![Disk Registration
struct gendisk (<linux/gendisk.h>) is the kernel’s representation of
an individual disk driver.
Fields :
int major
int firstminor
int minors
char disk_name[32]
struct block_device_operations *fops
struct request_queue *queue
structure used by kernel to manage I/O
requests for this device
int flags
sector_t capacity
void *private_data](https://image.slidesharecdn.com/linux-2-250526070118-2bc7597a/85/Sysfs-filesystem-to-provide-a-hierarchi-11-320.jpg)
Sysfs filesystem to provide a hierarchi..
- 1. Linux 2.6 Device Drivers and LKM Unified framework for device drivers. Complete support for device plug and play, power management by defining the interfaces that these subsystems can use when communicating with individual driver. Sysfs filesystem to provide a hierarchical view of each system’s device tree (prevent loading of proc filesystem). New naming convention for loadable kernel modules using the .ko extension (kernel object).
- 2. Updating the basic structure of a device driver You must use the module_init() and module_exit() macros to register the names of your initialization and exit routines. #define MODULE statement is no longer necessary, either in your code or in your make file. You need to add an instance of the MODULE_LICENSE() macro, such as the following: MODULE_LICENSE(“GPL”);
- 3. A generic template for a minimal 2.6 device driver would be the following: #include <linux/module.h> #include <linux/config.h> #include <linux/init.h> MODULE_LICENSE("GPL"); static int __init name_of_initialization_routine(void) { /* code goes here */ return 0; } static void __exit name_of_cleanup_routine(void) { /* code goes here */ } module_init(name_of_initialization_routine); module_exit(name_of_cleanup_routine);
- 4. Changes to the build process for the module Under 2.4, to produce a LKM named testmod.o gcc –D__KERNEL__ -DMODULE –I/usr/src/linux-2.4.21/include -O2 –c testmod.c In 2.6, you don’t have to specify MODULE oriented declarations such as MODULE, __KERNEL__ or –O2 options. The 2.6 compatible Makefile for the module testmod.ko obj-m := testmod.o A simple command line for building a module #make –C /usr/src/linux-2.6.1 SUBDIRS=$PWD modules assumes, your module’s source code and Makefile are located at the same directory.
- 5. Other 2.6 related changes - Kernel’s asynchronous I/O mechanism - DMA support layer - Memory and page allocation mechanism - The block device driver, a new generic disk interface Allowing and managing memory and pages using a new standard interface, known as mempool. Module reference counts, are managed and manipulated differently. Task queues replaced with work queues.
- 6. Other 2.6 related changes… MODULE_PARAM() macro replaced by explicit parameter declaration using the new module_param() macro. Enhanced preemptibility and SMP awareness of the 2.6 Linux kernel, some concern for drivers. Should use spinlock or mutex to protect data. Use of devfs filesystem marked as obsolete during 2.6 Linux kernel configuration. devfs is an intermediate steps between the hard coded device nodes and the integration of udev, hot plug and the sysfs file system.
- 7. Char Device Registration Two ways to define cdev structure (represents the char device) - struct cdev *my_cdev = cdev_alloc(); my_cdev->ops = &my_fops; - void cdev_init(struct cdev *dev, struct file_operations *fops); To resister a char device int cdev_add(struct cdev *dev, dev_t num, unsigned int count); To remove a char device from the system: void cdev_del(struct cdev *dev);
- 8. The inode structure inode structure is used by the kernel to represent files. Two fields of this structure are: dev_t i_rdev; struct cdev *i_cdev; // represents char devices. Two macros to obtain the major and minor number from an inode unsigned int iminor(struct inode inode); unsigned int imajor(struct inode *inode);
- 9. Work Queue Two mechanism to implement bottom half processing: tasklets and workqueue. Tasklets are very fast, but all tasklet code must be atomic. Workqueue higher latency, but allowed to sleep. static struct work_struct short_wq; INIT_WORK(&short_wq, (void (*) (void *))short_do_tasklet, NULL); /* in interrupt handler */ schedule_work(&short_wq); Workqueue have a type of struct workqueue_struct defined in <linux/workqueue.h>
- 10. Interrupt handling #include <linux/interrupt.h> In interrupt handler: If interrupt for someone else return IRQ_NONE otherwise return IRQ_HANDLED
- 11. Disk Registration struct gendisk (<linux/gendisk.h>) is the kernel’s representation of an individual disk driver. Fields : int major int firstminor int minors char disk_name[32] struct block_device_operations *fops struct request_queue *queue structure used by kernel to manage I/O requests for this device int flags sector_t capacity void *private_data
- 12. Disk Registration A set of functions working with gendisk structure. struct gendisk *alloc_disk(int minors); When a disk is no longer need, it should be freed. void del_gendisk(struct gendisk *gd); You must initialize the structure and call add_disk void add_disk(struct gendisk *gd);