Merge tag 'ovl-fixes-5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs

[mirror_ubuntu-hirsute-kernel.git] / drivers / virtio / virtio_ring.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* Virtio ring implementation.
 *
 *  Copyright 2007 Rusty Russell IBM Corporation
 */
#include <linux/virtio.h>
#include <linux/virtio_ring.h>
#include <linux/virtio_config.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/hrtimer.h>
#include <linux/dma-mapping.h>
#include <xen/xen.h>

#ifdef DEBUG
/* For development, we want to crash whenever the ring is screwed. */
#define BAD_RING(_vq, fmt, args...)                             \
        do {                                                    \
                dev_err(&(_vq)->vq.vdev->dev,                   \
                        "%s:"fmt, (_vq)->vq.name, ##args);      \
                BUG();                                          \
        } while (0)
/* Caller is supposed to guarantee no reentry. */
#define START_USE(_vq)                                          \
        do {                                                    \
                if ((_vq)->in_use)                              \
                        panic("%s:in_use = %i\n",               \
                              (_vq)->vq.name, (_vq)->in_use);   \
                (_vq)->in_use = __LINE__;                       \
        } while (0)
#define END_USE(_vq) \
        do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0)
#define LAST_ADD_TIME_UPDATE(_vq)                               \
        do {                                                    \
                ktime_t now = ktime_get();                      \
                                                                \
                /* No kick or get, with .1 second between?  Warn. */ \
                if ((_vq)->last_add_time_valid)                 \
                        WARN_ON(ktime_to_ms(ktime_sub(now,      \
                                (_vq)->last_add_time)) > 100);  \
                (_vq)->last_add_time = now;                     \
                (_vq)->last_add_time_valid = true;              \
        } while (0)
#define LAST_ADD_TIME_CHECK(_vq)                                \
        do {                                                    \
                if ((_vq)->last_add_time_valid) {               \
                        WARN_ON(ktime_to_ms(ktime_sub(ktime_get(), \
                                      (_vq)->last_add_time)) > 100); \
                }                                               \
        } while (0)
#define LAST_ADD_TIME_INVALID(_vq)                              \
        ((_vq)->last_add_time_valid = false)
#else
#define BAD_RING(_vq, fmt, args...)                             \
        do {                                                    \
                dev_err(&_vq->vq.vdev->dev,                     \
                        "%s:"fmt, (_vq)->vq.name, ##args);      \
                (_vq)->broken = true;                           \
        } while (0)
#define START_USE(vq)
#define END_USE(vq)
#define LAST_ADD_TIME_UPDATE(vq)
#define LAST_ADD_TIME_CHECK(vq)
#define LAST_ADD_TIME_INVALID(vq)
#endif

struct vring_desc_state_split {
        void *data;                     /* Data for callback. */
        struct vring_desc *indir_desc;  /* Indirect descriptor, if any. */
};

struct vring_desc_state_packed {
        void *data;                     /* Data for callback. */
        struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
        u16 num;                        /* Descriptor list length. */
        u16 next;                       /* The next desc state in a list. */
        u16 last;                       /* The last desc state in a list. */
};

struct vring_desc_extra_packed {
        dma_addr_t addr;                /* Buffer DMA addr. */
        u32 len;                        /* Buffer length. */
        u16 flags;                      /* Descriptor flags. */
};

struct vring_virtqueue {
        struct virtqueue vq;

        /* Is this a packed ring? */
        bool packed_ring;

        /* Is DMA API used? */
        bool use_dma_api;

        /* Can we use weak barriers? */
        bool weak_barriers;

        /* Other side has made a mess, don't try any more. */
        bool broken;

        /* Host supports indirect buffers */
        bool indirect;

        /* Host publishes avail event idx */
        bool event;

        /* Head of free buffer list. */
        unsigned int free_head;
        /* Number we've added since last sync. */
        unsigned int num_added;

        /* Last used index we've seen. */
        u16 last_used_idx;

        union {
                /* Available for split ring */
                struct {
                        /* Actual memory layout for this queue. */
                        struct vring vring;

                        /* Last written value to avail->flags */
                        u16 avail_flags_shadow;

                        /*
                         * Last written value to avail->idx in
                         * guest byte order.
                         */
                        u16 avail_idx_shadow;

                        /* Per-descriptor state. */
                        struct vring_desc_state_split *desc_state;

                        /* DMA address and size information */
                        dma_addr_t queue_dma_addr;
                        size_t queue_size_in_bytes;
                } split;

                /* Available for packed ring */
                struct {
                        /* Actual memory layout for this queue. */
                        struct {
                                unsigned int num;
                                struct vring_packed_desc *desc;
                                struct vring_packed_desc_event *driver;
                                struct vring_packed_desc_event *device;
                        } vring;

                        /* Driver ring wrap counter. */
                        bool avail_wrap_counter;

                        /* Device ring wrap counter. */
                        bool used_wrap_counter;

                        /* Avail used flags. */
                        u16 avail_used_flags;

                        /* Index of the next avail descriptor. */
                        u16 next_avail_idx;

                        /*
                         * Last written value to driver->flags in
                         * guest byte order.
                         */
                        u16 event_flags_shadow;

                        /* Per-descriptor state. */
                        struct vring_desc_state_packed *desc_state;
                        struct vring_desc_extra_packed *desc_extra;

                        /* DMA address and size information */
                        dma_addr_t ring_dma_addr;
                        dma_addr_t driver_event_dma_addr;
                        dma_addr_t device_event_dma_addr;
                        size_t ring_size_in_bytes;
                        size_t event_size_in_bytes;
                } packed;
        };

        /* How to notify other side. FIXME: commonalize hcalls! */
        bool (*notify)(struct virtqueue *vq);

        /* DMA, allocation, and size information */
        bool we_own_ring;

#ifdef DEBUG
        /* They're supposed to lock for us. */
        unsigned int in_use;

        /* Figure out if their kicks are too delayed. */
        bool last_add_time_valid;
        ktime_t last_add_time;
#endif
};


/*
 * Helpers.
 */

#define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)

static inline bool virtqueue_use_indirect(struct virtqueue *_vq,
                                          unsigned int total_sg)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        /*
         * If the host supports indirect descriptor tables, and we have multiple
         * buffers, then go indirect. FIXME: tune this threshold
         */
        return (vq->indirect && total_sg > 1 && vq->vq.num_free);
}

/*
 * Modern virtio devices have feature bits to specify whether they need a
 * quirk and bypass the IOMMU. If not there, just use the DMA API.
 *
 * If there, the interaction between virtio and DMA API is messy.
 *
 * On most systems with virtio, physical addresses match bus addresses,
 * and it doesn't particularly matter whether we use the DMA API.
 *
 * On some systems, including Xen and any system with a physical device
 * that speaks virtio behind a physical IOMMU, we must use the DMA API
 * for virtio DMA to work at all.
 *
 * On other systems, including SPARC and PPC64, virtio-pci devices are
 * enumerated as though they are behind an IOMMU, but the virtio host
 * ignores the IOMMU, so we must either pretend that the IOMMU isn't
 * there or somehow map everything as the identity.
 *
 * For the time being, we preserve historic behavior and bypass the DMA
 * API.
 *
 * TODO: install a per-device DMA ops structure that does the right thing
 * taking into account all the above quirks, and use the DMA API
 * unconditionally on data path.
 */

static bool vring_use_dma_api(struct virtio_device *vdev)
{
        if (!virtio_has_iommu_quirk(vdev))
                return true;

        /* Otherwise, we are left to guess. */
        /*
         * In theory, it's possible to have a buggy QEMU-supposed
         * emulated Q35 IOMMU and Xen enabled at the same time.  On
         * such a configuration, virtio has never worked and will
         * not work without an even larger kludge.  Instead, enable
         * the DMA API if we're a Xen guest, which at least allows
         * all of the sensible Xen configurations to work correctly.
         */
        if (xen_domain())
                return true;

        return false;
}

size_t virtio_max_dma_size(struct virtio_device *vdev)
{
        size_t max_segment_size = SIZE_MAX;

        if (vring_use_dma_api(vdev))
                max_segment_size = dma_max_mapping_size(&vdev->dev);

        return max_segment_size;
}
EXPORT_SYMBOL_GPL(virtio_max_dma_size);

static void *vring_alloc_queue(struct virtio_device *vdev, size_t size,
                              dma_addr_t *dma_handle, gfp_t flag)
{
        if (vring_use_dma_api(vdev)) {
                return dma_alloc_coherent(vdev->dev.parent, size,
                                          dma_handle, flag);
        } else {
                void *queue = alloc_pages_exact(PAGE_ALIGN(size), flag);

                if (queue) {
                        phys_addr_t phys_addr = virt_to_phys(queue);
                        *dma_handle = (dma_addr_t)phys_addr;

