/*
 * 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 <linux/highmem.h>

#include <net/tcp.h>

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

#include <asm/xen/hypercall.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 = true;
module_param(separate_tx_rx_irq, bool, 0644);

/* The time that packets can stay on the guest Rx internal queue
 * before they are dropped.
 */
unsigned int rx_drain_timeout_msecs = 10000;
module_param(rx_drain_timeout_msecs, uint, 0444);

/* The length of time before the frontend is considered unresponsive
 * because it isn't providing Rx slots.
 */
unsigned int rx_stall_timeout_msecs = 60000;
module_param(rx_stall_timeout_msecs, uint, 0444);

unsigned int xenvif_max_queues;
module_param_named(max_queues, xenvif_max_queues, uint, 0644);
MODULE_PARM_DESC(max_queues,
                 "Maximum number of queues per virtual interface");

/*
 * 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);

/* The amount to copy out of the first guest Tx slot into the skb's
 * linear area.  If the first slot has more data, it will be mapped
 * and put into the first frag.
 *
 * This is sized to avoid pulling headers from the frags for most
 * TCP/IP packets.
 */
#define XEN_NETBACK_TX_COPY_LEN 128


static void xenvif_idx_release(struct xenvif_queue *queue, u16 pending_idx,
                               u8 status);

static void make_tx_response(struct xenvif_queue *queue,
                             struct xen_netif_tx_request *txp,
                             s8       st);
static void push_tx_responses(struct xenvif_queue *queue);

static inline int tx_work_todo(struct xenvif_queue *queue);

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

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

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

#define callback_param(vif, pending_idx) \
        (vif->pending_tx_info[pending_idx].callback_struct)

/* Find the containing VIF's structure from a pointer in pending_tx_info array
 */
static inline struct xenvif_queue *ubuf_to_queue(const struct ubuf_info *ubuf)
{
        u16 pending_idx = ubuf->desc;
        struct pending_tx_info *temp =
                container_of(ubuf, struct pending_tx_info, callback_struct);
        return container_of(temp - pending_idx,
                            struct xenvif_queue,
                            pending_tx_info[0]);
}

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);
}

bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue, int needed)
{
        RING_IDX prod, cons;

        do {
                prod = queue->rx.sring->req_prod;
                cons = queue->rx.req_cons;

                if (prod - cons >= needed)
                        return true;

                queue->rx.sring->req_event = prod + 1;

                /* Make sure event is visible before we check prod
                 * again.
                 */
                mb();
        } while (queue->rx.sring->req_prod != prod);

        return false;
}

void xenvif_rx_queue_tail(struct xenvif_queue *queue, struct sk_buff *skb)
{
        unsigned long flags;

        spin_lock_irqsave(&queue->rx_queue.lock, flags);

        __skb_queue_tail(&queue->rx_queue, skb);

        queue->rx_queue_len += skb->len;
        if (queue->rx_queue_len > queue->rx_queue_max)
                netif_tx_stop_queue(netdev_get_tx_queue(queue->vif->dev, queue->id));

        spin_unlock_irqrestore(&queue->rx_queue.lock, flags);
}

static struct sk_buff *xenvif_rx_dequeue(struct xenvif_queue *queue)
{
        struct sk_buff *skb;

        spin_lock_irq(&queue->rx_queue.lock);

        skb = __skb_dequeue(&queue->rx_queue);
        if (skb)
                queue->rx_queue_len -= skb->len;

        spin_unlock_irq(&queue->rx_queue.lock);

        return skb;
}

static void xenvif_rx_queue_maybe_wake(struct xenvif_queue *queue)
{
        spin_lock_irq(&queue->rx_queue.lock);

        if (queue->rx_queue_len < queue->rx_queue_max)
                netif_tx_wake_queue(netdev_get_tx_queue(queue->vif->dev, queue->id));

        spin_unlock_irq(&queue->rx_queue.lock);
}


static void xenvif_rx_queue_purge(struct xenvif_queue *queue)
{
        struct sk_buff *skb;
        while ((skb = xenvif_rx_dequeue(queue)) != NULL)
                kfree_skb(skb);
}

static void xenvif_rx_queue_drop_expired(struct xenvif_queue *queue)
{
        struct sk_buff *skb;

        for(;;) {
                skb = skb_peek(&queue->rx_queue);
                if (!skb)
                        break;
                if (time_before(jiffies, XENVIF_RX_CB(skb)->expires))
                        break;
                xenvif_rx_dequeue(queue);
                kfree_skb(skb);
        }
}

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_queue *queue,
                                                 struct netrx_pending_operations *npo)
{
        struct xenvif_rx_meta *meta;
        struct xen_netif_rx_request *req;

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

        meta = npo->meta + npo->meta_prod++;
        meta->gso_type = XEN_NETIF_GSO_TYPE_NONE;
        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_queue *queue, 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;
        int gso_type = XEN_NETIF_GSO_TYPE_NONE;

        /* 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) {
                struct xen_page_foreign *foreign;

                BUG_ON(offset >= PAGE_SIZE);
                BUG_ON(npo->copy_off > MAX_BUFFER_OFFSET);

                if (npo->copy_off == MAX_BUFFER_OFFSET)
                        meta = get_next_rx_buffer(queue, npo);

                bytes = PAGE_SIZE - offset;
                if (bytes > size)
                        bytes = size;

                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;

                foreign = xen_page_foreign(page);
                if (foreign) {
                        copy_gop->source.domid = foreign->domid;
                        copy_gop->source.u.ref = foreign->gref;
                        copy_gop->flags |= GNTCOPY_source_gref;
                } else {
                        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 = queue->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 (skb_is_gso(skb)) {
                        if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4)
                                gso_type = XEN_NETIF_GSO_TYPE_TCPV4;
                        else if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6)
                                gso_type = XEN_NETIF_GSO_TYPE_TCPV6;
                }

                if (*head && ((1 << gso_type) & queue->vif->gso_mask))
                        queue->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_queue *queue)
{
        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;
        int gso_type;

        old_meta_prod = npo->meta_prod;

        gso_type = XEN_NETIF_GSO_TYPE_NONE;
        if (skb_is_gso(skb)) {
                if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4)
                        gso_type = XEN_NETIF_GSO_TYPE_TCPV4;
                else if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6)
                        gso_type = XEN_NETIF_GSO_TYPE_TCPV6;
        }

