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Diffstat (limited to 'docs/gettingstarted/developers/metadata.md')
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diff --git a/docs/gettingstarted/developers/metadata.md b/docs/gettingstarted/developers/metadata.md new file mode 100644 index 00000000000..1f7f5c72bcf --- /dev/null +++ b/docs/gettingstarted/developers/metadata.md @@ -0,0 +1,190 @@ +Buffer Metadata +=============== + +Each vlib_buffer_t (packet buffer) carries buffer metadata which +describes the current packet-processing state. The underlying +techniques have been used for decades, across multiple packet +processing environments. + +We will examine vpp buffer metadata in some detail, but folks who need +to manipulate and/or extend the scheme should expect to do a certain +level of code inspection. + +Vlib (Vector library) primary buffer metatdata +---------------------------------------------- + +The first 64 octets of each vlib_buffer_t carries the primary buffer +metadata. See .../src/vlib/buffer.h for full details. + +Important fields: + +* i16 current_data: the signed offset in data[], pre_data[] that we +are currently processing. If negative current header points into +the pre-data (rewrite space) area. +* u16 current_length: nBytes between current_data and the end of this buffer. +* u32 flags: Buffer flag bits. Heavily used, not many bits left + * src/vlib/buffer.h flag bits + * VLIB_BUFFER_IS_TRACED: buffer is traced + * VLIB_BUFFER_NEXT_PRESENT: buffer has multiple chunks + * VLIB_BUFFER_TOTAL_LENGTH_VALID: total_length_not_including_first_buffer is valid (see below) + * src/vnet/buffer.h flag bits + * VNET_BUFFER_F_L4_CHECKSUM_COMPUTED: tcp/udp checksum has been computed + * VNET_BUFFER_F_L4_CHECKSUM_CORRECT: tcp/udp checksum is correct + * VNET_BUFFER_F_VLAN_2_DEEP: two vlan tags present + * VNET_BUFFER_F_VLAN_1_DEEP: one vlag tag present + * VNET_BUFFER_F_SPAN_CLONE: packet has already been cloned (span feature) + * VNET_BUFFER_F_LOOP_COUNTER_VALID: packet look-up loop count valid + * VNET_BUFFER_F_LOCALLY_ORIGINATED: packet built by vpp + * VNET_BUFFER_F_IS_IP4: packet is ipv4, for checksum offload + * VNET_BUFFER_F_IS_IP6: packet is ipv6, for checksum offload + * VNET_BUFFER_F_OFFLOAD_IP_CKSUM: hardware ip checksum offload requested + * VNET_BUFFER_F_OFFLOAD_TCP_CKSUM: hardware tcp checksum offload requested + * VNET_BUFFER_F_OFFLOAD_UDP_CKSUM: hardware udp checksum offload requested + * VNET_BUFFER_F_IS_NATED: natted packet, skip input checks + * VNET_BUFFER_F_L2_HDR_OFFSET_VALID: L2 header offset valid + * VNET_BUFFER_F_L3_HDR_OFFSET_VALID: L3 header offset valid + * VNET_BUFFER_F_L4_HDR_OFFSET_VALID: L4 header offset valid + * VNET_BUFFER_F_FLOW_REPORT: packet is an ipfix packet + * VNET_BUFFER_F_IS_DVR: packet to be reinjected into the l2 output path + * VNET_BUFFER_F_QOS_DATA_VALID: QoS data valid in vnet_buffer_opaque2 + * VNET_BUFFER_F_GSO: generic segmentation offload requested + * VNET_BUFFER_F_AVAIL1: avaliable bit + * VNET_BUFFER_F_AVAIL2: avaliable bit + * VNET_BUFFER_F_AVAIL3: avaliable bit + * VNET_BUFFER_F_AVAIL4: avaliable bit + * VNET_BUFFER_F_AVAIL5: avaliable bit + * VNET_BUFFER_F_AVAIL6: avaliable bit + * VNET_BUFFER_F_AVAIL7: avaliable bit +* u32 flow_id: generic flow identifier +* u8 ref_count: buffer reference / clone count (e.g. for span replication) +* u8 buffer_pool_index: buffer pool index which owns this buffer +* vlib_error_t (u16) error: error code for buffers enqueued to error handler +* u32 next_buffer: buffer index of next buffer in chain. Only valid if VLIB_BUFFER_NEXT_PRESENT is set +* union + * u32 current_config_index: current index on feature arc + * u32 punt_reason: reason code once packet punted. Mutually exclusive with current_config_index +* u32 opaque[10]: primary vnet-layer opaque data (see below) +* END of first cache line / data initialized by the buffer allocator +* u32 trace_index: buffer's index in the packet trace subsystem +* u32 total_length_not_including_first_buffer: see VLIB_BUFFER_TOTAL_LENGTH_VALID above +* u32 opaque2[14]: secondary vnet-layer opaque data (see below) +* u8 pre_data[VLIB_BUFFER_PRE_DATA_SIZE]: rewrite