x86/xen: resume timer irqs early

[linux/fpc-iii.git] / drivers / net / xen-netback / netback.c

/*
 * Back-end of the driver for virtual network devices. This portion of the
 * driver exports a 'unified' network-device interface that can be accessed
 * by any operating system that implements a compatible front end. A
 * reference front-end implementation can be found in:
 *  drivers/net/xen-netfront.c
 *
 * Copyright (c) 2002-2005, K A Fraser
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation; or, when distributed
 * separately from the Linux kernel or incorporated into other
 * software packages, subject to the following license:
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this source file (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include "common.h"

#include <linux/kthread.h>
#include <linux/if_vlan.h>
#include <linux/udp.h>

#include <net/tcp.h>
#include <net/ip6_checksum.h>

#include <xen/xen.h>
#include <xen/events.h>
#include <xen/interface/memory.h>

#include <asm/xen/hypercall.h>
#include <asm/xen/page.h>

/* Provide an option to disable split event channels at load time as
 * event channels are limited resource. Split event channels are
 * enabled by default.
 */
bool separate_tx_rx_irq = 1;
module_param(separate_tx_rx_irq, bool, 0644);

/*
 * This is the maximum slots a skb can have. If a guest sends a skb
 * which exceeds this limit it is considered malicious.
 */
#define FATAL_SKB_SLOTS_DEFAULT 20
static unsigned int fatal_skb_slots = FATAL_SKB_SLOTS_DEFAULT;
module_param(fatal_skb_slots, uint, 0444);

/*
 * To avoid confusion, we define XEN_NETBK_LEGACY_SLOTS_MAX indicating
 * the maximum slots a valid packet can use. Now this value is defined
 * to be XEN_NETIF_NR_SLOTS_MIN, which is supposed to be supported by
 * all backend.
 */
#define XEN_NETBK_LEGACY_SLOTS_MAX XEN_NETIF_NR_SLOTS_MIN

/*
 * If head != INVALID_PENDING_RING_IDX, it means this tx request is head of
 * one or more merged tx requests, otherwise it is the continuation of
 * previous tx request.
 */
static inline int pending_tx_is_head(struct xenvif *vif, RING_IDX idx)
{
        return vif->pending_tx_info[idx].head != INVALID_PENDING_RING_IDX;
}

static void xenvif_idx_release(struct xenvif *vif, u16 pending_idx,
                               u8 status);

static void make_tx_response(struct xenvif *vif,
                             struct xen_netif_tx_request *txp,
                             s8       st);

static inline int tx_work_todo(struct xenvif *vif);
static inline int rx_work_todo(struct xenvif *vif);

static struct xen_netif_rx_response *make_rx_response(struct xenvif *vif,
                                             u16      id,
                                             s8       st,
                                             u16      offset,
                                             u16      size,
                                             u16      flags);

static inline unsigned long idx_to_pfn(struct xenvif *vif,
                                       u16 idx)
{
        return page_to_pfn(vif->mmap_pages[idx]);
}

static inline unsigned long idx_to_kaddr(struct xenvif *vif,
                                         u16 idx)
{
        return (unsigned long)pfn_to_kaddr(idx_to_pfn(vif, idx));
}

/*
 * This is the amount of packet we copy rather than map, so that the
 * guest can't fiddle with the contents of the headers while we do
 * packet processing on them (netfilter, routing, etc).
 */
#define PKT_PROT_LEN    (ETH_HLEN + \
                         VLAN_HLEN + \
                         sizeof(struct iphdr) + MAX_IPOPTLEN + \
                         sizeof(struct tcphdr) + MAX_TCP_OPTION_SPACE)

static u16 frag_get_pending_idx(skb_frag_t *frag)
{
        return (u16)frag->page_offset;
}

static void frag_set_pending_idx(skb_frag_t *frag, u16 pending_idx)
{
        frag->page_offset = pending_idx;
}

static inline pending_ring_idx_t pending_index(unsigned i)
{
        return i & (MAX_PENDING_REQS-1);
}

static inline pending_ring_idx_t nr_pending_reqs(struct xenvif *vif)
{
        return MAX_PENDING_REQS -
                vif->pending_prod + vif->pending_cons;
}

static int max_required_rx_slots(struct xenvif *vif)
{
        int max = DIV_ROUND_UP(vif->dev->mtu, PAGE_SIZE);

        /* XXX FIXME: RX path dependent on MAX_SKB_FRAGS */
        if (vif->can_sg || vif->gso || vif->gso_prefix)
                max += MAX_SKB_FRAGS + 1; /* extra_info + frags */

        return max;
}

int xenvif_rx_ring_full(struct xenvif *vif)
{
        RING_IDX peek   = vif->rx_req_cons_peek;
        RING_IDX needed = max_required_rx_slots(vif);

        return ((vif->rx.sring->req_prod - peek) < needed) ||
               ((vif->rx.rsp_prod_pvt + XEN_NETIF_RX_RING_SIZE - peek) < needed);
}

int xenvif_must_stop_queue(struct xenvif *vif)
{
        if (!xenvif_rx_ring_full(vif))
                return 0;

        vif->rx.sring->req_event = vif->rx_req_cons_peek +
                max_required_rx_slots(vif);
        mb(); /* request notification /then/ check the queue */

        return xenvif_rx_ring_full(vif);
}

/*
 * Returns true if we should start a new receive buffer instead of
 * adding 'size' bytes to a buffer which currently contains 'offset'
 * bytes.
 */
static bool start_new_rx_buffer(int offset, unsigned long size, int head)
{
        /* simple case: we have completely filled the current buffer. */
        if (offset == MAX_BUFFER_OFFSET)
                return true;

        /*
         * complex case: start a fresh buffer if the current frag
         * would overflow the current buffer but only if:
         *     (i)   this frag would fit completely in the next buffer
         * and (ii)  there is already some data in the current buffer
         * and (iii) this is not the head buffer.
         *
         * Where:
         * - (i) stops us splitting a frag into two copies
         *   unless the frag is too large for a single buffer.
         * - (ii) stops us from leaving a buffer pointlessly empty.
         * - (iii) stops us leaving the first buffer
         *   empty. Strictly speaking this is already covered
         *   by (ii) but is explicitly checked because
         *   netfront relies on the first buffer being
         *   non-empty and can crash otherwise.
         *
         * This means we will effectively linearise small
         * frags but do not needlessly split large buffers
         * into multiple copies tend to give large frags their
         * own buffers as before.
         */
        BUG_ON(size > MAX_BUFFER_OFFSET);
        if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
                return true;

        return false;
}

struct xenvif_count_slot_state {
        unsigned long copy_off;
        bool head;
};

