/*
 * XenBSD block device driver
 *
 * Copyright (c) 2010-2013 Spectra Logic Corporation
 * Copyright (c) 2009 Scott Long, Yahoo!
 * Copyright (c) 2009 Frank Suchomel, Citrix
 * Copyright (c) 2009 Doug F. Rabson, Citrix
 * Copyright (c) 2005 Kip Macy
 * Copyright (c) 2003-2004, Keir Fraser & Steve Hand
 * Modifications by Mark A. Williamson are (c) Intel Research Cambridge
 *
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/kernel.h>
#include <vm/vm.h>
#include <vm/pmap.h>

#include <sys/bio.h>
#include <sys/bus.h>
#include <sys/conf.h>
#include <sys/module.h>
#include <sys/sysctl.h>

#include <machine/bus.h>
#include <sys/rman.h>
#include <machine/resource.h>
#include <machine/vmparam.h>

#include <xen/xen-os.h>
#include <xen/hypervisor.h>
#include <xen/xen_intr.h>
#include <xen/gnttab.h>
#include <contrib/xen/grant_table.h>
#include <contrib/xen/io/protocols.h>
#include <xen/xenbus/xenbusvar.h>

#include <machine/_inttypes.h>

#include <geom/geom_disk.h>

#include <dev/xen/blkfront/block.h>

#include "xenbus_if.h"

/*--------------------------- Forward Declarations ---------------------------*/
static void xbd_closing(device_t);
static void xbd_startio(struct xbd_softc *sc);

/*---------------------------------- Macros ----------------------------------*/
#if 0
#define DPRINTK(fmt, args...) printf("[XEN] %s:%d: " fmt ".\n", __func__, __LINE__, ##args)
#else
#define DPRINTK(fmt, args...) 
#endif

#define XBD_SECTOR_SHFT         9

/*---------------------------- Global Static Data ----------------------------*/
static MALLOC_DEFINE(M_XENBLOCKFRONT, "xbd", "Xen Block Front driver data");

static int xbd_enable_indirect = 1;
SYSCTL_NODE(_hw, OID_AUTO, xbd, CTLFLAG_RD | CTLFLAG_MPSAFE, 0,
    "xbd driver parameters");
SYSCTL_INT(_hw_xbd, OID_AUTO, xbd_enable_indirect, CTLFLAG_RDTUN,
    &xbd_enable_indirect, 0, "Enable xbd indirect segments");

/*---------------------------- Command Processing ----------------------------*/
static void
xbd_freeze(struct xbd_softc *sc, xbd_flag_t xbd_flag)
{
        if (xbd_flag != XBDF_NONE && (sc->xbd_flags & xbd_flag) != 0)
                return;

        sc->xbd_flags |= xbd_flag;
        sc->xbd_qfrozen_cnt++;
}

static void
xbd_thaw(struct xbd_softc *sc, xbd_flag_t xbd_flag)
{
        if (xbd_flag != XBDF_NONE && (sc->xbd_flags & xbd_flag) == 0)
                return;

        if (sc->xbd_qfrozen_cnt == 0)
                panic("%s: Thaw with flag 0x%x while not frozen.",
                    __func__, xbd_flag);

        sc->xbd_flags &= ~xbd_flag;
        sc->xbd_qfrozen_cnt--;
}

static void
xbd_cm_freeze(struct xbd_softc *sc, struct xbd_command *cm, xbdc_flag_t cm_flag)
{
        if ((cm->cm_flags & XBDCF_FROZEN) != 0)
                return;

        cm->cm_flags |= XBDCF_FROZEN|cm_flag;
        xbd_freeze(sc, XBDF_NONE);
}

static void
xbd_cm_thaw(struct xbd_softc *sc, struct xbd_command *cm)
{
        if ((cm->cm_flags & XBDCF_FROZEN) == 0)
                return;

        cm->cm_flags &= ~XBDCF_FROZEN;
        xbd_thaw(sc, XBDF_NONE);
}

static inline void 
xbd_flush_requests(struct xbd_softc *sc)
{
        int notify;

        RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&sc->xbd_ring, notify);

        if (notify)
                xen_intr_signal(sc->xen_intr_handle);
}

static void
xbd_free_command(struct xbd_command *cm)
{

        KASSERT((cm->cm_flags & XBDCF_Q_MASK) == XBD_Q_NONE,
            ("Freeing command that is still on queue %d.",
            cm->cm_flags & XBDCF_Q_MASK));

        cm->cm_flags = XBDCF_INITIALIZER;
        cm->cm_bp = NULL;
        cm->cm_complete = NULL;
        xbd_enqueue_cm(cm, XBD_Q_FREE);
        xbd_thaw(cm->cm_sc, XBDF_CM_SHORTAGE);
}

static void
xbd_mksegarray(bus_dma_segment_t *segs, int nsegs,
    grant_ref_t * gref_head, int otherend_id, int readonly,
    grant_ref_t * sg_ref, struct blkif_request_segment *sg,
    unsigned int sector_size)
{
        struct blkif_request_segment *last_block_sg = sg + nsegs;
        vm_paddr_t buffer_ma;
        uint64_t fsect, lsect;
        int ref;

        while (sg < last_block_sg) {
                KASSERT((segs->ds_addr & (sector_size - 1)) == 0,
                    ("XEN disk driver I/O must be sector aligned"));
                KASSERT((segs->ds_len & (sector_size - 1)) == 0,
                    ("XEN disk driver I/Os must be a multiple of "
                    "the sector length"));
                buffer_ma = segs->ds_addr;
                fsect = (buffer_ma & PAGE_MASK) >> XBD_SECTOR_SHFT;
                lsect = fsect + (segs->ds_len  >> XBD_SECTOR_SHFT) - 1;

                KASSERT(lsect <= 7, ("XEN disk driver data cannot "
                    "cross a page boundary"));

                /* install a grant reference. */
                ref = gnttab_claim_grant_reference(gref_head);

                /*
                 * GNTTAB_LIST_END == 0xffffffff, but it is private
                 * to gnttab.c.
                 */
                KASSERT(ref != ~0, ("grant_reference failed"));

                gnttab_grant_foreign_access_ref(
                    ref,
                    otherend_id,
                    buffer_ma >> PAGE_SHIFT,
                    readonly);

                *sg_ref = ref;
                *sg = (struct blkif_request_segment) {
                        .gref       = ref,
                        .first_sect = fsect, 
                        .last_sect  = lsect
                };
                sg++;
                sg_ref++;
                segs++;
        }
}

static void
xbd_queue_cb(void *arg, bus_dma_segment_t *segs, int nsegs, int error)
{
        struct xbd_softc *sc;
        struct xbd_command *cm;
        int op;

        cm = arg;
        sc = cm->cm_sc;

        if (error) {
                cm->cm_bp->bio_error = EIO;
                biodone(cm->cm_bp);
                xbd_free_command(cm);
                return;
        }

        KASSERT(nsegs <= sc->xbd_max_request_segments,
            ("Too many segments in a blkfront I/O"));

        if (nsegs <= BLKIF_MAX_SEGMENTS_PER_REQUEST) {
                blkif_request_t *ring_req;

