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.durr...@citrix.com> Cc: Ian Campbell <ian.campb...@citrix.com> Cc: Ian Jackson <ian.jack...@eu.citrix.com> Cc: Jan Beulich <jbeul...@suse.com> Cc: Keir Fraser <k...@xen.org> Cc: Tim Deegan <t...@xen.org> --- v6: - v4 of the original patch was committed so this is an incremental version of the patch in v5. v5: - Add extra clarifications. --- xen/include/public/io/netif.h | 28 ++++++++++++++++++++++++---- 1 file 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) -- 2.1.4 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
