Linux: Ways to communicate with kernel module from user space.

Question

Hello,

What are the ways to communicate with a kernel module from user space? By communication i mean sending information and commands between the module and a user space process.

I currently know of two way:

1. open/close/read/write/ioctl on published device node.
2. read/write on exported and hooked /proc file.

More specifically, can someone advice the best way to communicate with a kernel module that does not actually drives any hardware and therefore should not be littering /dev with stub nodes that exists solely for ioctl calls? I mostly need to check its various status variables and send it a block of data with a request type tag and see if the request succeeded.

Inso.

Answer 1

Third one is add a new syscall, but the two you have written are the preferred ones, I think. I've found this document that might help, but I still think this option is unadvised: http://www.csee.umbc.edu/courses/undergraduate/CMSC421/fall02/burt/projects/howto_add_systemcall.html

Another acceptable option might be sharing memory.

Answer 2

You could also read/write from /dev device nodes.

IMHO, /dev is already littered with stuff and adding your own nodes there isn't a big issue. Don't forget that you can have lots of ioctl codes for a single device node, and the ioctl paramters are passed by reference so can be as big as you like.

Answer 3

There's also the /sys filesystem (sysfs):

Sysfs exports information about devices and drivers from the kernel device model to userspace, and is also used for configuration.

(from Wikipedia)

Answer 4

Netlink sockets are designed for that kind of requirements, too...

Also see

• man 7 netlink
• libnl - Netlink library
• The libnl Archives