xen/io/xnb.c

	xnb.c revision 0dc2366f7b9f9f36e10909b1e95edbf2a261c2ac
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#ifdef DEBUG
#define XNB_DEBUG 1
#endif /* DEBUG */

#include "xnb.h"

#include <sys/sunddi.h>
#include <sys/sunndi.h>
#include <sys/modctl.h>
#include <sys/conf.h>
#include <sys/mac.h>
#include <sys/mac_impl.h> /* For mac_fix_cksum(). */
#include <sys/dlpi.h>
#include <sys/strsubr.h>
#include <sys/strsun.h>
#include <sys/types.h>
#include <sys/pattr.h>
#include <vm/seg_kmem.h>
#include <vm/hat_i86.h>
#include <xen/sys/xenbus_impl.h>
#include <xen/sys/xendev.h>
#include <sys/balloon_impl.h>
#include <sys/evtchn_impl.h>
#include <sys/gnttab.h>
#include <vm/vm_dep.h>
#include <sys/note.h>
#include <sys/gld.h>
#include <inet/ip.h>
#include <inet/ip_impl.h>

/*
 * The terms "transmit" and "receive" are used in alignment with domU,
 * which means that packets originating from the peer domU are "transmitted"
 * to other parts of the system and packets are "received" from them.
 */

/*
 * Should we allow guests to manipulate multicast group membership?
 */
static boolean_t    xnb_multicast_control = B_TRUE;

static boolean_t    xnb_connect_rings(dev_info_t *);
static void     xnb_disconnect_rings(dev_info_t *);
static void     xnb_oe_state_change(dev_info_t *, ddi_eventcookie_t,
    void *, void *);
static void     xnb_hp_state_change(dev_info_t *, ddi_eventcookie_t,
    void *, void *);

static int  xnb_txbuf_constructor(void *, void *, int);
static void xnb_txbuf_destructor(void *, void *);
static void xnb_tx_notify_peer(xnb_t *, boolean_t);
static void xnb_tx_mark_complete(xnb_t *, RING_IDX, int16_t);

mblk_t      *xnb_to_peer(xnb_t *, mblk_t *);
mblk_t      *xnb_copy_to_peer(xnb_t *, mblk_t *);

static void     setup_gop(xnb_t *, gnttab_copy_t *, uchar_t *,
    size_t, size_t, size_t, grant_ref_t);
#pragma inline(setup_gop)
static boolean_t    is_foreign(void *);
#pragma inline(is_foreign)

#define INVALID_GRANT_HANDLE    ((grant_handle_t)-1)
#define INVALID_GRANT_REF   ((grant_ref_t)-1)

static kmutex_t xnb_alloc_page_lock;

/*
 * On a 32 bit PAE system physical and machine addresses are larger
 * than 32 bits.  ddi_btop() on such systems take an unsigned long
 * argument, and so addresses above 4G are truncated before ddi_btop()
 * gets to see them.  To avoid this, code the shift operation here.
 */
#define xnb_btop(addr)  ((addr) >> PAGESHIFT)

/* DMA attributes for transmit and receive data */
static ddi_dma_attr_t buf_dma_attr = {
    DMA_ATTR_V0,        /* version of this structure */
    0,          /* lowest usable address */
    0xffffffffffffffffULL,  /* highest usable address */
    0x7fffffff,     /* maximum DMAable byte count */
    MMU_PAGESIZE,       /* alignment in bytes */
    0x7ff,          /* bitmap of burst sizes */
    1,          /* minimum transfer */
    0xffffffffU,        /* maximum transfer */
    0xffffffffffffffffULL,  /* maximum segment length */
    1,          /* maximum number of segments */
    1,          /* granularity */
    0,          /* flags (reserved) */
};

/* DMA access attributes for data: NOT to be byte swapped. */
static ddi_device_acc_attr_t data_accattr = {
    DDI_DEVICE_ATTR_V0,
    DDI_NEVERSWAP_ACC,
    DDI_STRICTORDER_ACC
};

/*
 * Statistics.
 */
static const char * const aux_statistics[] = {
    "rx_cksum_deferred",
    "tx_cksum_no_need",
    "rx_rsp_notok",
    "tx_notify_deferred",
    "tx_notify_sent",
    "rx_notify_deferred",
    "rx_notify_sent",
    "tx_too_early",
    "rx_too_early",
    "rx_allocb_failed",
    "tx_allocb_failed",
    "rx_foreign_page",
    "mac_full",
    "spurious_intr",
    "allocation_success",
    "allocation_failure",
    "small_allocation_success",
    "small_allocation_failure",
    "other_allocation_failure",
    "rx_pageboundary_crossed",
    "rx_cpoparea_grown",
    "csum_hardware",
    "csum_software",
    "tx_overflow_page",
    "tx_unexpected_flags",
};

static int
xnb_ks_aux_update(kstat_t *ksp, int flag)
{
    xnb_t *xnbp;
    kstat_named_t *knp;

    if (flag != KSTAT_READ)
        return (EACCES);

    xnbp = ksp->ks_private;
    knp = ksp->ks_data;

    /*
     * Assignment order should match that of the names in
     * aux_statistics.
     */
    (knp++)->value.ui64 = xnbp->xnb_stat_rx_cksum_deferred;
    (knp++)->value.ui64 = xnbp->xnb_stat_tx_cksum_no_need;
    (knp++)->value.ui64 = xnbp->xnb_stat_rx_rsp_notok;
    (knp++)->value.ui64 = xnbp->xnb_stat_tx_notify_deferred;
    (knp++)->value.ui64 = xnbp->xnb_stat_tx_notify_sent;
    (knp++)->value.ui64 = xnbp->xnb_stat_rx_notify_deferred;
    (knp++)->value.ui64 = xnbp->xnb_stat_rx_notify_sent;
    (knp++)->value.ui64 = xnbp->xnb_stat_tx_too_early;
    (knp++)->value.ui64 = xnbp->xnb_stat_rx_too_early;
    (knp++)->value.ui64 = xnbp->xnb_stat_rx_allocb_failed;
    (knp++)->value.ui64 = xnbp->xnb_stat_tx_allocb_failed;
    (knp++)->value.ui64 = xnbp->xnb_stat_rx_foreign_page;
    (knp++)->value.ui64 = xnbp->xnb_stat_mac_full;
    (knp++)->value.ui64 = xnbp->xnb_stat_spurious_intr;
    (knp++)->value.ui64 = xnbp->xnb_stat_allocation_success;
    (knp++)->value.ui64 = xnbp->xnb_stat_allocation_failure;
    (knp++)->value.ui64 = xnbp->xnb_stat_small_allocation_success;
    (knp++)->value.ui64 = xnbp->xnb_stat_small_allocation_failure;
    (knp++)->value.ui64 = xnbp->xnb_stat_other_allocation_failure;
    (knp++)->value.ui64 = xnbp->xnb_stat_rx_pagebndry_crossed;
    (knp++)->value.ui64 = xnbp->xnb_stat_rx_cpoparea_grown;
    (knp++)->value.ui64 = xnbp->xnb_stat_csum_hardware;
    (knp++)->value.ui64 = xnbp->xnb_stat_csum_software;
    (knp++)->value.ui64 = xnbp->xnb_stat_tx_overflow_page;
    (knp++)->value.ui64 = xnbp->xnb_stat_tx_unexpected_flags;

    return (0);
}

static boolean_t
xnb_ks_init(xnb_t *xnbp)
{
    int nstat = sizeof (aux_statistics) /
        sizeof (aux_statistics[0]);
    const char * const *cp = aux_statistics;
    kstat_named_t *knp;

    /*
     * Create and initialise kstats.
     */
    xnbp->xnb_kstat_aux = kstat_create(ddi_driver_name(xnbp->xnb_devinfo),
        ddi_get_instance(xnbp->xnb_devinfo), "aux_statistics", "net",
        KSTAT_TYPE_NAMED, nstat, 0);
    if (xnbp->xnb_kstat_aux == NULL)
        return (B_FALSE);

    xnbp->xnb_kstat_aux->ks_private = xnbp;
    xnbp->xnb_kstat_aux->ks_update = xnb_ks_aux_update;

    knp = xnbp->xnb_kstat_aux->ks_data;
    while (nstat > 0) {
        kstat_named_init(knp, *cp, KSTAT_DATA_UINT64);

        knp++;
        cp++;
        nstat--;
    }

    kstat_install(xnbp->xnb_kstat_aux);

    return (B_TRUE);
}

static void
xnb_ks_free(xnb_t *xnbp)
{
    kstat_delete(xnbp->xnb_kstat_aux);
}

/*
 * Calculate and insert the transport checksum for an arbitrary packet.
 */
static mblk_t *
xnb_software_csum(xnb_t *xnbp, mblk_t *mp)
{
    _NOTE(ARGUNUSED(xnbp));

