Introduction It’s rarely necessary to make an issue of installing and maintaining the GRUB bootloader. However, for reasons explained in a separate post, I wanted to install GRUB 2.12 on an old distribution (Debian 8). So it required some acrobatics. That said, it doesn’t limit the possibility to install new kernels in the future etc. [...]
Introduction My Debian 8-based web server had been running for several years as an OpenVZ container, when the web host told me that containers are phased out, and it’s time to move on to a KVM. This is an opportunity to upgrade to a newer distribution, most of you would say, but if a machine [...]
Introduction This post is a spin-off from another post of mine. It’s the result of my wish to limit the battery’s charge level, so it doesn’t turn into a balloon again. I’ve written this post in chronological order (i.e. in the order that I found out things). If you’re here for the “what do I [...]
Just in case this helps anyone, this is the output of the dmesg command. The phone was rooted with Magisk, or else how would I get this? But at this stage, I hadn’t install Zygisk or any other module to hide the fact that the phone is rooted. Note that there’s also logcat for the [...]
Introduction Since I maintain a module in the Linux kernel, I also need to maintain its documentation. Sometime in the past, the rst format was adopted for files under Documentation/ in the kernel tree, with Sphinx chosen as the tool for making formatted documents. Which is pretty nice, as rst human readable and can also [...]
After making a lot of whitespace reorganization in a kernel module (indentation, line breaks, fixing things reported by sparse and checkpatch), I wanted to make sure I didn’t really change anything. All edits were of the type that the compiler should be indifferent about, but how can I be sure I didn’t change anything accidentally? [...]
Upgrading the kernel should be quick and painless… After upgrading the kernel from v5.3 to 5.7, a lot of systemd services failed (Debian 8), in particular systemd-remount-fs: ● systemd-remount-fs.service – Remount Root and Kernel File Systems Loaded: loaded (/lib/systemd/system/systemd-remount-fs.service; static) Active: failed (Result: exit-code) since Sun 2020-07-26 15:28:15 IDT; 17min ago Docs: man:systemd-remount-fs.service(8) http://www.freedesktop.org/wiki/Software/systemd/APIFileSystems Process: [...]
What’s this Every now and then I find myself looking at an Oops or kernel panic, reminding myself how to approach this. So this is where I write down the jots as I go. This isn’t very organized. Disassembly First thing first: Disassemble the relevant parts: $ objdump -DS driver.ko > ~/Desktop/driver.asm Doing this on [...]
Introduction I ran into ftrace completely by chance, while trying to figure out why the call to usb_submit_urb() took so long time. In fact, it wasn’t. It was pr_info() that delayed the output. And it was ftrace that got me to realize that. Whether you’re into dissecting existing kernel code, and want to know which [...]
Introduction Most device drivers hook onto an already existing subsystem: Audio, networking, I2C, whatever. If it’s a specialized piece of hardware, a single device file is typically enough, and you get away with a misc device or, as shown in the kernel’s USB example (drivers/usb/usb-skeleton.c), with the USB framework’s usb_register_dev() call. However in some cases, [...]