Re: [Xen-devel] [PATCH v2 1/1] public/io/netif.h: add gref mapping control messages

2017-09-07 Thread Paul Durrant 
> -Original Message-
> From: Joao Martins [mailto:joao.m.mart...@oracle.com]
> Sent: 06 September 2017 17:07
> To: Paul Durrant 
> Subject: Re: [PATCH v2 1/1] public/io/netif.h: add gref mapping control
> messages
> 
> [Is it meant to be offlist?]

Nope. My mistake.

> 
> On 09/06/2017 03:49 PM, Paul Durrant wrote:
> >> -Original Message-
> >> From: Joao Martins [mailto:joao.m.mart...@oracle.com]
> >> Sent: 06 September 2017 15:37
> >> To: Paul Durrant 
> >> Cc: Xen-devel ; Wei Liu ;
> >> Konrad Rzeszutek Wilk 
> >> Subject: Re: [PATCH v2 1/1] public/io/netif.h: add gref mapping control
> >> messages
> >>
> >> On 09/06/2017 02:49 PM, Paul Durrant wrote:
>  -Original Message-
>  From: Joao Martins [mailto:joao.m.mart...@oracle.com]
>  Sent: 01 September 2017 15:51
>  To: Xen-devel 
>  Cc: Wei Liu ; Paul Durrant
> >> ;
>  Konrad Rzeszutek Wilk ; Joao Martins
>  
>  Subject: [PATCH v2 1/1] public/io/netif.h: add gref mapping control
> >> messages
> 
>  Adds 3 messages to allow guest to let backend keep grants mapped,
>  such that 1) guests allowing fast recycling of pages can avoid doing
>  grant ops for those cases, or otherwise 2) preferring copies over
>  grants and 3) always using a fixed set of pages for network I/O.
> 
>  The three control ring messages added are:
>   - Add grefs to be mapped by backend
>   - Remove grefs mappings (If they are not in use)
>   - Get maximum amount of grefs kept mapped.
> 
>  Signed-off-by: Joao Martins 
>  ---
>   xen/include/public/io/netif.h | 114
>  ++
>   1 file changed, 114 insertions(+)
> 
>  diff --git a/xen/include/public/io/netif.h
> b/xen/include/public/io/netif.h
>  index ca0061410d..264c317471 100644
>  --- a/xen/include/public/io/netif.h
>  +++ b/xen/include/public/io/netif.h
>  @@ -353,6 +353,9 @@ struct xen_netif_ctrl_request {
>   #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING_SIZE 5
>   #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING  6
>   #define XEN_NETIF_CTRL_TYPE_SET_HASH_ALGORITHM7
>  +#define XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE 8
>  +#define XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING  9
>  +#define XEN_NETIF_CTRL_TYPE_PUT_GREF_MAPPING 10
> 
>   uint32_t data[3];
>   };
>  @@ -391,6 +394,41 @@ struct xen_netif_ctrl_response {
>   };
> 
>   /*
>  + * Static Grants (struct xen_netif_gref_alloc)
>  + * ===
>  + *
>  + * A frontend may provide a fixed set of grant references to be
> mapped
> >> on
>  + * the backend. The message of type
>  XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
>  + * prior its usage in the command ring allows for creation of these
> >> mappings.
>  + * The backend will maintain a fixed amount of these mappings.
>  + *
>  + * XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE lets a frontend
>  query how many
>  + * of these mappings can be kept.
>  + *
>  + * Each entry in the
> >> XEN_NETIF_CTRL_TYPE_{ADD,PUT}_GREF_MAPPING
>  input table has
> >>>
> >>> ADD and PUT are slightly odd choices for opposites. Normally you'd have
> >> 'get' and 'put' or 'add' and 'remove' (or 'delete').
> >>>
> >> That's true - I probably was too obsessed into fitting in 3 characters to
> avoid
> >> realigning the earlier chunk listing all ctrl messages types. ADD, DEL
> probably
> >> is a better one (GET would sound a bit strange for these ops).
> >
> > ADD/DEL sounds fine to me.
> >
> OK. In case you prefer a slightly less verbose/long name like
> XEN_NETIF_CTRL_TYPE_{MAP,UNMAP}_GREF let me know :)
> 
> >>
>  + * the following format:
>  + *
>  + *0 1 2 3 4 5 6 7  octet
>  + * +-+-+-+-+-+-+-+-+
>  + * | grant ref |  flags|  padding  |
>  + * +-+-+-+-+-+-+-+-+
>  + *
>  + * grant ref: grant reference
>  + * flags: flags describing the control operation
>  + *
>  + */
>  +
>  +struct xen_netif_gref_alloc {
> >>>
> >>> Is 'alloc' really desirable here? What's being allocated?
> >>>
> >> Probably not my best choice of naming, but given that we aren't actually
> >> mapping
> >> on the frontend but rather the backend hence I choose 'alloc'. But as you
> hint
> >> it might be misleading. Would 'map' or 'mapping' be better candidates?
> >
> > I would just call it 'xen_netif_gref'. It's used for mapping and unmapping.
> >
> OK, got it.
> 
>  + *  data[2] = size of list in entries
>  + *
>  +

