The Linux 2.6 Kernel: Cracking the Code - page 2
What is the Linux Kernel?
The build gets more stable with each release and support levels.
Take the first 2.6 kernel version, which hit the open source world in December of 2003 .
It sported improvements over its 2.4 kernel predecessor such as support for multi-processor configurations and 64 bit computing.
It also supported native POSIX Thread Library (NPTL), which enables efficient thread handling.
In fact, performance, security and driver enhancements are key parts of the entire 2.6.x Linux kernel branch.
By December of 2004, a year after the first 2.6.x kernel release, the number of major point releases was up to 10 with the "Woozy Numbat" 2.6.10 Linux kernel. Though 10 releases in a year may sound like a lot, it is actually fewer than the number that the 2.4.x kernel had in its first year of release.
Between January 2001 when the 2.4.0 kernel was released and December of that year, 17 versions of the kernel were released. However the above comparison isn't entirely an apples-to-apples comparison. There are no minor point releases within the 2.4.x series (i.e., a 2.4.1 for example). Starting with the 188.8.131.52 kernel and continued as official policy starting with the 2.6.11 kernel, minor kernel bug and security fixes get minor point releases (i.e., 184.108.40.206).
The 2.6.11 kernel which was released in February of 2005 introduced InfiniBand support to the Linux kernel.
By June of 2005 a very public spat surrounding the BitKeeper tool that Torvalds was using to help manage development of the Linux kernel caused a changed in development tools. The 2.6.12 kernel is the first that made use of Torvald's Git program instead of BitKeeper. Ultimately though the change had little to no impact on the actual development of the Linux kernel itself.
By August of 2005, it had become apparent that quality of code in the 2.6.x Linux kernel was actually improving. A study done by code analysis firm Coverity in August of 2005, found that the "defect density" in the Linux kernel fell between December 2004 and July 2005.
Though the Linux kernel code itself had grown in the same period by 4.7 percent from 5.76 million lines of code in December 2004 to 6.03 million in July 2005 defect density declined by 2.2 percent. The 2.6.13 kernel debut in late August and included "Kexec," which allows for a fast reboot without the need to go through a bootloader. It also included the Inotify file system event monitoring mechanism which uses a more efficient API (define) than its predecessor dnotify.
Two months later, in late October the 2.6.14 kernel ushered in a new era in the development process for kernel development.
New features for this release kernel forward are now only supposed to be accepted in the first two weeks after the predecessor kernel is released. The 2.6.15 kernel was released just a few days into the new 2006 year. IPv6 support is much improved in that kernel. PowerPC users now have a generic tree for both 64 and 32 bit PowerPC which enables kernel compilation on either architecture.
The sixteenth release of the 2.6 kernel series appeared three months after its predecessor. It also introduced support for the Cell processor and Oracle's OCFS2 cluster filesystem.
The 2.6.16 release also had numerous fixes in it that had been discovered via the Coverity code analysis tool.