[Xen-changelog] [xen master] public/io/netif.h: clarifications to wire formats

[patchbot@xxxxxxx]

commit 0ebdfa144463eaf8fb762c72798a803111b5b544
Author:     Paul Durrant <paul.durrant@xxxxxxxxxx>
AuthorDate: Tue Jan 12 09:58:55 2016 +0000
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Tue Jan 19 10:43:30 2016 +0000

    public/io/netif.h: clarifications to wire formats
    
    My previous patch 03809ae7 "document transmit and receive wire formats
    separately" improved documentation of the receive and transmit wire
    formats but further clarifications were requested.
    
    This patch adds those clarifications.
    
    Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
    Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
    Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
    Cc: Jan Beulich <jbeulich@xxxxxxxx>
    Cc: Keir Fraser <keir@xxxxxxx>
    Cc: Tim Deegan <tim@xxxxxxx>
    Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 xen/include/public/io/netif.h |   28 ++++++++++++++++++++++++----
 1 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/xen/include/public/io/netif.h b/xen/include/public/io/netif.h
index 1790ea0..0a3272f 100644
--- a/xen/include/public/io/netif.h
+++ b/xen/include/public/io/netif.h
@@ -154,19 +154,29 @@
  * Guest transmit
  * ==============
  *
- * This is the 'wire' format for packets:
+ * This is the 'wire' format for transmit (frontend -> backend) 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)
+ *                                     NETTXF_more_data - flags on preceding
+ *                                     extras are not relevent here)
  *                                    flags = 0
  *                                    size = fragment size
  *
+ * NOTE:
+ *
+ * This format slightly is different from that used for receive
+ * (backend -> frontend) packets. Specifically, in a multi-fragment
+ * packet the actual size of fragment 1 can only be determined by
+ * subtracting the sizes of fragments 2..N from the total packet size.
+ *
  * Ring slot size is 12 octets, however not all request/response
  * structs use the full size.
  *
@@ -202,19 +212,29 @@
  * Guest receive
  * =============
  *
- * This is the 'wire' format for packets:
+ * This is the 'wire' format for receive (backend -> frontend) 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)
+ *                                     NETRXF_more_data - flags on preceding
+ *                                     extras are not relevent here)
  *                                    flags = 0
  *                                    size = fragment size
  *
+ * NOTE:
+ *
+ * This format slightly is different from that used for transmit
+ * (frontend -> backend) packets. Specifically, in a multi-fragment
+ * packet the size of the packet can only be determined by summing the
+ * sizes of fragments 1..N.
+ *
  * Ring slot size is 8 octets.
  *
  * rx request (netif_rx_request_t)
--
generated by git-patchbot for /home/xen/git/xen.git#master

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