        /* Set up a GSO prefix descriptor, if necessary */
        if ((1 << gso_type) & vif->gso_prefix_mask) {
                req = RING_GET_REQUEST(&queue->rx, queue->rx.req_cons++);
                meta = npo->meta + npo->meta_prod++;
                meta->gso_type = gso_type;
                meta->gso_size = skb_shinfo(skb)->gso_size;
                meta->size = 0;
                meta->id = req->id;
        }

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

        if ((1 << gso_type) & vif->gso_mask) {
                meta->gso_type = gso_type;
                meta->gso_size = skb_shinfo(skb)->gso_size;
        } else {
                meta->gso_type = XEN_NETIF_GSO_TYPE_NONE;
                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(queue, skb, npo,
                                     virt_to_page(data), len, offset, &head);
                data += len;
        }

        for (i = 0; i < nr_frags; i++) {
                xenvif_gop_frag_copy(queue, 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_queue *queue, 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(queue, meta[i].id, status, offset,
                                 meta[i].size, flags);
        }
}

void xenvif_kick_thread(struct xenvif_queue *queue)
{
        wake_up(&queue->wq);
}

static void xenvif_rx_action(struct xenvif_queue *queue)
{
        s8 status;
        u16 flags;
        struct xen_netif_rx_response *resp;
        struct sk_buff_head rxq;
        struct sk_buff *skb;
        LIST_HEAD(notify);
        int ret;
        unsigned long offset;
        bool need_to_notify = false;

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

        skb_queue_head_init(&rxq);

        while (xenvif_rx_ring_slots_available(queue, XEN_NETBK_RX_SLOTS_MAX)
               && (skb = xenvif_rx_dequeue(queue)) != NULL) {
                queue->last_rx_time = jiffies;

                XENVIF_RX_CB(skb)->meta_slots_used = xenvif_gop_skb(skb, &npo, queue);

                __skb_queue_tail(&rxq, skb);
        }

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

        if (!npo.copy_prod)
                goto done;

        BUG_ON(npo.copy_prod > MAX_GRANT_COPY_OPS);
        gnttab_batch_copy(queue->grant_copy_op, npo.copy_prod);

        while ((skb = __skb_dequeue(&rxq)) != NULL) {

                if ((1 << queue->meta[npo.meta_cons].gso_type) &
                    queue->vif->gso_prefix_mask) {
                        resp = RING_GET_RESPONSE(&queue->rx,
                                                 queue->rx.rsp_prod_pvt++);

                        resp->flags = XEN_NETRXF_gso_prefix | XEN_NETRXF_more_data;

                        resp->offset = queue->meta[npo.meta_cons].gso_size;
                        resp->id = queue->meta[npo.meta_cons].id;
                        resp->status = XENVIF_RX_CB(skb)->meta_slots_used;

                        npo.meta_cons++;
                        XENVIF_RX_CB(skb)->meta_slots_used--;
                }


                queue->stats.tx_bytes += skb->len;
                queue->stats.tx_packets++;

                status = xenvif_check_gop(queue->vif,
                                          XENVIF_RX_CB(skb)->meta_slots_used,
                                          &npo);

                if (XENVIF_RX_CB(skb)->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(queue, queue->meta[npo.meta_cons].id,
                                        status, offset,
                                        queue->meta[npo.meta_cons].size,
                                        flags);

                if ((1 << queue->meta[npo.meta_cons].gso_type) &
                    queue->vif->gso_mask) {
                        struct xen_netif_extra_info *gso =
                                (struct xen_netif_extra_info *)
                                RING_GET_RESPONSE(&queue->rx,
                                                  queue->rx.rsp_prod_pvt++);

                        resp->flags |= XEN_NETRXF_extra_info;

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

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

                xenvif_add_frag_responses(queue, status,
                                          queue->meta + npo.meta_cons + 1,
                                          XENVIF_RX_CB(skb)->meta_slots_used);

                RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&queue->rx, ret);

                need_to_notify |= !!ret;

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

done:
        if (need_to_notify)
                notify_remote_via_irq(queue->rx_irq);
}

void xenvif_napi_schedule_or_enable_events(struct xenvif_queue *queue)
{
        int more_to_do;

        RING_FINAL_CHECK_FOR_REQUESTS(&queue->tx, more_to_do);

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

static void tx_add_credit(struct xenvif_queue *queue)
{
        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(&queue->tx, queue->tx.req_cons)->size;
        max_burst = min(max_burst, 131072UL);
        max_burst = max(max_burst, queue->credit_bytes);

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

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

void xenvif_tx_credit_callback(unsigned long data)
{
        struct xenvif_queue *queue = (struct xenvif_queue *)data;
        tx_add_credit(queue);
        xenvif_napi_schedule_or_enable_events(queue);
}

static void xenvif_tx_err(struct xenvif_queue *queue,
                          struct xen_netif_tx_request *txp, RING_IDX end)
{
        RING_IDX cons = queue->tx.req_cons;
        unsigned long flags;

        do {
                spin_lock_irqsave(&queue->response_lock, flags);
                make_tx_response(queue, txp, XEN_NETIF_RSP_ERROR);
                push_tx_responses(queue);
                spin_unlock_irqrestore(&queue->response_lock, flags);
                if (cons == end)
                        break;
                txp = RING_GET_REQUEST(&queue->tx, cons++);
        } while (1);
        queue->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;
        /* Disable the vif from queue 0's kthread */
        if (vif->queues)
                xenvif_kick_thread(&vif->queues[0]);
}

static int xenvif_count_requests(struct xenvif_queue *queue,
                                 struct xen_netif_tx_request *first,
                                 struct xen_netif_tx_request *txp,
                                 int work_to_do)
{
        RING_IDX cons = queue->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(queue->vif->dev,
                                   "Asked for %d slots but exceeds this limit\n",
                                   work_to_do);
                        xenvif_fatal_tx_err(queue->vif);
                        return -ENODATA;
                }

