drivers/virtio/virtio_ring.c - github/trini/u-boot - Gitiles

 // SPDX-License-Identifier: GPL-2.0+
 /*
  * Copyright (C) 2018, Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
  * Copyright (C) 2018, Bin Meng <bmeng.cn@gmail.com>
  *
  * virtio ring implementation
  */

 #include <bouncebuf.h>
 #include <common.h>
 #include <dm.h>
 #include <log.h>
 #include <malloc.h>
 #include <virtio_types.h>
 #include <virtio.h>
 #include <virtio_ring.h>
 #include <linux/bug.h>
 #include <linux/compat.h>
 #include <linux/kernel.h>

 static void *virtio_alloc_pages(struct udevice *vdev, u32 npages)
 {
 	return memalign(PAGE_SIZE, npages * PAGE_SIZE);
 }

 static void virtio_free_pages(struct udevice *vdev, void *ptr, u32 npages)
 {
 	free(ptr);
 }

 static unsigned int virtqueue_attach_desc(struct virtqueue *vq, unsigned int i,
 					  struct virtio_sg *sg, u16 flags)
 {
 	struct vring_desc_shadow *desc_shadow = &vq->vring_desc_shadow[i];
 	struct vring_desc *desc = &vq->vring.desc[i];

 	/* Update the shadow descriptor. */
 	desc_shadow->addr = (u64)(uintptr_t)sg->addr;
 	desc_shadow->len = sg->length;
 	desc_shadow->flags = flags;

 	/* Update the shared descriptor to match the shadow. */
 	desc->addr = cpu_to_virtio64(vq->vdev, desc_shadow->addr);
 	desc->len = cpu_to_virtio32(vq->vdev, desc_shadow->len);
 	desc->flags = cpu_to_virtio16(vq->vdev, desc_shadow->flags);
 	desc->next = cpu_to_virtio16(vq->vdev, desc_shadow->next);

 	return desc_shadow->next;
 }

 static void virtqueue_detach_desc(struct virtqueue *vq, unsigned int idx)
 {
 }

 int virtqueue_add(struct virtqueue *vq, struct virtio_sg *sgs[],
 		  unsigned int out_sgs, unsigned int in_sgs)
 {
 	struct vring_desc *desc;
 	unsigned int descs_used = out_sgs + in_sgs;
 	unsigned int i, n, avail, uninitialized_var(prev);
 	int head;

 	WARN_ON(descs_used == 0);

 	head = vq->free_head;

 	desc = vq->vring.desc;
 	i = head;

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

 	for (n = 0; n < descs_used; n++) {
 		u16 flags = VRING_DESC_F_NEXT;

 		if (n >= out_sgs)
 			flags |= VRING_DESC_F_WRITE;
 		prev = i;
 		i = virtqueue_attach_desc(vq, i, sgs[n], flags);
 	}
 	/* Last one doesn't continue */
 	vq->vring_desc_shadow[prev].flags &= ~VRING_DESC_F_NEXT;
 	desc[prev].flags = cpu_to_virtio16(vq->vdev, vq->vring_desc_shadow[prev].flags);

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

 	/* Update free pointer */
 	vq->free_head = i;

 	/* Mark the descriptor as the head of a chain. */
 	vq->vring_desc_shadow[head].chain_head = true;

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

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

 	return 0;
 }

 static bool virtqueue_kick_prepare(struct virtqueue *vq)
 {
 	u16 new, old;
 	bool needs_kick;

 	/*
 	 * We need to expose available array entries before checking
 	 * avail event.
 	 */
 	virtio_mb();

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

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

 	return needs_kick;
 }

 void virtqueue_kick(struct virtqueue *vq)
 {
 	if (virtqueue_kick_prepare(vq))
 		virtio_notify(vq->vdev, vq);
 }

 static void detach_buf(struct virtqueue *vq, unsigned int head)
 {
 	unsigned int i;

