内核中的UDP socket流程（6）——sendto

SYSCALL_DEFINE6(sendto, int, fd, void __user *, buff, size_t, len,
          unsigned, flags, struct sockaddr __user *, addr,
          int, addr_len)
{
     struct socket *sock;
     struct sockaddr_storage address;
     int err;
     struct msghdr msg;
     struct iovec iov;
     int fput_needed;

     sock = sockfd_lookup_light(fd, &err, &fput_needed);
     if (!sock)
          goto out;

     iov.iov_base = buff;
     iov.iov_len = len;
     msg.msg_name = NULL;
     msg.msg_iov = &iov;
     msg.msg_iovlen = 1;
     msg.msg_control = NULL;
     msg.msg_controllen = 0;
     msg.msg_namelen = 0;

struct msghdr {
     void * msg_name; /* Socket name */
     int msg_namelen; /* Length of name */
     struct iovec * msg_iov; /* Data blocks */
     __kernel_size_t msg_iovlen; /* Number of blocks */
     void * msg_control; /* Per protocol magic (eg BSD file descriptor passing) */
     __kernel_size_t msg_controllen; /* Length of cmsg list */
     unsigned msg_flags;
};

    if (addr) {
          err = move_addr_to_kernel(addr, addr_len, (struct sockaddr *)&address);
          if (err 0)
               goto out_put;
          msg.msg_name = (struct sockaddr *)&address;
          msg.msg_namelen = addr_len;
     }
     if (sock->file->f_flags & O_NONBLOCK)
          flags |= MSG_DONTWAIT;
     msg.msg_flags = flags;