                /* This guest is really using too many slots and
                 * considered malicious.
                 */
                if (unlikely(slots >= fatal_skb_slots)) {
                        netdev_err(queue->vif->dev,
                                   "Malicious frontend using %d slots, threshold %u\n",
                                   slots, fatal_skb_slots);
                        xenvif_fatal_tx_err(queue->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(queue->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(&queue->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(queue->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(queue->vif->dev, "Cross page boundary, txp->offset: %u, size: %u\n",
                                 txp->offset, txp->size);
                        xenvif_fatal_tx_err(queue->vif);
                        return -EINVAL;
                }

                more_data = txp->flags & XEN_NETTXF_more_data;

                if (!drop_err)
                        txp++;

        } while (more_data);

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

        return slots;
}


struct xenvif_tx_cb {
        u16 pending_idx;
};

#define XENVIF_TX_CB(skb) ((struct xenvif_tx_cb *)(skb)->cb)

static inline void xenvif_tx_create_map_op(struct xenvif_queue *queue,
                                          u16 pending_idx,
                                          struct xen_netif_tx_request *txp,
                                          struct gnttab_map_grant_ref *mop)
{
        queue->pages_to_map[mop-queue->tx_map_ops] = queue->mmap_pages[pending_idx];
        gnttab_set_map_op(mop, idx_to_kaddr(queue, pending_idx),
                          GNTMAP_host_map | GNTMAP_readonly,
                          txp->gref, queue->vif->domid);

        memcpy(&queue->pending_tx_info[pending_idx].req, txp,
               sizeof(*txp));
}

static inline struct sk_buff *xenvif_alloc_skb(unsigned int size)
{
        struct sk_buff *skb =
                alloc_skb(size + NET_SKB_PAD + NET_IP_ALIGN,
                          GFP_ATOMIC | __GFP_NOWARN);
        if (unlikely(skb == NULL))
                return NULL;

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

        /* Initialize it here to avoid later surprises */
        skb_shinfo(skb)->destructor_arg = NULL;

        return skb;
}

static struct gnttab_map_grant_ref *xenvif_get_requests(struct xenvif_queue *queue,
                                                        struct sk_buff *skb,
                                                        struct xen_netif_tx_request *txp,
                                                        struct gnttab_map_grant_ref *gop,
                                                        unsigned int frag_overflow,
                                                        struct sk_buff *nskb)
{
        struct skb_shared_info *shinfo = skb_shinfo(skb);
        skb_frag_t *frags = shinfo->frags;
        u16 pending_idx = XENVIF_TX_CB(skb)->pending_idx;
        int start;
        pending_ring_idx_t index;
        unsigned int nr_slots;

        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);

        for (shinfo->nr_frags = start; shinfo->nr_frags < nr_slots;
             shinfo->nr_frags++, txp++, gop++) {
                index = pending_index(queue->pending_cons++);
                pending_idx = queue->pending_ring[index];
                xenvif_tx_create_map_op(queue, pending_idx, txp, gop);
                frag_set_pending_idx(&frags[shinfo->nr_frags], pending_idx);
        }

        if (frag_overflow) {

                shinfo = skb_shinfo(nskb);
                frags = shinfo->frags;

                for (shinfo->nr_frags = 0; shinfo->nr_frags < frag_overflow;
                     shinfo->nr_frags++, txp++, gop++) {
                        index = pending_index(queue->pending_cons++);
                        pending_idx = queue->pending_ring[index];
                        xenvif_tx_create_map_op(queue, pending_idx, txp, gop);
                        frag_set_pending_idx(&frags[shinfo->nr_frags],
                                             pending_idx);
                }

                skb_shinfo(skb)->frag_list = nskb;
        }

        return gop;
}

static inline void xenvif_grant_handle_set(struct xenvif_queue *queue,
                                           u16 pending_idx,
                                           grant_handle_t handle)
{
        if (unlikely(queue->grant_tx_handle[pending_idx] !=
                     NETBACK_INVALID_HANDLE)) {
                netdev_err(queue->vif->dev,
                           "Trying to overwrite active handle! pending_idx: 0x%x\n",
                           pending_idx);
                BUG();
        }
        queue->grant_tx_handle[pending_idx] = handle;
}

static inline void xenvif_grant_handle_reset(struct xenvif_queue *queue,
                                             u16 pending_idx)
{
        if (unlikely(queue->grant_tx_handle[pending_idx] ==
                     NETBACK_INVALID_HANDLE)) {
                netdev_err(queue->vif->dev,
                           "Trying to unmap invalid handle! pending_idx: 0x%x\n",
                           pending_idx);
                BUG();
        }
        queue->grant_tx_handle[pending_idx] = NETBACK_INVALID_HANDLE;
}

static int xenvif_tx_check_gop(struct xenvif_queue *queue,
                               struct sk_buff *skb,
                               struct gnttab_map_grant_ref **gopp_map,
                               struct gnttab_copy **gopp_copy)
{
        struct gnttab_map_grant_ref *gop_map = *gopp_map;
        u16 pending_idx = XENVIF_TX_CB(skb)->pending_idx;
        /* This always points to the shinfo of the skb being checked, which
         * could be either the first or the one on the frag_list
         */
        struct skb_shared_info *shinfo = skb_shinfo(skb);
        /* If this is non-NULL, we are currently checking the frag_list skb, and
         * this points to the shinfo of the first one
         */
        struct skb_shared_info *first_shinfo = NULL;
        int nr_frags = shinfo->nr_frags;
        const bool sharedslot = nr_frags &&
                                frag_get_pending_idx(&shinfo->frags[0]) == pending_idx;
        int i, err;

