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Direct memory access (DMA) I/O is simple in concept: a peripheral device moves data directly to or from memory while the CPU is busy doing other things. As is so often the case, DMA is rather more complicated in practice, and the kernel has developed a complicated internal API to support it. It turns out that the DMA API, as it exists now, can affect the performance of some high-bandwidth devices. In an effort to address that problem, Leon Romanovsky is making the API even more complex with this patch series adding a new two-step mapping API.

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Programming language polyglots are files that are valid programs in multiple languages, and do different things in each. While polyglots are normally nothing more than a curiosity, the Cosmopolitan Libc project has been trying to put them to a novel use: producing native, multi-platform binaries that run directly on several operating systems and architectures. There are still some rough edges with the project's approach, but it is generally possible to build C programs into a polyglot format with with minimal tweaking.

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Over the years, there has been steady progress in adding security features to compilers and other tools to assist with hardening the Linux kernel (and, of course, other programs). In something of a tradition in the toolchains track at the Linux Plumbers Conference, Kees Cook and Qing Zhao have led a session on that progress and further plans; this year, they were joined by Justin Stitt (YouTube video).

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What have been the most significant security-related incidents for the open-source community in 2024 (so far)? Marta Rybczyńska recently ran a poll and got some interesting results. At the 2024 Open Source Summit Japan, she presented those results along with some commentary of her own. The events in question are unlikely to be a surprise to LWN readers, but the overall picture that was presented was worth a look.

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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.

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Fedora Linux, as a rule, handles version upgrades reasonably well. However, there are times when users may want to do a fresh installation rather than an upgrade but preserve existing users and data under /home. This is a scenario that the Fedora installer, currently, does not address. Users can maintain a separate /home partition, of course, but the installer does not incorporate existing users into the new install—that is an exercise left to the user to handle. One solution might be to use systemd-homed, a systemd service for managing users and home directories. However, a discussion proposing the use systemd-homed as part of Fedora installation uncovered some hurdles, such as trying to blend its approach to managing users with tools that centralize user management.

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Flexible arrays — arrays that are declared as the final member of a structure and which have a size determined at run time — have long drawn the attention of developers seeking to harden the kernel against buffer-overflow vulnerabilities. These arrays have reliably been a source of bugs, so anything that can be done to ensure that operations on them stay within bounds is a welcome improvement. While many improvements, including the recent counted-by work, have been made, one of the most difficult cases remains. Now, however, developers who are interested in using recent compiler bounds-checking features are trying to get a handle on struct sockaddr.

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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.

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