/*
 * 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.
 */

/*
 * Copyright (c) 2014, 2017 by Delphix. All rights reserved.
 * Copyright 2020 RackTop Systems, Inc.
 */

/*
 *
 * Copyright (c) 2004 Christian Limpach.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. This section intentionally left blank.
 * 4. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
/*
 * Section 3 of the above license was updated in response to bug 6379571.
 */

/*
 * xnf.c - GLDv3 network driver for domU.
 */

/*
 * This driver uses four per-instance locks:
 *
 * xnf_gref_lock:
 *
 *    Protects access to the grant reference list stored in
 *    xnf_gref_head. Grant references should be acquired and released
 *    using gref_get() and gref_put() respectively.
 *
 * xnf_schedlock:
 *
 *    Protects:
 *    xnf_need_sched - used to record that a previous transmit attempt
 *       failed (and consequently it will be necessary to call
 *       mac_tx_update() when transmit resources are available).
 *    xnf_pending_multicast - the number of multicast requests that
 *       have been submitted to the backend for which we have not
 *       processed responses.
 *
 * xnf_txlock:
 *
 *    Protects the transmit ring (xnf_tx_ring) and associated
 *    structures (notably xnf_tx_pkt_id and xnf_tx_pkt_id_head).
 *
 * xnf_rxlock:
 *
 *    Protects the receive ring (xnf_rx_ring) and associated
 *    structures (notably xnf_rx_pkt_info).
 *
 * If driver-global state that affects both the transmit and receive
 * rings is manipulated, both xnf_txlock and xnf_rxlock should be
 * held, in that order.
 *
 * xnf_schedlock is acquired both whilst holding xnf_txlock and
 * without. It should always be acquired after xnf_txlock if both are
 * held.
 *
 * Notes:
 * - atomic_add_64() is used to manipulate counters where we require
 *   accuracy. For counters intended only for observation by humans,
 *   post increment/decrement are used instead.
 */

#include <sys/types.h>
#include <sys/errno.h>
#include <sys/param.h>
#include <sys/sysmacros.h>
#include <sys/systm.h>
#include <sys/stream.h>
#include <sys/strsubr.h>
#include <sys/strsun.h>
#include <sys/conf.h>
#include <sys/ddi.h>
#include <sys/devops.h>
#include <sys/sunddi.h>
#include <sys/sunndi.h>
#include <sys/dlpi.h>
#include <sys/ethernet.h>
#include <sys/strsun.h>
#include <sys/pattr.h>
#include <inet/ip.h>
#include <inet/ip_impl.h>
#include <inet/tcp.h>
#include <netinet/udp.h>
#include <sys/gld.h>
#include <sys/modctl.h>
#include <sys/mac_provider.h>
#include <sys/mac_ether.h>
#include <sys/bootinfo.h>
#include <sys/mach_mmu.h>
#ifdef  XPV_HVM_DRIVER
#include <sys/xpv_support.h>
#include <sys/hypervisor.h>
#else
#include <sys/hypervisor.h>
#include <sys/evtchn_impl.h>
#include <sys/balloon_impl.h>
#endif
#include <xen/public/io/netif.h>
#include <sys/gnttab.h>
#include <xen/sys/xendev.h>
#include <sys/sdt.h>
#include <sys/note.h>
#include <sys/debug.h>

#include <io/xnf.h>

/*
 * 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 xnf_btop(addr)  ((addr) >> PAGESHIFT)

/*
 * The parameters below should only be changed in /etc/system, never in mdb.
 */

/*
 * Should we use the multicast control feature if the backend provides
 * it?
 */
boolean_t xnf_multicast_control = B_TRUE;

/*
 * Should we allow scatter-gather for tx if backend allows it?
 */
boolean_t xnf_enable_tx_sg = B_TRUE;

/*
 * Should we allow scatter-gather for rx if backend allows it?
 */
boolean_t xnf_enable_rx_sg = B_TRUE;

/*
 * Should we allow lso for tx sends if backend allows it?
 * Requires xnf_enable_tx_sg to be also set to TRUE.
 */
boolean_t xnf_enable_lso = B_TRUE;

/*
 * Should we allow lro on rx if backend supports it?
 * Requires xnf_enable_rx_sg to be also set to TRUE.
 *
 * !! WARNING !!
 * LRO is not yet supported in the OS so this should be left as FALSE.
 * !! WARNING !!
 */
boolean_t xnf_enable_lro = B_FALSE;

/*
 * Received packets below this size are copied to a new streams buffer
 * rather than being desballoc'ed.
 *
 * This value is chosen to accommodate traffic where there are a large
 * number of small packets. For data showing a typical distribution,
 * see:
 *
 * Sinha07a:
 *      Rishi Sinha, Christos Papadopoulos, and John
 *      Heidemann. Internet Packet Size Distributions: Some
 *      Observations. Technical Report ISI-TR-2007-643,
 *      USC/Information Sciences Institute, May, 2007. Orignally
 *      released October 2005 as web page
 *      http://netweb.usc.edu/~sinha/pkt-sizes/.
 *      <http://www.isi.edu/~johnh/PAPERS/Sinha07a.html>.
 */
size_t xnf_rx_copy_limit = 64;

#define INVALID_GRANT_HANDLE    ((grant_handle_t)-1)
#define INVALID_GRANT_REF       ((grant_ref_t)-1)
#define INVALID_TX_ID           ((uint16_t)-1)

#define TX_ID_TO_TXID(p, id) (&((p)->xnf_tx_pkt_id[(id)]))
#define TX_ID_VALID(i) \
        (((i) != INVALID_TX_ID) && ((i) < NET_TX_RING_SIZE))

/*
 * calculate how many pages are spanned by an mblk fragment
 */
#define xnf_mblk_pages(mp)      (MBLKL(mp) == 0 ? 0 : \
    xnf_btop((uintptr_t)mp->b_wptr - 1) - xnf_btop((uintptr_t)mp->b_rptr) + 1)

/* Required system entry points */
static int      xnf_attach(dev_info_t *, ddi_attach_cmd_t);
static int      xnf_detach(dev_info_t *, ddi_detach_cmd_t);

/* Required driver entry points for Nemo */
static int      xnf_start(void *);
static void     xnf_stop(void *);
static int      xnf_set_mac_addr(void *, const uint8_t *);
static int      xnf_set_multicast(void *, boolean_t, const uint8_t *);
static int      xnf_set_promiscuous(void *, boolean_t);
static mblk_t   *xnf_send(void *, mblk_t *);
static uint_t   xnf_intr(caddr_t);
static int      xnf_stat(void *, uint_t, uint64_t *);
static boolean_t xnf_getcapab(void *, mac_capab_t, void *);
static int xnf_getprop(void *, const char *, mac_prop_id_t, uint_t, void *);
static int xnf_setprop(void *, const char *, mac_prop_id_t, uint_t,
    const void *);
static void xnf_propinfo(void *, const char *, mac_prop_id_t,
    mac_prop_info_handle_t);

/* Driver private functions */
static int xnf_alloc_dma_resources(xnf_t *);
static void xnf_release_dma_resources(xnf_t *);
static void xnf_release_mblks(xnf_t *);

static int xnf_buf_constructor(void *, void *, int);
static void xnf_buf_destructor(void *, void *);
static xnf_buf_t *xnf_buf_get(xnf_t *, int, boolean_t);
static void xnf_buf_put(xnf_t *, xnf_buf_t *, boolean_t);
static void xnf_buf_refresh(xnf_buf_t *);
static void xnf_buf_recycle(xnf_buf_t *);

static int xnf_tx_buf_constructor(void *, void *, int);
static void xnf_tx_buf_destructor(void *, void *);

static grant_ref_t xnf_gref_get(xnf_t *);
static void xnf_gref_put(xnf_t *, grant_ref_t);

static xnf_txid_t *xnf_txid_get(xnf_t *);
static void xnf_txid_put(xnf_t *, xnf_txid_t *);

static void xnf_rxbuf_hang(xnf_t *, xnf_buf_t *);
static int xnf_tx_clean_ring(xnf_t  *);
static void oe_state_change(dev_info_t *, ddi_eventcookie_t,
    void *, void *);
static boolean_t xnf_kstat_init(xnf_t *);
static void xnf_rx_collect(xnf_t *);

#define XNF_CALLBACK_FLAGS      (MC_GETCAPAB | MC_PROPERTIES)

static mac_callbacks_t xnf_callbacks = {
        .mc_callbacks = XNF_CALLBACK_FLAGS,
        .mc_getstat = xnf_stat,
        .mc_start = xnf_start,
        .mc_stop = xnf_stop,
        .mc_setpromisc = xnf_set_promiscuous,
        .mc_multicst = xnf_set_multicast,
        .mc_unicst = xnf_set_mac_addr,
        .mc_tx = xnf_send,
        .mc_getcapab = xnf_getcapab,
        .mc_setprop = xnf_setprop,
        .mc_getprop = xnf_getprop,
        .mc_propinfo = xnf_propinfo,
};

/* DMA attributes for network ring buffer */
static ddi_dma_attr_t ringbuf_dma_attr = {
        .dma_attr_version = DMA_ATTR_V0,
        .dma_attr_addr_lo = 0,
        .dma_attr_addr_hi = 0xffffffffffffffffULL,
        .dma_attr_count_max = 0x7fffffff,
        .dma_attr_align = MMU_PAGESIZE,
        .dma_attr_burstsizes = 0x7ff,
        .dma_attr_minxfer = 1,
        .dma_attr_maxxfer = 0xffffffffU,
        .dma_attr_seg = 0xffffffffffffffffULL,
        .dma_attr_sgllen = 1,
        .dma_attr_granular = 1,
        .dma_attr_flags = 0
};

/* DMA attributes for receive data */
static ddi_dma_attr_t rx_buf_dma_attr = {
        .dma_attr_version = DMA_ATTR_V0,
        .dma_attr_addr_lo = 0,
        .dma_attr_addr_hi = 0xffffffffffffffffULL,
        .dma_attr_count_max = MMU_PAGEOFFSET,
        .dma_attr_align = MMU_PAGESIZE, /* allocation alignment */
        .dma_attr_burstsizes = 0x7ff,
        .dma_attr_minxfer = 1,
        .dma_attr_maxxfer = 0xffffffffU,
        .dma_attr_seg = 0xffffffffffffffffULL,
        .dma_attr_sgllen = 1,
        .dma_attr_granular = 1,
        .dma_attr_flags = 0
};

/* DMA attributes for transmit data */
static ddi_dma_attr_t tx_buf_dma_attr = {
        .dma_attr_version = DMA_ATTR_V0,
        .dma_attr_addr_lo = 0,
        .dma_attr_addr_hi = 0xffffffffffffffffULL,
        .dma_attr_count_max = MMU_PAGEOFFSET,
        .dma_attr_align = 1,
        .dma_attr_burstsizes = 0x7ff,
        .dma_attr_minxfer = 1,
        .dma_attr_maxxfer = 0xffffffffU,
        .dma_attr_seg = XEN_DATA_BOUNDARY - 1, /* segment boundary */
        .dma_attr_sgllen = XEN_MAX_TX_DATA_PAGES, /* max number of segments */
        .dma_attr_granular = 1,
        .dma_attr_flags = 0
};

/* DMA access attributes for registers and descriptors */
static ddi_device_acc_attr_t accattr = {
        DDI_DEVICE_ATTR_V0,
        DDI_STRUCTURE_LE_ACC,   /* This is a little-endian device */
        DDI_STRICTORDER_ACC
};

/* 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
};

DDI_DEFINE_STREAM_OPS(xnf_dev_ops, nulldev, nulldev, xnf_attach, xnf_detach,
    nodev, NULL, D_MP, NULL, ddi_quiesce_not_supported);

static struct modldrv xnf_modldrv = {
        &mod_driverops,
        "Virtual Ethernet driver",
        &xnf_dev_ops
};

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

int
_init(void)
{
        int r;

        mac_init_ops(&xnf_dev_ops, "xnf");
        r = mod_install(&modlinkage);
        if (r != DDI_SUCCESS)
                mac_fini_ops(&xnf_dev_ops);

        return (r);
}

int
_fini(void)
{
        return (EBUSY); /* XXPV should be removable */
}

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

/*
 * Acquire a grant reference.
 */
static grant_ref_t
xnf_gref_get(xnf_t *xnfp)
{
        grant_ref_t gref;

        mutex_enter(&xnfp->xnf_gref_lock);

        do {
                gref = gnttab_claim_grant_reference(&xnfp->xnf_gref_head);

        } while ((gref == INVALID_GRANT_REF) &&
            (gnttab_alloc_grant_references(16, &xnfp->xnf_gref_head) == 0));

        mutex_exit(&xnfp->xnf_gref_lock);

        if (gref == INVALID_GRANT_REF) {
                xnfp->xnf_stat_gref_failure++;
        } else {
                atomic_inc_64(&xnfp->xnf_stat_gref_outstanding);
                if (xnfp->xnf_stat_gref_outstanding > xnfp->xnf_stat_gref_peak)
                        xnfp->xnf_stat_gref_peak =
                            xnfp->xnf_stat_gref_outstanding;
        }

        return (gref);
}

/*
 * Release a grant reference.
 */
static void
xnf_gref_put(xnf_t *xnfp, grant_ref_t gref)
{
        ASSERT(gref != INVALID_GRANT_REF);

        mutex_enter(&xnfp->xnf_gref_lock);
        gnttab_release_grant_reference(&xnfp->xnf_gref_head, gref);
        mutex_exit(&xnfp->xnf_gref_lock);

        atomic_dec_64(&xnfp->xnf_stat_gref_outstanding);
}

/*
 * Acquire a transmit id.
 */
static xnf_txid_t *
xnf_txid_get(xnf_t *xnfp)
{
        xnf_txid_t *tidp;

        ASSERT(MUTEX_HELD(&xnfp->xnf_txlock));

        if (xnfp->xnf_tx_pkt_id_head == INVALID_TX_ID)
                return (NULL);