        /* Check status of header. */
        err = (*gopp_copy)->status;
        if (unlikely(err)) {
                if (net_ratelimit())
                        netdev_dbg(queue->vif->dev,
                                   "Grant copy of header failed! status: %d pending_idx: %u ref: %u\n",
                                   (*gopp_copy)->status,
                                   pending_idx,
                                   (*gopp_copy)->source.u.ref);
                /* The first frag might still have this slot mapped */
                if (!sharedslot)
                        xenvif_idx_release(queue, pending_idx,
                                           XEN_NETIF_RSP_ERROR);
        }
        (*gopp_copy)++;

check_frags:
        for (i = 0; i < nr_frags; i++, gop_map++) {
                int j, newerr;

                pending_idx = frag_get_pending_idx(&shinfo->frags[i]);

                /* Check error status: if okay then remember grant handle. */
                newerr = gop_map->status;

                if (likely(!newerr)) {
                        xenvif_grant_handle_set(queue,
                                                pending_idx,
                                                gop_map->handle);
                        /* Had a previous error? Invalidate this fragment. */
                        if (unlikely(err)) {
                                xenvif_idx_unmap(queue, pending_idx);
                                /* If the mapping of the first frag was OK, but
                                 * the header's copy failed, and they are
                                 * sharing a slot, send an error
                                 */
                                if (i == 0 && sharedslot)
                                        xenvif_idx_release(queue, pending_idx,
                                                           XEN_NETIF_RSP_ERROR);
                                else
                                        xenvif_idx_release(queue, pending_idx,
                                                           XEN_NETIF_RSP_OKAY);
                        }
                        continue;
                }

                /* Error on this fragment: respond to client with an error. */
                if (net_ratelimit())
                        netdev_dbg(queue->vif->dev,
                                   "Grant map of %d. frag failed! status: %d pending_idx: %u ref: %u\n",
                                   i,
                                   gop_map->status,
                                   pending_idx,
                                   gop_map->ref);

                xenvif_idx_release(queue, pending_idx, XEN_NETIF_RSP_ERROR);

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

                /* First error: if the header haven't shared a slot with the
                 * first frag, release it as well.
                 */
                if (!sharedslot)
                        xenvif_idx_release(queue,
                                           XENVIF_TX_CB(skb)->pending_idx,
                                           XEN_NETIF_RSP_OKAY);

                /* Invalidate preceding fragments of this skb. */
                for (j = 0; j < i; j++) {
                        pending_idx = frag_get_pending_idx(&shinfo->frags[j]);
                        xenvif_idx_unmap(queue, pending_idx);
                        xenvif_idx_release(queue, pending_idx,
                                           XEN_NETIF_RSP_OKAY);
                }

                /* And if we found the error while checking the frag_list, unmap
                 * the first skb's frags
                 */
                if (first_shinfo) {
                        for (j = 0; j < first_shinfo->nr_frags; j++) {
                                pending_idx = frag_get_pending_idx(&first_shinfo->frags[j]);
                                xenvif_idx_unmap(queue, pending_idx);
                                xenvif_idx_release(queue, pending_idx,
                                                   XEN_NETIF_RSP_OKAY);
                        }
                }

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

        if (skb_has_frag_list(skb) && !first_shinfo) {
                first_shinfo = skb_shinfo(skb);
                shinfo = skb_shinfo(skb_shinfo(skb)->frag_list);
                nr_frags = shinfo->nr_frags;

                goto check_frags;
        }

        *gopp_map = gop_map;
        return err;
}

static void xenvif_fill_frags(struct xenvif_queue *queue, struct sk_buff *skb)
{
        struct skb_shared_info *shinfo = skb_shinfo(skb);
        int nr_frags = shinfo->nr_frags;
        int i;
        u16 prev_pending_idx = INVALID_PENDING_IDX;

        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);

                /* If this is not the first frag, chain it to the previous*/
                if (prev_pending_idx == INVALID_PENDING_IDX)
                        skb_shinfo(skb)->destructor_arg =
                                &callback_param(queue, pending_idx);
                else
                        callback_param(queue, prev_pending_idx).ctx =
                                &callback_param(queue, pending_idx);

                callback_param(queue, pending_idx).ctx = NULL;
                prev_pending_idx = pending_idx;

                txp = &queue->pending_tx_info[pending_idx].req;
                page = virt_to_page(idx_to_kaddr(queue, 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 network stack's put_page */
                get_page(queue->mmap_pages[pending_idx]);
        }
}

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

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

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

                memcpy(&extras[extra.type - 1], &extra, sizeof(extra));
                queue->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;
        }

        switch (gso->u.gso.type) {
        case XEN_NETIF_GSO_TYPE_TCPV4:
                skb_shinfo(skb)->gso_type = SKB_GSO_TCPV4;
                break;
        case XEN_NETIF_GSO_TYPE_TCPV6:
                skb_shinfo(skb)->gso_type = SKB_GSO_TCPV6;
                break;
        default:
                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;
        /* gso_segs will be calculated later */

        return 0;
}

static int checksum_setup(struct xenvif_queue *queue, struct sk_buff *skb)
{
        bool recalculate_partial_csum = false;

        /* 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)) {
                queue->stats.rx_gso_checksum_fixup++;
                skb->ip_summed = CHECKSUM_PARTIAL;
                recalculate_partial_csum = true;
        }

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

        return skb_checksum_setup(skb, recalculate_partial_csum);
}

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

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

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

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

                return true;
        }

        return false;
}

static void xenvif_tx_build_gops(struct xenvif_queue *queue,
                                     int budget,
                                     unsigned *copy_ops,
                                     unsigned *map_ops)
{
        struct gnttab_map_grant_ref *gop = queue->tx_map_ops;
        struct sk_buff *skb, *nskb;
        int ret;
        unsigned int frag_overflow;

        while (skb_queue_len(&queue->tx_queue) < budget) {
                struct xen_netif_tx_request txreq;
                struct xen_netif_tx_request txfrags[XEN_NETBK_LEGACY_SLOTS_MAX];
                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 (queue->tx.sring->req_prod - queue->tx.req_cons >
                    XEN_NETIF_TX_RING_SIZE) {
                        netdev_err(queue->vif->dev,
                                   "Impossible number of requests. "
                                   "req_prod %d, req_cons %d, size %ld\n",
                                   queue->tx.sring->req_prod, queue->tx.req_cons,
                                   XEN_NETIF_TX_RING_SIZE);
                        xenvif_fatal_tx_err(queue->vif);
                        break;
                }

                work_to_do = RING_HAS_UNCONSUMED_REQUESTS(&queue->tx);
                if (!work_to_do)
                        break;