    /*
     * XXPV dme: shouldn't rely on mac_fix_cksum(), not least
     * because it doesn't cover all of the interesting cases :-(
     */
    mac_hcksum_set(mp, 0, 0, 0, 0, HCK_FULLCKSUM);

    return (mac_fix_cksum(mp));
}

mblk_t *
xnb_process_cksum_flags(xnb_t *xnbp, mblk_t *mp, uint32_t capab)
{
    struct ether_header *ehp;
    uint16_t sap;
    uint32_t offset;
    ipha_t *ipha;

    ASSERT(mp->b_next == NULL);

    /*
     * Check that the packet is contained in a single mblk.  In
     * the "from peer" path this is true today, but may change
     * when scatter gather support is added.  In the "to peer"
     * path we cannot be sure, but in most cases it will be true
     * (in the xnbo case the packet has come from a MAC device
     * which is unlikely to split packets).
     */
    if (mp->b_cont != NULL)
        goto software;

    /*
     * If the MAC has no hardware capability don't do any further
     * checking.
     */
    if (capab == 0)
        goto software;

    ASSERT(MBLKL(mp) >= sizeof (struct ether_header));
    ehp = (struct ether_header *)mp->b_rptr;

    if (ntohs(ehp->ether_type) == VLAN_TPID) {
        struct ether_vlan_header *evhp;

        ASSERT(MBLKL(mp) >= sizeof (struct ether_vlan_header));
        evhp = (struct ether_vlan_header *)mp->b_rptr;
        sap = ntohs(evhp->ether_type);
        offset = sizeof (struct ether_vlan_header);
    } else {
        sap = ntohs(ehp->ether_type);
        offset = sizeof (struct ether_header);
    }

    /*
     * We only attempt to do IPv4 packets in hardware.
     */
    if (sap != ETHERTYPE_IP)
        goto software;

    /*
     * We know that this is an IPv4 packet.
     */
    ipha = (ipha_t *)(mp->b_rptr + offset);

    switch (ipha->ipha_protocol) {
    case IPPROTO_TCP:
    case IPPROTO_UDP: {
        uint32_t start, length, stuff, cksum;
        uint16_t *stuffp;

        /*
         * This is a TCP/IPv4 or UDP/IPv4 packet, for which we
         * can use full IPv4 and partial checksum offload.
         */
        if ((capab & (HCKSUM_INET_FULL_V4|HCKSUM_INET_PARTIAL)) == 0)
            break;

        start = IP_SIMPLE_HDR_LENGTH;
        length = ntohs(ipha->ipha_length);
        if (ipha->ipha_protocol == IPPROTO_TCP) {
            stuff = start + TCP_CHECKSUM_OFFSET;
            cksum = IP_TCP_CSUM_COMP;
        } else {
            stuff = start + UDP_CHECKSUM_OFFSET;
            cksum = IP_UDP_CSUM_COMP;
        }
        stuffp = (uint16_t *)(mp->b_rptr + offset + stuff);

        if (capab & HCKSUM_INET_FULL_V4) {
            /*
             * Some devices require that the checksum
             * field of the packet is zero for full
             * offload.
             */
            *stuffp = 0;

            mac_hcksum_set(mp, 0, 0, 0, 0, HCK_FULLCKSUM);

            xnbp->xnb_stat_csum_hardware++;

            return (mp);
        }

        if (capab & HCKSUM_INET_PARTIAL) {
            if (*stuffp == 0) {
                ipaddr_t src, dst;

                /*
                 * Older Solaris guests don't insert
                 * the pseudo-header checksum, so we
                 * calculate it here.
                 */
                src = ipha->ipha_src;
                dst = ipha->ipha_dst;

                cksum += (dst >> 16) + (dst & 0xFFFF);
                cksum += (src >> 16) + (src & 0xFFFF);
                cksum += length - IP_SIMPLE_HDR_LENGTH;

                cksum = (cksum >> 16) + (cksum & 0xFFFF);
                cksum = (cksum >> 16) + (cksum & 0xFFFF);

                ASSERT(cksum <= 0xFFFF);

                *stuffp = (uint16_t)(cksum ? cksum : ~cksum);
            }

            mac_hcksum_set(mp, start, stuff, length, 0,
                HCK_PARTIALCKSUM);

            xnbp->xnb_stat_csum_hardware++;

            return (mp);
        }

        /* NOTREACHED */
        break;
    }

    default:
        /* Use software. */
        break;
    }

software:
    /*
     * We are not able to use any offload so do the whole thing in
     * software.
     */
    xnbp->xnb_stat_csum_software++;

    return (xnb_software_csum(xnbp, mp));
}

int
xnb_attach(dev_info_t *dip, xnb_flavour_t *flavour, void *flavour_data)
{
    xnb_t *xnbp;
    char *xsname;
    char cachename[32];

    xnbp = kmem_zalloc(sizeof (*xnbp), KM_SLEEP);

    xnbp->xnb_flavour = flavour;
    xnbp->xnb_flavour_data = flavour_data;
    xnbp->xnb_devinfo = dip;
    xnbp->xnb_evtchn = INVALID_EVTCHN;
    xnbp->xnb_irq = B_FALSE;
    xnbp->xnb_tx_ring_handle = INVALID_GRANT_HANDLE;
    xnbp->xnb_rx_ring_handle = INVALID_GRANT_HANDLE;
    xnbp->xnb_connected = B_FALSE;
    xnbp->xnb_hotplugged = B_FALSE;
    xnbp->xnb_detachable = B_FALSE;
    xnbp->xnb_peer = xvdi_get_oeid(dip);
    xnbp->xnb_be_status = XNB_STATE_INIT;
    xnbp->xnb_fe_status = XNB_STATE_INIT;

    xnbp->xnb_tx_buf_count = 0;

    xnbp->xnb_rx_hv_copy = B_FALSE;
    xnbp->xnb_multicast_control = B_FALSE;

    xnbp->xnb_rx_va = vmem_alloc(heap_arena, PAGESIZE, VM_SLEEP);
    ASSERT(xnbp->xnb_rx_va != NULL);

    if (ddi_get_iblock_cookie(dip, 0, &xnbp->xnb_icookie)
        != DDI_SUCCESS)
        goto failure;

    /* Allocated on demand, when/if we enter xnb_copy_to_peer(). */
    xnbp->xnb_rx_cpop = NULL;
    xnbp->xnb_rx_cpop_count = 0;

    mutex_init(&xnbp->xnb_tx_lock, NULL, MUTEX_DRIVER,
        xnbp->xnb_icookie);
    mutex_init(&xnbp->xnb_rx_lock, NULL, MUTEX_DRIVER,
        xnbp->xnb_icookie);
    mutex_init(&xnbp->xnb_state_lock, NULL, MUTEX_DRIVER,
        xnbp->xnb_icookie);

    /* Set driver private pointer now. */
    ddi_set_driver_private(dip, xnbp);

    (void) sprintf(cachename, "xnb_tx_buf_cache_%d", ddi_get_instance(dip));
    xnbp->xnb_tx_buf_cache = kmem_cache_create(cachename,
        sizeof (xnb_txbuf_t), 0,
        xnb_txbuf_constructor, xnb_txbuf_destructor,
        NULL, xnbp, NULL, 0);
    if (xnbp->xnb_tx_buf_cache == NULL)
        goto failure_0;

    if (!xnb_ks_init(xnbp))
        goto failure_1;

    /*
     * Receive notification of changes in the state of the
     * driver in the guest domain.
     */
    if (xvdi_add_event_handler(dip, XS_OE_STATE, xnb_oe_state_change,
        NULL) != DDI_SUCCESS)
        goto failure_2;

    /*
     * Receive notification of hotplug events.
     */
    if (xvdi_add_event_handler(dip, XS_HP_STATE, xnb_hp_state_change,
        NULL) != DDI_SUCCESS)
        goto failure_2;

    xsname = xvdi_get_xsname(dip);

    if (xenbus_printf(XBT_NULL, xsname,
        "feature-multicast-control", "%d",
        xnb_multicast_control ? 1 : 0) != 0)
        goto failure_3;

    if (xenbus_printf(XBT_NULL, xsname,
        "feature-rx-copy", "%d",  1) != 0)
        goto failure_3;
    /*
     * Linux domUs seem to depend on "feature-rx-flip" being 0
     * in addition to "feature-rx-copy" being 1. It seems strange
     * to use four possible states to describe a binary decision,
     * but we might as well play nice.
     */
    if (xenbus_printf(XBT_NULL, xsname,
        "feature-rx-flip", "%d", 0) != 0)
        goto failure_3;