        ASSERT(TX_ID_VALID(xnfp->xnf_tx_pkt_id_head));

        tidp = TX_ID_TO_TXID(xnfp, xnfp->xnf_tx_pkt_id_head);
        xnfp->xnf_tx_pkt_id_head = tidp->next;
        tidp->next = INVALID_TX_ID;

        ASSERT(tidp->txbuf == NULL);

        return (tidp);
}

/*
 * Release a transmit id.
 */
static void
xnf_txid_put(xnf_t *xnfp, xnf_txid_t *tidp)
{
        ASSERT(MUTEX_HELD(&xnfp->xnf_txlock));
        ASSERT(TX_ID_VALID(tidp->id));
        ASSERT(tidp->next == INVALID_TX_ID);

        tidp->txbuf = NULL;
        tidp->next = xnfp->xnf_tx_pkt_id_head;
        xnfp->xnf_tx_pkt_id_head = tidp->id;
}

static void
xnf_data_txbuf_free(xnf_t *xnfp, xnf_txbuf_t *txp)
{
        ASSERT3U(txp->tx_type, ==, TX_DATA);

        /*
         * We are either using a lookaside buffer or we are mapping existing
         * buffers.
         */
        if (txp->tx_bdesc != NULL) {
                ASSERT(!txp->tx_handle_bound);
                xnf_buf_put(xnfp, txp->tx_bdesc, B_TRUE);
        } else {
                if (txp->tx_txreq.gref != INVALID_GRANT_REF) {
                        if (gnttab_query_foreign_access(txp->tx_txreq.gref) !=
                            0) {
                                cmn_err(CE_PANIC, "tx grant %d still in use by "
                                    "backend domain", txp->tx_txreq.gref);
                        }
                        (void) gnttab_end_foreign_access_ref(
                            txp->tx_txreq.gref, 1);
                        xnf_gref_put(xnfp, txp->tx_txreq.gref);
                }

                if (txp->tx_handle_bound)
                        (void) ddi_dma_unbind_handle(txp->tx_dma_handle);
        }

        if (txp->tx_mp != NULL)
                freemsg(txp->tx_mp);

        if (txp->tx_prev != NULL) {
                ASSERT3P(txp->tx_prev->tx_next, ==, txp);
                txp->tx_prev->tx_next = NULL;
        }

        if (txp->tx_txreq.id != INVALID_TX_ID) {
                /*
                 * This should be only possible when resuming from a suspend.
                 */
                ASSERT(!xnfp->xnf_connected);
                xnf_txid_put(xnfp, TX_ID_TO_TXID(xnfp, txp->tx_txreq.id));
                txp->tx_txreq.id = INVALID_TX_ID;
        }

        kmem_cache_free(xnfp->xnf_tx_buf_cache, txp);
}

static void
xnf_data_txbuf_free_chain(xnf_t *xnfp, xnf_txbuf_t *txp)
{
        if (txp == NULL)
                return;

        while (txp->tx_next != NULL)
                txp = txp->tx_next;

        /*
         * We free the chain in reverse order so that grants can be released
         * for all dma chunks before unbinding the dma handles. The mblk is
         * freed last, after all its fragments' dma handles are unbound.
         */
        xnf_txbuf_t *prev;
        for (; txp != NULL; txp = prev) {
                prev = txp->tx_prev;
                xnf_data_txbuf_free(xnfp, txp);
        }
}

static xnf_txbuf_t *
xnf_data_txbuf_alloc(xnf_t *xnfp, int flag)
{
        xnf_txbuf_t *txp;

        if ((txp = kmem_cache_alloc(xnfp->xnf_tx_buf_cache, flag)) == NULL) {
                return (NULL);
        }

        txp->tx_type = TX_DATA;
        txp->tx_next = NULL;
        txp->tx_prev = NULL;
        txp->tx_head = txp;
        txp->tx_frags_to_ack = 0;
        txp->tx_mp = NULL;
        txp->tx_bdesc = NULL;
        txp->tx_handle_bound = B_FALSE;
        txp->tx_txreq.gref = INVALID_GRANT_REF;
        txp->tx_txreq.id = INVALID_TX_ID;

        return (txp);
}

/*
 * Get `wanted' slots in the transmit ring, waiting for at least that
 * number if `wait' is B_TRUE. Force the ring to be cleaned by setting
 * `wanted' to zero.
 *
 * Return the number of slots available.
 */
static int
xnf_tx_slots_get(xnf_t *xnfp, int wanted, boolean_t wait)
{
        int slotsfree;
        boolean_t forced_clean = (wanted == 0);

        ASSERT(MUTEX_HELD(&xnfp->xnf_txlock));

        /* LINTED: constant in conditional context */
        while (B_TRUE) {
                slotsfree = RING_FREE_REQUESTS(&xnfp->xnf_tx_ring);

                if ((slotsfree < wanted) || forced_clean)
                        slotsfree = xnf_tx_clean_ring(xnfp);

                /*
                 * If there are more than we need free, tell other
                 * people to come looking again. We hold txlock, so we
                 * are able to take our slots before anyone else runs.
                 */
                if (slotsfree > wanted)
                        cv_broadcast(&xnfp->xnf_cv_tx_slots);

                if (slotsfree >= wanted)
                        break;

                if (!wait)
                        break;

                cv_wait(&xnfp->xnf_cv_tx_slots, &xnfp->xnf_txlock);
        }

        ASSERT(slotsfree <= RING_SIZE(&(xnfp->xnf_tx_ring)));

        return (slotsfree);
}

static int
xnf_setup_rings(xnf_t *xnfp)
{
        domid_t                 oeid;
        struct xenbus_device    *xsd;
        RING_IDX                i;
        int                     err;
        xnf_txid_t              *tidp;
        xnf_buf_t **bdescp;

        oeid = xvdi_get_oeid(xnfp->xnf_devinfo);
        xsd = xvdi_get_xsd(xnfp->xnf_devinfo);

        if (xnfp->xnf_tx_ring_ref != INVALID_GRANT_REF)
                gnttab_end_foreign_access(xnfp->xnf_tx_ring_ref, 0, 0);

        err = gnttab_grant_foreign_access(oeid,
            xnf_btop(pa_to_ma(xnfp->xnf_tx_ring_phys_addr)), 0);
        if (err <= 0) {
                err = -err;
                xenbus_dev_error(xsd, err, "granting access to tx ring page");
                goto out;
        }
        xnfp->xnf_tx_ring_ref = (grant_ref_t)err;

        if (xnfp->xnf_rx_ring_ref != INVALID_GRANT_REF)
                gnttab_end_foreign_access(xnfp->xnf_rx_ring_ref, 0, 0);

        err = gnttab_grant_foreign_access(oeid,
            xnf_btop(pa_to_ma(xnfp->xnf_rx_ring_phys_addr)), 0);
        if (err <= 0) {
                err = -err;
                xenbus_dev_error(xsd, err, "granting access to rx ring page");
                goto out;
        }
        xnfp->xnf_rx_ring_ref = (grant_ref_t)err;

        mutex_enter(&xnfp->xnf_txlock);

        /*
         * We first cleanup the TX ring in case we are doing a resume.
         * Note that this can lose packets, but we expect to stagger on.
         */
        xnfp->xnf_tx_pkt_id_head = INVALID_TX_ID; /* I.e. emtpy list. */
        for (i = 0, tidp = &xnfp->xnf_tx_pkt_id[0];
            i < NET_TX_RING_SIZE;
            i++, tidp++) {
                xnf_txbuf_t *txp = tidp->txbuf;
                if (txp == NULL)
                        continue;

                switch (txp->tx_type) {
                case TX_DATA:
                        /*
                         * txid_put() will be called for each txbuf's txid in
                         * the chain which will result in clearing tidp->txbuf.
                         */
                        xnf_data_txbuf_free_chain(xnfp, txp);

                        break;

                case TX_MCAST_REQ:
                        txp->tx_type = TX_MCAST_RSP;
                        txp->tx_status = NETIF_RSP_DROPPED;
                        cv_broadcast(&xnfp->xnf_cv_multicast);

                        /*
                         * The request consumed two slots in the ring,
                         * yet only a single xnf_txid_t is used. Step
                         * over the empty slot.
                         */
                        i++;
                        ASSERT3U(i, <, NET_TX_RING_SIZE);
                        break;

                case TX_MCAST_RSP:
                        break;
                }
        }

        /*
         * Now purge old list and add each txid to the new free list.
         */
        xnfp->xnf_tx_pkt_id_head = INVALID_TX_ID; /* I.e. emtpy list. */
        for (i = 0, tidp = &xnfp->xnf_tx_pkt_id[0];
            i < NET_TX_RING_SIZE;
            i++, tidp++) {
                tidp->id = i;
                ASSERT3P(tidp->txbuf, ==, NULL);
                tidp->next = INVALID_TX_ID; /* Appease txid_put(). */
                xnf_txid_put(xnfp, tidp);
        }

        /* LINTED: constant in conditional context */
        SHARED_RING_INIT(xnfp->xnf_tx_ring.sring);
        /* LINTED: constant in conditional context */
        FRONT_RING_INIT(&xnfp->xnf_tx_ring,
            xnfp->xnf_tx_ring.sring, PAGESIZE);

        mutex_exit(&xnfp->xnf_txlock);

        mutex_enter(&xnfp->xnf_rxlock);

        /*
         * Clean out any buffers currently posted to the receive ring
         * before we reset it.
         */
        for (i = 0, bdescp = &xnfp->xnf_rx_pkt_info[0];
            i < NET_RX_RING_SIZE;
            i++, bdescp++) {
                if (*bdescp != NULL) {
                        xnf_buf_put(xnfp, *bdescp, B_FALSE);
                        *bdescp = NULL;
                }
        }

        /* LINTED: constant in conditional context */
        SHARED_RING_INIT(xnfp->xnf_rx_ring.sring);
        /* LINTED: constant in conditional context */
        FRONT_RING_INIT(&xnfp->xnf_rx_ring,
            xnfp->xnf_rx_ring.sring, PAGESIZE);

        /*
         * Fill the ring with buffers.
         */
        for (i = 0; i < NET_RX_RING_SIZE; i++) {
                xnf_buf_t *bdesc;

                bdesc = xnf_buf_get(xnfp, KM_SLEEP, B_FALSE);
                VERIFY(bdesc != NULL);
                xnf_rxbuf_hang(xnfp, bdesc);
        }

        /* LINTED: constant in conditional context */
        RING_PUSH_REQUESTS(&xnfp->xnf_rx_ring);

        mutex_exit(&xnfp->xnf_rxlock);

        return (0);

out:
        if (xnfp->xnf_tx_ring_ref != INVALID_GRANT_REF)
                gnttab_end_foreign_access(xnfp->xnf_tx_ring_ref, 0, 0);
        xnfp->xnf_tx_ring_ref = INVALID_GRANT_REF;

        if (xnfp->xnf_rx_ring_ref != INVALID_GRANT_REF)
                gnttab_end_foreign_access(xnfp->xnf_rx_ring_ref, 0, 0);
        xnfp->xnf_rx_ring_ref = INVALID_GRANT_REF;

        return (err);
}

/*
 * Connect driver to back end, called to set up communication with
 * back end driver both initially and on resume after restore/migrate.
 */
void
xnf_be_connect(xnf_t *xnfp)
{
        const char      *message;
        xenbus_transaction_t xbt;
        struct          xenbus_device *xsd;
        char            *xsname;
        int             err;

        ASSERT(!xnfp->xnf_connected);

        xsd = xvdi_get_xsd(xnfp->xnf_devinfo);
        xsname = xvdi_get_xsname(xnfp->xnf_devinfo);

        err = xnf_setup_rings(xnfp);
        if (err != 0) {
                cmn_err(CE_WARN, "failed to set up tx/rx rings");
                xenbus_dev_error(xsd, err, "setting up ring");
                return;
        }

again:
        err = xenbus_transaction_start(&xbt);
        if (err != 0) {
                xenbus_dev_error(xsd, EIO, "starting transaction");
                return;
        }

        err = xenbus_printf(xbt, xsname, "tx-ring-ref", "%u",
            xnfp->xnf_tx_ring_ref);
        if (err != 0) {
                message = "writing tx ring-ref";
                goto abort_transaction;
        }

        err = xenbus_printf(xbt, xsname, "rx-ring-ref", "%u",
            xnfp->xnf_rx_ring_ref);
        if (err != 0) {
                message = "writing rx ring-ref";
                goto abort_transaction;
        }

        err = xenbus_printf(xbt, xsname, "event-channel", "%u",
            xnfp->xnf_evtchn);
        if (err != 0) {
                message = "writing event-channel";
                goto abort_transaction;
        }

        err = xenbus_printf(xbt, xsname, "feature-rx-notify", "%d", 1);
        if (err != 0) {
                message = "writing feature-rx-notify";
                goto abort_transaction;
        }

        err = xenbus_printf(xbt, xsname, "request-rx-copy", "%d", 1);
        if (err != 0) {
                message = "writing request-rx-copy";
                goto abort_transaction;
        }

        if (xnfp->xnf_be_mcast_control) {
                err = xenbus_printf(xbt, xsname, "request-multicast-control",
                    "%d", 1);
                if (err != 0) {
                        message = "writing request-multicast-control";
                        goto abort_transaction;
                }
        }

        /*
         * Tell backend if we support scatter-gather lists on the rx side.
         */
        err = xenbus_printf(xbt, xsname, "feature-sg", "%d",
            xnf_enable_rx_sg ? 1 : 0);
        if (err != 0) {
                message = "writing feature-sg";
                goto abort_transaction;
        }