space, often used to prepend tunnel encapsulations +* u8 data[0]: buffer data received from the wire. Ordinarily, hardware devices use b->data[0] as the DMA target but there are exceptions. Do not write code which blindly assumes that packet data starts in b->data[0]. Use vlib_buffer_get_current(...). + +Vnet (network stack) primary buffer metadata +-------------------------------------------- + +Vnet primary buffer metadata occupies space reserved in the vlib +opaque field shown above, and has the type name +vnet_buffer_opaque_t. Ordinarily accessed using the vnet_buffer(b) +macro. See ../src/vnet/buffer.h for full details. + +Important fields: + +* u32 sw_if_index[2]: RX and TX interface handles. At the ip lookup + stage, vnet_buffer(b)->sw_if_index[VLIB_TX] is interpreted as a FIB + index. +* i16 l2_hdr_offset: offset from b->data[0] of the packet L2 header. + Valid only if b->flags & VNET_BUFFER_F_L2_HDR_OFFSET_VALID is set +* i16 l3_hdr_offset: offset from b->data[0] of the packet L3 header. + Valid only if b->flags & VNET_BUFFER_F_L3_HDR_OFFSET_VALID is set +* i16 l4_hdr_offset: offset from b->data[0] of the packet L4 header. + Valid only if b->flags & VNET_BUFFER_F_L4_HDR_OFFSET_VALID is set +* u8 feature_arc_index: feature arc that the packet is currently traversing +* union + * ip + * u32 adj_index[2]: adjacency from dest IP lookup in [VLIB_TX], adjacency + from source ip lookup in [VLIB_RX], set to ~0 until source lookup done + * union + * generic fields + * ICMP fields + * reassembly fields + * mpls fields + * l2 bridging fields, only valid in the L2 path + * l2tpv3 fields + * l2 classify fields + * vnet policer fields + * MAP fields + * MAP-T fields + * ip fragmentation fields + * COP (whitelist/blacklist filter) fields + * LISP fields + * TCP fields + * connection index + * sequence numbers + * header and data offsets + * data length + * flags + * SCTP fields + * NAT fields + * u32 unused[6] + +Vnet (network stack) secondary buffer metatdata +----------------------------------------------- + +Vnet primary buffer metadata occupies space reserved in the vlib +opaque2 field shown above, and has the type name +vnet_buffer_opaque2_t. Ordinarily accessed using the vnet_buffer2(b) +macro. See ../src/vnet/buffer.h for full details. + +Important fields: + +* qos fields + * u8 bits + * u8 source +* u8 loop_counter: used to detect and report internal forwarding loops +* group-based policy fields + * u8 flags + * u16 sclass: the packet's source class +* u16 gso_size: L4 payload size, persists all the way to + interface-output in case GSO is not enabled +* u16 gso_l4_hdr_sz: size of the L4 protocol header +* union + * packet trajectory tracer (largely deprecated) + * u16 *trajectory_trace; only #if VLIB_BUFFER_TRACE_TRAJECTORY > 0 + * packet generator + * u64 pg_replay_timestamp: timestamp for replayed pcap trace packets + * u32 unused[8] + +Buffer Metadata Extensions +========================== + +Plugin developers may wish to extend either the primary or secondary +vnet buffer opaque unions. Please perform a +manual live variable analysis, otherwise nodes which use shared buffer metadata space may break things. + +It's not OK to add plugin or proprietary metadata to the core vpp +engine header files named above. Instead, proceed as follows. The +example concerns the vnet primary buffer opaque union +vlib_buffer_opaque_t. It's a very simple variation to use the vnet +secondary buffer opaque union vlib_buffer_opaque2_t. + +In a plugin header file: + +``` + /* Add arbitrary buffer metadata */ + #include <vnet/buffer.h> + + typedef struct + { + u32 my_stuff[6]; + } my_buffer_opaque_t; + + STATIC_ASSERT (sizeof (my_buffer_opaque_t) <= + STRUCT_SIZE_OF (vnet_buffer_opaque_t, unused), + "Custom meta-data too large for vnet_buffer_opaque_t"); + + #define my_buffer_opaque(b) \ + ((my_buffer_opaque_t *)((u8 *)((b)->opaque) + STRUCT_OFFSET_OF (vnet_buffer_opaque_t, unused))) +``` +To set data in the custom buffer opaque type given a vlib_buffer_t *b: + +``` + my_buffer_opaque (b)->my_stuff[2] = 123; +``` + +To read data from the custom buffer opaque type: + +``` + stuff0 = my_buffer_opaque (b)->my_stuff[2]; +``` |