Homework: Kernel debugging

05_debug/Makefile

@@ -0,0 +1,16 @@
+ifneq ($(KERNELRELEASE),)
+# kbuild part of makefile
+obj-m   := main.o
+else
+# normal makefile
+KDIR ?= /lib/modules/`uname -r`/build
+
+default:
+	$(MAKE) -C $(KDIR) M=$$PWD
+check:
+	$(KDIR)/scripts/checkpatch.pl -f main.c
+move:
+	cd ../ && sudo cp -r 05_debug /srv/nfs/busybox/tmp/
+clean:
+	$(MAKE) -C $(KDIR) M=$$PWD clean
+endif

05_debug/README.md

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+# Kernel module debugging
+
+Create a simple string uppercase converter using procfs
+(write: input string, read: that string in uppercase).
+
+Create a simple string lowercase converter using sysfs
+(store: input string, show: that string in lowercase).
+
+Add read only attributes for both filesystems
+showing statistics (using cat):
+e.g. total calls, total characters processed, characters converted etc.

05_debug/kernel.log

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+/tmp/05_debug # sh test.sh 
+[ 3664.961436] Module initialized successfully
+Fill the list...
+[ 3665.018721] mymodule: new item in list sysfs VaSyA
+[ 3665.024794] mymodule: new item in list procfs VaSyA
+[ 3665.024794] 
+[ 3665.322123] mymodule: new item in list sysfs PeTyA
+[ 3665.330267] mymodule: new item in list procfs PeTyA
+[ 3665.330267] 
+[ 3665.648062] mymodule: new item in list sysfs AnToN
+[ 3665.654327] mymodule: new item in list procfs AnToN
+[ 3665.654327] 
+[ 3665.994581] mymodule: new item in list sysfs VlaD
+[ 3666.003032] mymodule: new item in list procfs VlaD
+[ 3666.003032] 
+Now we call 3 times cat for sysfs
+[ 3666.342746] mymodule : success reading
+[ 3666.343015] mymodule : success reading
+[ 3666.343244] mymodule : success reading
+[ 3666.343498] mymodule : success reading
+vlad
+anton
+petya
+vasya
+[ 3666.413266] mymodule : success reading
+[ 3666.413508] mymodule : success reading
+[ 3666.413715] mymodule : success reading
+[ 3666.413909] mymodule : success reading
+vlad
+anton
+petya
+vasya
+[ 3666.480709] mymodule : success reading
+[ 3666.480987] mymodule : success reading
+[ 3666.481254] mymodule : success reading
+[ 3666.481636] mymodule : success reading
+vlad
+anton
+petya
+vasya
+Now we call 4 times cat for sysfs
+[ 3666.740211] mymodule : success reading
+[ 3666.740466] mymodule : success reading
+[ 3666.740692] mymodule : success reading
+[ 3666.740906] mymodule : success reading
+VLAD
+ANTON
+PETYA
+VASYA
+[ 3666.801943] mymodule : success reading
+[ 3666.802467] mymodule : success reading
+[ 3666.803027] mymodule : success reading
+[ 3666.803510] mymodule : success reading
+VLAD
+ANTON
+PETYA
+VASYA
+[ 3666.872316] mymodule : success reading
+[ 3666.872563] mymodule : success reading
+[ 3666.872808] mymodule : success reading
+[ 3666.873066] mymodule : success reading
+VLAD
+ANTON
+PETYA
+VASYA
+[ 3666.927977] mymodule : success reading
+[ 3666.928216] mymodule : success reading
+[ 3666.928523] mymodule : success reading
+[ 3666.928780] mymodule : success reading
+VLAD
+ANTON
+PETYA
+VASYA
+Statistics
+
+Using 'cat' for procfs 4
+Total read bytes: 23
+Total converted character: 8
+
+
+Using 'cat' for sysfs: 3
+Total read bytes: 23
+Total converted character: 11
+
+[ 3667.281739] Task 05. Done!
+Try to read file after deleting
+cat: can't open '/sys/kernel/kobject_list/list': No such file or directory
+cat: can't open '/proc/procfs_list/list': No such file or directory

