Kernel watch

Jon Masters summarises the latest happenings in the Linux kernel, so you don’t have to.

Jon Masters is late as always…

Linus Torvalds announced the release of Linux 5.11, just in time for Valentine’s Day 2021. In his announcement, Linus noted that just because it was Valentine’s Day didn’t mean it wasn’t a good time to do some kernel testing, “Because I’m sure your SO [Significant Other] will understand”. The new kernel includes many features. Among them is support for faster system call emulation in Wine, the ability to have unprivileged Overlayfs mounts, and support for Intel’s Software Guard Extensions (SGX). We’ve previously covered the saga that was the implausibly long journey toward the merging of SGX after many dozens of tries.

The announcement of Linux 5.11 would ordinarily lead to the immediate opening of the “merge window” for Linux 5.12. The merge window was delayed this time, however, on account of the ongoing severe weather affecting the Pacific North West of the US. Linus lives in Portland, Oregon, which hasn’t been in the news as much as Texas of late, but has also suffered power failures. It’s presumed that normal operations will resume within the next week or so. Many users who want to run Windows binaries on their Linux system will no doubt be familiar with Wine (“Wine Is Not an Emulator”). The newly added system call “user dispatch” feature makes it straightforward for an application such as Wine to toggle a trap on any attempt by the program it’s emulating to perform native system calls. This quickly enables the emulator to provide the expected Windows behaviour. It’ll be interesting to see how much speedup this offers for Windows applications.

Overlayfs is used to mount overlays. These are parts of a filesystem that override the content of another. They were originally useful in embedded Linux systems, such as network routers, where a read-write filesystem could replace or otherwise augment binaries and configuration files contained on read-only storage. Later, overlays became a part of the container experience. Modern containers are formed from layers that override other layers, often mounted using Overlayfs. Reducing privilege required to use them is a good thing.

As usual, Linux Kernel Newbies covers the new features in depth at: https://kernelnewbies.org/Linux_5.11.