Beispiele und Notizen 5.5.2025

20250505/Makefile

-obj-m += hellomod-02.o
+obj-m += hellomod-05.o
 obj-m += chardev-01.o
+obj-m += chardev-02.o
+obj-m += chardev-03.o
+obj-m += chardev-04.o
 
 all:
 	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

20250505/chardev-01.c

 /*
- *  chardev.c: Creates a read-only char device that says how many times
+ *  chardev-01.c: Creates a read-only char device that says how many times
  *  you've read from the dev file
  */
 
@@ -158,10 +158,9 @@ static ssize_t device_read(struct file *filp,	/* see include/linux/fs.h   */
 }
 
 /*  
- * Called when a process writes to dev file: echo "hi" > /dev/hello 
+ * Called when a process writes to dev file: echo "hi" > /dev/chardev 
  */
-static ssize_t
-device_write(struct file *filp, const char *buff, size_t len, loff_t * off)
+static ssize_t device_write(struct file *filp, const char *buff, size_t len, loff_t * off)
 {
 	printk(KERN_ALERT "Sorry, this operation isn't supported.\n");
 	return -EINVAL;

20250505/chardev-02.c

 /*
- *  chardev.c: Creates a read-only char device that says how many times
+ *  chardev-02.c: Creates a read-only char device that says how many times
  *  you've read from the dev file
  */
 
@@ -63,7 +63,7 @@ int init_module(void)
         if( dev_Class == NULL)
         {
             printk (KERN_ALERT "Error! Class couldn't be created!\n");
-            return 1;
+            return 1;  // !!! 2 Fehler: (a) unregister_chrdev() fehlt, (b) 1 ist ungültig
         }
         printk (KERN_INFO "Class created!\n");
         // Create device in /dev/...
@@ -72,10 +72,12 @@ int init_module(void)
         if (chr_dev == NULL)
         {
             printk( KERN_ALERT "Error! Device couldn't be created!\n" );
-            return 1 ;
+            return 1 ;  // !!! 2 Fehler: (a) unregister_chrdev() und class_unregister() fehlt, (b) 1 ist ungültig
         }
 
 	return SUCCESS;
+
+        // !!! Lösung für die o.a. Probleme: selbst cleanup_module() aufrufen.
 }
 
