Usporedba prema "02-simple-device"
(napravljen je diff, ali onda maknuto ono što ne prikazuje novosti;
 ne može se ovaj diff ovako aplicirati - mnoge stvari nedostaju!)

u config.h
-----------
+#define MAX_MSGS		16
+#define MAX_MSG_SIZE		64
+#define MAX_THREADS		5
 
+struct msg {
+	struct list_head list;	//poruke ce biti u listi
+	size_t size;
+	char d[1];		//prvi bajt poruke, ostali neposredno iza
+};
+
+struct msg_queue {
+	size_t max_msgs;
+	size_t msg_cnt;
+	size_t max_msg_size;
+	size_t max_threads;
+	size_t thread_cnt;
+
+	struct list_head msgs;		//lista za poruke
+	struct semaphore readers;	//blokirani citaci
+	struct semaphore writers;	//blokirani pisaci
+	struct mutex lock;		//za medjusobno iskljucivanje
 };
 
 /* Device driver */
 struct shofer_dev {
+	struct msg_queue msg_queue;	/* red poruka */
 };
+


u shofer.c
-----------
+static int max_msgs = MAX_MSGS;
+static int max_msg_size = MAX_MSG_SIZE;
+static int max_threads = MAX_THREADS;
+
+module_param(max_msgs, int, S_IRUGO);
+MODULE_PARM_DESC(max_msgs, "Maximal number of messages in a queue");
+module_param(max_msg_size, int, S_IRUGO);
+MODULE_PARM_DESC(max_msg_size, "Maximal message size");
+module_param(max_threads, int, S_IRUGO);
+MODULE_PARM_DESC(max_threads, "Maximal number of threads simultaneously using message queue");
 
+void msgq_init(struct msg_queue *msg_queue, 
+	size_t max_msgs, size_t max_msg_size, size_t max_threads)
+{
+	msg_queue->max_msgs = max_msgs;
+	msg_queue->msg_cnt = 0;
+	msg_queue->max_msg_size = max_msg_size;
+	msg_queue->max_threads = max_threads;
+	msg_queue->thread_cnt = 0;
+	INIT_LIST_HEAD(&msg_queue->msgs);
+	sema_init(&msg_queue->readers, 0);
+	sema_init(&msg_queue->writers, max_msgs);
+	mutex_init(&msg_queue->lock);
+}
+
+static void msgq_delete(struct msg_queue *msg_queue)
+{
+	//todo - obrisi sve poruke ako ih ima
+	struct msg *msg, *m;
+	list_for_each_entry_safe (msg, m, &msg_queue->msgs, list) {
+		list_del (&msg->list);
+		kfree(msg);
+	}
 }
 
 /* Create and initialize a single shofer_dev */
 static struct shofer_dev *shofer_create(dev_t dev_no,
+	struct file_operations *fops, int *retval)
 {
+	/* initialize the message queue */
+	msgq_init(&shofer->msg_queue, max_msgs, max_msg_size, max_threads);
+
 	return shofer;
 }
 static void shofer_delete(struct shofer_dev *shofer)
 {
+	msgq_delete(&shofer->msg_queue);
 }
 
+/* Called when the process calls "open" on this device */
 static int shofer_open(struct inode *inode, struct file *filp)
 {
+	if (shofer->msg_queue.thread_cnt == shofer->msg_queue.max_threads)
+		return -EBUSY;
+
+	shofer->msg_queue.thread_cnt++;
+
 	return 0;
 }
 
 /* Called when a process performs "close" operation */
 static int shofer_release(struct inode *inode, struct file *filp)
 {
+	shofer->msg_queue.thread_cnt--;
+
+	return 0;
+}
+
+/* Uzmi poruku iz reda */
 static ssize_t shofer_read(struct file *filp, char __user *ubuf, size_t count,
 	loff_t *f_pos /* ignoring f_pos */)
 {
+	struct msg_queue *msg_queue = &shofer->msg_queue;
+	struct msg *msg;
+
+	if ( (filp->f_flags & O_ACCMODE) != O_RDONLY)
+		return -EPERM;
+
+	if (count < msg_queue->max_msg_size)
+		return -EFBIG;
+
+	if (down_interruptible(&msg_queue->readers)) //ima li poruka? ako ne čekaj
+		return -ERESTARTSYS; //čekanje prekinuto signalom
+
+	//uđi u KO
+	if (mutex_lock_interruptible(&msg_queue->lock)) {
+		//čekanje na ulaz u KO prekinuto signalom
+		up(&msg_queue->readers); //nismo uzeli poruku
 		return -ERESTARTSYS;
+	}
+
+	//ima poruka, uzmi prvu
+	msg = list_first_entry_or_null(&msg_queue->msgs, struct msg, list);
+	if (msg == NULL) {
+		klog(KERN_WARNING, "No messages in queue! Something is wrong!\n");
+		mutex_unlock(&msg_queue->lock);
+		return -ENOENT;
+	}
+
+	list_del(&msg->list); //makni iz liste
+	msg_queue->msg_cnt--;
+
+	mutex_unlock(&msg_queue->lock); //izađi iz KO
+
+	if (!copy_to_user(ubuf, &msg->d[0], msg->size)) {
+		retval = msg->size;
+	}
+	else {
+		klog(KERN_WARNING, "copy_to_user failed");
+		retval = -EFAULT;
+	}
+	kfree(msg);
+	up(&msg_queue->writers); //makli jednu poruku, može nova u red
 
