drivers/virtio/virtio_ring.c - android_kernel_htc_msm8960 - Gitiles

 /* Virtio ring implementation.
  *
  *  Copyright 2007 Rusty Russell IBM Corporation
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
  *  the Free Software Foundation; either version 2 of the License, or
  *  (at your option) any later version.
  *
  *  This program is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *  GNU General Public License for more details.
  *
  *  You should have received a copy of the GNU General Public License
  *  along with this program; if not, write to the Free Software
  *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 #include <linux/virtio.h>
 #include <linux/virtio_ring.h>
 #include <linux/virtio_config.h>
 #include <linux/device.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__;			\
 		mb();						\
 	} while (0)
 #define END_USE(_vq) \
 	do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; mb(); } while(0)
 #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)
 #endif

 struct vring_virtqueue
 {
 	struct virtqueue vq;

 	/* Actual memory layout for this queue */
 	struct vring vring;

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

 	/* Host supports indirect buffers */
 	bool indirect;

 	/* Number of free buffers */
 	unsigned int num_free;
 	/* 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;

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

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

 	/* Tokens for callbacks. */
 	void *data[];
 };

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

 /* Set up an indirect table of descriptors and add it to the queue. */
 static int vring_add_indirect(struct vring_virtqueue *vq,
 			      struct scatterlist sg[],
 			      unsigned int out,
 			      unsigned int in)
 {
 	struct vring_desc *desc;
 	unsigned head;
 	int i;

 	desc = kmalloc((out + in) * sizeof(struct vring_desc), GFP_ATOMIC);
 	if (!desc)
 		return vq->vring.num;

 	/* Transfer entries from the sg list into the indirect page */
 	for (i = 0; i < out; i++) {
 		desc[i].flags = VRING_DESC_F_NEXT;
 		desc[i].addr = sg_phys(sg);
 		desc[i].len = sg->length;
 		desc[i].next = i+1;
 		sg++;
 	}
 	for (; i < (out + in); i++) {
 		desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
 		desc[i].addr = sg_phys(sg);
 		desc[i].len = sg->length;
 		desc[i].next = i+1;
 		sg++;
 	}

 	/* Last one doesn't continue. */
 	desc[i-1].flags &= ~VRING_DESC_F_NEXT;
 	desc[i-1].next = 0;

 	/* We're about to use a buffer */
 	vq->num_free--;

 	/* Use a single buffer which doesn't continue */
 	head = vq->free_head;
 	vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
 	vq->vring.desc[head].addr = virt_to_phys(desc);
 	vq->vring.desc[head].len = i * sizeof(struct vring_desc);

 	/* Update free pointer */
 	vq->free_head = vq->vring.desc[head].next;

 	return head;
 }

 static int vring_add_buf(struct virtqueue *_vq,
 			 struct scatterlist sg[],
 			 unsigned int out,
 			 unsigned int in,
 			 void *data)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	unsigned int i, avail, head, uninitialized_var(prev);

 	START_USE(vq);

 	BUG_ON(data == NULL);

 	/* If the host supports indirect descriptor tables, and we have multiple
 	 * buffers, then go indirect. FIXME: tune this threshold */
 	if (vq->indirect && (out + in) > 1 && vq->num_free) {
 		head = vring_add_indirect(vq, sg, out, in);
 		if (head != vq->vring.num)
 			goto add_head;
 	}

 	BUG_ON(out + in > vq->vring.num);
 	BUG_ON(out + in == 0);

 	if (vq->num_free < out + in) {
 		pr_debug("Can't add buf len %i - avail = %i\n",
 			 out + in, 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)
 			vq->notify(&vq->vq);
 		END_USE(vq);
 		return -ENOSPC;
 	}

 	/* We're about to use some buffers from the free list. */
 	vq->num_free -= out + in;

 	head = vq->free_head;
 	for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
 		vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
 		vq->vring.desc[i].addr = sg_phys(sg);
 		vq->vring.desc[i].len = sg->length;
 		prev = i;
 		sg++;
 	}
 	for (; in; i = vq->vring.desc[i].next, in--) {
 		vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
 		vq->vring.desc[i].addr = sg_phys(sg);
 		vq->vring.desc[i].len = sg->length;
 		prev = i;
 		sg++;
 	}
 	/* Last one doesn't continue. */
 	vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;

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

 add_head:
 	/* Set token. */
 	vq->data[head] = data;

 	/* Put entry in available array (but don't update avail->idx until they
 	 * do sync).  FIXME: avoid modulus here? */
 	avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num;
 	vq->vring.avail->ring[avail] = head;

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

 	/* If we're indirect, we can fit many (assuming not OOM). */
 	if (vq->indirect)
 		return vq->num_free ? vq->vring.num : 0;
 	return vq->num_free;
 }

 static void vring_kick(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	START_USE(vq);
 	/* Descriptors and available array need to be set before we expose the
 	 * new available array entries. */
 	wmb();

 	vq->vring.avail->idx += vq->num_added;
 	vq->num_added = 0;

 	/* Need to update avail index before checking if we should notify */
 	mb();

 	if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
 		/* Prod other side to tell it about changes. */
 		vq->notify(&vq->vq);

