On Nov 26, 2018, at 12:43 PM, Dave Barach (dbarach) <dbar...@cisco.com> wrote:
> On November 26, 2018, at 3:01 PM, Guy Harris <g...@alum.mit.edu> wrote:
>
>> So which of those structures describes the primary metadata?
>
> vlib_buffer_t. The key fields are flags, current_data, and current_length.
So that's:
> /* VLIB buffer representation. */
> typedef struct
> {
> /* Offset within data[] that we are currently processing.
> If negative current header points into predata area. */
> i16 current_data; /**< signed offset in data[], pre_data[]
> that we are currently processing.
> If negative current header points into predata area.
> */
> u16 current_length; /**< Nbytes between current data and
> the end of this buffer.
> */
> u32 flags; /**< buffer flags */
> u32 flow_id; /**< Generic flow identifier */
>
>
> u32 next_buffer; /**< Next buffer for this linked-list of buffers.
> Only valid if VLIB_BUFFER_NEXT_PRESENT flag is set.
> */
>
> u32 current_config_index; /**< Used by feature subgraph arcs to
> visit enabled feature nodes
> */
> u16 error; /**< Error code for buffers to be enqueued
> to error handler.
> */
> u8 n_add_refs; /**< Number of additional references to this buffer. */
>
> u8 buffer_pool_index; /**< index of buffer pool this buffer belongs.
> */
>
> u32 opaque[10]; /**< Opaque data used by sub-graphs for their own purposes.
> See above */
> u32 trace_index; /**< Specifies index into trace buffer
> if VLIB_PACKET_IS_TRACED flag is set.
> */
> u32 recycle_count; /**< Used by L2 path recycle code */
>
> u32 total_length_not_including_first_buffer;
> /**< Only valid for first buffer in chain. Current length plus
> total length given here give total number of bytes in buffer chain.
> */
> u8 free_list_index; /** < only used if
>
> VLIB_BUFFER_NON_DEFAULT_FREELIST
> flag is set */
> u8 align_pad[3]; /**< available */
> u32 opaque2[12]; /**< More opaque data, see ../vnet/vnet/buffer.h */
>
> /***** end of second cache line */
> u8 pre_data[VLIB_BUFFER_PRE_DATA_SIZE]; /**< Space for inserting data
> before buffer start.
> Packet rewrite string will be
> rewritten backwards and may
> extend
> back before buffer->data[0].
> Must come directly before
> packet data.
> */
>
> u8 data[0]; /**< Packet data. Hardware DMA here */
> } vlib_buffer_t; /* Must be a multiple of 64B. */
which is 128 bytes followed by VLIB_BUFFER_PRE_DATA_SIZE bytes of data.
Which of those 64 of those 128 bytes are the primary metadata?
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