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[$] A generic ring buffer for the kernel
The kernel's user-space ABI does not lack for ring buffers; they have been defined for subsystems like BPF, io_uring, perf, and tracing, for example. Naturally, each of those ring buffers is unique, with no common interface between them. The natural response to this ABI proliferation is, of course, to add yet another ring buffer as the generic option; that is the intent of this patch series from Kent Overstreet adding a new set of system calls for ring buffers.
[$] LWN.net Weekly Edition for June 6, 2024
Posted Jun 6, 2024 1:12 UTC (Thu)The LWN.net Weekly Edition for June 6, 2024 is available.
Inside this week's LWN.net Weekly Edition
- Front: PostgreSQL CommitFests; Tmpfs on Debian; Pidfdfs; More LSFMM+BPF coverage.
- Briefs: Maintainers Summit CFP; F40 election; FreeBSD 14.1; Incus 6.2; KDE Eco; LyX 2.4.0; Mike Karels; New comment feature; Quotes; ...
- Announcements: Newsletters, conferences, security updates, patches, and more.
[$] Measuring and improving buffered I/O
There are two types of file I/O on Linux, buffered I/O, which goes through the page cache, and direct I/O, which goes directly to the storage device. The performance of buffered I/O was reported to be a lot worse than direct I/O, especially for one specific test, in Luis Chamberlain's topic proposal for a session at the 2024 Linux Storage, Filesystem, Memory Management, and BPF Summit. The proposal resulted in a lengthy mailing-list discussion, which also came up in Paul McKenney's RCU session the next day; Chamberlain led a combined storage and filesystem session to discuss those results with an eye toward improving buffered I/O performance.
[$] Rethinking the PostgreSQL CommitFest model
Many years ago, the PostgreSQL project started holding regular CommitFests to help tackle the work of reviewing and committing patches in a more organized fashion. That has served the project well, but some in the project are concerned that CommitFests are no longer meeting the needs of PostgreSQL or its contributors. A lengthy discussion on the pgsql-hackers mailing list turned up a number of complaints, a few suggestions for improvement, but little consensus or momentum toward a solution.
[$] Removing GFP_NOFS
The GFP_NOFS flag is meant for kernel memory allocations that should not cause a call into the filesystems to reclaim memory because there are already locks held that can potentially cause a deadlock. The "scoped allocation" API is a better choice for filesystems to indicate that they are holding a lock, so GFP_NOFS has long been on the chopping block, though progress has been slow. In a filesystem-track session at the 2024 Linux Storage, Filesystem, Memory Management, and BPF Summit, Matthew Wilcox wanted to discuss how to move kernel filesystems away from the flag with the eventual goal of removing it completely.
[$] Comparing BPF performance between implementations
Alan Jowett returned for a second remote presentation at the 2024 Linux Storage, Filesystem, Memory Management, and BPF Summit to compare the performance of different BPF runtimes. He showed the results of the MIT-licensed BPF microbenchmark suite he has been working on. The benchmark suite does not yet provide a good direct comparison between all platforms, so the results should be taken with a grain of salt. They do seem to indicate that there is some significant variation between implementations, especially for different types of BPF maps.
[$] Handling the NFS change attribute
The saga of the i_version field for inodes, which tracks the occurrence of changes to the data or metadata of a file, continued in a discussion at the 2024 Linux Storage, Filesystem, Memory Management, and BPF Summit. In a session led by Jeff Layton, who has been doing a lot the work on changing the semantics and functioning of i_version over the years, he updated attendees on the status of the effort since a session at last year's summit. His summary was that things are "pretty much where we started last year", but the discussion this time pointed to some possible ways forward.
[$] An instruction-level BPF memory model
There are few topics as arcane as memory models, so it was a pleasant surprise when the double-length session on the BPF memory model at the Linux Storage, Filesystem, Memory Management, and BPF Summit turned out to be understandable. Paul McKenney led the session, although he was clear that the work he was presenting was also due to Puranjay Mohan, who unfortunately could not attend the summit. BPF does not actually have a formalized memory model yet; instead it has relied on a history of talks like this one and a general informal understanding. Unfortunately, ignoring memory models does not make them go away, and this has already caused at least one BPF-related bug on weakly-ordered architectures. Figuring out what a formal memory model for BPF should define was the focus of McKenney's talk.
[$] Debian's /tmpest in a teapot
Debian had a major discussion
about mounting /tmp as a RAM-based tmpfs in 2012 but inertia
won out in the end. Debian systems have continued to
store temporary files on disk by default. Until now. A mere
12 years later, the project will be switching to a RAM-based /tmp in the Debian
13 ("Trixie") release. Additionally, starting with Trixie, the
default will be to periodically clean up temporary files automatically in
[$] One more pidfdfs surprise
The "pidfdfs" virtual filesystem was added to the 6.9 kernel release as a way to export better information about running processes to user space. It replaced a previous implementation in a way that was, on its surface, fully compatible while adding a number of new capabilities. This transition, which was intended to be entirely invisible to existing applications, already ran into trouble in March, when a misunderstanding with SELinux caused systems with pidfdfs to fail to boot properly. That problem was quickly fixed, but it turns out that there was one more surprise in store, showing just how hard ABI compatibility can be at times.
