== Why writing files from the kernel is bad ? ==

=== Reasons ===

The question "how to I open/read/write files from the kernel ?" is often asked on the kernelnewbies mailing list. However, the question cannot really be answered: opening, reading and writing files from within the kernel is usually a bad idea. Generally speaking, trying to use any of the sys_*() functions from the kernel itself is a bad idea.

For several reasons:
 * it is not the role of the kernel

=== The good ways to exchange data with user space ===

There are several ways to exchange informations between userspace and the kernel, and the one to use really depends on what you want to do:
 * kernel module parameters are useful to set general configuration options for your modules
 * [http://sosdg.org/~coywolf/lxr/source/Documentation/filesystems/sysfs.txt sysfs] is useful to get/set attributes to devices
 * [http://lwn.net/Articles/115405/ debugfs]
 * [http://sosdg.org/~coywolf/lxr/source/Documentation/filesystems/relayfs.txt relayfs]
 * netlink sockets

Using /proc is not anymore a good idea these days, except if you want to export information related to processes.

=== The good way to create device nodes ===

The good way is to have your device exported in ''sysfs'' and to let ''udev'' create the device node in /dev. Do not call try to call sys_mknod() from the kernel.