unsigned int xenvif_count_frag_slots(struct xenvif *vif,
                                     unsigned long offset, unsigned long size,
                                     struct xenvif_count_slot_state *state)
{
        unsigned count = 0;

        offset &= ~PAGE_MASK;

        while (size > 0) {
                unsigned long bytes;

                bytes = PAGE_SIZE - offset;

                if (bytes > size)
                        bytes = size;

                if (start_new_rx_buffer(state->copy_off, bytes, state->head)) {
                        count++;
                        state->copy_off = 0;
                }

                if (state->copy_off + bytes > MAX_BUFFER_OFFSET)
                        bytes = MAX_BUFFER_OFFSET - state->copy_off;

                state->copy_off += bytes;

                offset += bytes;
                size -= bytes;

                if (offset == PAGE_SIZE)
                        offset = 0;

                state->head = false;
        }

        return count;
}

/*
 * Figure out how many ring slots we're going to need to send @skb to
 * the guest. This function is essentially a dry run of
 * xenvif_gop_frag_copy.
 */
unsigned int xenvif_count_skb_slots(struct xenvif *vif, struct sk_buff *skb)
{
        struct xenvif_count_slot_state state;
        unsigned int count;
        unsigned char *data;
        unsigned i;

        state.head = true;
        state.copy_off = 0;

        /* Slot for the first (partial) page of data. */
        count = 1;

        /* Need a slot for the GSO prefix for GSO extra data? */
        if (skb_shinfo(skb)->gso_size)
                count++;

        data = skb->data;
        while (data < skb_tail_pointer(skb)) {
                unsigned long offset = offset_in_page(data);
                unsigned long size = PAGE_SIZE - offset;

                if (data + size > skb_tail_pointer(skb))
                        size = skb_tail_pointer(skb) - data;

                count += xenvif_count_frag_slots(vif, offset, size, &state);

                data += size;
        }

        for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
                unsigned long size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
                unsigned long offset = skb_shinfo(skb)->frags[i].page_offset;

                count += xenvif_count_frag_slots(vif, offset, size, &state);
        }
        return count;
}

struct netrx_pending_operations {
        unsigned copy_prod, copy_cons;
        unsigned meta_prod, meta_cons;
        struct gnttab_copy *copy;
        struct xenvif_rx_meta *meta;
        int copy_off;
        grant_ref_t copy_gref;
};

static struct xenvif_rx_meta *get_next_rx_buffer(struct xenvif *vif,
                                                 struct netrx_pending_operations *npo)
{
        struct xenvif_rx_meta *meta;
        struct xen_netif_rx_request *req;

        req = RING_GET_REQUEST(&vif->rx, vif->rx.req_cons++);

        meta = npo->meta + npo->meta_prod++;
        meta->gso_size = 0;
        meta->size = 0;
        meta->id = req->id;

        npo->copy_off = 0;
        npo->copy_gref = req->gref;

        return meta;
}

/*
 * Set up the grant operations for this fragment. If it's a flipping
 * interface, we also set up the unmap request from here.
 */
static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
                                 struct netrx_pending_operations *npo,
                                 struct page *page, unsigned long size,
                                 unsigned long offset, int *head)
{
        struct gnttab_copy *copy_gop;
        struct xenvif_rx_meta *meta;
        unsigned long bytes;

        /* Data must not cross a page boundary. */
        BUG_ON(size + offset > PAGE_SIZE<<compound_order(page));

        meta = npo->meta + npo->meta_prod - 1;

        /* Skip unused frames from start of page */
        page += offset >> PAGE_SHIFT;
        offset &= ~PAGE_MASK;

        while (size > 0) {
                BUG_ON(offset >= PAGE_SIZE);
                BUG_ON(npo->copy_off > MAX_BUFFER_OFFSET);

                bytes = PAGE_SIZE - offset;

                if (bytes > size)
                        bytes = size;

                if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {
                        /*
                         * Netfront requires there to be some data in the head
                         * buffer.
                         */
                        BUG_ON(*head);

                        meta = get_next_rx_buffer(vif, npo);
                }

                if (npo->copy_off + bytes > MAX_BUFFER_OFFSET)
                        bytes = MAX_BUFFER_OFFSET - npo->copy_off;

                copy_gop = npo->copy + npo->copy_prod++;
                copy_gop->flags = GNTCOPY_dest_gref;
                copy_gop->len = bytes;

                copy_gop->source.domid = DOMID_SELF;
                copy_gop->source.u.gmfn = virt_to_mfn(page_address(page));
                copy_gop->source.offset = offset;

                copy_gop->dest.domid = vif->domid;
                copy_gop->dest.offset = npo->copy_off;
                copy_gop->dest.u.ref = npo->copy_gref;

                npo->copy_off += bytes;
                meta->size += bytes;

                offset += bytes;
                size -= bytes;

                /* Next frame */
                if (offset == PAGE_SIZE && size) {
                        BUG_ON(!PageCompound(page));
                        page++;
                        offset = 0;
                }

                /* Leave a gap for the GSO descriptor. */
                if (*head && skb_shinfo(skb)->gso_size && !vif->gso_prefix)
                        vif->rx.req_cons++;

                *head = 0; /* There must be something in this buffer now. */

        }
}

/*
 * Prepare an SKB to be transmitted to the frontend.
 *
 * This function is responsible for allocating grant operations, meta
 * structures, etc.
 *
 * It returns the number of meta structures consumed. The number of
 * ring slots used is always equal to the number of meta slots used
 * plus the number of GSO descriptors used. Currently, we use either
 * zero GSO descriptors (for non-GSO packets) or one descriptor (for
 * frontend-side LRO).
 */
static int xenvif_gop_skb(struct sk_buff *skb,
                          struct netrx_pending_operations *npo)
{
        struct xenvif *vif = netdev_priv(skb->dev);
        int nr_frags = skb_shinfo(skb)->nr_frags;
        int i;
        struct xen_netif_rx_request *req;
        struct xenvif_rx_meta *meta;
        unsigned char *data;
        int head = 1;
        int old_meta_prod;

        old_meta_prod = npo->meta_prod;

