From 03809ae77daf17a7e3104019758aa4c4b23b631c Mon Sep 17 00:00:00 2001 From: Paul Durrant Date: Thu, 7 Jan 2016 15:28:33 +0100 Subject: [PATCH] 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 --- 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 e103cf39d6..1790ea0ea2 100644 --- 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) -- 2.30.2