Missing slab.h from linux includes - Ubuntu 16 VM - linux

Question

I'm working on a linux kernel driver and need access to the kmalloc and kfree functions. From my research these should be available in the slab.h header, but that file doesn't exist in my filesystem.
I tried updating my includes using this solution: https://askubuntu.com/questions/75709/how-do-i-install-kernel-header-files but it shows that I already have all relevant files.
My system is a VMWare Ubuntu 16.04 installation running kernel 4.15.0.
Any ideas?

Answer 1

Here is a very simple demo module that calls kmalloc and kfree:
demo.c:
#define pr_fmt(fmt) "demo: " fmt
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
MODULE_LICENSE("GPL");
static int __init demo_init(void) {
void *buf;
buf = kmalloc(1000, GFP_KERNEL);
pr_info("kmalloc returned %p\n", buf);
kfree(buf);
return 0;
}
static void __exit demo_exit(void) {
}
module_init(demo_init);
module_exit(demo_exit);
Makefile:
ifneq ($(KERNELRELEASE),)
# KBuild part of Makefile
obj-m += demo.o
else
# Normal part of Makefile
#
# Kernel build directory specified by KDIR variable
# Default to running kernel's build directory if KDIR not set externally
KDIR ?= "/lib/modules/`uname -r`/build"
all:
$(MAKE) -C "$(KDIR)" M=`pwd` modules
clean:
$(MAKE) -C "$(KDIR)" M=`pwd` clean
endif
You can just run make to build the module for the currently running kernel version:
$ make
Or you can set KDIR to build the module for an arbitrary kernel version (defined by ${KERNELVER} in the following example):
$ make KDIR="/lib/modules/${KERNELVER}/build"
(If KDIR is unspecified, the Makefile sets it to the build path for the currently running kernel: "/lib/modules/`uname -r`/build".)
If it builds successfully, then you definitely have the kernel headers installed!
To test the module, run:
$ sudo /sbin/insmod demo.ko
$ sudo /sbin/rmmod demo
$ sudo dmesg
There should be a message on the kernel log similar to this showing the return value from the kmalloc() call:
[TIMESTAMP] demo: kmalloc returned xxxxxxxxxxxxxxx
The module also calls kfree() to free the allocated block.