                        /*
                         * Sanity check: make sure we dind't truncate
                         * the address.  The only arches I can find that
                         * have 64-bit phys_addr_t but 32-bit dma_addr_t
                         * are certain non-highmem MIPS and x86
                         * configurations, but these configurations
                         * should never allocate physical pages above 32
                         * bits, so this is fine.  Just in case, throw a
                         * warning and abort if we end up with an
                         * unrepresentable address.
                         */
                        if (WARN_ON_ONCE(*dma_handle != phys_addr)) {
                                free_pages_exact(queue, PAGE_ALIGN(size));
                                return NULL;
                        }
                }
                return queue;
        }
}

static void vring_free_queue(struct virtio_device *vdev, size_t size,
                             void *queue, dma_addr_t dma_handle)
{
        if (vring_use_dma_api(vdev))
                dma_free_coherent(vdev->dev.parent, size, queue, dma_handle);
        else
                free_pages_exact(queue, PAGE_ALIGN(size));
}

/*
 * The DMA ops on various arches are rather gnarly right now, and
 * making all of the arch DMA ops work on the vring device itself
 * is a mess.  For now, we use the parent device for DMA ops.
 */
static inline struct device *vring_dma_dev(const struct vring_virtqueue *vq)
{
        return vq->vq.vdev->dev.parent;
}

/* Map one sg entry. */
static dma_addr_t vring_map_one_sg(const struct vring_virtqueue *vq,
                                   struct scatterlist *sg,
                                   enum dma_data_direction direction)
{
        if (!vq->use_dma_api)
                return (dma_addr_t)sg_phys(sg);

        /*
         * We can't use dma_map_sg, because we don't use scatterlists in
         * the way it expects (we don't guarantee that the scatterlist
         * will exist for the lifetime of the mapping).
         */
        return dma_map_page(vring_dma_dev(vq),
                            sg_page(sg), sg->offset, sg->length,
                            direction);
}

static dma_addr_t vring_map_single(const struct vring_virtqueue *vq,
                                   void *cpu_addr, size_t size,
                                   enum dma_data_direction direction)
{
        if (!vq->use_dma_api)
                return (dma_addr_t)virt_to_phys(cpu_addr);

        return dma_map_single(vring_dma_dev(vq),
                              cpu_addr, size, direction);
}

static int vring_mapping_error(const struct vring_virtqueue *vq,
                               dma_addr_t addr)
{
        if (!vq->use_dma_api)
                return 0;

        return dma_mapping_error(vring_dma_dev(vq), addr);
}


/*
 * Split ring specific functions - *_split().
 */

static void vring_unmap_one_split(const struct vring_virtqueue *vq,
                                  struct vring_desc *desc)
{
        u16 flags;

        if (!vq->use_dma_api)
                return;

        flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);

        if (flags & VRING_DESC_F_INDIRECT) {
                dma_unmap_single(vring_dma_dev(vq),
                                 virtio64_to_cpu(vq->vq.vdev, desc->addr),
                                 virtio32_to_cpu(vq->vq.vdev, desc->len),
                                 (flags & VRING_DESC_F_WRITE) ?
                                 DMA_FROM_DEVICE : DMA_TO_DEVICE);
        } else {
                dma_unmap_page(vring_dma_dev(vq),
                               virtio64_to_cpu(vq->vq.vdev, desc->addr),
                               virtio32_to_cpu(vq->vq.vdev, desc->len),
                               (flags & VRING_DESC_F_WRITE) ?
                               DMA_FROM_DEVICE : DMA_TO_DEVICE);
        }
}

static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
                                               unsigned int total_sg,
                                               gfp_t gfp)
{
        struct vring_desc *desc;
        unsigned int i;

        /*
         * We require lowmem mappings for the descriptors because
         * otherwise virt_to_phys will give us bogus addresses in the
         * virtqueue.
         */
        gfp &= ~__GFP_HIGHMEM;

        desc = kmalloc_array(total_sg, sizeof(struct vring_desc), gfp);
        if (!desc)
                return NULL;

        for (i = 0; i < total_sg; i++)
                desc[i].next = cpu_to_virtio16(_vq->vdev, i + 1);
        return desc;
}

static inline int virtqueue_add_split(struct virtqueue *_vq,
                                      struct scatterlist *sgs[],
                                      unsigned int total_sg,
                                      unsigned int out_sgs,
                                      unsigned int in_sgs,
                                      void *data,
                                      void *ctx,
                                      gfp_t gfp)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        struct scatterlist *sg;
        struct vring_desc *desc;
        unsigned int i, n, avail, descs_used, uninitialized_var(prev), err_idx;
        int head;
        bool indirect;

        START_USE(vq);

        BUG_ON(data == NULL);
        BUG_ON(ctx && vq->indirect);

        if (unlikely(vq->broken)) {
                END_USE(vq);
                return -EIO;
        }

        LAST_ADD_TIME_UPDATE(vq);

        BUG_ON(total_sg == 0);

        head = vq->free_head;

        if (virtqueue_use_indirect(_vq, total_sg))
                desc = alloc_indirect_split(_vq, total_sg, gfp);
        else {
                desc = NULL;
                WARN_ON_ONCE(total_sg > vq->split.vring.num && !vq->indirect);
        }

        if (desc) {
                /* Use a single buffer which doesn't continue */
                indirect = true;
                /* Set up rest to use this indirect table. */
                i = 0;
                descs_used = 1;
        } else {
                indirect = false;
                desc = vq->split.vring.desc;
                i = head;
                descs_used = total_sg;
        }

        if (vq->vq.num_free < descs_used) {
                pr_debug("Can't add buf len %i - avail = %i\n",
                         descs_used, vq->vq.num_free);
                /* FIXME: for historical reasons, we force a notify here if
                 * there are outgoing parts to the buffer.  Presumably the
                 * host should service the ring ASAP. */
                if (out_sgs)
                        vq->notify(&vq->vq);
                if (indirect)
                        kfree(desc);
                END_USE(vq);
                return -ENOSPC;
        }

        for (n = 0; n < out_sgs; n++) {
                for (sg = sgs[n]; sg; sg = sg_next(sg)) {
                        dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_TO_DEVICE);
                        if (vring_mapping_error(vq, addr))
                                goto unmap_release;

                        desc[i].flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT);
                        desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
                        desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length);
                        prev = i;
                        i = virtio16_to_cpu(_vq->vdev, desc[i].next);
                }
        }
        for (; n < (out_sgs + in_sgs); n++) {
                for (sg = sgs[n]; sg; sg = sg_next(sg)) {
                        dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_FROM_DEVICE);
                        if (vring_mapping_error(vq, addr))
                                goto unmap_release;

                        desc[i].flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT | VRING_DESC_F_WRITE);
                        desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
                        desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length);
                        prev = i;
                        i = virtio16_to_cpu(_vq->vdev, desc[i].next);
                }
        }
        /* Last one doesn't continue. */
        desc[prev].flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT);

        if (indirect) {
                /* Now that the indirect table is filled in, map it. */
                dma_addr_t addr = vring_map_single(
                        vq, desc, total_sg * sizeof(struct vring_desc),
                        DMA_TO_DEVICE);
                if (vring_mapping_error(vq, addr))
                        goto unmap_release;

                vq->split.vring.desc[head].flags = cpu_to_virtio16(_vq->vdev,
                                VRING_DESC_F_INDIRECT);
                vq->split.vring.desc[head].addr = cpu_to_virtio64(_vq->vdev,
                                addr);

                vq->split.vring.desc[head].len = cpu_to_virtio32(_vq->vdev,
                                total_sg * sizeof(struct vring_desc));
        }

        /* We're using some buffers from the free list. */
        vq->vq.num_free -= descs_used;

        /* Update free pointer */
        if (indirect)
                vq->free_head = virtio16_to_cpu(_vq->vdev,
                                        vq->split.vring.desc[head].next);
        else
                vq->free_head = i;

        /* Store token and indirect buffer state. */
        vq->split.desc_state[head].data = data;
        if (indirect)
                vq->split.desc_state[head].indir_desc = desc;
        else
                vq->split.desc_state[head].indir_desc = ctx;

        /* Put entry in available array (but don't update avail->idx until they
         * do sync). */
        avail = vq->split.avail_idx_shadow & (vq->split.vring.num - 1);
        vq->split.vring.avail->ring[avail] = cpu_to_virtio16(_vq->vdev, head);

        /* Descriptors and available array need to be set before we expose the
         * new available array entries. */
        virtio_wmb(vq->weak_barriers);
        vq->split.avail_idx_shadow++;
        vq->split.vring.avail->idx = cpu_to_virtio16(_vq->vdev,
                                                vq->split.avail_idx_shadow);
        vq->num_added++;

        pr_debug("Added buffer head %i to %p\n", head, vq);
        END_USE(vq);

        /* This is very unlikely, but theoretically possible.  Kick
         * just in case. */
        if (unlikely(vq->num_added == (1 << 16) - 1))
                virtqueue_kick(_vq);

        return 0;

unmap_release:
        err_idx = i;

        if (indirect)
                i = 0;
        else
                i = head;

        for (n = 0; n < total_sg; n++) {
                if (i == err_idx)
                        break;
                vring_unmap_one_split(vq, &desc[i]);
                i = virtio16_to_cpu(_vq->vdev, desc[i].next);
        }

        if (indirect)
                kfree(desc);

