[RFC,07/13] vhost: format-independent API for used buffers
diff mbox series

Message ID 20200602130543.578420-8-mst@redhat.com
State New
Headers show
Series
  • vhost: format independence
Related show

Commit Message

Michael S. Tsirkin June 2, 2020, 1:06 p.m. UTC
Add a new API that doesn't assume used ring, heads, etc.
For now, we keep the old APIs around to make it easier
to convert drivers.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/vhost/vhost.c | 52 ++++++++++++++++++++++++++++++++++---------
 drivers/vhost/vhost.h | 17 +++++++++++++-
 2 files changed, 58 insertions(+), 11 deletions(-)

Comments

Jason Wang June 3, 2020, 7:58 a.m. UTC | #1
On 2020/6/2 下午9:06, Michael S. Tsirkin wrote:
> Add a new API that doesn't assume used ring, heads, etc.
> For now, we keep the old APIs around to make it easier
> to convert drivers.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>   drivers/vhost/vhost.c | 52 ++++++++++++++++++++++++++++++++++---------
>   drivers/vhost/vhost.h | 17 +++++++++++++-
>   2 files changed, 58 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index b4a6e44d56a8..be822f0c9428 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2292,13 +2292,12 @@ static int fetch_descs(struct vhost_virtqueue *vq)
>    * number of output then some number of input descriptors, it's actually two
>    * iovecs, but we pack them into one and note how many of each there were.
>    *
> - * This function returns the descriptor number found, or vq->num (which is
> - * never a valid descriptor number) if none was found.  A negative code is
> - * returned on error. */
> -int vhost_get_vq_desc(struct vhost_virtqueue *vq,
> -		      struct iovec iov[], unsigned int iov_size,
> -		      unsigned int *out_num, unsigned int *in_num,
> -		      struct vhost_log *log, unsigned int *log_num)
> + * This function returns a value > 0 if a descriptor was found, or 0 if none were found.
> + * A negative code is returned on error. */
> +int vhost_get_avail_buf(struct vhost_virtqueue *vq, struct vhost_buf *buf,
> +			struct iovec iov[], unsigned int iov_size,
> +			unsigned int *out_num, unsigned int *in_num,
> +			struct vhost_log *log, unsigned int *log_num)
>   {
>   	int ret = fetch_descs(vq);
>   	int i;
> @@ -2311,6 +2310,8 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
>   	*out_num = *in_num = 0;
>   	if (unlikely(log))
>   		*log_num = 0;
> +	buf->in_len = buf->out_len = 0;
> +	buf->descs = 0;
>   
>   	for (i = vq->first_desc; i < vq->ndescs; ++i) {
>   		unsigned iov_count = *in_num + *out_num;
> @@ -2340,6 +2341,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
>   			/* If this is an input descriptor,
>   			 * increment that count. */
>   			*in_num += ret;
> +			buf->in_len += desc->len;
>   			if (unlikely(log && ret)) {
>   				log[*log_num].addr = desc->addr;
>   				log[*log_num].len = desc->len;
> @@ -2355,9 +2357,11 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
>   				goto err;
>   			}
>   			*out_num += ret;
> +			buf->out_len += desc->len;
>   		}
>   
> -		ret = desc->id;
> +		buf->id = desc->id;
> +		++buf->descs;
>   
>   		if (!(desc->flags & VRING_DESC_F_NEXT))
>   			break;
> @@ -2365,7 +2369,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
>   
>   	vq->first_desc = i + 1;
>   
> -	return ret;
> +	return 1;
>   
>   err:
>   	for (i = vq->first_desc; i < vq->ndescs; ++i)
> @@ -2375,7 +2379,15 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
>   
>   	return ret;
>   }
> -EXPORT_SYMBOL_GPL(vhost_get_vq_desc);
> +EXPORT_SYMBOL_GPL(vhost_get_avail_buf);
> +
> +/* Reverse the effect of vhost_get_avail_buf. Useful for error handling. */
> +void vhost_discard_avail_bufs(struct vhost_virtqueue *vq,
> +			      struct vhost_buf *buf, unsigned count)
> +{
> +	vhost_discard_vq_desc(vq, count);
> +}
> +EXPORT_SYMBOL_GPL(vhost_discard_avail_bufs);
>   
>   static int __vhost_add_used_n(struct vhost_virtqueue *vq,
>   			    struct vring_used_elem *heads,
> @@ -2459,6 +2471,26 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
>   }
>   EXPORT_SYMBOL_GPL(vhost_add_used);
>   
> +int vhost_put_used_buf(struct vhost_virtqueue *vq, struct vhost_buf *buf)
> +{
> +	return vhost_add_used(vq, buf->id, buf->in_len);
> +}
> +EXPORT_SYMBOL_GPL(vhost_put_used_buf);
> +
> +int vhost_put_used_n_bufs(struct vhost_virtqueue *vq,
> +			  struct vhost_buf *bufs, unsigned count)
> +{
> +	unsigned i;
> +
> +	for (i = 0; i < count; ++i) {
> +		vq->heads[i].id = cpu_to_vhost32(vq, bufs[i].id);
> +		vq->heads[i].len = cpu_to_vhost32(vq, bufs[i].in_len);
> +	}
> +
> +	return vhost_add_used_n(vq, vq->heads, count);
> +}
> +EXPORT_SYMBOL_GPL(vhost_put_used_n_bufs);
> +
>   static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
>   {
>   	__u16 old, new;
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index a67bda9792ec..6c10e99ff334 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -67,6 +67,13 @@ struct vhost_desc {
>   	u16 id;
>   };
>   
> +struct vhost_buf {
> +	u32 out_len;
> +	u32 in_len;
> +	u16 descs;
> +	u16 id;
> +};


