4.16 Merge window part 1

As of this writing, just over 6,700 non-merge changesets have been pulled into the mainline repository for the 4.16 development cycle. Given that there are a number of significant trees yet to be pulled, the early indications are that 4.16 will be yet another busy development cycle. What follows is a summary of the significant changes merged in the first half of this merge window.

Core kernel

• Initial support for the Jailhouse hypervisor has been added for the x86-64 architecture. With this support, it's possible to run Linux in a non-root cell.
• The deadline scheduler has been given an understanding of CPU frequency and voltage scaling; that allows it to operate properly without the need to disable power-saving features.
• The arm64 architecture can now work with 52-bit physical addresses on suitably equipped hardware.
• The Berkeley Packet Filter (BPF) virtual machine now has support for the defining and calling of functions within BPF programs.

Filesystems and block layer

• The MultiMediaCard subsystem (which handles storage devices like Secure Digital cards) has been reworked to use the multiqueue block API. That should bring performance improvements among other benefits.

• The I/O schedulers have gained support for locked zones on block devices; this is used to prevent reordering of writes on zoned devices where writes must be performed sequentially.

• The CIFS filesystem has experimental support for SMB Direct, which can use remote DMA (RDMA) to transfer SMB packets.

• The Btrfs filesystem now supports the fallocate() FALLOCATE_FL_ZERO_RANGE operation.

• The NFS client can now use the query flags in the statx() system call to avoid calling to the remote server if the needed information is available locally.

• The new RWF_APPEND flag to pwritev2() will append the data to the file regardless of the current offset.

Networking

• The new "netdevsim" virtual device exists to help in the testing of hardware-offload features in the networking stack. It simulates various offload operations so that higher-level code can be tested without the relevant hardware being present. The initial use case is for testing BPF offload support.

• The Netware IPX and NCPFS protocol implementations are old, unmaintained, and unused; they have been moved to the staging tree ahead of their eventual deletion from the kernel.

Security-related

• The arm64 architecture has gained the ability to invalidate the branch prediction unit, a defense against the Spectre variant-2 vulnerability. Also added to arm64 is kernel page-table isolation to defend against Meltdown.

Hardware support

• Audio: Texas Instruments PCM186x and TLV320AIC32x4 codecs, Texas Instruments TAS6424 quad-channel audio amplifiers, Maxim integrated MAX98373 speaker amplifiers, STMicroelectronics STM32 DFSDM digital audio interfaces, Tempo Semiconductor TSCS42xx codecs, and Socionext UniPhier LD11/20 codecs.
• Bus: Eckelmann SIOX buses, SLIMbus buses, Qualcomm SLIMbus controllers, and SoundWire two-pin buses.
• Cryptographic: STMicroelectronics STM32 CRYP1 cryptographic accelerators, Chelsio IPSec XFRM Tx crypto offload engines, and Samsung Exynos true random number generators.
• Industrial I/O: IDT ZOPT2201 ALS and UV B sensors and STMicroelectronics UVIS25 UV sensors.
• Networking: Hisilicon HNS3VF network acceleration engines, MediaTek MT76x2E wireless network interfaces, Socionext AVE Ethernet interfaces, SocioNext NetSec gigabit Ethernet controllers, and Cortina Gemini Ethernet controllers.
• Miscellaneous: Realtek rts5260 card readers, RAVE supervisory processor units, Nuvoton W83773G hardware-monitoring chips, Spreadtrum SC2731 power regulators, Texas Instruments DDR3 ECC controllers, Texas Instruments LM3692x LED controllers, Winbond Super I/O GPIO controllers, and Oracle SPARC data analytics accelerators.
• The LED subsystem has a new trigger type (NETDEV) that can trigger an LED based on network activity.

Internal kernel changes

• The handling of the inode i_version field has changed to eliminate changes (which must be expensively flushed to storage) when nobody is paying attention. There is a new API (found in this commit) for working with i_version.
• High-resolution timer (hrtimer) functions have traditionally run in hard-interrupt context. Many users actually need to be running in software-interrupt context, though, leading to a situation where a lot of hrtimer functions do nothing except start a tasklet to get the real work done. 4.16 adds two new timer modes (HRTIMER_MODE_REL_SOFT and HRTIMER_MODE_ABS_SOFT) that run the timer function in software-interrupt context to begin with, eliminating the need for the tasklet.
• The return type of the poll() method in struct file_operations has been changed to the new __poll_t type. It is a bitwise type that facilitates automatic checking for a number of common mistakes in poll() implementations.
• The new snap-pkg target in the build system can be used to create a Snap package containing a built kernel.
• The parser used by the configuration system is now directly generated with flex and bison; those tools are thus now part of the kernel's build requirements.

The 4.16 merge window will probably close on February 11; the final 4.16 kernel release can, barring another significant security surprise, be expected on April 1 or 8. Stay tuned for the second article in this series, which will cover the second half of the merge window for this development cycle.

Index entries for this article
Kernel	Releases/4.16

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