        END_USE(vq);
        return -EIO;
}

static bool virtqueue_kick_prepare_split(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        u16 new, old;
        bool needs_kick;

        START_USE(vq);
        /* We need to expose available array entries before checking avail
         * event. */
        virtio_mb(vq->weak_barriers);

        old = vq->split.avail_idx_shadow - vq->num_added;
        new = vq->split.avail_idx_shadow;
        vq->num_added = 0;

        LAST_ADD_TIME_CHECK(vq);
        LAST_ADD_TIME_INVALID(vq);

        if (vq->event) {
                needs_kick = vring_need_event(virtio16_to_cpu(_vq->vdev,
                                        vring_avail_event(&vq->split.vring)),
                                              new, old);
        } else {
                needs_kick = !(vq->split.vring.used->flags &
                                        cpu_to_virtio16(_vq->vdev,
                                                VRING_USED_F_NO_NOTIFY));
        }
        END_USE(vq);
        return needs_kick;
}

static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
                             void **ctx)
{
        unsigned int i, j;
        __virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);

        /* Clear data ptr. */
        vq->split.desc_state[head].data = NULL;

        /* Put back on free list: unmap first-level descriptors and find end */
        i = head;

        while (vq->split.vring.desc[i].flags & nextflag) {
                vring_unmap_one_split(vq, &vq->split.vring.desc[i]);
                i = virtio16_to_cpu(vq->vq.vdev, vq->split.vring.desc[i].next);
                vq->vq.num_free++;
        }

        vring_unmap_one_split(vq, &vq->split.vring.desc[i]);
        vq->split.vring.desc[i].next = cpu_to_virtio16(vq->vq.vdev,
                                                vq->free_head);
        vq->free_head = head;

        /* Plus final descriptor */
        vq->vq.num_free++;

        if (vq->indirect) {
                struct vring_desc *indir_desc =
                                vq->split.desc_state[head].indir_desc;
                u32 len;

                /* Free the indirect table, if any, now that it's unmapped. */
                if (!indir_desc)
                        return;

                len = virtio32_to_cpu(vq->vq.vdev,
                                vq->split.vring.desc[head].len);

                BUG_ON(!(vq->split.vring.desc[head].flags &
                         cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT)));
                BUG_ON(len == 0 || len % sizeof(struct vring_desc));

                for (j = 0; j < len / sizeof(struct vring_desc); j++)
                        vring_unmap_one_split(vq, &indir_desc[j]);

                kfree(indir_desc);
                vq->split.desc_state[head].indir_desc = NULL;
        } else if (ctx) {
                *ctx = vq->split.desc_state[head].indir_desc;
        }
}

static inline bool more_used_split(const struct vring_virtqueue *vq)
{
        return vq->last_used_idx != virtio16_to_cpu(vq->vq.vdev,
                        vq->split.vring.used->idx);
}

static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq,
                                         unsigned int *len,
                                         void **ctx)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        void *ret;
        unsigned int i;
        u16 last_used;

        START_USE(vq);

        if (unlikely(vq->broken)) {
                END_USE(vq);
                return NULL;
        }

        if (!more_used_split(vq)) {
                pr_debug("No more buffers in queue\n");
                END_USE(vq);
                return NULL;
        }

        /* Only get used array entries after they have been exposed by host. */
        virtio_rmb(vq->weak_barriers);

        last_used = (vq->last_used_idx & (vq->split.vring.num - 1));
        i = virtio32_to_cpu(_vq->vdev,
                        vq->split.vring.used->ring[last_used].id);
        *len = virtio32_to_cpu(_vq->vdev,
                        vq->split.vring.used->ring[last_used].len);

        if (unlikely(i >= vq->split.vring.num)) {
                BAD_RING(vq, "id %u out of range\n", i);
                return NULL;
        }
        if (unlikely(!vq->split.desc_state[i].data)) {
                BAD_RING(vq, "id %u is not a head!\n", i);
                return NULL;
        }

        /* detach_buf_split clears data, so grab it now. */
        ret = vq->split.desc_state[i].data;
        detach_buf_split(vq, i, ctx);
        vq->last_used_idx++;
        /* If we expect an interrupt for the next entry, tell host
         * by writing event index and flush out the write before
         * the read in the next get_buf call. */
        if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT))
                virtio_store_mb(vq->weak_barriers,
                                &vring_used_event(&vq->split.vring),
                                cpu_to_virtio16(_vq->vdev, vq->last_used_idx));

        LAST_ADD_TIME_INVALID(vq);

        END_USE(vq);
        return ret;
}

static void virtqueue_disable_cb_split(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) {
                vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
                if (!vq->event)
                        vq->split.vring.avail->flags =
                                cpu_to_virtio16(_vq->vdev,
                                                vq->split.avail_flags_shadow);
        }
}

static unsigned virtqueue_enable_cb_prepare_split(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        u16 last_used_idx;

        START_USE(vq);

        /* We optimistically turn back on interrupts, then check if there was
         * more to do. */
        /* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
         * either clear the flags bit or point the event index at the next
         * entry. Always do both to keep code simple. */
        if (vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) {
                vq->split.avail_flags_shadow &= ~VRING_AVAIL_F_NO_INTERRUPT;
                if (!vq->event)
                        vq->split.vring.avail->flags =
                                cpu_to_virtio16(_vq->vdev,
                                                vq->split.avail_flags_shadow);
        }
        vring_used_event(&vq->split.vring) = cpu_to_virtio16(_vq->vdev,
                        last_used_idx = vq->last_used_idx);
        END_USE(vq);
        return last_used_idx;
}

static bool virtqueue_poll_split(struct virtqueue *_vq, unsigned last_used_idx)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev,
                        vq->split.vring.used->idx);
}

static bool virtqueue_enable_cb_delayed_split(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        u16 bufs;

        START_USE(vq);

        /* We optimistically turn back on interrupts, then check if there was
         * more to do. */
        /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
         * either clear the flags bit or point the event index at the next
         * entry. Always update the event index to keep code simple. */
        if (vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) {
                vq->split.avail_flags_shadow &= ~VRING_AVAIL_F_NO_INTERRUPT;
                if (!vq->event)
                        vq->split.vring.avail->flags =
                                cpu_to_virtio16(_vq->vdev,
                                                vq->split.avail_flags_shadow);
        }
        /* TODO: tune this threshold */
        bufs = (u16)(vq->split.avail_idx_shadow - vq->last_used_idx) * 3 / 4;

        virtio_store_mb(vq->weak_barriers,
                        &vring_used_event(&vq->split.vring),
                        cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs));

        if (unlikely((u16)(virtio16_to_cpu(_vq->vdev, vq->split.vring.used->idx)
                                        - vq->last_used_idx) > bufs)) {
                END_USE(vq);
                return false;
        }

        END_USE(vq);
        return true;
}

static void *virtqueue_detach_unused_buf_split(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        unsigned int i;
        void *buf;

        START_USE(vq);

        for (i = 0; i < vq->split.vring.num; i++) {
                if (!vq->split.desc_state[i].data)
                        continue;
                /* detach_buf_split clears data, so grab it now. */
                buf = vq->split.desc_state[i].data;
                detach_buf_split(vq, i, NULL);
                vq->split.avail_idx_shadow--;
                vq->split.vring.avail->idx = cpu_to_virtio16(_vq->vdev,
                                vq->split.avail_idx_shadow);
                END_USE(vq);
                return buf;
        }
        /* That should have freed everything. */
        BUG_ON(vq->vq.num_free != vq->split.vring.num);

        END_USE(vq);
        return NULL;
}

static struct virtqueue *vring_create_virtqueue_split(
        unsigned int index,
        unsigned int num,
        unsigned int vring_align,
        struct virtio_device *vdev,
        bool weak_barriers,
        bool may_reduce_num,
        bool context,
        bool (*notify)(struct virtqueue *),
        void (*callback)(struct virtqueue *),
        const char *name)
{
        struct virtqueue *vq;
        void *queue = NULL;
        dma_addr_t dma_addr;
        size_t queue_size_in_bytes;
        struct vring vring;

        /* We assume num is a power of 2. */
        if (num & (num - 1)) {
                dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
                return NULL;
        }