So it looks to me the struct vhost_buf can work for both split ring and 
packed ring.

If this is true, we'd better make struct vhost_desc work for both.

Thanks


> +
>   /* The virtqueue structure describes a queue attached to a device. */
>   struct vhost_virtqueue {
>   	struct vhost_dev *dev;
> @@ -193,7 +200,12 @@ int vhost_get_vq_desc(struct vhost_virtqueue *,
>   		      unsigned int *out_num, unsigned int *in_num,
>   		      struct vhost_log *log, unsigned int *log_num);
>   void vhost_discard_vq_desc(struct vhost_virtqueue *, int n);
> -
> +int vhost_get_avail_buf(struct vhost_virtqueue *, struct vhost_buf *buf,
> +			struct iovec iov[], unsigned int iov_count,
> +			unsigned int *out_num, unsigned int *in_num,
> +			struct vhost_log *log, unsigned int *log_num);
> +void vhost_discard_avail_bufs(struct vhost_virtqueue *,
> +			      struct vhost_buf *, unsigned count);
>   int vhost_vq_init_access(struct vhost_virtqueue *);
>   int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
>   int vhost_add_used_n(struct vhost_virtqueue *, struct vring_used_elem *heads,
> @@ -202,6 +214,9 @@ void vhost_add_used_and_signal(struct vhost_dev *, struct vhost_virtqueue *,
>   			       unsigned int id, int len);
>   void vhost_add_used_and_signal_n(struct vhost_dev *, struct vhost_virtqueue *,
>   			       struct vring_used_elem *heads, unsigned count);
> +int vhost_put_used_buf(struct vhost_virtqueue *, struct vhost_buf *buf);
> +int vhost_put_used_n_bufs(struct vhost_virtqueue *,
> +			  struct vhost_buf *bufs, unsigned count);
>   void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
>   void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
>   bool vhost_vq_avail_empty(struct vhost_dev *, struct vhost_virtqueue *);
Michael S. Tsirkin June 4, 2020, 9:03 a.m. UTC | #2
On Wed, Jun 03, 2020 at 03:58:26PM +0800, Jason Wang wrote:
> 
> On 2020/6/2 下午9:06, Michael S. Tsirkin wrote:
> > Add a new API that doesn't assume used ring, heads, etc.
> > For now, we keep the old APIs around to make it easier
> > to convert drivers.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >   drivers/vhost/vhost.c | 52 ++++++++++++++++++++++++++++++++++---------
> >   drivers/vhost/vhost.h | 17 +++++++++++++-
> >   2 files changed, 58 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index b4a6e44d56a8..be822f0c9428 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -2292,13 +2292,12 @@ static int fetch_descs(struct vhost_virtqueue *vq)
> >    * number of output then some number of input descriptors, it's actually two
> >    * iovecs, but we pack them into one and note how many of each there were.
> >    *
> > - * This function returns the descriptor number found, or vq->num (which is
> > - * never a valid descriptor number) if none was found.  A negative code is
> > - * returned on error. */
> > -int vhost_get_vq_desc(struct vhost_virtqueue *vq,
> > -		      struct iovec iov[], unsigned int iov_size,
> > -		      unsigned int *out_num, unsigned int *in_num,
> > -		      struct vhost_log *log, unsigned int *log_num)
> > + * This function returns a value > 0 if a descriptor was found, or 0 if none were found.
> > + * A negative code is returned on error. */
> > +int vhost_get_avail_buf(struct vhost_virtqueue *vq, struct vhost_buf *buf,
> > +			struct iovec iov[], unsigned int iov_size,
