LWN on Kernel: 5.12 Merge, Lockless Algorithms, and opy_file_range()

• 5.12 Merge window, part 1 [LWN.net]

  The beginning of the 5.12 merge window was delayed as the result of severe weather in the US Pacific Northwest. Once Linus Torvalds got going, though, he wasted little time; as of this writing, just over 8,600 non-merge changesets have been pulled into the mainline repository for the 5.12 release — over a period of about two days. As one might imagine, that work contains a long list of significant changes.

• An introduction to lockless algorithms [LWN.net]

  Low-level knowledge of the memory model is universally recognized as advanced material that can scare even the most seasoned kernel hackers; our editor wrote (in the July article) that "it takes a special kind of mind to really understand the memory model". It's been said that the Linux kernel memory model (and in particular Documentation/memory-barriers.txt) can be used to frighten small children, and the same is probably true of just the words "acquire" and "release". At the same time, mechanisms like RCU and seqlocks are in such widespread use in the kernel that almost every developer will sooner or later encounter fundamentally lockless programming interfaces. For this reason, it is a good idea to equip yourself with at least a basic understanding of lockless primitives. Throughout this series I will describe what acquire and release semantics are really about, and present five relatively simple patterns that alone can cover most uses of the primitives.

• How useful should copy_file_range() be? [LWN.net]

  Its job is to copy len bytes of data from the file represented by fd_in to fd_out, observing the requested offsets at both ends. The flags argument must be zero. This call first appeared in the 4.5 release. Over time it turned out to have a number of unpleasant bugs, leading to a long series of fixes and some significant grumbling along the way. In 2019 Amir Goldstein fixed more issues and, in the process, removed a significant limitation: until then, copy_file_range() refused to copy between files that were not located on the same filesystem. After this patch was merged (for 5.3), it could copy between any two files, falling back on splice() for the cross-filesystem case. It appeared that copy_file_range() was finally settling into a solid and useful system call. Indeed, it seemed useful enough that the Go developers decided to use it for the io.Copy() function in their standard library. Then they ran into a problem: copy_file_range() will, when given a kernel-generated file as input, copy zero bytes of data and claim success. These files, which include files in /proc, tracefs, and a large range of other virtual filesystems, generally indicate a length of zero when queried with a system call like stat(). copy_file_range(), seeing that zero length, concludes that there is no data to copy and the job is already done; it then returns success. But there is actually data to be read from this kind of file, it just doesn't show in the advertised length of the file; the real length often cannot be known before the file is actually read. Before 5.3, the prohibition on cross-filesystem copies would have caused most such attempts to return an error code; afterward, they fail but appear to work. The kernel is happy, but some users can be surprisingly stubborn about actually wanting to copy the data they asked to be copied; they were rather less happy.

Banana Pi BPI-M2 Pro is a compact Amlogic S905X3 SBC

Banana Pi has already designed an Amlogic S905X3 SBC with Banana Pi BPI-M5 that closely follows Raspberry Pi 3 Model B form factor, but they’ve now unveiled a more compact model with Banana Pi BPI-M2 Pro that follow the design of the company’ earlier BPI-MP2+ SBC powered by the good old Allwinner H3 processor. BPI-M2 Pro comes with 2GB RAM, 16GB eMMC storage, HDMI video output, Gigabit Ethernet, Wifi & Bluetooth connectivity, as well as two USB 3.0 ports.

Chrome 89 vs. Firefox 86 Performance Benchmarks On AMD Ryzen + Ubuntu Linux

Given this week's launch of Chrome 89 and the recent Firefox 86 debut, here are some quick benchmarks for those curious about the current performance when using Ubuntu Linux with a AMD Ryzen 9 5900X and Radeon graphics. Curious about the latest standing of the newest Firefox and Chrome releases on Linux, here are some quick benchmarks carried out on one of the systems locally. A larger comparison will come soon while this is just a quick one-page article for those eager to see some new browser numbers for AMD on Linux. The Ryzen 9 5900X was at stock speeds - the reported CPU frequency is due to a kernel bug working its way to 5.11/5.10 stable still.

today's howtos

• How to install Budgie desktop on Manjaro

  Budgie is an elegant and simplified desktop environment that integrates very well with Manjaro. Budgie is developed and maintained by the Solus team. This article will delve into the details of everything you need to know while installing the Budgie Desktop on Manjaro.

• How To Update Fedora Linux using terminal to apply updates - nixCraft

  I recently switched from Windows server to Fedora 32/33 server running in the cloud. How do I apply software updates and patches on Fedora 32/33 server using the terminal application? Fedora Linux uses dnf command. It is the next upcoming major version of yum command. Yum is a package manager for RPM-based Linux distributions such as CentOS/RHEL 7.x and older version of Fedora Linux. You need to use the dnf command to update Fedora Linux using terminal for latest software patches. This page explains how to update a Fedora Linux using the terminal.

• How to Turn Off Automatic Brightness on Ubuntu Linux

  Some new laptops come with built-in integrated light sensor. Operating systems use this sensor to measure the ambient light conditions and change the screen brightness automatically. This helps in reducing eye strain. You can see that this is a useful feature. But not everyone might like it all the time. For example, while watching Netflix on Linux at night, it reduces the screen brightness at the lowest for me. This makes the movie scene quite dull. This is one of the many cases when you probably would not want automatic brightness. Turning off automatic brightness on Ubuntu is quite simple. I’ll show that to you in this quick article. This tutorial is valid for GNOME desktop environment. The command line method should work for MATE desktop as well. If you are not certain, check which desktop environment you are using.

• MultiCD - A Shell Script to Combine Multiple Bootable ISO's into One CD

  If you’ve ever used a multiboot CD that contains different utilities or bootable ISOs then creating one for yourself would be amazing. In this article, we shall take a look at MultiCD.sh, a shell script that is designed to help you build a multiboot CD image that can contain different, small Linux distros and/or utilities. There are many advantages of using this script and they include among others; no need for different CDs for small Linux distributions or utilities, you can simply use ISO images that you already have without downloading them again and in case of new versions, simply download them and run the script again and build a new multiboot image.

• Linux Sponge - Soak Up Standard Input and Write to a File - Putorius

  The sponge command is part of the moreutils package. It is a utility that provides a function that is so simple it’s genius. It’s basic use is to soak up (get it? sponge..) standard input and write it to a file. The terminology “soak up” is more important than just creating a fun play on words. In this short tutorial we show you the sponge commands basic usage and why the term “soak up” is important.