        /*
         * Tell backend if we support LRO for IPv4. Scatter-gather on rx is
         * a prerequisite.
         */
        err = xenbus_printf(xbt, xsname, "feature-gso-tcpv4", "%d",
            (xnf_enable_rx_sg && xnf_enable_lro) ? 1 : 0);
        if (err != 0) {
                message = "writing feature-gso-tcpv4";
                goto abort_transaction;
        }

        err = xvdi_switch_state(xnfp->xnf_devinfo, xbt, XenbusStateConnected);
        if (err != 0) {
                message = "switching state to XenbusStateConnected";
                goto abort_transaction;
        }

        err = xenbus_transaction_end(xbt, 0);
        if (err != 0) {
                if (err == EAGAIN)
                        goto again;
                xenbus_dev_error(xsd, err, "completing transaction");
        }

        return;

abort_transaction:
        (void) xenbus_transaction_end(xbt, 1);
        xenbus_dev_error(xsd, err, "%s", message);
}

/*
 * Read configuration information from xenstore.
 */
void
xnf_read_config(xnf_t *xnfp)
{
        int err, be_cap;
        char mac[ETHERADDRL * 3];
        char *oename = xvdi_get_oename(xnfp->xnf_devinfo);

        err = xenbus_scanf(XBT_NULL, oename, "mac",
            "%s", (char *)&mac[0]);
        if (err != 0) {
                /*
                 * bad: we're supposed to be set up with a proper mac
                 * addr. at this point
                 */
                cmn_err(CE_WARN, "%s%d: no mac address",
                    ddi_driver_name(xnfp->xnf_devinfo),
                    ddi_get_instance(xnfp->xnf_devinfo));
                        return;
        }
        if (ether_aton(mac, xnfp->xnf_mac_addr) != ETHERADDRL) {
                err = ENOENT;
                xenbus_dev_error(xvdi_get_xsd(xnfp->xnf_devinfo), ENOENT,
                    "parsing %s/mac", xvdi_get_xsname(xnfp->xnf_devinfo));
                return;
        }

        err = xenbus_scanf(XBT_NULL, oename,
            "feature-rx-copy", "%d", &be_cap);
        /*
         * If we fail to read the store we assume that the key is
         * absent, implying an older domain at the far end.  Older
         * domains cannot do HV copy.
         */
        if (err != 0)
                be_cap = 0;
        xnfp->xnf_be_rx_copy = (be_cap != 0);

        err = xenbus_scanf(XBT_NULL, oename,
            "feature-multicast-control", "%d", &be_cap);
        /*
         * If we fail to read the store we assume that the key is
         * absent, implying an older domain at the far end.  Older
         * domains do not support multicast control.
         */
        if (err != 0)
                be_cap = 0;
        xnfp->xnf_be_mcast_control = (be_cap != 0) && xnf_multicast_control;

        /*
         * See if back-end supports scatter-gather for transmits. If not,
         * we will not support LSO and limit the mtu to 1500.
         */
        err = xenbus_scanf(XBT_NULL, oename, "feature-sg", "%d", &be_cap);
        if (err != 0) {
                be_cap = 0;
                dev_err(xnfp->xnf_devinfo, CE_WARN, "error reading "
                    "'feature-sg' from backend driver");
        }
        if (be_cap == 0) {
                dev_err(xnfp->xnf_devinfo, CE_WARN, "scatter-gather is not "
                    "supported for transmits in the backend driver. LSO is "
                    "disabled and MTU is restricted to 1500 bytes.");
        }
        xnfp->xnf_be_tx_sg = (be_cap != 0) && xnf_enable_tx_sg;

        if (xnfp->xnf_be_tx_sg) {
                /*
                 * Check if LSO is supported. Currently we only check for
                 * IPv4 as Illumos doesn't support LSO for IPv6.
                 */
                err = xenbus_scanf(XBT_NULL, oename, "feature-gso-tcpv4", "%d",
                    &be_cap);
                if (err != 0) {
                        be_cap = 0;
                        dev_err(xnfp->xnf_devinfo, CE_WARN, "error reading "
                            "'feature-gso-tcpv4' from backend driver");
                }
                if (be_cap == 0) {
                        dev_err(xnfp->xnf_devinfo, CE_WARN, "LSO is not "
                            "supported by the backend driver. Performance "
                            "will be affected.");
                }
                xnfp->xnf_be_lso = (be_cap != 0) && xnf_enable_lso;
        }
}

/*
 *  attach(9E) -- Attach a device to the system
 */
static int
xnf_attach(dev_info_t *devinfo, ddi_attach_cmd_t cmd)
{
        mac_register_t *macp;
        xnf_t *xnfp;
        int err;
        char cachename[32];

        switch (cmd) {
        case DDI_RESUME:
                xnfp = ddi_get_driver_private(devinfo);
                xnfp->xnf_gen++;

                (void) xvdi_resume(devinfo);
                (void) xvdi_alloc_evtchn(devinfo);
                xnfp->xnf_evtchn = xvdi_get_evtchn(devinfo);
#ifdef XPV_HVM_DRIVER
                ec_bind_evtchn_to_handler(xnfp->xnf_evtchn, IPL_VIF, xnf_intr,
                    xnfp);
#else
                (void) ddi_add_intr(devinfo, 0, NULL, NULL, xnf_intr,
                    (caddr_t)xnfp);
#endif
                return (DDI_SUCCESS);

        case DDI_ATTACH:
                break;

        default:
                return (DDI_FAILURE);
        }

        /*
         *  Allocate gld_mac_info_t and xnf_instance structures
         */
        macp = mac_alloc(MAC_VERSION);
        if (macp == NULL)
                return (DDI_FAILURE);
        xnfp = kmem_zalloc(sizeof (*xnfp), KM_SLEEP);

        xnfp->xnf_tx_pkt_id =
            kmem_zalloc(sizeof (xnf_txid_t) * NET_TX_RING_SIZE, KM_SLEEP);

        xnfp->xnf_rx_pkt_info =
            kmem_zalloc(sizeof (xnf_buf_t *) * NET_RX_RING_SIZE, KM_SLEEP);

        macp->m_dip = devinfo;
        macp->m_driver = xnfp;
        xnfp->xnf_devinfo = devinfo;

        macp->m_type_ident = MAC_PLUGIN_IDENT_ETHER;
        macp->m_src_addr = xnfp->xnf_mac_addr;
        macp->m_callbacks = &xnf_callbacks;
        macp->m_min_sdu = 0;
        xnfp->xnf_mtu = ETHERMTU;
        macp->m_max_sdu = xnfp->xnf_mtu;

        xnfp->xnf_running = B_FALSE;
        xnfp->xnf_connected = B_FALSE;
        xnfp->xnf_be_rx_copy = B_FALSE;
        xnfp->xnf_be_mcast_control = B_FALSE;
        xnfp->xnf_need_sched = B_FALSE;

        xnfp->xnf_rx_head = NULL;
        xnfp->xnf_rx_tail = NULL;
        xnfp->xnf_rx_new_buffers_posted = B_FALSE;

#ifdef XPV_HVM_DRIVER
        /* Report our version to dom0 */
        (void) xenbus_printf(XBT_NULL, "guest/xnf", "version", "%d",
            HVMPV_XNF_VERS);
#endif

        /*
         * Get the iblock cookie with which to initialize the mutexes.
         */
        if (ddi_get_iblock_cookie(devinfo, 0, &xnfp->xnf_icookie)
            != DDI_SUCCESS)
                goto failure;

        mutex_init(&xnfp->xnf_txlock,
            NULL, MUTEX_DRIVER, xnfp->xnf_icookie);
        mutex_init(&xnfp->xnf_rxlock,
            NULL, MUTEX_DRIVER, xnfp->xnf_icookie);
        mutex_init(&xnfp->xnf_schedlock,
            NULL, MUTEX_DRIVER, xnfp->xnf_icookie);
        mutex_init(&xnfp->xnf_gref_lock,
            NULL, MUTEX_DRIVER, xnfp->xnf_icookie);

        cv_init(&xnfp->xnf_cv_state, NULL, CV_DEFAULT, NULL);
        cv_init(&xnfp->xnf_cv_multicast, NULL, CV_DEFAULT, NULL);
        cv_init(&xnfp->xnf_cv_tx_slots, NULL, CV_DEFAULT, NULL);

        (void) sprintf(cachename, "xnf_buf_cache_%d",
            ddi_get_instance(devinfo));
        xnfp->xnf_buf_cache = kmem_cache_create(cachename,
            sizeof (xnf_buf_t), 0,
            xnf_buf_constructor, xnf_buf_destructor,
            NULL, xnfp, NULL, 0);
        if (xnfp->xnf_buf_cache == NULL)
                goto failure_0;

        (void) sprintf(cachename, "xnf_tx_buf_cache_%d",
            ddi_get_instance(devinfo));
        xnfp->xnf_tx_buf_cache = kmem_cache_create(cachename,
            sizeof (xnf_txbuf_t), 0,
            xnf_tx_buf_constructor, xnf_tx_buf_destructor,
            NULL, xnfp, NULL, 0);
        if (xnfp->xnf_tx_buf_cache == NULL)
                goto failure_1;

        xnfp->xnf_gref_head = INVALID_GRANT_REF;

        if (xnf_alloc_dma_resources(xnfp) == DDI_FAILURE) {
                cmn_err(CE_WARN, "xnf%d: failed to allocate and initialize "
                    "driver data structures",
                    ddi_get_instance(xnfp->xnf_devinfo));
                goto failure_2;
        }

        xnfp->xnf_rx_ring.sring->rsp_event =
            xnfp->xnf_tx_ring.sring->rsp_event = 1;

        xnfp->xnf_tx_ring_ref = INVALID_GRANT_REF;
        xnfp->xnf_rx_ring_ref = INVALID_GRANT_REF;

        /* set driver private pointer now */
        ddi_set_driver_private(devinfo, xnfp);

        if (!xnf_kstat_init(xnfp))
                goto failure_3;

        /*
         * Allocate an event channel, add the interrupt handler and
         * bind it to the event channel.
         */
        (void) xvdi_alloc_evtchn(devinfo);
        xnfp->xnf_evtchn = xvdi_get_evtchn(devinfo);
#ifdef XPV_HVM_DRIVER
        ec_bind_evtchn_to_handler(xnfp->xnf_evtchn, IPL_VIF, xnf_intr, xnfp);
#else
        (void) ddi_add_intr(devinfo, 0, NULL, NULL, xnf_intr, (caddr_t)xnfp);
#endif

        err = mac_register(macp, &xnfp->xnf_mh);
        mac_free(macp);
        macp = NULL;
        if (err != 0)
                goto failure_4;

        if (xvdi_add_event_handler(devinfo, XS_OE_STATE, oe_state_change, NULL)
            != DDI_SUCCESS)
                goto failure_5;

#ifdef XPV_HVM_DRIVER
        /*
         * In the HVM case, this driver essentially replaces a driver for
         * a 'real' PCI NIC. Without the "model" property set to
         * "Ethernet controller", like the PCI code does, netbooting does
         * not work correctly, as strplumb_get_netdev_path() will not find
         * this interface.
         */
        (void) ndi_prop_update_string(DDI_DEV_T_NONE, devinfo, "model",
            "Ethernet controller");
#endif

        return (DDI_SUCCESS);

failure_5:
        (void) mac_unregister(xnfp->xnf_mh);

failure_4:
#ifdef XPV_HVM_DRIVER
        ec_unbind_evtchn(xnfp->xnf_evtchn);
        xvdi_free_evtchn(devinfo);
#else
        ddi_remove_intr(devinfo, 0, xnfp->xnf_icookie);
#endif
        xnfp->xnf_evtchn = INVALID_EVTCHN;
        kstat_delete(xnfp->xnf_kstat_aux);

failure_3:
        xnf_release_dma_resources(xnfp);

failure_2:
        kmem_cache_destroy(xnfp->xnf_tx_buf_cache);

failure_1:
        kmem_cache_destroy(xnfp->xnf_buf_cache);

failure_0:
        cv_destroy(&xnfp->xnf_cv_tx_slots);
        cv_destroy(&xnfp->xnf_cv_multicast);
        cv_destroy(&xnfp->xnf_cv_state);

        mutex_destroy(&xnfp->xnf_gref_lock);
        mutex_destroy(&xnfp->xnf_schedlock);
        mutex_destroy(&xnfp->xnf_rxlock);
        mutex_destroy(&xnfp->xnf_txlock);

failure:
        kmem_free(xnfp, sizeof (*xnfp));
        if (macp != NULL)
                mac_free(macp);

        return (DDI_FAILURE);
}

/*  detach(9E) -- Detach a device from the system */
static int
xnf_detach(dev_info_t *devinfo, ddi_detach_cmd_t cmd)
{
        xnf_t *xnfp;            /* Our private device info */

        xnfp = ddi_get_driver_private(devinfo);

        switch (cmd) {
        case DDI_SUSPEND:
#ifdef XPV_HVM_DRIVER
                ec_unbind_evtchn(xnfp->xnf_evtchn);
                xvdi_free_evtchn(devinfo);
#else
                ddi_remove_intr(devinfo, 0, xnfp->xnf_icookie);
#endif

                xvdi_suspend(devinfo);

                mutex_enter(&xnfp->xnf_rxlock);
                mutex_enter(&xnfp->xnf_txlock);

                xnfp->xnf_evtchn = INVALID_EVTCHN;
                xnfp->xnf_connected = B_FALSE;
                mutex_exit(&xnfp->xnf_txlock);
                mutex_exit(&xnfp->xnf_rxlock);

                /* claim link to be down after disconnect */
                mac_link_update(xnfp->xnf_mh, LINK_STATE_DOWN);
                return (DDI_SUCCESS);

        case DDI_DETACH:
                break;

        default:
                return (DDI_FAILURE);
        }

        if (xnfp->xnf_connected)
                return (DDI_FAILURE);

        /*
         * Cannot detach if we have xnf_buf_t outstanding.
         */
        if (xnfp->xnf_stat_buf_allocated > 0)
                return (DDI_FAILURE);

        if (mac_unregister(xnfp->xnf_mh) != 0)
                return (DDI_FAILURE);

        kstat_delete(xnfp->xnf_kstat_aux);