        /* Set up a GSO prefix descriptor, if necessary */
        if (skb_shinfo(skb)->gso_size && vif->gso_prefix) {
                req = RING_GET_REQUEST(&vif->rx, vif->rx.req_cons++);
                meta = npo->meta + npo->meta_prod++;
                meta->gso_size = skb_shinfo(skb)->gso_size;
                meta->size = 0;
                meta->id = req->id;
        }

        req = RING_GET_REQUEST(&vif->rx, vif->rx.req_cons++);
        meta = npo->meta + npo->meta_prod++;

        if (!vif->gso_prefix)
                meta->gso_size = skb_shinfo(skb)->gso_size;
        else
                meta->gso_size = 0;

        meta->size = 0;
        meta->id = req->id;
        npo->copy_off = 0;
        npo->copy_gref = req->gref;

        data = skb->data;
        while (data < skb_tail_pointer(skb)) {
                unsigned int offset = offset_in_page(data);
                unsigned int len = PAGE_SIZE - offset;

                if (data + len > skb_tail_pointer(skb))
                        len = skb_tail_pointer(skb) - data;

                xenvif_gop_frag_copy(vif, skb, npo,
                                     virt_to_page(data), len, offset, &head);
                data += len;
        }

        for (i = 0; i < nr_frags; i++) {
                xenvif_gop_frag_copy(vif, skb, npo,
                                     skb_frag_page(&skb_shinfo(skb)->frags[i]),
                                     skb_frag_size(&skb_shinfo(skb)->frags[i]),
                                     skb_shinfo(skb)->frags[i].page_offset,
                                     &head);
        }

        return npo->meta_prod - old_meta_prod;
}

/*
 * This is a twin to xenvif_gop_skb.  Assume that xenvif_gop_skb was
 * used to set up the operations on the top of
 * netrx_pending_operations, which have since been done.  Check that
 * they didn't give any errors and advance over them.
 */
static int xenvif_check_gop(struct xenvif *vif, int nr_meta_slots,
                            struct netrx_pending_operations *npo)
{
        struct gnttab_copy     *copy_op;
        int status = XEN_NETIF_RSP_OKAY;
        int i;

        for (i = 0; i < nr_meta_slots; i++) {
                copy_op = npo->copy + npo->copy_cons++;
                if (copy_op->status != GNTST_okay) {
                        netdev_dbg(vif->dev,
                                   "Bad status %d from copy to DOM%d.\n",
                                   copy_op->status, vif->domid);
                        status = XEN_NETIF_RSP_ERROR;
                }
        }

        return status;
}

static void xenvif_add_frag_responses(struct xenvif *vif, int status,
                                      struct xenvif_rx_meta *meta,
                                      int nr_meta_slots)
{
        int i;
        unsigned long offset;

        /* No fragments used */
        if (nr_meta_slots <= 1)
                return;

        nr_meta_slots--;

        for (i = 0; i < nr_meta_slots; i++) {
                int flags;
                if (i == nr_meta_slots - 1)
                        flags = 0;
                else
                        flags = XEN_NETRXF_more_data;

                offset = 0;
                make_rx_response(vif, meta[i].id, status, offset,
                                 meta[i].size, flags);
        }
}

struct skb_cb_overlay {
        int meta_slots_used;
};

static void xenvif_kick_thread(struct xenvif *vif)
{
        wake_up(&vif->wq);
}

void xenvif_rx_action(struct xenvif *vif)
{
        s8 status;
        u16 flags;
        struct xen_netif_rx_response *resp;
        struct sk_buff_head rxq;
        struct sk_buff *skb;
        LIST_HEAD(notify);
        int ret;
        int nr_frags;
        int count;
        unsigned long offset;
        struct skb_cb_overlay *sco;
        int need_to_notify = 0;

        struct netrx_pending_operations npo = {
                .copy  = vif->grant_copy_op,
                .meta  = vif->meta,
        };

        skb_queue_head_init(&rxq);

        count = 0;

        while ((skb = skb_dequeue(&vif->rx_queue)) != NULL) {
                vif = netdev_priv(skb->dev);
                nr_frags = skb_shinfo(skb)->nr_frags;

                sco = (struct skb_cb_overlay *)skb->cb;
                sco->meta_slots_used = xenvif_gop_skb(skb, &npo);

                count += nr_frags + 1;

                __skb_queue_tail(&rxq, skb);

                /* Filled the batch queue? */
                /* XXX FIXME: RX path dependent on MAX_SKB_FRAGS */
                if (count + MAX_SKB_FRAGS >= XEN_NETIF_RX_RING_SIZE)
                        break;
        }

        BUG_ON(npo.meta_prod > ARRAY_SIZE(vif->meta));

        if (!npo.copy_prod)
                return;

        BUG_ON(npo.copy_prod > ARRAY_SIZE(vif->grant_copy_op));
        gnttab_batch_copy(vif->grant_copy_op, npo.copy_prod);

        while ((skb = __skb_dequeue(&rxq)) != NULL) {
                sco = (struct skb_cb_overlay *)skb->cb;

                vif = netdev_priv(skb->dev);

                if (vif->meta[npo.meta_cons].gso_size && vif->gso_prefix) {
                        resp = RING_GET_RESPONSE(&vif->rx,
                                                 vif->rx.rsp_prod_pvt++);

                        resp->flags = XEN_NETRXF_gso_prefix | XEN_NETRXF_more_data;

                        resp->offset = vif->meta[npo.meta_cons].gso_size;
                        resp->id = vif->meta[npo.meta_cons].id;
                        resp->status = sco->meta_slots_used;

                        npo.meta_cons++;
                        sco->meta_slots_used--;
                }


                vif->dev->stats.tx_bytes += skb->len;
                vif->dev->stats.tx_packets++;

                status = xenvif_check_gop(vif, sco->meta_slots_used, &npo);

                if (sco->meta_slots_used == 1)
                        flags = 0;
                else
                        flags = XEN_NETRXF_more_data;

                if (skb->ip_summed == CHECKSUM_PARTIAL) /* local packet? */
                        flags |= XEN_NETRXF_csum_blank | XEN_NETRXF_data_validated;
                else if (skb->ip_summed == CHECKSUM_UNNECESSARY)
                        /* remote but checksummed. */
                        flags |= XEN_NETRXF_data_validated;

                offset = 0;
                resp = make_rx_response(vif, vif->meta[npo.meta_cons].id,
                                        status, offset,
                                        vif->meta[npo.meta_cons].size,
                                        flags);

                if (vif->meta[npo.meta_cons].gso_size && !vif->gso_prefix) {
                        struct xen_netif_extra_info *gso =
                                (struct xen_netif_extra_info *)
                                RING_GET_RESPONSE(&vif->rx,
                                                  vif->rx.rsp_prod_pvt++);

                        resp->flags |= XEN_NETRXF_extra_info;

                        gso->u.gso.size = vif->meta[npo.meta_cons].gso_size;
                        gso->u.gso.type = XEN_NETIF_GSO_TYPE_TCPV4;
                        gso->u.gso.pad = 0;
                        gso->u.gso.features = 0;

                        gso->type = XEN_NETIF_EXTRA_TYPE_GSO;
                        gso->flags = 0;
                }

                xenvif_add_frag_responses(vif, status,
                                          vif->meta + npo.meta_cons + 1,
                                          sco->meta_slots_used);

                RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&vif->rx, ret);

                if (ret)
                        need_to_notify = 1;

                xenvif_notify_tx_completion(vif);

                npo.meta_cons += sco->meta_slots_used;
                dev_kfree_skb(skb);
        }

        if (need_to_notify)
                notify_remote_via_irq(vif->rx_irq);

        /* More work to do? */
        if (!skb_queue_empty(&vif->rx_queue))
                xenvif_kick_thread(vif);
}

void xenvif_queue_tx_skb(struct xenvif *vif, struct sk_buff *skb)
{
        skb_queue_tail(&vif->rx_queue, skb);

        xenvif_kick_thread(vif);
}

void xenvif_check_rx_xenvif(struct xenvif *vif)
{
        int more_to_do;

        RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, more_to_do);

        if (more_to_do)
                napi_schedule(&vif->napi);
}

static void tx_add_credit(struct xenvif *vif)
{
        unsigned long max_burst, max_credit;

        /*
         * Allow a burst big enough to transmit a jumbo packet of up to 128kB.
         * Otherwise the interface can seize up due to insufficient credit.
         */
        max_burst = RING_GET_REQUEST(&vif->tx, vif->tx.req_cons)->size;
        max_burst = min(max_burst, 131072UL);
        max_burst = max(max_burst, vif->credit_bytes);

        /* Take care that adding a new chunk of credit doesn't wrap to zero. */
        max_credit = vif->remaining_credit + vif->credit_bytes;
        if (max_credit < vif->remaining_credit)
                max_credit = ULONG_MAX; /* wrapped: clamp to ULONG_MAX */

        vif->remaining_credit = min(max_credit, max_burst);
}

static void tx_credit_callback(unsigned long data)
{
        struct xenvif *vif = (struct xenvif *)data;
        tx_add_credit(vif);
        xenvif_check_rx_xenvif(vif);
}

static void xenvif_tx_err(struct xenvif *vif,
                          struct xen_netif_tx_request *txp, RING_IDX end)
{
        RING_IDX cons = vif->tx.req_cons;

        do {
                make_tx_response(vif, txp, XEN_NETIF_RSP_ERROR);
                if (cons == end)
                        break;
                txp = RING_GET_REQUEST(&vif->tx, cons++);
        } while (1);
        vif->tx.req_cons = cons;
}

static void xenvif_fatal_tx_err(struct xenvif *vif)
{
        netdev_err(vif->dev, "fatal error; disabling device\n");
        vif->disabled = true;
        xenvif_kick_thread(vif);
}

static int xenvif_count_requests(struct xenvif *vif,
                                 struct xen_netif_tx_request *first,
                                 struct xen_netif_tx_request *txp,
                                 int work_to_do)
{
        RING_IDX cons = vif->tx.req_cons;
        int slots = 0;
        int drop_err = 0;
        int more_data;

        if (!(first->flags & XEN_NETTXF_more_data))
                return 0;

        do {
                struct xen_netif_tx_request dropped_tx = { 0 };

                if (slots >= work_to_do) {
                        netdev_err(vif->dev,
                                   "Asked for %d slots but exceeds this limit\n",
                                   work_to_do);
                        xenvif_fatal_tx_err(vif);
                        return -ENODATA;
                }

                /* This guest is really using too many slots and
                 * considered malicious.
                 */
                if (unlikely(slots >= fatal_skb_slots)) {
                        netdev_err(vif->dev,
                                   "Malicious frontend using %d slots, threshold %u\n",
                                   slots, fatal_skb_slots);
                        xenvif_fatal_tx_err(vif);
                        return -E2BIG;
                }

                /* Xen network protocol had implicit dependency on
                 * MAX_SKB_FRAGS. XEN_NETBK_LEGACY_SLOTS_MAX is set to
                 * the historical MAX_SKB_FRAGS value 18 to honor the
                 * same behavior as before. Any packet using more than
                 * 18 slots but less than fatal_skb_slots slots is
                 * dropped
                 */
                if (!drop_err && slots >= XEN_NETBK_LEGACY_SLOTS_MAX) {
                        if (net_ratelimit())
                                netdev_dbg(vif->dev,
                                           "Too many slots (%d) exceeding limit (%d), dropping packet\n",
                                           slots, XEN_NETBK_LEGACY_SLOTS_MAX);
                        drop_err = -E2BIG;
                }

                if (drop_err)
                        txp = &dropped_tx;

                memcpy(txp, RING_GET_REQUEST(&vif->tx, cons + slots),
                       sizeof(*txp));

                /* If the guest submitted a frame >= 64 KiB then
                 * first->size overflowed and following slots will
                 * appear to be larger than the frame.
                 *
                 * This cannot be fatal error as there are buggy
                 * frontends that do this.
                 *
                 * Consume all slots and drop the packet.
                 */
                if (!drop_err && txp->size > first->size) {
                        if (net_ratelimit())
                                netdev_dbg(vif->dev,
                                           "Invalid tx request, slot size %u > remaining size %u\n",
                                           txp->size, first->size);
                        drop_err = -EIO;
                }

                first->size -= txp->size;
                slots++;

                if (unlikely((txp->offset + txp->size) > PAGE_SIZE)) {
                        netdev_err(vif->dev, "Cross page boundary, txp->offset: %x, size: %u\n",
                                 txp->offset, txp->size);
                        xenvif_fatal_tx_err(vif);
                        return -EINVAL;
                }

                more_data = txp->flags & XEN_NETTXF_more_data;

                if (!drop_err)
                        txp++;

        } while (more_data);

        if (drop_err) {
                xenvif_tx_err(vif, first, cons + slots);
                return drop_err;
        }

        return slots;
}

static struct page *xenvif_alloc_page(struct xenvif *vif,
                                      u16 pending_idx)
{
        struct page *page;

        page = alloc_page(GFP_ATOMIC|__GFP_COLD);
        if (!page)
                return NULL;
        vif->mmap_pages[pending_idx] = page;

        return page;
}

static struct gnttab_copy *xenvif_get_requests(struct xenvif *vif,
                                               struct sk_buff *skb,
                                               struct xen_netif_tx_request *txp,
                                               struct gnttab_copy *gop)
{
        struct skb_shared_info *shinfo = skb_shinfo(skb);
        skb_frag_t *frags = shinfo->frags;
        u16 pending_idx = *((u16 *)skb->data);
        u16 head_idx = 0;
        int slot, start;
        struct page *page;
        pending_ring_idx_t index, start_idx = 0;
        uint16_t dst_offset;
        unsigned int nr_slots;
        struct pending_tx_info *first = NULL;

        /* At this point shinfo->nr_frags is in fact the number of
         * slots, which can be as large as XEN_NETBK_LEGACY_SLOTS_MAX.
         */
        nr_slots = shinfo->nr_frags;