> > +			unsigned int *out_num, unsigned int *in_num,
> > +			struct vhost_log *log, unsigned int *log_num)
> >   {
> >   	int ret = fetch_descs(vq);
> >   	int i;
> > @@ -2311,6 +2310,8 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
> >   	*out_num = *in_num = 0;
> >   	if (unlikely(log))
> >   		*log_num = 0;
> > +	buf->in_len = buf->out_len = 0;
> > +	buf->descs = 0;
> >   	for (i = vq->first_desc; i < vq->ndescs; ++i) {
> >   		unsigned iov_count = *in_num + *out_num;
> > @@ -2340,6 +2341,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
> >   			/* If this is an input descriptor,
> >   			 * increment that count. */
> >   			*in_num += ret;
> > +			buf->in_len += desc->len;
> >   			if (unlikely(log && ret)) {
> >   				log[*log_num].addr = desc->addr;
> >   				log[*log_num].len = desc->len;
> > @@ -2355,9 +2357,11 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
> >   				goto err;
> >   			}
> >   			*out_num += ret;
> > +			buf->out_len += desc->len;
> >   		}
> > -		ret = desc->id;
> > +		buf->id = desc->id;
> > +		++buf->descs;
> >   		if (!(desc->flags & VRING_DESC_F_NEXT))
> >   			break;
> > @@ -2365,7 +2369,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
> >   	vq->first_desc = i + 1;
> > -	return ret;
> > +	return 1;
> >   err:
> >   	for (i = vq->first_desc; i < vq->ndescs; ++i)
> > @@ -2375,7 +2379,15 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
> >   	return ret;
> >   }
> > -EXPORT_SYMBOL_GPL(vhost_get_vq_desc);
> > +EXPORT_SYMBOL_GPL(vhost_get_avail_buf);
> > +
> > +/* Reverse the effect of vhost_get_avail_buf. Useful for error handling. */
> > +void vhost_discard_avail_bufs(struct vhost_virtqueue *vq,
> > +			      struct vhost_buf *buf, unsigned count)
> > +{
> > +	vhost_discard_vq_desc(vq, count);
> > +}
> > +EXPORT_SYMBOL_GPL(vhost_discard_avail_bufs);
> >   static int __vhost_add_used_n(struct vhost_virtqueue *vq,
> >   			    struct vring_used_elem *heads,
> > @@ -2459,6 +2471,26 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
> >   }
> >   EXPORT_SYMBOL_GPL(vhost_add_used);
> > +int vhost_put_used_buf(struct vhost_virtqueue *vq, struct vhost_buf *buf)
> > +{
> > +	return vhost_add_used(vq, buf->id, buf->in_len);
> > +}
> > +EXPORT_SYMBOL_GPL(vhost_put_used_buf);
> > +
> > +int vhost_put_used_n_bufs(struct vhost_virtqueue *vq,
> > +			  struct vhost_buf *bufs, unsigned count)
> > +{
> > +	unsigned i;
> > +
> > +	for (i = 0; i < count; ++i) {
> > +		vq->heads[i].id = cpu_to_vhost32(vq, bufs[i].id);
> > +		vq->heads[i].len = cpu_to_vhost32(vq, bufs[i].in_len);
> > +	}
> > +
> > +	return vhost_add_used_n(vq, vq->heads, count);
> > +}
> > +EXPORT_SYMBOL_GPL(vhost_put_used_n_bufs);
> > +
> >   static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
> >   {
> >   	__u16 old, new;
> > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> > index a67bda9792ec..6c10e99ff334 100644
> > --- a/drivers/vhost/vhost.h
> > +++ b/drivers/vhost/vhost.h
> > @@ -67,6 +67,13 @@ struct vhost_desc {
> >   	u16 id;
> >   };
> > +struct vhost_buf {
> > +	u32 out_len;
> > +	u32 in_len;
> > +	u16 descs;
> > +	u16 id;
> > +};
> 
> 
> So it looks to me the struct vhost_buf can work for both split ring and
> packed ring.
> 
> If this is true, we'd better make struct vhost_desc work for both.
> 
> Thanks

