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Rust is making progress with Linux 6.11. Linux creator Torvalds introduces “Runtime Constants”. Old Unix behavior is put to the test.

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The latest version of the Linux kernel was released overnight from Sunday to Monday. The anticipated “extensible scheduler” was not included in Linux 6.11 as expected. Instead, Linux creator Torvalds introduced a new feature called “runtime constants.” Additionally, the integration of Rust continues to make progress.

Despite Linus Torvalds’ intentions to integrate the extensible scheduler sched_ext into Linux 6.11, it was omitted from the release. Torvalds had previously expressed a reluctance to delay the implementation of the scheduler, which is based on eBPF. Developers are expected to collaborate to address any issues that arise with it in the mainline kernel. Torvalds reiterated his preference against adding features developed externally to the kernel, as had been the case with the extensible scheduler.

Following Torvalds’ announcement to include the eBPF-based scheduler, compatibility problems arose within the kernel. The scheduler’s integration wasn’t as seamless as hoped, leading Torvalds to exclude the over 14,000 lines of related code submitted by Tejun Heo in his Linux 6.11 pull request, which Torvalds did not publicly comment on.

However, a comment by Qais Yousef suggests potential reasons for the rejection. Yousef mentioned that the integration of sched_ext could result in substantial changes to kernel behavior, potentially impacting the reliability of bug and regression reports. The rushed inclusion might be misguided, thus leaving sched_ext excluded from this release. The timeline for its eventual inclusion in the mainline kernel remains uncertain.

The latest kernel update now allows for Rust-based driver programming for block-oriented devices. This advancement means that it is now possible to develop drivers in Rust for devices like hard disks and DVD drives. Initially, this feature is utilized by the zero-block driver, aiming to facilitate the creation of more block device drivers directly in Rust within the mainline kernel.

The zero-block driver serves to simulate block-oriented devices, appearing as /dev/nullb0, /dev/nullb1, etc. Primarily used for block layer benchmarking, this driver is not designed for production environments but rather for development and testing purposes. It features straightforward C code making it an exemplary candidate for initial experiments with block device driver development in Rust.

The Rust-based driver, named rnull, can be enabled via the kernel configuration process (make menuconfig), found under block devices as BLK_DEV_RUST_NULL. When activated, rnull serves as an experimental variant of the conventional null block device, although it is a simplified version of its C counterpart.

Moreover, a new abstraction layer for the Linux firmware API has been introduced. This represents an initial step toward implementing firmware loading directly from Rust code. The API facilitates the updating of firmware from user-space, addressing issues like processor microcode errors or updating firmware on various hardware components like storage devices, expansion cards, and controllers.

This abstraction layer is necessary to be able to program “real” drivers for devices in Rust in the future. Finally, practical Rust drivers will also be able to adapt the firmware of the associated devices. Another piece of the puzzle for the overall picture of “device drivers in Rust” has thus been laid. However, a few more pieces are still missing before any drivers can be programmed in Rust in the same way as in C. The gaps in the picture are slowly but surely shrinking.

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