cdev_add()

Purpose

Registers a struct cdev with the VFS so file operations can be reached through a device node.

Header

#include <linux/cdev.h>

Prototype

int cdev_add(struct cdev *p, dev_t dev, unsigned count);

Parameters

• p: initialized struct cdev.
• dev: first device number.
• count: number of device numbers handled.

Return Value

• Success: returns 0.
• Failure: returns a negative errno value.

Minimal Example

cdev_init(&mydev->cdev, &mydev_fops);
mydev->cdev.owner = THIS_MODULE;
ret = cdev_add(&mydev->cdev, devt, 1);

Common Pitfalls

• Call cdev_del() during cleanup.
• Initialize file_operations before cdev_add().
• Do not expose the device node before the driver state is ready.

Related Topics

• Kernel Driver