Marcus Folkesson

Embedded Linux Artist

Expose network namespace created by Docker

Expose network namespace created by Docker Disclaimer: this is probably *not* the best way for doing this, but it's pretty good for educational purposes. During a debug session I wanted to connect an application to a service tha ran in a docker container. This was for test-purposes only, so hackish and fast are the keywords. First of all, I'm not a Docker expert, but I've a pretty good understanding on Linux internals, namespaces and how things works on a Linux system.

Posted by Marcus Folkesson on Wednesday, December 20, 2023

Skip flashing unused blocks with UUU

Skip flashing unused blocks with UUU TL;DR: UUU does now (or will shortly) support blockmaps for flashing images. Use it. It will shorten your flashing time *a lot.* It will soon be time to manufacture circuit boards for a project I'm currently working on. After manufacturing, it will need some firmware for sure, but how do we flash it in the most efficient way? The board is based on an i.

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Posted by Marcus Folkesson on Monday, December 11, 2023

Mutex guards in the Linux kernel

Mutex guards in the Linux kernel I found an interresting thread [1] while searching my inbox for something completely unrelated. Peter Zijistra has written a few cleanup functions that where introduced in v6.4 with this commit: commit 54da6a0924311c7cf5015533991e44fb8eb12773 Author: Peter Zijlstra <peterz@infradead.org> Date: Fri May 26 12:23:48 2023 +0200 locking: Introduce __cleanup() based infrastructure Use __attribute__((__cleanup__(func))) to build: - simple auto-release pointers using __free() - 'classes' with constructor and destructor semantics for scope-based resource management.

Posted by Marcus Folkesson on Friday, December 1, 2023

Test packages in Buildroot

Test packages in Buildroot When writing packages for Buildroot there are several conditions that you have to test your package against. This includes different toolchains, architectures, C-libraries, thread-implementations and more. To help you with that, Buildroot provides the utils/test-pkg script. Nothing describes the script better than its own help text [1]: test-pkg: test-build a package against various toolchains and architectures The supplied config snippet is appended to each toolchain config, the resulting configuration is checked to ensure it still contains all options specified in the snippet; if any is missing, the build is skipped, on the assumption that the package under test requires a toolchain or architecture feature that is missing.

Posted by Marcus Folkesson on Tuesday, November 28, 2023

TIL - docker scratch image

TIL - Docker scratch image TIL, Today I Learned, is more of a "I just figured this out: here are my notes, you may find them useful too" rather than a full blog post The scratch image is the smallest possible image for docker. It does not contain any libraries nor other executables. It is simply a new, fresh and empty setup of namespaces. The FROM scratch line is even a no-op [1] in the Dockerfile, which results in that it will not create an extra layer in you image.

Posted by Marcus Folkesson on Wednesday, November 15, 2023

Git version in cmake

Git version in CMake All applications have versions. The version should somehow be exposed in the application to make it possible to determine which application we are actually running. I've seen a plenty of variants on how this is achieved, some are good and some are really bad. Since it's such a common thing, I thought I'd show how I usually do it. I use to let CMake determine the version based on git describe and tags, the benefit's that it is part of the build process (i.

Posted by Marcus Folkesson on Tuesday, November 14, 2023

TIL - sort in vim

TIL - Sort in VIM TIL, Today I Learned, is more of a "I just figured this out: here are my notes, you may find them useful too" rather than a full blog post After 15+ years of daily VIM usage I just discovered the :sort function. Quite embarassing. It is also possible to sort in revese ( :sort!) and remove duplicate lines ( :sort u).

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Posted by Marcus Folkesson on Thursday, November 2, 2023

Burn eFuses for MAC address on iMX8MP

Burn eFuses for MAC address on iMX8MP The iMX (iMX6, iMX7, iMX8) has a similiar OCOTP (On-Chip One Time Programmable) module that store, for example the MAC addresses for the internal ethernet controllers. The reference manual is not clear either on the byte order or which bytes belong to which MAC address when there are several. In fact, I had to look at the U-boot implementation [1] to know for sure how these fuses is used:

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Posted by Marcus Folkesson on Saturday, October 28, 2023

Loopback with two (physical) ethernet interfaces

Loopback with two (physical) ethernet interfaces Imagine that you have an embedded device with two physical ethernet ports. You want to verify the functionality of both these ports in the manufacturing process, so you connect an ethernet cable between the ports, setup IP addresses and now what? As Linux (actually the default network namespace) is aware of the both adapters and their IP/MAC-addresses, the system see no reason to send any traffic out.

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Posted by Marcus Folkesson on Saturday, October 21, 2023

TIL - notmuch-lore

TIL - notmuch-lore TIL, Today I Learned, is more of a "I just figured this out: here are my notes, you may find them useful too" rather than a full blog post Notmuch [1] is an mail indexer and is a great tool to search in high-volume mailboxes (e.g. mailing lists). Being subscribed to all these mailing lists and retreiving all mails over IMAP daily could be quite annoying and harm your mail quota.

Posted by Marcus Folkesson on Saturday, October 21, 2023