                /* Fill out a blkif_request_t structure. */
                ring_req = (blkif_request_t *)
                    RING_GET_REQUEST(&sc->xbd_ring, sc->xbd_ring.req_prod_pvt);
                sc->xbd_ring.req_prod_pvt++;
                ring_req->id = cm->cm_id;
                ring_req->operation = cm->cm_operation;
                ring_req->sector_number = cm->cm_sector_number;
                ring_req->handle = (blkif_vdev_t)(uintptr_t)sc->xbd_disk;
                ring_req->nr_segments = nsegs;
                cm->cm_nseg = nsegs;
                xbd_mksegarray(segs, nsegs, &cm->cm_gref_head,
                    xenbus_get_otherend_id(sc->xbd_dev),
                    cm->cm_operation == BLKIF_OP_WRITE,
                    cm->cm_sg_refs, ring_req->seg,
                    sc->xbd_disk->d_sectorsize);
        } else {
                blkif_request_indirect_t *ring_req;

                /* Fill out a blkif_request_indirect_t structure. */
                ring_req = (blkif_request_indirect_t *)
                    RING_GET_REQUEST(&sc->xbd_ring, sc->xbd_ring.req_prod_pvt);
                sc->xbd_ring.req_prod_pvt++;
                ring_req->id = cm->cm_id;
                ring_req->operation = BLKIF_OP_INDIRECT;
                ring_req->indirect_op = cm->cm_operation;
                ring_req->sector_number = cm->cm_sector_number;
                ring_req->handle = (blkif_vdev_t)(uintptr_t)sc->xbd_disk;
                ring_req->nr_segments = nsegs;
                cm->cm_nseg = nsegs;
                xbd_mksegarray(segs, nsegs, &cm->cm_gref_head,
                    xenbus_get_otherend_id(sc->xbd_dev),
                    cm->cm_operation == BLKIF_OP_WRITE,
                    cm->cm_sg_refs, cm->cm_indirectionpages,
                    sc->xbd_disk->d_sectorsize);
                memcpy(ring_req->indirect_grefs, &cm->cm_indirectionrefs,
                    sizeof(grant_ref_t) * sc->xbd_max_request_indirectpages);
        }

        if (cm->cm_operation == BLKIF_OP_READ)
                op = BUS_DMASYNC_PREREAD;
        else if (cm->cm_operation == BLKIF_OP_WRITE)
                op = BUS_DMASYNC_PREWRITE;
        else
                op = 0;
        bus_dmamap_sync(sc->xbd_io_dmat, cm->cm_map, op);

        gnttab_free_grant_references(cm->cm_gref_head);

        xbd_enqueue_cm(cm, XBD_Q_BUSY);

        /*
         * If bus dma had to asynchronously call us back to dispatch
         * this command, we are no longer executing in the context of 
         * xbd_startio().  Thus we cannot rely on xbd_startio()'s call to
         * xbd_flush_requests() to publish this command to the backend
         * along with any other commands that it could batch.
         */
        if ((cm->cm_flags & XBDCF_ASYNC_MAPPING) != 0)
                xbd_flush_requests(sc);

        return;
}

static int
xbd_queue_request(struct xbd_softc *sc, struct xbd_command *cm)
{
        int error;

        if (cm->cm_bp != NULL)
                error = bus_dmamap_load_bio(sc->xbd_io_dmat, cm->cm_map,
                    cm->cm_bp, xbd_queue_cb, cm, 0);
        else
                error = bus_dmamap_load(sc->xbd_io_dmat, cm->cm_map,
                    cm->cm_data, cm->cm_datalen, xbd_queue_cb, cm, 0);
        if (error == EINPROGRESS) {
                /*
                 * Maintain queuing order by freezing the queue.  The next
                 * command may not require as many resources as the command
                 * we just attempted to map, so we can't rely on bus dma
                 * blocking for it too.
                 */
                xbd_cm_freeze(sc, cm, XBDCF_ASYNC_MAPPING);
                return (0);
        }

        return (error);
}

static void
xbd_restart_queue_callback(void *arg)
{
        struct xbd_softc *sc = arg;

        mtx_lock(&sc->xbd_io_lock);

        xbd_thaw(sc, XBDF_GNT_SHORTAGE);

        xbd_startio(sc);

        mtx_unlock(&sc->xbd_io_lock);
}

static struct xbd_command *
xbd_bio_command(struct xbd_softc *sc)
{
        struct xbd_command *cm;
        struct bio *bp;

        if (__predict_false(sc->xbd_state != XBD_STATE_CONNECTED))
                return (NULL);

        bp = xbd_dequeue_bio(sc);
        if (bp == NULL)
                return (NULL);

        if ((cm = xbd_dequeue_cm(sc, XBD_Q_FREE)) == NULL) {
                xbd_freeze(sc, XBDF_CM_SHORTAGE);
                xbd_requeue_bio(sc, bp);
                return (NULL);
        }

        if (gnttab_alloc_grant_references(sc->xbd_max_request_segments,
            &cm->cm_gref_head) != 0) {
                gnttab_request_free_callback(&sc->xbd_callback,
                    xbd_restart_queue_callback, sc,
                    sc->xbd_max_request_segments);
                xbd_freeze(sc, XBDF_GNT_SHORTAGE);
                xbd_requeue_bio(sc, bp);
                xbd_enqueue_cm(cm, XBD_Q_FREE);
                return (NULL);
        }

        cm->cm_bp = bp;
        cm->cm_sector_number =
            ((blkif_sector_t)bp->bio_pblkno * sc->xbd_disk->d_sectorsize) >>
            XBD_SECTOR_SHFT;

        switch (bp->bio_cmd) {
        case BIO_READ:
                cm->cm_operation = BLKIF_OP_READ;
                break;
        case BIO_WRITE:
                cm->cm_operation = BLKIF_OP_WRITE;
                if ((bp->bio_flags & BIO_ORDERED) != 0) {
                        if ((sc->xbd_flags & XBDF_BARRIER) != 0) {
                                cm->cm_operation = BLKIF_OP_WRITE_BARRIER;
                        } else {
                                /*
                                 * Single step this command.
                                 */
                                cm->cm_flags |= XBDCF_Q_FREEZE;
                                if (xbd_queue_length(sc, XBD_Q_BUSY) != 0) {
                                        /*
                                         * Wait for in-flight requests to
                                         * finish.
                                         */
                                        xbd_freeze(sc, XBDF_WAIT_IDLE);
                                        xbd_requeue_cm(cm, XBD_Q_READY);
                                        return (NULL);
                                }
                        }
                }
                break;
        case BIO_FLUSH:
                if ((sc->xbd_flags & XBDF_FLUSH) != 0)
                        cm->cm_operation = BLKIF_OP_FLUSH_DISKCACHE;
                else if ((sc->xbd_flags & XBDF_BARRIER) != 0)
                        cm->cm_operation = BLKIF_OP_WRITE_BARRIER;
                else
                        panic("flush request, but no flush support available");
                break;
        default:
                biofinish(bp, NULL, EOPNOTSUPP);
                xbd_enqueue_cm(cm, XBD_Q_FREE);
                return (NULL);
        }

        return (cm);
}

/*
 * Dequeue buffers and place them in the shared communication ring.
 * Return when no more requests can be accepted or all buffers have 
 * been queued.
 *
 * Signal XEN once the ring has been filled out.
 */
static void
xbd_startio(struct xbd_softc *sc)
{
        struct xbd_command *cm;
        int error, queued = 0;

