CPSC 451 Editors and Systems Calls1 Minix editors Mined - (mined) is a simple screen editor. Elle - (elle) is a clone of Emacs. Elvis - (elvis, ex, vi) is a clone of vi.

CPSC 451 Editors and Systems Calls2 Minix System Calls System calls are an interface between the operating system and the application programs. Minix has 53 system calls. Posix standard specifies a number of procedures that a conformant system must supply without stating if these are system calls, library calls or something else.

CPSC 451 Editors and Systems Calls3 System calls description Manual pages include a name, synopsis and description of each system call. E.g., to find out about the fork system call use: man fork For very detail description of system calls check man pages on titan.

CPSC 451 Editors and Systems Calls4 Process Management System Calls These are the calls that provide for process: –creation –execution –termination –suspending of a process –resizing of process data segment –obtaining process id and group.

CPSC 451 Editors and Systems Calls5 Process management calls - fork () #include #include /* include files */ pid_t fork(void); /* synopsis */ The fork() function creates a new process. The new process (child process) is an exact copy of the calling process. Upon successful completion, fork() returns 0 to the child process and returns the process ID of the child process to the parent process. Otherwise, (pid_t)-1 is returned to the parent process and no child process is created.

CPSC 451 Editors and Systems Calls6 Example of fork usage # include if (fork() == 0) { printf("After fork, child process %d, group %d.\n", getpid(), getpgrp()); } else {printf("After fork, parent process %d, group %d.\n”,getpid(),getpgrp()); }

CPSC 451 Editors and Systems Calls7 Process management calls - waitpid #include pid_t waitpid(pid_t pid, int *stat_loc, int options); waitpid() suspends the calling process until one of its children changes state (e.g. exits or terminates) if a child process changed state, prior to the call to waitpid(), return is immediate. pid specifies a set of child processes for which status is requested.

CPSC 451 Editors and Systems Calls8 Process management calls - execve #include int execve (const char *path, char *const argv[], char *const envp[]); The execve function overlays a new process image on an old process. The new process image is constructed from an ordinary, executable file. This file is either an executable object file, or a file of data for an interpreter. There can be no return from a successful call to one of these functions because the calling process image is overlaid by the new process image.

CPSC 451 Editors and Systems Calls9 Process management calls exit, size, brk, getpid exit(status) - terminates process execution and returns status size=brk(data) - gets and sets the data segment getpid() - returns caller’s process id getgid() - returns caller’s group id

CPSC 451 Editors and Systems Calls10 Signals Signals handle unplanned inter-process communication events. E.g. if the user wants to interrupt current event such as editing a long file, she should be able to press a specified key to do it. When a signal is send to process that does not have a signal handling routine, either the process is killed or the signal is ignored.

CPSC 451 Editors and Systems Calls11 Signals -sigaction #include int sigaction(int sig, const struct sigaction *act, struct sigaction *oact); ( struct sigaction is a structure defined in signal.h) The sigaction() function allows the calling process to examine or specify the action to be taken on delivery of a specific signal.

CPSC 451 Editors and Systems Calls12 Example of signal handler #include... void termination_handler (int signum) {... struct temp_file *p; for (p = temp_file_list; p; p = p- >next) unlink (p->name); }

CPSC 451 Editors and Systems Calls13 int main(void) { struct sigaction new_action, old_action; /* Set up the structure to specify the new action. */ new_action.sa_handler = termination_handler; new_action.sa_flags = 0; sigaction (SIGINT, NULL, &old_action); if (old_action.sa_handler != SIG_IGN) sigaction (SIGINT, &new_action, NULL);..}

CPSC 451 Editors and Systems Calls14 Signals-sigprocmask, sigpending, sigsuspend, kill, alarm, pause sigprocmask(how,&set, &old)- examines or changes signal mask sigpending(set) - gets the set of blocked signals sigsuspend(sigmask) - replaces the signal mask and suspends the process kill(pid,sig) - sends a signal to a process alarm(seconds) - sets the alarm pause() - suspends the caller until the next signal