05_debug/main.c

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+// SPDX-License-Identifier: MIT and GPL
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/err.h>
+
+#include <linux/sysfs.h>
+#include <linux/proc_fs.h>
+#include <linux/uaccess.h>
+#include <linux/device.h>
+
+#include <linux/types.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/ctype.h>
+#define BUFF_SIZE 255
+static struct kobject *sys_data;
+
+static LIST_HEAD(procfs_list);
+static LIST_HEAD(sysfs_list);
+
+size_t try_sysfs_read;
+size_t sysfs_count;
+size_t try_procfs_read;
+size_t procfs_count;
+size_t pconv_ch;
+size_t sconv_ch;
+
+struct data_node {
+	struct list_head head;
+	char *string_fs;
+};
+
+
+static ssize_t stat_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	int offset = 0;
+	int state = 0;
+
+	state = snprintf(buf + offset, PAGE_SIZE - offset,
+			"\nUsing 'cat' for sysfs: %d\nTotal read bytes: %d\nTotal converted character: %d\n\n",
+			try_sysfs_read, sysfs_count, sconv_ch);
+	if (state < 0) {
+		pr_err("stat : error reading\n");
+		return state;
+	}
+	offset += state;
+	return offset;
+}
+
+static ssize_t rw_show(struct kobject *kobj,
+				struct kobj_attribute *attr, char *buf)
+{
+	struct data_node *item = NULL;
+	int offset = 0;
+	int state = 0;
+
+	try_sysfs_read++;
+	list_for_each_entry(item, &sysfs_list, head) {
+		state = snprintf(buf + offset, PAGE_SIZE - offset, "%s",
+				item->string_fs);
+		if (state < 0) {
+			pr_err("mymodule : error reading\n");
+			return state;
+		}
+		pr_info("mymodule : success reading\n");
+		offset += state;
+	}
+	return offset;
+}
+
+static ssize_t rw_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	struct data_node *item = kzalloc(sizeof(*item), GFP_KERNEL);
+	size_t i = 0;
+
+	sysfs_count += count;
+	if (strlen(buf) != count)
+		return -EINVAL;
+	item->string_fs = kmalloc_array(count, sizeof(char), GFP_KERNEL);
+	while (i < count) {
+		if (buf[i] != tolower(buf[i])) {
+			item->string_fs[i] = tolower(buf[i]);
+			sconv_ch++;
+		} else
+			item->string_fs[i] = buf[i];
+		i++;
+	}
+	item->string_fs[i] = '\0';
+	list_add(&item->head, &sysfs_list);
+	pr_info("mymodule: new item in list sysfs %s", buf);
+	return count;
+}
+
+static struct kobj_attribute attr =
+	__ATTR(list, 0660, rw_show, rw_store);
+static struct kobj_attribute stat =
+	__ATTR(statistics, 0660, stat_show, NULL);
+
+static int mysysfs_init(void)
+{
+	int state = 0;
+
+	sys_data = kobject_create_and_add("kobject_list", kernel_kobj);
+	if (sys_data == NULL) {
+		pr_info("impossible to create Kobject!\n");
+		return state;
+	}
+	state = sysfs_create_file(sys_data, &attr.attr);
+	if (state)
+		goto fail_sysfs;
+	state = sysfs_create_file(sys_data, &stat.attr);
+	if (state)
+		goto fail_sysfs;
+	return state;
+fail_sysfs:
+	pr_info("impossible to create File with data!\n");
+	kobject_put(sys_data);
+	return state;
+}
+
+static ssize_t rw_write(struct file *file, const char __user *pbuf,
+		size_t count, loff_t *ppos)
+{
+	struct data_node *item = kzalloc(sizeof(*item), GFP_KERNEL);
+	size_t i = 0;
+	ssize_t res;
+	char tmp;
+
+	procfs_count += count;