        mtx_assert(&sc->xbd_io_lock, MA_OWNED);

        if (sc->xbd_state != XBD_STATE_CONNECTED)
                return;

        while (!RING_FULL(&sc->xbd_ring)) {
                if (sc->xbd_qfrozen_cnt != 0)
                        break;

                cm = xbd_dequeue_cm(sc, XBD_Q_READY);

                if (cm == NULL)
                    cm = xbd_bio_command(sc);

                if (cm == NULL)
                        break;

                if ((cm->cm_flags & XBDCF_Q_FREEZE) != 0) {
                        /*
                         * Single step command.  Future work is
                         * held off until this command completes.
                         */
                        xbd_cm_freeze(sc, cm, XBDCF_Q_FREEZE);
                }

                if ((error = xbd_queue_request(sc, cm)) != 0) {
                        printf("xbd_queue_request returned %d\n", error);
                        break;
                }
                queued++;
        }

        if (queued != 0) 
                xbd_flush_requests(sc);
}

static void
xbd_bio_complete(struct xbd_softc *sc, struct xbd_command *cm)
{
        struct bio *bp;

        bp = cm->cm_bp;

        if (__predict_false(cm->cm_status != BLKIF_RSP_OKAY)) {
                disk_err(bp, "disk error" , -1, 0);
                printf(" status: %x\n", cm->cm_status);
                bp->bio_flags |= BIO_ERROR;
        }

        if (bp->bio_flags & BIO_ERROR)
                bp->bio_error = EIO;
        else
                bp->bio_resid = 0;

        xbd_free_command(cm);
        biodone(bp);
}

static void
xbd_int(void *xsc)
{
        struct xbd_softc *sc = xsc;
        struct xbd_command *cm;
        blkif_response_t *bret;
        RING_IDX i, rp;
        int op;

        mtx_lock(&sc->xbd_io_lock);

        if (__predict_false(sc->xbd_state == XBD_STATE_DISCONNECTED)) {
                mtx_unlock(&sc->xbd_io_lock);
                return;
        }

 again:
        rp = sc->xbd_ring.sring->rsp_prod;
        rmb(); /* Ensure we see queued responses up to 'rp'. */

        for (i = sc->xbd_ring.rsp_cons; i != rp;) {
                bret = RING_GET_RESPONSE(&sc->xbd_ring, i);
                cm   = &sc->xbd_shadow[bret->id];

                xbd_remove_cm(cm, XBD_Q_BUSY);
                gnttab_end_foreign_access_references(cm->cm_nseg,
                    cm->cm_sg_refs);
                i++;

                if (cm->cm_operation == BLKIF_OP_READ)
                        op = BUS_DMASYNC_POSTREAD;
                else if (cm->cm_operation == BLKIF_OP_WRITE ||
                    cm->cm_operation == BLKIF_OP_WRITE_BARRIER)
                        op = BUS_DMASYNC_POSTWRITE;
                else
                        op = 0;
                bus_dmamap_sync(sc->xbd_io_dmat, cm->cm_map, op);
                bus_dmamap_unload(sc->xbd_io_dmat, cm->cm_map);

                /*
                 * Release any hold this command has on future command
                 * dispatch. 
                 */
                xbd_cm_thaw(sc, cm);

                /*
                 * Directly call the i/o complete routine to save an
                 * an indirection in the common case.
                 */
                cm->cm_status = bret->status;
                if (cm->cm_bp)
                        xbd_bio_complete(sc, cm);
                else if (cm->cm_complete != NULL)
                        cm->cm_complete(cm);
                else
                        xbd_free_command(cm);
        }

        sc->xbd_ring.rsp_cons = i;

        if (i != sc->xbd_ring.req_prod_pvt) {
                int more_to_do;
                RING_FINAL_CHECK_FOR_RESPONSES(&sc->xbd_ring, more_to_do);
                if (more_to_do)
                        goto again;
        } else {
                sc->xbd_ring.sring->rsp_event = i + 1;
        }

        if (xbd_queue_length(sc, XBD_Q_BUSY) == 0)
                xbd_thaw(sc, XBDF_WAIT_IDLE);

        xbd_startio(sc);

        if (__predict_false(sc->xbd_state == XBD_STATE_SUSPENDED))
                wakeup(&sc->xbd_cm_q[XBD_Q_BUSY]);

        mtx_unlock(&sc->xbd_io_lock);
}

/*------------------------------- Dump Support -------------------------------*/
/**
 * Quiesce the disk writes for a dump file before allowing the next buffer.
 */
static void
xbd_quiesce(struct xbd_softc *sc)
{
        int mtd;

        // While there are outstanding requests
        while (xbd_queue_length(sc, XBD_Q_BUSY) != 0) {
                RING_FINAL_CHECK_FOR_RESPONSES(&sc->xbd_ring, mtd);
                if (mtd) {
                        /* Received request completions, update queue. */
                        xbd_int(sc);
                }
                if (xbd_queue_length(sc, XBD_Q_BUSY) != 0) {
                        /*
                         * Still pending requests, wait for the disk i/o
                         * to complete.
                         */
                        HYPERVISOR_yield();
                }
        }
}

/* Kernel dump function for a paravirtualized disk device */
static void
xbd_dump_complete(struct xbd_command *cm)
{

        xbd_enqueue_cm(cm, XBD_Q_COMPLETE);
}

static int
xbd_dump(void *arg, void *virtual, off_t offset, size_t length)
{
        struct disk *dp = arg;
        struct xbd_softc *sc = dp->d_drv1;
        struct xbd_command *cm;
        size_t chunk;
        int rc = 0;

        if (length == 0)
                return (0);

        xbd_quiesce(sc);        /* All quiet on the western front. */

        /*
         * If this lock is held, then this module is failing, and a
         * successful kernel dump is highly unlikely anyway.
         */
        mtx_lock(&sc->xbd_io_lock);

        /* Split the 64KB block as needed */
        while (length > 0) {
                cm = xbd_dequeue_cm(sc, XBD_Q_FREE);
                if (cm == NULL) {
                        mtx_unlock(&sc->xbd_io_lock);
                        device_printf(sc->xbd_dev, "dump: no more commands?\n");
                        return (EBUSY);
                }

                if (gnttab_alloc_grant_references(sc->xbd_max_request_segments,
                    &cm->cm_gref_head) != 0) {
                        xbd_free_command(cm);
                        mtx_unlock(&sc->xbd_io_lock);
                        device_printf(sc->xbd_dev, "no more grant allocs?\n");
                        return (EBUSY);
                }

                chunk = length > sc->xbd_max_request_size ?
                    sc->xbd_max_request_size : length;
                cm->cm_data = virtual;
                cm->cm_datalen = chunk;
                cm->cm_operation = BLKIF_OP_WRITE;
                cm->cm_sector_number = offset >> XBD_SECTOR_SHFT;
                cm->cm_complete = xbd_dump_complete;

                xbd_enqueue_cm(cm, XBD_Q_READY);

                length -= chunk;
                offset += chunk;
                virtual = (char *) virtual + chunk;
        }

        /* Tell DOM0 to do the I/O */
        xbd_startio(sc);
        mtx_unlock(&sc->xbd_io_lock);

