[Xen-devel] [PATCH v4 1/1] public/io/netif.h: add gref mapping control messages

[Joao Martins <joao.m.martins@xxxxxxxxxx>]

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 <joao.m.martins@xxxxxxxxxx>
---
v4:
* Declare xen_netif_gref parameters are input or output.
* Clarify status field and that it doesn't require to be set to zero
prior to its usage.
* Clarify on ADD_GREF_MAPPING is 'all or nothing'
* Improve last paragraph of DEL_GREF_MAPPING

v3:
* Use DEL for unmapping grefs instead of PUT
* Rname from xen_netif_gref_alloc to xen_netif_gref
* Add 'status' field on xen_netif_gref
* Clarify what 'inflight' means
* Use "beginning of the page" instead of "beginning of the grant"
* Mention that page needs to be r/w (as it will have to modify \.status)
---
 xen/include/public/io/netif.h | 123 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 123 insertions(+)

diff --git a/xen/include/public/io/netif.h b/xen/include/public/io/netif.h
index ca0061410d..2454448baa 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_ALGORITHM    7
+#define XEN_NETIF_CTRL_TYPE_GET_GREF_MAPPING_SIZE 8
+#define XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING      9
+#define XEN_NETIF_CTRL_TYPE_DEL_GREF_MAPPING     10
 
     uint32_t data[3];
 };
@@ -391,6 +394,44 @@ struct xen_netif_ctrl_response {
 };
 
 /*
+ * Static Grants (struct xen_netif_gref)
+ * =====================================
+ *
+ * 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,DEL}_GREF_MAPPING input table has
+ * the following format:
+ *
+ *    0     1     2     3     4     5     6     7  octet
+ * +-----+-----+-----+-----+-----+-----+-----+-----+
+ * | grant ref             |  flags    |  status   |
+ * +-----+-----+-----+-----+-----+-----+-----+-----+
+ *
+ * grant ref: grant reference (IN)
+ * flags: flags describing the control operation (IN)
+ * status: XEN_NETIF_CTRL_STATUS_* (OUT)
+ *
+ * 'status' is an output parameter which does not require to be set to zero
+ * prior to its usage in the corresponding control messages.
+ */
+
+struct xen_netif_gref {
+       grant_ref_t ref;
+       uint16_t flags;
+
+#define _XEN_NETIF_CTRLF_GREF_readonly    0
+#define XEN_NETIF_CTRLF_GREF_readonly    (1U<<_XEN_NETIF_CTRLF_GREF_readonly)
+
+       uint16_t status;
+};
+
+/*
  * Control messages
  * ================
  *
@@ -609,6 +650,88 @@ 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 it is not supported.
+ *
+ * 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
+ *            (r/w and assumed to start at beginning of page)
+ *  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.
+ *       Contrary to XEN_NETIF_CTRL_TYPE_DEL_GREF_MAPPING, the struct
+ *       xen_netif_gref 'status' field is not used and therefore the response
+ *       'status' determines the success of this operation. In case of
+ *       failure none of grants mappings get added in the backend.
+ *
+ * XEN_NETIF_CTRL_TYPE_DEL_GREF_MAPPING
+ * ------------------------------------
+ *
+ * This is sent by the frontend for backend to unmap a list of grant
+ * references.
+ *
+ * Request:
+ *
+ *  type    = XEN_NETIF_CTRL_TYPE_DEL_GREF_MAPPING
+ *  data[0] = queue index
+ *  data[1] = grant reference of page containing the mapping list
+ *            (r/w and assumed to start at beginning of page)
+ *  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
+ *  data   = number of entries that were unmapped
+ *
+ * NOTE: Each entry in the input table has the format outlined in struct
+ *       xen_netif_gref.
+ *       The struct xen_netif_gref 'status' field determines if the entry
+ *       was successfully removed.
+ *       The entries used are only the ones representing grant references that
+ *       were previously the subject of a XEN_NETIF_CTRL_TYPE_ADD_GREF_MAPPING
+ *       operation. Any other entries will have their status set to
+ *       XEN_NETIF_CTRL_STATUS_INVALID_PARAMETER upon completion.
  */
 
 DEFINE_RING_TYPES(xen_netif_ctrl,
-- 
2.11.0


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