Linux-Kernel-Internals

- Linux Kernel Internals: https://ankitkdev.com/blog/
- Char Driver: https://ankitkdev.com/blog/linux-kernel/device-driver/char-driver/
- Ioctl Interface: https://ankitkdev.com/blog/linux-kernel/device-driver/ioctl/
- Proc-Interface: https://ankitkdev.com/blog/linux-kernel/device-driver/proc/
- Completion-Variable: https://ankitkdev.com/blog/linux-kernel/concurrency/completion-variable/
- container_of(): https://ankitkdev.com/blog/linux-kernel/macros/container_of/
- Module Parameters: https://ankitkdev.com/blog/linux-kernel/macros/kernel-module/
- pr_fmt(): https://ankitkdev.com/blog/linux-kernel/macros/pr-family/
- Stringification: https://ankitkdev.com/blog/linux-kernel/macros/string/
- Debugging Macros: https://ankitkdev.com/blog/linux-kernel/macros/debug/
- Error Handling with Pointers: https://ankitkdev.com/blog/kernal-internals/error-handling/
- Kbuild Makefile: https://ankitkdev.com/blog/kernal-internals/kbuild/
- SLUB debug: https://ankitkdev.com/blog/kernel-debugging/debug-slub-memory/
- unsigned :\ 0 Bit-Fields in c: https://ankitkdev.com/blog/c/zero-width-bit-field/
- do { ... } while (0): https://ankitkdev.com/blog/c/do-while-loop/
- Error Handling: https://ankitkdev.com/blog/c/error-handling/
- C Memory Layout: https://ankitkdev.com/blog/c/c-memory-layout/
- Forward Declarations: https://ankitkdev.com/blog/c/forward-declaration-in-c/
- Return value by Macro: https://ankitkdev.com/blog/c/return-by-macro/
- Variadic Macro: https://ankitkdev.com/blog/c/variadic-macro/
- programming concepts: https://ankitkdev.com/blog/theory/
- Build & Install Linux Kernel for BBB: https://ankitkdev.com/blog/misc/build-linux-kernel-BBB/
- Configure U-boot for BBB: https://ankitkdev.com/blog/misc/configure-uboot-bbb/
- Install Ubuntu Server on Qemu: https://ankitkdev.com/blog/misc/install-ubuntu-server-on-qemu/
- Linux Kernel Mentorship Program: https://ankitkdev.com/blog/misc/linux-kernel-mentorship-program/


### `container_of()`

#### Accessing a custom struct from `struct inode` via `struct cdev`

`container_of()` lets you walk backward from an embedded member (here, `struct cdev`) to the containing struct. This is how a driver recovers its private device context inside `file_operations` callbacks.

```c
#include <linux/kernel.h>   /* container_of() */
#include <linux/fs.h>       /* struct inode, struct file */
#include <linux/cdev.h>     /* struct cdev */

struct scull_dev {
	/* ... */
	struct cdev cdev;
};

int scull_open(struct inode *inode, struct file *filp)
{
	struct scull_dev *dev;

	dev = container_of(inode->i_cdev, struct scull_dev, cdev);
	filp->private_data = dev;

	/* ... */
}

ssize_t scull_read(struct file *filp, char __user *buff, size_t count,
		    loff_t *f_pos)
{
	struct scull_dev *dev = filp->private_data;

	/* ... */
}
```

> Pattern: stash the recovered pointer in `filp->private_data` on `open()` so every later callback (`read`, `write`, `ioctl`, `release`, ...) can grab it back in one line.