Linux Device Drivers Development

The release method

The release method is called when the device gets closed, the reverse of the open method. You must then undo everything you have done in the open task. What you have to do is roughly:

1. Free any private memory allocated during the open() step
2. Shut down the device (if supported) and discard every buffer on the last closing (if the device supports multi opening, or if the driver can handle more than one device at a time)

The following is an excerpt from a release function:

static int sram_release(struct inode *inode, struct file *filp) { struct pcf2127 *pcf = NULL; pcf = container_of(inode->i_cdev, struct pcf2127, cdev); mutex_lock(&device_list_lock); filp->private_data = NULL; /* last close? */ pcf2127->users--; if (!pcf2127->users) ...