        /* Stop the receiver */
        xnf_stop(xnfp);

        xvdi_remove_event_handler(devinfo, XS_OE_STATE);

        /* Remove the interrupt */
#ifdef XPV_HVM_DRIVER
        ec_unbind_evtchn(xnfp->xnf_evtchn);
        xvdi_free_evtchn(devinfo);
#else
        ddi_remove_intr(devinfo, 0, xnfp->xnf_icookie);
#endif

        /* Release any pending xmit mblks */
        xnf_release_mblks(xnfp);

        /* Release all DMA resources */
        xnf_release_dma_resources(xnfp);

        cv_destroy(&xnfp->xnf_cv_tx_slots);
        cv_destroy(&xnfp->xnf_cv_multicast);
        cv_destroy(&xnfp->xnf_cv_state);

        kmem_cache_destroy(xnfp->xnf_tx_buf_cache);
        kmem_cache_destroy(xnfp->xnf_buf_cache);

        mutex_destroy(&xnfp->xnf_gref_lock);
        mutex_destroy(&xnfp->xnf_schedlock);
        mutex_destroy(&xnfp->xnf_rxlock);
        mutex_destroy(&xnfp->xnf_txlock);

        kmem_free(xnfp, sizeof (*xnfp));

        return (DDI_SUCCESS);
}

/*
 *  xnf_set_mac_addr() -- set the physical network address on the board.
 */
static int
xnf_set_mac_addr(void *arg, const uint8_t *macaddr)
{
        _NOTE(ARGUNUSED(arg, macaddr));

        /*
         * We can't set our macaddr.
         */
        return (ENOTSUP);
}

/*
 *  xnf_set_multicast() -- set (enable) or disable a multicast address.
 *
 *  Program the hardware to enable/disable the multicast address
 *  in "mca".  Enable if "add" is true, disable if false.
 */
static int
xnf_set_multicast(void *arg, boolean_t add, const uint8_t *mca)
{
        xnf_t *xnfp = arg;
        xnf_txbuf_t *txp;
        int n_slots;
        RING_IDX slot;
        xnf_txid_t *tidp;
        netif_tx_request_t *txrp;
        struct netif_extra_info *erp;
        boolean_t notify, result;

        /*
         * If the backend does not support multicast control then we
         * must assume that the right packets will just arrive.
         */
        if (!xnfp->xnf_be_mcast_control)
                return (0);

        txp = kmem_cache_alloc(xnfp->xnf_tx_buf_cache, KM_SLEEP);

        mutex_enter(&xnfp->xnf_txlock);

        /*
         * If we're not yet connected then claim success. This is
         * acceptable because we refresh the entire set of multicast
         * addresses when we get connected.
         *
         * We can't wait around here because the MAC layer expects
         * this to be a non-blocking operation - waiting ends up
         * causing a deadlock during resume.
         */
        if (!xnfp->xnf_connected) {
                mutex_exit(&xnfp->xnf_txlock);
                return (0);
        }

        /*
         * 1. Acquire two slots in the ring.
         * 2. Fill in the slots.
         * 3. Request notification when the operation is done.
         * 4. Kick the peer.
         * 5. Wait for the response via xnf_tx_clean_ring().
         */

        n_slots = xnf_tx_slots_get(xnfp, 2, B_TRUE);
        ASSERT(n_slots >= 2);

        slot = xnfp->xnf_tx_ring.req_prod_pvt;
        tidp = xnf_txid_get(xnfp);
        VERIFY(tidp != NULL);

        txp->tx_type = TX_MCAST_REQ;
        txp->tx_slot = slot;

        txrp = RING_GET_REQUEST(&xnfp->xnf_tx_ring, slot);
        erp = (struct netif_extra_info *)
            RING_GET_REQUEST(&xnfp->xnf_tx_ring, slot + 1);

        txrp->gref = 0;
        txrp->size = 0;
        txrp->offset = 0;
        /* Set tx_txreq.id to appease xnf_tx_clean_ring(). */
        txrp->id = txp->tx_txreq.id = tidp->id;
        txrp->flags = NETTXF_extra_info;

        erp->type = add ? XEN_NETIF_EXTRA_TYPE_MCAST_ADD :
            XEN_NETIF_EXTRA_TYPE_MCAST_DEL;
        bcopy((void *)mca, &erp->u.mcast.addr, ETHERADDRL);

        tidp->txbuf = txp;

        xnfp->xnf_tx_ring.req_prod_pvt = slot + 2;

        mutex_enter(&xnfp->xnf_schedlock);
        xnfp->xnf_pending_multicast++;
        mutex_exit(&xnfp->xnf_schedlock);

        /* LINTED: constant in conditional context */
        RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&xnfp->xnf_tx_ring,
            notify);
        if (notify)
                ec_notify_via_evtchn(xnfp->xnf_evtchn);

        while (txp->tx_type == TX_MCAST_REQ)
                cv_wait(&xnfp->xnf_cv_multicast, &xnfp->xnf_txlock);

        ASSERT3U(txp->tx_type, ==, TX_MCAST_RSP);

        mutex_enter(&xnfp->xnf_schedlock);
        xnfp->xnf_pending_multicast--;
        mutex_exit(&xnfp->xnf_schedlock);

        result = (txp->tx_status == NETIF_RSP_OKAY);

        xnf_txid_put(xnfp, tidp);

        mutex_exit(&xnfp->xnf_txlock);

        kmem_cache_free(xnfp->xnf_tx_buf_cache, txp);

        return (result ? 0 : 1);
}

/*
 * xnf_set_promiscuous() -- set or reset promiscuous mode on the board
 *
 *  Program the hardware to enable/disable promiscuous mode.
 */
static int
xnf_set_promiscuous(void *arg, boolean_t on)
{
        _NOTE(ARGUNUSED(arg, on));

        /*
         * We can't really do this, but we pretend that we can in
         * order that snoop will work.
         */
        return (0);
}

/*
 * Clean buffers that we have responses for from the transmit ring.
 */
static int
xnf_tx_clean_ring(xnf_t *xnfp)
{
        boolean_t work_to_do;

        ASSERT(MUTEX_HELD(&xnfp->xnf_txlock));

loop:
        while (RING_HAS_UNCONSUMED_RESPONSES(&xnfp->xnf_tx_ring)) {
                RING_IDX cons, prod, i;

                cons = xnfp->xnf_tx_ring.rsp_cons;
                prod = xnfp->xnf_tx_ring.sring->rsp_prod;
                membar_consumer();
                /*
                 * Clean tx requests from ring that we have responses
                 * for.
                 */
                DTRACE_PROBE2(xnf_tx_clean_range, int, cons, int, prod);
                for (i = cons; i != prod; i++) {
                        netif_tx_response_t *trp;
                        xnf_txid_t *tidp;
                        xnf_txbuf_t *txp;

                        trp = RING_GET_RESPONSE(&xnfp->xnf_tx_ring, i);
                        /*
                         * if this slot was occupied by netif_extra_info_t,
                         * then the response will be NETIF_RSP_NULL. In this
                         * case there are no resources to clean up.
                         */
                        if (trp->status == NETIF_RSP_NULL)
                                continue;

                        ASSERT(TX_ID_VALID(trp->id));

                        tidp = TX_ID_TO_TXID(xnfp, trp->id);
                        ASSERT3U(tidp->id, ==, trp->id);
                        ASSERT3U(tidp->next, ==, INVALID_TX_ID);

                        txp = tidp->txbuf;
                        ASSERT(txp != NULL);
                        ASSERT3U(txp->tx_txreq.id, ==, trp->id);

                        switch (txp->tx_type) {
                        case TX_DATA:
                                /*
                                 * We must put the txid for each response we
                                 * acknowledge to make sure that we never have
                                 * more free slots than txids. Because of this
                                 * we do it here instead of waiting for it to
                                 * be done in xnf_data_txbuf_free_chain().
                                 */
                                xnf_txid_put(xnfp, tidp);
                                txp->tx_txreq.id = INVALID_TX_ID;
                                ASSERT3S(txp->tx_head->tx_frags_to_ack, >, 0);
                                txp->tx_head->tx_frags_to_ack--;

                                /*
                                 * We clean the whole chain once we got a
                                 * response for each fragment.
                                 */
                                if (txp->tx_head->tx_frags_to_ack == 0)
                                        xnf_data_txbuf_free_chain(xnfp, txp);

                                break;

                        case TX_MCAST_REQ:
                                txp->tx_type = TX_MCAST_RSP;
                                txp->tx_status = trp->status;
                                cv_broadcast(&xnfp->xnf_cv_multicast);

                                break;

                        default:
                                cmn_err(CE_PANIC, "xnf_tx_clean_ring: "
                                    "invalid xnf_txbuf_t type: %d",
                                    txp->tx_type);
                                break;
                        }
                }
                /*
                 * Record the last response we dealt with so that we
                 * know where to start next time around.
                 */
                xnfp->xnf_tx_ring.rsp_cons = prod;
                membar_enter();
        }

        /* LINTED: constant in conditional context */
        RING_FINAL_CHECK_FOR_RESPONSES(&xnfp->xnf_tx_ring, work_to_do);
        if (work_to_do)
                goto loop;

        return (RING_FREE_REQUESTS(&xnfp->xnf_tx_ring));
}

/*
 * Allocate and fill in a look-aside buffer for the packet `mp'. Used
 * to ensure that the packet is physically contiguous and contained
 * within a single page.
 */
static xnf_buf_t *
xnf_tx_get_lookaside(xnf_t *xnfp, mblk_t *mp, size_t *plen)
{
        xnf_buf_t *bd;
        caddr_t bp;

        if ((bd = xnf_buf_get(xnfp, KM_NOSLEEP, B_TRUE)) == NULL) {
                return (NULL);
        }

        bp = bd->buf;
        while (mp != NULL) {
                size_t len = MBLKL(mp);

                bcopy(mp->b_rptr, bp, len);
                bp += len;

                mp = mp->b_cont;
        }

        *plen = bp - bd->buf;
        ASSERT3U(*plen, <=, PAGESIZE);

        xnfp->xnf_stat_tx_lookaside++;

        return (bd);
}

/*
 * Insert the pseudo-header checksum into the packet.
 * Assumes packet is IPv4, TCP/UDP since we only advertised support for
 * HCKSUM_INET_FULL_V4.
 */
int
xnf_pseudo_cksum(mblk_t *mp)
{
        struct ether_header *ehp;
        uint16_t sap, iplen, *stuff;
        uint32_t cksum;
        size_t len;
        ipha_t *ipha;
        ipaddr_t src, dst;
        uchar_t *ptr;

        ptr = mp->b_rptr;
        len = MBLKL(mp);

        /* Each header must fit completely in an mblk. */
        ASSERT3U(len, >=, sizeof (*ehp));

        ehp = (struct ether_header *)ptr;

        if (ntohs(ehp->ether_type) == VLAN_TPID) {
                struct ether_vlan_header *evhp;
                ASSERT3U(len, >=, sizeof (*evhp));
                evhp = (struct ether_vlan_header *)ptr;
                sap = ntohs(evhp->ether_type);
                ptr += sizeof (*evhp);
                len -= sizeof (*evhp);
        } else {
                sap = ntohs(ehp->ether_type);
                ptr += sizeof (*ehp);
                len -= sizeof (*ehp);
        }

        ASSERT3U(sap, ==, ETHERTYPE_IP);

        /*
         * Ethernet and IP headers may be in different mblks.
         */
        ASSERT3P(ptr, <=, mp->b_wptr);
        if (ptr == mp->b_wptr) {
                mp = mp->b_cont;
                ptr = mp->b_rptr;
                len = MBLKL(mp);
        }

        ASSERT3U(len, >=, sizeof (ipha_t));
        ipha = (ipha_t *)ptr;

        /*
         * We assume the IP header has no options. (This is enforced in
         * ire_send_wire_v4() -- search for IXAF_NO_HW_CKSUM).
         */
        ASSERT3U(IPH_HDR_LENGTH(ipha), ==, IP_SIMPLE_HDR_LENGTH);
        iplen = ntohs(ipha->ipha_length) - IP_SIMPLE_HDR_LENGTH;

        ptr += IP_SIMPLE_HDR_LENGTH;
        len -= IP_SIMPLE_HDR_LENGTH;

        /*
         * IP and L4 headers may be in different mblks.
         */
        ASSERT3P(ptr, <=, mp->b_wptr);
        if (ptr == mp->b_wptr) {
                mp = mp->b_cont;
                ptr = mp->b_rptr;
                len = MBLKL(mp);
        }

        switch (ipha->ipha_protocol) {
        case IPPROTO_TCP:
                ASSERT3U(len, >=, sizeof (tcph_t));
                stuff = (uint16_t *)(ptr + TCP_CHECKSUM_OFFSET);
                cksum = IP_TCP_CSUM_COMP;
                break;
        case IPPROTO_UDP:
                ASSERT3U(len, >=, sizeof (struct udphdr));
                stuff = (uint16_t *)(ptr + UDP_CHECKSUM_OFFSET);
                cksum = IP_UDP_CSUM_COMP;
                break;
        default:
                cmn_err(CE_WARN, "xnf_pseudo_cksum: unexpected protocol %d",
                    ipha->ipha_protocol);
                return (EINVAL);
        }

        src = ipha->ipha_src;
        dst = ipha->ipha_dst;

        cksum += (dst >> 16) + (dst & 0xFFFF);
        cksum += (src >> 16) + (src & 0xFFFF);
        cksum += htons(iplen);

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

        ASSERT(cksum <= 0xFFFF);

        *stuff = (uint16_t)(cksum ? cksum : ~cksum);

        return (0);
}

/*
 * Push a packet into the transmit ring.
 *
 * Note: the format of a tx packet that spans multiple slots is similar to
 * what is described in xnf_rx_one_packet().
 */
static void
xnf_tx_push_packet(xnf_t *xnfp, xnf_txbuf_t *head)
{
        int nslots = 0;
        int extras = 0;
        RING_IDX slot;
        boolean_t notify;