 /*

20250505/chardev-03.c

+/*
+ *  chardev-03.c: Creates a read-only char device that says how many times
+ *  you've read from the dev file
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/fs.h>
+#include <asm/uaccess.h>	/* for put_user */
+
+MODULE_LICENSE("GPL");
+
+/*  
+ *  Prototypes - this would normally go in a .h file
+ */
+int init_module(void);
+void cleanup_module(void);
+static int device_open(struct inode *, struct file *);
+static int device_release(struct inode *, struct file *);
+static ssize_t device_read(struct file *, char *, size_t, loff_t *);
+static ssize_t device_write(struct file *, const char *, size_t, loff_t *);
+
+struct class *dev_Class;
+struct device *chr_dev;
+
+#define SUCCESS 0
+#define DEVICE_NAME "chardev"	/* Dev name as it appears in /proc/devices   */
+#define BUF_LEN 80		/* Max length of the message from the device */
+
+/* 
+ * Global variables are declared as static, so are global within the file. 
+ */
+
+static int Major;		/* Major number assigned to our device driver */
+static int Device_Open = 0;	/* Is device open?  
+				 * Used to prevent multiple access to device */
+static char msg[BUF_LEN];	/* The msg the device will give when asked */
+static char *msg_Ptr;
+
+static struct file_operations fops = {
+	.read = device_read,
+	.write = device_write,
+	.open = device_open,
+	.release = device_release
+};
+
+/*
+ * This function is called when the module is loaded
+ */
+int init_module(void)
+{
+        Major = register_chrdev(0, DEVICE_NAME, &fops);
+
+	if (Major < 0) {
+	  printk(KERN_ALERT "Registering char device failed with %d\n", Major);
+	  return Major;
+	}
+
+        // Create module class
+        printk (KERN_INFO "Creating device class \"chardev\" ...\n");
+        dev_Class = class_create (THIS_MODULE,DEVICE_NAME);
+        if( dev_Class == NULL)
+        {
+            printk (KERN_ALERT "Error! Class couldn't be created!\n");
+            return 1;  // !!! 2 Fehler: (a) unregister_chrdev() fehlt, (b) 1 ist ungültig
+        }
+        printk (KERN_INFO "Class created!\n");
+        // Create device in /dev/...
+        printk (KERN_INFO "Creating device\n");
+        chr_dev = device_create (dev_Class, NULL, MKDEV (Major,0), NULL, DEVICE_NAME);
+        if (chr_dev == NULL)
+        {
+            printk( KERN_ALERT "Error! Device couldn't be created!\n" );
+            return 1 ;  // !!! 2 Fehler: (a) unregister_chrdev() und class_unregister() fehlt, (b) 1 ist ungültig
+        }
+
+	return SUCCESS;
+
+        // !!! Lösung für die o.a. Probleme: selbst cleanup_module() aufrufen.
+}
+
+/*
+ * This function is called when the module is unloaded
+ */
+void cleanup_module(void)
+{
+        printk(KERN_INFO "module chardev-3 cleanup\n");
+        //Unregister the device
+        if (chr_dev)
+          {
+            printk(KERN_INFO "Unregister device ...\n");
+            device_unregister(chr_dev);
+            printk(KERN_INFO "OK\n");
+          }
+
+        if (dev_Class)
+          {
+            printk(KERN_INFO "Unregister class ...\n");
+            class_unregister(dev_Class);
+            printk(KERN_INFO "OK\n");
+          }
+
+        printk(KERN_INFO "Unregister Chardev ...\n");
+        unregister_chrdev(Major, DEVICE_NAME);
+        printk(KERN_INFO "Device %s unregistered!\n", DEVICE_NAME);
+}
+
+/*
+ * Methods
+ */
+
+/* 
+ * Called when a process tries to open the device file, like
+ * "cat /dev/mycharfile"
+ */
+static int device_open(struct inode *inode, struct file *file)
+{
+	static int counter = 0;
+
+	if (Device_Open)
+		return -EBUSY;
+
+	Device_Open++;
+
+        int Minor = iminor (inode);
+        if (Minor)
+          counter = Minor;
+
+	sprintf(msg, "I already told you %d times Hello world!\n", counter++);
+	msg_Ptr = msg;
+	try_module_get(THIS_MODULE);
+
+	return SUCCESS;
+}
+
+/* 
+ * Called when a process closes the device file.
+ */
+static int device_release(struct inode *inode, struct file *file)
+{
+	Device_Open--;		/* We're now ready for our next caller */
+
+	/* 
+	 * Decrement the usage count, or else once you opened the file, you'll
+	 * never get get rid of the module. 
+	 */
+	module_put(THIS_MODULE);
+
+	return 0;
+}
+
+/* 
+ * Called when a process, which already opened the dev file, attempts to
+ * read from it.
+ */
+static ssize_t device_read(struct file *filp,	/* see include/linux/fs.h   */
+			   char *buffer,	/* buffer to fill with data */
+			   size_t length,	/* length of the buffer     */
+			   loff_t * offset)
+{
+	/*
+	 * Number of bytes actually written to the buffer 
+	 */
+	int bytes_read = 0;
+
+	/*
+	 * If we're at the end of the message, 
+	 * return 0 signifying end of file 
+	 */
+	if (*msg_Ptr == 0)
+		return 0;
+
+	/* 
+	 * Actually put the data into the buffer 
+	 */
+	while (length && *msg_Ptr) {
+
+		/* 
+		 * The buffer is in the user data segment, not the kernel 
+		 * segment so "*" assignment won't work.  We have to use 
+		 * put_user which copies data from the kernel data segment to
+		 * the user data segment. 
+		 */
+		put_user(*(msg_Ptr++), buffer++);
+
+		length--;
+		bytes_read++;
+	}
+
+	/* 
+	 * Most read functions return the number of bytes put into the buffer
+	 */
+	return bytes_read;
+}
+
+/*  
+ * Called when a process writes to dev file: echo "hi" > /dev/hello 
+ */
+static ssize_t
+device_write(struct file *filp, const char *buff, size_t len, loff_t * off)
+{
+	printk(KERN_ALERT "Sorry, this operation isn't supported.\n");
+	return -EINVAL;
+}