        /* Poll for the completion. */
        xbd_quiesce(sc);        /* All quite on the eastern front */

        /* If there were any errors, bail out... */
        while ((cm = xbd_dequeue_cm(sc, XBD_Q_COMPLETE)) != NULL) {
                if (cm->cm_status != BLKIF_RSP_OKAY) {
                        device_printf(sc->xbd_dev,
                            "Dump I/O failed at sector %jd\n",
                            cm->cm_sector_number);
                        rc = EIO;
                }
                xbd_free_command(cm);
        }

        return (rc);
}

/*----------------------------- Disk Entrypoints -----------------------------*/
static int
xbd_open(struct disk *dp)
{
        struct xbd_softc *sc = dp->d_drv1;

        if (sc == NULL) {
                printf("xbd%d: not found", dp->d_unit);
                return (ENXIO);
        }

        sc->xbd_flags |= XBDF_OPEN;
        sc->xbd_users++;
        return (0);
}

static int
xbd_close(struct disk *dp)
{
        struct xbd_softc *sc = dp->d_drv1;

        if (sc == NULL)
                return (ENXIO);
        sc->xbd_flags &= ~XBDF_OPEN;
        if (--(sc->xbd_users) == 0) {
                /*
                 * Check whether we have been instructed to close.  We will
                 * have ignored this request initially, as the device was
                 * still mounted.
                 */
                if (xenbus_get_otherend_state(sc->xbd_dev) ==
                    XenbusStateClosing)
                        xbd_closing(sc->xbd_dev);
        }
        return (0);
}

static int
xbd_ioctl(struct disk *dp, u_long cmd, void *addr, int flag, struct thread *td)
{
        struct xbd_softc *sc = dp->d_drv1;

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

        return (ENOTTY);
}

/*
 * Read/write routine for a buffer.  Finds the proper unit, place it on
 * the sortq and kick the controller.
 */
static void
xbd_strategy(struct bio *bp)
{
        struct xbd_softc *sc = bp->bio_disk->d_drv1;

        /* bogus disk? */
        if (sc == NULL) {
                bp->bio_error = EINVAL;
                bp->bio_flags |= BIO_ERROR;
                bp->bio_resid = bp->bio_bcount;
                biodone(bp);
                return;
        }

        /*
         * Place it in the queue of disk activities for this disk
         */
        mtx_lock(&sc->xbd_io_lock);

        xbd_enqueue_bio(sc, bp);
        xbd_startio(sc);

        mtx_unlock(&sc->xbd_io_lock);
        return;
}

/*------------------------------ Ring Management -----------------------------*/
static int 
xbd_alloc_ring(struct xbd_softc *sc)
{
        blkif_sring_t *sring;
        uintptr_t sring_page_addr;
        int error;
        int i;

        sring = malloc(sc->xbd_ring_pages * PAGE_SIZE, M_XENBLOCKFRONT,
            M_NOWAIT|M_ZERO);
        if (sring == NULL) {
                xenbus_dev_fatal(sc->xbd_dev, ENOMEM, "allocating shared ring");
                return (ENOMEM);
        }
        SHARED_RING_INIT(sring);
        FRONT_RING_INIT(&sc->xbd_ring, sring, sc->xbd_ring_pages * PAGE_SIZE);

        for (i = 0, sring_page_addr = (uintptr_t)sring;
             i < sc->xbd_ring_pages;
             i++, sring_page_addr += PAGE_SIZE) {
                error = xenbus_grant_ring(sc->xbd_dev,
                    (vtophys(sring_page_addr) >> PAGE_SHIFT),
                    &sc->xbd_ring_ref[i]);
                if (error) {
                        xenbus_dev_fatal(sc->xbd_dev, error,
                            "granting ring_ref(%d)", i);
                        return (error);
                }
        }
        if (sc->xbd_ring_pages == 1) {
                error = xs_printf(XST_NIL, xenbus_get_node(sc->xbd_dev),
                    "ring-ref", "%u", sc->xbd_ring_ref[0]);
                if (error) {
                        xenbus_dev_fatal(sc->xbd_dev, error,
                            "writing %s/ring-ref",
                            xenbus_get_node(sc->xbd_dev));
                        return (error);
                }
        } else {
                for (i = 0; i < sc->xbd_ring_pages; i++) {
                        char ring_ref_name[]= "ring_refXX";

                        snprintf(ring_ref_name, sizeof(ring_ref_name),
                            "ring-ref%u", i);
                        error = xs_printf(XST_NIL, xenbus_get_node(sc->xbd_dev),
                             ring_ref_name, "%u", sc->xbd_ring_ref[i]);
                        if (error) {
                                xenbus_dev_fatal(sc->xbd_dev, error,
                                    "writing %s/%s",
                                    xenbus_get_node(sc->xbd_dev),
                                    ring_ref_name);
                                return (error);
                        }
                }
        }

        error = xen_intr_alloc_and_bind_local_port(sc->xbd_dev,
            xenbus_get_otherend_id(sc->xbd_dev), NULL, xbd_int, sc,
            INTR_TYPE_BIO | INTR_MPSAFE, &sc->xen_intr_handle);
        if (error) {
                xenbus_dev_fatal(sc->xbd_dev, error,
                    "xen_intr_alloc_and_bind_local_port failed");
                return (error);
        }

        return (0);
}

static void
xbd_free_ring(struct xbd_softc *sc)
{
        int i;

        if (sc->xbd_ring.sring == NULL)
                return;

        for (i = 0; i < sc->xbd_ring_pages; i++) {
                if (sc->xbd_ring_ref[i] != GRANT_REF_INVALID) {
                        gnttab_end_foreign_access_ref(sc->xbd_ring_ref[i]);
                        sc->xbd_ring_ref[i] = GRANT_REF_INVALID;
                }
        }
        free(sc->xbd_ring.sring, M_XENBLOCKFRONT);
        sc->xbd_ring.sring = NULL;
}

/*-------------------------- Initialization/Teardown -------------------------*/
static int
xbd_feature_string(struct xbd_softc *sc, char *features, size_t len)
{
        struct sbuf sb;
        int feature_cnt;

        sbuf_new(&sb, features, len, SBUF_FIXEDLEN);

        feature_cnt = 0;
        if ((sc->xbd_flags & XBDF_FLUSH) != 0) {
                sbuf_printf(&sb, "flush");
                feature_cnt++;
        }

        if ((sc->xbd_flags & XBDF_BARRIER) != 0) {
                if (feature_cnt != 0)
                        sbuf_printf(&sb, ", ");
                sbuf_printf(&sb, "write_barrier");
                feature_cnt++;
        }

        if ((sc->xbd_flags & XBDF_DISCARD) != 0) {
                if (feature_cnt != 0)
                        sbuf_printf(&sb, ", ");
                sbuf_printf(&sb, "discard");
                feature_cnt++;
        }

        if ((sc->xbd_flags & XBDF_PERSISTENT) != 0) {
                if (feature_cnt != 0)
                        sbuf_printf(&sb, ", ");
                sbuf_printf(&sb, "persistent_grants");
                feature_cnt++;
        }

