5.9 Merge window, part 2

By the time Linus Torvalds released 5.9-rc1 and closed the merge window for this cycle, 12,866 non-merge changesets had been pulled into the mainline repository. Nearly 9,000 of those came in after the first 5.9 merge-window summary was written. Clearly the kernel-development community remains busy. Much of what was merged takes the form of cleanups and restructuring, as always, but there was also a substantial set of new features.

Architecture-specific

• The xtensa architecture has gained support for the audit and seccomp mechanisms.
• The csky architecture has also gained seccomp support.
• The RISC-V architecture now has support for a number of features, including code-coverage tracking with kcov, the kmemleak tester, stack protection, jump labels, and tickless operation.
• PowerPC has gained a queued spinlock implementation that provides "significantly improved" performance in highly contended situations.
• The arm and arm64 architectures now use the schedutil CPU-frequency governor by default.

Core kernel

• The proactive compaction patches have been merged. They perform memory compaction in the background, hopefully increasing the supply of large pages available to the kernel.

Filesystems and block I/O

• The SCSI subsystem can now make use of encryption hardware on UFS controllers to implement inline encryption.
• The device mapper's dm-crypt target now has options to avoid the use of workqueues for cryptographic processing. Not using workqueues can improve latency; it is also required to properly support zoned block devices (devices with regions that must be written sequentially) with dm-crypt.
• The NFSv4.2 client has gained support for extended attributes.

Hardware support

• Clock: Broadcom BCM2711 DVP clock controllers, Qualcomm IPQ APSS clock controllers, Qualcomm MSM8996 CPU clock controllers, and Qualcomm SM8150 and SM8250 graphics clock controllers.
• Graphics: Ingenic image processing units and Xilinx ZinqMP DisplayPort DMA engines and controllers.
• Industrial I/O: InvenSense ICM-426xx motion trackers and Sensirion SCD30 carbon-dioxide sensors.
• Miscellaneous: multi-color LEDs in a general way (see this commit for documentation), Turris Omnia LED controllers, Microchip timer counter capture devices, Qualcomm inline crypto engines, TI J721E PCIe platform host controllers, Xilinx Versal CPM host bridges, TI BQ2515X battery chargers, Mediatek MT6779 pin controllers, TI C66x and C71x DSP remote processor subsystems, and Khadas system control microcontroller interfaces.
• Networking: Vitesse Seville VSC9953 switches and Solarflare EF100 Ethernet cards.
• Sound: Maxim integrated MAX98373 speaker amplifiers and NVIDIA Tegra audio processing engines.
• Video4Linux: Xilinx CSI-2 Rx subsystems, Chrontel CH7322 CEC controllers, Mediatek DW9768 lens voice coils, Maxim MAX9286 GMSL deserializers, and IMI RDACM20 cameras.
• It's also worth noting that the "speakup" console speech driver, which has lived in the staging tree since the 2.6.37 kernel, has finally graduated out of staging.

Networking

• "BPF iterators" have been added for TCP and UDP sockets; these allow a BPF program to work through the list of open sockets and extract whatever information is of interest. Sample programs for TCP and UDP are included.
• The new BPF_PROG_TYPE_SK_LOOKUP BPF program type will run when the kernel is looking for an open socket for an incoming connection. The program can then decide which socket should receive the connection. This mechanism has been added as a way to "bind" a socket to a range of addresses or port numbers in a simple way.
• The parallel redundancy protocol is now supported.

Virtualization and containers

• The 32-bit PV guest mode has been removed from the Xen hypervisor; any remaining users (there are expected to be few) can use the better-supported "PVH" mode instead.

Internal kernel changes

• The way that priorities are assigned to kernel threads has been significantly reworked. The new API brings a lot more consistency in how realtime priorities are assigned across the kernel.
• The initrd code can no longer cope with a disk image stored on multiple floppies. Christoph Hellwig noted: "No one should be using floppies for booting these days. (famous last words..)".
• Kernel modules that import symbols from proprietary modules will themselves be marked as tainted, eliminating their ability to access GPL-only symbols in the rest of the kernel. This change, along with its motivation, is explained in this article from July.

Now the development community will take seven or eight weeks to stabilize this release, with a final 5.9 release expected in the first half of October.

Index entries for this article
Kernel	Releases/5.9

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