Linux Device Drivers, Second Edition

Quick Reference

This chapter introduced the following symbols and header files. The list of the fields in struct file_operations and struct file is not repeated here.

#include <linux/fs.h>

The “file system” header is the header required for writing device drivers. All the important functions are declared in here.

int register_chrdev(unsigned int major, const char *name, struct file_operations *fops);

Registers a character device driver. If the major number is not 0, it is used unchanged; if the number is 0, then a dynamic number is assigned for this device.

int unregister_chrdev(unsigned int major, const char *name);

Unregisters the driver at unload time. Both major and the name string must contain the same values that were used to register the driver.

kdev_t inode->i_rdev;

The device “number” for the current device is accessible from the inode structure.

int MAJOR(kdev_t dev); , int MINOR(kdev_t dev);

These macros extract the major and minor numbers from a device item.

kdev_t MKDEV(int major, int minor);

This macro builds a kdev_t data item from the major and minor numbers.

SET_MODULE_OWNER(struct file_operations *fops)

This macro sets the owner field in the given file_operations structure.

#include <asm/semaphore.h>

Defines functions and types for the use of semaphores.

void sema_init (struct semaphore *sem, int val);

Initializes a semaphore to a known value. Mutual exclusion semaphores are usually initialized to a value of 1.

int down_interruptible (struct semaphore *sem); , void up (struct semaphore *sem);

Obtains a semaphore (sleeping, if necessary) and releases it, respectively.

#include <asm/segment.h> , #include <asm/uaccess.h>

segment.h defines functions related to cross-space copying in all kernels up to and including 2.0. The name was changed to uaccess.h in the 2.1 development series.

unsigned long __copy_from_user (void *to, const void *from, unsigned long count); , unsigned long __copy_to_user (void *to, const void *from, unsigned long count);

Copy data between user space and kernel space.

void memcpy_fromfs(void *to, const void *from, unsigned long count); , void memcpy_tofs(void *to, const void *from, unsigned long count);

These functions were used to copy an array of bytes from user space to kernel space and vice versa in version 2.0 of the kernel.

#include <linux/devfs_fs_kernel.h> , devfs_handle_t devfs_mk_dir (devfs_handle_t dir, const char *name, void *info); , devfs_handle_t devfs_register (devfs_handle_t dir, const char *name, unsigned int flags, , unsigned int major, unsigned int minor, umode_t mode, void *ops, void *info); , void devfs_unregister (devfs_handle_t de);

These are the basic functions for registering devices with the device filesystem (devfs).