        (void) sbuf_finish(&sb);
        return (sbuf_len(&sb));
}

static int
xbd_sysctl_features(SYSCTL_HANDLER_ARGS)
{
        char features[80];
        struct xbd_softc *sc = arg1;
        int error;
        int len;

        error = sysctl_wire_old_buffer(req, 0);
        if (error != 0)
                return (error);

        len = xbd_feature_string(sc, features, sizeof(features));

        /* len is -1 on error, which will make the SYSCTL_OUT a no-op. */
        return (SYSCTL_OUT(req, features, len + 1/*NUL*/));
}

static void
xbd_setup_sysctl(struct xbd_softc *xbd)
{
        struct sysctl_ctx_list *sysctl_ctx = NULL;
        struct sysctl_oid *sysctl_tree = NULL;
        struct sysctl_oid_list *children;

        sysctl_ctx = device_get_sysctl_ctx(xbd->xbd_dev);
        if (sysctl_ctx == NULL)
                return;

        sysctl_tree = device_get_sysctl_tree(xbd->xbd_dev);
        if (sysctl_tree == NULL)
                return;

        children = SYSCTL_CHILDREN(sysctl_tree);
        SYSCTL_ADD_UINT(sysctl_ctx, children, OID_AUTO,
            "max_requests", CTLFLAG_RD, &xbd->xbd_max_requests, -1,
            "maximum outstanding requests (negotiated)");

        SYSCTL_ADD_UINT(sysctl_ctx, children, OID_AUTO,
            "max_request_segments", CTLFLAG_RD,
            &xbd->xbd_max_request_segments, 0,
            "maximum number of pages per requests (negotiated)");

        SYSCTL_ADD_UINT(sysctl_ctx, children, OID_AUTO,
            "max_request_size", CTLFLAG_RD, &xbd->xbd_max_request_size, 0,
            "maximum size in bytes of a request (negotiated)");

        SYSCTL_ADD_UINT(sysctl_ctx, children, OID_AUTO,
            "ring_pages", CTLFLAG_RD, &xbd->xbd_ring_pages, 0,
            "communication channel pages (negotiated)");

        SYSCTL_ADD_PROC(sysctl_ctx, children, OID_AUTO,
            "features", CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, xbd,
            0, xbd_sysctl_features, "A", "protocol features (negotiated)");
}

/*
 * Translate Linux major/minor to an appropriate name and unit
 * number. For HVM guests, this allows us to use the same drive names
 * with blkfront as the emulated drives, easing transition slightly.
 */
static void
xbd_vdevice_to_unit(uint32_t vdevice, int *unit, const char **name)
{
        static struct vdev_info {
                int major;
                int shift;
                int base;
                const char *name;
        } info[] = {
                {3,     6,      0,      "ada"}, /* ide0 */
                {22,    6,      2,      "ada"}, /* ide1 */
                {33,    6,      4,      "ada"}, /* ide2 */
                {34,    6,      6,      "ada"}, /* ide3 */
                {56,    6,      8,      "ada"}, /* ide4 */
                {57,    6,      10,     "ada"}, /* ide5 */
                {88,    6,      12,     "ada"}, /* ide6 */
                {89,    6,      14,     "ada"}, /* ide7 */
                {90,    6,      16,     "ada"}, /* ide8 */
                {91,    6,      18,     "ada"}, /* ide9 */

                {8,     4,      0,      "da"},  /* scsi disk0 */
                {65,    4,      16,     "da"},  /* scsi disk1 */
                {66,    4,      32,     "da"},  /* scsi disk2 */
                {67,    4,      48,     "da"},  /* scsi disk3 */
                {68,    4,      64,     "da"},  /* scsi disk4 */
                {69,    4,      80,     "da"},  /* scsi disk5 */
                {70,    4,      96,     "da"},  /* scsi disk6 */
                {71,    4,      112,    "da"},  /* scsi disk7 */
                {128,   4,      128,    "da"},  /* scsi disk8 */
                {129,   4,      144,    "da"},  /* scsi disk9 */
                {130,   4,      160,    "da"},  /* scsi disk10 */
                {131,   4,      176,    "da"},  /* scsi disk11 */
                {132,   4,      192,    "da"},  /* scsi disk12 */
                {133,   4,      208,    "da"},  /* scsi disk13 */
                {134,   4,      224,    "da"},  /* scsi disk14 */
                {135,   4,      240,    "da"},  /* scsi disk15 */

                {202,   4,      0,      "xbd"}, /* xbd */

                {0,     0,      0,      NULL},
        };
        int major = vdevice >> 8;
        int minor = vdevice & 0xff;
        int i;

        if (vdevice & (1 << 28)) {
                *unit = (vdevice & ((1 << 28) - 1)) >> 8;
                *name = "xbd";
                return;
        }

        for (i = 0; info[i].major; i++) {
                if (info[i].major == major) {
                        *unit = info[i].base + (minor >> info[i].shift);
                        *name = info[i].name;
                        return;
                }
        }

        *unit = minor >> 4;
        *name = "xbd";
}

int
xbd_instance_create(struct xbd_softc *sc, blkif_sector_t sectors,
    int vdevice, uint16_t vdisk_info, unsigned long sector_size,
    unsigned long phys_sector_size)
{
        char features[80];
        int unit, error = 0;
        const char *name;

        xbd_vdevice_to_unit(vdevice, &unit, &name);

        sc->xbd_unit = unit;

        if (strcmp(name, "xbd") != 0)
                device_printf(sc->xbd_dev, "attaching as %s%d\n", name, unit);

        if (xbd_feature_string(sc, features, sizeof(features)) > 0) {
                device_printf(sc->xbd_dev, "features: %s\n",
                    features);
        }

        sc->xbd_disk = disk_alloc();
        sc->xbd_disk->d_unit = sc->xbd_unit;
        sc->xbd_disk->d_open = xbd_open;
        sc->xbd_disk->d_close = xbd_close;
        sc->xbd_disk->d_ioctl = xbd_ioctl;
        sc->xbd_disk->d_strategy = xbd_strategy;
        sc->xbd_disk->d_dump = xbd_dump;
        sc->xbd_disk->d_name = name;
        sc->xbd_disk->d_drv1 = sc;
        sc->xbd_disk->d_sectorsize = sector_size;
        sc->xbd_disk->d_stripesize = phys_sector_size;
        sc->xbd_disk->d_stripeoffset = 0;

        /*
         * The 'sectors' xenbus node is always in units of 512b, regardless of
         * the 'sector-size' xenbus node value.
         */
        sc->xbd_disk->d_mediasize = sectors << XBD_SECTOR_SHFT;
        if ((sc->xbd_disk->d_mediasize % sc->xbd_disk->d_sectorsize) != 0) {
                error = EINVAL;
                xenbus_dev_fatal(sc->xbd_dev, error,
                    "Disk size (%ju) not a multiple of sector size (%ju)",
                    (uintmax_t)sc->xbd_disk->d_mediasize,
                    (uintmax_t)sc->xbd_disk->d_sectorsize);
                return (error);
        }
        sc->xbd_disk->d_maxsize = sc->xbd_max_request_size;
        sc->xbd_disk->d_flags = DISKFLAG_UNMAPPED_BIO;
        if ((sc->xbd_flags & (XBDF_FLUSH|XBDF_BARRIER)) != 0) {
                sc->xbd_disk->d_flags |= DISKFLAG_CANFLUSHCACHE;
                device_printf(sc->xbd_dev,
                    "synchronize cache commands enabled.\n");
        }
        disk_create(sc->xbd_disk, DISK_VERSION);

        return error;
}

static void 
xbd_free(struct xbd_softc *sc)
{
        int i;

