5. Pipes & named pipes Pipes are the classical method of interprocess communication. For example ls –l | more The symbol | indicates a pipe and the shell in the above example runs the processes ls and more which are linked with a pipe. ls writes data to the pipe and more reads it. Named pipes otherwise called as the FIFO (First in First Out) is the other variant of pipe.
6. Pipes & named pipes # mkfifo pathname Example # mkfifo hello # ls –l hello prw-r- -r- – 1 temp users 0 Aug 28 10.45 hello |
7. Pipes & named pipes there are many similarities between the pipes and the FIFO, but the inode specification for the both are more or less the same. following is the inode specification for the pipe
8. Pipes & named pipes structpipe_inode_info { wait_queue_head_t wait; //wait queue char * base; //address of the FIFO buffer unsigned int readers; //no of processes reading at this moment unsigned int writers; //no of processes writing at this moment unsigned intwaiting_readers; //no of blocked process reading at this moment unsigned intwaiting_writers; //no of blocked processes writing at this moment unsigned intr_counter; //no of read processes that have opened unsigned intw_counter; //no of write processes that have opened };
10. ptrace Ptrace is a system call provided in unix for one process to take control of another process to debug errors or bugs in the system The process under control can be run step by step and its memory can be read and modified. intsys_ptrace(long request, long pid, long addr, long data); the function processes various request defined in the parameter request and pid indicates the process id of the process to be controlled. Using the request PTRACE_TRACEME, a process can specify that its parent process controls iut via ptrace().
11. Sockets Socket programming interfaces provides communication via a network as well as locally on a single computer. Example is INET daemon which waits for incoming network service requests and then call the appropriate service program using the socket file descriptor as standard input and output. Implementation of Unix domain sockets Represented by a kernel data structure socket Socket specific functions like Socket(), setsockout() The functions are implemented with a single system call socketcall which calls all the necessary functions by reference to the first parameter. The file operation read(), write(), poll(), ioctl(), lseek(), close() are called directly
12. Sockets Operations of Unix domain sockets long sys_socket(int family, int type, int protocol);// creates a socket file descriptor long sys_connect(intfd, structsockaddr * uservaddr, intaddrlen); //bind the socket to the unix domain address with specified length long sys_listen(intfd, int backlog);//checks whether any connections are being accepted at the server address. long sys_accept(intfd, structsockaddr *upeer_sockaddr, int *upeer_addrlen));//server informs the kernel that the connections are being accepted from now on long sys_getsockname(intfd, structsockaddr *usockaddr, int *usockaddr_len); //the address bound to the socket is returned.
13. Sockets long sys_shutdown(intfd, int how); //to shutdown but status to be given that whether the sending and receiving still allowed sending and receiving from the sockets Messages can be sent either as a datagram or stream of bytes long sys_send(intfd, void *buff, intlen, unsigned flags); long sys_sendmsg(intfd, structmsghdr *msg, unsigned int flags); long sys_recv(intfd, void *buff, intlen, unsigned flags); long sys_recvmsg(intfd, structmsghdr *msg, unsigned int flags)
