finished code

Code/Makefile

@@ -1,4 +1,4 @@
-obj-m += module.o 
+obj-m += assignment.o 
 
 PWD := $(CURDIR) 
 

Code/assignment.c

@@ -20,14 +20,15 @@
 #include <linux/module.h>
 #include <linux/poll.h>
 
-/* Prototypes - this would normally go in a .h file */
+/*  Prototypes - this would normally go in a .h file */
 static int device_open(struct inode *, struct file *);
 static int device_release(struct inode *, struct file *);
 static ssize_t device_read(struct file *, char __user *, size_t, loff_t *);
-static ssize_t device_write(struct file *, const char __user *, size_t, loff_t *);
+static ssize_t device_write(struct file *, const char __user *, size_t,
+                            loff_t *);
 
 #define SUCCESS 0
-#define DEVICE_NAME "chardev" /* Dev name as it appears in /proc/devices */
+#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. */
@@ -74,6 +75,8 @@ static int __init chardev_init(void)
 
 static void __exit chardev_exit(void)
 {
+    pr_info("Goodbye");
+
     device_destroy(cls, MKDEV(major, 0));
     class_destroy(cls);
 
@@ -84,8 +87,8 @@ static void __exit chardev_exit(void)
 /* Methods */
 
 /* Called when a process tries to open the device file, like
-* "sudo cat /dev/chardev"
-*/
+ * "sudo cat /dev/chardev"
+ */
 static int device_open(struct inode *inode, struct file *file)
 {
     static int counter = 0;
@@ -114,30 +117,28 @@ static int device_release(struct inode *inode, struct file *file)
 }
 
 /* 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 */
+ * read from it.
+ */
+static ssize_t device_read(struct file *filp, /* see include/linux/fs.h   */
                            char __user *buffer, /* buffer to fill with data */
-                           size_t length,       /* length of the buffer */
+                           size_t length, /* length of the buffer     */
                            loff_t *offset)
 {
     /* Number of bytes actually written to the buffer */
     int bytes_read = 0;
     const char *msg_ptr = msg;
 
-    if (!*(msg_ptr + *offset))
-    {                /* we are at the end of message */
+    if (!*(msg_ptr + *offset)) { /* we are at the end of message */
         *offset = 0; /* reset the offset */
-        return 0;    /* signify end of file */
+        return 0; /* signify end of file */
     }
 
     msg_ptr += *offset;
 
     /* Actually put the data into the buffer */
-    while (length && *msg_ptr)
-    {
+    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
+         * 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.
          */
@@ -147,6 +148,7 @@ static ssize_t device_read(struct file *filp,   /* see include/linux/fs.h */
     }
 
     *offset += bytes_read;
+
     /* Most read functions return the number of bytes put into the buffer. */
     return bytes_read;
 }

README.md

@@ -10,6 +10,7 @@ Deadline of homework: Oct 30, 2022 (in case that you cannot finish in the class)
 ## Prerequisits
   - requires the correct linux headers to be installed
   - root access is needed
+  - the Code file is NOT named module.c
 
 ## how to run the kernel module
   - `make` to build the module

output.txt

@@ -0,0 +1,67 @@
+Character devices:
+  1 mem
+  4 /dev/vc/0
+  4 tty
+  4 ttyS
+  5 /dev/tty
+  5 /dev/console
+  5 /dev/ptmx
+  7 vcs
+ 10 misc
+ 13 input
+ 29 fb
+116 alsa
+128 ptm
+136 pts
+180 usb
+188 ttyUSB
+189 usb_device
+202 cpu/msr
+203 cpu/cpuid
+226 drm
+235 chardev
+236 binder
+237 hidraw
+238 wwan_port
+239 nvme-generic
+240 nvme
+241 aux
+242 bsg
+243 watchdog
+244 remoteproc
+245 ptp
+246 pps
+247 cec
+248 lirc
+249 rtc
+250 dma_heap
+251 dax
+252 dimmctl
+253 ndctl
+254 gpiochip
+
+Block devices:
+  8 sd
+ 65 sd
+ 66 sd
+ 67 sd
+ 68 sd
+ 69 sd
+ 70 sd
+ 71 sd
+128 sd
+129 sd
+130 sd
+131 sd
+132 sd
+133 sd
+134 sd
+135 sd
+259 blkext
+==================================================
+I already told you 0 times Hello world!
+I already told you 1 times Hello world!
+==================================================
+[Fri Oct 28 15:47:13 2022] I was assigned major number 235.
+[Fri Oct 28 15:47:13 2022] Device created on /dev/chardev
+[Fri Oct 28 15:47:13 2022] Goodbye

run.sh

@@ -0,0 +1,12 @@
+cd ./Code
+make
+sudo insmod assignment.ko
+cat /proc/devices > ../output.txt
+echo "==================================================" >> ../output.txt
+sudo cat /dev/chardev >> ../output.txt
+sudo cat /dev/chardev >> ../output.txt
+echo "==================================================" >> ../output.txt
+sudo rmmod assignment
+sleep 5
+sudo dmesg -T -l info | tail -3 >> ../output.txt
+echo "Done"