        /* Prevent new requests being issued until we fix things up. */
        mtx_lock(&sc->xbd_io_lock);
        sc->xbd_state = XBD_STATE_DISCONNECTED; 
        mtx_unlock(&sc->xbd_io_lock);

        /* Free resources associated with old device channel. */
        xbd_free_ring(sc);
        if (sc->xbd_shadow) {
                for (i = 0; i < sc->xbd_max_requests; i++) {
                        struct xbd_command *cm;

                        cm = &sc->xbd_shadow[i];
                        if (cm->cm_sg_refs != NULL) {
                                free(cm->cm_sg_refs, M_XENBLOCKFRONT);
                                cm->cm_sg_refs = NULL;
                        }

                        if (cm->cm_indirectionpages != NULL) {
                                gnttab_end_foreign_access_references(
                                    sc->xbd_max_request_indirectpages,
                                    &cm->cm_indirectionrefs[0]);
                                free(cm->cm_indirectionpages, M_XENBLOCKFRONT);
                                cm->cm_indirectionpages = NULL;
                        }

                        bus_dmamap_destroy(sc->xbd_io_dmat, cm->cm_map);
                }
                free(sc->xbd_shadow, M_XENBLOCKFRONT);
                sc->xbd_shadow = NULL;

                bus_dma_tag_destroy(sc->xbd_io_dmat);
                
                xbd_initq_cm(sc, XBD_Q_FREE);
                xbd_initq_cm(sc, XBD_Q_READY);
                xbd_initq_cm(sc, XBD_Q_COMPLETE);
        }
                
        xen_intr_unbind(&sc->xen_intr_handle);

}

/*--------------------------- State Change Handlers --------------------------*/
static void
xbd_initialize(struct xbd_softc *sc)
{
        const char *otherend_path;
        const char *node_path;
        uint32_t max_ring_page_order;
        int error;

        if (xenbus_get_state(sc->xbd_dev) != XenbusStateInitialising) {
                /* Initialization has already been performed. */
                return;
        }

        /*
         * Protocol defaults valid even if negotiation for a
         * setting fails.
         */
        max_ring_page_order = 0;
        sc->xbd_ring_pages = 1;

        /*
         * Protocol negotiation.
         *
         * \note xs_gather() returns on the first encountered error, so
         *       we must use independent calls in order to guarantee
         *       we don't miss information in a sparsly populated back-end
         *       tree.
         *
         * \note xs_scanf() does not update variables for unmatched
         *       fields.
         */
        otherend_path = xenbus_get_otherend_path(sc->xbd_dev);
        node_path = xenbus_get_node(sc->xbd_dev);

        /* Support both backend schemes for relaying ring page limits. */
        (void)xs_scanf(XST_NIL, otherend_path,
            "max-ring-page-order", NULL, "%" PRIu32,
            &max_ring_page_order);
        sc->xbd_ring_pages = 1 << max_ring_page_order;
        (void)xs_scanf(XST_NIL, otherend_path,
            "max-ring-pages", NULL, "%" PRIu32,
            &sc->xbd_ring_pages);
        if (sc->xbd_ring_pages < 1)
                sc->xbd_ring_pages = 1;

        if (sc->xbd_ring_pages > XBD_MAX_RING_PAGES) {
                device_printf(sc->xbd_dev,
                    "Back-end specified ring-pages of %u "
                    "limited to front-end limit of %u.\n",
                    sc->xbd_ring_pages, XBD_MAX_RING_PAGES);
                sc->xbd_ring_pages = XBD_MAX_RING_PAGES;
        }

        if (powerof2(sc->xbd_ring_pages) == 0) {
                uint32_t new_page_limit;

                new_page_limit = 0x01 << (fls(sc->xbd_ring_pages) - 1);
                device_printf(sc->xbd_dev,
                    "Back-end specified ring-pages of %u "
                    "is not a power of 2. Limited to %u.\n",
                    sc->xbd_ring_pages, new_page_limit);
                sc->xbd_ring_pages = new_page_limit;
        }

        sc->xbd_max_requests =
            BLKIF_MAX_RING_REQUESTS(sc->xbd_ring_pages * PAGE_SIZE);
        if (sc->xbd_max_requests > XBD_MAX_REQUESTS) {
                device_printf(sc->xbd_dev,
                    "Back-end specified max_requests of %u "
                    "limited to front-end limit of %zu.\n",
                    sc->xbd_max_requests, XBD_MAX_REQUESTS);
                sc->xbd_max_requests = XBD_MAX_REQUESTS;
        }

        if (xbd_alloc_ring(sc) != 0)
                return;

        /* Support both backend schemes for relaying ring page limits. */
        if (sc->xbd_ring_pages > 1) {
                error = xs_printf(XST_NIL, node_path,
                    "num-ring-pages","%u",
                    sc->xbd_ring_pages);
                if (error) {
                        xenbus_dev_fatal(sc->xbd_dev, error,
                            "writing %s/num-ring-pages",
                            node_path);
                        return;
                }

                error = xs_printf(XST_NIL, node_path,
                    "ring-page-order", "%u",
                    fls(sc->xbd_ring_pages) - 1);
                if (error) {
                        xenbus_dev_fatal(sc->xbd_dev, error,
                            "writing %s/ring-page-order",
                            node_path);
                        return;
                }
        }

        error = xs_printf(XST_NIL, node_path, "event-channel",
            "%u", xen_intr_port(sc->xen_intr_handle));
        if (error) {
                xenbus_dev_fatal(sc->xbd_dev, error,
                    "writing %s/event-channel",
                    node_path);
                return;
        }

        error = xs_printf(XST_NIL, node_path, "protocol",
            "%s", XEN_IO_PROTO_ABI_NATIVE);
        if (error) {
                xenbus_dev_fatal(sc->xbd_dev, error,
                    "writing %s/protocol",
                    node_path);
                return;
        }

        xenbus_set_state(sc->xbd_dev, XenbusStateInitialised);
}

/* 
 * Invoked when the backend is finally 'ready' (and has published
 * the details about the physical device - #sectors, size, etc). 
 */
static void 
xbd_connect(struct xbd_softc *sc)
{
        device_t dev = sc->xbd_dev;
        blkif_sector_t sectors;
        unsigned long sector_size, phys_sector_size;
        unsigned int binfo;
        int err, feature_barrier, feature_flush;
        int i, j;