Re: [Xen-devel] [PATCH v2 1/1] public/io/netif.h: add gref mapping control messages

2017-09-07 Thread Paul Durrant 
[Accidentally dropped list and other ccs]

> -Original Message-
> From: Paul Durrant
> Sent: 06 September 2017 15:49
> To: 'Joao Martins' 
> Subject: RE: [PATCH v2 1/1] public/io/netif.h: add gref mapping control
> messages
> 
> > -Original Message-
> > From: Joao Martins [mailto:joao.m.mart...@oracle.com]
> > Sent: 06 September 2017 15:37
> > To: Paul Durrant 
> > Cc: Xen-devel ; Wei Liu ;
> > Konrad Rzeszutek Wilk 
> > Subject: Re: [PATCH v2 1/1] public/io/netif.h: add gref mapping control
> > messages
> >
> > On 09/06/2017 02:49 PM, Paul Durrant wrote:
> > >> -Original Message-
> > >> From: Joao Martins [mailto:joao.m.mart...@oracle.com]
> > >> Sent: 01 September 2017 15:51
> > >> To: Xen-devel 
> > >> Cc: Wei Liu ; Paul Durrant
> > ;
> > >> Konrad Rzeszutek Wilk ; Joao Martins
> > >> 
> > >> Subject: [PATCH v2 1/1] public/io/netif.h: add gref mapping control
> > messages
> > >>
> > >> Adds 3 messages to allow guest to let backend keep grants mapped,
> > >> such that 1) guests allowing fast recycling of pages can avoid doing
> > >> grant ops for those cases, or otherwise 2) preferring copies over
> > >> grants and 3) always using a fixed set of pages for network I/O.
> > >>
> > >> The three control ring messages added are:
> > >>  - Add grefs to be mapped by backend
> > >>  - Remove grefs mappings (If they are not in use)
> > >>  - Get maximum amount of grefs kept mapped.
> > >>
> > >> Signed-off-by: Joao Martins 
> > >> ---
> > >>  xen/include/public/io/netif.h | 114
> > >> ++
> > >>  1 file changed, 114 insertions(+)
> > >>
> > >> diff --git a/xen/include/public/io/netif.h 
> > >> b/xen/include/public/io/netif.h
> > >> index ca0061410d..264c317471 100644
> > >> --- a/xen/include/public/io/netif.h
> > >> +++ b/xen/include/public/io/netif.h
> > >> @@ -353,6 +353,9 @@ struct xen_netif_ctrl_request {
> > >>  #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING_SIZE 5
> > >>  #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING  6
> > >>  #define XEN_NETIF_CTRL_TYPE_SET_HASH_ALGORITHM7
> > >> +#define XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE 8
> > >> +#define XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING  9
> > >> +#define XEN_NETIF_CTRL_TYPE_PUT_GREF_MAPPING 10
> > >>
> > >>  uint32_t data[3];
> > >>  };
> > >> @@ -391,6 +394,41 @@ struct xen_netif_ctrl_response {
> > >>  };
> > >>
> > >>  /*
> > >> + * Static Grants (struct xen_netif_gref_alloc)
> > >> + * ===
> > >> + *
> > >> + * A frontend may provide a fixed set of grant references to be
> mapped
> > on
> > >> + * the backend. The message of type
> > >> XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
> > >> + * prior its usage in the command ring allows for creation of these
> > mappings.
> > >> + * The backend will maintain a fixed amount of these mappings.
> > >> + *
> > >> + * XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE lets a frontend
> > >> query how many
> > >> + * of these mappings can be kept.
> > >> + *
> > >> + * Each entry in the
> > XEN_NETIF_CTRL_TYPE_{ADD,PUT}_GREF_MAPPING
> > >> input table has
> > >
> > > ADD and PUT are slightly odd choices for opposites. Normally you'd have
> > 'get' and 'put' or 'add' and 'remove' (or 'delete').
> > >
> > That's true - I probably was too obsessed into fitting in 3 characters to 
> > avoid
> > realigning the earlier chunk listing all ctrl messages types. ADD, DEL
> probably
> > is a better one (GET would sound a bit strange for these ops).
> 
> ADD/DEL sounds fine to me.
> 
> >
> > >> + * the following format:
> > >> + *
> > >> + *0 1 2 3 4 5 6 7  octet
> > >> + * +-+-+-+-+-+-+-+-+
> > >> + * | grant ref |  flags|  padding  |
> > >> + * +-+-+-+-+-+-+-+-+
> > >> + *
> > >> + * grant ref: grant reference
> > >> + * flags: flags describing the control operation
> > >> + *
> > >> + */
> > >> +
> > >> +struct xen_netif_gref_alloc {
> > >
> > > Is 'alloc' really desirable here? What's being allocated?
> > >
> > Probably not my best choice of naming, but given that we aren't actually
> > mapping
> > on the frontend but rather the backend hence I choose 'alloc'. But as you
> hint
> > it might be misleading. Would 'map' or 'mapping' be better candidates?
> 
> I would just call it 'xen_netif_gref'. It's used for mapping and unmapping.
> 
> >
> > >> +   grant_ref_t ref;
> > >> +   uint16_t flags;
> > >> +
> > >> +#define _XEN_NETIF_CTRLF_GREF_readonly0
> > >> +#define XEN_NETIF_CTRLF_GREF_readonly
> > >> (1U<<_XEN_NETIF_CTRLF_GREF_readonly)
> > >> +
> > >> +   uint8_t pad[2];
> > >> +};
> > >> +
> > >> +/*
> > >>   * Control