20250505/chardev-04.c

+/*
+ *  chardev-04.c: Creates a read-only char device that says how many times
+ *  you've read from the dev file
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/fs.h>
+#include <asm/uaccess.h>	/* for put_user */
+
+MODULE_LICENSE("GPL");
+
+/*  
+ *  Prototypes - this would normally go in a .h file
+ */
+int init_module(void);
+void cleanup_module(void);
+static int device_open(struct inode *, struct file *);
+static int device_release(struct inode *, struct file *);
+static ssize_t device_read(struct file *, char *, size_t, loff_t *);
+static ssize_t device_write(struct file *, const char *, size_t, loff_t *);
+
+struct class *dev_Class;
+struct device *chr_dev;
+
+#define SUCCESS 0
+#define DEVICE_NAME "chardev2"	/* Dev name as it appears in /proc/devices   */
+#define BUF_LEN 80		/* Max length of the message from the device */
+
+/* 
+ * Global variables are declared as static, so are global within the file. 
+ */
+
+static int Major;		/* Major number assigned to our device driver */
+static int Device_Open = 0;	/* Is device open?  
+				 * Used to prevent multiple access to device */
+static char msg[BUF_LEN];	/* The msg the device will give when asked */
+static char *msg_Ptr;
+
+static struct file_operations fops = {
+	.read = device_read,
+	.write = device_write,
+	.open = device_open,
+	.release = device_release
+};
+
+/*
+ * This function is called when the module is loaded
+ */
+int init_module(void)
+{
+        Major = register_chrdev(0, DEVICE_NAME, &fops);
+
+	if (Major < 0) {
+	  printk(KERN_ALERT "Registering char device failed with %d\n", Major);
+	  return Major;
+	}
+
+        // Create module class
+        printk (KERN_INFO "Creating device class \"%s\" ...\n", DEVICE_NAME);
+        dev_Class = class_create (THIS_MODULE,DEVICE_NAME);
+        if( dev_Class == NULL)
+        {
+            printk (KERN_ALERT "Error! Class couldn't be created!\n");
+            return 1;  // !!! 2 Fehler: (a) unregister_chrdev() fehlt, (b) 1 ist ungültig
+        }
+        printk (KERN_INFO "Class created!\n");
+        // Create device in /dev/...
+        printk (KERN_INFO "Creating device\n");
+        chr_dev = device_create (dev_Class, NULL, MKDEV (Major,0), NULL, DEVICE_NAME);
+        if (chr_dev == NULL)
+        {
+            printk( KERN_ALERT "Error! Device couldn't be created!\n" );
+            return 1 ;  // !!! 2 Fehler: (a) unregister_chrdev() und class_unregister() fehlt, (b) 1 ist ungültig
+        }
+
+	return SUCCESS;
+
+        // !!! Lösung für die o.a. Probleme: selbst cleanup_module() aufrufen.
+}
+
+/*
+ * This function is called when the module is unloaded
+ */
+void cleanup_module(void)
+{
+        printk(KERN_INFO "module chardev-4 cleanup\n");
+        //Unregister the device
+        if (chr_dev)
+          {
+            printk(KERN_INFO "Unregister device ...\n");
+            device_unregister(chr_dev);
+            printk(KERN_INFO "OK\n");
+          }
+
+        if (dev_Class)
+          {
+            printk(KERN_INFO "Unregister class ...\n");
+            class_unregister(dev_Class);
+            printk(KERN_INFO "OK\n");
+          }
+
+        printk(KERN_INFO "Unregister Chardev ...\n");
+        unregister_chrdev(Major, DEVICE_NAME);
+        printk(KERN_INFO "Device %s unregistered!\n", DEVICE_NAME);
+}
+
+/*
+ * Methods
+ */
+
+/* 
+ * Called when a process tries to open the device file, like
+ * "cat /dev/mycharfile"
+ */
+static int device_open(struct inode *inode, struct file *file)
+{
+	static int counter = 0;
+
+	if (Device_Open)
+		return -EBUSY;
+
+	Device_Open++;
+
+        int Minor = iminor (inode);
+        if (Minor)
+          counter = Minor;
+
+	sprintf(msg, "I already told you %d times Hello world!\n", counter++);
+	msg_Ptr = msg;
+	try_module_get(THIS_MODULE);
+
+	return SUCCESS;
+}
+
+/* 
+ * Called when a process closes the device file.
+ */
+static int device_release(struct inode *inode, struct file *file)
+{
+	Device_Open--;		/* We're now ready for our next caller */
+
+	/* 
+	 * Decrement the usage count, or else once you opened the file, you'll
+	 * never get get rid of the module. 
+	 */
+	module_put(THIS_MODULE);
+
+	return 0;
+}
+
+/* 
+ * Called when a process, which already opened the dev file, attempts to
+ * read from it.
+ */
+static ssize_t device_read(struct file *filp,	/* see include/linux/fs.h   */
+			   char *buffer,	/* buffer to fill with data */
+			   size_t length,	/* length of the buffer     */
+			   loff_t * offset)
+{
+	/*
+	 * Number of bytes actually written to the buffer 
+	 */
+	int bytes_read = 0;
+
+	/*
+	 * If we're at the end of the message, 
+	 * return 0 signifying end of file 
+	 */
+	if (*msg_Ptr == 0)
+		return 0;
+
+	/* 
+	 * Actually put the data into the buffer 
+	 */
+	while (length && *msg_Ptr) {
+
+		/* 
+		 * The buffer is in the user data segment, not the kernel 
+		 * segment so "*" assignment won't work.  We have to use 
+		 * put_user which copies data from the kernel data segment to
+		 * the user data segment. 
+		 */
+		put_user(*(msg_Ptr++), buffer++);
+
+		length--;
+		bytes_read++;
+	}
+
+	/* 
+	 * Most read functions return the number of bytes put into the buffer
+	 */
+	return bytes_read;
+}
+
+/*  
+ * Called when a process writes to dev file: echo "hi" > /dev/hello 
+ */
+static ssize_t
+device_write(struct file *filp, const char *buff, size_t len, loff_t * off)
+{
+	printk(KERN_ALERT "Sorry, this operation isn't supported.\n");
+	return -EINVAL;
+}