    (void) xvdi_switch_state(dip, XBT_NULL, XenbusStateInitWait);
    (void) xvdi_post_event(dip, XEN_HP_ADD);

    return (DDI_SUCCESS);

failure_3:
    xvdi_remove_event_handler(dip, NULL);

failure_2:
    xnb_ks_free(xnbp);

failure_1:
    kmem_cache_destroy(xnbp->xnb_tx_buf_cache);

failure_0:
    mutex_destroy(&xnbp->xnb_state_lock);
    mutex_destroy(&xnbp->xnb_rx_lock);
    mutex_destroy(&xnbp->xnb_tx_lock);

failure:
    vmem_free(heap_arena, xnbp->xnb_rx_va, PAGESIZE);
    kmem_free(xnbp, sizeof (*xnbp));
    return (DDI_FAILURE);
}

void
xnb_detach(dev_info_t *dip)
{
    xnb_t *xnbp = ddi_get_driver_private(dip);

    ASSERT(xnbp != NULL);
    ASSERT(!xnbp->xnb_connected);
    ASSERT(xnbp->xnb_tx_buf_count == 0);

    xnb_disconnect_rings(dip);

    xvdi_remove_event_handler(dip, NULL);

    xnb_ks_free(xnbp);

    kmem_cache_destroy(xnbp->xnb_tx_buf_cache);

    ddi_set_driver_private(dip, NULL);

    mutex_destroy(&xnbp->xnb_state_lock);
    mutex_destroy(&xnbp->xnb_rx_lock);
    mutex_destroy(&xnbp->xnb_tx_lock);

    if (xnbp->xnb_rx_cpop_count > 0)
        kmem_free(xnbp->xnb_rx_cpop, sizeof (xnbp->xnb_rx_cpop[0])
            * xnbp->xnb_rx_cpop_count);

    ASSERT(xnbp->xnb_rx_va != NULL);
    vmem_free(heap_arena, xnbp->xnb_rx_va, PAGESIZE);

    kmem_free(xnbp, sizeof (*xnbp));
}

/*
 * Allocate a page from the hypervisor to be flipped to the peer.
 *
 * Try to get pages in batches to reduce the overhead of calls into
 * the balloon driver.
 */
static mfn_t
xnb_alloc_page(xnb_t *xnbp)
{
#define WARNING_RATE_LIMIT 100
#define BATCH_SIZE 256
    static mfn_t mfns[BATCH_SIZE];  /* common across all instances */
    static int nth = BATCH_SIZE;
    mfn_t mfn;

    mutex_enter(&xnb_alloc_page_lock);
    if (nth == BATCH_SIZE) {
        if (balloon_alloc_pages(BATCH_SIZE, mfns) != BATCH_SIZE) {
            xnbp->xnb_stat_allocation_failure++;
            mutex_exit(&xnb_alloc_page_lock);

            /*
             * Try for a single page in low memory situations.
             */
            if (balloon_alloc_pages(1, &mfn) != 1) {
                if ((xnbp->xnb_stat_small_allocation_failure++
                    % WARNING_RATE_LIMIT) == 0)
                    cmn_err(CE_WARN, "xnb_alloc_page: "
                        "Cannot allocate memory to "
                        "transfer packets to peer.");
                return (0);
            } else {
                xnbp->xnb_stat_small_allocation_success++;
                return (mfn);
            }
        }

        nth = 0;
        xnbp->xnb_stat_allocation_success++;
    }

    mfn = mfns[nth++];
    mutex_exit(&xnb_alloc_page_lock);

    ASSERT(mfn != 0);

    return (mfn);
#undef BATCH_SIZE
#undef WARNING_RATE_LIMIT
}

/*
 * Free a page back to the hypervisor.
 *
 * This happens only in the error path, so batching is not worth the
 * complication.
 */
static void
xnb_free_page(xnb_t *xnbp, mfn_t mfn)
{
    _NOTE(ARGUNUSED(xnbp));
    int r;
    pfn_t pfn;

    pfn = xen_assign_pfn(mfn);
    pfnzero(pfn, 0, PAGESIZE);
    xen_release_pfn(pfn);

    if ((r = balloon_free_pages(1, &mfn, NULL, NULL)) != 1) {
        cmn_err(CE_WARN, "free_page: cannot decrease memory "
            "reservation (%d): page kept but unusable (mfn = 0x%lx).",
            r, mfn);
    }
}

/*
 * Similar to RING_HAS_UNCONSUMED_REQUESTS(&xnbp->rx_ring) but using
 * local variables. Used in both xnb_to_peer() and xnb_copy_to_peer().
 */
#define XNB_RING_HAS_UNCONSUMED_REQUESTS(_r)        \
    ((((_r)->sring->req_prod - loop) <      \
        (RING_SIZE(_r) - (loop - prod))) ?  \
        ((_r)->sring->req_prod - loop) :        \
        (RING_SIZE(_r) - (loop - prod)))

/*
 * Pass packets to the peer using page flipping.
 */
mblk_t *
xnb_to_peer(xnb_t *xnbp, mblk_t *mp)
{
    mblk_t *free = mp, *prev = NULL;
    size_t len;
    gnttab_transfer_t *gop;
    boolean_t notify;
    RING_IDX loop, prod, end;

    /*
     * For each packet the sequence of operations is:
     *
     * 1. get a new page from the hypervisor.
     * 2. get a request slot from the ring.
     * 3. copy the data into the new page.
     * 4. transfer the page to the peer.
     * 5. update the request slot.
     * 6. kick the peer.
     * 7. free mp.
     *
     * In order to reduce the number of hypercalls, we prepare
     * several packets for the peer and perform a single hypercall
     * to transfer them.
     */

    mutex_enter(&xnbp->xnb_rx_lock);

    /*
     * If we are not connected to the peer or have not yet
     * finished hotplug it is too early to pass packets to the
     * peer.
     */
    if (!(xnbp->xnb_connected && xnbp->xnb_hotplugged)) {
        mutex_exit(&xnbp->xnb_rx_lock);
        DTRACE_PROBE(flip_rx_too_early);
        xnbp->xnb_stat_rx_too_early++;
        return (mp);
    }

    loop = xnbp->xnb_rx_ring.req_cons;
    prod = xnbp->xnb_rx_ring.rsp_prod_pvt;
    gop = xnbp->xnb_rx_top;

    while ((mp != NULL) &&
        XNB_RING_HAS_UNCONSUMED_REQUESTS(&xnbp->xnb_rx_ring)) {

        mfn_t mfn;
        pfn_t pfn;
        netif_rx_request_t *rxreq;
        netif_rx_response_t *rxresp;
        char *valoop;
        mblk_t *ml;
        uint16_t cksum_flags;

        /* 1 */
        if ((mfn = xnb_alloc_page(xnbp)) == 0) {
            xnbp->xnb_stat_rx_defer++;
            break;
        }

        /* 2 */
        rxreq = RING_GET_REQUEST(&xnbp->xnb_rx_ring, loop);

#ifdef XNB_DEBUG
        if (!(rxreq->id < NET_RX_RING_SIZE))
            cmn_err(CE_PANIC, "xnb_to_peer: "
                "id %d out of range in request 0x%p",
                rxreq->id, (void *)rxreq);
#endif /* XNB_DEBUG */

        /* Assign a pfn and map the new page at the allocated va. */
        pfn = xen_assign_pfn(mfn);
        hat_devload(kas.a_hat, xnbp->xnb_rx_va, PAGESIZE,
            pfn, PROT_READ | PROT_WRITE, HAT_LOAD);

        /* 3 */
        len = 0;
        valoop = xnbp->xnb_rx_va;
        for (ml = mp; ml != NULL; ml = ml->b_cont) {
            size_t chunk = ml->b_wptr - ml->b_rptr;

            bcopy(ml->b_rptr, valoop, chunk);
            valoop += chunk;
            len += chunk;
        }

        ASSERT(len < PAGESIZE);

        /* Release the pfn. */
        hat_unload(kas.a_hat, xnbp->xnb_rx_va, PAGESIZE,
            HAT_UNLOAD_UNMAP);
        xen_release_pfn(pfn);

        /* 4 */
        gop->mfn = mfn;
        gop->domid = xnbp->xnb_peer;
        gop->ref = rxreq->gref;

        /* 5.1 */
        rxresp = RING_GET_RESPONSE(&xnbp->xnb_rx_ring, prod);
        rxresp->offset = 0;
        rxresp->flags = 0;

        cksum_flags = xnbp->xnb_flavour->xf_cksum_to_peer(xnbp, mp);
        if (cksum_flags != 0)
            xnbp->xnb_stat_rx_cksum_deferred++;
        rxresp->flags |= cksum_flags;

        rxresp->id = RING_GET_REQUEST(&xnbp->xnb_rx_ring, prod)->id;
        rxresp->status = len;

        loop++;
        prod++;
        gop++;
        prev = mp;
        mp = mp->b_next;
    }