Both vhost_desc and vhost_buf can work for split and packed.

Do you mean we should add packed ring support based on this?
For sure, this is one of the motivators for the patchset.


> 
> > +
> >   /* The virtqueue structure describes a queue attached to a device. */
> >   struct vhost_virtqueue {
> >   	struct vhost_dev *dev;
> > @@ -193,7 +200,12 @@ int vhost_get_vq_desc(struct vhost_virtqueue *,
> >   		      unsigned int *out_num, unsigned int *in_num,
> >   		      struct vhost_log *log, unsigned int *log_num);
> >   void vhost_discard_vq_desc(struct vhost_virtqueue *, int n);
> > -
> > +int vhost_get_avail_buf(struct vhost_virtqueue *, struct vhost_buf *buf,
> > +			struct iovec iov[], unsigned int iov_count,
> > +			unsigned int *out_num, unsigned int *in_num,
> > +			struct vhost_log *log, unsigned int *log_num);
> > +void vhost_discard_avail_bufs(struct vhost_virtqueue *,
> > +			      struct vhost_buf *, unsigned count);
> >   int vhost_vq_init_access(struct vhost_virtqueue *);
> >   int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
> >   int vhost_add_used_n(struct vhost_virtqueue *, struct vring_used_elem *heads,
> > @@ -202,6 +214,9 @@ void vhost_add_used_and_signal(struct vhost_dev *, struct vhost_virtqueue *,
> >   			       unsigned int id, int len);
> >   void vhost_add_used_and_signal_n(struct vhost_dev *, struct vhost_virtqueue *,
> >   			       struct vring_used_elem *heads, unsigned count);
> > +int vhost_put_used_buf(struct vhost_virtqueue *, struct vhost_buf *buf);
> > +int vhost_put_used_n_bufs(struct vhost_virtqueue *,
> > +			  struct vhost_buf *bufs, unsigned count);
> >   void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
> >   void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
> >   bool vhost_vq_avail_empty(struct vhost_dev *, struct vhost_virtqueue *);
Jason Wang June 4, 2020, 9:18 a.m. UTC | #3
On 2020/6/4 下午5:03, Michael S. Tsirkin wrote:
>>>    static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
>>>    {
>>>    	__u16 old, new;
>>> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
>>> index a67bda9792ec..6c10e99ff334 100644
>>> --- a/drivers/vhost/vhost.h
>>> +++ b/drivers/vhost/vhost.h
>>> @@ -67,6 +67,13 @@ struct vhost_desc {
>>>    	u16 id;
>>>    };
>>> +struct vhost_buf {
>>> +	u32 out_len;
>>> +	u32 in_len;
>>> +	u16 descs;
>>> +	u16 id;
>>> +};
>> So it looks to me the struct vhost_buf can work for both split ring and
>> packed ring.
>>
>> If this is true, we'd better make struct vhost_desc work for both.
>>
>> Thanks
> Both vhost_desc and vhost_buf can work for split and packed.
>
> Do you mean we should add packed ring support based on this?
> For sure, this is one of the motivators for the patchset.
>

Somehow. But the reason I ask is that I see "split" suffix is used in 
patch 1 as:

peek_split_desc()
pop_split_desc()
push_split_desc()

But that suffix is not used for the new used ring API invented in this 
patch.

