api: pktio: lso: revise and clarify IP and TCP LSO specification

Modify certain details of IP and TCP LSO, specify missing details, add
restrictions and clarify the API in general.

- Specify that the DF flag of the IPv4 header is to be preserved as it was
  in the original packet and not cleared as the current spec says. Disallow
  IPv4 LSO for packets that contain IPv4 options that may not simply be
  copied to all fragments. Describe IPv4 ID generation in more detail.

- Specify IPv6 fragmentation in more detail. Specify that the payload
  offset must point to the offset in which the fragment header is to be
  inserted, allowing flexible handling of different types of extension
  headers. Add restrictions on for what kind of packets IPv6 fragmentation
  can be requested.

- Specify that IPv4 or IPv6 LSO is not permitted for packets that are
  already fragments or for which L4 checksum offload is requested.

- Specify TCP segmentation in more detail and add restriction on what
  kind of TCP control bits and options may be present in packets for
  which the offload is attempted.

- Clarify how L3 offset, L4 offset and payload offset must be set.

Signed-off-by: Janne Peltonen <janne.peltonen@nokia.com>

include/odp/api/spec/packet_io_types.h

@@ -794,22 +794,99 @@ typedef enum odp_lso_protocol_t {
 
 	/** LSO performs IPv4 fragmentation.
 	 *
-	 *  IP header length and checksum fields are updated. IP fragmentation related fields are
-	 *  filled and IPv4 Identification field value is copied from the original packet. */
+	 *  The total length, MF flag, fragment offset and checksum fields
+	 *  of the IP header are updated according to the IPv4 standard and
+	 *  other fields are copied from the original packet. All IP options
+	 *  in the original packets are copied to the fragments.
+	 *
+	 *  IPv4 LSO must not be attempted for the following packets:
+	 *  - packets that are not IPv4 packets
+	 *  - packets that are already IPv4 fragments
+	 *  - packets that have IP options that may not be copied to all
+	 *    fragments
+	 *  - packets for which L4 checksum offload is requested
+	 *
+	 *  L3 offset must point to the start of the IP header.
+	 *  Payload offset must point to the start of the IP payload.
+	 */
 	ODP_LSO_PROTO_IPV4,
 
-	/** LSO performs IPv6 fragmentation. */
+	/** LSO performs IPv6 fragmentation.
+	 *
+	 *  Header updates and fragment header generation are done according
+	 *  to the IPv6 standard. The identification field of the fragment
+	 *  header is generated in an implementation specific manner.
+	 *
+	 *  Fragment header is inserted in the packets in the offset pointed
+	 *  to by the payload offset metadata. IPv6 base header and extension
+	 *  headers up to and including the inserted fragment header are
+	 *  copied to all created fragments.
+	 *
+	 *  IPv6 LSO must not be attempted for the following packets:
+	 *  - packets that are not IPv6 packets
+	 *  - packets that are already IPv6 fragments
+	 *  - packets for which L4 checksum offload is requested
+	 *
+	 *  L3 offset must point to the start of the IP header.
+	 *  Payload offset must point to the first byte of after the
+	 *  per-fragment headers as defined in RFC 8200, i.e. to the
+	 *  packet offset where the fragment header is to be inserted.
+	 */
 	ODP_LSO_PROTO_IPV6,
 
 	/** LSO performs TCP segmentation on top of IPv4.
 	 *
-	 *  IP header length and checksum fields are updated. IP fragmentation is not performed
-	 *  and IPv4 Don't Fragment bit is not set. Unique IPv4 Identification field values
-	 *  are generated. Those are usually increments of the IPv4 ID field value in the packet.
+	 *  TCP header is updated as if the payload data was originally sent
+	 *  in multiple TCP segments.
+	 *
+	 *  TCP headers of the created segments are copied from the original
+	 *  packet, with the sequence number and checksum updated. All TCP
+	 *  options are copied from the original packet. The FIN flag is copied
+	 *  to the last created segment and cleared in other segments. The CWR
+	 *  flag is copied to the first created segment and cleared in other
+	 *  segments.
+	 *
+	 *  IP headers (including IP options) of the created segments are
+	 *  copied from the original packet, with total length, checksum
+	 *  and identification fields updated. Unique IPv4 identification
+	 *  field values are generated for non-atomic IPv4 datagrams. The
+	 *  values are usually increments of the IPv4 ID field value in
+	 *  the original packet so an application should not send packets
+	 *  with consecutive identification values if the DF flag is not set.
+	 *
+	 *  TCP_IPV4 LSO must not be attempted for the following packets;
+	 *  - packets that are not TCP over IPv4
+	 *  - packets that are IP fragments
+	 *  - packets that have the SYN, RST or URG flag set
+	 *  - packets that have TCP options that may not be copied to all
+	 *    segments
+	 *
+	 * L3 offset must point to the start of the IP header.
+	 * L4 offset must point to the start of the TCP header.
+	 * Payload offset must point to the start of the TCP payload.
 	 */
 	ODP_LSO_PROTO_TCP_IPV4,
 
-	/** LSO performs TCP segmentation on top of IPv6. */
+	/** LSO performs TCP segmentation on top of IPv6.
+	 *
+	 *  TCP headers of the created segments are created in the same way
+	 *  as in ODP_LSO_PROTO_TCP_IPV4.
+	 *
+	 *  IP headers (including extension headers) of the created segments
+	 *  are copied from the original packet, with the payload length
+	 *  updated.
+	 *
+	 *  TCP_IPV6 LSO must not be attempted for the following packets;
+	 *  - packets that are not TCP over IPv6
+	 *  - packets that are IP fragments
+	 *  - packets that have the SYN, RST or URG flag set
+	 *  - packets that have TCP options that may not be copied to all
+	 *    segments
+	 *
+	 * L3 offset must point to the start of the IP header.
+	 * L4 offset must point to the start of the TCP header.
+	 * Payload offset must point to the start of the TCP payload.
+	 */
 	ODP_LSO_PROTO_TCP_IPV6,
 
 	/** LSO performs SCTP segmentation on top of IPv4. */