                name = g_sched_argi(req, i);
                if (name == NULL)
                        break;
                pp = g_provider_by_name(name);
                if (pp == NULL || pp->geom->class != mp) {
                        G_SCHED_DEBUG(1, "Provider %s is invalid.", name);
                        gctl_error(req, "Provider %s is invalid.", name);
                        break;
                }
                if (g_sched_change_algo(req, mp, pp, gsp) != 0)
                        break;
        }

        g_gsched_unref(gsp);
}

static struct g_geom *
g_sched_find_geom(struct g_class *mp, const char *name)
{
        struct g_geom *gp;

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

static void
g_sched_ctl_destroy(struct gctl_req *req, struct g_class *mp)
{
        int nargs, *force, error, i;
        struct g_geom *gp;
        const char *name;

        g_topology_assert();

        nargs = g_sched_get_nargs(req);

        force = gctl_get_paraml(req, "force", sizeof(*force));
        if (force == NULL) {
                gctl_error(req, "No 'force' argument");
                return;
        }

        for (i = 0; i < nargs; i++) {
                name = g_sched_argi(req, i);
                if (name == NULL)
                        break;

                gp = g_sched_find_geom(mp, name);
                if (gp == NULL) {
                        G_SCHED_DEBUG(1, "Device %s is invalid.", name);
                        gctl_error(req, "Device %s is invalid.", name);
                        break;
                }

                error = g_sched_destroy(gp, *force);
                if (error != 0) {
                        gctl_error(req, "Cannot destroy device %s (error=%d).",
                            gp->name, error);
                        break;
                }
        }
}

static void
g_sched_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_SCHED_VERSION) {
                gctl_error(req, "Userland and kernel parts are "
                    "out of sync.");
                return;
        }

        if (strcmp(verb, "create") == 0) {
                g_sched_ctl_create(req, mp, 0);
                return;
        } else if (strcmp(verb, "insert") == 0) {
                g_sched_ctl_create(req, mp, 1);
                return;
        } else if (strcmp(verb, "configure") == 0) {
                g_sched_ctl_configure(req, mp);
                return;
        } else if (strcmp(verb, "destroy") == 0) {
                g_sched_ctl_destroy(req, mp);
                return;
        }

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

static void
g_sched_dumpconf(struct sbuf *sb, const char *indent, struct g_geom *gp,
    struct g_consumer *cp, struct g_provider *pp)
{
        struct g_sched_softc *sc = gp->softc;
        struct g_gsched *gsp = sc->sc_gsched;
        if (indent == NULL) {   /* plaintext */
                sbuf_printf(sb, " algo %s", gsp ? gsp->gs_name : "--");
        }
        if (gsp != NULL && gsp->gs_dumpconf)
                gsp->gs_dumpconf(sb, indent, gp, cp, pp);
}

DECLARE_GEOM_CLASS(g_sched_class, g_sched);
MODULE_VERSION(geom_sched, 0);