public/io/netif.h: document transmit and receive wire formats separately

Currently there is no documented wire format for guest receive-side
packets but the location of the 'wire format' comment block suggests
it is the same as transmit-side. This is almost true but there is a
subtle difference in the use of the 'size' field for the first fragment.

For clarity this patch creates separate comment blocks for receive
and transmit side packet wire formats, tries to be more clear about the
distinction between 'fragments' and 'extras', and documents the subtlety
concerning the size field of the first fragment.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>

diff --git a/xen/include/public/io/netif.h b/xen/include/public/io/netif.h
index e103cf39d616393ba28b98c6a23a7aa35310a5b3..1790ea0ea201bb15680695945aec8487ed4a253c 100644 (file)
--- a/xen/include/public/io/netif.h
+++ b/xen/include/public/io/netif.h
@@ -150,23 +150,23 @@
  * closing and re-connecting to the backend.
  */
 
-/*
- * This is the 'wire' format for packets:
- *  Request 1: netif_tx_request_t -- NETTXF_* (any flags)
- * [Request 2: netif_extra_info_t] (only if request 1 has
- *                                  NETTXF_extra_info)
- * [Request 3: netif_extra_info_t] (only if request 2 has
- *                                  XEN_NETIF_EXTRA_MORE)
- *  Request 4: netif_tx_request_t -- NETTXF_more_data
- *  Request 5: netif_tx_request_t -- NETTXF_more_data
- *  ...
- *  Request N: netif_tx_request_t -- 0
- */
-
 /*
  * Guest transmit
  * ==============
  *
+ * This is the 'wire' format for packets:
+ *  Fragment 1: netif_tx_request_t  - flags = NETTXF_*
+ *                                    size = total packet size
+ * [Extra 1: netif_extra_info_t]    - (only if fragment 1 flags include
+ *                                     NETTXF_extra_info)
+ * [Extra N: netif_extra_info_t]    - (only if extra N-1 flags include
+ *                                     XEN_NETIF_EXTRA_MORE)
+ *  ...
+ *  Fragment N: netif_tx_request_t  - (only if fragment N-1 flags include
+ *                                     NETTXF_more_data)
+ *                                    flags = 0
+ *                                    size = fragment size
+ *
  * Ring slot size is 12 octets, however not all request/response
  * structs use the full size.
  *
@@ -202,6 +202,19 @@
  * Guest receive
  * =============
  *
+ * This is the 'wire' format for packets:
+ *  Fragment 1: netif_rx_request_t  - flags = NETRXF_*
+ *                                    size = fragment size
+ * [Extra 1: netif_extra_info_t]    - (only if fragment 1 flags include
+ *                                     NETRXF_extra_info)
+ * [Extra N: netif_extra_info_t]    - (only if extra N-1 flags include
+ *                                     XEN_NETIF_EXTRA_MORE)
+ *  ...
+ *  Fragment N: netif_rx_request_t  - (only if fragment N-1 flags include
+ *                                     NETRXF_more_data)
+ *                                    flags = 0
+ *                                    size = fragment size
+ *
  * Ring slot size is 8 octets.
  *
  * rx request (netif_rx_request_t)