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

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

                queue->remaining_credit -= txreq.size;

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

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

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

                idx += ret;

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

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

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

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

                skb = xenvif_alloc_skb(data_len);
                if (unlikely(skb == NULL)) {
                        netdev_dbg(queue->vif->dev,
                                   "Can't allocate a skb in start_xmit.\n");
                        xenvif_tx_err(queue, &txreq, idx);
                        break;
                }

                skb_shinfo(skb)->nr_frags = ret;
                if (data_len < txreq.size)
                        skb_shinfo(skb)->nr_frags++;
                /* At this point shinfo->nr_frags is in fact the number of
                 * slots, which can be as large as XEN_NETBK_LEGACY_SLOTS_MAX.
                 */
                frag_overflow = 0;
                nskb = NULL;
                if (skb_shinfo(skb)->nr_frags > MAX_SKB_FRAGS) {
                        frag_overflow = skb_shinfo(skb)->nr_frags - MAX_SKB_FRAGS;
                        BUG_ON(frag_overflow > MAX_SKB_FRAGS);
                        skb_shinfo(skb)->nr_frags = MAX_SKB_FRAGS;
                        nskb = xenvif_alloc_skb(0);
                        if (unlikely(nskb == NULL)) {
                                kfree_skb(skb);
                                xenvif_tx_err(queue, &txreq, idx);
                                if (net_ratelimit())
                                        netdev_err(queue->vif->dev,
                                                   "Can't allocate the frag_list skb.\n");
                                break;
                        }
                }

                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(queue->vif, skb, gso)) {
                                /* Failure in xenvif_set_skb_gso is fatal. */
                                kfree_skb(skb);
                                kfree_skb(nskb);
                                break;
                        }
                }

                XENVIF_TX_CB(skb)->pending_idx = pending_idx;

                __skb_put(skb, data_len);
                queue->tx_copy_ops[*copy_ops].source.u.ref = txreq.gref;
                queue->tx_copy_ops[*copy_ops].source.domid = queue->vif->domid;
                queue->tx_copy_ops[*copy_ops].source.offset = txreq.offset;

                queue->tx_copy_ops[*copy_ops].dest.u.gmfn =
                        virt_to_mfn(skb->data);
                queue->tx_copy_ops[*copy_ops].dest.domid = DOMID_SELF;
                queue->tx_copy_ops[*copy_ops].dest.offset =
                        offset_in_page(skb->data);

                queue->tx_copy_ops[*copy_ops].len = data_len;
                queue->tx_copy_ops[*copy_ops].flags = GNTCOPY_source_gref;

                (*copy_ops)++;

                if (data_len < txreq.size) {
                        frag_set_pending_idx(&skb_shinfo(skb)->frags[0],
                                             pending_idx);
                        xenvif_tx_create_map_op(queue, pending_idx, &txreq, gop);
                        gop++;
                } else {
                        frag_set_pending_idx(&skb_shinfo(skb)->frags[0],
                                             INVALID_PENDING_IDX);
                        memcpy(&queue->pending_tx_info[pending_idx].req, &txreq,
                               sizeof(txreq));
                }

                queue->pending_cons++;

                gop = xenvif_get_requests(queue, skb, txfrags, gop,
                                          frag_overflow, nskb);

                __skb_queue_tail(&queue->tx_queue, skb);

                queue->tx.req_cons = idx;

                if (((gop-queue->tx_map_ops) >= ARRAY_SIZE(queue->tx_map_ops)) ||
                    (*copy_ops >= ARRAY_SIZE(queue->tx_copy_ops)))
                        break;
        }

        (*map_ops) = gop - queue->tx_map_ops;
        return;
}

/* Consolidate skb with a frag_list into a brand new one with local pages on
 * frags. Returns 0 or -ENOMEM if can't allocate new pages.
 */
static int xenvif_handle_frag_list(struct xenvif_queue *queue, struct sk_buff *skb)
{
        unsigned int offset = skb_headlen(skb);
        skb_frag_t frags[MAX_SKB_FRAGS];
        int i, f;
        struct ubuf_info *uarg;
        struct sk_buff *nskb = skb_shinfo(skb)->frag_list;

        queue->stats.tx_zerocopy_sent += 2;
        queue->stats.tx_frag_overflow++;

        xenvif_fill_frags(queue, nskb);
        /* Subtract frags size, we will correct it later */
        skb->truesize -= skb->data_len;
        skb->len += nskb->len;
        skb->data_len += nskb->len;

        /* create a brand new frags array and coalesce there */
        for (i = 0; offset < skb->len; i++) {
                struct page *page;
                unsigned int len;

                BUG_ON(i >= MAX_SKB_FRAGS);
                page = alloc_page(GFP_ATOMIC);
                if (!page) {
                        int j;
                        skb->truesize += skb->data_len;
                        for (j = 0; j < i; j++)
                                put_page(frags[j].page.p);
                        return -ENOMEM;
                }

                if (offset + PAGE_SIZE < skb->len)
                        len = PAGE_SIZE;
                else
                        len = skb->len - offset;
                if (skb_copy_bits(skb, offset, page_address(page), len))
                        BUG();

                offset += len;
                frags[i].page.p = page;
                frags[i].page_offset = 0;
                skb_frag_size_set(&frags[i], len);
        }