    /*
     * Did we actually do anything?
     */
    if (loop == xnbp->xnb_rx_ring.req_cons) {
        mutex_exit(&xnbp->xnb_rx_lock);
        return (mp);
    }

    end = loop;

    /*
     * Unlink the end of the 'done' list from the remainder.
     */
    ASSERT(prev != NULL);
    prev->b_next = NULL;

    if (HYPERVISOR_grant_table_op(GNTTABOP_transfer, xnbp->xnb_rx_top,
        loop - xnbp->xnb_rx_ring.req_cons) != 0) {
        cmn_err(CE_WARN, "xnb_to_peer: transfer operation failed");
    }

    loop = xnbp->xnb_rx_ring.req_cons;
    prod = xnbp->xnb_rx_ring.rsp_prod_pvt;
    gop = xnbp->xnb_rx_top;

    while (loop < end) {
        int16_t status = NETIF_RSP_OKAY;

        if (gop->status != 0) {
            status = NETIF_RSP_ERROR;

            /*
             * If the status is anything other than
             * GNTST_bad_page then we don't own the page
             * any more, so don't try to give it back.
             */
            if (gop->status != GNTST_bad_page)
                gop->mfn = 0;
        } else {
            /* The page is no longer ours. */
            gop->mfn = 0;
        }

        if (gop->mfn != 0)
            /*
             * Give back the page, as we won't be using
             * it.
             */
            xnb_free_page(xnbp, gop->mfn);
        else
            /*
             * We gave away a page, update our accounting
             * now.
             */
            balloon_drv_subtracted(1);

        /* 5.2 */
        if (status != NETIF_RSP_OKAY) {
            RING_GET_RESPONSE(&xnbp->xnb_rx_ring, prod)->status =
                status;
        } else {
            xnbp->xnb_stat_ipackets++;
            xnbp->xnb_stat_rbytes += len;
        }

        loop++;
        prod++;
        gop++;
    }

    xnbp->xnb_rx_ring.req_cons = loop;
    xnbp->xnb_rx_ring.rsp_prod_pvt = prod;

    /* 6 */
    /* LINTED: constant in conditional context */
    RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&xnbp->xnb_rx_ring, notify);
    if (notify) {
        ec_notify_via_evtchn(xnbp->xnb_evtchn);
        xnbp->xnb_stat_rx_notify_sent++;
    } else {
        xnbp->xnb_stat_rx_notify_deferred++;
    }

    if (mp != NULL)
        xnbp->xnb_stat_rx_defer++;

    mutex_exit(&xnbp->xnb_rx_lock);

    /* Free mblk_t's that we consumed. */
    freemsgchain(free);

    return (mp);
}

/* Helper functions for xnb_copy_to_peer(). */

/*
 * Grow the array of copy operation descriptors.
 */
static boolean_t
grow_cpop_area(xnb_t *xnbp)
{
    size_t count;
    gnttab_copy_t *new;

    ASSERT(MUTEX_HELD(&xnbp->xnb_rx_lock));

    count = xnbp->xnb_rx_cpop_count + CPOP_DEFCNT;

    if ((new = kmem_alloc(sizeof (new[0]) * count, KM_NOSLEEP)) == NULL) {
        xnbp->xnb_stat_other_allocation_failure++;
        return (B_FALSE);
    }

    bcopy(xnbp->xnb_rx_cpop, new,
        sizeof (xnbp->xnb_rx_cpop[0]) * xnbp->xnb_rx_cpop_count);

    kmem_free(xnbp->xnb_rx_cpop,
        sizeof (xnbp->xnb_rx_cpop[0]) * xnbp->xnb_rx_cpop_count);

    xnbp->xnb_rx_cpop = new;
    xnbp->xnb_rx_cpop_count = count;

    xnbp->xnb_stat_rx_cpoparea_grown++;

    return (B_TRUE);
}

/*
 * Check whether an address is on a page that's foreign to this domain.
 */
static boolean_t
is_foreign(void *addr)
{
    pfn_t pfn = hat_getpfnum(kas.a_hat, addr);

    return ((pfn & PFN_IS_FOREIGN_MFN) == PFN_IS_FOREIGN_MFN);
}

/*
 * Insert a newly allocated mblk into a chain, replacing the old one.
 */
static mblk_t *
replace_msg(mblk_t *mp, size_t len, mblk_t *mp_prev, mblk_t *ml_prev)
{
    uint32_t    start, stuff, end, value, flags;
    mblk_t      *new_mp;

    new_mp = copyb(mp);
    if (new_mp == NULL) {
        cmn_err(CE_PANIC, "replace_msg: cannot alloc new message"
            "for %p, len %lu", (void *) mp, len);
    }

    mac_hcksum_get(mp, &start, &stuff, &end, &value, &flags);
    mac_hcksum_set(new_mp, start, stuff, end, value, flags);

    new_mp->b_next = mp->b_next;
    new_mp->b_prev = mp->b_prev;
    new_mp->b_cont = mp->b_cont;

    /* Make sure we only overwrite pointers to the mblk being replaced. */
    if (mp_prev != NULL && mp_prev->b_next == mp)
        mp_prev->b_next = new_mp;

    if (ml_prev != NULL && ml_prev->b_cont == mp)
        ml_prev->b_cont = new_mp;

    mp->b_next = mp->b_prev = mp->b_cont = NULL;
    freemsg(mp);

    return (new_mp);
}

/*
 * Set all the fields in a gnttab_copy_t.
 */
static void
setup_gop(xnb_t *xnbp, gnttab_copy_t *gp, uchar_t *rptr,
    size_t s_off, size_t d_off, size_t len, grant_ref_t d_ref)
{
    ASSERT(xnbp != NULL && gp != NULL);

    gp->source.offset = s_off;
    gp->source.u.gmfn = pfn_to_mfn(hat_getpfnum(kas.a_hat, (caddr_t)rptr));
    gp->source.domid = DOMID_SELF;

    gp->len = (uint16_t)len;
    gp->flags = GNTCOPY_dest_gref;
    gp->status = 0;

    gp->dest.u.ref = d_ref;
    gp->dest.offset = d_off;
    gp->dest.domid = xnbp->xnb_peer;
}

/*
 * Pass packets to the peer using hypervisor copy operations.
 */
mblk_t *
xnb_copy_to_peer(xnb_t *xnbp, mblk_t *mp)
{
    mblk_t      *free = mp, *mp_prev = NULL, *saved_mp = mp;
    mblk_t      *ml, *ml_prev;
    boolean_t   notify;
    RING_IDX    loop, prod;
    int     i;

    /*
     * If the peer does not pre-post buffers for received packets,
     * use page flipping to pass packets to it.
     */
    if (!xnbp->xnb_rx_hv_copy)
        return (xnb_to_peer(xnbp, mp));

    /*
     * For each packet the sequence of operations is:
     *
     *  1. get a request slot from the ring.
     *  2. set up data for hypercall (see NOTE below)
     *  3. have the hypervisore copy the data
     *  4. update the request slot.
     *  5. kick the peer.
     *
     * NOTE ad 2.
     *  In order to reduce the number of hypercalls, we prepare
     *  several mblks (mp->b_cont != NULL) for the peer and
     *  perform a single hypercall to transfer them.  We also have
     *  to set up a seperate copy operation for every page.
     *
     * If we have more than one packet (mp->b_next != NULL), we do
     * this whole dance repeatedly.
     */

    mutex_enter(&xnbp->xnb_rx_lock);

    if (!(xnbp->xnb_connected && xnbp->xnb_hotplugged)) {
        mutex_exit(&xnbp->xnb_rx_lock);
        DTRACE_PROBE(copy_rx_too_early);
        xnbp->xnb_stat_rx_too_early++;
        return (mp);
    }

    loop = xnbp->xnb_rx_ring.req_cons;
    prod = xnbp->xnb_rx_ring.rsp_prod_pvt;

    while ((mp != NULL) &&
        XNB_RING_HAS_UNCONSUMED_REQUESTS(&xnbp->xnb_rx_ring)) {
        netif_rx_request_t  *rxreq;
        size_t          d_offset, len;
        int         item_count;
        gnttab_copy_t       *gop_cp;
        netif_rx_response_t *rxresp;
        uint16_t        cksum_flags;
        int16_t         status = NETIF_RSP_OKAY;

        /* 1 */
        rxreq = RING_GET_REQUEST(&xnbp->xnb_rx_ring, loop);

#ifdef XNB_DEBUG
        if (!(rxreq->id < NET_RX_RING_SIZE))
            cmn_err(CE_PANIC, "xnb_copy_to_peer: "
                "id %d out of range in request 0x%p",
                rxreq->id, (void *)rxreq);
#endif /* XNB_DEBUG */

