5.3.4. The open and release methods

• open
  • called when device opened
  • prepares actual device for use (initalize it, enable interrupts ...)
  • every open gets its own filp (this allow virtual devices: one for each open)

• release
  • called when device is finally closed (once)
  • multiple close (fork, dup) avoided by ref counting.
  • flush is called for every close(), but seldomly used.
  • does cleanup (stop device, free memory, ...)

• Problem: how identify which device has been opened?
  1. imajor(), iminor()
  2. use container_of macro to find superstructure from inode->i_cdev

API

open and release:

int open(struct inode *i, struct file *filp)
int release(struct inode *i, struct file *filp)

find device numbers given an inode:

unsigned int imajor(struct inode* i);
unsigned int iminor(struct inode* i);

find containing structure:

container_of(container_field_ptr, container_type, name_of_container_field);