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The kmap() interface in the kernel is a bit of a strange beast. It only exists to overcome the virtual addressing limitations of 32-bit CPUs, but it affects code across the kernel and has side effects on 64-bit machines as well. A recent discussion on the handling of preemption within the kernel identified a number of problems in need of attention, one of which was the kmap() API. Now, an extension to this API called kmap_local() is being proposed to address some of the problems; it signals another step in the kernel community's slow move away from supporting 32-bit machines as first-class citizens.
The 5.10-rc3 kernel prepatch is out for testing. "Things look normal. rc3 is neither particularly small or particularly large - it's pretty much average for an rc3 release for the last couple of years."
The scp command, which uses the SSH protocol to copy files between machines, is deeply wired into the fingers of many Linux users and developers — doubly so for those of us who still think of it as a more secure replacement for rcp. Many users may be surprised to learn, though, that the resemblance to rcp goes beyond the name; much of the underlying protocol is the same as well. That protocol is showing its age, and the OpenSSH community has considered it deprecated for a while. Replacing scp in a way that keeps users happy may not be an easy task, though.
Version 2.0 of the Mutt email client is out. "This release was bumped to 2.0, not because of the magnitude of features (which is actually smaller than past releases), but because of a few changes that are backward incompatible". New features include a cd command to change directories, automatic IMAP reconnection, and "MuttLisp", a Lisp-like language for the configuration file. See the release notes for details.
The LWN.net Weekly Edition for November 5, 2020 is available.
Inside this week's LWN.net Weekly Edition
The 2020 editions of Open Source Summit Europe (OSS EU) and Embedded Linux Conference Europe (ELC EU) were held virtually October 26-30, along with some other events (KVM Forum, Linux Security Summit, and more). The videos, Q&A, and presentations from those conferences are now available to all at the event site through the month of November. The videos will also be posted to YouTube during the month so that they will be available for the future. The schedule is available as well.
At this year's (virtual) Open Source Summit Europe, Oleg Fiksel gave an overview talk on the Matrix decentralized, secure communication network project. Matrix has been seeing increasing adoption recently, he said, including by governments (beyond France, which we already reported on in an article on a FOSDEM 2019 talk) and other organizations. It also aims to bridge all of the different chat mechanisms that people are using in order to provide a unified interface for all of them.
As described in this Let's Encrypt blog entry, certificates issued by Let's Encrypt will soon be signed solely by that organization's own root certificate, which is accepted by all modern browsers. There is one little catch, though: versions of Android prior to 7.1.1 (released in late 2016) do not recognize that certificate and will start throwing errors. "Currently, 66.2% of Android devices are running version 7.1 or above. The remaining 33.8% of Android devices will eventually start getting certificate errors when users visit sites that have a Let’s Encrypt certificate. In our communications with large integrators, we have found that this represents around 1-5% of traffic to their sites." There appears to be little to be done about this problem other than to encourage owners of older Android devices to install Firefox.
Pluto is a new computational notebook for the Julia programming language. Computational notebooks are a way to program inside of a web browser, storing code, annotations, and output, including graphics, in a single place. They became popular with the advent of the Jupyter notebook, which originally targeted Julia, Python, and R—the names got mashed together to make the word "Jupyter".
Security updates have been issued by Debian (sddm and wordpress), Fedora (blueman, chromium, pngcheck, and salt), openSUSE (chromium, salt, tiff, tigervnc, tmux, tomcat, transfig, and xen), Oracle (freetype, kernel, libX11, thunderbird, and xorg-x11-server), SUSE (bluez, ImageMagick, java-1_8_0-openjdk, rmt-server, salt, and u-boot), and Ubuntu (dom4j, firefox, netqmail, phpldapadmin, and tmux).
Overclocking the processor — running it above its specified maximum frequency to increase performance — is a familiar operation for many readers. Sometimes, however, it is necessary to go the other direction and decrease a processor's operating power point by lowering its voltage to avoid overheating. Recently, Jason Donenfeld submitted a short patch removing a warning emitted by the kernel when user space accesses special processor registers that allow this "undervolting" on x86 processors. It caused a long discussion that might result in a kernel interface to allow users to safely control their processor's voltage.
Four new stable kernels have been released: 5.9.5, 5.4.75, 4.19.155, and 4.14.204. They are fairly large updates with lots of important fixes throughout the kernel tree; users should upgrade.
