Sysprog 12
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The document discusses various topics related to user-space system programming in Linux, including sending and handling signals, signal sets, masking signals, scheduling, inter-process communication (IPC), and timing functions. It provides examples of how to use signals, set priorities, affinity, timers, and IPC between processes.
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Sysprog 12
- 7. Masking Example - ssh/server_loop.c /* block SIGCHLD while we check for dead children */ sigemptyset(&nset); sigaddset(&nset, SIGCHLD); sigprocmask(SIG_BLOCK, &nset, &oset); if (child_terminated) { debug("Received SIGCHLD."); while ((pid = waitpid(-1, &status, WNOHANG)) > 0 || (pid < 0 && errno == EINTR)) if (pid > 0) session_close_by_pid(pid, status); child_terminated = 0; } sigprocmask(SIG_SETMASK, &oset, NULL); }
- 9. Example - inetd memset(&sa, 0, sizeof(sa)); sigaddset(&sa.sa_mask, SIGALRM); sigaddset(&sa.sa_mask, SIGCHLD); sigaddset(&sa.sa_mask, SIGHUP); sa.sa_handler = retry_network_setup; sigaction_set(SIGALRM, &sa); sa.sa_handler = reread_config_file; sigaction_set(SIGHUP, &sa); sa.sa_handler = reap_child; sigaction_set(SIGCHLD, &sa); sa.sa_handler = clean_up_and_exit; sigaction_set(SIGTERM, &sa); sa.sa_handler = clean_up_and_exit; sigaction_set(SIGINT, &sa); sa.sa_handler = SIG_IGN; sigaction(SIGPIPE, &sa, &saved_pipe_handler); static void clean_up_and_exit(int sig UNUSED_PARAM){ ,,,, remove_pidfile(_PATH_INETDPID); exit(EXIT_SUCCESS); } int FAST_FUNC sigaction_set(int signum, const struct sigaction *act){ return sigaction(signum, act, NULL); }
- 19. Examples from NTP gettimeofday(&tv, 0); epoch = tv.tv_sec; ... fprintf(stdout, "# %s# %s", filename, ctime(&epoch)); curtime = time(0); printf("Starting: %s", ctime(&curtime));
- 21. Example – ping.c static void noresp(int ign UNUSED_PARAM) { printf("No response from %s", hostname); exit(EXIT_FAILURE); } main() { ... signal(SIGALRM, noresp); alarm(5); /* give the host 5000ms to respond */ ... }