        ASSERT(MUTEX_HELD(&xnfp->xnf_txlock));
        ASSERT(xnfp->xnf_running);

        slot = xnfp->xnf_tx_ring.req_prod_pvt;

        /*
         * The caller has already checked that we have enough slots to proceed.
         */
        for (xnf_txbuf_t *txp = head; txp != NULL; txp = txp->tx_next) {
                xnf_txid_t *tidp;
                netif_tx_request_t *txrp;

                tidp = xnf_txid_get(xnfp);
                VERIFY(tidp != NULL);
                txrp = RING_GET_REQUEST(&xnfp->xnf_tx_ring, slot);

                txp->tx_slot = slot;
                txp->tx_txreq.id = tidp->id;
                *txrp = txp->tx_txreq;

                tidp->txbuf = txp;
                slot++;
                nslots++;

                /*
                 * When present, LSO info is placed in a slot after the first
                 * data segment, and doesn't require a txid.
                 */
                if (txp->tx_txreq.flags & NETTXF_extra_info) {
                        netif_extra_info_t *extra;
                        ASSERT3U(nslots, ==, 1);

                        extra = (netif_extra_info_t *)
                            RING_GET_REQUEST(&xnfp->xnf_tx_ring, slot);
                        *extra = txp->tx_extra;
                        slot++;
                        nslots++;
                        extras = 1;
                }
        }

        ASSERT3U(nslots, <=, XEN_MAX_SLOTS_PER_TX);

        /*
         * Store the number of data fragments.
         */
        head->tx_frags_to_ack = nslots - extras;

        xnfp->xnf_tx_ring.req_prod_pvt = slot;

        /*
         * Tell the peer that we sent something, if it cares.
         */
        /* LINTED: constant in conditional context */
        RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&xnfp->xnf_tx_ring, notify);
        if (notify)
                ec_notify_via_evtchn(xnfp->xnf_evtchn);
}

static xnf_txbuf_t *
xnf_mblk_copy(xnf_t *xnfp, mblk_t *mp)
{
        xnf_txbuf_t *txp;
        size_t length;

        if ((txp = xnf_data_txbuf_alloc(xnfp, KM_NOSLEEP)) == NULL) {
                return (NULL);
        }

        txp->tx_bdesc = xnf_tx_get_lookaside(xnfp, mp, &length);
        if (txp->tx_bdesc == NULL) {
                xnf_data_txbuf_free(xnfp, txp);
                return (NULL);
        }
        txp->tx_mfn = txp->tx_bdesc->buf_mfn;
        txp->tx_txreq.gref = txp->tx_bdesc->grant_ref;
        txp->tx_txreq.size = length;
        txp->tx_txreq.offset = (uintptr_t)txp->tx_bdesc->buf & PAGEOFFSET;
        txp->tx_txreq.flags = 0;

        return (txp);
}

static xnf_txbuf_t *
xnf_mblk_map(xnf_t *xnfp, mblk_t *mp, int *countp)
{
        xnf_txbuf_t *head = NULL;
        xnf_txbuf_t *tail = NULL;
        domid_t oeid;
        int nsegs = 0;

        oeid = xvdi_get_oeid(xnfp->xnf_devinfo);

        for (mblk_t *ml = mp; ml != NULL; ml = ml->b_cont) {
                ddi_dma_handle_t dma_handle;
                const ddi_dma_cookie_t *dma_cookie, *dma_cookie_prev;
                xnf_txbuf_t *txp;

                if (MBLKL(ml) == 0)
                        continue;

                if ((txp = xnf_data_txbuf_alloc(xnfp, KM_NOSLEEP)) == NULL) {
                        goto error;
                }

                if (head == NULL) {
                        head = txp;
                } else {
                        ASSERT(tail != NULL);
                        TXBUF_SETNEXT(tail, txp);
                        txp->tx_head = head;
                }

                /*
                 * The necessary segmentation rules (e.g. not crossing a page
                 * boundary) are enforced by the dma attributes of the handle.
                 */
                dma_handle = txp->tx_dma_handle;
                int ret = ddi_dma_addr_bind_handle(dma_handle,
                    NULL, (char *)ml->b_rptr, MBLKL(ml),
                    DDI_DMA_WRITE | DDI_DMA_STREAMING,
                    DDI_DMA_DONTWAIT, 0, NULL, NULL);
                if (ret != DDI_DMA_MAPPED) {
                        if (ret != DDI_DMA_NORESOURCES) {
                                dev_err(xnfp->xnf_devinfo, CE_WARN,
                                    "ddi_dma_addr_bind_handle() failed "
                                    "[dma_error=%d]", ret);
                        }
                        goto error;
                }
                txp->tx_handle_bound = B_TRUE;

                dma_cookie_prev = NULL;
                while ((dma_cookie = ddi_dma_cookie_iter(dma_handle,
                    dma_cookie_prev)) != NULL) {
                        if (nsegs == XEN_MAX_TX_DATA_PAGES) {
                                dev_err(xnfp->xnf_devinfo, CE_WARN,
                                    "xnf_dmamap_alloc() failed: "
                                    "too many segments");
                                goto error;
                        }
                        if (dma_cookie_prev != NULL) {
                                if ((txp = xnf_data_txbuf_alloc(xnfp,
                                    KM_NOSLEEP)) == NULL) {
                                        goto error;
                                }
                                ASSERT(tail != NULL);
                                TXBUF_SETNEXT(tail, txp);
                                txp->tx_head = head;
                        }

                        txp->tx_mfn =
                            xnf_btop(pa_to_ma(dma_cookie->dmac_laddress));
                        txp->tx_txreq.gref = xnf_gref_get(xnfp);
                        if (txp->tx_txreq.gref == INVALID_GRANT_REF) {
                                dev_err(xnfp->xnf_devinfo, CE_WARN,
                                    "xnf_dmamap_alloc() failed: "
                                    "invalid grant ref");
                                goto error;
                        }
                        gnttab_grant_foreign_access_ref(txp->tx_txreq.gref,
                            oeid, txp->tx_mfn, 1);
                        txp->tx_txreq.offset =
                            dma_cookie->dmac_laddress & PAGEOFFSET;
                        txp->tx_txreq.size = dma_cookie->dmac_size;
                        txp->tx_txreq.flags = 0;

                        nsegs++;

                        if (tail != NULL)
                                tail->tx_txreq.flags = NETTXF_more_data;
                        tail = txp;

                        dma_cookie_prev = dma_cookie;
                }
        }

        *countp = nsegs;
        return (head);

error:
        xnf_data_txbuf_free_chain(xnfp, head);
        return (NULL);
}

static void
xnf_tx_setup_offload(xnf_t *xnfp, xnf_txbuf_t *head,
    uint32_t cksum_flags, uint32_t lso_flags, uint32_t mss)
{
        if (lso_flags != 0) {
                ASSERT3U(lso_flags, ==, HW_LSO);
                ASSERT3P(head->tx_bdesc, ==, NULL);

                head->tx_txreq.flags |= NETTXF_extra_info;
                netif_extra_info_t *extra = &head->tx_extra;
                extra->type = XEN_NETIF_EXTRA_TYPE_GSO;
                extra->flags = 0;
                extra->u.gso.type = XEN_NETIF_GSO_TYPE_TCPV4;
                extra->u.gso.size = mss;
                extra->u.gso.features = 0;
                extra->u.gso.pad = 0;
        } else if (cksum_flags != 0) {
                ASSERT3U(cksum_flags, ==, HCK_FULLCKSUM);
                /*
                 * If the local protocol stack requests checksum
                 * offload we set the 'checksum blank' flag,
                 * indicating to the peer that we need the checksum
                 * calculated for us.
                 *
                 * We _don't_ set the validated flag, because we haven't
                 * validated that the data and the checksum match.
                 *
                 * Note: we already called xnf_pseudo_cksum() in
                 * xnf_send(), so we just set the txreq flag here.
                 */
                head->tx_txreq.flags |= NETTXF_csum_blank;
                xnfp->xnf_stat_tx_cksum_deferred++;
        }
}

/*
 * Send packet mp. Called by the MAC framework.
 */
static mblk_t *
xnf_send(void *arg, mblk_t *mp)
{
        xnf_t *xnfp = arg;
        xnf_txbuf_t *head;
        mblk_t *ml;
        int length;
        int pages, chunks, slots, slots_free;
        uint32_t cksum_flags, lso_flags, mss;
        boolean_t pulledup = B_FALSE;
        boolean_t force_copy = B_FALSE;

        ASSERT3P(mp->b_next, ==, NULL);

        mutex_enter(&xnfp->xnf_txlock);

        /*
         * Wait until we are connected to the backend.
         */
        while (!xnfp->xnf_connected)
                cv_wait(&xnfp->xnf_cv_state, &xnfp->xnf_txlock);

        /*
         * To simplify logic and be in sync with the rescheduling mechanism,
         * we require the maximum amount of slots that could be used by a
         * transaction to be free before proceeding. The only downside of doing
         * this is that it slightly reduces the effective size of the ring.
         */
        slots_free = xnf_tx_slots_get(xnfp, XEN_MAX_SLOTS_PER_TX, B_FALSE);
        if (slots_free < XEN_MAX_SLOTS_PER_TX) {
                /*
                 * We need to ask for a re-schedule later as the ring is full.
                 */
                mutex_enter(&xnfp->xnf_schedlock);
                xnfp->xnf_need_sched = B_TRUE;
                mutex_exit(&xnfp->xnf_schedlock);

                xnfp->xnf_stat_tx_defer++;
                mutex_exit(&xnfp->xnf_txlock);
                return (mp);
        }

        /*
         * Get hw offload parameters.
         * This must be done before pulling up the mp as those parameters
         * are not copied over.
         */
        mac_hcksum_get(mp, NULL, NULL, NULL, NULL, &cksum_flags);
        mac_lso_get(mp, &mss, &lso_flags);

        /*
         * XXX: fix MAC framework so that we can advertise support for
         * partial checksum for IPv4 only. This way we won't need to calculate
         * the pseudo header checksum ourselves.
         */
        if (cksum_flags != 0) {
                ASSERT3U(cksum_flags, ==, HCK_FULLCKSUM);
                (void) xnf_pseudo_cksum(mp);
        }

pulledup:
        for (ml = mp, pages = 0, chunks = 0, length = 0; ml != NULL;
            ml = ml->b_cont, chunks++) {
                pages += xnf_mblk_pages(ml);
                length += MBLKL(ml);
        }
        DTRACE_PROBE3(packet, int, length, int, chunks, int, pages);
        DTRACE_PROBE3(lso, int, length, uint32_t, lso_flags, uint32_t, mss);

        /*
         * If the ethernet header crosses a page boundary the packet
         * will be dropped by the backend. In practice it seems like
         * this happens fairly rarely so we'll do nothing unless the
         * packet is small enough to fit in a look-aside buffer.
         */
        if (((uintptr_t)mp->b_rptr & PAGEOFFSET) +
            sizeof (struct ether_header) > PAGESIZE) {
                xnfp->xnf_stat_tx_eth_hdr_split++;
                if (length <= PAGESIZE)
                        force_copy = B_TRUE;
        }

        if (force_copy || (pages > 1 && !xnfp->xnf_be_tx_sg)) {
                /*
                 * If the packet spans several pages and scatter-gather is not
                 * supported then use a look-aside buffer.
                 */
                ASSERT3U(length, <=, PAGESIZE);
                head = xnf_mblk_copy(xnfp, mp);
                if (head == NULL) {
                        dev_err(xnfp->xnf_devinfo, CE_WARN,
                            "xnf_mblk_copy() failed");
                        goto drop;
                }
        } else {
                /*
                 * There's a limit for how many pages can be passed to the
                 * backend. If we pass that limit, the packet will be dropped
                 * and some backend implementations (e.g. Linux) could even
                 * offline the interface.
                 */
                if (pages > XEN_MAX_TX_DATA_PAGES) {
                        if (pulledup) {
                                dev_err(xnfp->xnf_devinfo, CE_WARN,
                                    "too many pages, even after pullup: %d.",
                                    pages);
                                goto drop;
                        }

                        /*
                         * Defragment packet if it spans too many pages.
                         */
                        mblk_t *newmp = msgpullup(mp, -1);
                        if (newmp == NULL) {
                                dev_err(xnfp->xnf_devinfo, CE_WARN,
                                    "msgpullup() failed");
                                goto drop;
                        }

                        freemsg(mp);
                        mp = newmp;
                        xnfp->xnf_stat_tx_pullup++;
                        pulledup = B_TRUE;
                        goto pulledup;
                }

                head = xnf_mblk_map(xnfp, mp, &slots);
                if (head == NULL)
                        goto drop;

                IMPLY(slots > 1, xnfp->xnf_be_tx_sg);
        }

        /*
         * Set tx_mp so that mblk is freed when the txbuf chain is freed.
         */
        head->tx_mp = mp;

        xnf_tx_setup_offload(xnfp, head, cksum_flags, lso_flags, mss);

        /*
         * The first request must store the total length of the packet.
         */
        head->tx_txreq.size = length;

        /*
         * Push the packet we have prepared into the ring.
         */
        xnf_tx_push_packet(xnfp, head);
        xnfp->xnf_stat_opackets++;
        xnfp->xnf_stat_obytes += length;

        mutex_exit(&xnfp->xnf_txlock);
        return (NULL);

drop:
        freemsg(mp);
        xnfp->xnf_stat_tx_drop++;
        mutex_exit(&xnfp->xnf_txlock);
        return (NULL);
}

/*
 * Notification of RX packets. Currently no TX-complete interrupt is
 * used, as we clean the TX ring lazily.
 */
static uint_t
xnf_intr(caddr_t arg)
{
        xnf_t *xnfp = (xnf_t *)arg;
        mblk_t *mp;
        boolean_t need_sched, clean_ring;

        mutex_enter(&xnfp->xnf_rxlock);

