CODEWITHSUNDEEP
clinuxlinux-device-driverdevice-driverioctl
Chinna
Chinna

Reputation: 3992

Why prototype of ioctl call is using unsigned long as third argument?

Below is the prototype of an ioctl call

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

Why third argument of an ioctl is unsigned long by default? Some times we pass a pointer to it. But it is using unsigned long.

Upvotes: 2

Views: 1874

Answers (1)

Stephan Roslen
Stephan Roslen

Reputation: 331

In kernel unsigned long is often used as a substitution for pointers, for pointers always have this size on every architecture. Ioctls may take an integer as an argument as well, so this makes sense here. This must be defined for each ioctl.

Please mind, that ioctls are deprecated and unlocked_ioctls must be used in current kernel versions: http://lwn.net/Articles/119652/

Upvotes: 3

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