recvmsg函数参数问题，谢谢

yjh777

是caller分配的一个buffer的地址，用来存放报文的源地址:

       The  msg_name  field points to a caller-allocated buffer that is used to return the source address if the socket is unconnected.  The caller should set msg_namelen to the size of this buffer before this call; upon return from a successful call, msg_namelen will contain the length of the returned address.  If the application  does  not  need  to  know  the source address, msg_name can be specified as NULL.

报文地址类型:  struct sockaddr_in
#define __SOCK_SIZE__   16              /* sizeof(struct sockaddr)      */
struct sockaddr_in {
  __kernel_sa_family_t  sin_family;     /* Address family               */
  __be16                sin_port;       /* Port number                  */
  struct in_addr        sin_addr;       /* Internet address             */

  /* Pad to size of `struct sockaddr'. */
  unsigned char         __pad[__SOCK_SIZE__ - sizeof(short int) -
                        sizeof(unsigned short int) - sizeof(struct in_addr)];
};

脚丫子1987

楼主想要表达什么没看懂