        /* 2 */
        d_offset = 0;
        len = 0;
        item_count = 0;

        gop_cp = xnbp->xnb_rx_cpop;

        /*
         * We walk the b_cont pointers and set up a
         * gnttab_copy_t for each sub-page chunk in each data
         * block.
         */
        /* 2a */
        for (ml = mp, ml_prev = NULL; ml != NULL; ml = ml->b_cont) {
            size_t  chunk = ml->b_wptr - ml->b_rptr;
            uchar_t *r_tmp, *rpt_align;
            size_t  r_offset;

            /*
             * The hypervisor will not allow us to
             * reference a foreign page (e.g. one
             * belonging to another domain) by mfn in the
             * copy operation. If the data in this mblk is
             * on such a page we must copy the data into a
             * local page before initiating the hypervisor
             * copy operation.
             */
            if (is_foreign(ml->b_rptr) || is_foreign(ml->b_wptr)) {
                mblk_t *ml_new = replace_msg(ml, chunk,
                    mp_prev, ml_prev);

                /* We can still use old ml, but not *ml! */
                if (free == ml)
                    free = ml_new;
                if (mp == ml)
                    mp = ml_new;
                ml = ml_new;

                xnbp->xnb_stat_rx_foreign_page++;
            }

            rpt_align = (uchar_t *)ALIGN2PAGE(ml->b_rptr);
            r_offset = (uint16_t)(ml->b_rptr - rpt_align);
            r_tmp = ml->b_rptr;

            if (d_offset + chunk > PAGESIZE)
                cmn_err(CE_PANIC, "xnb_copy_to_peer: mp %p "
                    "(svd: %p), ml %p,rpt_alg. %p, d_offset "
                    "(%lu) + chunk (%lu) > PAGESIZE %d!",
                    (void *)mp, (void *)saved_mp, (void *)ml,
                    (void *)rpt_align,
                    d_offset, chunk, (int)PAGESIZE);

            while (chunk > 0) {
                size_t part_len;

                if (item_count == xnbp->xnb_rx_cpop_count) {
                    if (!grow_cpop_area(xnbp))
                        goto failure;
                    gop_cp = &xnbp->xnb_rx_cpop[item_count];
                }
                /*
                 * If our mblk crosses a page boundary, we need
                 * to do a seperate copy for each page.
                 */
                if (r_offset + chunk > PAGESIZE) {
                    part_len = PAGESIZE - r_offset;

                    DTRACE_PROBE3(mblk_page_crossed,
                        (mblk_t *), ml, int, chunk, int,
                        (int)r_offset);

                    xnbp->xnb_stat_rx_pagebndry_crossed++;
                } else {
                    part_len = chunk;
                }

                setup_gop(xnbp, gop_cp, r_tmp, r_offset,
                    d_offset, part_len, rxreq->gref);

                chunk -= part_len;

                len += part_len;
                d_offset += part_len;
                r_tmp += part_len;
                /*
                 * The 2nd, 3rd ... last copies will always
                 * start at r_tmp, therefore r_offset is 0.
                 */
                r_offset = 0;
                gop_cp++;
                item_count++;
            }
            ml_prev = ml;

            DTRACE_PROBE4(mblk_loop_end, (mblk_t *), ml, int,
                chunk, int, len, int, item_count);
        }
        /* 3 */
        if (HYPERVISOR_grant_table_op(GNTTABOP_copy, xnbp->xnb_rx_cpop,
            item_count) != 0) {
            cmn_err(CE_WARN, "xnb_copy_to_peer: copy op. failed");
            DTRACE_PROBE(HV_granttableopfailed);
        }

        /* 4 */
        rxresp = RING_GET_RESPONSE(&xnbp->xnb_rx_ring, prod);
        rxresp->offset = 0;

        rxresp->flags = 0;

        DTRACE_PROBE4(got_RX_rsp, int, (int)rxresp->id, int,
            (int)rxresp->offset, int, (int)rxresp->flags, int,
            (int)rxresp->status);

        cksum_flags = xnbp->xnb_flavour->xf_cksum_to_peer(xnbp, mp);
        if (cksum_flags != 0)
            xnbp->xnb_stat_rx_cksum_deferred++;
        rxresp->flags |= cksum_flags;

        rxresp->id = RING_GET_REQUEST(&xnbp->xnb_rx_ring, prod)->id;
        rxresp->status = len;

        DTRACE_PROBE4(RX_rsp_set, int, (int)rxresp->id, int,
            (int)rxresp->offset, int, (int)rxresp->flags, int,
            (int)rxresp->status);

        for (i = 0; i < item_count; i++) {
            if (xnbp->xnb_rx_cpop[i].status != 0) {
                DTRACE_PROBE2(cpop_status_nonnull, int,
                    (int)xnbp->xnb_rx_cpop[i].status,
                    int, i);
                status = NETIF_RSP_ERROR;
            }
        }

        /* 5.2 */
        if (status != NETIF_RSP_OKAY) {
            RING_GET_RESPONSE(&xnbp->xnb_rx_ring, prod)->status =
                status;
            xnbp->xnb_stat_rx_rsp_notok++;
        } else {
            xnbp->xnb_stat_ipackets++;
            xnbp->xnb_stat_rbytes += len;
        }

        loop++;
        prod++;
        mp_prev = mp;
        mp = mp->b_next;
    }
failure:
    /*
     * Did we actually do anything?
     */
    if (loop == xnbp->xnb_rx_ring.req_cons) {
        mutex_exit(&xnbp->xnb_rx_lock);
        return (mp);
    }

    /*
     * Unlink the end of the 'done' list from the remainder.
     */
    ASSERT(mp_prev != NULL);
    mp_prev->b_next = NULL;

    xnbp->xnb_rx_ring.req_cons = loop;
    xnbp->xnb_rx_ring.rsp_prod_pvt = prod;

    /* 6 */
    /* LINTED: constant in conditional context */
    RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&xnbp->xnb_rx_ring, notify);
    if (notify) {
        ec_notify_via_evtchn(xnbp->xnb_evtchn);
        xnbp->xnb_stat_rx_notify_sent++;
    } else {
        xnbp->xnb_stat_rx_notify_deferred++;
    }

    if (mp != NULL)
        xnbp->xnb_stat_rx_defer++;

    mutex_exit(&xnbp->xnb_rx_lock);

    /* Free mblk_t structs we have consumed. */
    freemsgchain(free);

    return (mp);
}


static void
xnb_tx_notify_peer(xnb_t *xnbp, boolean_t force)
{
    boolean_t notify;

    ASSERT(MUTEX_HELD(&xnbp->xnb_tx_lock));

    /* LINTED: constant in conditional context */
    RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&xnbp->xnb_tx_ring, notify);
    if (notify || force) {
        ec_notify_via_evtchn(xnbp->xnb_evtchn);
        xnbp->xnb_stat_tx_notify_sent++;
    } else {
        xnbp->xnb_stat_tx_notify_deferred++;
    }
}

static void
xnb_tx_mark_complete(xnb_t *xnbp, RING_IDX id, int16_t status)
{
    RING_IDX i;
    netif_tx_response_t *txresp;

    ASSERT(MUTEX_HELD(&xnbp->xnb_tx_lock));

    i = xnbp->xnb_tx_ring.rsp_prod_pvt;

    txresp = RING_GET_RESPONSE(&xnbp->xnb_tx_ring, i);
    txresp->id = id;
    txresp->status = status;

    xnbp->xnb_tx_ring.rsp_prod_pvt = i + 1;

    /*
     * Note that we don't push the change to the peer here - that
     * is the callers responsibility.
     */
}

static void
xnb_txbuf_recycle(xnb_txbuf_t *txp)
{
    xnb_t *xnbp = txp->xt_xnbp;

    kmem_cache_free(xnbp->xnb_tx_buf_cache, txp);

    xnbp->xnb_tx_buf_outstanding--;
}

static int
xnb_txbuf_constructor(void *buf, void *arg, int kmflag)
{
    _NOTE(ARGUNUSED(kmflag));
    xnb_txbuf_t *txp = buf;
    xnb_t *xnbp = arg;
    size_t len;
    ddi_dma_cookie_t dma_cookie;
    uint_t ncookies;

    txp->xt_free_rtn.free_func = xnb_txbuf_recycle;
    txp->xt_free_rtn.free_arg = (caddr_t)txp;
    txp->xt_xnbp = xnbp;
    txp->xt_next = NULL;

    if (ddi_dma_alloc_handle(xnbp->xnb_devinfo, &buf_dma_attr,
        0, 0, &txp->xt_dma_handle) != DDI_SUCCESS)
        goto failure;

    if (ddi_dma_mem_alloc(txp->xt_dma_handle, PAGESIZE, &data_accattr,
        DDI_DMA_STREAMING, 0, 0, &txp->xt_buf, &len,
        &txp->xt_acc_handle) != DDI_SUCCESS)
        goto failure_1;

    if (ddi_dma_addr_bind_handle(txp->xt_dma_handle, NULL, txp->xt_buf,
        len, DDI_DMA_RDWR | DDI_DMA_STREAMING, DDI_DMA_DONTWAIT, 0,
        &dma_cookie, &ncookies)
        != DDI_DMA_MAPPED)
        goto failure_2;
    ASSERT(ncookies == 1);

    txp->xt_mfn = xnb_btop(dma_cookie.dmac_laddress);
    txp->xt_buflen = dma_cookie.dmac_size;