        /* TODO: allocate each queue chunk individually */
        for (; num && vring_size(num, vring_align) > PAGE_SIZE; num /= 2) {
                queue = vring_alloc_queue(vdev, vring_size(num, vring_align),
                                          &dma_addr,
                                          GFP_KERNEL|__GFP_NOWARN|__GFP_ZERO);
                if (queue)
                        break;
                if (!may_reduce_num)
                        return NULL;
        }

        if (!num)
                return NULL;

        if (!queue) {
                /* Try to get a single page. You are my only hope! */
                queue = vring_alloc_queue(vdev, vring_size(num, vring_align),
                                          &dma_addr, GFP_KERNEL|__GFP_ZERO);
        }
        if (!queue)
                return NULL;

        queue_size_in_bytes = vring_size(num, vring_align);
        vring_init(&vring, num, queue, vring_align);

        vq = __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
                                   notify, callback, name);
        if (!vq) {
                vring_free_queue(vdev, queue_size_in_bytes, queue,
                                 dma_addr);
                return NULL;
        }

        to_vvq(vq)->split.queue_dma_addr = dma_addr;
        to_vvq(vq)->split.queue_size_in_bytes = queue_size_in_bytes;
        to_vvq(vq)->we_own_ring = true;

        return vq;
}


/*
 * Packed ring specific functions - *_packed().
 */

static void vring_unmap_state_packed(const struct vring_virtqueue *vq,
                                     struct vring_desc_extra_packed *state)
{
        u16 flags;

        if (!vq->use_dma_api)
                return;

        flags = state->flags;

        if (flags & VRING_DESC_F_INDIRECT) {
                dma_unmap_single(vring_dma_dev(vq),
                                 state->addr, state->len,
                                 (flags & VRING_DESC_F_WRITE) ?
                                 DMA_FROM_DEVICE : DMA_TO_DEVICE);
        } else {
                dma_unmap_page(vring_dma_dev(vq),
                               state->addr, state->len,
                               (flags & VRING_DESC_F_WRITE) ?
                               DMA_FROM_DEVICE : DMA_TO_DEVICE);
        }
}

static void vring_unmap_desc_packed(const struct vring_virtqueue *vq,
                                   struct vring_packed_desc *desc)
{
        u16 flags;

        if (!vq->use_dma_api)
                return;

        flags = le16_to_cpu(desc->flags);

        if (flags & VRING_DESC_F_INDIRECT) {
                dma_unmap_single(vring_dma_dev(vq),
                                 le64_to_cpu(desc->addr),
                                 le32_to_cpu(desc->len),
                                 (flags & VRING_DESC_F_WRITE) ?
                                 DMA_FROM_DEVICE : DMA_TO_DEVICE);
        } else {
                dma_unmap_page(vring_dma_dev(vq),
                               le64_to_cpu(desc->addr),
                               le32_to_cpu(desc->len),
                               (flags & VRING_DESC_F_WRITE) ?
                               DMA_FROM_DEVICE : DMA_TO_DEVICE);
        }
}

static struct vring_packed_desc *alloc_indirect_packed(unsigned int total_sg,
                                                       gfp_t gfp)
{
        struct vring_packed_desc *desc;

        /*
         * We require lowmem mappings for the descriptors because
         * otherwise virt_to_phys will give us bogus addresses in the
         * virtqueue.
         */
        gfp &= ~__GFP_HIGHMEM;

        desc = kmalloc_array(total_sg, sizeof(struct vring_packed_desc), gfp);

        return desc;
}

static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
                                       struct scatterlist *sgs[],
                                       unsigned int total_sg,
                                       unsigned int out_sgs,
                                       unsigned int in_sgs,
                                       void *data,
                                       gfp_t gfp)
{
        struct vring_packed_desc *desc;
        struct scatterlist *sg;
        unsigned int i, n, err_idx;
        u16 head, id;
        dma_addr_t addr;

        head = vq->packed.next_avail_idx;
        desc = alloc_indirect_packed(total_sg, gfp);

        if (unlikely(vq->vq.num_free < 1)) {
                pr_debug("Can't add buf len 1 - avail = 0\n");
                kfree(desc);
                END_USE(vq);
                return -ENOSPC;
        }

        i = 0;
        id = vq->free_head;
        BUG_ON(id == vq->packed.vring.num);

        for (n = 0; n < out_sgs + in_sgs; n++) {
                for (sg = sgs[n]; sg; sg = sg_next(sg)) {
                        addr = vring_map_one_sg(vq, sg, n < out_sgs ?
                                        DMA_TO_DEVICE : DMA_FROM_DEVICE);
                        if (vring_mapping_error(vq, addr))
                                goto unmap_release;

                        desc[i].flags = cpu_to_le16(n < out_sgs ?
                                                0 : VRING_DESC_F_WRITE);
                        desc[i].addr = cpu_to_le64(addr);
                        desc[i].len = cpu_to_le32(sg->length);
                        i++;
                }
        }

        /* Now that the indirect table is filled in, map it. */
        addr = vring_map_single(vq, desc,
                        total_sg * sizeof(struct vring_packed_desc),
                        DMA_TO_DEVICE);
        if (vring_mapping_error(vq, addr))
                goto unmap_release;

        vq->packed.vring.desc[head].addr = cpu_to_le64(addr);
        vq->packed.vring.desc[head].len = cpu_to_le32(total_sg *
                                sizeof(struct vring_packed_desc));
        vq->packed.vring.desc[head].id = cpu_to_le16(id);

        if (vq->use_dma_api) {
                vq->packed.desc_extra[id].addr = addr;
                vq->packed.desc_extra[id].len = total_sg *
                                sizeof(struct vring_packed_desc);
                vq->packed.desc_extra[id].flags = VRING_DESC_F_INDIRECT |
                                                  vq->packed.avail_used_flags;
        }

        /*
         * A driver MUST NOT make the first descriptor in the list
         * available before all subsequent descriptors comprising
         * the list are made available.
         */
        virtio_wmb(vq->weak_barriers);
        vq->packed.vring.desc[head].flags = cpu_to_le16(VRING_DESC_F_INDIRECT |
                                                vq->packed.avail_used_flags);

        /* We're using some buffers from the free list. */
        vq->vq.num_free -= 1;

        /* Update free pointer */
        n = head + 1;
        if (n >= vq->packed.vring.num) {
                n = 0;
                vq->packed.avail_wrap_counter ^= 1;
                vq->packed.avail_used_flags ^=
                                1 << VRING_PACKED_DESC_F_AVAIL |
                                1 << VRING_PACKED_DESC_F_USED;
        }
        vq->packed.next_avail_idx = n;
        vq->free_head = vq->packed.desc_state[id].next;

        /* Store token and indirect buffer state. */
        vq->packed.desc_state[id].num = 1;
        vq->packed.desc_state[id].data = data;
        vq->packed.desc_state[id].indir_desc = desc;
        vq->packed.desc_state[id].last = id;

        vq->num_added += 1;

        pr_debug("Added buffer head %i to %p\n", head, vq);
        END_USE(vq);

        return 0;

unmap_release:
        err_idx = i;

        for (i = 0; i < err_idx; i++)
                vring_unmap_desc_packed(vq, &desc[i]);

        kfree(desc);

        END_USE(vq);
        return -EIO;
}

static inline int virtqueue_add_packed(struct virtqueue *_vq,
                                       struct scatterlist *sgs[],
                                       unsigned int total_sg,
                                       unsigned int out_sgs,
                                       unsigned int in_sgs,
                                       void *data,
                                       void *ctx,
                                       gfp_t gfp)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        struct vring_packed_desc *desc;
        struct scatterlist *sg;
        unsigned int i, n, c, descs_used, err_idx;
        __le16 uninitialized_var(head_flags), flags;
        u16 head, id, uninitialized_var(prev), curr, avail_used_flags;

        START_USE(vq);

        BUG_ON(data == NULL);
        BUG_ON(ctx && vq->indirect);

        if (unlikely(vq->broken)) {
                END_USE(vq);
                return -EIO;
        }

        LAST_ADD_TIME_UPDATE(vq);

        BUG_ON(total_sg == 0);

        if (virtqueue_use_indirect(_vq, total_sg))
                return virtqueue_add_indirect_packed(vq, sgs, total_sg,
                                out_sgs, in_sgs, data, gfp);

        head = vq->packed.next_avail_idx;
        avail_used_flags = vq->packed.avail_used_flags;

        WARN_ON_ONCE(total_sg > vq->packed.vring.num && !vq->indirect);

        desc = vq->packed.vring.desc;
        i = head;
        descs_used = total_sg;

        if (unlikely(vq->vq.num_free < descs_used)) {
                pr_debug("Can't add buf len %i - avail = %i\n",
                         descs_used, vq->vq.num_free);
                END_USE(vq);
                return -ENOSPC;
        }

        id = vq->free_head;
        BUG_ON(id == vq->packed.vring.num);

        curr = id;
        c = 0;
        for (n = 0; n < out_sgs + in_sgs; n++) {
                for (sg = sgs[n]; sg; sg = sg_next(sg)) {
                        dma_addr_t addr = vring_map_one_sg(vq, sg, n < out_sgs ?
                                        DMA_TO_DEVICE : DMA_FROM_DEVICE);
                        if (vring_mapping_error(vq, addr))
                                goto unmap_release;

                        flags = cpu_to_le16(vq->packed.avail_used_flags |
                                    (++c == total_sg ? 0 : VRING_DESC_F_NEXT) |
                                    (n < out_sgs ? 0 : VRING_DESC_F_WRITE));
                        if (i == head)
                                head_flags = flags;
                        else
                                desc[i].flags = flags;