Thanks
Michael S. Tsirkin June 4, 2020, 10:17 a.m. UTC | #4
On Thu, Jun 04, 2020 at 05:18:00PM +0800, Jason Wang wrote:
> 
> On 2020/6/4 下午5:03, Michael S. Tsirkin wrote:
> > > >    static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
> > > >    {
> > > >    	__u16 old, new;
> > > > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> > > > index a67bda9792ec..6c10e99ff334 100644
> > > > --- a/drivers/vhost/vhost.h
> > > > +++ b/drivers/vhost/vhost.h
> > > > @@ -67,6 +67,13 @@ struct vhost_desc {
> > > >    	u16 id;
> > > >    };
> > > > +struct vhost_buf {
> > > > +	u32 out_len;
> > > > +	u32 in_len;
> > > > +	u16 descs;
> > > > +	u16 id;
> > > > +};
> > > So it looks to me the struct vhost_buf can work for both split ring and
> > > packed ring.
> > > 
> > > If this is true, we'd better make struct vhost_desc work for both.
> > > 
> > > Thanks
> > Both vhost_desc and vhost_buf can work for split and packed.
> > 
> > Do you mean we should add packed ring support based on this?
> > For sure, this is one of the motivators for the patchset.
> > 
> 
> Somehow. But the reason I ask is that I see "split" suffix is used in patch
> 1 as:
> 
> peek_split_desc()
> pop_split_desc()
> push_split_desc()
> 
> But that suffix is not used for the new used ring API invented in this
> patch.
> 
> Thanks
> 

And that is intentional: split is *not* part of API. The whole idea is
that ring APIs are format agnostic using "buffer" terminology from spec.
The split things are all static within vhost.c

OK so where I had to add a bunch of new format specific code, that was
tagged as "split" to make it easier to spot that they only support a
specific format.  At the same time, I did not rename existing code
adding "split" in the name. I agree it's a useful additional step for
packed ring format support, and it's fairly easy. I just didn't want
to do it automatically.

Patch
diff mbox series

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index b4a6e44d56a8..be822f0c9428 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2292,13 +2292,12 @@  static int fetch_descs(struct vhost_virtqueue *vq)
  * number of output then some number of input descriptors, it's actually two
  * iovecs, but we pack them into one and note how many of each there were.
  *
- * This function returns the descriptor number found, or vq->num (which is
- * never a valid descriptor number) if none was found.  A negative code is
- * returned on error. */
-int vhost_get_vq_desc(struct vhost_virtqueue *vq,
-		      struct iovec iov[], unsigned int iov_size,
-		      unsigned int *out_num, unsigned int *in_num,
-		      struct vhost_log *log, unsigned int *log_num)
+ * This function returns a value > 0 if a descriptor was found, or 0 if none were found.
+ * A negative code is returned on error. */
+int vhost_get_avail_buf(struct vhost_virtqueue *vq, struct vhost_buf *buf,
+			struct iovec iov[], unsigned int iov_size,
+			unsigned int *out_num, unsigned int *in_num,
+			struct vhost_log *log, unsigned int *log_num)
 {
 	int ret = fetch_descs(vq);
 	int i;
@@ -2311,6 +2310,8 @@  int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 	*out_num = *in_num = 0;
 	if (unlikely(log))
 		*log_num = 0;
+	buf->in_len = buf->out_len = 0;
+	buf->descs = 0;
 
 	for (i = vq->first_desc; i < vq->ndescs; ++i) {
 		unsigned iov_count = *in_num + *out_num;
@@ -2340,6 +2341,7 @@  int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 			/* If this is an input descriptor,
 			 * increment that count. */
 			*in_num += ret;
+			buf->in_len += desc->len;
 			if (unlikely(log && ret)) {
 				log[*log_num].addr = desc->addr;
 				log[*log_num].len = desc->len;
@@ -2355,9 +2357,11 @@  int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 				goto err;
 			}
 			*out_num += ret;
+			buf->out_len += desc->len;
 		}
 