        /* Skip first skb fragment if it is on same page as header fragment. */
        start = (frag_get_pending_idx(&shinfo->frags[0]) == pending_idx);

        /* Coalesce tx requests, at this point the packet passed in
         * should be <= 64K. Any packets larger than 64K have been
         * handled in xenvif_count_requests().
         */
        for (shinfo->nr_frags = slot = start; slot < nr_slots;
             shinfo->nr_frags++) {
                struct pending_tx_info *pending_tx_info =
                        vif->pending_tx_info;

                page = alloc_page(GFP_ATOMIC|__GFP_COLD);
                if (!page)
                        goto err;

                dst_offset = 0;
                first = NULL;
                while (dst_offset < PAGE_SIZE && slot < nr_slots) {
                        gop->flags = GNTCOPY_source_gref;

                        gop->source.u.ref = txp->gref;
                        gop->source.domid = vif->domid;
                        gop->source.offset = txp->offset;

                        gop->dest.domid = DOMID_SELF;

                        gop->dest.offset = dst_offset;
                        gop->dest.u.gmfn = virt_to_mfn(page_address(page));

                        if (dst_offset + txp->size > PAGE_SIZE) {
                                /* This page can only merge a portion
                                 * of tx request. Do not increment any
                                 * pointer / counter here. The txp
                                 * will be dealt with in future
                                 * rounds, eventually hitting the
                                 * `else` branch.
                                 */
                                gop->len = PAGE_SIZE - dst_offset;
                                txp->offset += gop->len;
                                txp->size -= gop->len;
                                dst_offset += gop->len; /* quit loop */
                        } else {
                                /* This tx request can be merged in the page */
                                gop->len = txp->size;
                                dst_offset += gop->len;

                                index = pending_index(vif->pending_cons++);

                                pending_idx = vif->pending_ring[index];

                                memcpy(&pending_tx_info[pending_idx].req, txp,
                                       sizeof(*txp));

                                /* Poison these fields, corresponding
                                 * fields for head tx req will be set
                                 * to correct values after the loop.
                                 */
                                vif->mmap_pages[pending_idx] = (void *)(~0UL);
                                pending_tx_info[pending_idx].head =
                                        INVALID_PENDING_RING_IDX;

                                if (!first) {
                                        first = &pending_tx_info[pending_idx];
                                        start_idx = index;
                                        head_idx = pending_idx;
                                }

                                txp++;
                                slot++;
                        }

                        gop++;
                }

                first->req.offset = 0;
                first->req.size = dst_offset;
                first->head = start_idx;
                vif->mmap_pages[head_idx] = page;
                frag_set_pending_idx(&frags[shinfo->nr_frags], head_idx);
        }

        BUG_ON(shinfo->nr_frags > MAX_SKB_FRAGS);

        return gop;
err:
        /* Unwind, freeing all pages and sending error responses. */
        while (shinfo->nr_frags-- > start) {
                xenvif_idx_release(vif,
                                frag_get_pending_idx(&frags[shinfo->nr_frags]),
                                XEN_NETIF_RSP_ERROR);
        }
        /* The head too, if necessary. */
        if (start)
                xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_ERROR);

        return NULL;
}

static int xenvif_tx_check_gop(struct xenvif *vif,
                               struct sk_buff *skb,
                               struct gnttab_copy **gopp)
{
        struct gnttab_copy *gop = *gopp;
        u16 pending_idx = *((u16 *)skb->data);
        struct skb_shared_info *shinfo = skb_shinfo(skb);
        struct pending_tx_info *tx_info;
        int nr_frags = shinfo->nr_frags;
        int i, err, start;
        u16 peek; /* peek into next tx request */

        /* Check status of header. */
        err = gop->status;
        if (unlikely(err))
                xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_ERROR);

        /* Skip first skb fragment if it is on same page as header fragment. */
        start = (frag_get_pending_idx(&shinfo->frags[0]) == pending_idx);

        for (i = start; i < nr_frags; i++) {
                int j, newerr;
                pending_ring_idx_t head;

                pending_idx = frag_get_pending_idx(&shinfo->frags[i]);
                tx_info = &vif->pending_tx_info[pending_idx];
                head = tx_info->head;

                /* Check error status: if okay then remember grant handle. */
                do {
                        newerr = (++gop)->status;
                        if (newerr)
                                break;
                        peek = vif->pending_ring[pending_index(++head)];
                } while (!pending_tx_is_head(vif, peek));

                if (likely(!newerr)) {
                        /* Had a previous error? Invalidate this fragment. */
                        if (unlikely(err))
                                xenvif_idx_release(vif, pending_idx,
                                                   XEN_NETIF_RSP_OKAY);
                        continue;
                }

                /* Error on this fragment: respond to client with an error. */
                xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_ERROR);

                /* Not the first error? Preceding frags already invalidated. */
                if (err)
                        continue;

                /* First error: invalidate header and preceding fragments. */
                pending_idx = *((u16 *)skb->data);
                xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_OKAY);
                for (j = start; j < i; j++) {
                        pending_idx = frag_get_pending_idx(&shinfo->frags[j]);
                        xenvif_idx_release(vif, pending_idx,
                                           XEN_NETIF_RSP_OKAY);
                }

                /* Remember the error: invalidate all subsequent fragments. */
                err = newerr;
        }

        *gopp = gop + 1;
        return err;
}

static void xenvif_fill_frags(struct xenvif *vif, struct sk_buff *skb)
{
        struct skb_shared_info *shinfo = skb_shinfo(skb);
        int nr_frags = shinfo->nr_frags;
        int i;

        for (i = 0; i < nr_frags; i++) {
                skb_frag_t *frag = shinfo->frags + i;
                struct xen_netif_tx_request *txp;
                struct page *page;
                u16 pending_idx;

                pending_idx = frag_get_pending_idx(frag);

                txp = &vif->pending_tx_info[pending_idx].req;
                page = virt_to_page(idx_to_kaddr(vif, pending_idx));
                __skb_fill_page_desc(skb, i, page, txp->offset, txp->size);
                skb->len += txp->size;
                skb->data_len += txp->size;
                skb->truesize += txp->size;