Re: [Xen-devel] [PATCH v2 1/1] public/io/netif.h: add gref mapping control messages

2017-09-06 Thread Joao Martins 
On 09/06/2017 02:49 PM, Paul Durrant wrote:
>> -Original Message-
>> From: Joao Martins [mailto:joao.m.mart...@oracle.com]
>> Sent: 01 September 2017 15:51
>> To: Xen-devel 
>> Cc: Wei Liu ; Paul Durrant ;
>> Konrad Rzeszutek Wilk ; Joao Martins
>> 
>> Subject: [PATCH v2 1/1] public/io/netif.h: add gref mapping control messages
>>
>> Adds 3 messages to allow guest to let backend keep grants mapped,
>> such that 1) guests allowing fast recycling of pages can avoid doing
>> grant ops for those cases, or otherwise 2) preferring copies over
>> grants and 3) always using a fixed set of pages for network I/O.
>>
>> The three control ring messages added are:
>>  - Add grefs to be mapped by backend
>>  - Remove grefs mappings (If they are not in use)
>>  - Get maximum amount of grefs kept mapped.
>>
>> Signed-off-by: Joao Martins 
>> ---
>>  xen/include/public/io/netif.h | 114
>> ++
>>  1 file changed, 114 insertions(+)
>>
>> diff --git a/xen/include/public/io/netif.h b/xen/include/public/io/netif.h
>> index ca0061410d..264c317471 100644
>> --- a/xen/include/public/io/netif.h
>> +++ b/xen/include/public/io/netif.h
>> @@ -353,6 +353,9 @@ struct xen_netif_ctrl_request {
>>  #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING_SIZE 5
>>  #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING  6
>>  #define XEN_NETIF_CTRL_TYPE_SET_HASH_ALGORITHM7
>> +#define XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE 8
>> +#define XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING  9
>> +#define XEN_NETIF_CTRL_TYPE_PUT_GREF_MAPPING 10
>>
>>  uint32_t data[3];
>>  };
>> @@ -391,6 +394,41 @@ struct xen_netif_ctrl_response {
>>  };
>>
>>  /*
>> + * Static Grants (struct xen_netif_gref_alloc)
>> + * ===
>> + *
>> + * A frontend may provide a fixed set of grant references to be mapped on
>> + * the backend. The message of type
>> XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
>> + * prior its usage in the command ring allows for creation of these 
>> mappings.
>> + * The backend will maintain a fixed amount of these mappings.
>> + *
>> + * XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE lets a frontend
>> query how many
>> + * of these mappings can be kept.
>> + *
>> + * Each entry in the XEN_NETIF_CTRL_TYPE_{ADD,PUT}_GREF_MAPPING
>> input table has
> 
> ADD and PUT are slightly odd choices for opposites. Normally you'd have 'get' 
> and 'put' or 'add' and 'remove' (or 'delete').
> 
That's true - I probably was too obsessed into fitting in 3 characters to avoid
realigning the earlier chunk listing all ctrl messages types. ADD, DEL probably
is a better one (GET would sound a bit strange for these ops).