 	END_USE(vq);
 }

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

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

 	/* Put back on free list: find end */
 	i = head;

 	/* Free the indirect table */
 	if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT)
 		kfree(phys_to_virt(vq->vring.desc[i].addr));

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

 	vq->vring.desc[i].next = vq->free_head;
 	vq->free_head = head;
 	/* Plus final descriptor */
 	vq->num_free++;
 }

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

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

 	START_USE(vq);

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

 	if (!more_used(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. */
 	rmb();

 	i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id;
 	*len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;

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

 	/* detach_buf clears data, so grab it now. */
 	ret = vq->data[i];
 	detach_buf(vq, i);
 	vq->last_used_idx++;
 	END_USE(vq);
 	return ret;
 }

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

 	vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
 }

 static bool vring_enable_cb(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. */
 	vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
 	mb();
 	if (unlikely(more_used(vq))) {
 		END_USE(vq);
 		return false;
 	}

 	END_USE(vq);
 	return true;
 }

 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);

 static struct virtqueue_ops vring_vq_ops = {
 	.add_buf = vring_add_buf,
 	.get_buf = vring_get_buf,
 	.kick = vring_kick,
 	.disable_cb = vring_disable_cb,
 	.enable_cb = vring_enable_cb,
 };

 struct virtqueue *vring_new_virtqueue(unsigned int num,
 				      unsigned int vring_align,
 				      struct virtio_device *vdev,
 				      void *pages,
 				      void (*notify)(struct virtqueue *),
 				      void (*callback)(struct virtqueue *),
 				      const char *name)
 {
 	struct vring_virtqueue *vq;
 	unsigned int i;

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

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

 	vring_init(&vq->vring, num, pages, vring_align);
 	vq->vq.callback = callback;
 	vq->vq.vdev = vdev;
 	vq->vq.vq_ops = &vring_vq_ops;
 	vq->vq.name = name;
 	vq->notify = notify;
 	vq->broken = false;
 	vq->last_used_idx = 0;
 	vq->num_added = 0;
 	list_add_tail(&vq->vq.list, &vdev->vqs);
 #ifdef DEBUG
 	vq->in_use = false;
 #endif

 	vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC);

 	/* No callback?  Tell other side not to bother us. */
 	if (!callback)
 		vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;

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

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

 void vring_del_virtqueue(struct virtqueue *vq)
 {
 	list_del(&vq->list);
 	kfree(to_vvq(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;
 		default:
 			/* We don't understand this bit. */
 			clear_bit(i, vdev->features);
 		}
 	}
 }
 EXPORT_SYMBOL_GPL(vring_transport_features);

 MODULE_LICENSE("GPL");
	/* Virtio ring implementation.
	*
	* Copyright 2007 Rusty Russell IBM Corporation
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
	*/
	#include <linux/virtio.h>
	#include <linux/virtio_ring.h>
	#include <linux/virtio_config.h>
	#include <linux/device.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__; \
	mb(); \
	} while (0)
	#define END_USE(_vq) \
	do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; mb(); } while(0)
	#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)
	#endif

	struct vring_virtqueue
	{
	struct virtqueue vq;

	/* Actual memory layout for this queue */
	struct vring vring;

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

	/* Host supports indirect buffers */
	bool indirect;

	/* Number of free buffers */
	unsigned int num_free;
	/* 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;

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

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

	/* Tokens for callbacks. */
	void *data[];
	};

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

	/* Set up an indirect table of descriptors and add it to the queue. */
	static int vring_add_indirect(struct vring_virtqueue *vq,
	struct scatterlist sg[],
	unsigned int out,
	unsigned int in)
	{
	struct vring_desc *desc;
	unsigned head;
	int i;

	desc = kmalloc((out + in) * sizeof(struct vring_desc), GFP_ATOMIC);
	if (!desc)
	return vq->vring.num;

	/* Transfer entries from the sg list into the indirect page */
	for (i = 0; i < out; i++) {
	desc[i].flags = VRING_DESC_F_NEXT;
	desc[i].addr = sg_phys(sg);
	desc[i].len = sg->length;
	desc[i].next = i+1;
	sg++;
	}
	for (; i < (out + in); i++) {
	desc[i].flags = VRING_DESC_F_NEXT\|VRING_DESC_F_WRITE;
	desc[i].addr = sg_phys(sg);
	desc[i].len = sg->length;
	desc[i].next = i+1;
	sg++;
	}

	/* Last one doesn't continue. */
	desc[i-1].flags &= ~VRING_DESC_F_NEXT;
	desc[i-1].next = 0;

	/* We're about to use a buffer */
	vq->num_free--;

	/* Use a single buffer which doesn't continue */
	head = vq->free_head;
	vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
	vq->vring.desc[head].addr = virt_to_phys(desc);
	vq->vring.desc[head].len = i * sizeof(struct vring_desc);

	/* Update free pointer */
	vq->free_head = vq->vring.desc[head].next;

	return head;
	}

	static int vring_add_buf(struct virtqueue *_vq,
	struct scatterlist sg[],
	unsigned int out,
	unsigned int in,
	void *data)
	{
	struct vring_virtqueue *vq = to_vvq(_vq);
	unsigned int i, avail, head, uninitialized_var(prev);