        DPRINTK("blkfront.c:connect:%s.\n", xenbus_get_otherend_path(dev));

        if (sc->xbd_state == XBD_STATE_SUSPENDED) {
                return;
        }

        if (sc->xbd_state == XBD_STATE_CONNECTED) {
                struct disk *disk;

                disk = sc->xbd_disk;
                if (disk == NULL) {
                        return;
                }
                err = xs_gather(XST_NIL, xenbus_get_otherend_path(dev),
                    "sectors", "%"PRIu64, &sectors, NULL);
                if (err != 0) {
                        xenbus_dev_error(dev, err,
                            "reading sectors at %s",
                            xenbus_get_otherend_path(dev));
                        return;
                }
                disk->d_mediasize = disk->d_sectorsize * sectors;
                err = disk_resize(disk, M_NOWAIT);
                if (err) {
                        xenbus_dev_error(dev, err,
                            "unable to resize disk %s%u",
                            disk->d_name, disk->d_unit);
                        return;
                }
                device_printf(sc->xbd_dev,
                    "changed capacity to %jd\n",
                    (intmax_t)disk->d_mediasize);
                return;
        }

        err = xs_gather(XST_NIL, xenbus_get_otherend_path(dev),
            "sectors", "%"PRIu64, &sectors,
            "info", "%u", &binfo,
            "sector-size", "%lu", &sector_size,
            NULL);
        if (err) {
                xenbus_dev_fatal(dev, err,
                    "reading backend fields at %s",
                    xenbus_get_otherend_path(dev));
                return;
        }
        if ((sectors == 0) || (sector_size == 0)) {
                xenbus_dev_fatal(dev, 0,
                    "invalid parameters from %s:"
                    " sectors = %"PRIu64", sector_size = %lu",
                    xenbus_get_otherend_path(dev),
                    sectors, sector_size);
                return;
        }
        err = xs_gather(XST_NIL, xenbus_get_otherend_path(dev),
             "physical-sector-size", "%lu", &phys_sector_size,
             NULL);
        if (err || phys_sector_size <= sector_size)
                phys_sector_size = 0;
        err = xs_gather(XST_NIL, xenbus_get_otherend_path(dev),
             "feature-barrier", "%d", &feature_barrier,
             NULL);
        if (err == 0 && feature_barrier != 0)
                sc->xbd_flags |= XBDF_BARRIER;

        err = xs_gather(XST_NIL, xenbus_get_otherend_path(dev),
             "feature-flush-cache", "%d", &feature_flush,
             NULL);
        if (err == 0 && feature_flush != 0)
                sc->xbd_flags |= XBDF_FLUSH;

        err = xs_gather(XST_NIL, xenbus_get_otherend_path(dev),
            "feature-max-indirect-segments", "%" PRIu32,
            &sc->xbd_max_request_segments, NULL);
        if ((err != 0) || (xbd_enable_indirect == 0))
                sc->xbd_max_request_segments = 0;
        if (sc->xbd_max_request_segments > XBD_MAX_INDIRECT_SEGMENTS)
                sc->xbd_max_request_segments = XBD_MAX_INDIRECT_SEGMENTS;
        if (sc->xbd_max_request_segments > XBD_SIZE_TO_SEGS(maxphys))
                sc->xbd_max_request_segments = XBD_SIZE_TO_SEGS(maxphys);
        sc->xbd_max_request_indirectpages =
            XBD_INDIRECT_SEGS_TO_PAGES(sc->xbd_max_request_segments);
        if (sc->xbd_max_request_segments < BLKIF_MAX_SEGMENTS_PER_REQUEST)
                sc->xbd_max_request_segments = BLKIF_MAX_SEGMENTS_PER_REQUEST;
        sc->xbd_max_request_size =
            XBD_SEGS_TO_SIZE(sc->xbd_max_request_segments);

        /* Allocate datastructures based on negotiated values. */
        err = bus_dma_tag_create(
            bus_get_dma_tag(sc->xbd_dev),       /* parent */
            sector_size, PAGE_SIZE,             /* algnmnt, boundary */
            BUS_SPACE_MAXADDR,                  /* lowaddr */
            BUS_SPACE_MAXADDR,                  /* highaddr */
            NULL, NULL,                         /* filter, filterarg */
            sc->xbd_max_request_size,
            sc->xbd_max_request_segments,
            PAGE_SIZE,                          /* maxsegsize */
            BUS_DMA_ALLOCNOW,                   /* flags */
            busdma_lock_mutex,                  /* lockfunc */
            &sc->xbd_io_lock,                   /* lockarg */
            &sc->xbd_io_dmat);
        if (err != 0) {
                xenbus_dev_fatal(sc->xbd_dev, err,
                    "Cannot allocate parent DMA tag\n");
                return;
        }

        /* Per-transaction data allocation. */
        sc->xbd_shadow = malloc(sizeof(*sc->xbd_shadow) * sc->xbd_max_requests,
            M_XENBLOCKFRONT, M_NOWAIT|M_ZERO);
        if (sc->xbd_shadow == NULL) {
                bus_dma_tag_destroy(sc->xbd_io_dmat);
                xenbus_dev_fatal(sc->xbd_dev, ENOMEM,
                    "Cannot allocate request structures\n");
                return;
        }

        for (i = 0; i < sc->xbd_max_requests; i++) {
                struct xbd_command *cm;
                void * indirectpages;

                cm = &sc->xbd_shadow[i];
                cm->cm_sg_refs = malloc(
                    sizeof(grant_ref_t) * sc->xbd_max_request_segments,
                    M_XENBLOCKFRONT, M_NOWAIT);
                if (cm->cm_sg_refs == NULL)
                        break;
                cm->cm_id = i;
                cm->cm_flags = XBDCF_INITIALIZER;
                cm->cm_sc = sc;
                if (bus_dmamap_create(sc->xbd_io_dmat, 0, &cm->cm_map) != 0)
                        break;
                if (sc->xbd_max_request_indirectpages > 0) {
                        indirectpages = contigmalloc(
                            PAGE_SIZE * sc->xbd_max_request_indirectpages,
                            M_XENBLOCKFRONT, M_ZERO | M_NOWAIT, 0, ~0,
                            PAGE_SIZE, 0);
                        if (indirectpages == NULL)
                                sc->xbd_max_request_indirectpages = 0;
                } else {
                        indirectpages = NULL;
                }
                for (j = 0; j < sc->xbd_max_request_indirectpages; j++) {
                        if (gnttab_grant_foreign_access(
                            xenbus_get_otherend_id(sc->xbd_dev),
                            (vtophys(indirectpages) >> PAGE_SHIFT) + j,
                            1 /* grant read-only access */,
                            &cm->cm_indirectionrefs[j]))
                                break;
                }
                if (j < sc->xbd_max_request_indirectpages) {
                        free(indirectpages, M_XENBLOCKFRONT);
                        break;
                }
                cm->cm_indirectionpages = indirectpages;
                xbd_free_command(cm);
        }

        if (sc->xbd_disk == NULL) {
                device_printf(dev, "%juMB <%s> at %s",
                    (uintmax_t)((sectors << XBD_SECTOR_SHFT) / 1048576),
                    device_get_desc(dev),
                    xenbus_get_node(dev));
                bus_print_child_footer(device_get_parent(dev), dev);

                err = xbd_instance_create(sc, sectors, sc->xbd_vdevice, binfo,
                    sector_size, phys_sector_size);
                if (err != 0) {
                        xenbus_dev_fatal(dev, err, "Unable to create instance");
                        return;
                }
        }

        (void)xenbus_set_state(dev, XenbusStateConnected); 

        /* Kick pending requests. */
        mtx_lock(&sc->xbd_io_lock);
        sc->xbd_state = XBD_STATE_CONNECTED;
        xbd_startio(sc);
        sc->xbd_flags |= XBDF_READY;
        mtx_unlock(&sc->xbd_io_lock);
}

