On Thu, 2016-01-07 at 13:05 +0000, Paul Durrant wrote: > 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.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> > --- > 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)
For Fragment 2 is it the Flags of Fragment N-1 = 1 which are relevant, or the flags in the optional Extra N which may be in the middle (i.e. the immediately preceding slot)? Am I correct in remembering that in the presence of NETTXF_more_data the only way to know the actual size of Fragment 1 is to take away the total of all the extras from Frag 1's size? > + * 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 Same Q re which NETRXF_more_data is relevant. In this path there is no indication of the total packet size other than adding everything up? Given that they differ in a subtle way would a quick but explicit "NOTE: RX and TX differ" be a useful addition do you think? > + * > * Ring slot size is 8 octets. > * > * rx request (netif_rx_request_t) _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