>> + * the following format:
>> + *
>> + *0 1 2 3 4 5 6 7  octet
>> + * +-+-+-+-+-+-+-+-+
>> + * | grant ref |  flags|  padding  |
>> + * +-+-+-+-+-+-+-+-+
>> + *
>> + * grant ref: grant reference
>> + * flags: flags describing the control operation
>> + *
>> + */
>> +
>> +struct xen_netif_gref_alloc {
> 
> Is 'alloc' really desirable here? What's being allocated?
> 
Probably not my best choice of naming, but given that we aren't actually mapping
on the frontend but rather the backend hence I choose 'alloc'. But as you hint
it might be misleading. Would 'map' or 'mapping' be better candidates?

>> +   grant_ref_t ref;
>> +   uint16_t flags;
>> +
>> +#define _XEN_NETIF_CTRLF_GREF_readonly0
>> +#define XEN_NETIF_CTRLF_GREF_readonly
>> (1U<<_XEN_NETIF_CTRLF_GREF_readonly)
>> +
>> +   uint8_t pad[2];
>> +};
>> +
>> +/*
>>   * Control messages
>>   * 
>>   *
>> @@ -609,6 +647,82 @@ struct xen_netif_ctrl_response {
>>   *   invalidate any table data outside that range.
>>   *   The grant reference may be read-only and must remain valid until
>>   *   the response has been processed.
>> + *
>> + * XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE
>> + * -
>> + *
>> + * This is sent by the frontend to fetch the number of grefs that can be 
>> kept
>> + * mapped in the backend.
>> + *
>> + * Request:
>> + *
>> + *  type= XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE
>> + *  data[0] = queue index (assumed 0 for single queue)
>> + *  data[1] = 0
>> + *  data[2] = 0
>> + *
>> + * Response:
>> + *
>> + *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED - Operation not
>> + * supported
>> + *   XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - The queue index
>> is
>> + * out of range
>> + *   XEN_NETIF_CTRL_STATUS_SUCCESS   - Operation successful
>> + *  data   = maximum number of entries allowed in the gref mapping table
>> + *   (if

Re: [Xen-devel] [PATCH v2 1/1] public/io/netif.h: add gref mapping control messages