        /*
         * Interrupts before we are connected are spurious.
         */
        if (!xnfp->xnf_connected) {
                mutex_exit(&xnfp->xnf_rxlock);
                xnfp->xnf_stat_unclaimed_interrupts++;
                return (DDI_INTR_UNCLAIMED);
        }

        /*
         * Receive side processing.
         */
        do {
                /*
                 * Collect buffers from the ring.
                 */
                xnf_rx_collect(xnfp);

                /*
                 * Interrupt me when the next receive buffer is consumed.
                 */
                xnfp->xnf_rx_ring.sring->rsp_event =
                    xnfp->xnf_rx_ring.rsp_cons + 1;
                xen_mb();

        } while (RING_HAS_UNCONSUMED_RESPONSES(&xnfp->xnf_rx_ring));

        if (xnfp->xnf_rx_new_buffers_posted) {
                boolean_t notify;

                /*
                 * Indicate to the peer that we have re-filled the
                 * receive ring, if it cares.
                 */
                /* LINTED: constant in conditional context */
                RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&xnfp->xnf_rx_ring, notify);
                if (notify)
                        ec_notify_via_evtchn(xnfp->xnf_evtchn);
                xnfp->xnf_rx_new_buffers_posted = B_FALSE;
        }

        mp = xnfp->xnf_rx_head;
        xnfp->xnf_rx_head = xnfp->xnf_rx_tail = NULL;

        xnfp->xnf_stat_interrupts++;
        mutex_exit(&xnfp->xnf_rxlock);

        if (mp != NULL)
                mac_rx(xnfp->xnf_mh, NULL, mp);

        /*
         * Transmit side processing.
         *
         * If a previous transmit attempt failed or we have pending
         * multicast requests, clean the ring.
         *
         * If we previously stalled transmission and cleaning produces
         * some free slots, tell upstream to attempt sending again.
         *
         * The odd style is to avoid acquiring xnf_txlock unless we
         * will actually look inside the tx machinery.
         */
        mutex_enter(&xnfp->xnf_schedlock);
        need_sched = xnfp->xnf_need_sched;
        clean_ring = need_sched || (xnfp->xnf_pending_multicast > 0);
        mutex_exit(&xnfp->xnf_schedlock);

        if (clean_ring) {
                int free_slots;

                mutex_enter(&xnfp->xnf_txlock);
                free_slots = xnf_tx_slots_get(xnfp, 0, B_FALSE);

                if (need_sched && (free_slots >= XEN_MAX_SLOTS_PER_TX)) {
                        mutex_enter(&xnfp->xnf_schedlock);
                        xnfp->xnf_need_sched = B_FALSE;
                        mutex_exit(&xnfp->xnf_schedlock);

                        mac_tx_update(xnfp->xnf_mh);
                }
                mutex_exit(&xnfp->xnf_txlock);
        }

        return (DDI_INTR_CLAIMED);
}

/*
 *  xnf_start() -- start the board receiving and enable interrupts.
 */
static int
xnf_start(void *arg)
{
        xnf_t *xnfp = arg;

        mutex_enter(&xnfp->xnf_rxlock);
        mutex_enter(&xnfp->xnf_txlock);

        /* Accept packets from above. */
        xnfp->xnf_running = B_TRUE;

        mutex_exit(&xnfp->xnf_txlock);
        mutex_exit(&xnfp->xnf_rxlock);

        return (0);
}

/* xnf_stop() - disable hardware */
static void
xnf_stop(void *arg)
{
        xnf_t *xnfp = arg;

        mutex_enter(&xnfp->xnf_rxlock);
        mutex_enter(&xnfp->xnf_txlock);

        xnfp->xnf_running = B_FALSE;

        mutex_exit(&xnfp->xnf_txlock);
        mutex_exit(&xnfp->xnf_rxlock);
}

/*
 * Hang buffer `bdesc' on the RX ring.
 */
static void
xnf_rxbuf_hang(xnf_t *xnfp, xnf_buf_t *bdesc)
{
        netif_rx_request_t *reqp;
        RING_IDX hang_ix;

        ASSERT(MUTEX_HELD(&xnfp->xnf_rxlock));

        reqp = RING_GET_REQUEST(&xnfp->xnf_rx_ring,
            xnfp->xnf_rx_ring.req_prod_pvt);
        hang_ix = (RING_IDX) (reqp - RING_GET_REQUEST(&xnfp->xnf_rx_ring, 0));
        ASSERT(xnfp->xnf_rx_pkt_info[hang_ix] == NULL);

        reqp->id = bdesc->id = hang_ix;
        reqp->gref = bdesc->grant_ref;

        xnfp->xnf_rx_pkt_info[hang_ix] = bdesc;
        xnfp->xnf_rx_ring.req_prod_pvt++;

        xnfp->xnf_rx_new_buffers_posted = B_TRUE;
}

/*
 * Receive an entire packet from the ring, starting from slot *consp.
 * prod indicates the slot of the latest response.
 * On return, *consp will point to the head of the next packet.
 *
 * Note: If slot prod was reached before we could gather a full packet, we will
 * drop the partial packet; this would most likely indicate a bug in either
 * the front-end or the back-end driver.
 *
 * An rx packet can consist of several fragments and thus span multiple slots.
 * Each fragment can contain up to 4k of data.
 *
 * A typical 9000 MTU packet with look like this:
 * +------+---------------------+-------------------+-----------------------+
 * | SLOT | TYPE                | CONTENTS          | FLAGS                 |
 * +------+---------------------+-------------------+-----------------------+
 * | 1    | netif_rx_response_t | 1st data fragment | more_data             |
 * +------+---------------------+-------------------+-----------------------+
 * | 2    | netif_rx_response_t | 2nd data fragment | more_data             |
 * +------+---------------------+-------------------+-----------------------+
 * | 3    | netif_rx_response_t | 3rd data fragment | [none]                |
 * +------+---------------------+-------------------+-----------------------+
 *
 * Fragments are chained by setting NETRXF_more_data in the previous
 * response's flags. If there are additional flags, such as
 * NETRXF_data_validated or NETRXF_extra_info, those should be set on the
 * first fragment.
 *
 * Sometimes extra info can be present. If so, it will follow the first
 * fragment, and NETRXF_extra_info flag will be set on the first response.
 * If LRO is set on a packet, it will be stored in the extra info. Conforming
 * to the spec, extra info can also be chained, but must all be present right
 * after the first fragment.
 *
 * Example of a packet with 2 extra infos:
 * +------+---------------------+-------------------+-----------------------+
 * | SLOT | TYPE                | CONTENTS          | FLAGS                 |
 * +------+---------------------+-------------------+-----------------------+
 * | 1    | netif_rx_response_t | 1st data fragment | extra_info, more_data |
 * +------+---------------------+-------------------+-----------------------+
 * | 2    | netif_extra_info_t  | 1st extra info    | EXTRA_FLAG_MORE       |
 * +------+---------------------+-------------------+-----------------------+
 * | 3    | netif_extra_info_t  | 2nd extra info    | [none]                |
 * +------+---------------------+-------------------+-----------------------+
 * | 4    | netif_rx_response_t | 2nd data fragment | more_data             |
 * +------+---------------------+-------------------+-----------------------+
 * | 5    | netif_rx_response_t | 3rd data fragment | more_data             |
 * +------+---------------------+-------------------+-----------------------+
 * | 6    | netif_rx_response_t | 4th data fragment | [none]                |
 * +------+---------------------+-------------------+-----------------------+
 *
 * In practice, the only extra we expect is for LRO, but only if we advertise
 * that we support it to the backend (xnf_enable_lro == TRUE).
 */
static int
xnf_rx_one_packet(xnf_t *xnfp, RING_IDX prod, RING_IDX *consp, mblk_t **mpp)
{
        mblk_t *head = NULL;
        mblk_t *tail = NULL;
        mblk_t *mp;
        int error = 0;
        RING_IDX cons = *consp;
        netif_extra_info_t lro;
        boolean_t is_lro = B_FALSE;
        boolean_t is_extra = B_FALSE;

        netif_rx_response_t rsp = *RING_GET_RESPONSE(&xnfp->xnf_rx_ring, cons);

        boolean_t hwcsum = (rsp.flags & NETRXF_data_validated) != 0;
        boolean_t more_data = (rsp.flags & NETRXF_more_data) != 0;
        boolean_t more_extra = (rsp.flags & NETRXF_extra_info) != 0;

        IMPLY(more_data, xnf_enable_rx_sg);

        while (cons != prod) {
                xnf_buf_t *bdesc;
                int len, off;
                int rxidx = cons & (NET_RX_RING_SIZE - 1);

                bdesc = xnfp->xnf_rx_pkt_info[rxidx];
                xnfp->xnf_rx_pkt_info[rxidx] = NULL;

                if (is_extra) {
                        netif_extra_info_t *extra = (netif_extra_info_t *)&rsp;
                        /*
                         * The only extra we expect is for LRO, and it should
                         * only be present once.
                         */
                        if (extra->type == XEN_NETIF_EXTRA_TYPE_GSO &&
                            !is_lro) {
                                ASSERT(xnf_enable_lro);
                                lro = *extra;
                                is_lro = B_TRUE;
                                DTRACE_PROBE1(lro, netif_extra_info_t *, &lro);
                        } else {
                                dev_err(xnfp->xnf_devinfo, CE_WARN, "rx packet "
                                    "contains unexpected extra info of type %d",
                                    extra->type);
                                error = EINVAL;
                        }
                        more_extra =
                            (extra->flags & XEN_NETIF_EXTRA_FLAG_MORE) != 0;

                        goto hang_buf;
                }

                ASSERT3U(bdesc->id, ==, rsp.id);

                /*
                 * status stores packet length when >= 0, or errors when < 0.
                 */
                len = rsp.status;
                off = rsp.offset;
                more_data = (rsp.flags & NETRXF_more_data) != 0;

                /*
                 * sanity checks.
                 */
                if (!xnfp->xnf_running) {
                        error = EBUSY;
                } else if (len <= 0) {
                        xnfp->xnf_stat_errrx++;

                        switch (len) {
                        case 0:
                                xnfp->xnf_stat_runt++;
                                break;
                        case NETIF_RSP_ERROR:
                                xnfp->xnf_stat_mac_rcv_error++;
                                break;
                        case NETIF_RSP_DROPPED:
                                xnfp->xnf_stat_norxbuf++;
                                break;
                        }
                        error = EINVAL;
                } else if (bdesc->grant_ref == INVALID_GRANT_REF) {
                        dev_err(xnfp->xnf_devinfo, CE_WARN,
                            "Bad rx grant reference, rsp id %d", rsp.id);
                        error = EINVAL;
                } else if ((off + len) > PAGESIZE) {
                        dev_err(xnfp->xnf_devinfo, CE_WARN, "Rx packet crosses "
                            "page boundary (offset %d, length %d)", off, len);
                        error = EINVAL;
                }

                if (error != 0) {
                        /*
                         * If an error has been detected, we do not attempt
                         * to read the data but we still need to replace
                         * the rx bufs.
                         */
                        goto hang_buf;
                }

                xnf_buf_t *nbuf = NULL;

                /*
                 * If the packet is below a pre-determined size we will
                 * copy data out of the buf rather than replace it.
                 */
                if (len > xnf_rx_copy_limit)
                        nbuf = xnf_buf_get(xnfp, KM_NOSLEEP, B_FALSE);

                if (nbuf != NULL) {
                        mp = desballoc((unsigned char *)bdesc->buf,
                            bdesc->len, 0, &bdesc->free_rtn);

                        if (mp == NULL) {
                                xnfp->xnf_stat_rx_desballoc_fail++;
                                xnfp->xnf_stat_norxbuf++;
                                error = ENOMEM;
                                /*
                                 * we free the buf we just allocated as we
                                 * will re-hang the old buf.
                                 */
                                xnf_buf_put(xnfp, nbuf, B_FALSE);
                                goto hang_buf;
                        }

                        mp->b_rptr = mp->b_rptr + off;
                        mp->b_wptr = mp->b_rptr + len;

                        /*
                         * Release the grant as the backend doesn't need to
                         * access this buffer anymore and grants are scarce.
                         */
                        (void) gnttab_end_foreign_access_ref(bdesc->grant_ref,
                            0);
                        xnf_gref_put(xnfp, bdesc->grant_ref);
                        bdesc->grant_ref = INVALID_GRANT_REF;

                        bdesc = nbuf;
                } else {
                        /*
                         * We failed to allocate a new buf or decided to reuse
                         * the old one. In either case we copy the data off it
                         * and put it back into the ring.
                         */
                        mp = allocb(len, 0);
                        if (mp == NULL) {
                                xnfp->xnf_stat_rx_allocb_fail++;
                                xnfp->xnf_stat_norxbuf++;
                                error = ENOMEM;
                                goto hang_buf;
                        }
                        bcopy(bdesc->buf + off, mp->b_wptr, len);
                        mp->b_wptr += len;
                }

                if (head == NULL)
                        head = mp;
                else
                        tail->b_cont = mp;
                tail = mp;

hang_buf:
                /*
                 * No matter what happens, for each response we need to hang
                 * a new buf on the rx ring. Put either the old one, or a new
                 * one if the old one is borrowed by the kernel via desballoc().
                 */
                xnf_rxbuf_hang(xnfp, bdesc);
                cons++;

                /* next response is an extra */
                is_extra = more_extra;

                if (!more_data && !more_extra)
                        break;

                /*
                 * Note that since requests and responses are union'd on the
                 * same ring, we copy the response to a local variable instead
                 * of keeping a pointer. Otherwise xnf_rxbuf_hang() would have
                 * overwritten contents of rsp.
                 */
                rsp = *RING_GET_RESPONSE(&xnfp->xnf_rx_ring, cons);
        }