    DTRACE_PROBE(txbuf_allocated);

    atomic_add_32(&xnbp->xnb_tx_buf_count, 1);
    xnbp->xnb_tx_buf_outstanding++;

    return (0);

failure_2:
    ddi_dma_mem_free(&txp->xt_acc_handle);

failure_1:
    ddi_dma_free_handle(&txp->xt_dma_handle);

failure:

    return (-1);
}

static void
xnb_txbuf_destructor(void *buf, void *arg)
{
    xnb_txbuf_t *txp = buf;
    xnb_t *xnbp = arg;

    (void) ddi_dma_unbind_handle(txp->xt_dma_handle);
    ddi_dma_mem_free(&txp->xt_acc_handle);
    ddi_dma_free_handle(&txp->xt_dma_handle);

    atomic_add_32(&xnbp->xnb_tx_buf_count, -1);
}

/*
 * Take packets from the peer and deliver them onward.
 */
static mblk_t *
xnb_from_peer(xnb_t *xnbp)
{
    RING_IDX start, end, loop;
    gnttab_copy_t *cop;
    xnb_txbuf_t **txpp;
    netif_tx_request_t *txreq;
    boolean_t work_to_do, need_notify = B_FALSE;
    mblk_t *head, *tail;
    int n_data_req, i;

    ASSERT(MUTEX_HELD(&xnbp->xnb_tx_lock));

    head = tail = NULL;
around:

    /* LINTED: constant in conditional context */
    RING_FINAL_CHECK_FOR_REQUESTS(&xnbp->xnb_tx_ring, work_to_do);
    if (!work_to_do) {
finished:
        xnb_tx_notify_peer(xnbp, need_notify);

        return (head);
    }

    start = xnbp->xnb_tx_ring.req_cons;
    end = xnbp->xnb_tx_ring.sring->req_prod;

    if ((end - start) > NET_TX_RING_SIZE) {
        /*
         * This usually indicates that the frontend driver is
         * misbehaving, as it's not possible to have more than
         * NET_TX_RING_SIZE ring elements in play at any one
         * time.
         *
         * We reset the ring pointers to the state declared by
         * the frontend and try to carry on.
         */
        cmn_err(CE_WARN, "xnb_from_peer: domain %d tried to give us %u "
            "items in the ring, resetting and trying to recover.",
            xnbp->xnb_peer, (end - start));

        /* LINTED: constant in conditional context */
        BACK_RING_ATTACH(&xnbp->xnb_tx_ring,
            (netif_tx_sring_t *)xnbp->xnb_tx_ring_addr, PAGESIZE);

        goto around;
    }

    loop = start;
    cop = xnbp->xnb_tx_cop;
    txpp = xnbp->xnb_tx_bufp;
    n_data_req = 0;

    while (loop < end) {
        static const uint16_t acceptable_flags =
            NETTXF_csum_blank |
            NETTXF_data_validated |
            NETTXF_extra_info;
        uint16_t unexpected_flags;

        txreq = RING_GET_REQUEST(&xnbp->xnb_tx_ring, loop);

        unexpected_flags = txreq->flags & ~acceptable_flags;
        if (unexpected_flags != 0) {
            /*
             * The peer used flag bits that we do not
             * recognize.
             */
            cmn_err(CE_WARN, "xnb_from_peer: "
                "unexpected flag bits (0x%x) from peer "
                "in transmit request",
                unexpected_flags);
            xnbp->xnb_stat_tx_unexpected_flags++;

            /* Mark this entry as failed. */
            xnb_tx_mark_complete(xnbp, txreq->id, NETIF_RSP_ERROR);
            need_notify = B_TRUE;

        } else if (txreq->flags & NETTXF_extra_info) {
            struct netif_extra_info *erp;
            boolean_t status;

            loop++; /* Consume another slot in the ring. */
            ASSERT(loop <= end);

            erp = (struct netif_extra_info *)
                RING_GET_REQUEST(&xnbp->xnb_tx_ring, loop);

            switch (erp->type) {
            case XEN_NETIF_EXTRA_TYPE_MCAST_ADD:
                ASSERT(xnbp->xnb_multicast_control);
                status = xnbp->xnb_flavour->xf_mcast_add(xnbp,
                    &erp->u.mcast.addr);
                break;
            case XEN_NETIF_EXTRA_TYPE_MCAST_DEL:
                ASSERT(xnbp->xnb_multicast_control);
                status = xnbp->xnb_flavour->xf_mcast_del(xnbp,
                    &erp->u.mcast.addr);
                break;
            default:
                status = B_FALSE;
                cmn_err(CE_WARN, "xnb_from_peer: "
                    "unknown extra type %d", erp->type);
                break;
            }

            xnb_tx_mark_complete(xnbp, txreq->id,
                status ? NETIF_RSP_OKAY : NETIF_RSP_ERROR);
            need_notify = B_TRUE;

        } else if ((txreq->offset > PAGESIZE) ||
            (txreq->offset + txreq->size > PAGESIZE)) {
            /*
             * Peer attempted to refer to data beyond the
             * end of the granted page.
             */
            cmn_err(CE_WARN, "xnb_from_peer: "
                "attempt to refer beyond the end of granted "
                "page in txreq (offset %d, size %d).",
                txreq->offset, txreq->size);
            xnbp->xnb_stat_tx_overflow_page++;

            /* Mark this entry as failed. */
            xnb_tx_mark_complete(xnbp, txreq->id, NETIF_RSP_ERROR);
            need_notify = B_TRUE;

        } else {
            xnb_txbuf_t *txp;

            txp = kmem_cache_alloc(xnbp->xnb_tx_buf_cache,
                KM_NOSLEEP);
            if (txp == NULL)
                break;

            txp->xt_mblk = desballoc((unsigned char *)txp->xt_buf,
                txp->xt_buflen, 0, &txp->xt_free_rtn);
            if (txp->xt_mblk == NULL) {
                kmem_cache_free(xnbp->xnb_tx_buf_cache, txp);
                break;
            }

            txp->xt_idx = loop;
            txp->xt_id = txreq->id;

            cop->source.u.ref = txreq->gref;
            cop->source.domid = xnbp->xnb_peer;
            cop->source.offset = txreq->offset;

            cop->dest.u.gmfn = txp->xt_mfn;
            cop->dest.domid = DOMID_SELF;
            cop->dest.offset = 0;

            cop->len = txreq->size;
            cop->flags = GNTCOPY_source_gref;
            cop->status = 0;

            *txpp = txp;

            txpp++;
            cop++;
            n_data_req++;

            ASSERT(n_data_req <= NET_TX_RING_SIZE);
        }

        loop++;
    }

    xnbp->xnb_tx_ring.req_cons = loop;

    if (n_data_req == 0)
        goto around;

    if (HYPERVISOR_grant_table_op(GNTTABOP_copy,
        xnbp->xnb_tx_cop, n_data_req) != 0) {

        cmn_err(CE_WARN, "xnb_from_peer: copy operation failed");

        txpp = xnbp->xnb_tx_bufp;
        i = n_data_req;
        while (i > 0) {
            kmem_cache_free(xnbp->xnb_tx_buf_cache, *txpp);
            txpp++;
            i--;
        }

        goto finished;
    }

    txpp = xnbp->xnb_tx_bufp;
    cop = xnbp->xnb_tx_cop;
    i = n_data_req;

    while (i > 0) {
        xnb_txbuf_t *txp = *txpp;

        txreq = RING_GET_REQUEST(&xnbp->xnb_tx_ring, txp->xt_idx);

        if (cop->status != 0) {
#ifdef XNB_DEBUG
            cmn_err(CE_WARN, "xnb_from_peer: "
                "txpp 0x%p failed (%d)",
                (void *)*txpp, cop->status);
#endif /* XNB_DEBUG */
            xnb_tx_mark_complete(xnbp, txp->xt_id, NETIF_RSP_ERROR);
            freemsg(txp->xt_mblk);
        } else {
            mblk_t *mp;

            mp = txp->xt_mblk;
            mp->b_rptr = mp->b_wptr = (unsigned char *)txp->xt_buf;
            mp->b_wptr += txreq->size;
            mp->b_next = NULL;

