[PATCH v3 1/3] public/io/netif.h: document transmit and receive wire formats separately

[Paul Durrant <paul.durrant@citrix.com>]

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>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Keir Fraser <keir@xen.org>
Cc: Tim Deegan <tim@xen.org>
---
 xen/include/public/io/netif.h | 39 ++++++++++++++++++++++++++-------------
 1 file changed, 26 insertions(+), 13 deletions(-)

diff --git a/xen/include/public/io/netif.h b/xen/include/public/io/netif.h
index e103cf3..1790ea0 100644
--- a/xen/include/public/io/netif.h
+++ b/xen/include/public/io/netif.h
@@ -151,22 +151,22 @@
  */
 
 /*
- * 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)
-- 
2.1.4