 	/* Unmark the descriptor as the head of a chain. */
 	vq->vring_desc_shadow[head].chain_head = false;

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

 	while (vq->vring_desc_shadow[i].flags & VRING_DESC_F_NEXT) {
 		virtqueue_detach_desc(vq, i);
 		i = vq->vring_desc_shadow[i].next;
 		vq->num_free++;
 	}

 	virtqueue_detach_desc(vq, i);
 	vq->vring_desc_shadow[i].next = vq->free_head;
 	vq->free_head = head;

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

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

 void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len)
 {
 	unsigned int i;
 	u16 last_used;

 	if (!more_used(vq)) {
 		debug("(%s.%d): No more buffers in queue\n",
 		      vq->vdev->name, vq->index);
 		return NULL;
 	}

 	/* Only get used array entries after they have been exposed by host */
 	virtio_rmb();

 	last_used = (vq->last_used_idx & (vq->vring.num - 1));
 	i = virtio32_to_cpu(vq->vdev, vq->vring.used->ring[last_used].id);
 	if (len) {
 		*len = virtio32_to_cpu(vq->vdev,
 				       vq->vring.used->ring[last_used].len);
 		debug("(%s.%d): last used idx %u with len %u\n",
 		      vq->vdev->name, vq->index, i, *len);
 	}

 	if (unlikely(i >= vq->vring.num)) {
 		printf("(%s.%d): id %u out of range\n",
 		       vq->vdev->name, vq->index, i);
 		return NULL;
 	}

 	if (unlikely(!vq->vring_desc_shadow[i].chain_head)) {
 		printf("(%s.%d): id %u is not a head\n",
 		       vq->vdev->name, vq->index, i);
 		return NULL;
 	}

 	detach_buf(vq, i);
 	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->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT))
 		virtio_store_mb(&vring_used_event(&vq->vring),
 				cpu_to_virtio16(vq->vdev, vq->last_used_idx));

 	return (void *)(uintptr_t)vq->vring_desc_shadow[i].addr;
 }

 static struct virtqueue *__vring_new_virtqueue(unsigned int index,
 					       struct vring vring,
 					       struct udevice *udev)
 {
 	unsigned int i;
 	struct virtqueue *vq;
 	struct vring_desc_shadow *vring_desc_shadow;
 	struct virtio_dev_priv *uc_priv = dev_get_uclass_priv(udev);
 	struct udevice *vdev = uc_priv->vdev;

 	vq = malloc(sizeof(*vq));
 	if (!vq)
 		return NULL;

 	vring_desc_shadow = calloc(vring.num, sizeof(struct vring_desc_shadow));
 	if (!vring_desc_shadow) {
 		free(vq);
 		return NULL;
 	}

 	vq->vdev = vdev;
 	vq->index = index;
 	vq->num_free = vring.num;
 	vq->vring = vring;
 	vq->vring_desc_shadow = vring_desc_shadow;
 	vq->last_used_idx = 0;
 	vq->avail_flags_shadow = 0;
 	vq->avail_idx_shadow = 0;
 	vq->num_added = 0;
 	list_add_tail(&vq->list, &uc_priv->vqs);

 	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);

 	/* Tell other side not to bother us */
 	vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
 	if (!vq->event)
 		vq->vring.avail->flags = cpu_to_virtio16(vdev,
 				vq->avail_flags_shadow);

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

 	return vq;
 }

 struct virtqueue *vring_create_virtqueue(unsigned int index, unsigned int num,
 					 unsigned int vring_align,
 					 struct udevice *udev)
 {
 	struct virtio_dev_priv *uc_priv = dev_get_uclass_priv(udev);
 	struct udevice *vdev = uc_priv->vdev;
 	struct virtqueue *vq;
 	void *queue = NULL;
 	struct bounce_buffer *bbs = NULL;
 	struct vring vring;