                /* Take an extra reference to offset xenvif_idx_release */
                get_page(vif->mmap_pages[pending_idx]);
                xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_OKAY);
        }
}

static int xenvif_get_extras(struct xenvif *vif,
                                struct xen_netif_extra_info *extras,
                                int work_to_do)
{
        struct xen_netif_extra_info extra;
        RING_IDX cons = vif->tx.req_cons;

        do {
                if (unlikely(work_to_do-- <= 0)) {
                        netdev_err(vif->dev, "Missing extra info\n");
                        xenvif_fatal_tx_err(vif);
                        return -EBADR;
                }

                memcpy(&extra, RING_GET_REQUEST(&vif->tx, cons),
                       sizeof(extra));
                if (unlikely(!extra.type ||
                             extra.type >= XEN_NETIF_EXTRA_TYPE_MAX)) {
                        vif->tx.req_cons = ++cons;
                        netdev_err(vif->dev,
                                   "Invalid extra type: %d\n", extra.type);
                        xenvif_fatal_tx_err(vif);
                        return -EINVAL;
                }

                memcpy(&extras[extra.type - 1], &extra, sizeof(extra));
                vif->tx.req_cons = ++cons;
        } while (extra.flags & XEN_NETIF_EXTRA_FLAG_MORE);

        return work_to_do;
}

static int xenvif_set_skb_gso(struct xenvif *vif,
                              struct sk_buff *skb,
                              struct xen_netif_extra_info *gso)
{
        if (!gso->u.gso.size) {
                netdev_err(vif->dev, "GSO size must not be zero.\n");
                xenvif_fatal_tx_err(vif);
                return -EINVAL;
        }

        /* Currently only TCPv4 S.O. is supported. */
        if (gso->u.gso.type != XEN_NETIF_GSO_TYPE_TCPV4) {
                netdev_err(vif->dev, "Bad GSO type %d.\n", gso->u.gso.type);
                xenvif_fatal_tx_err(vif);
                return -EINVAL;
        }

        skb_shinfo(skb)->gso_size = gso->u.gso.size;
        skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;

        /* Header must be checked, and gso_segs computed. */
        skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY;
        skb_shinfo(skb)->gso_segs = 0;

        return 0;
}

static int checksum_setup(struct xenvif *vif, struct sk_buff *skb)
{
        struct iphdr *iph;
        int err = -EPROTO;
        int recalculate_partial_csum = 0;

        /*
         * A GSO SKB must be CHECKSUM_PARTIAL. However some buggy
         * peers can fail to set NETRXF_csum_blank when sending a GSO
         * frame. In this case force the SKB to CHECKSUM_PARTIAL and
         * recalculate the partial checksum.
         */
        if (skb->ip_summed != CHECKSUM_PARTIAL && skb_is_gso(skb)) {
                vif->rx_gso_checksum_fixup++;
                skb->ip_summed = CHECKSUM_PARTIAL;
                recalculate_partial_csum = 1;
        }

        /* A non-CHECKSUM_PARTIAL SKB does not require setup. */
        if (skb->ip_summed != CHECKSUM_PARTIAL)
                return 0;

        if (skb->protocol != htons(ETH_P_IP))
                goto out;

        iph = (void *)skb->data;
        switch (iph->protocol) {
        case IPPROTO_TCP:
                if (!skb_partial_csum_set(skb, 4 * iph->ihl,
                                          offsetof(struct tcphdr, check)))
                        goto out;

                if (recalculate_partial_csum) {
                        struct tcphdr *tcph = tcp_hdr(skb);
                        tcph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
                                                         skb->len - iph->ihl*4,
                                                         IPPROTO_TCP, 0);
                }
                break;
        case IPPROTO_UDP:
                if (!skb_partial_csum_set(skb, 4 * iph->ihl,
                                          offsetof(struct udphdr, check)))
                        goto out;

                if (recalculate_partial_csum) {
                        struct udphdr *udph = udp_hdr(skb);
                        udph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
                                                         skb->len - iph->ihl*4,
                                                         IPPROTO_UDP, 0);
                }
                break;
        default:
                if (net_ratelimit())
                        netdev_err(vif->dev,
                                   "Attempting to checksum a non-TCP/UDP packet, dropping a protocol %d packet\n",
                                   iph->protocol);
                goto out;
        }

        err = 0;

out:
        return err;
}

static bool tx_credit_exceeded(struct xenvif *vif, unsigned size)
{
        u64 now = get_jiffies_64();
        u64 next_credit = vif->credit_window_start +
                msecs_to_jiffies(vif->credit_usec / 1000);

        /* Timer could already be pending in rare cases. */
        if (timer_pending(&vif->credit_timeout))
                return true;

        /* Passed the point where we can replenish credit? */
        if (time_after_eq64(now, next_credit)) {
                vif->credit_window_start = now;
                tx_add_credit(vif);
        }

        /* Still too big to send right now? Set a callback. */
        if (size > vif->remaining_credit) {
                vif->credit_timeout.data     =
                        (unsigned long)vif;
                vif->credit_timeout.function =
                        tx_credit_callback;
                mod_timer(&vif->credit_timeout,
                          next_credit);
                vif->credit_window_start = next_credit;

                return true;
        }

        return false;
}

static unsigned xenvif_tx_build_gops(struct xenvif *vif)
{
        struct gnttab_copy *gop = vif->tx_copy_ops, *request_gop;
        struct sk_buff *skb;
        int ret;

        while ((nr_pending_reqs(vif) + XEN_NETBK_LEGACY_SLOTS_MAX
                < MAX_PENDING_REQS)) {
                struct xen_netif_tx_request txreq;
                struct xen_netif_tx_request txfrags[XEN_NETBK_LEGACY_SLOTS_MAX];
                struct page *page;
                struct xen_netif_extra_info extras[XEN_NETIF_EXTRA_TYPE_MAX-1];
                u16 pending_idx;
                RING_IDX idx;
                int work_to_do;
                unsigned int data_len;
                pending_ring_idx_t index;

                if (vif->tx.sring->req_prod - vif->tx.req_cons >
                    XEN_NETIF_TX_RING_SIZE) {
                        netdev_err(vif->dev,
                                   "Impossible number of requests. "
                                   "req_prod %d, req_cons %d, size %ld\n",
                                   vif->tx.sring->req_prod, vif->tx.req_cons,
                                   XEN_NETIF_TX_RING_SIZE);
                        xenvif_fatal_tx_err(vif);
                        break;
                }

                RING_FINAL_CHECK_FOR_REQUESTS(&vif->tx, work_to_do);
                if (!work_to_do)
                        break;

                idx = vif->tx.req_cons;
                rmb(); /* Ensure that we see the request before we copy it. */
                memcpy(&txreq, RING_GET_REQUEST(&vif->tx, idx), sizeof(txreq));