        /* Copied all the bits from the frag list -- free it. */
        skb_frag_list_init(skb);
        xenvif_skb_zerocopy_prepare(queue, nskb);
        kfree_skb(nskb);

        /* Release all the original (foreign) frags. */
        for (f = 0; f < skb_shinfo(skb)->nr_frags; f++)
                skb_frag_unref(skb, f);
        uarg = skb_shinfo(skb)->destructor_arg;
        /* increase inflight counter to offset decrement in callback */
        atomic_inc(&queue->inflight_packets);
        uarg->callback(uarg, true);
        skb_shinfo(skb)->destructor_arg = NULL;

        /* Fill the skb with the new (local) frags. */
        memcpy(skb_shinfo(skb)->frags, frags, i * sizeof(skb_frag_t));
        skb_shinfo(skb)->nr_frags = i;
        skb->truesize += i * PAGE_SIZE;

        return 0;
}

static int xenvif_tx_submit(struct xenvif_queue *queue)
{
        struct gnttab_map_grant_ref *gop_map = queue->tx_map_ops;
        struct gnttab_copy *gop_copy = queue->tx_copy_ops;
        struct sk_buff *skb;
        int work_done = 0;

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

                pending_idx = XENVIF_TX_CB(skb)->pending_idx;
                txp = &queue->pending_tx_info[pending_idx].req;

                /* Check the remap error code. */
                if (unlikely(xenvif_tx_check_gop(queue, skb, &gop_map, &gop_copy))) {
                        /* If there was an error, xenvif_tx_check_gop is
                         * expected to release all the frags which were mapped,
                         * so kfree_skb shouldn't do it again
                         */
                        skb_shinfo(skb)->nr_frags = 0;
                        if (skb_has_frag_list(skb)) {
                                struct sk_buff *nskb =
                                                skb_shinfo(skb)->frag_list;
                                skb_shinfo(nskb)->nr_frags = 0;
                        }
                        kfree_skb(skb);
                        continue;
                }

                data_len = skb->len;
                callback_param(queue, pending_idx).ctx = NULL;
                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(queue, 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(queue, skb);

                if (unlikely(skb_has_frag_list(skb))) {
                        if (xenvif_handle_frag_list(queue, skb)) {
                                if (net_ratelimit())
                                        netdev_err(queue->vif->dev,
                                                   "Not enough memory to consolidate frag_list!\n");
                                xenvif_skb_zerocopy_prepare(queue, skb);
                                kfree_skb(skb);
                                continue;
                        }
                }

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

                if (checksum_setup(queue, skb)) {
                        netdev_dbg(queue->vif->dev,
                                   "Can't setup checksum in net_tx_action\n");
                        /* We have to set this flag to trigger the callback */
                        if (skb_shinfo(skb)->destructor_arg)
                                xenvif_skb_zerocopy_prepare(queue, skb);
                        kfree_skb(skb);
                        continue;
                }

                skb_probe_transport_header(skb, 0);

                /* If the packet is GSO then we will have just set up the
                 * transport header offset in checksum_setup so it's now
                 * straightforward to calculate gso_segs.
                 */
                if (skb_is_gso(skb)) {
                        int mss = skb_shinfo(skb)->gso_size;
                        int hdrlen = skb_transport_header(skb) -
                                skb_mac_header(skb) +
                                tcp_hdrlen(skb);

                        skb_shinfo(skb)->gso_segs =
                                DIV_ROUND_UP(skb->len - hdrlen, mss);
                }

                queue->stats.rx_bytes += skb->len;
                queue->stats.rx_packets++;

                work_done++;

                /* Set this flag right before netif_receive_skb, otherwise
                 * someone might think this packet already left netback, and
                 * do a skb_copy_ubufs while we are still in control of the
                 * skb. E.g. the __pskb_pull_tail earlier can do such thing.
                 */
                if (skb_shinfo(skb)->destructor_arg) {
                        xenvif_skb_zerocopy_prepare(queue, skb);
                        queue->stats.tx_zerocopy_sent++;
                }

                netif_receive_skb(skb);
        }

        return work_done;
}

void xenvif_zerocopy_callback(struct ubuf_info *ubuf, bool zerocopy_success)
{
        unsigned long flags;
        pending_ring_idx_t index;
        struct xenvif_queue *queue = ubuf_to_queue(ubuf);

        /* This is the only place where we grab this lock, to protect callbacks
         * from each other.
         */
        spin_lock_irqsave(&queue->callback_lock, flags);
        do {
                u16 pending_idx = ubuf->desc;
                ubuf = (struct ubuf_info *) ubuf->ctx;
                BUG_ON(queue->dealloc_prod - queue->dealloc_cons >=
                        MAX_PENDING_REQS);
                index = pending_index(queue->dealloc_prod);
                queue->dealloc_ring[index] = pending_idx;
                /* Sync with xenvif_tx_dealloc_action:
                 * insert idx then incr producer.
                 */
                smp_wmb();
                queue->dealloc_prod++;
        } while (ubuf);
        spin_unlock_irqrestore(&queue->callback_lock, flags);

        if (likely(zerocopy_success))
                queue->stats.tx_zerocopy_success++;
        else
                queue->stats.tx_zerocopy_fail++;
        xenvif_skb_zerocopy_complete(queue);
}

static inline void xenvif_tx_dealloc_action(struct xenvif_queue *queue)
{
        struct gnttab_unmap_grant_ref *gop;
        pending_ring_idx_t dc, dp;
        u16 pending_idx, pending_idx_release[MAX_PENDING_REQS];
        unsigned int i = 0;

        dc = queue->dealloc_cons;
        gop = queue->tx_unmap_ops;

        /* Free up any grants we have finished using */
        do {
                dp = queue->dealloc_prod;

                /* Ensure we see all indices enqueued by all
                 * xenvif_zerocopy_callback().
                 */
                smp_rmb();

                while (dc != dp) {
                        BUG_ON(gop - queue->tx_unmap_ops >= MAX_PENDING_REQS);
                        pending_idx =
                                queue->dealloc_ring[pending_index(dc++)];

