Add procfs and kernel topic page

6 files changed, 247 insertions, 1 deletions

diff --git a/md/notes/kernel/create_procfs_entry.md b/md/notes/kernel/create_procfs_entry.md
new file mode 100644
index 0000000..03d186f
--- /dev/null
+++ b/md/notes/kernel/create_procfs_entry.md
@@ -0,0 +1,144 @@
+title:Create procfs entry
+keywords:kernel,linux,threads
+
+# Create procfs entry
+
+Lets extend hello world driver. 
+
+
+__Makefile__
+```Makefile
+obj-m += procfs_entry.o
+
+KDIR ?= /lib/modules/$(shell uname -r)/build
+
+all:
+	make -C $(KDIR) M=$(PWD) modules
+
+clean:
+	make -C $(KDIR) M=$(PWD) clean
+```
+
+__procfs_entry.c__
+```c
+#include <linux/module.h>  /* Needed by all modules */
+#include <linux/kernel.h>
+
+int procfs_entry_init( void )
+{
+	printk(KERN_DEBUG "Hello Procfs!\n");
+	return 0;
+}
+
+void procfs_entry_exit( void )
+{
+	printk(KERN_DEBUG "Exit Procfs!\n");
+}
+
+module_init( procfs_entry_init );
+module_exit( procfs_entry_exit );
+
+MODULE_LICENSE("GPL");
+```
+
+
+Create proc directory with
+
+```c
+dir = proc_mkdir(DIR_NAME, PARENT_DIR);
+```
+
+under the directory create file that will contain data
+
+```c
+proc_create("file", MODE, PARENT_DIR, PROC_FOPS)
+```
+
+Lets create /proc/secret/file. And define basic read/write operations. That at this 
+stage will do nothing.
+
+```c
+#include <linux/proc_fs.h>
+
+static struct proc_dir_entry *procdir, *procfile;
+
+static int secret_open(struct inode *inode, struct file *file) {
+        return 0;
+}
+
+static int secret_release(struct inode *inode, struct file *file) {
+        return 0;
+}
+
+static ssize_t secret_read(struct file *file, char __user *buffer, size_t length, loff_t *offset) {
+        return 0;
+}
+
+static ssize_t secret_write(struct file *file, const char *buffer, size_t length, loff_t *offset) {
+        return 0;
+}
+
+static struct proc_ops procfs_ops = {
+        .proc_open = secret_open,
+        .proc_read = secret_read,
+        .proc_write = secret_write,
+        .proc_release = secret_release
+};
+
+
+int procfs_entry_init( void ) {
+...
+procdir = proc_mkdir("secret", NULL);
+if (procdir == NULL) {
+	pr_err("Cant create secret directory\n");
+	return -1;
+}
+
+procfile = proc_create("file", 0644, procdir, &procfs_ops);
+if (procfile == NULL) {
+	pr_err("Cant create file under the secret\n");
+	return -1;
+}
+...
+}
+
+void procfs_entry_exit( void )
+{
+	...
+	//remove entries after unloading module
+	proc_remove(procdir);
+	proc_remove(procfile);
+	...
+}
+```
+
+Next step add data to read from file entry
+
+
+
+
+## List of procfs functions used
+
+| Function name | Note |
+|---|---|
+| proc_mkdir | Create procfs directory |
+| proc_create | Create procfs file |
+| proc_remove | Remove procfs entry |
+
+## Final result
+
+__Makefile__
+```Makefile
+```
+
+__procfs_entry.c__
+```c
+```
+
+## Links
+
+https://elixir.bootlin.com/linux/v6.1.21/source/include/linux/proc_fs.h
+
+
+
+
diff --git a/md/notes/kernel/create_thread.md b/md/notes/kernel/create_thread.md
new file mode 100644
index 0000000..87830b1
--- /dev/null
+++ b/md/notes/kernel/create_thread.md
@@ -0,0 +1,45 @@
+title:Create threads
+keywords:kernel,linux,threads
+
+# Create threads
+
+State of kernel thread  - include/linux/sched.h
+
+```c