 	return retval;
 }
 
+/* Stavi poruku u red */
 static ssize_t shofer_write(struct file *filp, const char __user *ubuf,
 	size_t count, loff_t *f_pos /* ignoring f_pos */)
 {
+	struct msg_queue *msg_queue = &shofer->msg_queue;
+	struct msg *msg;
+
+	if ( (filp->f_flags & O_ACCMODE) != O_WRONLY)
+		return -EPERM;
+
+	if (count > msg_queue->max_msg_size)
+		return -EFBIG;
+
+	if (down_interruptible(&msg_queue->writers)) //ima li mjesta za poruku? ako ne čekaj
 		return -ERESTARTSYS;
 
+	//napravi poruku
+	msg = kmalloc(sizeof(struct msg) + count - 1, GFP_KERNEL);
+	if (!msg){
+		klog(KERN_WARNING, "kmalloc failed\n");
+		up(&msg_queue->writers);
+		return -ENOMEM;
+	}
+
+	msg->size = count;
+
+	if (copy_from_user(&msg->d[0], ubuf, msg->size)) {
+		klog(KERN_WARNING, "copy_from_user failed");
+		kfree(msg);
+		up(&msg_queue->writers);
+		return -EFAULT;
+	}
+
+	//uđi u KO
+	if (mutex_lock_interruptible(&msg_queue->lock)) {
+		kfree(msg);
+		up(&msg_queue->writers);
+		return -ERESTARTSYS;
+	}
+
+	//stavi poruku na kraj liste
+	list_add_tail(&msg->list, &msg_queue->msgs);
+	msg_queue->msg_cnt++;
+
+	mutex_unlock(&msg_queue->lock); //izađi iz KO
+
+	up(&msg_queue->readers);
+
+	return count;
+}


Programi za testiranje:
citac.c
--------
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>


#define RED	"/dev/shofer"
#define MAXSZ	64

int main(int argc, char *argv[])
{
	int fp;
	char buffer[MAXSZ];
	size_t size;
	long pid = (long) getpid();

	fp = open(RED, O_RDONLY);
	if (fp == -1) {
		perror("Nisam otvorio cjevovod! Greska: ");
		return -1;
	}

	while(1) {
		memset(buffer, 0, MAXSZ);
		printf("Citac %ld poziva read\n", pid);
		size = read(fp, buffer, MAXSZ);
		if (size == -1) {
			perror("Greska pri citanju! Greska: ");
			break;
		}
		printf("Citac %ld procitao (%ld): %s\n", pid, size, buffer);
		sleep(1);
	}

	return -1;
}

pisac.c
-------
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>


#define RED	"/dev/shofer"
#define MAXSZ	64

void gen_text(char *text, size_t size)
{
	int i;

	for (i = 0; i < size; i++)
		text[i] = 'A' + random() % ('Z' - 'A');
}

int main(int argc, char *argv[])
{
	int fp;
	char buffer[MAXSZ];
	size_t size;
	long pid = (long) getpid();

	fp = open(RED, O_WRONLY);
	if (fp == -1) {
		perror("Nisam otvorio cjevovod! Greska: ");
		return -1;
	}

	srandom(pid);
	while(1) {
		memset(buffer, 0, MAXSZ);
		size = MAXSZ / 3 + random() % (2 * MAXSZ / 3);
		gen_text(buffer, size);
		printf("Pisac %ld poziva write s tekstom (%ld): %s\n", pid, size, buffer);
		size = write(fp, buffer, size);
		if (size == -1) {
			perror("Greska pri pisanju! Greska: ");
			break;
		}
		printf("Pisac %ld poslao (%ld): %s\n", pid, size, buffer);
		sleep(2);
	}

	return -1;
}