                        pending_idx_release[gop - queue->tx_unmap_ops] =
                                pending_idx;
                        queue->pages_to_unmap[gop - queue->tx_unmap_ops] =
                                queue->mmap_pages[pending_idx];
                        gnttab_set_unmap_op(gop,
                                            idx_to_kaddr(queue, pending_idx),
                                            GNTMAP_host_map,
                                            queue->grant_tx_handle[pending_idx]);
                        xenvif_grant_handle_reset(queue, pending_idx);
                        ++gop;
                }

        } while (dp != queue->dealloc_prod);

        queue->dealloc_cons = dc;

        if (gop - queue->tx_unmap_ops > 0) {
                int ret;
                ret = gnttab_unmap_refs(queue->tx_unmap_ops,
                                        NULL,
                                        queue->pages_to_unmap,
                                        gop - queue->tx_unmap_ops);
                if (ret) {
                        netdev_err(queue->vif->dev, "Unmap fail: nr_ops %tu ret %d\n",
                                   gop - queue->tx_unmap_ops, ret);
                        for (i = 0; i < gop - queue->tx_unmap_ops; ++i) {
                                if (gop[i].status != GNTST_okay)
                                        netdev_err(queue->vif->dev,
                                                   " host_addr: 0x%llx handle: 0x%x status: %d\n",
                                                   gop[i].host_addr,
                                                   gop[i].handle,
                                                   gop[i].status);
                        }
                        BUG();
                }
        }

        for (i = 0; i < gop - queue->tx_unmap_ops; ++i)
                xenvif_idx_release(queue, pending_idx_release[i],
                                   XEN_NETIF_RSP_OKAY);
}


/* Called after netfront has transmitted */
int xenvif_tx_action(struct xenvif_queue *queue, int budget)
{
        unsigned nr_mops, nr_cops = 0;
        int work_done, ret;

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

        xenvif_tx_build_gops(queue, budget, &nr_cops, &nr_mops);

        if (nr_cops == 0)
                return 0;

        gnttab_batch_copy(queue->tx_copy_ops, nr_cops);
        if (nr_mops != 0) {
                ret = gnttab_map_refs(queue->tx_map_ops,
                                      NULL,
                                      queue->pages_to_map,
                                      nr_mops);
                BUG_ON(ret);
        }

        work_done = xenvif_tx_submit(queue);

        return work_done;
}

static void xenvif_idx_release(struct xenvif_queue *queue, u16 pending_idx,
                               u8 status)
{
        struct pending_tx_info *pending_tx_info;
        pending_ring_idx_t index;
        unsigned long flags;

        pending_tx_info = &queue->pending_tx_info[pending_idx];

        spin_lock_irqsave(&queue->response_lock, flags);

        make_tx_response(queue, &pending_tx_info->req, status);

        /* Release the pending index before pusing the Tx response so
         * its available before a new Tx request is pushed by the
         * frontend.
         */
        index = pending_index(queue->pending_prod++);
        queue->pending_ring[index] = pending_idx;

        push_tx_responses(queue);

        spin_unlock_irqrestore(&queue->response_lock, flags);
}


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

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

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

        queue->tx.rsp_prod_pvt = ++i;
}

static void push_tx_responses(struct xenvif_queue *queue)
{
        int notify;

        RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&queue->tx, notify);
        if (notify)
                notify_remote_via_irq(queue->tx_irq);
}

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

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

        queue->rx.rsp_prod_pvt = ++i;

        return resp;
}

void xenvif_idx_unmap(struct xenvif_queue *queue, u16 pending_idx)
{
        int ret;
        struct gnttab_unmap_grant_ref tx_unmap_op;

        gnttab_set_unmap_op(&tx_unmap_op,
                            idx_to_kaddr(queue, pending_idx),
                            GNTMAP_host_map,
                            queue->grant_tx_handle[pending_idx]);
        xenvif_grant_handle_reset(queue, pending_idx);

        ret = gnttab_unmap_refs(&tx_unmap_op, NULL,
                                &queue->mmap_pages[pending_idx], 1);
        if (ret) {
                netdev_err(queue->vif->dev,
                           "Unmap fail: ret: %d pending_idx: %d host_addr: %llx handle: 0x%x status: %d\n",
                           ret,
                           pending_idx,
                           tx_unmap_op.host_addr,
                           tx_unmap_op.handle,
                           tx_unmap_op.status);
                BUG();
        }
}

static inline int tx_work_todo(struct xenvif_queue *queue)
{
        if (likely(RING_HAS_UNCONSUMED_REQUESTS(&queue->tx)))
                return 1;

        return 0;
}

static inline bool tx_dealloc_work_todo(struct xenvif_queue *queue)
{
        return queue->dealloc_cons != queue->dealloc_prod;
}

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

int xenvif_map_frontend_rings(struct xenvif_queue *queue,
                              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(queue->vif),
                                     &tx_ring_ref, 1, &addr);
        if (err)
                goto err;

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

        err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(queue->vif),
                                     &rx_ring_ref, 1, &addr);
        if (err)
                goto err;

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

        return 0;

err:
        xenvif_unmap_frontend_rings(queue);
        return err;
}

static void xenvif_queue_carrier_off(struct xenvif_queue *queue)
{
        struct xenvif *vif = queue->vif;

        queue->stalled = true;

        /* At least one queue has stalled? Disable the carrier. */
        spin_lock(&vif->lock);
        if (vif->stalled_queues++ == 0) {
                netdev_info(vif->dev, "Guest Rx stalled");
                netif_carrier_off(vif->dev);
        }
        spin_unlock(&vif->lock);
}

static void xenvif_queue_carrier_on(struct xenvif_queue *queue)
{
        struct xenvif *vif = queue->vif;

        queue->last_rx_time = jiffies; /* Reset Rx stall detection. */
        queue->stalled = false;