20250505/devices-01.txt

+l: [1048869.989202]  <TASK>
+l: [1048869.989204]  dump_stack_lvl+0x44/0x5c
+l: [1048869.989210]  do_init_module.cold+0x21/0x26
+l: [1048869.989213]  __do_sys_finit_module+0xac/0x120
+l: [1048869.989219]  do_syscall_64+0x55/0xb0
+l: [1048869.989223]  ? vm_mmap_pgoff+0x103/0x180
+l: [1048869.989227]  ? syscall_exit_to_user_mode+0x1e/0x40
+l: [1048869.989232]  ? ksys_mmap_pgoff+0xe8/0x1f0
+l: [1048869.989235]  ? exit_to_user_mode_prepare+0x40/0x1e0
+l: [1048869.989237]  ? syscall_exit_to_user_mode+0x1e/0x40
+l: [1048869.989240]  ? do_syscall_64+0x61/0xb0
+l: [1048869.989243]  ? exit_to_user_mode_prepare+0x40/0x1e0
+l: [1048869.989245]  ? syscall_exit_to_user_mode+0x1e/0x40
+l: [1048869.989248]  ? do_syscall_64+0x61/0xb0
+l: [1048869.989250]  ? exit_to_user_mode_prepare+0x40/0x1e0
+l: [1048869.989253]  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
+l: [1048869.989257] RIP: 0033:0x7f5d93f207d9
+l: [1048869.989259] Code: 08 89 e8 5b 5d c3 66 2e 0f 1f 84 00 00 00 00 00 90 48 89 f8 48 89 >
+24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d f7 05 0d 00 f7 d8 64 89 01 48
+l: [1048869.989262] RSP: 002b:00007ffd8081baa8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
+l: [1048869.989264] RAX: ffffffffffffffda RBX: 000055e022ecf7a0 RCX: 00007f5d93f207d9
+l: [1048869.989266] RDX: 0000000000000000 RSI: 000055dfebf194a0 RDI: 0000000000000003
+l: [1048869.989267] RBP: 000055dfebf194a0 R08: 0000000000000000 R09: 00007f5d93ff92a0
+l: [1048869.989268] R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000000
+l: [1048869.989269] R13: 0000000000000000 R14: 000055e022ecf760 R15: 0000000000000000
+l: [1048869.989272]  </TASK>
+l: [1049353.876194] Hello world 4.
+l: [1049846.730590] usb 1-1.1: new full-speed USB device number 18 using xhci_hcd
+l: [1049846.833628] usb 1-1.1: New USB device found, idVendor=2a03, idProduct=0043, bcdDevic>
+l: [1049846.833637] usb 1-1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=220
+l: [1049846.833641] usb 1-1.1: Product: Arduino Uno
+l: [1049846.833644] usb 1-1.1: Manufacturer: Arduino Srl
+l: [1049846.833647] usb 1-1.1: SerialNumber: 8543930323335131F120
+l: [1049846.843682] cdc_acm 1-1.1:1.0: ttyACM0: USB ACM device
+l: [1049928.172019] usb 1-1.1: USB disconnect, device number 18
+l: [1053830.018442] Goodbye world 5.
+l: [1053893.311904] I was assigned major number 238. To talk to
+l: [1053893.311911] the driver, create a dev file with
+l: [1053893.311912] 'mknod /dev/chardev c 238 0'.
+l: [1053893.311914] Try various minor numbers. Try to cat and echo to
+l: [1053893.311915] the device file.
+l: [1053893.311916] Remove the device file and module when done.
+~
+cassini/home/peter/bo/2025ss/bs/20250505> mknod chardev c 238 0
+mknod: chardev: Die Operation ist nicht erlaubt
+cassini/home/peter/bo/2025ss/bs/20250505> sudo mknod chardev c 238 0
+cassini/home/peter/bo/2025ss/bs/20250505> ls -l chardev
+crw-r--r-- 1 root root 238, 0  5. Mai 14:11 chardev
+cassini/home/peter/bo/2025ss/bs/20250505>