-		ret = desc->id;
+		buf->id = desc->id;
+		++buf->descs;
 
 		if (!(desc->flags & VRING_DESC_F_NEXT))
 			break;
@@ -2365,7 +2369,7 @@  int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 
 	vq->first_desc = i + 1;
 
-	return ret;
+	return 1;
 
 err:
 	for (i = vq->first_desc; i < vq->ndescs; ++i)
@@ -2375,7 +2379,15 @@  int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 
 	return ret;
 }
-EXPORT_SYMBOL_GPL(vhost_get_vq_desc);
+EXPORT_SYMBOL_GPL(vhost_get_avail_buf);
+
+/* Reverse the effect of vhost_get_avail_buf. Useful for error handling. */
+void vhost_discard_avail_bufs(struct vhost_virtqueue *vq,
+			      struct vhost_buf *buf, unsigned count)
+{
+	vhost_discard_vq_desc(vq, count);
+}
+EXPORT_SYMBOL_GPL(vhost_discard_avail_bufs);
 
 static int __vhost_add_used_n(struct vhost_virtqueue *vq,
 			    struct vring_used_elem *heads,
@@ -2459,6 +2471,26 @@  int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
 }
 EXPORT_SYMBOL_GPL(vhost_add_used);
 
+int vhost_put_used_buf(struct vhost_virtqueue *vq, struct vhost_buf *buf)
+{
+	return vhost_add_used(vq, buf->id, buf->in_len);
+}
+EXPORT_SYMBOL_GPL(vhost_put_used_buf);
+
+int vhost_put_used_n_bufs(struct vhost_virtqueue *vq,
+			  struct vhost_buf *bufs, unsigned count)
+{
+	unsigned i;
+
+	for (i = 0; i < count; ++i) {
+		vq->heads[i].id = cpu_to_vhost32(vq, bufs[i].id);
+		vq->heads[i].len = cpu_to_vhost32(vq, bufs[i].in_len);
+	}
+
+	return vhost_add_used_n(vq, vq->heads, count);
+}
+EXPORT_SYMBOL_GPL(vhost_put_used_n_bufs);
+
 static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 {
 	__u16 old, new;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index a67bda9792ec..6c10e99ff334 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -67,6 +67,13 @@  struct vhost_desc {
 	u16 id;
 };
 
+struct vhost_buf {
+	u32 out_len;
+	u32 in_len;
+	u16 descs;
+	u16 id;
+};
+
 /* The virtqueue structure describes a queue attached to a device. */
 struct vhost_virtqueue {
 	struct vhost_dev *dev;
@@ -193,7 +200,12 @@  int vhost_get_vq_desc(struct vhost_virtqueue *,
 		      unsigned int *out_num, unsigned int *in_num,
 		      struct vhost_log *log, unsigned int *log_num);
 void vhost_discard_vq_desc(struct vhost_virtqueue *, int n);
-
+int vhost_get_avail_buf(struct vhost_virtqueue *, struct vhost_buf *buf,
+			struct iovec iov[], unsigned int iov_count,
+			unsigned int *out_num, unsigned int *in_num,
+			struct vhost_log *log, unsigned int *log_num);
+void vhost_discard_avail_bufs(struct vhost_virtqueue *,
+			      struct vhost_buf *, unsigned count);
 int vhost_vq_init_access(struct vhost_virtqueue *);
 int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
 int vhost_add_used_n(struct vhost_virtqueue *, struct vring_used_elem *heads,
@@ -202,6 +214,9 @@  void vhost_add_used_and_signal(struct vhost_dev *, struct vhost_virtqueue *,
 			       unsigned int id, int len);
 void vhost_add_used_and_signal_n(struct vhost_dev *, struct vhost_virtqueue *,
 			       struct vring_used_elem *heads, unsigned count);
+int vhost_put_used_buf(struct vhost_virtqueue *, struct vhost_buf *buf);
+int vhost_put_used_n_bufs(struct vhost_virtqueue *,
+			  struct vhost_buf *bufs, unsigned count);
 void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
 void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
 bool vhost_vq_avail_empty(struct vhost_dev *, struct vhost_virtqueue *);