What are the ways to communicate with a kernel module from user space? By communication i mean sending information and commands between the kernel module and a user space process.
I currently know of two way:
- open/close/read/write/ioctl on published device node.
- 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.
Netlink sockets are designed for that kind of requirements, too...
Also see
- man 7 netlink
- libnl - Netlink library
- The libnl Archives
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)
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.
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.
You could also use Shared Memory and IOCTL
debugfs is another good possibility for APIs that are less stable than sysfs, but the API is basically the same. Here is a minimal runnable example.
configfs is another one. It allows easy dynamic creation of kernel objects from userspace through the filesystem: https://www.kernel.org/doc/Documentation/filesystems/configfs/configfs.txt
In any case, you will have to dirty some namespace... a filesystem entry in case of sysfs and debugfs. Just choose your poison.
Also, udev rules make /dev very similar to sysfs and debugfs: How to create a device in /dev automatically upon loading of the kernel module for a device driver?
来源：https://stackoverflow.com/questions/2903572/how-to-communicate-with-a-linux-kernel-module-from-user-space-without-littering