 	/* We assume num is a power of 2 */
 	if (num & (num - 1)) {
 		printf("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) {
 		size_t sz = vring_size(num, vring_align);

 		queue = virtio_alloc_pages(vdev, DIV_ROUND_UP(sz, PAGE_SIZE));
 		if (queue)
 			break;
 	}

 	if (!num)
 		return NULL;

 	if (!queue) {
 		/* Try to get a single page. You are my only hope! */
 		queue = virtio_alloc_pages(vdev, 1);
 	}
 	if (!queue)
 		return NULL;

 	memset(queue, 0, vring_size(num, vring_align));

 	if (virtio_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) {
 		bbs = calloc(num, sizeof(*bbs));
 		if (!bbs)
 			goto err_free_queue;
 	}

 	vring_init(&vring, num, queue, vring_align, bbs);

 	vq = __vring_new_virtqueue(index, vring, udev);
 	if (!vq)
 		goto err_free_bbs;

 	debug("(%s): created vring @ %p for vq @ %p with num %u\n", udev->name,
 	      queue, vq, num);

 	return vq;

 err_free_bbs:
 	free(bbs);
 err_free_queue:
 	virtio_free_pages(vdev, queue, DIV_ROUND_UP(vring.size, PAGE_SIZE));
 	return NULL;
 }

 void vring_del_virtqueue(struct virtqueue *vq)
 {
 	virtio_free_pages(vq->vdev, vq->vring.desc,
 			  DIV_ROUND_UP(vq->vring.size, PAGE_SIZE));
 	free(vq->vring_desc_shadow);
 	list_del(&vq->list);
 	free(vq->vring.bouncebufs);
 	free(vq);
 }

 unsigned int virtqueue_get_vring_size(struct virtqueue *vq)
 {
 	return vq->vring.num;
 }

 ulong virtqueue_get_desc_addr(struct virtqueue *vq)
 {
 	return (ulong)vq->vring.desc;
 }

 ulong virtqueue_get_avail_addr(struct virtqueue *vq)
 {
 	return (ulong)vq->vring.desc +
 	       ((char *)vq->vring.avail - (char *)vq->vring.desc);
 }

 ulong virtqueue_get_used_addr(struct virtqueue *vq)
 {
 	return (ulong)vq->vring.desc +
 	       ((char *)vq->vring.used - (char *)vq->vring.desc);
 }

 bool virtqueue_poll(struct virtqueue *vq, u16 last_used_idx)
 {
 	virtio_mb();

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

 void virtqueue_dump(struct virtqueue *vq)
 {
 	unsigned int i;

 	printf("virtqueue %p for dev %s:\n", vq, vq->vdev->name);
 	printf("\tindex %u, phys addr %p num %u\n",
 	       vq->index, vq->vring.desc, vq->vring.num);
 	printf("\tfree_head %u, num_added %u, num_free %u\n",
 	       vq->free_head, vq->num_added, vq->num_free);
 	printf("\tlast_used_idx %u, avail_flags_shadow %u, avail_idx_shadow %u\n",
 	       vq->last_used_idx, vq->avail_flags_shadow, vq->avail_idx_shadow);

 	printf("Shadow descriptor dump:\n");
 	for (i = 0; i < vq->vring.num; i++) {
 		struct vring_desc_shadow *desc = &vq->vring_desc_shadow[i];

 		printf("\tdesc_shadow[%u] = { 0x%llx, len %u, flags %u, next %u }\n",
 		       i, desc->addr, desc->len, desc->flags, desc->next);
 	}

 	printf("Avail ring dump:\n");
 	printf("\tflags %u, idx %u\n",
 	       vq->vring.avail->flags, vq->vring.avail->idx);
 	for (i = 0; i < vq->vring.num; i++) {
 		printf("\tavail[%u] = %u\n",
 		       i, vq->vring.avail->ring[i]);
 	}

 	printf("Used ring dump:\n");
 	printf("\tflags %u, idx %u\n",
 	       vq->vring.used->flags, vq->vring.used->idx);
 	for (i = 0; i < vq->vring.num; i++) {
 		printf("\tused[%u] = { %u, %u }\n", i,
 		       vq->vring.used->ring[i].id, vq->vring.used->ring[i].len);
 	}
 }
	// SPDX-License-Identifier: GPL-2.0+
	/*
	* Copyright (C) 2018, Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
	* Copyright (C) 2018, Bin Meng <bmeng.cn@gmail.com>
	*
	* virtio ring implementation
	*/