2017-09-06 Thread Paul Durrant 
> -Original Message-
> From: Joao Martins [mailto:joao.m.mart...@oracle.com]
> Sent: 01 September 2017 15:51
> To: Xen-devel 
> Cc: Wei Liu ; Paul Durrant ;
> Konrad Rzeszutek Wilk ; Joao Martins
> 
> Subject: [PATCH v2 1/1] public/io/netif.h: add gref mapping control messages
> 
> Adds 3 messages to allow guest to let backend keep grants mapped,
> such that 1) guests allowing fast recycling of pages can avoid doing
> grant ops for those cases, or otherwise 2) preferring copies over
> grants and 3) always using a fixed set of pages for network I/O.
> 
> The three control ring messages added are:
>  - Add grefs to be mapped by backend
>  - Remove grefs mappings (If they are not in use)
>  - Get maximum amount of grefs kept mapped.
> 
> Signed-off-by: Joao Martins 
> ---
>  xen/include/public/io/netif.h | 114
> ++
>  1 file changed, 114 insertions(+)
> 
> diff --git a/xen/include/public/io/netif.h b/xen/include/public/io/netif.h
> index ca0061410d..264c317471 100644
> --- a/xen/include/public/io/netif.h
> +++ b/xen/include/public/io/netif.h
> @@ -353,6 +353,9 @@ struct xen_netif_ctrl_request {
>  #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING_SIZE 5
>  #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING  6
>  #define XEN_NETIF_CTRL_TYPE_SET_HASH_ALGORITHM7
> +#define XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE 8
> +#define XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING  9
> +#define XEN_NETIF_CTRL_TYPE_PUT_GREF_MAPPING 10
> 
>  uint32_t data[3];
>  };
> @@ -391,6 +394,41 @@ struct xen_netif_ctrl_response {
>  };
> 
>  /*
> + * Static Grants (struct xen_netif_gref_alloc)
> + * ===
> + *
> + * A frontend may provide a fixed set of grant references to be mapped on
> + * the backend. The message of type
> XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
> + * prior its usage in the command ring allows for creation of these mappings.
> + * The backend will maintain a fixed amount of these mappings.
> + *
> + * XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE lets a frontend
> query how many
> + * of these mappings can be kept.
> + *
> + * Each entry in the XEN_NETIF_CTRL_TYPE_{ADD,PUT}_GREF_MAPPING
> input table has

ADD and PUT are slightly odd choices for opposites. Normally you'd have 'get' 
and 'put' or 'add' and 'remove' (or 'delete').

> + * the following format:
> + *
> + *0 1 2 3 4 5 6 7  octet
> + * +-+-+-+-+-+-+-+-+
> + * | grant ref |  flags|  padding  |
> + * +-+-+-+-+-+-+-+-+
> + *
> + * grant ref: grant reference
> + * flags: flags describing the control operation
> + *
> + */
> +
> +struct xen_netif_gref_alloc {

Is 'alloc' really desirable here? What's being allocated?

> +   grant_ref_t ref;
> +   uint16_t flags;
> +
> +#define _XEN_NETIF_CTRLF_GREF_readonly0
> +#define XEN_NETIF_CTRLF_GREF_readonly
> (1U<<_XEN_NETIF_CTRLF_GREF_readonly)
> +
> +   uint8_t pad[2];
> +};
> +
> +/*
>   * Control messages
>   * 
>   *
> @@ -609,6 +647,82 @@ struct xen_netif_ctrl_response {
>   *   invalidate any table data outside that range.
>   *   The grant reference may be read-only and must remain valid until
>   *   the response has been processed.
> + *
> + * XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE
> + * -
> + *
> + * This is sent by the frontend to fetch the number of grefs that can be kept
> + * mapped in the backend.
> + *
> + * Request:
> + *
> + *  type= XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE
> + *  data[0] = queue index (assumed 0 for single queue)
> + *  data[1] = 0
> + *  data[2] = 0
> + *
> + * Response:
> + *
> + *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED - Operation not
> + * supported
> + *   XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - The queue index
> is
> + * out of range
> + *   XEN_NETIF_CTRL_STATUS_SUCCESS   - Operation successful
> + *  data   = maximum number of entries allowed in the gref mapping table
> + *   (if operation was successful) or zero if a mapping table is
> + *   not supported (i.e. hash mapping is done only by modular
> + *   arithmetic).

Too much cut'n'paste here methinks ;-)

> + *
> + * XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
> + * 
> + *
> + * This is sent by the frontend for backend to map a list of grant
> + * references.
> + *
> + * Request:
> + *
> + *  type= XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
> + *  data[0] = queue index
> + *  data[1] = grant reference of page containing the mapping list
> + *(assumed to start at beginning of grant)

Should

[Xen-devel] [PATCH v2 1/1] public/io/netif.h: add gref mapping control messages

2017-09-01 Thread Joao Martins 
Adds 3 messages to allow guest to let backend keep grants mapped,
such that 1) guests allowing fast recycling of pages can avoid doing
grant ops for those cases, or otherwise 2) preferring copies over
grants and 3) always using a fixed set of pages for network I/O.

The three control ring messages added are:
 - Add grefs to be mapped by backend
 - Remove grefs mappings (If they are not in use)
 - Get maximum amount of grefs kept mapped.