	START_USE(vq);

	BUG_ON(data == NULL);

	/* If the host supports indirect descriptor tables, and we have multiple
	* buffers, then go indirect. FIXME: tune this threshold */
	if (vq->indirect && (out + in) > 1 && vq->num_free) {
	head = vring_add_indirect(vq, sg, out, in);
	if (head != vq->vring.num)
	goto add_head;
	}

	BUG_ON(out + in > vq->vring.num);
	BUG_ON(out + in == 0);

	if (vq->num_free < out + in) {
	pr_debug("Can't add buf len %i - avail = %i\n",
	out + in, 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)
	vq->notify(&vq->vq);
	END_USE(vq);
	return -ENOSPC;
	}

	/* We're about to use some buffers from the free list. */
	vq->num_free -= out + in;

	head = vq->free_head;
	for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
	vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
	vq->vring.desc[i].addr = sg_phys(sg);
	vq->vring.desc[i].len = sg->length;
	prev = i;
	sg++;
	}
	for (; in; i = vq->vring.desc[i].next, in--) {
	vq->vring.desc[i].flags = VRING_DESC_F_NEXT\|VRING_DESC_F_WRITE;
	vq->vring.desc[i].addr = sg_phys(sg);
	vq->vring.desc[i].len = sg->length;
	prev = i;
	sg++;
	}
	/* Last one doesn't continue. */
	vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;

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

	add_head:
	/* Set token. */
	vq->data[head] = data;

	/* Put entry in available array (but don't update avail->idx until they
	* do sync). FIXME: avoid modulus here? */
	avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num;
	vq->vring.avail->ring[avail] = head;

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

	/* If we're indirect, we can fit many (assuming not OOM). */
	if (vq->indirect)
	return vq->num_free ? vq->vring.num : 0;
	return vq->num_free;
	}

	static void vring_kick(struct virtqueue *_vq)
	{
	struct vring_virtqueue *vq = to_vvq(_vq);
	START_USE(vq);
	/* Descriptors and available array need to be set before we expose the
	* new available array entries. */
	wmb();

	vq->vring.avail->idx += vq->num_added;
	vq->num_added = 0;

	/* Need to update avail index before checking if we should notify */
	mb();

	if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
	/* Prod other side to tell it about changes. */
	vq->notify(&vq->vq);

	END_USE(vq);
	}

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

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

	/* Put back on free list: find end */
	i = head;

	/* Free the indirect table */
	if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT)
	kfree(phys_to_virt(vq->vring.desc[i].addr));

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

	vq->vring.desc[i].next = vq->free_head;
	vq->free_head = head;
	/* Plus final descriptor */
	vq->num_free++;
	}

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

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

	START_USE(vq);

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

	if (!more_used(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. */
	rmb();

	i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id;
	*len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;

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

	/* detach_buf clears data, so grab it now. */
	ret = vq->data[i];
	detach_buf(vq, i);
	vq->last_used_idx++;
	END_USE(vq);
	return ret;
	}

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

	vq->vring.avail->flags \|= VRING_AVAIL_F_NO_INTERRUPT;
	}

	static bool vring_enable_cb(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. */
	vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
	mb();
	if (unlikely(more_used(vq))) {
	END_USE(vq);
	return false;
	}

	END_USE(vq);
	return true;
	}

	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);

	static struct virtqueue_ops vring_vq_ops = {
	.add_buf = vring_add_buf,
	.get_buf = vring_get_buf,
	.kick = vring_kick,
	.disable_cb = vring_disable_cb,
	.enable_cb = vring_enable_cb,
	};

	struct virtqueue *vring_new_virtqueue(unsigned int num,
	unsigned int vring_align,
	struct virtio_device *vdev,
	void *pages,
	void (notify)(struct virtqueue ),
	void (callback)(struct virtqueue ),
	const char *name)
	{
	struct vring_virtqueue *vq;
	unsigned int i;

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

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

	vring_init(&vq->vring, num, pages, vring_align);
	vq->vq.callback = callback;
	vq->vq.vdev = vdev;
	vq->vq.vq_ops = &vring_vq_ops;
	vq->vq.name = name;
	vq->notify = notify;
	vq->broken = false;
	vq->last_used_idx = 0;
	vq->num_added = 0;
	list_add_tail(&vq->vq.list, &vdev->vqs);
	#ifdef DEBUG
	vq->in_use = false;
	#endif

	vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC);

	/* No callback? Tell other side not to bother us. */
	if (!callback)
	vq->vring.avail->flags \|= VRING_AVAIL_F_NO_INTERRUPT;

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

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

	void vring_del_virtqueue(struct virtqueue *vq)
	{
	list_del(&vq->list);
	kfree(to_vvq(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;
	default:
	/* We don't understand this bit. */
	clear_bit(i, vdev->features);
	}
	}
	}
	EXPORT_SYMBOL_GPL(vring_transport_features);

	MODULE_LICENSE("GPL");