+/* Used in tsk->state: */
+#define TASK_RUNNING			0x00000000
+#define TASK_INTERRUPTIBLE		0x00000001
+#define TASK_UNINTERRUPTIBLE		0x00000002
+#define __TASK_STOPPED			0x00000004
+#define __TASK_TRACED			0x00000008
+/* Used in tsk->exit_state: */
+#define EXIT_DEAD			0x00000010
+#define EXIT_ZOMBIE			0x00000020
+#define EXIT_TRACE			(EXIT_ZOMBIE | EXIT_DEAD)
+/* Used in tsk->state again: */
+#define TASK_PARKED			0x00000040
+#define TASK_DEAD			0x00000080
+#define TASK_WAKEKILL			0x00000100
+#define TASK_WAKING			0x00000200
+#define TASK_NOLOAD			0x00000400
+#define TASK_NEW			0x00000800
+#define TASK_RTLOCK_WAIT		0x00001000
+#define TASK_FREEZABLE			0x00002000
+#define __TASK_FREEZABLE_UNSAFE	       (0x00004000 * IS_ENABLED(CONFIG_LOCKDEP))
+#define TASK_FROZEN			0x00008000
+#define TASK_STATE_MAX			0x00010000
+
+#define TASK_ANY			(TASK_STATE_MAX-1)
+```
+
+## Links
+
+
+https://www.linuxtoday.com/blog/kernel-threads/  
+http://www.embeddedlinux.org.cn/EssentialLinuxDeviceDrivers/final/ch03lev1sec1.html  
+https://elixir.bootlin.com/linux/v6.1.21/source/include/linux/sched.h  
+https://elixir.bootlin.com/linux/v6.1.21/source/kernel/sysctl.c  
+
+
+
+
diff --git a/md/notes/kernel/topics.md b/md/notes/kernel/topics.md
new file mode 100644
index 0000000..b959bad
--- /dev/null
+++ b/md/notes/kernel/topics.md
@@ -0,0 +1,22 @@
+title: Topics
+keywords:blog,projects
+
+#
+
+Linux kernel programming topics
+
+## Topic
+
+[Compile kernel](/writeup/compile_linux_kernel.md)  
+[Hello world driver](/writeup/kernel_hello_world.md)  
+<!-- DMA programming   -->
+<!--[Create thread](/notes/kernel/create_thread.md)  -->
+<!-- Sysfs  -->
+[Procfs](/notes/kernel/create_procfs_entry.md)  
+<!-- Ramfs   -->
+<!-- Systemcalls   -->
+<!-- Write files to user space   -->
+<!-- Read files from user space   -->
+<!-- Netlink -->  
+<!--[User mode helpers](/notes/kernel/usermode_helper.md)  -->
+[Kernel /dev/hwrng](/writeup/kernel_dev_hwrng.md)
diff --git a/md/notes/kernel/usermode_helper.md b/md/notes/kernel/usermode_helper.md
new file mode 100644
index 0000000..dd8155a
--- /dev/null
+++ b/md/notes/kernel/usermode_helper.md
@@ -0,0 +1,8 @@
+title:User mode helper
+keywords:kernel,linux,threads
+
+# User mode helper
+
+
+## Links
+
diff --git a/md/random.md b/md/random.md
index 2faa541..c6c3b1f 100644
--- a/md/random.md
+++ b/md/random.md
@@ -11,7 +11,7 @@ keywords:blog,projects
 | Project | Description |
 | --- | --- |
 | [Undefined C](notes/undefined_c/tutorial.md) | Undefined C tutorial              |
-
+| [Kernel programming](notes/kernel/topics.md) | Linux Kernel programming          |
 
 ### Non active
 
diff --git a/md/writeup/kernel_hello_world.md b/md/writeup/kernel_hello_world.md
index 5f1e7e6..eb4fdc8 100644
--- a/md/writeup/kernel_hello_world.md
+++ b/md/writeup/kernel_hello_world.md
@@ -53,3 +53,30 @@ Now if you havent done so ... install kernel headers of kernel that your system
 ```sh
 make
 ```
+
+## Load module
+
+```sh
+sudo insmod hello_world.ko
+```
+
+check that module is running
+
+```sh
+lsmod | grep hello
+```
+
+## Unload module
+
+```sh
+rmmod hello_world
+```
+
+
+### Install kernel headers raspbian
+
+RaspberryPi4 ARMv8 
+
+```bash
+sudo apt-get install raspberrypi-kernel-headers
+```