Übung 5

Assets/Betriebssysteme_uebung/u6-a2-anlage/Makefile

@@ -0,0 +1,13 @@
+CFLAGS = -g
+
+all: daemon
+
+clean:
+	rm -f helpers.o daemon.o daemon
+
+helpers.o: helpers.c helpers.h
+
+daemon.o: daemon.c helpers.h
+
+daemon: daemon.o helpers.o
+	$(CC) -o daemon daemon.o helpers.o

Assets/Betriebssysteme_uebung/u6-a2-anlage/daemon.c

@@ -0,0 +1,54 @@
+#include <stdio.h>
+#include <signal.h>
+
+#include "helpers.h"
+
+void got_signal(int s) {
+	/*
+	 * For demonstration purposes only!
+	 *
+	 * In real-world applications avoid the execution of complex
+	 * tasks in signal handlers, this cries for race conditions and
+	 * exploits.
+	 *
+	 * https://web.archive.org/web/20070204064240/http://www.bindview.com:80/
+	 % Services/Razor/Papers/2001/signals.cfm
+	 */
+
+	static int count = 2;
+
+	fprintf(stderr, "Caught Ctrl-C, press %i more time%s to really"
+		" quit.\n", count, count == 1 ? "" : "s");
+
+	if (count-- > 1) {
+		/* Catch subsequent SIGINTs */
+		signal(SIGINT, got_signal);
+	}
+	else {
+		/* Don't catch SIGINT anymore */
+		signal(SIGINT, SIG_DFL);
+	}
+}
+
+int main(void) {
+	/*
+	 * Initialization...
+	 */
+	void load_cfg(int x) // Wrapper um die inkompatibilität durch die fehlerhafte methodendeklaration zu beheben
+	{
+		load_config();
+	}
+	load_config();
+	signal(SIGHUP, load_cfg); 
+	signal(SIGINT, got_signal);
+	signal(SIGKILL, SIG_IGN); // Unaufhaltsam, da SIGKILL sich ja eben genau nicht um das Programm kümmern soll, sondern einfach immer töten soll
+	signal(SIGTERM, SIG_IGN); // Aufhaltbar
+	
+	/*
+	 * Do some work.
+	 */
+
+	main_loop();
+
+	return 0;
+}

Assets/Betriebssysteme_uebung/u6-a2-anlage/helpers.c

@@ -0,0 +1,103 @@
+/*
+ * This is just some code behind the curtain.
+ * You really don't need to touch this.
+ *
+ */
+
+#include <stdio.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include "helpers.h"
+
+int do_quit = 0;
+int do_reload = 0;
+
+int load_config(void) {
+	static char firsttime_message[] = "Loading";
+	static char subsequent_message[] = "Reloading";
+	static char *message = firsttime_message;
+
+	fprintf(stderr, "%s configuration... ", message);
+	fprintf(stderr, "done.\n");
+
+	message = subsequent_message;
+	do_reload = 0;
+
+	return 1;
+}
+
+int main_loop(void) {
+	fd_set rfds;
+	struct timeval tv;
+	int retval;
+	char buf[1024];
+	ssize_t len;
+
+#if 0
+	/* fork() to the background */
+	if(fork()) return 0;
+#endif
+
+	fprintf(stderr, "I'm just a simple daemon, my PID is: %i\n",
+		getpid());
+
+	while (!do_quit) {
+		/* 
+		 * Let's just do our really simple job:
+		 * Copy stdin to stdout (just another cat(1)).
+		 */
+
+		if (do_reload) {
+			load_config();
+		}
+
+		/* Watch stdin (fd 0) to see when it has input. */
+		FD_ZERO(&rfds);
+		FD_SET(0, &rfds);
+
+		/* Wait up to five seconds. */
+		tv.tv_sec = 5;
+		tv.tv_usec = 0;
+
+		retval = select(1, &rfds, NULL, NULL, &tv);
+		/* Don't rely on the value of tv now! */
+
+		if (retval == -1) {
+			if (errno == EINTR) {
+				continue;
+			}
+
+			perror("select()");
+			continue;
+		}
+
+		if (retval == 0) {
+			/* fprintf(stderr, "Timeout reached.\n"); */
+			continue;
+		}
+
+		if (!FD_ISSET(0, &rfds)) {
+			fprintf(stderr, "BUG: Empty read-set, this should"
+				" never happen. Never ever. Really! :-)\n");
+			continue;
+		}
+
+		len = read(0, buf, sizeof(buf) - 1);
+		if (len < 0) {
+			perror("read()");
+			continue;
+		}
+
+		buf[len] = 0;
+		printf("%s", buf);
+
+		if (len == 0) {
+			do_quit = 1;
+		}
+	}
+
+	return 1;
+}

Assets/Betriebssysteme_uebung/u6-a2-anlage/helpers.h

@@ -0,0 +1,7 @@
+#ifndef	_HELPERS_H
+#define	_HELPERS_H
+
+int load_config(void);	/* load/reload our daemon's configuration */
+int main_loop(void);	/* our daemon's main task */
+
+#endif	/* _HELPERS_H */