            /*
             * If there are checksum flags, process them
             * appropriately.
             */
            if ((txreq->flags &
                (NETTXF_csum_blank | NETTXF_data_validated))
                != 0) {
                mp = xnbp->xnb_flavour->xf_cksum_from_peer(xnbp,
                    mp, txreq->flags);
                xnbp->xnb_stat_tx_cksum_no_need++;

                txp->xt_mblk = mp;
            }

            if (head == NULL) {
                ASSERT(tail == NULL);
                head = mp;
            } else {
                ASSERT(tail != NULL);
                tail->b_next = mp;
            }
            tail = mp;

            xnbp->xnb_stat_opackets++;
            xnbp->xnb_stat_obytes += txreq->size;

            xnb_tx_mark_complete(xnbp, txp->xt_id, NETIF_RSP_OKAY);
        }

        txpp++;
        cop++;
        i--;
    }

    goto around;
    /* NOTREACHED */
}

static uint_t
xnb_intr(caddr_t arg)
{
    xnb_t *xnbp = (xnb_t *)arg;
    mblk_t *mp;

    xnbp->xnb_stat_intr++;

    mutex_enter(&xnbp->xnb_tx_lock);

    ASSERT(xnbp->xnb_connected);

    mp = xnb_from_peer(xnbp);

    mutex_exit(&xnbp->xnb_tx_lock);

    if (!xnbp->xnb_hotplugged) {
        xnbp->xnb_stat_tx_too_early++;
        goto fail;
    }
    if (mp == NULL) {
        xnbp->xnb_stat_spurious_intr++;
        goto fail;
    }

    xnbp->xnb_flavour->xf_from_peer(xnbp, mp);

    return (DDI_INTR_CLAIMED);

fail:
    freemsgchain(mp);
    return (DDI_INTR_CLAIMED);
}

/*
 * Read our configuration from xenstore.
 */
boolean_t
xnb_read_xs_config(xnb_t *xnbp)
{
    char *xsname;
    char mac[ETHERADDRL * 3];

    xsname = xvdi_get_xsname(xnbp->xnb_devinfo);

    if (xenbus_scanf(XBT_NULL, xsname,
        "mac", "%s", mac) != 0) {
        cmn_err(CE_WARN, "xnb_attach: "
            "cannot read mac address from %s",
            xsname);
        return (B_FALSE);
    }

    if (ether_aton(mac, xnbp->xnb_mac_addr) != ETHERADDRL) {
        cmn_err(CE_WARN,
            "xnb_attach: cannot parse mac address %s",
            mac);
        return (B_FALSE);
    }

    return (B_TRUE);
}

/*
 * Read the configuration of the peer from xenstore.
 */
boolean_t
xnb_read_oe_config(xnb_t *xnbp)
{
    char *oename;
    int i;

    oename = xvdi_get_oename(xnbp->xnb_devinfo);

    if (xenbus_gather(XBT_NULL, oename,
        "event-channel", "%u", &xnbp->xnb_fe_evtchn,
        "tx-ring-ref", "%lu", &xnbp->xnb_tx_ring_ref,
        "rx-ring-ref", "%lu", &xnbp->xnb_rx_ring_ref,
        NULL) != 0) {
        cmn_err(CE_WARN, "xnb_read_oe_config: "
            "cannot read other-end details from %s",
            oename);
        return (B_FALSE);
    }

    /*
     * Check whether our peer requests receive side hypervisor
     * copy.
     */
    if (xenbus_scanf(XBT_NULL, oename,
        "request-rx-copy", "%d", &i) != 0)
        i = 0;
    if (i != 0)
        xnbp->xnb_rx_hv_copy = B_TRUE;

    /*
     * Check whether our peer requests multicast_control.
     */
    if (xenbus_scanf(XBT_NULL, oename,
        "request-multicast-control", "%d", &i) != 0)
        i = 0;
    if (i != 0)
        xnbp->xnb_multicast_control = B_TRUE;

    /*
     * The Linux backend driver here checks to see if the peer has
     * set 'feature-no-csum-offload'. This is used to indicate
     * that the guest cannot handle receiving packets without a
     * valid checksum. We don't check here, because packets passed
     * to the peer _always_ have a valid checksum.
     *
     * There are three cases:
     *
     * - the NIC is dedicated: packets from the wire should always
     *   have a valid checksum. If the hardware validates the
     *   checksum then the relevant bit will be set in the packet
     *   attributes and we will inform the peer. It can choose to
     *   ignore the hardware verification.
     *
     * - the NIC is shared (VNIC) and a packet originates from the
     *   wire: this is the same as the case above - the packets
     *   will have a valid checksum.
     *
     * - the NIC is shared (VNIC) and a packet originates from the
     *   host: the MAC layer ensures that all such packets have a
     *   valid checksum by calculating one if the stack did not.
     */

    return (B_TRUE);
}

void
xnb_start_connect(xnb_t *xnbp)
{
    dev_info_t  *dip = xnbp->xnb_devinfo;

    if (!xnb_connect_rings(dip)) {
        cmn_err(CE_WARN, "xnb_start_connect: "
            "cannot connect rings");
        goto failed;
    }

    if (!xnbp->xnb_flavour->xf_start_connect(xnbp)) {
        cmn_err(CE_WARN, "xnb_start_connect: "
            "flavour failed to connect");
        goto failed;
    }

    (void) xvdi_switch_state(dip, XBT_NULL, XenbusStateConnected);
    return;

failed:
    xnbp->xnb_flavour->xf_peer_disconnected(xnbp);
    xnb_disconnect_rings(dip);
    (void) xvdi_switch_state(dip, XBT_NULL,
        XenbusStateClosed);
    (void) xvdi_post_event(dip, XEN_HP_REMOVE);
}

static boolean_t
xnb_connect_rings(dev_info_t *dip)
{
    xnb_t *xnbp = ddi_get_driver_private(dip);
    struct gnttab_map_grant_ref map_op;

    /*
     * Cannot attempt to connect the rings if already connected.
     */
    ASSERT(!xnbp->xnb_connected);

    /*
     * 1. allocate a vaddr for the tx page, one for the rx page.
     * 2. call GNTTABOP_map_grant_ref to map the relevant pages
     *    into the allocated vaddr (one for tx, one for rx).
     * 3. call EVTCHNOP_bind_interdomain to have the event channel
     *    bound to this domain.
     * 4. associate the event channel with an interrupt.
     * 5. enable the interrupt.
     */

    /* 1.tx */
    xnbp->xnb_tx_ring_addr = vmem_xalloc(heap_arena, PAGESIZE, PAGESIZE,
        0, 0, 0, 0, VM_SLEEP);
    ASSERT(xnbp->xnb_tx_ring_addr != NULL);

    /* 2.tx */
    map_op.host_addr = (uint64_t)((long)xnbp->xnb_tx_ring_addr);
    map_op.flags = GNTMAP_host_map;
    map_op.ref = xnbp->xnb_tx_ring_ref;
    map_op.dom = xnbp->xnb_peer;
    hat_prepare_mapping(kas.a_hat, xnbp->xnb_tx_ring_addr, NULL);
    if (xen_map_gref(GNTTABOP_map_grant_ref, &map_op, 1, B_FALSE) != 0 ||
        map_op.status != 0) {
        cmn_err(CE_WARN, "xnb_connect_rings: cannot map tx-ring page.");
        goto fail;
    }
    xnbp->xnb_tx_ring_handle = map_op.handle;

    /* LINTED: constant in conditional context */
    BACK_RING_INIT(&xnbp->xnb_tx_ring,
        (netif_tx_sring_t *)xnbp->xnb_tx_ring_addr, PAGESIZE);

    /* 1.rx */
    xnbp->xnb_rx_ring_addr = vmem_xalloc(heap_arena, PAGESIZE, PAGESIZE,
        0, 0, 0, 0, VM_SLEEP);
    ASSERT(xnbp->xnb_rx_ring_addr != NULL);

    /* 2.rx */
    map_op.host_addr = (uint64_t)((long)xnbp->xnb_rx_ring_addr);
    map_op.flags = GNTMAP_host_map;
    map_op.ref = xnbp->xnb_rx_ring_ref;
    map_op.dom = xnbp->xnb_peer;
    hat_prepare_mapping(kas.a_hat, xnbp->xnb_rx_ring_addr, NULL);
    if (xen_map_gref(GNTTABOP_map_grant_ref, &map_op, 1, B_FALSE) != 0 ||
        map_op.status != 0) {
        cmn_err(CE_WARN, "xnb_connect_rings: cannot map rx-ring page.");
        goto fail;
    }
    xnbp->xnb_rx_ring_handle = map_op.handle;

    /* LINTED: constant in conditional context */
    BACK_RING_INIT(&xnbp->xnb_rx_ring,
        (netif_rx_sring_t *)xnbp->xnb_rx_ring_addr, PAGESIZE);