                /* Credit-based scheduling. */
                if (txreq.size > vif->remaining_credit &&
                    tx_credit_exceeded(vif, txreq.size))
                        break;

                vif->remaining_credit -= txreq.size;

                work_to_do--;
                vif->tx.req_cons = ++idx;

                memset(extras, 0, sizeof(extras));
                if (txreq.flags & XEN_NETTXF_extra_info) {
                        work_to_do = xenvif_get_extras(vif, extras,
                                                       work_to_do);
                        idx = vif->tx.req_cons;
                        if (unlikely(work_to_do < 0))
                                break;
                }

                ret = xenvif_count_requests(vif, &txreq, txfrags, work_to_do);
                if (unlikely(ret < 0))
                        break;

                idx += ret;

                if (unlikely(txreq.size < ETH_HLEN)) {
                        netdev_dbg(vif->dev,
                                   "Bad packet size: %d\n", txreq.size);
                        xenvif_tx_err(vif, &txreq, idx);
                        break;
                }

                /* No crossing a page as the payload mustn't fragment. */
                if (unlikely((txreq.offset + txreq.size) > PAGE_SIZE)) {
                        netdev_err(vif->dev,
                                   "txreq.offset: %x, size: %u, end: %lu\n",
                                   txreq.offset, txreq.size,
                                   (txreq.offset&~PAGE_MASK) + txreq.size);
                        xenvif_fatal_tx_err(vif);
                        break;
                }

                index = pending_index(vif->pending_cons);
                pending_idx = vif->pending_ring[index];

                data_len = (txreq.size > PKT_PROT_LEN &&
                            ret < XEN_NETBK_LEGACY_SLOTS_MAX) ?
                        PKT_PROT_LEN : txreq.size;

                skb = alloc_skb(data_len + NET_SKB_PAD + NET_IP_ALIGN,
                                GFP_ATOMIC | __GFP_NOWARN);
                if (unlikely(skb == NULL)) {
                        netdev_dbg(vif->dev,
                                   "Can't allocate a skb in start_xmit.\n");
                        xenvif_tx_err(vif, &txreq, idx);
                        break;
                }

                /* Packets passed to netif_rx() must have some headroom. */
                skb_reserve(skb, NET_SKB_PAD + NET_IP_ALIGN);

                if (extras[XEN_NETIF_EXTRA_TYPE_GSO - 1].type) {
                        struct xen_netif_extra_info *gso;
                        gso = &extras[XEN_NETIF_EXTRA_TYPE_GSO - 1];

                        if (xenvif_set_skb_gso(vif, skb, gso)) {
                                /* Failure in xenvif_set_skb_gso is fatal. */
                                kfree_skb(skb);
                                break;
                        }
                }

                /* XXX could copy straight to head */
                page = xenvif_alloc_page(vif, pending_idx);
                if (!page) {
                        kfree_skb(skb);
                        xenvif_tx_err(vif, &txreq, idx);
                        break;
                }

                gop->source.u.ref = txreq.gref;
                gop->source.domid = vif->domid;
                gop->source.offset = txreq.offset;

                gop->dest.u.gmfn = virt_to_mfn(page_address(page));
                gop->dest.domid = DOMID_SELF;
                gop->dest.offset = txreq.offset;

                gop->len = txreq.size;
                gop->flags = GNTCOPY_source_gref;

                gop++;

                memcpy(&vif->pending_tx_info[pending_idx].req,
                       &txreq, sizeof(txreq));
                vif->pending_tx_info[pending_idx].head = index;
                *((u16 *)skb->data) = pending_idx;

                __skb_put(skb, data_len);

                skb_shinfo(skb)->nr_frags = ret;
                if (data_len < txreq.size) {
                        skb_shinfo(skb)->nr_frags++;
                        frag_set_pending_idx(&skb_shinfo(skb)->frags[0],
                                             pending_idx);
                } else {
                        frag_set_pending_idx(&skb_shinfo(skb)->frags[0],
                                             INVALID_PENDING_IDX);
                }

                vif->pending_cons++;

                request_gop = xenvif_get_requests(vif, skb, txfrags, gop);
                if (request_gop == NULL) {
                        kfree_skb(skb);
                        xenvif_tx_err(vif, &txreq, idx);
                        break;
                }
                gop = request_gop;

                __skb_queue_tail(&vif->tx_queue, skb);

                vif->tx.req_cons = idx;

                if ((gop-vif->tx_copy_ops) >= ARRAY_SIZE(vif->tx_copy_ops))
                        break;
        }

        return gop - vif->tx_copy_ops;
}


static int xenvif_tx_submit(struct xenvif *vif, int budget)
{
        struct gnttab_copy *gop = vif->tx_copy_ops;
        struct sk_buff *skb;
        int work_done = 0;

        while (work_done < budget &&
               (skb = __skb_dequeue(&vif->tx_queue)) != NULL) {
                struct xen_netif_tx_request *txp;
                u16 pending_idx;
                unsigned data_len;

                pending_idx = *((u16 *)skb->data);
                txp = &vif->pending_tx_info[pending_idx].req;

                /* Check the remap error code. */
                if (unlikely(xenvif_tx_check_gop(vif, skb, &gop))) {
                        netdev_dbg(vif->dev, "netback grant failed.\n");
                        skb_shinfo(skb)->nr_frags = 0;
                        kfree_skb(skb);
                        continue;
                }

                data_len = skb->len;
                memcpy(skb->data,
                       (void *)(idx_to_kaddr(vif, pending_idx)|txp->offset),
                       data_len);
                if (data_len < txp->size) {
                        /* Append the packet payload as a fragment. */
                        txp->offset += data_len;
                        txp->size -= data_len;
                } else {
                        /* Schedule a response immediately. */
                        xenvif_idx_release(vif, pending_idx,
                                           XEN_NETIF_RSP_OKAY);
                }

                if (txp->flags & XEN_NETTXF_csum_blank)
                        skb->ip_summed = CHECKSUM_PARTIAL;
                else if (txp->flags & XEN_NETTXF_data_validated)
                        skb->ip_summed = CHECKSUM_UNNECESSARY;

                xenvif_fill_frags(vif, skb);

                /*
                 * If the initial fragment was < PKT_PROT_LEN then
                 * pull through some bytes from the other fragments to
                 * increase the linear region to PKT_PROT_LEN bytes.
                 */
                if (skb_headlen(skb) < PKT_PROT_LEN && skb_is_nonlinear(skb)) {
                        int target = min_t(int, skb->len, PKT_PROT_LEN);
                        __pskb_pull_tail(skb, target - skb_headlen(skb));
                }

                skb->dev      = vif->dev;
                skb->protocol = eth_type_trans(skb, skb->dev);
                skb_reset_network_header(skb);

                if (checksum_setup(vif, skb)) {
                        netdev_dbg(vif->dev,
                                   "Can't setup checksum in net_tx_action\n");
                        kfree_skb(skb);
                        continue;
                }

                skb_probe_transport_header(skb, 0);

                vif->dev->stats.rx_bytes += skb->len;
                vif->dev->stats.rx_packets++;

                work_done++;

                netif_receive_skb(skb);
        }

        return work_done;
}

/* Called after netfront has transmitted */
int xenvif_tx_action(struct xenvif *vif, int budget)
{
        unsigned nr_gops;
        int work_done;

        if (unlikely(!tx_work_todo(vif)))
                return 0;

        nr_gops = xenvif_tx_build_gops(vif);

        if (nr_gops == 0)
                return 0;

        gnttab_batch_copy(vif->tx_copy_ops, nr_gops);

        work_done = xenvif_tx_submit(vif, nr_gops);

        return work_done;
}

static void xenvif_idx_release(struct xenvif *vif, u16 pending_idx,
                               u8 status)
{
        struct pending_tx_info *pending_tx_info;
        pending_ring_idx_t head;
        u16 peek; /* peek into next tx request */

