I would like to know is there any caveats in using sched_clock()? Any case when it is not safe to use? And is it okay if I use it very early in kernel.bootup?
Btw the Linux runs on ARM platform
Related
I was told to use this driver to control some chip via I2C, which has a number of linux include statements. For example:
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/i2c.h>
Being a newbie to embedded programming can someone please clarify if this implies I can run this driver on:
a Linux OS machine (e.g. Ubuntu running on a PC) assuming I have some means of acting as an I2C master (e.g. FTDI USB-2-I2C chip or similar)?
an embedded Linux OS like that on a Raspberry Pi where I2C pins are readily available?
any ol' MCU (not running a linux OS) so long as the PC used to compile the
firmware has the access to the required linux kernel libraries?
Are all/some/none of the above possible? Am I missing the mark entirely and the use case is totally different?
Do linux kernal dependencies imply the need for a system running a linux OS?
Yes.
a Linux OS machine (e.g. Ubuntu running on a PC)
Yes.
an embedded Linux OS
Yes.
any ol' MCU (not running a linux OS)
No.
Are all/some/none of the above possible?
In my worldview, everything is possible. Theoretically, you or a vendor can provide a portability library to allow compilation of the kernel modules for non-linux devices. For example, they implement all the functions provided internally in linux kernel translating them to windows instructions, write all the used functions and headers. Because of instability of internal API in kernel and the size of the driver you mentioned, this is highly unprobable to happen.
I am going through the CXL support in Linux Kernel and I found that there is no function or support for cxl.cache. I'm confused if the cache part is not yet implemented in linux kernel or if the kernel should not have access to the cache commands?
(I have seen up to the latest Kernel release, 5.19)
I am trying to read the LDD book by Jonathan Corbet, Greg Kroah-Hartman, Alessandro Rubini and implement the sample modules. So to begin with, I tried setting up a development system. Installed Ubuntu 16.04 Xenial. Now, I just created a directory and wrote the hello_world module with a Makefile. Got it built and run it, verified the dmesg logs.
Is that all the development setup? I searched online and found articles where they are asking to download and compile the kernel, use a VM to boot the kernel. What is the reason? Or what am I missing?
Is there any better article which clarifies this?
Thanks
hago
You can try one more way:
If you have native windows, install virtual machine software such as
Virtual box. Get your favourite Linux distribution (no bias, just
an example - Ubuntu) and install it through Virtual box.
Get the latest kernel (or of your choice) from kernel.org.
Choose the platform you want to build this kernel for. E.g arm64 or x86.
In case you do not have real boards (e.g RPi for arm variant), you can use qemu-arm64 or qemu-x86 to run your compiled kernel. This is also a good option when users do not have the boards.
Another good use case for using qemu for the newbie kernel developers is even they write some modules which crashes, then the qemu instance is crashed so no harm.
I think using qemu is a good option for people who starts to learn kernel programming and also want to try writing some of their modules and do not intend to purchase hardware at this point of time.
It depends on your target. For your case, you have made a kernel driver for your computer (it run Linux kernel).
But if you want to develop a Kernel driver for another target like Rasberry Pi, ARM board, X86-X64 board, ... you must learn to compile, edit Kernel config, boot Kernel image, ... because each target has different kernel versions.
You can refer to this training for more detail: https://bootlin.com/training/embedded-linux/
I am studying Linux driver programming and in it, it is recommended that I work on self-compiled Linux kernels and not any distributions. I have tried compiling Linux 2.6.9 in ubuntu but the process returns errors in 'make menuconfig' stage.
I would prefer to work with Linux in a virtual environment so that I can fearlessly experiment with the kernel. So, is there any way I can compile and run Linux in a virtual machine (say VMware installed on Windows)? I can use live CDs for the purpose of compiling the kernel.
So in short, please suggest, how can I compile, install and run Linux kernel in a virtual machine in an error-free way?
I searched and read this. But after following these steps when I restarted my computer there was no separate Linux 3.2.17 OS. But my ubuntu 12.04 was now showing 3.2.17 kernel. Although this is the first time I could compile a whole kernel on ubuntu without any error, I want to load that kernel on other partition and use it as an independent OS. So, if anyone can tell, what to do in addition to the steps in the tutorial so that I can achieve this?
The simplest thing to do is probably to install some Linux distribution on a VM, such as VMWare or VirtualBox, and continue from there. You could try using a live-cd, but I'm guessing that the lack of persistent storage might get irritating. There are, of course, ways around that, but installing some distribution is probably simpler, and you don't really need that much disk space for it if all you want to do is compile a kernel.
If all you want to do is compile a kernel module, and if you already have some pre-installed Linux environment, you should also note that modern Linux installations allow you to compile modules without the need to re-compile the entire kernel. You will need the kernel source and headers, though. See, for example, this document.
And BTW, speaking of modern kernels, why did you choose to use 2.6.9? It's almost 8 years old by now. Newer kernels might actually be easier to develop for. Also, there's no guarantee that
modules developed with such an old kernel would still work with current ones.
I suggest you to read this page. This document shows you how to boot your personal kernel on qemu and how to use the debugger on it.
Kernelnewbies is the right place to start kernel hacking. This website contains a set of rich tutorials about kernel hacking and tweaking just for newbie Linux developers. Also, you can join the community and start contributing to some tiny Linux projects.
For a quick start, follow the instruction from the "kernel first patch" tutorial. Since you're cloning the "origin" remote repository in this tutorial, you'll work on the latest branches of Linux kernel. So, there's no need to worry about working on an old version of Linux. Meanwhile, if you're not comfortable working with git trees, you can always download the latest version of Linux from front page of "kernel.org".
I am aware of windows kernel but new to linux kernel. I just need to know how its done in linux, i.e. the program development.
You can check there (free-electrons.com), it's a good informations source for kernel developement. (specialized in embedded linux, but most of the docs are available for standard development)
You have also the classical Linux Devices Drivers, which is very complete and detailled.
And last but not least, the Linux kernel documentation.
Linux does not have a stable kernel API. This is by design, so you should generally avoid writing kernel code if you can; it is unlikely to remain source-compatible indefinitely, and will definitely NOT be binary-compatible, even between minor releases.
This is less-or-more true for vendor kernels; Redhat etc DO maintain source & binary kernel compatibility between major revisions.
More work is gradually being done in the kernel to reduce the amount of kernel-code required to carry out various tasks, such as driver development (for example, USB drivers can typically be done in userspace with libusb), filesystem development (FUSE) and network filtering (NFQUEUE). However, there are still some cases where you need to; in particular, block devices still need to be in the kernel to be able to be usefully used for boot devices and swap.