Linus Torvalds yesterday released the Linux 4.4 kernel. This is a long-term support (LTS) release, as was determined at the Linux Kernel Summit and announced in October by Greg Kroah-Hartman, who will maintain it for 2 years.
This release checks in at more than 20.8 million lines of code, which is up considerably from Version 4.1, released in June 2015 with slightly more than 19.5 million lines of code, according to Phoronix. For historical comparison, version 0.01 of the Linux kernel — released in 1991 — had just 10,239 lines of code (source: Wikipedia).
The Linux kernel is a huge collaborative effort. According to the “Who Writes Linux” report published last year, nearly 12,000 developers from more than 1,200 companies have contributed to the Linux kernel since tracking began 10 years ago. Additionally, the average number of changes accepted into the kernel per hour is 7.71, or roughly 185 changes every day and nearly 1,300 per week.
Yet, 4.4 is a modest release, with various release candidate (rc) stages characterized by Linus Torvalds as “pretty calm,” and “fairly normal.”
“The changes since rc8 aren’t big,” Linus wrote in his 4.4 release notes. “There’s about one third arch updates, one third drivers, and one third “misc” (mainly some core kernel and networking), But it’s all small. Notable might be unbreaking the x86-32 “sysenter” ABI, when somebody (*cough*android-x86*cough*) misused it by not using the vdso and instead using the instruction directly.”
The important features for 4.4 can be broken down into a few main categories:
Graphics and Audio
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AMD Stoney support.
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Intel Lewisburg sound support and other audio driver enhancements.
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Raspberry Pi KMS driver.
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Many other Direct Rendering Manager (DRM) updates.
Zack Brown’s Kernel News in the December 2015 issue of Linux Magazine covered a recent discussion of DRM on the mailing list. Zack wrote: “Tomi Valkeinen pointed out that although fbdev (the Linux graphical framebuffer) was still maintained, it had been deprecated in favor of the DRM (Direct Rendering Manager) subsystem. Because of that, Tomi asked developers to stop submitting new fbdev drivers and to work through DRM instead.” The thread included some dismay about the many lines of code involved in writing DRM drivers — an order of magnitude more than needed for fbdev by some accounts — resulting in reluctance to move away from fbdev entirely.
Zack summed up this way: “…the upshot is that fbdev is still deprecated, and folks are motivated to make DRM support simpler hardware more gently. It’s a nice discussion to watch, because everyone seemed to have a fair sense of balance and of the need to continue to support features that were actually needed in the wild, while at the same time allowing older code to age gracefully out of the kernel.”
Networking
Notable networking updates include:
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Completely lockless TCP listener handling, which allows for faster and more scalable TCP servers.
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VRF (Virtual Routing and Forwarding) support in the IPv6 stack.
Security
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EXT4 fixes for the filesystem’s native encryption support.
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Optimized code for using Intel SHA extensions.
Hardware Support
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Support for Open-Channel solid state drives (SSDs) through LightNVM.
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Many new and updated drivers.
And More
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A new mlock2() syscall that allows users to request memory to be locked on page fault.
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Clustered RAID1 and Journaled RAID5 support.
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A lot of x86 KVM work.
You can download the sources for 4.4 from the kernel.org website and start compiling now.
