Politecnico di Milano FACOLTÀ DI INGEGNERIA DELL INFORMAZIONE. Advanced Operating Systems A.A Exam date: 28 June 2016

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Politecnico di Milano FACOLTÀ DI INGEGNERIA DELL INFORMAZIONE Advanced Operating Systems A.A. 2015-2016 Exam date: 28 June 2016 Prof. William FORNACIARI Surname (readable)... Matr... Name (readable).

Anyone found in possession of documents relating to the course, although not directly relevant to the subject of the examination will cancel the test.

1 Politecnico di Milano FACOLTÀ DI INGEGNERIA DELL INFORMAZIONE Advanced Operating Systems A.A Exam date: 28 June 2016 Prof. William FORNACIARI Surname (readable)... Matr... Name (readable)... Signature... Q1 Q2 Q3 TOT NOTES It is forbidden to refer to texts or notes of any kind as well as interact with their neighbors. Anyone found in possession of documents relating to the course, although not directly relevant to the subject of the examination will cancel the test. It is not allowed to leave during the first half hour, the task must still be returned, even if it is withdrawn. The presence of the writing (not delivered) implies the renunciation of any previous ratings. Question Q1 Describe the main algorithms for the scheduling of a single CPU with a discussion on the response time to events and their implementation complexity. 1/7

2 Question Q2 Assume we have a library called Logger. The main purpose of the library is to allow external programs to safely and concurrently write into a system log file (located at /var/log/mysystem.log ). Here below it is shown an example of log file content: <Fri Jun 24 10:52: > [E] chrome: Plugin not found <Fri Jun 24 10:52: > [I] audio frm: Loading driver... <Fri Jun 24 10:53: > [I] audio frm: Driver successfully loaded <Fri Jun 24 10:54: > [W] installer: Found missing repositories <Fri Jun 24 10:57: > [D] myprog: Checking input data... As shown in the example each line includes: 1. the current date and time 2. the logging level (D=DEBUG, I=INFO, W=WARNING, E=ERROR) 3. the program producing the log message 4. the log message The library source code includes the following files: logger.c, time_utils.c, logger.h and time_utils.h. A) You are required to define and implement the write_to_log(...) library function, through which a program can add a line to the log file. The library source files must contain whatever is required to correctly compile and run the function. NOTE: Concerning the point (1) assume the following function, defined in time_utils.h, is already provided to get the string reporting the current date and time as shown in the example above. void get_curr_time_str(char * str, int size); B) You are also required to implement a very simple tool (writelog) that exploits the Logger library to allows a system user to write into the log file at command line, as follows: $ writelog <log level> <username> <message> 2/7

3 A) logger.h #ifndef LOGGER_H_INCLUDED #define LOGGER_H_INCLUDED #define SYS_SEM "/mysem" #define SYS_LOGFILE "/var/log/mysystem.log" int write_to_log( const char * level, const char * task_name, const char * message); #endif // LOGGER_H_INCLUDED logger.c #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <semaphore.h> #include <sys/types.h> #include <sys/stat.h> #include "logger.h" #include "time_utils.h" int write_to_log( const char level, const char * task_name, const char * message) { if ((level!= 'D') && (level!= 'I') && (level!= 'W') && (level!= 'E')) { printf("[e] Unexpected log message type (%c). " "'D/I/W/E' supported\n", level); return 1; sem_t * sem_id = sem_open( SYS_SEM, O_CREAT, S_IRUSR S_IWUSR, 1); if (!sem_id) { printf("[e] Error while opening semaphore\n"); return 2; sem_wait(sem_id); // TIME_STR_SIZE is defined in time_utils.h char time_str[time_str_size]; 3/7

4 get_curr_time_str(time_str, TIME_STR_SIZE); FILE * fp = fopen(sys_logfile, "a"); if (!fp) { printf( [E] Error while opening %s\n, SYS_LOGFILE); return 3; fprintf(fp, "<%s> [%c] %s: %s\n", time_str, level, task_name, message); fclose(fp); sem_post(sem_id); sem_close(sem_id); sem_unlink(sys_sem); return 0; B) main.c (writelog command line tool) #include <stdio.h> #include <stdlib.h> #include "logger.h" void print_usage(const char * exe_name) { printf("[e] Usage: %s D I W E taskname log_message\n", exe_name); int main(int argc, char * argv[]) { if (argc < 4) { print_usage(argv[0]); return 1; int result = write_to_log(argv[1][0], argv[2], argv[3]); if (result!= 0) { printf("[e] Failed while writing to log\n"); return result; printf("[i] Done.\n"); return 0; 4/7

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6 Question Q3 Given the Q2, assume the source files are arranged according to the current file-system tree: /home/projects/writelog/ include/ logger.h time_utils.h src/ logger.c time_utils.c main.c Makefile You are asked to: A) Write a correct Makefile to build (with gcc set to optimization level 3) and clean the writelog command-line tool; B) Write the correct sequence of GIT commands to perform the following actions: 1. Initialize the local repository; 2. Create and switch to a new development branch called dev ; 3. Commit the changes introduced in the Logger library files; 4. Commit the changes introduced in main.c ; 5. Push the dev branch up to the remote repository (origin) (assuming it is already been configured) 6. Switch back to the master branch 6/7

7 A) Makefile NAME = writelog CC = gcc CFLAGS = Wall O3 I $(INCDIR) LDFLAGS = lpthread INCDIR = include SRCDIR = src SOURCES = $(SRCDIR)/main.c $(SRCDIR)/time_utils.c $(SRCDIR)/logger.c OBJECTS = $(SOURCES:.c=.o) all: $(NAME) $(NAME): $(OBJECTS) $(CC) $^ o $@ $(CFLAGS) $(LDFLAGS) %(SRCDIR)/%.o: %.c $(CC) $^ c $< $(CFLAGS) $(LDFLAGS) clean: rm f $(NAME) rm f $(SRCDIR)/*.o B) GIT commands $ git init $ git checkout b dev $ git add logger.c logger.h $ git commit s m [logger] Added write_to_log function $ git add main.c $ git commit s m [writelog] First version of writelog $ git push origin dev $ git checkout master 7/7

Politecnico di Milano FACOLTÀ DI INGEGNERIA DELL INFORMAZIONE. Real-Time Operating Systems A.A Exam date: 11 Sep 2014

Politecnico di Milano FACOLTÀ DI INGEGNERIA DELL INFORMAZIONE Real-Time Operating Systems A.A. 2013-2014 Exam date: 11 Sep 2014 Prof. William FORNACIARI Surname (readable)... Matr... Name (readable)...