LddOpenAndRelease < Training2

%SECTION0{LddOpenAndRelease}% 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:*

<verbatim>
int open(struct inode *i, struct file *filp)
int release(struct inode *i, struct file *filp)
</verbatim>

*find device numbers given an inode:*

<verbatim>
unsigned int imajor(struct inode* i);
unsigned int iminor(struct inode* i);
</verbatim>

*find containing structure:*

<verbatim>
container_of(container_field_ptr, container_type, name_of_container_field);
</verbatim>

5.3.3. Registering a character driver		1. Denx Training Topics		5.3.5. The read and write system calls
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