        /* All queues are ready? Enable the carrier. */
        spin_lock(&vif->lock);
        if (--vif->stalled_queues == 0) {
                netdev_info(vif->dev, "Guest Rx ready");
                netif_carrier_on(vif->dev);
        }
        spin_unlock(&vif->lock);
}

static bool xenvif_rx_queue_stalled(struct xenvif_queue *queue)
{
        RING_IDX prod, cons;

        prod = queue->rx.sring->req_prod;
        cons = queue->rx.req_cons;

        return !queue->stalled
                && prod - cons < XEN_NETBK_RX_SLOTS_MAX
                && time_after(jiffies,
                              queue->last_rx_time + queue->vif->stall_timeout);
}

static bool xenvif_rx_queue_ready(struct xenvif_queue *queue)
{
        RING_IDX prod, cons;

        prod = queue->rx.sring->req_prod;
        cons = queue->rx.req_cons;

        return queue->stalled
                && prod - cons >= XEN_NETBK_RX_SLOTS_MAX;
}

static bool xenvif_have_rx_work(struct xenvif_queue *queue)
{
        return (!skb_queue_empty(&queue->rx_queue)
                && xenvif_rx_ring_slots_available(queue, XEN_NETBK_RX_SLOTS_MAX))
                || (queue->vif->stall_timeout &&
                    (xenvif_rx_queue_stalled(queue)
                     || xenvif_rx_queue_ready(queue)))
                || kthread_should_stop()
                || queue->vif->disabled;
}

static long xenvif_rx_queue_timeout(struct xenvif_queue *queue)
{
        struct sk_buff *skb;
        long timeout;

        skb = skb_peek(&queue->rx_queue);
        if (!skb)
                return MAX_SCHEDULE_TIMEOUT;

        timeout = XENVIF_RX_CB(skb)->expires - jiffies;
        return timeout < 0 ? 0 : timeout;
}

/* Wait until the guest Rx thread has work.
 *
 * The timeout needs to be adjusted based on the current head of the
 * queue (and not just the head at the beginning).  In particular, if
 * the queue is initially empty an infinite timeout is used and this
 * needs to be reduced when a skb is queued.
 *
 * This cannot be done with wait_event_timeout() because it only
 * calculates the timeout once.
 */
static void xenvif_wait_for_rx_work(struct xenvif_queue *queue)
{
        DEFINE_WAIT(wait);

        if (xenvif_have_rx_work(queue))
                return;

        for (;;) {
                long ret;

                prepare_to_wait(&queue->wq, &wait, TASK_INTERRUPTIBLE);
                if (xenvif_have_rx_work(queue))
                        break;
                ret = schedule_timeout(xenvif_rx_queue_timeout(queue));
                if (!ret)
                        break;
        }
        finish_wait(&queue->wq, &wait);
}

int xenvif_kthread_guest_rx(void *data)
{
        struct xenvif_queue *queue = data;
        struct xenvif *vif = queue->vif;

        if (!vif->stall_timeout)
                xenvif_queue_carrier_on(queue);

        for (;;) {
                xenvif_wait_for_rx_work(queue);

                if (kthread_should_stop())
                        break;

                /* 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 this thread is
                 * associated with queue 0.
                 */
                if (unlikely(vif->disabled && queue->id == 0)) {
                        xenvif_carrier_off(vif);
                        break;
                }

                if (!skb_queue_empty(&queue->rx_queue))
                        xenvif_rx_action(queue);

                /* If the guest hasn't provided any Rx slots for a
                 * while it's probably not responsive, drop the
                 * carrier so packets are dropped earlier.
                 */
                if (vif->stall_timeout) {
                        if (xenvif_rx_queue_stalled(queue))
                                xenvif_queue_carrier_off(queue);
                        else if (xenvif_rx_queue_ready(queue))
                                xenvif_queue_carrier_on(queue);
                }

                /* Queued packets may have foreign pages from other
                 * domains.  These cannot be queued indefinitely as
                 * this would starve guests of grant refs and transmit
                 * slots.
                 */
                xenvif_rx_queue_drop_expired(queue);

                xenvif_rx_queue_maybe_wake(queue);

                cond_resched();
        }

        /* Bin any remaining skbs */
        xenvif_rx_queue_purge(queue);

        return 0;
}

static bool xenvif_dealloc_kthread_should_stop(struct xenvif_queue *queue)
{
        /* Dealloc thread must remain running until all inflight
         * packets complete.
         */
        return kthread_should_stop() &&
                !atomic_read(&queue->inflight_packets);
}

int xenvif_dealloc_kthread(void *data)
{
        struct xenvif_queue *queue = data;

        for (;;) {
                wait_event_interruptible(queue->dealloc_wq,
                                         tx_dealloc_work_todo(queue) ||
                                         xenvif_dealloc_kthread_should_stop(queue));
                if (xenvif_dealloc_kthread_should_stop(queue))
                        break;

                xenvif_tx_dealloc_action(queue);
                cond_resched();
        }

        /* Unmap anything remaining*/
        if (tx_dealloc_work_todo(queue))
                xenvif_tx_dealloc_action(queue);

        return 0;
}

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

        if (!xen_domain())
                return -ENODEV;

        /* Allow as many queues as there are CPUs, by default */
        xenvif_max_queues = num_online_cpus();

        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;

#ifdef CONFIG_DEBUG_FS
        xen_netback_dbg_root = debugfs_create_dir("xen-netback", NULL);
        if (IS_ERR_OR_NULL(xen_netback_dbg_root))
                pr_warn("Init of debugfs returned %ld!\n",
                        PTR_ERR(xen_netback_dbg_root));
#endif /* CONFIG_DEBUG_FS */

        return 0;

failed_init:
        return rc;
}

module_init(netback_init);

static void __exit netback_fini(void)
{
#ifdef CONFIG_DEBUG_FS
        if (!IS_ERR_OR_NULL(xen_netback_dbg_root))
                debugfs_remove_recursive(xen_netback_dbg_root);
#endif /* CONFIG_DEBUG_FS */
        xenvif_xenbus_fini();
}
module_exit(netback_fini);

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