内核通过 sockaddr 唯一标识一个socket
struct sockaddr {
sa_family_t sa_family; /* address family, AF_xxx */
// 该字段保存特定协议的相关字段。如果是PF_INET,则保存IP地址(struct in_addr)和端口号(port)。
char sa_data[14]; /* 14 bytes of protocol address */
};
如果sa_family 是PF_INET, 则sockadd --> sockaddr_in
/* Structure describing an Internet (IP) socket address. */
#define __SOCK_SIZE__ 16 /* sizeof(struct sockaddr) */
struct sockaddr_in {
__kernel_sa_family_t sin_family; /* Address family */
__be16 sin_port; /* Port number */
// IP 地址
struct in_addr sin_addr; /* Internet address */
// 所以说这个数据结构是struct sockaddr 对于IP地址的具体实现
/* Pad to size of `struct sockaddr'. */
unsigned char __pad[__SOCK_SIZE__ - sizeof(short int) -
sizeof(unsigned short int) - sizeof(struct in_addr)];
};
IP 地址是一个32位的整数
/* Internet address. */
struct in_addr {
__be32 s_addr;
};