	#include <bouncebuf.h>
	#include <common.h>
	#include <dm.h>
	#include <log.h>
	#include <malloc.h>
	#include <virtio_types.h>
	#include <virtio.h>
	#include <virtio_ring.h>
	#include <linux/bug.h>
	#include <linux/compat.h>
	#include <linux/kernel.h>

	static void virtio_alloc_pages(struct udevice vdev, u32 npages)
	{
	return memalign(PAGE_SIZE, npages * PAGE_SIZE);
	}

	static void virtio_free_pages(struct udevice vdev, void ptr, u32 npages)
	{
	free(ptr);
	}

	static unsigned int virtqueue_attach_desc(struct virtqueue *vq, unsigned int i,
	struct virtio_sg *sg, u16 flags)
	{
	struct vring_desc_shadow *desc_shadow = &vq->vring_desc_shadow[i];
	struct vring_desc *desc = &vq->vring.desc[i];

	/* Update the shadow descriptor. */
	desc_shadow->addr = (u64)(uintptr_t)sg->addr;
	desc_shadow->len = sg->length;
	desc_shadow->flags = flags;

	/* Update the shared descriptor to match the shadow. */
	desc->addr = cpu_to_virtio64(vq->vdev, desc_shadow->addr);
	desc->len = cpu_to_virtio32(vq->vdev, desc_shadow->len);
	desc->flags = cpu_to_virtio16(vq->vdev, desc_shadow->flags);
	desc->next = cpu_to_virtio16(vq->vdev, desc_shadow->next);

	return desc_shadow->next;
	}

	static void virtqueue_detach_desc(struct virtqueue *vq, unsigned int idx)
	{
	}

	int virtqueue_add(struct virtqueue vq, struct virtio_sg sgs[],
	unsigned int out_sgs, unsigned int in_sgs)
	{
	struct vring_desc *desc;
	unsigned int descs_used = out_sgs + in_sgs;
	unsigned int i, n, avail, uninitialized_var(prev);
	int head;

	WARN_ON(descs_used == 0);

	head = vq->free_head;

	desc = vq->vring.desc;
	i = head;

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

	for (n = 0; n < descs_used; n++) {
	u16 flags = VRING_DESC_F_NEXT;

	if (n >= out_sgs)
	flags \|= VRING_DESC_F_WRITE;
	prev = i;
	i = virtqueue_attach_desc(vq, i, sgs[n], flags);
	}
	/* Last one doesn't continue */
	vq->vring_desc_shadow[prev].flags &= ~VRING_DESC_F_NEXT;
	desc[prev].flags = cpu_to_virtio16(vq->vdev, vq->vring_desc_shadow[prev].flags);

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

	/* Update free pointer */
	vq->free_head = i;

	/* Mark the descriptor as the head of a chain. */
	vq->vring_desc_shadow[head].chain_head = true;

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

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

	return 0;
	}

	static bool virtqueue_kick_prepare(struct virtqueue *vq)
	{
	u16 new, old;
	bool needs_kick;

	/*
	* We need to expose available array entries before checking
	* avail event.
	*/
	virtio_mb();

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

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

	return needs_kick;
	}

	void virtqueue_kick(struct virtqueue *vq)
	{
	if (virtqueue_kick_prepare(vq))
	virtio_notify(vq->vdev, vq);
	}

	static void detach_buf(struct virtqueue *vq, unsigned int head)
	{
	unsigned int i;