20250505/devices-02.txt

+cassini/home/peter/bo/2025ss/bs/20250505> sudo mknod chardev c 238 0
+cassini/home/peter/bo/2025ss/bs/20250505> ls -l chardev
+crw-r--r-- 1 root root 238, 0  5. Mai 14:11 chardev
+cassini/home/peter/bo/2025ss/bs/20250505>
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 0 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 1 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 2 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505>

20250505/devices-03.txt

+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+cat: chardev: Das Gerät oder die Ressource ist belegt
+cassini/home/peter/bo/2025ss/bs/20250505> echo "Hi!" > chardev
+bash: chardev: Keine Berechtigung
+cassini/home/peter/bo/2025ss/bs/20250505> ls -l chardev
+crw-r--r-- 1 root root 238, 0  5. Mai 14:11 chardev
+cassini/home/peter/bo/2025ss/bs/20250505> sudo chgrp peter chardev
+[sudo] Passwort für peter:
+cassini/home/peter/bo/2025ss/bs/20250505> ls -l chardev
+crw-r--r-- 1 root peter 238, 0  5. Mai 14:11 chardev
+cassini/home/peter/bo/2025ss/bs/20250505> chmod 664 chardev
+chmod: Beim Setzen der Zugriffsrechte für 'chardev': Die Operation ist nicht erlaubt
+cassini/home/peter/bo/2025ss/bs/20250505> sudo chmod 664 chardev
+cassini/home/peter/bo/2025ss/bs/20250505> ls -l chardev
+crw-rw-r-- 1 root peter 238, 0  5. Mai 14:11 chardev
+cassini/home/peter/bo/2025ss/bs/20250505> echo "Hi!" > chardev
+bash: chardev: Das Gerät oder die Ressource ist belegt
+cassini/home/peter/bo/2025ss/bs/20250505>

20250505/devices-04.txt

+cassini/home/peter/bo/2025ss/bs/20250505> echo "Hi!" > chardev
+bash: chardev: Das Gerät oder die Ressource ist belegt
+cassini/home/peter/bo/2025ss/bs/20250505>
+cassini/home/peter/bo/2025ss/bs/20250505> sudo rmmod chardev_01
+cassini/home/peter/bo/2025ss/bs/20250505> sudo insmod chardev_01
+insmod: ERROR: could not load module chardev_01: No such file or directory
+cassini/home/peter/bo/2025ss/bs/20250505> sudo insmod ./chardev-01.ko
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 0 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> echo "Hi!" > chardev
+bash: echo: Schreibfehler: Das Argument ist ungültig.
+cassini/home/peter/bo/2025ss/bs/20250505> LANG=C echo "Hi!" > chardev
+bash: echo: write error: Invalid argument
+cassini/home/peter/bo/2025ss/bs/20250505>