        BUG_ON(vif->mmap_pages[pending_idx] == (void *)(~0UL));

        /* Already complete? */
        if (vif->mmap_pages[pending_idx] == NULL)
                return;

        pending_tx_info = &vif->pending_tx_info[pending_idx];

        head = pending_tx_info->head;

        BUG_ON(!pending_tx_is_head(vif, head));
        BUG_ON(vif->pending_ring[pending_index(head)] != pending_idx);

        do {
                pending_ring_idx_t index;
                pending_ring_idx_t idx = pending_index(head);
                u16 info_idx = vif->pending_ring[idx];

                pending_tx_info = &vif->pending_tx_info[info_idx];
                make_tx_response(vif, &pending_tx_info->req, status);

                /* Setting any number other than
                 * INVALID_PENDING_RING_IDX indicates this slot is
                 * starting a new packet / ending a previous packet.
                 */
                pending_tx_info->head = 0;

                index = pending_index(vif->pending_prod++);
                vif->pending_ring[index] = vif->pending_ring[info_idx];

                peek = vif->pending_ring[pending_index(++head)];

        } while (!pending_tx_is_head(vif, peek));

        put_page(vif->mmap_pages[pending_idx]);
        vif->mmap_pages[pending_idx] = NULL;
}


static void make_tx_response(struct xenvif *vif,
                             struct xen_netif_tx_request *txp,
                             s8       st)
{
        RING_IDX i = vif->tx.rsp_prod_pvt;
        struct xen_netif_tx_response *resp;
        int notify;

        resp = RING_GET_RESPONSE(&vif->tx, i);
        resp->id     = txp->id;
        resp->status = st;

        if (txp->flags & XEN_NETTXF_extra_info)
                RING_GET_RESPONSE(&vif->tx, ++i)->status = XEN_NETIF_RSP_NULL;

        vif->tx.rsp_prod_pvt = ++i;
        RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&vif->tx, notify);
        if (notify)
                notify_remote_via_irq(vif->tx_irq);
}

static struct xen_netif_rx_response *make_rx_response(struct xenvif *vif,
                                             u16      id,
                                             s8       st,
                                             u16      offset,
                                             u16      size,
                                             u16      flags)
{
        RING_IDX i = vif->rx.rsp_prod_pvt;
        struct xen_netif_rx_response *resp;

        resp = RING_GET_RESPONSE(&vif->rx, i);
        resp->offset     = offset;
        resp->flags      = flags;
        resp->id         = id;
        resp->status     = (s16)size;
        if (st < 0)
                resp->status = (s16)st;

        vif->rx.rsp_prod_pvt = ++i;

        return resp;
}

static inline int rx_work_todo(struct xenvif *vif)
{
        return !skb_queue_empty(&vif->rx_queue);
}

static inline int tx_work_todo(struct xenvif *vif)
{

        if (likely(RING_HAS_UNCONSUMED_REQUESTS(&vif->tx)) &&
            (nr_pending_reqs(vif) + XEN_NETBK_LEGACY_SLOTS_MAX
             < MAX_PENDING_REQS))
                return 1;

        return 0;
}

void xenvif_unmap_frontend_rings(struct xenvif *vif)
{
        if (vif->tx.sring)
                xenbus_unmap_ring_vfree(xenvif_to_xenbus_device(vif),
                                        vif->tx.sring);
        if (vif->rx.sring)
                xenbus_unmap_ring_vfree(xenvif_to_xenbus_device(vif),
                                        vif->rx.sring);
}

int xenvif_map_frontend_rings(struct xenvif *vif,
                              grant_ref_t tx_ring_ref,
                              grant_ref_t rx_ring_ref)
{
        void *addr;
        struct xen_netif_tx_sring *txs;
        struct xen_netif_rx_sring *rxs;

        int err = -ENOMEM;

        err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(vif),
                                     tx_ring_ref, &addr);
        if (err)
                goto err;

        txs = (struct xen_netif_tx_sring *)addr;
        BACK_RING_INIT(&vif->tx, txs, PAGE_SIZE);

        err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(vif),
                                     rx_ring_ref, &addr);
        if (err)
                goto err;

        rxs = (struct xen_netif_rx_sring *)addr;
        BACK_RING_INIT(&vif->rx, rxs, PAGE_SIZE);

        vif->rx_req_cons_peek = 0;

        return 0;

err:
        xenvif_unmap_frontend_rings(vif);
        return err;
}

int xenvif_kthread(void *data)
{
        struct xenvif *vif = data;

        while (!kthread_should_stop()) {
                wait_event_interruptible(vif->wq,
                                         rx_work_todo(vif) ||
                                         vif->disabled ||
                                         kthread_should_stop());

                /* This frontend is found to be rogue, disable it in
                 * kthread context. Currently this is only set when
                 * netback finds out frontend sends malformed packet,
                 * but we cannot disable the interface in softirq
                 * context so we defer it here.
                 */
                if (unlikely(vif->disabled && netif_carrier_ok(vif->dev)))
                        xenvif_carrier_off(vif);

                if (kthread_should_stop())
                        break;

                if (rx_work_todo(vif))
                        xenvif_rx_action(vif);

                cond_resched();
        }

        return 0;
}

static int __init netback_init(void)
{
        int rc = 0;

        if (!xen_domain())
                return -ENODEV;

        if (fatal_skb_slots < XEN_NETBK_LEGACY_SLOTS_MAX) {
                pr_info("fatal_skb_slots too small (%d), bump it to XEN_NETBK_LEGACY_SLOTS_MAX (%d)\n",
                        fatal_skb_slots, XEN_NETBK_LEGACY_SLOTS_MAX);
                fatal_skb_slots = XEN_NETBK_LEGACY_SLOTS_MAX;
        }

        rc = xenvif_xenbus_init();
        if (rc)
                goto failed_init;

        return 0;

failed_init:
        return rc;
}

module_init(netback_init);

static void __exit netback_fini(void)
{
        xenvif_xenbus_fini();
}
module_exit(netback_fini);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_ALIAS("xen-backend:vif");