+	item->string_fs = kmalloc_array(count, sizeof(char), GFP_KERNEL);
+	res = copy_from_user(item->string_fs, pbuf, count);
+	pr_info("mymodule: new item in list procfs %s\n", item->string_fs);
+	while (i < count) {
+		tmp = item->string_fs[i];
+		item->string_fs[i] = toupper(item->string_fs[i]);
+		if (item->string_fs[i] != tmp)
+			pconv_ch++;
+		i++;
+	}
+	list_add(&item->head, &procfs_list);
+	return count;
+}
+
+static ssize_t rw_read(struct file *file, char __user *pbuf, size_t count,
+		loff_t *ppos)
+{
+	struct data_node *item = NULL;
+	int offset = 0;
+	int state = 0;
+
+	if (*ppos != 0)
+		return 0;
+	try_procfs_read++;
+	list_for_each_entry(item, &procfs_list, head) {
+		state = snprintf(pbuf + offset, PAGE_SIZE - offset,
+				"%s", item->string_fs);
+		if (state < 0) {
+			pr_err("mymodule : error reading\n");
+			return state;
+		}
+		pr_info("mymodule : success reading\n");
+		offset += state;
+	}
+	return offset;
+}
+
+static ssize_t stat_read(struct file *file, char __user *pbuf, size_t count,
+		loff_t *ppos)
+{
+	int state = 0;
+	char stat_buff[BUFF_SIZE];
+
+	state = snprintf(stat_buff, BUFF_SIZE,
+			"\nUsing 'cat' for procfs %d\nTotal read bytes: %d\nTotal converted character: %d\n\n",
+			try_procfs_read, procfs_count, pconv_ch);
+	return simple_read_from_buffer(pbuf, count, ppos, stat_buff, state);
+}
+
+static struct proc_dir_entry *entry;
+static struct proc_dir_entry *dir;
+static const struct file_operations oper = {
+	.owner = THIS_MODULE,
+	.read = rw_read,
+	.write = rw_write,
+};
+static const struct file_operations sstat = {
+	.owner = THIS_MODULE,
+	.read = stat_read,
+};
+
+static int myprocfs_init(void)
+{
+	dir = proc_mkdir("procfs_list", NULL);
+	if (dir == NULL) {
+		pr_err("mymodule: error creating procfs directory\n");
+		return -1;
+	}
+	entry = proc_create("list", 0666, dir, &oper);
+	if (entry == NULL)
+		goto fail_procfs;
+	entry = proc_create("stat", 0444, dir, &sstat);
+	if (entry == NULL)
+		goto fail_procfs;
+	return 0;
+fail_procfs:
+	pr_err("mymodule: error creating procfs entry\n");
+	remove_proc_entry("procfs_list", NULL);
+	return -1;
+}
+
+static int mymodule_init(void)
+{
+	if (mysysfs_init() == -1) {
+		pr_err("Sysfs initialized error!\n");
+		return -ENOMEM;
+	} else if (myprocfs_init() == -1) {
+		pr_err("Procfs initialized error!\n");
+		return -ENOMEM;
+	}
+	pr_info("Module initialized successfully\n");
+	return 0;
+}
+
+static void mymodule_exit(void)
+{
+	struct data_node *item = NULL;
+	struct data_node *tmp = NULL;
+
+	list_for_each_entry_safe(item, tmp, &sysfs_list, head) {
+		list_del(&item->head);
+		kfree(item->string_fs);
+		kfree(item);
+	}
+	list_for_each_entry_safe(item, tmp, &procfs_list, head) {
+		list_del(&item->head);
+		kfree(item->string_fs);
+		kfree(item);
+	}
+	pr_info("Task 05. Done!\n");
+	kobject_put(sys_data);
+	proc_remove(dir);
+}
+
+module_init(mymodule_init);
+module_exit(mymodule_exit);
+
+MODULE_AUTHOR("Vladyslav Andrishko <v.andrishko.v333@gmail.com>");
+MODULE_DESCRIPTION("Kernel module example with upper/lowercase convertor");
+MODULE_LICENSE("GPL");
+MODULE_VERSION("0.1");
+