        /*
         * Check that we do not get stuck in a loop.
         */
        ASSERT3U(*consp, !=, cons);
        *consp = cons;

        /*
         * We ran out of responses but the flags indicate there is more data.
         */
        if (more_data) {
                dev_err(xnfp->xnf_devinfo, CE_WARN, "rx: need more fragments.");
                error = EINVAL;
        }
        if (more_extra) {
                dev_err(xnfp->xnf_devinfo, CE_WARN, "rx: need more fragments "
                    "(extras).");
                error = EINVAL;
        }

        /*
         * An error means the packet must be dropped. If we have already formed
         * a partial packet, then discard it.
         */
        if (error != 0) {
                if (head != NULL)
                        freemsg(head);
                xnfp->xnf_stat_rx_drop++;
                return (error);
        }

        ASSERT(head != NULL);

        if (hwcsum) {
                /*
                 * If the peer says that the data has been validated then we
                 * declare that the full checksum has been verified.
                 *
                 * We don't look at the "checksum blank" flag, and hence could
                 * have a packet here that we are asserting is good with
                 * a blank checksum.
                 */
                mac_hcksum_set(head, 0, 0, 0, 0, HCK_FULLCKSUM_OK);
                xnfp->xnf_stat_rx_cksum_no_need++;
        }

        /* XXX: set lro info for packet once LRO is supported in OS. */

        *mpp = head;

        return (0);
}

/*
 * Collect packets from the RX ring, storing them in `xnfp' for later use.
 */
static void
xnf_rx_collect(xnf_t *xnfp)
{
        RING_IDX prod;

        ASSERT(MUTEX_HELD(&xnfp->xnf_rxlock));

        prod = xnfp->xnf_rx_ring.sring->rsp_prod;
        /*
         * Ensure we see queued responses up to 'prod'.
         */
        membar_consumer();

        while (xnfp->xnf_rx_ring.rsp_cons != prod) {
                mblk_t *mp;

                /*
                 * Collect a packet.
                 * rsp_cons is updated inside xnf_rx_one_packet().
                 */
                int error = xnf_rx_one_packet(xnfp, prod,
                    &xnfp->xnf_rx_ring.rsp_cons, &mp);
                if (error == 0) {
                        xnfp->xnf_stat_ipackets++;
                        xnfp->xnf_stat_rbytes += xmsgsize(mp);

                        /*
                         * Append the mblk to the rx list.
                         */
                        if (xnfp->xnf_rx_head == NULL) {
                                ASSERT3P(xnfp->xnf_rx_tail, ==, NULL);
                                xnfp->xnf_rx_head = mp;
                        } else {
                                ASSERT(xnfp->xnf_rx_tail != NULL);
                                xnfp->xnf_rx_tail->b_next = mp;
                        }
                        xnfp->xnf_rx_tail = mp;
                }
        }
}

/*
 *  xnf_alloc_dma_resources() -- initialize the drivers structures
 */
static int
xnf_alloc_dma_resources(xnf_t *xnfp)
{
        dev_info_t              *devinfo = xnfp->xnf_devinfo;
        size_t                  len;
        ddi_dma_cookie_t        dma_cookie;
        uint_t                  ncookies;
        int                     rc;
        caddr_t                 rptr;

        /*
         * The code below allocates all the DMA data structures that
         * need to be released when the driver is detached.
         *
         * Allocate page for the transmit descriptor ring.
         */
        if (ddi_dma_alloc_handle(devinfo, &ringbuf_dma_attr,
            DDI_DMA_SLEEP, 0, &xnfp->xnf_tx_ring_dma_handle) != DDI_SUCCESS)
                goto alloc_error;

        if (ddi_dma_mem_alloc(xnfp->xnf_tx_ring_dma_handle,
            PAGESIZE, &accattr, DDI_DMA_CONSISTENT,
            DDI_DMA_SLEEP, 0, &rptr, &len,
            &xnfp->xnf_tx_ring_dma_acchandle) != DDI_SUCCESS) {
                ddi_dma_free_handle(&xnfp->xnf_tx_ring_dma_handle);
                xnfp->xnf_tx_ring_dma_handle = NULL;
                goto alloc_error;
        }

        if ((rc = ddi_dma_addr_bind_handle(xnfp->xnf_tx_ring_dma_handle, NULL,
            rptr, PAGESIZE, DDI_DMA_RDWR | DDI_DMA_CONSISTENT,
            DDI_DMA_SLEEP, 0, &dma_cookie, &ncookies)) != DDI_DMA_MAPPED) {
                ddi_dma_mem_free(&xnfp->xnf_tx_ring_dma_acchandle);
                ddi_dma_free_handle(&xnfp->xnf_tx_ring_dma_handle);
                xnfp->xnf_tx_ring_dma_handle = NULL;
                xnfp->xnf_tx_ring_dma_acchandle = NULL;
                if (rc == DDI_DMA_NORESOURCES)
                        goto alloc_error;
                else
                        goto error;
        }

        ASSERT(ncookies == 1);
        bzero(rptr, PAGESIZE);
        /* LINTED: constant in conditional context */
        SHARED_RING_INIT((netif_tx_sring_t *)rptr);
        /* LINTED: constant in conditional context */
        FRONT_RING_INIT(&xnfp->xnf_tx_ring, (netif_tx_sring_t *)rptr, PAGESIZE);
        xnfp->xnf_tx_ring_phys_addr = dma_cookie.dmac_laddress;

        /*
         * Allocate page for the receive descriptor ring.
         */
        if (ddi_dma_alloc_handle(devinfo, &ringbuf_dma_attr,
            DDI_DMA_SLEEP, 0, &xnfp->xnf_rx_ring_dma_handle) != DDI_SUCCESS)
                goto alloc_error;

        if (ddi_dma_mem_alloc(xnfp->xnf_rx_ring_dma_handle,
            PAGESIZE, &accattr, DDI_DMA_CONSISTENT,
            DDI_DMA_SLEEP, 0, &rptr, &len,
            &xnfp->xnf_rx_ring_dma_acchandle) != DDI_SUCCESS) {
                ddi_dma_free_handle(&xnfp->xnf_rx_ring_dma_handle);
                xnfp->xnf_rx_ring_dma_handle = NULL;
                goto alloc_error;
        }

        if ((rc = ddi_dma_addr_bind_handle(xnfp->xnf_rx_ring_dma_handle, NULL,
            rptr, PAGESIZE, DDI_DMA_RDWR | DDI_DMA_CONSISTENT,
            DDI_DMA_SLEEP, 0, &dma_cookie, &ncookies)) != DDI_DMA_MAPPED) {
                ddi_dma_mem_free(&xnfp->xnf_rx_ring_dma_acchandle);
                ddi_dma_free_handle(&xnfp->xnf_rx_ring_dma_handle);
                xnfp->xnf_rx_ring_dma_handle = NULL;
                xnfp->xnf_rx_ring_dma_acchandle = NULL;
                if (rc == DDI_DMA_NORESOURCES)
                        goto alloc_error;
                else
                        goto error;
        }

        ASSERT(ncookies == 1);
        bzero(rptr, PAGESIZE);
        /* LINTED: constant in conditional context */
        SHARED_RING_INIT((netif_rx_sring_t *)rptr);
        /* LINTED: constant in conditional context */
        FRONT_RING_INIT(&xnfp->xnf_rx_ring, (netif_rx_sring_t *)rptr, PAGESIZE);
        xnfp->xnf_rx_ring_phys_addr = dma_cookie.dmac_laddress;

        return (DDI_SUCCESS);

alloc_error:
        cmn_err(CE_WARN, "xnf%d: could not allocate enough DMA memory",
            ddi_get_instance(xnfp->xnf_devinfo));
error:
        xnf_release_dma_resources(xnfp);
        return (DDI_FAILURE);
}

/*
 * Release all DMA resources in the opposite order from acquisition
 */
static void
xnf_release_dma_resources(xnf_t *xnfp)
{
        int i;

        /*
         * Free receive buffers which are currently associated with
         * descriptors.
         */
        mutex_enter(&xnfp->xnf_rxlock);
        for (i = 0; i < NET_RX_RING_SIZE; i++) {
                xnf_buf_t *bp;

                if ((bp = xnfp->xnf_rx_pkt_info[i]) == NULL)
                        continue;
                xnfp->xnf_rx_pkt_info[i] = NULL;
                xnf_buf_put(xnfp, bp, B_FALSE);
        }
        mutex_exit(&xnfp->xnf_rxlock);

        /* Free the receive ring buffer. */
        if (xnfp->xnf_rx_ring_dma_acchandle != NULL) {
                (void) ddi_dma_unbind_handle(xnfp->xnf_rx_ring_dma_handle);
                ddi_dma_mem_free(&xnfp->xnf_rx_ring_dma_acchandle);
                ddi_dma_free_handle(&xnfp->xnf_rx_ring_dma_handle);
                xnfp->xnf_rx_ring_dma_acchandle = NULL;
        }
        /* Free the transmit ring buffer. */
        if (xnfp->xnf_tx_ring_dma_acchandle != NULL) {
                (void) ddi_dma_unbind_handle(xnfp->xnf_tx_ring_dma_handle);
                ddi_dma_mem_free(&xnfp->xnf_tx_ring_dma_acchandle);
                ddi_dma_free_handle(&xnfp->xnf_tx_ring_dma_handle);
                xnfp->xnf_tx_ring_dma_acchandle = NULL;
        }

}

/*
 * Release any packets and associated structures used by the TX ring.
 */
static void
xnf_release_mblks(xnf_t *xnfp)
{
        RING_IDX i;
        xnf_txid_t *tidp;

        for (i = 0, tidp = &xnfp->xnf_tx_pkt_id[0];
            i < NET_TX_RING_SIZE;
            i++, tidp++) {
                xnf_txbuf_t *txp = tidp->txbuf;

                if (txp != NULL) {
                        ASSERT(txp->tx_mp != NULL);
                        freemsg(txp->tx_mp);

                        xnf_txid_put(xnfp, tidp);
                        kmem_cache_free(xnfp->xnf_tx_buf_cache, txp);
                }
        }
}

static int
xnf_buf_constructor(void *buf, void *arg, int kmflag)
{
        int (*ddiflags)(caddr_t) = DDI_DMA_SLEEP;
        xnf_buf_t *bdesc = buf;
        xnf_t *xnfp = arg;
        ddi_dma_cookie_t dma_cookie;
        uint_t ncookies;
        size_t len;

        if (kmflag & KM_NOSLEEP)
                ddiflags = DDI_DMA_DONTWAIT;

        /* Allocate a DMA access handle for the buffer. */
        if (ddi_dma_alloc_handle(xnfp->xnf_devinfo, &rx_buf_dma_attr,
            ddiflags, 0, &bdesc->dma_handle) != DDI_SUCCESS)
                goto failure;

        /* Allocate DMA-able memory for buffer. */
        if (ddi_dma_mem_alloc(bdesc->dma_handle,
            PAGESIZE, &data_accattr, DDI_DMA_STREAMING, ddiflags, 0,
            &bdesc->buf, &len, &bdesc->acc_handle) != DDI_SUCCESS)
                goto failure_1;

        /* Bind to virtual address of buffer to get physical address. */
        if (ddi_dma_addr_bind_handle(bdesc->dma_handle, NULL,
            bdesc->buf, len, DDI_DMA_RDWR | DDI_DMA_STREAMING,
            ddiflags, 0, &dma_cookie, &ncookies) != DDI_DMA_MAPPED)
                goto failure_2;
        ASSERT(ncookies == 1);

        bdesc->free_rtn.free_func = xnf_buf_recycle;
        bdesc->free_rtn.free_arg = (caddr_t)bdesc;
        bdesc->xnfp = xnfp;
        bdesc->buf_phys = dma_cookie.dmac_laddress;
        bdesc->buf_mfn = pfn_to_mfn(xnf_btop(bdesc->buf_phys));
        bdesc->len = dma_cookie.dmac_size;
        bdesc->grant_ref = INVALID_GRANT_REF;
        bdesc->gen = xnfp->xnf_gen;

        atomic_inc_64(&xnfp->xnf_stat_buf_allocated);

        return (0);

failure_2:
        ddi_dma_mem_free(&bdesc->acc_handle);

failure_1:
        ddi_dma_free_handle(&bdesc->dma_handle);

failure:

        ASSERT(kmflag & KM_NOSLEEP); /* Cannot fail for KM_SLEEP. */
        return (-1);
}

static void
xnf_buf_destructor(void *buf, void *arg)
{
        xnf_buf_t *bdesc = buf;
        xnf_t *xnfp = arg;

        (void) ddi_dma_unbind_handle(bdesc->dma_handle);
        ddi_dma_mem_free(&bdesc->acc_handle);
        ddi_dma_free_handle(&bdesc->dma_handle);

        atomic_dec_64(&xnfp->xnf_stat_buf_allocated);
}

static xnf_buf_t *
xnf_buf_get(xnf_t *xnfp, int flags, boolean_t readonly)
{
        grant_ref_t gref;
        xnf_buf_t *bufp;

        /*
         * Usually grant references are more scarce than memory, so we
         * attempt to acquire a grant reference first.
         */
        gref = xnf_gref_get(xnfp);
        if (gref == INVALID_GRANT_REF)
                return (NULL);

        bufp = kmem_cache_alloc(xnfp->xnf_buf_cache, flags);
        if (bufp == NULL) {
                xnf_gref_put(xnfp, gref);
                return (NULL);
        }