                        desc[i].addr = cpu_to_le64(addr);
                        desc[i].len = cpu_to_le32(sg->length);
                        desc[i].id = cpu_to_le16(id);

                        if (unlikely(vq->use_dma_api)) {
                                vq->packed.desc_extra[curr].addr = addr;
                                vq->packed.desc_extra[curr].len = sg->length;
                                vq->packed.desc_extra[curr].flags =
                                        le16_to_cpu(flags);
                        }
                        prev = curr;
                        curr = vq->packed.desc_state[curr].next;

                        if ((unlikely(++i >= vq->packed.vring.num))) {
                                i = 0;
                                vq->packed.avail_used_flags ^=
                                        1 << VRING_PACKED_DESC_F_AVAIL |
                                        1 << VRING_PACKED_DESC_F_USED;
                        }
                }
        }

        if (i < head)
                vq->packed.avail_wrap_counter ^= 1;

        /* We're using some buffers from the free list. */
        vq->vq.num_free -= descs_used;

        /* Update free pointer */
        vq->packed.next_avail_idx = i;
        vq->free_head = curr;

        /* Store token. */
        vq->packed.desc_state[id].num = descs_used;
        vq->packed.desc_state[id].data = data;
        vq->packed.desc_state[id].indir_desc = ctx;
        vq->packed.desc_state[id].last = prev;

        /*
         * A driver MUST NOT make the first descriptor in the list
         * available before all subsequent descriptors comprising
         * the list are made available.
         */
        virtio_wmb(vq->weak_barriers);
        vq->packed.vring.desc[head].flags = head_flags;
        vq->num_added += descs_used;

        pr_debug("Added buffer head %i to %p\n", head, vq);
        END_USE(vq);

        return 0;

unmap_release:
        err_idx = i;
        i = head;

        vq->packed.avail_used_flags = avail_used_flags;

        for (n = 0; n < total_sg; n++) {
                if (i == err_idx)
                        break;
                vring_unmap_desc_packed(vq, &desc[i]);
                i++;
                if (i >= vq->packed.vring.num)
                        i = 0;
        }

        END_USE(vq);
        return -EIO;
}

static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        u16 new, old, off_wrap, flags, wrap_counter, event_idx;
        bool needs_kick;
        union {
                struct {
                        __le16 off_wrap;
                        __le16 flags;
                };
                u32 u32;
        } snapshot;

        START_USE(vq);

        /*
         * We need to expose the new flags value before checking notification
         * suppressions.
         */
        virtio_mb(vq->weak_barriers);

        old = vq->packed.next_avail_idx - vq->num_added;
        new = vq->packed.next_avail_idx;
        vq->num_added = 0;

        snapshot.u32 = *(u32 *)vq->packed.vring.device;
        flags = le16_to_cpu(snapshot.flags);

        LAST_ADD_TIME_CHECK(vq);
        LAST_ADD_TIME_INVALID(vq);

        if (flags != VRING_PACKED_EVENT_FLAG_DESC) {
                needs_kick = (flags != VRING_PACKED_EVENT_FLAG_DISABLE);
                goto out;
        }

        off_wrap = le16_to_cpu(snapshot.off_wrap);

        wrap_counter = off_wrap >> VRING_PACKED_EVENT_F_WRAP_CTR;
        event_idx = off_wrap & ~(1 << VRING_PACKED_EVENT_F_WRAP_CTR);
        if (wrap_counter != vq->packed.avail_wrap_counter)
                event_idx -= vq->packed.vring.num;

        needs_kick = vring_need_event(event_idx, new, old);
out:
        END_USE(vq);
        return needs_kick;
}

static void detach_buf_packed(struct vring_virtqueue *vq,
                              unsigned int id, void **ctx)
{
        struct vring_desc_state_packed *state = NULL;
        struct vring_packed_desc *desc;
        unsigned int i, curr;

        state = &vq->packed.desc_state[id];

        /* Clear data ptr. */
        state->data = NULL;

        vq->packed.desc_state[state->last].next = vq->free_head;
        vq->free_head = id;
        vq->vq.num_free += state->num;

        if (unlikely(vq->use_dma_api)) {
                curr = id;
                for (i = 0; i < state->num; i++) {
                        vring_unmap_state_packed(vq,
                                &vq->packed.desc_extra[curr]);
                        curr = vq->packed.desc_state[curr].next;
                }
        }

        if (vq->indirect) {
                u32 len;

                /* Free the indirect table, if any, now that it's unmapped. */
                desc = state->indir_desc;
                if (!desc)
                        return;

                if (vq->use_dma_api) {
                        len = vq->packed.desc_extra[id].len;
                        for (i = 0; i < len / sizeof(struct vring_packed_desc);
                                        i++)
                                vring_unmap_desc_packed(vq, &desc[i]);
                }
                kfree(desc);
                state->indir_desc = NULL;
        } else if (ctx) {
                *ctx = state->indir_desc;
        }
}

static inline bool is_used_desc_packed(const struct vring_virtqueue *vq,
                                       u16 idx, bool used_wrap_counter)
{
        bool avail, used;
        u16 flags;

        flags = le16_to_cpu(vq->packed.vring.desc[idx].flags);
        avail = !!(flags & (1 << VRING_PACKED_DESC_F_AVAIL));
        used = !!(flags & (1 << VRING_PACKED_DESC_F_USED));

        return avail == used && used == used_wrap_counter;
}

static inline bool more_used_packed(const struct vring_virtqueue *vq)
{
        return is_used_desc_packed(vq, vq->last_used_idx,
                        vq->packed.used_wrap_counter);
}

static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq,
                                          unsigned int *len,
                                          void **ctx)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        u16 last_used, id;
        void *ret;

        START_USE(vq);

        if (unlikely(vq->broken)) {
                END_USE(vq);
                return NULL;
        }

        if (!more_used_packed(vq)) {
                pr_debug("No more buffers in queue\n");
                END_USE(vq);
                return NULL;
        }

        /* Only get used elements after they have been exposed by host. */
        virtio_rmb(vq->weak_barriers);

        last_used = vq->last_used_idx;
        id = le16_to_cpu(vq->packed.vring.desc[last_used].id);
        *len = le32_to_cpu(vq->packed.vring.desc[last_used].len);

        if (unlikely(id >= vq->packed.vring.num)) {
                BAD_RING(vq, "id %u out of range\n", id);
                return NULL;
        }
        if (unlikely(!vq->packed.desc_state[id].data)) {
                BAD_RING(vq, "id %u is not a head!\n", id);
                return NULL;
        }

        /* detach_buf_packed clears data, so grab it now. */
        ret = vq->packed.desc_state[id].data;
        detach_buf_packed(vq, id, ctx);

        vq->last_used_idx += vq->packed.desc_state[id].num;
        if (unlikely(vq->last_used_idx >= vq->packed.vring.num)) {
                vq->last_used_idx -= vq->packed.vring.num;
                vq->packed.used_wrap_counter ^= 1;
        }

        /*
         * If we expect an interrupt for the next entry, tell host
         * by writing event index and flush out the write before
         * the read in the next get_buf call.
         */
        if (vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DESC)
                virtio_store_mb(vq->weak_barriers,
                                &vq->packed.vring.driver->off_wrap,
                                cpu_to_le16(vq->last_used_idx |
                                        (vq->packed.used_wrap_counter <<
                                         VRING_PACKED_EVENT_F_WRAP_CTR)));

        LAST_ADD_TIME_INVALID(vq);

        END_USE(vq);
        return ret;
}

static void virtqueue_disable_cb_packed(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        if (vq->packed.event_flags_shadow != VRING_PACKED_EVENT_FLAG_DISABLE) {
                vq->packed.event_flags_shadow = VRING_PACKED_EVENT_FLAG_DISABLE;
                vq->packed.vring.driver->flags =
                        cpu_to_le16(vq->packed.event_flags_shadow);
        }
}

static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        START_USE(vq);

        /*
         * We optimistically turn back on interrupts, then check if there was
         * more to do.
         */

        if (vq->event) {
                vq->packed.vring.driver->off_wrap =
                        cpu_to_le16(vq->last_used_idx |
                                (vq->packed.used_wrap_counter <<
                                 VRING_PACKED_EVENT_F_WRAP_CTR));
                /*
                 * We need to update event offset and event wrap
                 * counter first before updating event flags.
                 */
                virtio_wmb(vq->weak_barriers);
        }

        if (vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DISABLE) {
                vq->packed.event_flags_shadow = vq->event ?
                                VRING_PACKED_EVENT_FLAG_DESC :
                                VRING_PACKED_EVENT_FLAG_ENABLE;
                vq->packed.vring.driver->flags =
                                cpu_to_le16(vq->packed.event_flags_shadow);
        }

