Back In Time is a GPL-2.0-licensed backup tool based on rsync and written in Python. It has both graphical and command-line interfaces, and supports backups to local disks or over SSH. Back In Time was originally written by Oprea Dan and released in 2009. The tool has been through some rough patches over the years, and is currently on its third set of maintainers. Christian Buhtz, one of the current maintainers, explained to me how he and his co-maintainers had revived the project, as well as why he thought Back In Time stood out from all of the existing backup solutions.

Greg Kroah-Hartman has shared another seven stable kernel updates: 6.6.60, 6.11.7, 6.1.116, 5.15.171, 5.10.229, 5.4.285, and 4.19.323.

Image-based Linux distributions have seen increasing popularity, recently. They promise reliability and security, but pose packaging problems for existing distributions. Ryan Lahfa and Niklas Sturm spoke about the work that NixOS has done to enable an image-based workflow at this year's All Systems Go! conference in Berlin. Unfortunately, LWN was not able to cover the conference for scheduling reasons, but the videos of the event are available for anyone interested in watching the talks. Lahfa and Sturm explained that it is currently possible to create a NixOS system that cryptographically verifies the kernel, initrd, and Nix store on boot — although doing so still has some rough edges. Making an image-based NixOS installation is similarly possible.

Joshua Liebow-Feeser took to the stage at RustConf to describe the methodology that his team uses to encode arbitrary constraints in the Rust type system when working on the Fuchsia operating system (slides). The technique is not unknown to the Rust community, but Liebow-Feeser did a good job of both explaining the method and making a case for why it should be used more widely.

Greg Kroah-Hartman has released another four stable Linux kernel updates: 6.11.6, 6.6.59, 6.1.115, and 5.15.170.

The first program that Martin Pool ever wrote, he said, had bugs; the ones he's writing now most likely have bugs too. The talk Pool gave at RustConf this year was about a way to try to write programs with fewer bugs. He has developed a tool called cargo-mutants that highlights gaps in test coverage by identifying functions that can be broken without causing any tests to fail. This can be a valuable complement to other testing techniques, he explained.

Sparrow Li presented virtually at RustConf 2024 about the current state of and future plans for the Rust compiler's performance. The compiler is relatively slow to compile large programs, although it has been getting better over time. The next big performance improvement to come will be parallelizing the compiler's parsing, type-checking, and related operations, but even after that, the project has several avenues left to explore.

Currently in Rust, there is no efficient and safe way to turn an array of bytes into a structure that corresponds to the array. Changing that was the topic of Jack Wrenn's talk this year at RustConf: "Safety Goggles for Alchemists". The goal is to be able to "transmute" — Rust's name for this kind of conversion — values into arbitrary user-defined types in a safer way. Wrenn justified the approach that the project has taken to accomplish this, and spoke about the future work required to stabilize it.

The Image-Based Linux Summit has by now established itself as a yearly event. Following on from last year's edition, the third edition was held in Berlin on September 24, the day before All Systems Go! 2024 (ASG). The purpose of this event is to gather stakeholders from various engineering groups and hold friendly but lively discussions around the topic of image-based Linux — that is, Linux distributions based around immutable images, instead of mutable root filesystems.

The Guix project has disclosed a security vulnerability in the build daemon that the distribution uses to build and install software locally. The vulnerability allows an existing unprivileged user to get access to a setuid binary, and from there potentially interfere with any other software built or installed on the computer. The project recommends upgrading the guix daemon now, to avoid the issue.

This exploit requires the ability to start a derivation build and the ability to run arbitrary code with access to the store in the root PID namespace on the machine the build occurs on. As such, this represents an increased risk primarily to multi-user systems and systems using dedicated privilege-separation users for various daemons: without special sandboxing measures, any process of theirs can take advantage of this vulnerability.

Rust, like C, has its own memory model describing how concurrent access to the same data by multiple threads can behave. The Linux kernel, however, has its own ideas. The Linux kernel memory model (LKMM) is subtly different from both the standard C memory model and Rust's model. At Kangrejos, Boqun Feng gave a presentation about the need to reconcile the memory models used by Rust and the kernel, including a few potential avenues for doing so. While no consensus was reached, it is an area of active discussion.

Paul McKenney gave a presentation at Kangrejos this year that wasn't (directly) related to Rust. Instead, he spoke about the work he has been doing in concert with many other contributors on improving the handling of subtle concurrency problems in C++. Although he cautioned that his talk was only an overview, and not a substitute for reading the relevant papers, he hoped that the things the C++ community is working on would be of interest to the Rust developers present as well, and potentially inform future work on the language. McKenney's talk was, as is his style, full of subtle examples of weird multithreaded behavior. Interested readers may wish to refer to his slides in an attempt to follow along.

At Kangrejos, Gary Guo wanted to discuss three problems with the way Rust and C code in the kernel interact: mismatched types, too many type casts, and the overhead of helper functions. To fix the first two problems, Guo proposed changing the way the kernel maps C types into Rust types. The last problem was a bit trickier, but he has a clever workaround for that, based on tricking the compiler into inlining the helper functions across language boundaries.

Bindgen is a widely used tool that automatically generates Rust bindings from C headers. The Rust-for-Linux project uses it to create some of the bindings between Rust code and the rest of the kernel. John Baublitz presented at Kangrejos about the improvements that he has made to the tool in order to make the generated bindings easier to use, including improved support for macros, bitfields, and enums.