I am trying to access tcp_pacing_ss_ratio defined in tcp_input.c from a kernel module. The variable can be modified using the sysctl command in user space. It is however not exported and cannot be referenced directly from the module. What is the simplest way to access a sysctl entry from a kernel module? Answ…
Tag: linux-kernel
Why can’t I mmap(MAP_FIXED) the highest virtual page in a 32-bit Linux process on a 64-bit kernel?
While attempting to test Is it allowed to access memory that spans the zero boundary in x86? in user-space on Linux, I wrote a 32-bit test program that tries to map the low and high pages of 32-bit virtual address space. After echo 0 | sudo tee /proc/sys/vm/mmap_min_addr, I can map the zero page, but I don…
Reverse engineering a zImage
So I have a custom kernel for an embedded arm device which I had worked on some time ago. I’ve revisited the project but since have reinstalled Ubuntu on my development machine. I can’t compile a new zImage correctly as before. I have found an old SD which card which has the correctly compiled and…
Error while creating react-native app in linux
I have installed node and checked it as the node js docs suggested by doing node -v and npm version and I got the same expected results as they showed in the docs But I couldnt run npm install -g react-native-cli This is the error that I get : Answer You need to use Or run your npm install as
How to debug USB HID scancode-keycode translation in Linux
I have recently converted a 122-key terminal keyboard to USB as a configfs USB gadget (the keyboard portion is using HID codes), it works quite well in except that I cannot seem to get my Archlinux installation to recognize certain HID codes (specifically at the moment F13-F24) and translate them into event c…
Error initialization from incompatible pointer of IOCTL function in Linux kernel 4.8.0-53-generic Linux Mint 64 bit
I’ve got an error while writing a char device module, using Ioctl command. Note: please ignore all my print_k. Please, help me fix this. My thanks to all of you. Here is my code : Answer The third argument unsigned long arg[b] in the function prototype is dubious. It should be simply unsigned long arg e…
IRQCHIP_DECLARE: init function is not being run
I am trying to use the Xilinx interrupt controller driver in an embedded ARM FPGA system I am developing. (https://github.com/torvalds/linux/blob/master/drivers/irqchip/irq-xilinx-intc.c) At the end of this driver is the line: IRQCHIP_DECLARE(xilinx_intc_xps, “xlnx,xps-intc-1.00.a”, xilinx_intc_of…
Get all mount points in kernel module
I’m trying to get all the mount points in a kernel module. Below is what I’ve come up with. It segfaults because of the strcat. Is this the correct way to get the mount points? Will this work? if so how do i fix the segfault? If not, how does one go about getting the mount points in a linux
How to proceed with Linux source code customization?
I am a non CS/IT student, but having knowledge of C, Java, DS and Algorithms. Now-a-days I am focusing on operating system and had gained some of its concepts. But I want some practical knowledge of it. Merely writing algo code in java/c has no fun in doing. I have gone through many articles where they mentio…
In the kernel space, how does one get the physical addresses corresponding to a file on ext4-formatted disk
If you’re here: https://github.com/torvalds/linux/blob/master/fs/ext4/file.c#L360 You have access to these two structs inside the ext4_file_mmap function: I am changing the implementation of this function for dax mode so that the page tables get entirely filled out for the file the moment you call mmap …