Kernel playground

Playground for practicing Linux kernel programming

"Funmod" driver

Consists of files: funmod_base.c funmod.h, funmod_ioctl.c, ioctl_user.c, funmod_sysfs.c.

Creates both a device which reacts to ioctl and a sysfs file that can store an integer.

ioctl

The kernel module creates a device at /dev/query. It contains a struct

typedef struct
{
	int foo;
	int foobar;
	int baz;
} query_arg_t;

that can be queried or modified using ioctls.

Description	Macro	Definition
Get values	QUERY_GET_VARIABLES	_IOR('q', 1, query_arg_t *)
Defaults values to foo=3, foobar=1, baz=4	QUERY_CLR_VARIABLES	_IO('q', 2)
Set values to the same as the struct passed	QUERY_SET_VARIABLES	_IOW('q', 3, query_arg_t *)

Sysfs file

Kernel module that creates a file in sysfs at /sys/funfile/number.

It's possible to write an integer to it and get it back out (default 42):

$ cat /sys/funfile/number
42
$ echo 123 > /sys/funfile/number
$ cat /sys/funfile/number
123

Ramdisk kernel driver (ramdisk.c)

• Simple RAM backed block device that has been successfully formatted.
• Can be configured to create more than one device upon loading. Dynamic creation and deletion of devices is not yet possible. Seems to leak some memory.

License

ramdisk.c GPLv3+, everything else GPLv2.