20250505/devices-05.txt

+drwxr-xr-x   2 root root         340  5. Mai 12:29 block
+drwxr-xr-x  21 root root        3820  5. Mai 14:39 .
+crw-------   1 root root    238,   0  5. Mai 14:39 chardev
+drwxr-xr-x   2 root root        4060  5. Mai 14:39 char
+crw-rw-rw-   1 root tty       5,   0  5. Mai 14:39 tty
+crw-rw-rw-   1 root tty       5,   2  5. Mai 14:39 ptmx
+cassini/home/peter/bo/2025ss/bs/20250505> cat /dev/chardev
+cat: /dev/chardev: Keine Berechtigung
+cassini/home/peter/bo/2025ss/bs/20250505> sudo cat /dev/chardev
+I already told you 0 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> sudo cat /dev/chardev
+I already told you 1 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> sudo rmmod chardev_02
+cassini/home/peter/bo/2025ss/bs/20250505> ls -l /dev/chardev
+ls: Zugriff auf '/dev/chardev' nicht möglich: Datei oder Verzeichnis nicht gefunden
+cassini/home/peter/bo/2025ss/bs/20250505>

20250505/devices-06.txt

+cassini/home/peter/bo/2025ss/bs/20250505> sudo insmod ./chardev-02.ko
+cassini/home/peter/bo/2025ss/bs/20250505> ls -l /dev/chardev
+crw------- 1 root root 238, 0  5. Mai 14:42 /dev/chardev
+cassini/home/peter/bo/2025ss/bs/20250505> sudo cat /dev/chardev
+I already told you 0 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> ls -l chardev
+crw-rw-r-- 1 root peter 238, 0  5. Mai 14:11 chardev
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 1 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> sudo cat /dev/chardev
+I already told you 2 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 3 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505>

20250505/devices-07.txt

+cassini/home/peter/bo/2025ss/bs/20250505> sudo mknod chardev42 c 238 42
+cassini/home/peter/bo/2025ss/bs/20250505> ls -l chardev*
+crw-rw-r-- 1 root  peter 238,  0  5. Mai 14:11 chardev
+-rw-r--r-- 1 peter peter    4097  5. Mai 14:30 chardev-01.c
+-rw-r--r-- 1 peter peter  248752  5. Mai 14:38 chardev-01.ko
+-rw-r--r-- 1 peter peter      47  5. Mai 14:09 chardev-01.mod
+-rw-r--r-- 1 peter peter    1044  5. Mai 14:09 chardev-01.mod.c
+-rw-r--r-- 1 peter peter   93992  5. Mai 14:09 chardev-01.mod.o
+-rw-r--r-- 1 peter peter  156232  5. Mai 14:38 chardev-01.o
+-rw-r--r-- 1 peter peter    5243  5. Mai 14:38 chardev-02.c
+-rw-r--r-- 1 peter peter  268136  5. Mai 14:38 chardev-02.ko
+-rw-r--r-- 1 peter peter      47  5. Mai 14:38 chardev-02.mod
+-rw-r--r-- 1 peter peter    1188  5. Mai 14:38 chardev-02.mod.c
+-rw-r--r-- 1 peter peter   94248  5. Mai 14:38 chardev-02.mod.o
+-rw-r--r-- 1 peter peter  175368  5. Mai 14:38 chardev-02.o
+crw-r--r-- 1 root  root  238, 42  5. Mai 14:45 chardev42
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev42
+I already told you 4 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> ls -l /dev/sda*
+brw-rw---- 1 root disk 8, 0  8. Apr 07:30 /dev/sda
+brw-rw---- 1 root disk 8, 1  8. Apr 07:30 /dev/sda1
+brw-rw---- 1 root disk 8, 2  8. Apr 07:30 /dev/sda2
+brw-rw---- 1 root disk 8, 5  8. Apr 07:30 /dev/sda5
+cassini/home/peter/bo/2025ss/bs/20250505>

20250505/devices-08.txt

+cassini/home/peter/bo/2025ss/bs/20250505> sudo insmod ./chardev-03.ko                        cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 5 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 6 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 7 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev42
+I already told you 8 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev42
+I already told you 9 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> lsmod | grep chardev
+chardev_03             16384  0
+chardev_02             16384  0
+cassini/home/peter/bo/2025ss/bs/20250505> sudo rmmod chardev_02
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev42
+cat: chardev42: Kein passendes Gerät bzw. keine passende Adresse gefunden
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+cat: chardev: Kein passendes Gerät bzw. keine passende Adresse gefunden
+cassini/home/peter/bo/2025ss/bs/20250505> sudo rmmod chardev_03
+Getötet
+cassini/home/peter/bo/2025ss/bs/20250505> sudo insmod ./chardev-03.ko
+insmod: ERROR: could not insert module ./chardev-03.ko: Device or resource busy
+cassini/home/peter/bo/2025ss/bs/20250505> sudo insmod ./chardev-03.ko
+insmod: ERROR: could not insert module ./chardev-03.ko: Device or resource busy
+cassini/home/peter/bo/2025ss/bs/20250505>