	/* Unmark the descriptor as the head of a chain. */
	vq->vring_desc_shadow[head].chain_head = false;

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

	while (vq->vring_desc_shadow[i].flags & VRING_DESC_F_NEXT) {
	virtqueue_detach_desc(vq, i);
	i = vq->vring_desc_shadow[i].next;
	vq->num_free++;
	}

	virtqueue_detach_desc(vq, i);
	vq->vring_desc_shadow[i].next = vq->free_head;
	vq->free_head = head;

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

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

	void virtqueue_get_buf(struct virtqueue vq, unsigned int *len)
	{
	unsigned int i;
	u16 last_used;

	if (!more_used(vq)) {
	debug("(%s.%d): No more buffers in queue\n",
	vq->vdev->name, vq->index);
	return NULL;
	}

	/* Only get used array entries after they have been exposed by host */
	virtio_rmb();

	last_used = (vq->last_used_idx & (vq->vring.num - 1));
	i = virtio32_to_cpu(vq->vdev, vq->vring.used->ring[last_used].id);
	if (len) {
	*len = virtio32_to_cpu(vq->vdev,
	vq->vring.used->ring[last_used].len);
	debug("(%s.%d): last used idx %u with len %u\n",
	vq->vdev->name, vq->index, i, *len);
	}

	if (unlikely(i >= vq->vring.num)) {
	printf("(%s.%d): id %u out of range\n",
	vq->vdev->name, vq->index, i);
	return NULL;
	}

	if (unlikely(!vq->vring_desc_shadow[i].chain_head)) {
	printf("(%s.%d): id %u is not a head\n",
	vq->vdev->name, vq->index, i);
	return NULL;
	}

	detach_buf(vq, i);
	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->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT))
	virtio_store_mb(&vring_used_event(&vq->vring),
	cpu_to_virtio16(vq->vdev, vq->last_used_idx));

	return (void *)(uintptr_t)vq->vring_desc_shadow[i].addr;
	}

	static struct virtqueue *__vring_new_virtqueue(unsigned int index,
	struct vring vring,
	struct udevice *udev)
	{
	unsigned int i;
	struct virtqueue *vq;
	struct vring_desc_shadow *vring_desc_shadow;
	struct virtio_dev_priv *uc_priv = dev_get_uclass_priv(udev);
	struct udevice *vdev = uc_priv->vdev;

	vq = malloc(sizeof(*vq));
	if (!vq)
	return NULL;

	vring_desc_shadow = calloc(vring.num, sizeof(struct vring_desc_shadow));
	if (!vring_desc_shadow) {
	free(vq);
	return NULL;
	}

	vq->vdev = vdev;
	vq->index = index;
	vq->num_free = vring.num;
	vq->vring = vring;
	vq->vring_desc_shadow = vring_desc_shadow;
	vq->last_used_idx = 0;
	vq->avail_flags_shadow = 0;
	vq->avail_idx_shadow = 0;
	vq->num_added = 0;
	list_add_tail(&vq->list, &uc_priv->vqs);

	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);

	/* Tell other side not to bother us */
	vq->avail_flags_shadow \|= VRING_AVAIL_F_NO_INTERRUPT;
	if (!vq->event)
	vq->vring.avail->flags = cpu_to_virtio16(vdev,
	vq->avail_flags_shadow);

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

	return vq;
	}

	struct virtqueue *vring_create_virtqueue(unsigned int index, unsigned int num,
	unsigned int vring_align,
	struct udevice *udev)
	{
	struct virtio_dev_priv *uc_priv = dev_get_uclass_priv(udev);
	struct udevice *vdev = uc_priv->vdev;
	struct virtqueue *vq;
	void *queue = NULL;
	struct bounce_buffer *bbs = NULL;
	struct vring vring;

