vppbuffer接口

　　#头条创作挑战赛#vpp buffer接口buffer/** VLIB buffer representation. */ typedef union  { // 使用union方便在结构体和byte（内存）之间转换   struct   {     CLIB_CACHE_LINE_ALIGN_MARK (cacheline0); // 用来做cacheline对齐      /** signed offset in data[], pre_data[] that we are currently       * processing. If negative current header points into predata area.  */     i16 current_data;      /** Nbytes between current data and the end of this buffer.  */     u16 current_length;      /** buffer flags:
　　VLIB_BUFFER_FREE_LIST_INDEX_MASK: bits used to store free list index,
　　VLIB_BUFFER_IS_TRACED: trace this buffer.
　　VLIB_BUFFER_NEXT_PRESENT: this is a multi-chunk buffer.
　　VLIB_BUFFER_TOTAL_LENGTH_VALID: as it says
　　VLIB_BUFFER_EXT_HDR_VALID: buffer contains valid external buffer manager header,     set to avoid adding it to a flow report
　　VLIB_BUFFER_FLAG_USER(n): user-defined bit N      */     u32 flags;      /** Generic flow identifier */     u32 flow_id;      /** Reference count for this buffer. */     volatile u8 ref_count;      /** index of buffer pool this buffer belongs. */     u8 buffer_pool_index;      /** Error code for buffers to be enqueued to error handler.  */     vlib_error_t error;      /** Next buffer for this linked-list of buffers. Only valid if       * VLIB_BUFFER_NEXT_PRESENT flag is set. */     u32 next_buffer;      /** The following fields can be in a union because once a packet enters      * the punt path, it is no longer on a feature arc */     union     {       /** Used by feature subgraph arcs to visit enabled feature nodes */       u32 current_config_index;       /* the reason the packet once punted */       u32 punt_reason;     };      /** Opaque data used by sub-graphs for their own purposes. */     u32 opaque[10];      /** part of buffer metadata which is initialized on alloc ends here. */       STRUCT_MARK (template_end);      /** start of 2nd half (2nd cacheline on systems where cacheline size is 64) */       CLIB_ALIGN_MARK (second_half, 64);      /** Specifies trace buffer handle if VLIB_PACKET_IS_TRACED flag is       * set. */     u32 trace_handle;      /** Only valid for first buffer in chain. Current length plus total length       * given here give total number of bytes in buffer chain. */     u32 total_length_not_including_first_buffer;      /**< More opaque data, see ../vnet/vnet/buffer.h */     u32 opaque2[14];  #if VLIB_BUFFER_TRACE_TRAJECTORY > 0     /** trace trajectory data - we use a specific cacheline for that in the      * buffer when it is compiled-in */ #define VLIB_BUFFER_TRACE_TRAJECTORY_MAX     31 #define VLIB_BUFFER_TRACE_TRAJECTORY_SZ      64 #define VLIB_BUFFER_TRACE_TRAJECTORY_INIT(b) (b)->trajectory_nb = 0     CLIB_ALIGN_MARK (trajectory, 64);     u16 trajectory_nb;     u16 trajectory_trace[VLIB_BUFFER_TRACE_TRAJECTORY_MAX]; #else /* VLIB_BUFFER_TRACE_TRAJECTORY */ #define VLIB_BUFFER_TRACE_TRAJECTORY_SZ 0 #define VLIB_BUFFER_TRACE_TRAJECTORY_INIT(b) #endif /* VLIB_BUFFER_TRACE_TRAJECTORY */      /** start of buffer headroom */       CLIB_ALIGN_MARK (headroom, 64);      /** 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 pre_data[VLIB_BUFFER_PRE_DATA_SIZE];      /** Packet data */     u8 data[]; // 变长数组，用来保存数据部分   }; #ifdef CLIB_HAVE_VEC128   u8x16 as_u8x16[4]; #endif #ifdef CLIB_HAVE_VEC256   u8x32 as_u8x32[2]; #endif #ifdef CLIB_HAVE_VEC512   u8x64 as_u8x64[1]; #endif } vlib_buffer_t;常用接口增// 将数据data添加到buffer里，没有空余的buffer会申请新的内存，同时会将buffer的索引赋值给buffer_index，方便后续用于访问
　　int    vlib_buffer_add_data   ( vlib_main_t    *    vm  ,  vlib_buffer_free_list_index_t    free_list_index  ,  u32    *    buffer_index  ,  void    *  data  , u32    n_data_bytes  ); 删always_inline    void
　　vlib_buffer_free   ( vlib_main_t    *    vm  ,
　　/* pointer to first buffer */
　　u32    *    buffers  ,
　　/* number of buffers to free */
　　u32    n_buffers  ); 改// 通过移动buffer的current_data指针来取数据或者添加数据，并同时修改buffer的current_length值
　　// 一般l为正数表示往前读取数据，当然也可以进行修改
　　// 一般l为负数表示往后添加数据
　　always_inline    void    vlib_buffer_advance   ( vlib_buffer_t    *    b  ,  word    l  ); 查 // vm是vpp运行时主结构体，buffer_index是buffer的索引，一般在添加buffer时可以获取到，或者遍历buffer时获取
　　always_inline    vlib_buffer_t    *  vlib_get_buffer   ( vlib_main_t    *    vm  ,  u32    buffer_index  );
　　// 获取当前数据所在的指针位置，一般用于对buffer进行指针偏移后使用
　　always_inline    void    *  vlib_buffer_get_current   ( vlib_buffer_t    *    b  );