sys_socketcall -->sys_sendmsg --> sock_sendmsg
-->__sock_sendmsg -->sock->ops->sendmsg
(tcp_sendmsg,defined in struct proto tcp_prot)-->tcp_push_one -->
tcp_transmit_skb
-->tp->af_specific->queue_xmit(ip_queue_xmit,defined in struct
tcp_func ipv4_specific) --> dst_output --> skb->dst->output
(ip_output,but i don't find where it defined now) -->
ip_finish_output -->ip_finish_output2 -->
dst->neighbour->output(i do not know what it given, maybe
neigh_connected_output) --> neigh->ops->queue_xmit
(dev_queue_xmit) --> dev->hard_start_xmit
sys_socket (kernel process the "socket" function in user level)
1.1-->sock_create
1.2-->sock_map_fd
1.2.1-->get_unused_fd
1.2.2-->get_empty_filp
1.2.3-->sock->file = file
1.2.4-->file->f_op = SOCK_INODE(sock)->i_fop =
&socket_file_ops; (where socket_file_ops.unlocked_ioctl =sock_ioctl)
1.2.5-->fd_install (fdt->fd[fd]=file,this can help us find the file by fd)