Linux: Atheros QCA6174′s Bluetooth disappearing after reboot
When Bluetooth goes poof Having rebooted my computer after a few months of continuous operation, I suddenly failed to use my Bluetooth headphones. It took some time to figure out that the problem...
View Articlexhci_hcd WARN Event TRB for slot x ep y with no TDs queued
What’s this? There’s a chance that you’re reading this because the message in the title appeared (or flooded) your kernel log. This post attempts to clarify what to do about it, depending on how much...
View ArticleLinux CUSE (and FUSE): Why I ditched two months of work with it
Introduction If you’re planning to use CUSE (or FUSE) for an application you care about, this post is for you. That includes future self. I’m summarizing my not-so-pleasant journey with this framework...
View ArticleFUSE / CUSE signal handling: The very gory details
First: If you’re planning on using FUSE / CUSE for an application, be sure to read this first. It also explains why I didn’t just take what libfuse offered. Overview This is a detour from another post...
View ArticleFUSE / CUSE kernel driver dissection notes
What this post is about Before anything: If you’re planning on using FUSE / CUSE for an application, be sure to read this first. It also explains why I bothered looking at the kernel code instead of...
View Articleusbpiper: A single-threaded /dev/cuse and libusb-based endpoint to device...
Introduction Based upon CUSE, libusb and the kernel’s epoll capability, this is a single-threaded utility which generates one /dev/usbpiper_* device file for each bulk / interrupt endpoint on a USB...
View ArticleJots on named pipes (FIFOs in Linuxish)
Major disclaimer These are pretty random jots that I made while evaluating named pipes as a solution for project. I eventually went for a driver in the kernel for various reasons, so I never got to...
View ArticleLinux kernel programming: Do I need a lock?
Introduction Writing a device driver for Linux (or other kernel programming) always requires keeping parallel execution in mind. It’s often enough to follow common programming patterns, using spinlocks...
View ArticleLinux driver: Creating device files for a hotpluggable device
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...
View ArticleFtrace: The Linux kernel hacker’s swiss knife
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...
View ArticleLinux kernel OOPS dissection notes
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....
View ArticleRoot over NFS remains read only with Linux v5.7
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: ●...
View ArticleLinux kernel: Dumping a module’s content for regression check
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....
View ArticleSetting up a small Sphinx project for validating Linux kernel documentation...
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...
View Articledmesg output of a Google Pixel 6 Pro
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...
View Articleusbpiper: A single-threaded /dev/cuse and libusb-based endpoint to device...
Introduction Based upon CUSE, libusb and the kernel’s epoll capability, this is a single-threaded utility which generates one /dev/usbpiper_* device file for each bulk / interrupt endpoint on a USB...
View ArticleJots on named pipes (FIFOs in Linuxish)
Major disclaimer These are pretty random jots that I made while evaluating named pipes as a solution for project. I eventually went for a driver in the kernel for various reasons, so I never got to...
View ArticleLinux kernel programming: Do I need a lock?
Introduction Writing a device driver for Linux (or other kernel programming) always requires keeping parallel execution in mind. It’s often enough to follow common programming patterns, using spinlocks...
View ArticleLinux driver: Creating device files for a hotpluggable device
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...
View ArticleFtrace: The Linux kernel hacker’s swiss knife
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...
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