How to call a kernel inserted module from a userland program??

raga4223688 · 02-22-2007, 04:16 AM

I have inserted a module having some functions defined in it. Now i have a c program in userspace andi need to call the functions in the kernel module....how to access/call these functions in the module?????

yogeshgaur · 02-22-2007, 05:22 AM

I dont know much about this but i think that you have to do IOCTL mapping of your API in user and kernel space and whenever you call function from user space then it internally calls the IOCTL and which calls the corresponding kernel mode API. So you have to just do the mapping from user space to kernel space through IOCTL.

For more info you can have a look for linux device driver by Rubin.

deardron · 02-24-2007, 10:54 AM

AFAIK you can only call it as a system call, so there must be an interface providing this, either via a wrapping glibc function or through the assembly command "int 0x80". The list of system calls is well-documented on the net:

http://www.lxhp.in-berlin.de/lhpsyscal.html

Otherwise you'll need to create a custom system call for your needs which will be interesting as a hack, but absolutely unpractical. The general rule is that kernelspace functions are closed for access from userland (except the mentioned system calls).

raga4223688 · 02-25-2007, 12:02 AM

can't a module be accessed from /proc filesystem??

syg00 · 02-25-2007, 12:11 AM

If you provide the interface. Nothing happens magically.

hal_2001 · 02-25-2007, 10:43 AM

For a user-space program to access a Kernel module a /dev entry can be used.

In user-space, the /dev entry is opened and can be accessed using IOCTL or indeed read, write methods etc. These methods are defined in the Kernel module.

In kernel-space, the Linux module needs to register itself as a driver, may be char or block device etc. This registration requires a MAJOR and MINOR device number. Using mknod your device node in /dev can be created. You need to pick a name for your device in /dev.

That is the basics, you then need to consider how to transfer data, eg. copy_to_user, copy_from_user. You'll need to concern yourself with understanding virtual address spaces.

gorg0th · 08-03-2011, 01:32 PM

This is a pretty good explanation of how to do what you're talking about, and what some of the relevant issues are.

http://tldp.org/LDP/lkmpg/2.6/html/lkmpg.html#AEN885

I had to access a kernel module I had written from a userland process and this is the route I ended using.

~g