Socket 套接字的系统调用

• socket 结构

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/**  *  struct socket - general BSD socket  *  @state: socket state (%SS_CONNECTED, etc)  *  @type: socket type (%SOCK_STREAM, etc)  *  @flags: socket flags (%SOCK_NOSPACE, etc)  *  @ops: protocol specific socket operations  *  @file: File back pointer for gc  *  @sk: internal networking protocol agnostic socket representation  *  @wq: wait queue for several uses  */ typedef enum {     SS_FREE = 0,            /* not allocated        */     SS_UNCONNECTED,         /* unconnected to any socket    */     SS_CONNECTING,          /* in process of connecting */     SS_CONNECTED,           /* connected to socket      */     SS_DISCONNECTING        /* in process of disconnecting  */ } socket_state;   /* Historically, SOCKWQ_ASYNC_NOSPACE & SOCKWQ_ASYNC_WAITDATA were located  * in sock->flags, but moved into sk->sk_wq->flags to be RCU protected.  * Eventually all flags will be in sk->sk_wq_flags.  */ #define SOCKWQ_ASYNC_NOSPACE    0 #define SOCKWQ_ASYNC_WAITDATA   1 #define SOCK_NOSPACE        2 #define SOCK_PASSCRED       3 #define SOCK_PASSSEC        4struct socket_wq {     /* Note: wait MUST be first field of socket_wq */     wait_queue_head_t    wait;     struct fasync_struct    *fasync_list;     unsigned long        flags; /* %SOCKWQ_ASYNC_NOSPACE, etc */     struct rcu_head        rcu; } ____cacheline_aligned_in_smp;  struct socket {     socket_state        state;//套接口所处的状态对tcp 套接口有意义 SS_CONNECTED       kmemcheck_bitfield_begin(type);     short           type;     kmemcheck_bitfield_end(type);       unsigned long       flags;       struct socket_wq __rcu  *wq;// 包含了等待该套接字的进程队列 以及异步通知队列       struct file     *file; //指向了和套接字相关联的file 结构     struct sock     *sk;//和套接字相关联的传输控制块     const struct proto_ops  *ops;    //对于tcp udp raw 分别对应 inet_stream_ops  inet_dgram_ops  inet_sockraw_ops };

 proto_ops 结构完成了从协议无关的socket 到协议层的传输层转接，结构proto 将传输层映射到网络层，

所以可知：每一个传输层都需要顶一个特定的proto_ops和proto实例，参考static struct inet_protosw inetsw_array[] 数组；

在网络子系统初始化的时候，根据其type 注册到一个list_head的结构数组inetsw[ ] 中， socket中类型相同的inet_protosw结构在inetsw[ ] 中以其对应的元素组层一个双向链表；

 

 

 

 

 

 Socket系统调用如下：

 

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/** family：创建socket的协议族 PF_INET PF_UNIX type:  创建socket的类型 SOCK_STREAM. SOCK_DGRAM.SOCK_RAW protocol: 传输层协议：IPPROTO_TCP IPPROTO_UDP **/ SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol) {     int retval;     struct socket *sock;     int flags;       /* Check the SOCK_* constants for consistency.  */     BUILD_BUG_ON(SOCK_CLOEXEC != O_CLOEXEC);     BUILD_BUG_ON((SOCK_MAX | SOCK_TYPE_MASK) != SOCK_TYPE_MASK);     BUILD_BUG_ON(SOCK_CLOEXEC & SOCK_TYPE_MASK);     BUILD_BUG_ON(SOCK_NONBLOCK & SOCK_TYPE_MASK);       flags = type & ~SOCK_TYPE_MASK;     if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))         return -EINVAL;     type &= SOCK_TYPE_MASK;       if (SOCK_NONBLOCK != O_NONBLOCK && (flags & SOCK_NONBLOCK))         flags = (flags & ~SOCK_NONBLOCK) | O_NONBLOCK;       retval = sock_create(family, type, protocol, &sock);//创建一个socket     if (retval < 0)         goto out; //给创建的socket 分配一个file fd 并绑定     retval = sock_map_fd(sock, flags & (O_CLOEXEC | O_NONBLOCK));     if (retval < 0)         goto out_release;   out:     /* It may be already another descriptor 8) Not kernel problem. */     return retval;   out_release:     sock_release(sock);     return retval;

 

socket相关函数的系统调用在 socket.c文件！

如下：

SYSCALL_DEFINE4(recv, int, fd, void __user *, ubuf, size_t, size,
        unsigned int, flags)
{
    return sys_recvfrom(fd, ubuf, size, flags, NULL, NULL);
}

SYSCALL_DEFINE6(recvfrom, int, fd, void __user *, ubuf, size_t, size,
unsigned int, flags, struct sockaddr __user *, addr,
int __user *, addr_len)
{
struct socket *sock;
struct iovec iov;
struct msghdr msg;

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}