Security updates for Thursday
Security updates have been issued by AlmaLinux (cockpit, kernel, kernel-rt, libxml2, ruby:3.1, and tomcat), Debian (libarchive, pillow, and tinyproxy), Fedora (apptainer), Mageia (amavisd-new and libxml2), Oracle (edk2), Red Hat (booth, cockpit, kernel-rt, less, libxml2, nghttp2, ruby:3.1, ruby:3.3, and tomcat), Slackware (kernel), and Ubuntu (atril, bluez, frr, gdk-pixbuf, openjdk-17, openjdk-21, openjdk-8, openjdk-lts, qemu, and unixodbc).
Kali Linux 2024.2 released
Version 2024.2 of the Kali Linux penetration testing distribution has been released. This release includes an update to GNOME 46, a high-resolution (HiDPI) mode for Xfce, as well as a number of new packages such as the AutoRecon network reconnaissance tool, pspy command-line utility for snooping on Linux processes, and SploitScan tool for fetching and displaying CVE information. Kali Linux is based on Debian testing, and 2024.2 incorporates Debian's work to transition to 64-bit time_t to avoid year 2038 problems. Users with existing Kali systems should be sure to follow the documentation when upgrading.
FreeBSD 14.1 released
Version 14.1 of FreeBSD has been released. This is the second release of the 14.x stable branch. Highlights of this release include upgrades to OpenZFS 2.2.4, Clang/LLVM 18.1.5, and OpenSSH 9.7p1. FreeBSD 14.1 also features cloud-init support, sound subsystem improvements, and more. See the what's new blog post from the FreeBSD Foundation, release notes, and errata for more information.
The state of SourceHut
Drew DeVault has published an update about the state of the SourceHut software development platform and its plans for the coming months. This is the first update since the January post-mortem following a distributed denial-of-service (DDoS) attack that resulted in a prolonged outage:
As you can imagine, it has been a stressful time for us. However, I wish to stress that everything we've been dealing with is planned for in our models, both technical and financial. There is no existential threat to SourceHut. Nevertheless, we are grateful for your patience and support.
[...] We have been focusing on two things this year: provisioning and managing our infrastructure and getting as much rest as possible. Our situation has calmed down, and while we still have a lot of loose ends to attend to I'm happy to say that we're resuming a sense of normalcy here and preparing to resume our work on the features you need.
Security updates for Wednesday
Security updates have been issued by Fedora (deepin-qt5integration, deepin-qt5platform-plugins, dotnet8.0, dwayland, fcitx-qt5, fcitx5-qt, gammaray, kddockwidgets, keepassxc, kf5-akonadi-server, kf5-frameworkintegration, kf5-kwayland, plasma-integration, python-qt5, qadwaitadecorations, qgnomeplatform, qt5, qt5-qt3d, qt5-qtbase, qt5-qtcharts, qt5-qtconnectivity, qt5-qtdatavis3d, qt5-qtdeclarative, qt5-qtdoc, qt5-qtgamepad, qt5-qtgraphicaleffects, qt5-qtimageformats, qt5-qtlocation, qt5-qtmultimedia, qt5-qtnetworkauth, qt5-qtquickcontrols, qt5-qtquickcontrols2, qt5-qtremoteobjects, qt5-qtscript, qt5-qtscxml, qt5-qtsensors, qt5-qtserialbus, qt5-qtserialport, and qt5-qtspeech), Oracle (389-ds-base and ruby:3.1), Red Hat (389-ds-base, glibc, and kernel), SUSE (python-PyMySQL), and Ubuntu (libarchive).
Mike Karels has passed away
We have just received the sad news that longtime core BSD developer Mike Karels has died; he will certainly be missed.
Incus 6.2 released
Version 6.2 of the Incus container-management system is out. "This
release contains the second wave of changes contributed by students of the
University of Texas at Austin and a few other features and
improvements.
" The features include a new incus top
command, a new API for system load information, and more.
New site feature: comment subthread hiding
In the recent discussion on commenting at LWN, several readers asked for the ability to hide subthreads of a long comment stream. That feature has just been added; it is also integrated with the three comment-display modes and with comment filtering, removing the need for JavaScript for filtering. Hiding is not persistent; no extra data is stored at either end.
Give it a try; if you have comments on the new mechanism, this is the place to put them.
Security updates for Tuesday
Security updates have been issued by Mageia (chromium-browser-stable, git, libreoffice, microcode, python-requests, webkit2, and wireshark), Oracle (container-tools:ol8, glibc, go-toolset:ol8, idm:DL1 and idm:client, less, python39:3.9 and python39-devel:3.9, ruby:3.0, and virt:ol and virt-devel:rhel), Red Hat (nodejs, nodejs:18, python-idna, and ruby:3.1), and SUSE (389-ds, ffmpeg, ffmpeg-4, gnutls, gstreamer-plugins-base, libhtp, mariadb104, poppler, python-python-jose, squid, and unbound).
LyX 2.4.0 Released
Version 2.4.0 of the LyX document processor has been released. LyX is a "What You See Is What You Mean" (WYSIWYM) application that offers GUI editing of LaTeX documents with import and export to PDF, HTML, OpenDocument, Word, and other formats. LyX 2.4.0 is the first major release in six years, and brings support for EPUB, DocBook 5, improved table styles, and now uses Unicode (utf8) as its default encoding. See the full list of new features on the LyX wiki, and release notes for information on known issues and caveats for those upgrading from earlier versions of LyX.