st_net

st_net也是一个网络属性相关的结构体，还没有接触太多，但在mysql启动的时候就会设置好里面的参数

typedef struct st_net {
#if !defined(CHECK_EMBEDDED_DIFFERENCES) || !defined(EMBEDDED_LIBRARY)
  Vio *vio;
  unsigned char *buff,*buff_end,*write_pos,*read_pos;
  my_socket fd;                    /* For Perl DBI/dbd */
  /*
    The following variable is set if we are doing several queries in one
    command ( as in LOAD TABLE ... FROM MASTER ),
    and do not want to confuse the client with OK at the wrong time
  */
  unsigned long remain_in_buf,length, buf_length, where_b;
  unsigned long max_packet,max_packet_size;
  unsigned int pkt_nr,compress_pkt_nr;
  unsigned int write_timeout, read_timeout, retry_count;
  int fcntl;
  unsigned int *return_status;
  unsigned char reading_or_writing;
  char save_char;
  my_bool unused1; /* Please remove with the next incompatible ABI change. */
  my_bool unused2; /* Please remove with the next incompatible ABI change */
  my_bool compress;
  my_bool unused3; /* Please remove with the next incompatible ABI change. */
  /*
    Pointer to query object in query cache, do not equal NULL (0) for
    queries in cache that have not stored its results yet
  */
#endif
  /*
    Unused, please remove with the next incompatible ABI change.
  */
  unsigned char *unused;
  unsigned int last_errno;
  unsigned char error; 
  my_bool unused4; /* Please remove with the next incompatible ABI change. */
  my_bool unused5; /* Please remove with the next incompatible ABI change. */
  /** Client library error message buffer. Actually belongs to struct MYSQL. */
  char last_error[MYSQL_ERRMSG_SIZE];
  /** Client library sqlstate buffer. Set along with the error message. */
  char sqlstate[SQLSTATE_LENGTH+1];
  void *extension;
#if defined(MYSQL_SERVER) && !defined(EMBEDDED_LIBRARY)
  /*
    Controls whether a big packet should be skipped.

    Initially set to FALSE by default. Unauthenticated sessions must have
    this set to FALSE so that the server can't be tricked to read packets
    indefinitely.
  */
  my_bool skip_big_packet;
#endif
} NET;