unlocked_ioctl()

long unlocked_ioctl(struct file *f, unsigned int cmd, unsigned long arg)

• Associated to the ioctl() system call Called unlocked because it doesn't hold the Big Kernel Lock.

• Allows to extend the driver capabilities beyond the limited read/write API

• For example: changing the speed of a serial port, setting video output format, querying a device serial number...

• cmd is a number identifying the operation to perform

• arg is the optional argument passed as third argument of the ioctl() system call. Can be an integer, an address, etc.

• The semantic of cmd and arg is driver-specific.