        END_USE(vq);
        return vq->last_used_idx | ((u16)vq->packed.used_wrap_counter <<
                        VRING_PACKED_EVENT_F_WRAP_CTR);
}

static bool virtqueue_poll_packed(struct virtqueue *_vq, u16 off_wrap)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        bool wrap_counter;
        u16 used_idx;

        wrap_counter = off_wrap >> VRING_PACKED_EVENT_F_WRAP_CTR;
        used_idx = off_wrap & ~(1 << VRING_PACKED_EVENT_F_WRAP_CTR);

        return is_used_desc_packed(vq, used_idx, wrap_counter);
}

static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        u16 used_idx, wrap_counter;
        u16 bufs;

        START_USE(vq);

        /*
         * We optimistically turn back on interrupts, then check if there was
         * more to do.
         */

        if (vq->event) {
                /* TODO: tune this threshold */
                bufs = (vq->packed.vring.num - vq->vq.num_free) * 3 / 4;
                wrap_counter = vq->packed.used_wrap_counter;

                used_idx = vq->last_used_idx + bufs;
                if (used_idx >= vq->packed.vring.num) {
                        used_idx -= vq->packed.vring.num;
                        wrap_counter ^= 1;
                }

                vq->packed.vring.driver->off_wrap = cpu_to_le16(used_idx |
                        (wrap_counter << VRING_PACKED_EVENT_F_WRAP_CTR));

                /*
                 * We need to update event offset and event wrap
                 * counter first before updating event flags.
                 */
                virtio_wmb(vq->weak_barriers);
        } else {
                used_idx = vq->last_used_idx;
                wrap_counter = vq->packed.used_wrap_counter;
        }

        if (vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DISABLE) {
                vq->packed.event_flags_shadow = vq->event ?
                                VRING_PACKED_EVENT_FLAG_DESC :
                                VRING_PACKED_EVENT_FLAG_ENABLE;
                vq->packed.vring.driver->flags =
                                cpu_to_le16(vq->packed.event_flags_shadow);
        }

        /*
         * We need to update event suppression structure first
         * before re-checking for more used buffers.
         */
        virtio_mb(vq->weak_barriers);

        if (is_used_desc_packed(vq, used_idx, wrap_counter)) {
                END_USE(vq);
                return false;
        }

        END_USE(vq);
        return true;
}

static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        unsigned int i;
        void *buf;

        START_USE(vq);

        for (i = 0; i < vq->packed.vring.num; i++) {
                if (!vq->packed.desc_state[i].data)
                        continue;
                /* detach_buf clears data, so grab it now. */
                buf = vq->packed.desc_state[i].data;
                detach_buf_packed(vq, i, NULL);
                END_USE(vq);
                return buf;
        }
        /* That should have freed everything. */
        BUG_ON(vq->vq.num_free != vq->packed.vring.num);

        END_USE(vq);
        return NULL;
}

static struct virtqueue *vring_create_virtqueue_packed(
        unsigned int index,
        unsigned int num,
        unsigned int vring_align,
        struct virtio_device *vdev,
        bool weak_barriers,
        bool may_reduce_num,
        bool context,
        bool (*notify)(struct virtqueue *),
        void (*callback)(struct virtqueue *),
        const char *name)
{
        struct vring_virtqueue *vq;
        struct vring_packed_desc *ring;
        struct vring_packed_desc_event *driver, *device;
        dma_addr_t ring_dma_addr, driver_event_dma_addr, device_event_dma_addr;
        size_t ring_size_in_bytes, event_size_in_bytes;
        unsigned int i;

        ring_size_in_bytes = num * sizeof(struct vring_packed_desc);

        ring = vring_alloc_queue(vdev, ring_size_in_bytes,
                                 &ring_dma_addr,
                                 GFP_KERNEL|__GFP_NOWARN|__GFP_ZERO);
        if (!ring)
                goto err_ring;

        event_size_in_bytes = sizeof(struct vring_packed_desc_event);

        driver = vring_alloc_queue(vdev, event_size_in_bytes,
                                   &driver_event_dma_addr,
                                   GFP_KERNEL|__GFP_NOWARN|__GFP_ZERO);
        if (!driver)
                goto err_driver;

        device = vring_alloc_queue(vdev, event_size_in_bytes,
                                   &device_event_dma_addr,
                                   GFP_KERNEL|__GFP_NOWARN|__GFP_ZERO);
        if (!device)
                goto err_device;

        vq = kmalloc(sizeof(*vq), GFP_KERNEL);
        if (!vq)
                goto err_vq;

        vq->vq.callback = callback;
        vq->vq.vdev = vdev;
        vq->vq.name = name;
        vq->vq.num_free = num;
        vq->vq.index = index;
        vq->we_own_ring = true;
        vq->notify = notify;
        vq->weak_barriers = weak_barriers;
        vq->broken = false;
        vq->last_used_idx = 0;
        vq->num_added = 0;
        vq->packed_ring = true;
        vq->use_dma_api = vring_use_dma_api(vdev);
        list_add_tail(&vq->vq.list, &vdev->vqs);
#ifdef DEBUG
        vq->in_use = false;
        vq->last_add_time_valid = false;
#endif

        vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC) &&
                !context;
        vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);

        if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
                vq->weak_barriers = false;

        vq->packed.ring_dma_addr = ring_dma_addr;
        vq->packed.driver_event_dma_addr = driver_event_dma_addr;
        vq->packed.device_event_dma_addr = device_event_dma_addr;

        vq->packed.ring_size_in_bytes = ring_size_in_bytes;
        vq->packed.event_size_in_bytes = event_size_in_bytes;

        vq->packed.vring.num = num;
        vq->packed.vring.desc = ring;
        vq->packed.vring.driver = driver;
        vq->packed.vring.device = device;

        vq->packed.next_avail_idx = 0;
        vq->packed.avail_wrap_counter = 1;
        vq->packed.used_wrap_counter = 1;
        vq->packed.event_flags_shadow = 0;
        vq->packed.avail_used_flags = 1 << VRING_PACKED_DESC_F_AVAIL;

        vq->packed.desc_state = kmalloc_array(num,
                        sizeof(struct vring_desc_state_packed),
                        GFP_KERNEL);
        if (!vq->packed.desc_state)
                goto err_desc_state;

        memset(vq->packed.desc_state, 0,
                num * sizeof(struct vring_desc_state_packed));

        /* Put everything in free lists. */
        vq->free_head = 0;
        for (i = 0; i < num-1; i++)
                vq->packed.desc_state[i].next = i + 1;

        vq->packed.desc_extra = kmalloc_array(num,
                        sizeof(struct vring_desc_extra_packed),
                        GFP_KERNEL);
        if (!vq->packed.desc_extra)
                goto err_desc_extra;

        memset(vq->packed.desc_extra, 0,
                num * sizeof(struct vring_desc_extra_packed));

        /* No callback?  Tell other side not to bother us. */
        if (!callback) {
                vq->packed.event_flags_shadow = VRING_PACKED_EVENT_FLAG_DISABLE;
                vq->packed.vring.driver->flags =
                        cpu_to_le16(vq->packed.event_flags_shadow);
        }

        return &vq->vq;

err_desc_extra:
        kfree(vq->packed.desc_state);
err_desc_state:
        kfree(vq);
err_vq:
        vring_free_queue(vdev, event_size_in_bytes, device, ring_dma_addr);
err_device:
        vring_free_queue(vdev, event_size_in_bytes, driver, ring_dma_addr);
err_driver:
        vring_free_queue(vdev, ring_size_in_bytes, ring, ring_dma_addr);
err_ring:
        return NULL;
}


/*
 * Generic functions and exported symbols.
 */

static inline int virtqueue_add(struct virtqueue *_vq,
                                struct scatterlist *sgs[],
                                unsigned int total_sg,
                                unsigned int out_sgs,
                                unsigned int in_sgs,
                                void *data,
                                void *ctx,
                                gfp_t gfp)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        return vq->packed_ring ? virtqueue_add_packed(_vq, sgs, total_sg,
                                        out_sgs, in_sgs, data, ctx, gfp) :
                                 virtqueue_add_split(_vq, sgs, total_sg,
                                        out_sgs, in_sgs, data, ctx, gfp);
}

/**
 * virtqueue_add_sgs - expose buffers to other end
 * @_vq: the struct virtqueue we're talking about.
 * @sgs: array of terminated scatterlists.
 * @out_sgs: the number of scatterlists readable by other side
 * @in_sgs: the number of scatterlists which are writable (after readable ones)
 * @data: the token identifying the buffer.
 * @gfp: how to do memory allocations (if necessary).
 *
 * Caller must ensure we don't call this with other virtqueue operations
 * at the same time (except where noted).
 *
 * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
 */
int virtqueue_add_sgs(struct virtqueue *_vq,
                      struct scatterlist *sgs[],
                      unsigned int out_sgs,
                      unsigned int in_sgs,
                      void *data,
                      gfp_t gfp)
{
        unsigned int i, total_sg = 0;