        ASSERT3U(bufp->grant_ref, ==, INVALID_GRANT_REF);

        bufp->grant_ref = gref;

        if (bufp->gen != xnfp->xnf_gen)
                xnf_buf_refresh(bufp);

        gnttab_grant_foreign_access_ref(bufp->grant_ref,
            xvdi_get_oeid(bufp->xnfp->xnf_devinfo),
            bufp->buf_mfn, readonly ? 1 : 0);

        atomic_inc_64(&xnfp->xnf_stat_buf_outstanding);

        return (bufp);
}

static void
xnf_buf_put(xnf_t *xnfp, xnf_buf_t *bufp, boolean_t readonly)
{
        if (bufp->grant_ref != INVALID_GRANT_REF) {
                (void) gnttab_end_foreign_access_ref(
                    bufp->grant_ref, readonly ? 1 : 0);
                xnf_gref_put(xnfp, bufp->grant_ref);
                bufp->grant_ref = INVALID_GRANT_REF;
        }

        kmem_cache_free(xnfp->xnf_buf_cache, bufp);

        atomic_dec_64(&xnfp->xnf_stat_buf_outstanding);
}

/*
 * Refresh any cached data about a buffer after resume.
 */
static void
xnf_buf_refresh(xnf_buf_t *bdesc)
{
        bdesc->buf_mfn = pfn_to_mfn(xnf_btop(bdesc->buf_phys));
        bdesc->gen = bdesc->xnfp->xnf_gen;
}

/*
 * Streams `freeb' routine for `xnf_buf_t' when used as transmit
 * look-aside buffers.
 */
static void
xnf_buf_recycle(xnf_buf_t *bdesc)
{
        xnf_t *xnfp = bdesc->xnfp;

        xnf_buf_put(xnfp, bdesc, B_TRUE);
}

static int
xnf_tx_buf_constructor(void *buf, void *arg, int kmflag)
{
        int (*ddiflags)(caddr_t) = DDI_DMA_SLEEP;
        xnf_txbuf_t *txp = buf;
        xnf_t *xnfp = arg;

        if (kmflag & KM_NOSLEEP)
                ddiflags = DDI_DMA_DONTWAIT;

        if (ddi_dma_alloc_handle(xnfp->xnf_devinfo, &tx_buf_dma_attr,
            ddiflags, 0, &txp->tx_dma_handle) != DDI_SUCCESS) {
                ASSERT(kmflag & KM_NOSLEEP); /* Cannot fail for KM_SLEEP. */
                return (-1);
        }

        return (0);
}

static void
xnf_tx_buf_destructor(void *buf, void *arg)
{
        _NOTE(ARGUNUSED(arg));
        xnf_txbuf_t *txp = buf;

        ddi_dma_free_handle(&txp->tx_dma_handle);
}

/*
 * Statistics.
 */
static char *xnf_aux_statistics[] = {
        "tx_cksum_deferred",
        "rx_cksum_no_need",
        "interrupts",
        "unclaimed_interrupts",
        "tx_pullup",
        "tx_lookaside",
        "tx_drop",
        "tx_eth_hdr_split",
        "buf_allocated",
        "buf_outstanding",
        "gref_outstanding",
        "gref_failure",
        "gref_peak",
        "rx_allocb_fail",
        "rx_desballoc_fail",
};

static int
xnf_kstat_aux_update(kstat_t *ksp, int flag)
{
        xnf_t *xnfp;
        kstat_named_t *knp;

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

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

        /*
         * Assignment order must match that of the names in
         * xnf_aux_statistics.
         */
        (knp++)->value.ui64 = xnfp->xnf_stat_tx_cksum_deferred;
        (knp++)->value.ui64 = xnfp->xnf_stat_rx_cksum_no_need;

        (knp++)->value.ui64 = xnfp->xnf_stat_interrupts;
        (knp++)->value.ui64 = xnfp->xnf_stat_unclaimed_interrupts;
        (knp++)->value.ui64 = xnfp->xnf_stat_tx_pullup;
        (knp++)->value.ui64 = xnfp->xnf_stat_tx_lookaside;
        (knp++)->value.ui64 = xnfp->xnf_stat_tx_drop;
        (knp++)->value.ui64 = xnfp->xnf_stat_tx_eth_hdr_split;

        (knp++)->value.ui64 = xnfp->xnf_stat_buf_allocated;
        (knp++)->value.ui64 = xnfp->xnf_stat_buf_outstanding;
        (knp++)->value.ui64 = xnfp->xnf_stat_gref_outstanding;
        (knp++)->value.ui64 = xnfp->xnf_stat_gref_failure;
        (knp++)->value.ui64 = xnfp->xnf_stat_gref_peak;
        (knp++)->value.ui64 = xnfp->xnf_stat_rx_allocb_fail;
        (knp++)->value.ui64 = xnfp->xnf_stat_rx_desballoc_fail;

        return (0);
}

static boolean_t
xnf_kstat_init(xnf_t *xnfp)
{
        int nstat = sizeof (xnf_aux_statistics) /
            sizeof (xnf_aux_statistics[0]);
        char **cp = xnf_aux_statistics;
        kstat_named_t *knp;

        /*
         * Create and initialise kstats.
         */
        if ((xnfp->xnf_kstat_aux = kstat_create("xnf",
            ddi_get_instance(xnfp->xnf_devinfo),
            "aux_statistics", "net", KSTAT_TYPE_NAMED,
            nstat, 0)) == NULL)
                return (B_FALSE);

        xnfp->xnf_kstat_aux->ks_private = xnfp;
        xnfp->xnf_kstat_aux->ks_update = xnf_kstat_aux_update;

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

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

        kstat_install(xnfp->xnf_kstat_aux);

        return (B_TRUE);
}

static int
xnf_stat(void *arg, uint_t stat, uint64_t *val)
{
        xnf_t *xnfp = arg;

        mutex_enter(&xnfp->xnf_rxlock);
        mutex_enter(&xnfp->xnf_txlock);

#define mac_stat(q, r)                          \
        case (MAC_STAT_##q):                    \
                *val = xnfp->xnf_stat_##r;      \
                break

#define ether_stat(q, r)                        \
        case (ETHER_STAT_##q):                  \
                *val = xnfp->xnf_stat_##r;      \
                break

        switch (stat) {

        mac_stat(IPACKETS, ipackets);
        mac_stat(OPACKETS, opackets);
        mac_stat(RBYTES, rbytes);
        mac_stat(OBYTES, obytes);
        mac_stat(NORCVBUF, norxbuf);
        mac_stat(IERRORS, errrx);
        mac_stat(NOXMTBUF, tx_defer);

        ether_stat(MACRCV_ERRORS, mac_rcv_error);
        ether_stat(TOOSHORT_ERRORS, runt);

        /* always claim to be in full duplex mode */
        case ETHER_STAT_LINK_DUPLEX:
                *val = LINK_DUPLEX_FULL;
                break;

        /* always claim to be at 1Gb/s link speed */
        case MAC_STAT_IFSPEED:
                *val = 1000000000ull;
                break;

        default:
                mutex_exit(&xnfp->xnf_txlock);
                mutex_exit(&xnfp->xnf_rxlock);

                return (ENOTSUP);
        }

#undef mac_stat
#undef ether_stat

        mutex_exit(&xnfp->xnf_txlock);
        mutex_exit(&xnfp->xnf_rxlock);

        return (0);
}

static int
xnf_change_mtu(xnf_t *xnfp, uint32_t mtu)
{
        if (mtu > ETHERMTU) {
                if (!xnf_enable_tx_sg) {
                        dev_err(xnfp->xnf_devinfo, CE_WARN, "MTU limited to %d "
                            "because scatter-gather is disabled for transmit "
                            "in driver settings", ETHERMTU);
                        return (EINVAL);
                } else if (!xnf_enable_rx_sg) {
                        dev_err(xnfp->xnf_devinfo, CE_WARN, "MTU limited to %d "
                            "because scatter-gather is disabled for receive "
                            "in driver settings", ETHERMTU);
                        return (EINVAL);
                } else if (!xnfp->xnf_be_tx_sg) {
                        dev_err(xnfp->xnf_devinfo, CE_WARN, "MTU limited to %d "
                            "because backend doesn't support scatter-gather",
                            ETHERMTU);
                        return (EINVAL);
                }
                if (mtu > XNF_MAXPKT)
                        return (EINVAL);
        }
        int error = mac_maxsdu_update(xnfp->xnf_mh, mtu);
        if (error == 0)
                xnfp->xnf_mtu = mtu;

        return (error);
}

/*ARGSUSED*/
static int
xnf_getprop(void *data, const char *prop_name, mac_prop_id_t prop_id,
    uint_t prop_val_size, void *prop_val)
{
        xnf_t *xnfp = data;

        switch (prop_id) {
        case MAC_PROP_MTU:
                ASSERT(prop_val_size >= sizeof (uint32_t));
                bcopy(&xnfp->xnf_mtu, prop_val, sizeof (uint32_t));
                break;
        default:
                return (ENOTSUP);
        }
        return (0);
}

/*ARGSUSED*/
static int
xnf_setprop(void *data, const char *prop_name, mac_prop_id_t prop_id,
    uint_t prop_val_size, const void *prop_val)
{
        xnf_t *xnfp = data;
        uint32_t new_mtu;
        int error;

        switch (prop_id) {
        case MAC_PROP_MTU:
                ASSERT(prop_val_size >= sizeof (uint32_t));
                bcopy(prop_val, &new_mtu, sizeof (new_mtu));
                error = xnf_change_mtu(xnfp, new_mtu);
                break;
        default:
                return (ENOTSUP);
        }

        return (error);
}

/*ARGSUSED*/
static void
xnf_propinfo(void *data, const char *prop_name, mac_prop_id_t prop_id,
    mac_prop_info_handle_t prop_handle)
{
        switch (prop_id) {
        case MAC_PROP_MTU:
                mac_prop_info_set_range_uint32(prop_handle, 0, XNF_MAXPKT);
                break;
        default:
                break;
        }
}

static boolean_t
xnf_getcapab(void *arg, mac_capab_t cap, void *cap_data)
{
        xnf_t *xnfp = arg;

        switch (cap) {
        case MAC_CAPAB_HCKSUM: {
                uint32_t *capab = cap_data;

                /*
                 * Whilst the flag used to communicate with the IO
                 * domain is called "NETTXF_csum_blank", the checksum
                 * in the packet must contain the pseudo-header
                 * checksum and not zero.
                 *
                 * To help out the IO domain, we might use
                 * HCKSUM_INET_PARTIAL. Unfortunately our stack will
                 * then use checksum offload for IPv6 packets, which
                 * the IO domain can't handle.
                 *
                 * As a result, we declare outselves capable of
                 * HCKSUM_INET_FULL_V4. This means that we receive
                 * IPv4 packets from the stack with a blank checksum
                 * field and must insert the pseudo-header checksum
                 * before passing the packet to the IO domain.
                 */
                *capab = HCKSUM_INET_FULL_V4;

                /*
                 * TODO: query the "feature-ipv6-csum-offload" capability.
                 * If enabled, that could allow us to use HCKSUM_INET_PARTIAL.
                 */

                break;
        }
        case MAC_CAPAB_LSO: {
                if (!xnfp->xnf_be_lso)
                        return (B_FALSE);

                mac_capab_lso_t *lso = cap_data;
                lso->lso_flags = LSO_TX_BASIC_TCP_IPV4;
                lso->lso_basic_tcp_ipv4.lso_max = IP_MAXPACKET;
                break;
        }
        default:
                return (B_FALSE);
        }

        return (B_TRUE);
}

/*
 * The state of the peer has changed - react accordingly.
 */
static void
oe_state_change(dev_info_t *dip, ddi_eventcookie_t id,
    void *arg, void *impl_data)
{
        _NOTE(ARGUNUSED(id, arg));
        xnf_t *xnfp = ddi_get_driver_private(dip);
        XenbusState new_state = *(XenbusState *)impl_data;

        ASSERT(xnfp != NULL);

        switch (new_state) {
        case XenbusStateUnknown:
        case XenbusStateInitialising:
        case XenbusStateInitialised:
        case XenbusStateClosing:
        case XenbusStateClosed:
        case XenbusStateReconfiguring:
        case XenbusStateReconfigured:
                break;

        case XenbusStateInitWait:
                xnf_read_config(xnfp);

                if (!xnfp->xnf_be_rx_copy) {
                        cmn_err(CE_WARN,
                            "The xnf driver requires a dom0 that "
                            "supports 'feature-rx-copy'.");
                        (void) xvdi_switch_state(xnfp->xnf_devinfo,
                            XBT_NULL, XenbusStateClosed);
                        break;
                }

                /*
                 * Connect to the backend.
                 */
                xnf_be_connect(xnfp);

                /*
                 * Our MAC address as discovered by xnf_read_config().
                 */
                mac_unicst_update(xnfp->xnf_mh, xnfp->xnf_mac_addr);

                /*
                 * We do not know if some features such as LSO are supported
                 * until we connect to the backend. We request the MAC layer
                 * to poll our capabilities again.
                 */
                mac_capab_update(xnfp->xnf_mh);

                break;

        case XenbusStateConnected:
                mutex_enter(&xnfp->xnf_rxlock);
                mutex_enter(&xnfp->xnf_txlock);

                xnfp->xnf_connected = B_TRUE;
                /*
                 * Wake up any threads waiting to send data to
                 * backend.
                 */
                cv_broadcast(&xnfp->xnf_cv_state);

                mutex_exit(&xnfp->xnf_txlock);
                mutex_exit(&xnfp->xnf_rxlock);

                /*
                 * Kick the peer in case it missed any transmits
                 * request in the TX ring.
                 */
                ec_notify_via_evtchn(xnfp->xnf_evtchn);

                /*
                 * There may already be completed receive requests in
                 * the ring sent by backend after it gets connected
                 * but before we see its state change here, so we call
                 * xnf_intr() to handle them, if any.
                 */
                (void) xnf_intr((caddr_t)xnfp);

                /*
                 * Mark the link up now that we are connected.
                 */
                mac_link_update(xnfp->xnf_mh, LINK_STATE_UP);

                /*
                 * Tell the backend about the multicast addresses in
                 * which we are interested.
                 */
                mac_multicast_refresh(xnfp->xnf_mh, NULL, xnfp, B_TRUE);

                break;

        default:
                break;
        }
}