oltandoci / lkm_procfs_entry

lkm_procfs_entry

This module is a simple example on how to create a procfs entry for debug purposes.
The Makefile is created based on the official Documentation. Here are some important information:

"kbuild" is the build system used by the Linux kernel.

• C $KDIR
  The directory where the kernel source is located. "make" will actually change to the specified directory when executing and will change back when finished.

• M=$PWD
  Informs kbuild that an external module is being built. The value given to "M" is the absolute path of the directory where the external module (kbuild file) is located.

The file may be as simple as a single line:

  obj-m := <module_name>.o

The kbuild system will build <module_name>.o from <module_name>.c, and, after linking, will result in the kernel module <module_name>.ko.

When the module is built from multiple sources, an additional line is needed listing the files:

  <module_name>-y := <src1>.o <src2>.o ...

Instead of adding all object files one by one, there is a quick command to do it:

  <module_name>-y := <src_files>:.c=.o

Where <src_files> contains all sources.

$(src) provides the absolute path by pointing to the directory where the currently executing kbuild file is located.

Additional functionality, such as test targets, can be included but should be filtered out from kbuild due to possible name clashes.

The check for KERNELRELEASE is used to separate the two parts of the makefile:

• the first pass is by the "make" instance run on the command line
• the second pass is by the kbuild system, which is initiated by the parameterized "make" in the default target.

Modules which are included in the kernel are installed in the directory (by running make with modules_install target):

  /lib/modules/$(KERNELRELEASE)/kernel/

And external modules are installed in:

  /lib/modules/$(KERNELRELEASE)/extra/

For another path see INSTALL_MOD_PATH