        /* Count them first. */
        for (i = 0; i < out_sgs + in_sgs; i++) {
                struct scatterlist *sg;

                for (sg = sgs[i]; sg; sg = sg_next(sg))
                        total_sg++;
        }
        return virtqueue_add(_vq, sgs, total_sg, out_sgs, in_sgs,
                             data, NULL, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_sgs);

/**
 * virtqueue_add_outbuf - expose output buffers to other end
 * @vq: the struct virtqueue we're talking about.
 * @sg: scatterlist (must be well-formed and terminated!)
 * @num: the number of entries in @sg readable by other side
 * @data: the token identifying the buffer.
 * @gfp: how to do memory allocations (if necessary).
 *
 * Caller must ensure we don't call this with other virtqueue operations
 * at the same time (except where noted).
 *
 * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
 */
int virtqueue_add_outbuf(struct virtqueue *vq,
                         struct scatterlist *sg, unsigned int num,
                         void *data,
                         gfp_t gfp)
{
        return virtqueue_add(vq, &sg, num, 1, 0, data, NULL, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_outbuf);

/**
 * virtqueue_add_inbuf - expose input buffers to other end
 * @vq: the struct virtqueue we're talking about.
 * @sg: scatterlist (must be well-formed and terminated!)
 * @num: the number of entries in @sg writable by other side
 * @data: the token identifying the buffer.
 * @gfp: how to do memory allocations (if necessary).
 *
 * Caller must ensure we don't call this with other virtqueue operations
 * at the same time (except where noted).
 *
 * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
 */
int virtqueue_add_inbuf(struct virtqueue *vq,
                        struct scatterlist *sg, unsigned int num,
                        void *data,
                        gfp_t gfp)
{
        return virtqueue_add(vq, &sg, num, 0, 1, data, NULL, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_inbuf);

/**
 * virtqueue_add_inbuf_ctx - expose input buffers to other end
 * @vq: the struct virtqueue we're talking about.
 * @sg: scatterlist (must be well-formed and terminated!)
 * @num: the number of entries in @sg writable by other side
 * @data: the token identifying the buffer.
 * @ctx: extra context for the token
 * @gfp: how to do memory allocations (if necessary).
 *
 * Caller must ensure we don't call this with other virtqueue operations
 * at the same time (except where noted).
 *
 * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
 */
int virtqueue_add_inbuf_ctx(struct virtqueue *vq,
                        struct scatterlist *sg, unsigned int num,
                        void *data,
                        void *ctx,
                        gfp_t gfp)
{
        return virtqueue_add(vq, &sg, num, 0, 1, data, ctx, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_inbuf_ctx);

/**
 * virtqueue_kick_prepare - first half of split virtqueue_kick call.
 * @_vq: the struct virtqueue
 *
 * Instead of virtqueue_kick(), you can do:
 *      if (virtqueue_kick_prepare(vq))
 *              virtqueue_notify(vq);
 *
 * This is sometimes useful because the virtqueue_kick_prepare() needs
 * to be serialized, but the actual virtqueue_notify() call does not.
 */
bool virtqueue_kick_prepare(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        return vq->packed_ring ? virtqueue_kick_prepare_packed(_vq) :
                                 virtqueue_kick_prepare_split(_vq);
}
EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);

/**
 * virtqueue_notify - second half of split virtqueue_kick call.
 * @_vq: the struct virtqueue
 *
 * This does not need to be serialized.
 *
 * Returns false if host notify failed or queue is broken, otherwise true.
 */
bool virtqueue_notify(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        if (unlikely(vq->broken))
                return false;

        /* Prod other side to tell it about changes. */
        if (!vq->notify(_vq)) {
                vq->broken = true;
                return false;
        }
        return true;
}
EXPORT_SYMBOL_GPL(virtqueue_notify);

/**
 * virtqueue_kick - update after add_buf
 * @vq: the struct virtqueue
 *
 * After one or more virtqueue_add_* calls, invoke this to kick
 * the other side.
 *
 * Caller must ensure we don't call this with other virtqueue
 * operations at the same time (except where noted).
 *
 * Returns false if kick failed, otherwise true.
 */
bool virtqueue_kick(struct virtqueue *vq)
{
        if (virtqueue_kick_prepare(vq))
                return virtqueue_notify(vq);
        return true;
}
EXPORT_SYMBOL_GPL(virtqueue_kick);

/**
 * virtqueue_get_buf - get the next used buffer
 * @_vq: the struct virtqueue we're talking about.
 * @len: the length written into the buffer
 * @ctx: extra context for the token
 *
 * If the device wrote data into the buffer, @len will be set to the
 * amount written.  This means you don't need to clear the buffer
 * beforehand to ensure there's no data leakage in the case of short
 * writes.
 *
 * Caller must ensure we don't call this with other virtqueue
 * operations at the same time (except where noted).
 *
 * Returns NULL if there are no used buffers, or the "data" token
 * handed to virtqueue_add_*().
 */
void *virtqueue_get_buf_ctx(struct virtqueue *_vq, unsigned int *len,
                            void **ctx)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        return vq->packed_ring ? virtqueue_get_buf_ctx_packed(_vq, len, ctx) :
                                 virtqueue_get_buf_ctx_split(_vq, len, ctx);
}
EXPORT_SYMBOL_GPL(virtqueue_get_buf_ctx);

void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
{
        return virtqueue_get_buf_ctx(_vq, len, NULL);
}
EXPORT_SYMBOL_GPL(virtqueue_get_buf);
/**
 * virtqueue_disable_cb - disable callbacks
 * @_vq: the struct virtqueue we're talking about.
 *
 * Note that this is not necessarily synchronous, hence unreliable and only
 * useful as an optimization.
 *
 * Unlike other operations, this need not be serialized.
 */
void virtqueue_disable_cb(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        if (vq->packed_ring)
                virtqueue_disable_cb_packed(_vq);
        else
                virtqueue_disable_cb_split(_vq);
}
EXPORT_SYMBOL_GPL(virtqueue_disable_cb);

/**
 * virtqueue_enable_cb_prepare - restart callbacks after disable_cb
 * @_vq: the struct virtqueue we're talking about.
 *
 * This re-enables callbacks; it returns current queue state
 * in an opaque unsigned value. This value should be later tested by
 * virtqueue_poll, to detect a possible race between the driver checking for
 * more work, and enabling callbacks.
 *
 * Caller must ensure we don't call this with other virtqueue
 * operations at the same time (except where noted).
 */
unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        return vq->packed_ring ? virtqueue_enable_cb_prepare_packed(_vq) :
                                 virtqueue_enable_cb_prepare_split(_vq);
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);

/**
 * virtqueue_poll - query pending used buffers
 * @_vq: the struct virtqueue we're talking about.
 * @last_used_idx: virtqueue state (from call to virtqueue_enable_cb_prepare).
 *
 * Returns "true" if there are pending used buffers in the queue.
 *
 * This does not need to be serialized.
 */
bool virtqueue_poll(struct virtqueue *_vq, unsigned last_used_idx)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        virtio_mb(vq->weak_barriers);
        return vq->packed_ring ? virtqueue_poll_packed(_vq, last_used_idx) :
                                 virtqueue_poll_split(_vq, last_used_idx);
}
EXPORT_SYMBOL_GPL(virtqueue_poll);

/**
 * virtqueue_enable_cb - restart callbacks after disable_cb.
 * @_vq: the struct virtqueue we're talking about.
 *
 * This re-enables callbacks; it returns "false" if there are pending
 * buffers in the queue, to detect a possible race between the driver
 * checking for more work, and enabling callbacks.
 *
 * Caller must ensure we don't call this with other virtqueue
 * operations at the same time (except where noted).
 */
bool virtqueue_enable_cb(struct virtqueue *_vq)
{
        unsigned last_used_idx = virtqueue_enable_cb_prepare(_vq);

        return !virtqueue_poll(_vq, last_used_idx);
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb);

/**
 * virtqueue_enable_cb_delayed - restart callbacks after disable_cb.
 * @_vq: the struct virtqueue we're talking about.
 *
 * This re-enables callbacks but hints to the other side to delay
 * interrupts until most of the available buffers have been processed;
 * it returns "false" if there are many pending buffers in the queue,
 * to detect a possible race between the driver checking for more work,
 * and enabling callbacks.
 *
 * Caller must ensure we don't call this with other virtqueue
 * operations at the same time (except where noted).
 */
bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        return vq->packed_ring ? virtqueue_enable_cb_delayed_packed(_vq) :
                                 virtqueue_enable_cb_delayed_split(_vq);
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);