/**
 * Handle the change of state of the backend to Closing.  We must delete our
 * device-layer structures now, to ensure that writes are flushed through to
 * the backend.  Once this is done, we can switch to Closed in
 * acknowledgement.
 */
static void
xbd_closing(device_t dev)
{
        struct xbd_softc *sc = device_get_softc(dev);

        xenbus_set_state(dev, XenbusStateClosing);

        DPRINTK("xbd_closing: %s removed\n", xenbus_get_node(dev));

        if (sc->xbd_disk != NULL) {
                disk_destroy(sc->xbd_disk);
                sc->xbd_disk = NULL;
        }

        xenbus_set_state(dev, XenbusStateClosed); 
}

/*---------------------------- NewBus Entrypoints ----------------------------*/
static int
xbd_probe(device_t dev)
{
        if (strcmp(xenbus_get_type(dev), "vbd") != 0)
                return (ENXIO);

        if (xen_pv_disks_disabled())
                return (ENXIO);

        if (xen_hvm_domain()) {
                int error;
                char *type;

                /*
                 * When running in an HVM domain, IDE disk emulation is
                 * disabled early in boot so that native drivers will
                 * not see emulated hardware.  However, CDROM device
                 * emulation cannot be disabled.
                 *
                 * Through use of FreeBSD's vm_guest and xen_hvm_domain()
                 * APIs, we could modify the native CDROM driver to fail its
                 * probe when running under Xen.  Unfortunatlely, the PV
                 * CDROM support in XenServer (up through at least version
                 * 6.2) isn't functional, so we instead rely on the emulated
                 * CDROM instance, and fail to attach the PV one here in
                 * the blkfront driver.
                 */
                error = xs_read(XST_NIL, xenbus_get_node(dev),
                    "device-type", NULL, (void **) &type);
                if (error)
                        return (ENXIO);

                if (strncmp(type, "cdrom", 5) == 0) {
                        free(type, M_XENSTORE);
                        return (ENXIO);
                }
                free(type, M_XENSTORE);
        }

        device_set_desc(dev, "Virtual Block Device");
        device_quiet(dev);
        return (0);
}

/*
 * Setup supplies the backend dir, virtual device.  We place an event
 * channel and shared frame entries.  We watch backend to wait if it's
 * ok.
 */
static int
xbd_attach(device_t dev)
{
        struct xbd_softc *sc;
        const char *name;
        uint32_t vdevice;
        int error;
        int i;
        int unit;

        /* FIXME: Use dynamic device id if this is not set. */
        error = xs_scanf(XST_NIL, xenbus_get_node(dev),
            "virtual-device", NULL, "%" PRIu32, &vdevice);
        if (error)
                error = xs_scanf(XST_NIL, xenbus_get_node(dev),
                    "virtual-device-ext", NULL, "%" PRIu32, &vdevice);
        if (error) {
                xenbus_dev_fatal(dev, error, "reading virtual-device");
                device_printf(dev, "Couldn't determine virtual device.\n");
                return (error);
        }

        xbd_vdevice_to_unit(vdevice, &unit, &name);
        if (!strcmp(name, "xbd"))
                device_set_unit(dev, unit);

        sc = device_get_softc(dev);
        mtx_init(&sc->xbd_io_lock, "blkfront i/o lock", NULL, MTX_DEF);
        xbd_initqs(sc);
        for (i = 0; i < XBD_MAX_RING_PAGES; i++)
                sc->xbd_ring_ref[i] = GRANT_REF_INVALID;

        sc->xbd_dev = dev;
        sc->xbd_vdevice = vdevice;
        sc->xbd_state = XBD_STATE_DISCONNECTED;

        xbd_setup_sysctl(sc);

        /* Wait for backend device to publish its protocol capabilities. */
        xenbus_set_state(dev, XenbusStateInitialising);

        return (0);
}

static int
xbd_detach(device_t dev)
{
        struct xbd_softc *sc = device_get_softc(dev);

        DPRINTK("%s: %s removed\n", __func__, xenbus_get_node(dev));

        xbd_free(sc);
        mtx_destroy(&sc->xbd_io_lock);

        return 0;
}

static int
xbd_suspend(device_t dev)
{
        struct xbd_softc *sc = device_get_softc(dev);
        int retval;
        int saved_state;

        /* Prevent new requests being issued until we fix things up. */
        mtx_lock(&sc->xbd_io_lock);
        saved_state = sc->xbd_state;
        sc->xbd_state = XBD_STATE_SUSPENDED;

        /* Wait for outstanding I/O to drain. */
        retval = 0;
        while (xbd_queue_length(sc, XBD_Q_BUSY) != 0) {
                if (msleep(&sc->xbd_cm_q[XBD_Q_BUSY], &sc->xbd_io_lock,
                    PRIBIO, "blkf_susp", 30 * hz) == EWOULDBLOCK) {
                        retval = EBUSY;
                        break;
                }
        }
        mtx_unlock(&sc->xbd_io_lock);

        if (retval != 0)
                sc->xbd_state = saved_state;

        return (retval);
}

static int
xbd_resume(device_t dev)
{
        struct xbd_softc *sc = device_get_softc(dev);

        if (xen_suspend_cancelled) {
                sc->xbd_state = XBD_STATE_CONNECTED;
                return (0);
        }

        DPRINTK("xbd_resume: %s\n", xenbus_get_node(dev));

        xbd_free(sc);
        xbd_initialize(sc);
        return (0);
}

/**
 * Callback received when the backend's state changes.
 */
static void
xbd_backend_changed(device_t dev, XenbusState backend_state)
{
        struct xbd_softc *sc = device_get_softc(dev);

        DPRINTK("backend_state=%d\n", backend_state);

        switch (backend_state) {
        case XenbusStateUnknown:
        case XenbusStateInitialising:
        case XenbusStateReconfigured:
        case XenbusStateReconfiguring:
        case XenbusStateClosed:
                break;

        case XenbusStateInitWait:
        case XenbusStateInitialised:
                xbd_initialize(sc);
                break;

        case XenbusStateConnected:
                xbd_initialize(sc);
                xbd_connect(sc);
                break;

        case XenbusStateClosing:
                if (sc->xbd_users > 0) {
                        device_printf(dev, "detaching with pending users\n");
                        KASSERT(sc->xbd_disk != NULL,
                            ("NULL disk with pending users\n"));
                        disk_gone(sc->xbd_disk);
                } else {
                        xbd_closing(dev);
                }
                break;  
        }
}

/*---------------------------- NewBus Registration ---------------------------*/
static device_method_t xbd_methods[] = { 
        /* Device interface */ 
        DEVMETHOD(device_probe,         xbd_probe), 
        DEVMETHOD(device_attach,        xbd_attach), 
        DEVMETHOD(device_detach,        xbd_detach), 
        DEVMETHOD(device_shutdown,      bus_generic_shutdown), 
        DEVMETHOD(device_suspend,       xbd_suspend), 
        DEVMETHOD(device_resume,        xbd_resume), 

        /* Xenbus interface */
        DEVMETHOD(xenbus_otherend_changed, xbd_backend_changed),

        DEVMETHOD_END
}; 

static driver_t xbd_driver = { 
        "xbd", 
        xbd_methods, 
        sizeof(struct xbd_softc),                      
}; 

DRIVER_MODULE(xbd, xenbusb_front, xbd_driver, 0, 0);