20250505/devices-09.txt

+cassini/home/peter/bo/2025ss/bs/20250505> ls -l /dev/chardev2
+crw------- 1 root root 238, 0  5. Mai 15:06 /dev/chardev2
+cassini/home/peter/bo/2025ss/bs/20250505> cat /dev/chardev2
+cat: /dev/chardev2: Keine Berechtigung
+cassini/home/peter/bo/2025ss/bs/20250505> sudo cat /dev/chardev2
+I already told you 0 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> ls -l chardev
+crw-rw-r-- 1 root peter 238, 0  5. Mai 14:11 chardev
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 1 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> ls -l chardev42
+crw-r--r-- 1 root root 238, 42  5. Mai 14:45 chardev42
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev42
+I already told you 42 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev42
+I already told you 42 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 43 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 44 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 45 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev42
+I already told you 42 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505> cat chardev
+I already told you 43 times Hello world!
+cassini/home/peter/bo/2025ss/bs/20250505>

20250505/hello-01.c

+#include <stdio.h>
+
+int main (void)
+{
+  printf ("Hello, world!\n");
+  return 0;
+}

20250505/hello-01.s

+	.file	"hello-01.c"
+	.text
+	.section	.rodata.str1.1,"aMS",@progbits,1
+.LC0:
+	.string	"Hello, world!"
+	.text
+	.globl	main
+	.type	main, @function
+main:
+.LFB11:
+	.cfi_startproc
+	subq	$8, %rsp
+	.cfi_def_cfa_offset 16
+	leaq	.LC0(%rip), %rdi
+	call	puts@PLT
+	movl	$0, %eax
+	addq	$8, %rsp
+	.cfi_def_cfa_offset 8
+	ret
+	.cfi_endproc
+.LFE11:
+	.size	main, .-main
+	.ident	"GCC: (Debian 12.2.0-14) 12.2.0"
+	.section	.note.GNU-stack,"",@progbits

20250505/hello-02.c

+#include <stdio.h>
+
+int main (void)
+{
+  puts ("Hello, world!");
+  return 0;
+}

20250505/hello-02.s

+	.file	"hello-02.c"
+	.text
+	.section	.rodata.str1.1,"aMS",@progbits,1
+.LC0:
+	.string	"Hello, world!"
+	.text
+	.globl	main
+	.type	main, @function
+main:
+.LFB11:
+	.cfi_startproc
+	subq	$8, %rsp
+	.cfi_def_cfa_offset 16
+	leaq	.LC0(%rip), %rdi
+	call	puts@PLT
+	movl	$0, %eax
+	addq	$8, %rsp
+	.cfi_def_cfa_offset 8
+	ret
+	.cfi_endproc
+.LFE11:
+	.size	main, .-main
+	.ident	"GCC: (Debian 12.2.0-14) 12.2.0"
+	.section	.note.GNU-stack,"",@progbits

20250505/hellomod-03.c

+/*  
+ *  hellomod-03.c - Does the kernel call cleanup_module() on failure?
+ */
+#include <linux/module.h>	/* Needed by all modules */
+#include <linux/kernel.h>	/* Needed for KERN_INFO */
+
+MODULE_LICENSE("GPL");
+
+int init_module(void)
+{
+	printk(KERN_INFO "Hello world 3.\n");
+
+	/* 
+	 * A non 0 return means init_module failed; module can't be loaded. 
+	 */
+	return -1;
+}
+
+void cleanup_module(void)
+{
+	printk(KERN_INFO "Goodbye world 3.\n");
+}

20250505/hellomod-04.c

+/*  
+ *  hellomod-04.c - Does the kernel call cleanup_module() on failure? Which error message?
+ */
+#include <linux/module.h>	/* Needed by all modules */
+#include <linux/kernel.h>	/* Needed for KERN_INFO */
+
+MODULE_LICENSE("GPL");
+
+int init_module(void)
+{
+	printk(KERN_INFO "Hello world 4.\n");
+
+	/* 
+	 * A non 0 return means init_module failed; module can't be loaded. 
+	 */
+	return -2;
+}
+
+void cleanup_module(void)
+{
+	printk(KERN_INFO "Goodbye world 4.\n");
+}