Signed-off-by: Joao Martins 
---
 xen/include/public/io/netif.h | 114 ++
 1 file changed, 114 insertions(+)

diff --git a/xen/include/public/io/netif.h b/xen/include/public/io/netif.h
index ca0061410d..264c317471 100644
--- a/xen/include/public/io/netif.h
+++ b/xen/include/public/io/netif.h
@@ -353,6 +353,9 @@ struct xen_netif_ctrl_request {
 #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING_SIZE 5
 #define XEN_NETIF_CTRL_TYPE_SET_HASH_MAPPING  6
 #define XEN_NETIF_CTRL_TYPE_SET_HASH_ALGORITHM7
+#define XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE 8
+#define XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING  9
+#define XEN_NETIF_CTRL_TYPE_PUT_GREF_MAPPING 10
 
 uint32_t data[3];
 };
@@ -391,6 +394,41 @@ struct xen_netif_ctrl_response {
 };
 
 /*
+ * Static Grants (struct xen_netif_gref_alloc)
+ * ===
+ *
+ * A frontend may provide a fixed set of grant references to be mapped on
+ * the backend. The message of type XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
+ * prior its usage in the command ring allows for creation of these mappings.
+ * The backend will maintain a fixed amount of these mappings.
+ *
+ * XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE lets a frontend query how many
+ * of these mappings can be kept.
+ *
+ * Each entry in the XEN_NETIF_CTRL_TYPE_{ADD,PUT}_GREF_MAPPING input table has
+ * the following format:
+ *
+ *0 1 2 3 4 5 6 7  octet
+ * +-+-+-+-+-+-+-+-+
+ * | grant ref |  flags|  padding  |
+ * +-+-+-+-+-+-+-+-+
+ *
+ * grant ref: grant reference
+ * flags: flags describing the control operation
+ *
+ */
+
+struct xen_netif_gref_alloc {
+   grant_ref_t ref;
+   uint16_t flags;
+
+#define _XEN_NETIF_CTRLF_GREF_readonly0
+#define XEN_NETIF_CTRLF_GREF_readonly(1U<<_XEN_NETIF_CTRLF_GREF_readonly)
+
+   uint8_t pad[2];
+};
+
+/*
  * Control messages
  * 
  *
@@ -609,6 +647,82 @@ struct xen_netif_ctrl_response {
  *   invalidate any table data outside that range.
  *   The grant reference may be read-only and must remain valid until
  *   the response has been processed.
+ *
+ * XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE
+ * -
+ *
+ * This is sent by the frontend to fetch the number of grefs that can be kept
+ * mapped in the backend.
+ *
+ * Request:
+ *
+ *  type= XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE
+ *  data[0] = queue index (assumed 0 for single queue)
+ *  data[1] = 0
+ *  data[2] = 0
+ *
+ * Response:
+ *
+ *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED - Operation not
+ * supported
+ *   XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - The queue index is
+ * out of range
+ *   XEN_NETIF_CTRL_STATUS_SUCCESS   - Operation successful
+ *  data   = maximum number of entries allowed in the gref mapping table
+ *   (if operation was successful) or zero if a mapping table is
+ *   not supported (i.e. hash mapping is done only by modular
+ *   arithmetic).
+ *
+ * XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
+ * 
+ *
+ * This is sent by the frontend for backend to map a list of grant
+ * references.
+ *
+ * Request:
+ *
+ *  type= XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
+ *  data[0] = queue index
+ *  data[1] = grant reference of page containing the mapping list
+ *(assumed to start at beginning of grant)
+ *  data[2] = size of list in entries
+ *
+ * Response:
+ *
+ *  status = XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED - Operation not
+ * supported
+ *   XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER - Operation failed
+ *   XEN_NETIF_CTRL_STATUS_SUCCESS   - Operation successful
+ *
+ * NOTE: Each entry in the input table has the format outlined
+ *   in struct xen_netif_gref_alloc.
+ *
+ * XEN_NETIF_CTRL_TYPE_PUT_GREF_MAPPING
+ * 
+ *
+ * This is sent by the frontend for backend to unmap a list of grant
+* references.
+ *
+ * Request:
+ *
+ *  type= XEN_NETIF_CTRL_TYPE_PUT_GREF_MAPPING
+ *  data[0] = queue index
+ *  data[1] = grant reference of page containing the mapping list
+ *(assumed to start at beginning of page)
+ *  data[2] = size