How can i call a function that written in kernel module, from the user program?

Question

sample driver created and loaded successfully, in that a user defined function is written, it does some actions. i need to write a user program that calls the user defined function in the driver module.

need help in following cases.

1. How can i get access to the driver code from a user program ?.
2. How can i call a function that written in kernel module, from the user program ?.

thanks.

Answer 1

You can make your driver to react on writes (or if necessary, ioctl) to a /dev/xxx file or a /proc/xxx file. Also, you can create a new syscall, but that's more of a toy as the module would only work on custom built kernels.

Edit: try http://www.faqs.org/docs/kernel/x571.html (on character device drivers.)

Answer 2

It depends on what your function does, but in general:

• If you want to store and show properties in the form of values (e.g. current brightness of a backlight), the standard way of doing would be using sysfs: http://kernel.org/doc/Documentation/filesystems/sysfs.txt

• If you want to write/read values from a device (real or virtual), export memory or IO regions of a device to user space, or more generally control a device (e.g. setting resolution of a camera and capturing frames), you would use a character or block devices with the read/write/mmap and ioctl functions: http://luv.asn.au/overheads/chrdev-talk.html

• Finally if your function just controls something from the kernel, then sysfs or procfs should be the way to go. I am not sure why people are still using procfs nowadays, except for misc devices maybe.

So in general, you need to export your kernel functions to user space through files, by defining hooks that will be called when the file is opened, read, written (to copy data from/to user space), mmap'ed (to share memory areas without copying) or when an ioctl is invoked (to perform more general control).