    /* 3 */
    if (xvdi_bind_evtchn(dip, xnbp->xnb_fe_evtchn) != DDI_SUCCESS) {
        cmn_err(CE_WARN, "xnb_connect_rings: "
            "cannot bind event channel %d", xnbp->xnb_evtchn);
        xnbp->xnb_evtchn = INVALID_EVTCHN;
        goto fail;
    }
    xnbp->xnb_evtchn = xvdi_get_evtchn(dip);

    /*
     * It would be good to set the state to XenbusStateConnected
     * here as well, but then what if ddi_add_intr() failed?
     * Changing the state in the store will be noticed by the peer
     * and cannot be "taken back".
     */
    mutex_enter(&xnbp->xnb_tx_lock);
    mutex_enter(&xnbp->xnb_rx_lock);

    xnbp->xnb_connected = B_TRUE;

    mutex_exit(&xnbp->xnb_rx_lock);
    mutex_exit(&xnbp->xnb_tx_lock);

    /* 4, 5 */
    if (ddi_add_intr(dip, 0, NULL, NULL, xnb_intr, (caddr_t)xnbp)
        != DDI_SUCCESS) {
        cmn_err(CE_WARN, "xnb_connect_rings: cannot add interrupt");
        goto fail;
    }
    xnbp->xnb_irq = B_TRUE;

    return (B_TRUE);

fail:
    mutex_enter(&xnbp->xnb_tx_lock);
    mutex_enter(&xnbp->xnb_rx_lock);

    xnbp->xnb_connected = B_FALSE;

    mutex_exit(&xnbp->xnb_rx_lock);
    mutex_exit(&xnbp->xnb_tx_lock);

    return (B_FALSE);
}

static void
xnb_disconnect_rings(dev_info_t *dip)
{
    xnb_t *xnbp = ddi_get_driver_private(dip);

    if (xnbp->xnb_irq) {
        ddi_remove_intr(dip, 0, NULL);
        xnbp->xnb_irq = B_FALSE;
    }

    if (xnbp->xnb_evtchn != INVALID_EVTCHN) {
        xvdi_free_evtchn(dip);
        xnbp->xnb_evtchn = INVALID_EVTCHN;
    }

    if (xnbp->xnb_rx_ring_handle != INVALID_GRANT_HANDLE) {
        struct gnttab_unmap_grant_ref unmap_op;

        unmap_op.host_addr = (uint64_t)(uintptr_t)
            xnbp->xnb_rx_ring_addr;
        unmap_op.dev_bus_addr = 0;
        unmap_op.handle = xnbp->xnb_rx_ring_handle;
        if (HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref,
            &unmap_op, 1) != 0)
            cmn_err(CE_WARN, "xnb_disconnect_rings: "
                "cannot unmap rx-ring page (%d)",
                unmap_op.status);

        xnbp->xnb_rx_ring_handle = INVALID_GRANT_HANDLE;
    }

    if (xnbp->xnb_rx_ring_addr != NULL) {
        hat_release_mapping(kas.a_hat, xnbp->xnb_rx_ring_addr);
        vmem_free(heap_arena, xnbp->xnb_rx_ring_addr, PAGESIZE);
        xnbp->xnb_rx_ring_addr = NULL;
    }

    if (xnbp->xnb_tx_ring_handle != INVALID_GRANT_HANDLE) {
        struct gnttab_unmap_grant_ref unmap_op;

        unmap_op.host_addr = (uint64_t)(uintptr_t)
            xnbp->xnb_tx_ring_addr;
        unmap_op.dev_bus_addr = 0;
        unmap_op.handle = xnbp->xnb_tx_ring_handle;
        if (HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref,
            &unmap_op, 1) != 0)
            cmn_err(CE_WARN, "xnb_disconnect_rings: "
                "cannot unmap tx-ring page (%d)",
                unmap_op.status);

        xnbp->xnb_tx_ring_handle = INVALID_GRANT_HANDLE;
    }

    if (xnbp->xnb_tx_ring_addr != NULL) {
        hat_release_mapping(kas.a_hat, xnbp->xnb_tx_ring_addr);
        vmem_free(heap_arena, xnbp->xnb_tx_ring_addr, PAGESIZE);
        xnbp->xnb_tx_ring_addr = NULL;
    }
}

static void
xnb_oe_state_change(dev_info_t *dip, ddi_eventcookie_t id,
    void *arg, void *impl_data)
{
    _NOTE(ARGUNUSED(id, arg));
    xnb_t *xnbp = ddi_get_driver_private(dip);
    XenbusState new_state = *(XenbusState *)impl_data;

    ASSERT(xnbp != NULL);

    switch (new_state) {
    case XenbusStateConnected:
        /* spurious state change */
        if (xnbp->xnb_connected)
            return;

        if (!xnb_read_oe_config(xnbp) ||
            !xnbp->xnb_flavour->xf_peer_connected(xnbp)) {
            cmn_err(CE_WARN, "xnb_oe_state_change: "
                "read otherend config error");
            (void) xvdi_switch_state(dip, XBT_NULL,
                XenbusStateClosed);
            (void) xvdi_post_event(dip, XEN_HP_REMOVE);

            break;
        }


        mutex_enter(&xnbp->xnb_state_lock);
        xnbp->xnb_fe_status = XNB_STATE_READY;
        if (xnbp->xnb_be_status == XNB_STATE_READY)
            xnb_start_connect(xnbp);
        mutex_exit(&xnbp->xnb_state_lock);

        /*
         * Now that we've attempted to connect it's reasonable
         * to allow an attempt to detach.
         */
        xnbp->xnb_detachable = B_TRUE;

        break;

    case XenbusStateClosing:
        (void) xvdi_switch_state(dip, XBT_NULL, XenbusStateClosing);

        break;

    case XenbusStateClosed:
        xnbp->xnb_flavour->xf_peer_disconnected(xnbp);

        mutex_enter(&xnbp->xnb_tx_lock);
        mutex_enter(&xnbp->xnb_rx_lock);

        xnb_disconnect_rings(dip);
        xnbp->xnb_connected = B_FALSE;

        mutex_exit(&xnbp->xnb_rx_lock);
        mutex_exit(&xnbp->xnb_tx_lock);

        (void) xvdi_switch_state(dip, XBT_NULL, XenbusStateClosed);
        (void) xvdi_post_event(dip, XEN_HP_REMOVE);
        /*
         * In all likelyhood this is already set (in the above
         * case), but if the peer never attempted to connect
         * and the domain is destroyed we get here without
         * having been through the case above, so we set it to
         * be sure.
         */
        xnbp->xnb_detachable = B_TRUE;

        break;

    default:
        break;
    }
}

static void
xnb_hp_state_change(dev_info_t *dip, ddi_eventcookie_t id,
    void *arg, void *impl_data)
{
    _NOTE(ARGUNUSED(id, arg));
    xnb_t *xnbp = ddi_get_driver_private(dip);
    xendev_hotplug_state_t state = *(xendev_hotplug_state_t *)impl_data;

    ASSERT(xnbp != NULL);

    switch (state) {
    case Connected:
        /* spurious hotplug event */
        if (xnbp->xnb_hotplugged)
            break;

        if (!xnb_read_xs_config(xnbp))
            break;

        if (!xnbp->xnb_flavour->xf_hotplug_connected(xnbp))
            break;

        mutex_enter(&xnbp->xnb_tx_lock);
        mutex_enter(&xnbp->xnb_rx_lock);

        xnbp->xnb_hotplugged = B_TRUE;

        mutex_exit(&xnbp->xnb_rx_lock);
        mutex_exit(&xnbp->xnb_tx_lock);

        mutex_enter(&xnbp->xnb_state_lock);
        xnbp->xnb_be_status = XNB_STATE_READY;
        if (xnbp->xnb_fe_status == XNB_STATE_READY)
            xnb_start_connect(xnbp);
        mutex_exit(&xnbp->xnb_state_lock);

        break;

    default:
        break;
    }
}

static struct modldrv modldrv = {
    &mod_miscops, "xnb",
};

static struct modlinkage modlinkage = {
    MODREV_1, &modldrv, NULL
};

int
_init(void)
{
    int i;

    mutex_init(&xnb_alloc_page_lock, NULL, MUTEX_DRIVER, NULL);

    i = mod_install(&modlinkage);
    if (i != DDI_SUCCESS)
        mutex_destroy(&xnb_alloc_page_lock);

    return (i);
}

int
_info(struct modinfo *modinfop)
{
    return (mod_info(&modlinkage, modinfop));
}

int
_fini(void)
{
    int i;

    i = mod_remove(&modlinkage);
    if (i == DDI_SUCCESS)
        mutex_destroy(&xnb_alloc_page_lock);

    return (i);
}