/**
 * virtqueue_detach_unused_buf - detach first unused buffer
 * @_vq: the struct virtqueue we're talking about.
 *
 * Returns NULL or the "data" token handed to virtqueue_add_*().
 * This is not valid on an active queue; it is useful only for device
 * shutdown.
 */
void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        return vq->packed_ring ? virtqueue_detach_unused_buf_packed(_vq) :
                                 virtqueue_detach_unused_buf_split(_vq);
}
EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);

static inline bool more_used(const struct vring_virtqueue *vq)
{
        return vq->packed_ring ? more_used_packed(vq) : more_used_split(vq);
}

irqreturn_t vring_interrupt(int irq, void *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        if (!more_used(vq)) {
                pr_debug("virtqueue interrupt with no work for %p\n", vq);
                return IRQ_NONE;
        }

        if (unlikely(vq->broken))
                return IRQ_HANDLED;

        pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
        if (vq->vq.callback)
                vq->vq.callback(&vq->vq);

        return IRQ_HANDLED;
}
EXPORT_SYMBOL_GPL(vring_interrupt);

/* Only available for split ring */
struct virtqueue *__vring_new_virtqueue(unsigned int index,
                                        struct vring vring,
                                        struct virtio_device *vdev,
                                        bool weak_barriers,
                                        bool context,
                                        bool (*notify)(struct virtqueue *),
                                        void (*callback)(struct virtqueue *),
                                        const char *name)
{
        unsigned int i;
        struct vring_virtqueue *vq;

        if (virtio_has_feature(vdev, VIRTIO_F_RING_PACKED))
                return NULL;

        vq = kmalloc(sizeof(*vq), GFP_KERNEL);
        if (!vq)
                return NULL;

        vq->packed_ring = false;
        vq->vq.callback = callback;
        vq->vq.vdev = vdev;
        vq->vq.name = name;
        vq->vq.num_free = vring.num;
        vq->vq.index = index;
        vq->we_own_ring = false;
        vq->notify = notify;
        vq->weak_barriers = weak_barriers;
        vq->broken = false;
        vq->last_used_idx = 0;
        vq->num_added = 0;
        vq->use_dma_api = vring_use_dma_api(vdev);
        list_add_tail(&vq->vq.list, &vdev->vqs);
#ifdef DEBUG
        vq->in_use = false;
        vq->last_add_time_valid = false;
#endif

        vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC) &&
                !context;
        vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);

        if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
                vq->weak_barriers = false;

        vq->split.queue_dma_addr = 0;
        vq->split.queue_size_in_bytes = 0;

        vq->split.vring = vring;
        vq->split.avail_flags_shadow = 0;
        vq->split.avail_idx_shadow = 0;

        /* No callback?  Tell other side not to bother us. */
        if (!callback) {
                vq->split.avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
                if (!vq->event)
                        vq->split.vring.avail->flags = cpu_to_virtio16(vdev,
                                        vq->split.avail_flags_shadow);
        }

        vq->split.desc_state = kmalloc_array(vring.num,
                        sizeof(struct vring_desc_state_split), GFP_KERNEL);
        if (!vq->split.desc_state) {
                kfree(vq);
                return NULL;
        }

        /* Put everything in free lists. */
        vq->free_head = 0;
        for (i = 0; i < vring.num-1; i++)
                vq->split.vring.desc[i].next = cpu_to_virtio16(vdev, i + 1);
        memset(vq->split.desc_state, 0, vring.num *
                        sizeof(struct vring_desc_state_split));

        return &vq->vq;
}
EXPORT_SYMBOL_GPL(__vring_new_virtqueue);

struct virtqueue *vring_create_virtqueue(
        unsigned int index,
        unsigned int num,
        unsigned int vring_align,
        struct virtio_device *vdev,
        bool weak_barriers,
        bool may_reduce_num,
        bool context,
        bool (*notify)(struct virtqueue *),
        void (*callback)(struct virtqueue *),
        const char *name)
{

        if (virtio_has_feature(vdev, VIRTIO_F_RING_PACKED))
                return vring_create_virtqueue_packed(index, num, vring_align,
                                vdev, weak_barriers, may_reduce_num,
                                context, notify, callback, name);

        return vring_create_virtqueue_split(index, num, vring_align,
                        vdev, weak_barriers, may_reduce_num,
                        context, notify, callback, name);
}
EXPORT_SYMBOL_GPL(vring_create_virtqueue);

/* Only available for split ring */
struct virtqueue *vring_new_virtqueue(unsigned int index,
                                      unsigned int num,
                                      unsigned int vring_align,
                                      struct virtio_device *vdev,
                                      bool weak_barriers,
                                      bool context,
                                      void *pages,
                                      bool (*notify)(struct virtqueue *vq),
                                      void (*callback)(struct virtqueue *vq),
                                      const char *name)
{
        struct vring vring;

        if (virtio_has_feature(vdev, VIRTIO_F_RING_PACKED))
                return NULL;

        vring_init(&vring, num, pages, vring_align);
        return __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
                                     notify, callback, name);
}
EXPORT_SYMBOL_GPL(vring_new_virtqueue);

void vring_del_virtqueue(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        if (vq->we_own_ring) {
                if (vq->packed_ring) {
                        vring_free_queue(vq->vq.vdev,
                                         vq->packed.ring_size_in_bytes,
                                         vq->packed.vring.desc,
                                         vq->packed.ring_dma_addr);

                        vring_free_queue(vq->vq.vdev,
                                         vq->packed.event_size_in_bytes,
                                         vq->packed.vring.driver,
                                         vq->packed.driver_event_dma_addr);

                        vring_free_queue(vq->vq.vdev,
                                         vq->packed.event_size_in_bytes,
                                         vq->packed.vring.device,
                                         vq->packed.device_event_dma_addr);

                        kfree(vq->packed.desc_state);
                        kfree(vq->packed.desc_extra);
                } else {
                        vring_free_queue(vq->vq.vdev,
                                         vq->split.queue_size_in_bytes,
                                         vq->split.vring.desc,
                                         vq->split.queue_dma_addr);

                        kfree(vq->split.desc_state);
                }
        }
        list_del(&_vq->list);
        kfree(vq);
}
EXPORT_SYMBOL_GPL(vring_del_virtqueue);

/* Manipulates transport-specific feature bits. */
void vring_transport_features(struct virtio_device *vdev)
{
        unsigned int i;

        for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
                switch (i) {
                case VIRTIO_RING_F_INDIRECT_DESC:
                        break;
                case VIRTIO_RING_F_EVENT_IDX:
                        break;
                case VIRTIO_F_VERSION_1:
                        break;
                case VIRTIO_F_IOMMU_PLATFORM:
                        break;
                case VIRTIO_F_RING_PACKED:
                        break;
                case VIRTIO_F_ORDER_PLATFORM:
                        break;
                default:
                        /* We don't understand this bit. */
                        __virtio_clear_bit(vdev, i);
                }
        }
}
EXPORT_SYMBOL_GPL(vring_transport_features);

/**
 * virtqueue_get_vring_size - return the size of the virtqueue's vring
 * @_vq: the struct virtqueue containing the vring of interest.
 *
 * Returns the size of the vring.  This is mainly used for boasting to
 * userspace.  Unlike other operations, this need not be serialized.
 */
unsigned int virtqueue_get_vring_size(struct virtqueue *_vq)
{

        struct vring_virtqueue *vq = to_vvq(_vq);

        return vq->packed_ring ? vq->packed.vring.num : vq->split.vring.num;
}
EXPORT_SYMBOL_GPL(virtqueue_get_vring_size);

bool virtqueue_is_broken(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        return vq->broken;
}
EXPORT_SYMBOL_GPL(virtqueue_is_broken);

/*
 * This should prevent the device from being used, allowing drivers to
 * recover.  You may need to grab appropriate locks to flush.
 */
void virtio_break_device(struct virtio_device *dev)
{
        struct virtqueue *_vq;

        list_for_each_entry(_vq, &dev->vqs, list) {
                struct vring_virtqueue *vq = to_vvq(_vq);
                vq->broken = true;
        }
}
EXPORT_SYMBOL_GPL(virtio_break_device);

dma_addr_t virtqueue_get_desc_addr(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        BUG_ON(!vq->we_own_ring);

        if (vq->packed_ring)
                return vq->packed.ring_dma_addr;

        return vq->split.queue_dma_addr;
}
EXPORT_SYMBOL_GPL(virtqueue_get_desc_addr);

dma_addr_t virtqueue_get_avail_addr(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        BUG_ON(!vq->we_own_ring);

        if (vq->packed_ring)
                return vq->packed.driver_event_dma_addr;

        return vq->split.queue_dma_addr +
                ((char *)vq->split.vring.avail - (char *)vq->split.vring.desc);
}
EXPORT_SYMBOL_GPL(virtqueue_get_avail_addr);

dma_addr_t virtqueue_get_used_addr(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        BUG_ON(!vq->we_own_ring);

        if (vq->packed_ring)
                return vq->packed.device_event_dma_addr;

        return vq->split.queue_dma_addr +
                ((char *)vq->split.vring.used - (char *)vq->split.vring.desc);
}
EXPORT_SYMBOL_GPL(virtqueue_get_used_addr);

/* Only available for split ring */
const struct vring *virtqueue_get_vring(struct virtqueue *vq)
{
        return &to_vvq(vq)->split.vring;
}
EXPORT_SYMBOL_GPL(virtqueue_get_vring);

MODULE_LICENSE("GPL");