Update: 5.9.6 has been released to fix a build problem with 5.9.5: "if 5.9.5 built properly for you, wonderful, no need to upgrade".
Linux distributors are in the business of integrating software from multiple sources, packaging the result, and making it available to their users. It has long been true that some projects are easier to package than others. The Debian technical committee (TC) is currently being asked to make a decision in a dispute over how an especially hard-to-package project — Kubernetes — should be handled. Regardless of the eventual outcome, this disagreement clearly shows how the packaging model used by Linux distributors is increasingly mismatched to how software is often developed in the 2020s; what should replace that model is rather less clear, though.
Security updates have been issued by Debian (bouncycastle, gdm3, and libonig), Fedora (arpwatch, thunderbird, and trousers), openSUSE (chromium, gn), Red Hat (freetype, libX11, thunderbird, and xorg-x11-server), and SUSE (ImageMagick, java-11-openjdk, salt, and wireshark).
The kernel's tracing infrastructure is designed to be fast and to interfere as little as possible with the normal operation of the system. One consequence of this requirement is that the code that runs when a tracepoint is hit cannot sleep; otherwise execution of the tracepoint could add an arbitrary delay to the execution of the real work the kernel should be doing. There are times, though, that the ability to sleep within a tracepoint would be handy, delays notwithstanding. The sleepable tracepoints patch set from Michael Jeanson sets the stage to make it possible for (some) tracepoint handlers to take a nap while performing their tasks — but stops short of completing the job for now.
Greg Kroah-Hartman has released stable kernel 5.9.4. "This is only a bugfix for the 5.9.3 kernel release which had some problems with some symlinks for the powerpc selftests." If you did not have any issues with 5.9.3 there is no need to upgrade.
The LWN.net Weekly Edition for October 29, 2020 is available.
Inside this week's LWN.net Weekly Edition
Security updates have been issued by Arch Linux (chromium and firefox), Fedora (nss), openSUSE (pacemaker), Red Hat (bind, binutils, bluez, cloud-init, container-tools:rhel8, cryptsetup, cups, curl, cyrus-imapd, cyrus-sasl, dovecot, dpdk, edk2, evolution, expat, file-roller, fontforge, freeradius:3.0, freerdp and vinagre, freetype, frr, gd, glibc, GNOME, gnome-software and fwupd, gnupg2, grafana, httpd:2.4, idm:DL1 and idm:client, kernel, kernel-rt, libarchive, libexif, libgcrypt, libldb, libpcap, librabbitmq, libreoffice, librsvg2, libsolv, libssh, libtiff, libvpx, libX11, libxml2, libxslt, mailman:2.1, mingw-expat, nodejs:12, oddjob, oniguruma, opensc, openssl, openwsman, pcre2, pki-core:10.6 and pki-deps:10.6, poppler, prometheus-jmx-exporter, python-pip, python27:2.7, python3, python38:3.8, qt5-qtbase and qt5-qtwebsockets, resource-agents, SDL, spamassassin, sqlite, squid:4, subversion:1.10, sysstat, systemd, targetcli, tcpdump, thunderbird, varnish:6, vim, and virt:rhel and virt-devel:rhel), SUSE (apache-commons-httpclient, gnome-settings-daemon, gnome-shell, kernel, libvirt, opensc, ovmf, python, rmt-server, and sane-backends), and Ubuntu (accountsservice, gdm3, libytnef, python-cryptography, and spice-vdagent).
Python has keyword arguments for functions that is a useful (and popular) feature; it can make reading the code more clear and eliminate the possibility of passing arguments in the wrong order. Python can also index an object in various ways to refer to a subset or an aspect of the object. Bringing the idea of keywords to indexing would provide a way to get the clarity benefit for indexing operations; doing so has been discussed in Python circles for a long time. Some renewed interest, in the form of lengthy discussions on the python-ideas mailing list and a new Python enhancement proposal (PEP), look like they just might take keyword indexing over the finish line.
Kernel.org manager Konstantin Ryabitsev describes the Git signed-push functionality, which is now supported by the kernel.org system. "To help hedge against this problem, git provides developers a way to sign their actual pushes, as a means to attest 'yes, I actually did intend to push these commits into this ref in this repository on this server, and here's my PGP signature to prove it.'" Among other things, these signatures can be preserved in a commit transparency log, which is also now provided by kernel.org.
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