	/* We assume num is a power of 2 */
	if (num & (num - 1)) {
	printf("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) {
	size_t sz = vring_size(num, vring_align);

	queue = virtio_alloc_pages(vdev, DIV_ROUND_UP(sz, PAGE_SIZE));
	if (queue)
	break;
	}

	if (!num)
	return NULL;

	if (!queue) {
	/* Try to get a single page. You are my only hope! */
	queue = virtio_alloc_pages(vdev, 1);
	}
	if (!queue)
	return NULL;

	memset(queue, 0, vring_size(num, vring_align));

	if (virtio_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) {
	bbs = calloc(num, sizeof(*bbs));
	if (!bbs)
	goto err_free_queue;
	}

	vring_init(&vring, num, queue, vring_align, bbs);

	vq = __vring_new_virtqueue(index, vring, udev);
	if (!vq)
	goto err_free_bbs;

	debug("(%s): created vring @ %p for vq @ %p with num %u\n", udev->name,
	queue, vq, num);

	return vq;

	err_free_bbs:
	free(bbs);
	err_free_queue:
	virtio_free_pages(vdev, queue, DIV_ROUND_UP(vring.size, PAGE_SIZE));
	return NULL;
	}

	void vring_del_virtqueue(struct virtqueue *vq)
	{
	virtio_free_pages(vq->vdev, vq->vring.desc,
	DIV_ROUND_UP(vq->vring.size, PAGE_SIZE));
	free(vq->vring_desc_shadow);
	list_del(&vq->list);
	free(vq->vring.bouncebufs);
	free(vq);
	}

	unsigned int virtqueue_get_vring_size(struct virtqueue *vq)
	{
	return vq->vring.num;
	}

	ulong virtqueue_get_desc_addr(struct virtqueue *vq)
	{
	return (ulong)vq->vring.desc;
	}

	ulong virtqueue_get_avail_addr(struct virtqueue *vq)
	{
	return (ulong)vq->vring.desc +
	((char )vq->vring.avail - (char )vq->vring.desc);
	}

	ulong virtqueue_get_used_addr(struct virtqueue *vq)
	{
	return (ulong)vq->vring.desc +
	((char )vq->vring.used - (char )vq->vring.desc);
	}

	bool virtqueue_poll(struct virtqueue *vq, u16 last_used_idx)
	{
	virtio_mb();

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

	void virtqueue_dump(struct virtqueue *vq)
	{
	unsigned int i;

	printf("virtqueue %p for dev %s:\n", vq, vq->vdev->name);
	printf("\tindex %u, phys addr %p num %u\n",
	vq->index, vq->vring.desc, vq->vring.num);
	printf("\tfree_head %u, num_added %u, num_free %u\n",
	vq->free_head, vq->num_added, vq->num_free);
	printf("\tlast_used_idx %u, avail_flags_shadow %u, avail_idx_shadow %u\n",
	vq->last_used_idx, vq->avail_flags_shadow, vq->avail_idx_shadow);

	printf("Shadow descriptor dump:\n");
	for (i = 0; i < vq->vring.num; i++) {
	struct vring_desc_shadow *desc = &vq->vring_desc_shadow[i];

	printf("\tdesc_shadow[%u] = { 0x%llx, len %u, flags %u, next %u }\n",
	i, desc->addr, desc->len, desc->flags, desc->next);
	}

	printf("Avail ring dump:\n");
	printf("\tflags %u, idx %u\n",
	vq->vring.avail->flags, vq->vring.avail->idx);
	for (i = 0; i < vq->vring.num; i++) {
	printf("\tavail[%u] = %u\n",
	i, vq->vring.avail->ring[i]);
	}

	printf("Used ring dump:\n");
	printf("\tflags %u, idx %u\n",
	vq->vring.used->flags, vq->vring.used->idx);
	for (i = 0; i < vq->vring.num; i++) {
	printf("\tused[%u] = { %u, %u }\n", i,
	vq->vring.used->ring[i].id, vq->vring.used->ring[i].len);
	}
	}