Lines Matching +full:in +full:- +full:kernel
6 Linux kernel development in the early 1990's was a pretty loose affair,
8 user base in the millions and with some 2,000 developers involved over the
9 course of one year, the kernel has since had to evolve a number of
11 how the process works is required in order to be an effective part of it.
14 ---------------
16 The kernel developers use a loosely time-based release process, with a new
17 major kernel release happening every two or three months. The recent
29 Every 5.x release is a major kernel release with new features, internal
32 the leading edge of Linux kernel development; the kernel uses a
39 community) is merged into the mainline kernel. The bulk of changes for a
46 and staged ahead of time. How that process works will be described in
51 first of the "rc" kernels. For the kernel which is destined to be 5.6,
53 be called 5.6-rc1. The -rc1 release is the signal that the time to
55 kernel has begun.
63 exception is made for drivers for previously-unsupported hardware; if they
64 touch no in-tree code, they cannot cause regressions and should be safe to
68 time. Linus releases new -rc kernels about once a week; a normal series
69 will get up to somewhere between -rc6 and -rc9 before the kernel is
73 As an example, here is how the 5.4 development cycle went (all dates in
78 September 30 5.4-rc1, merge window closes
79 October 6 5.4-rc2
80 October 13 5.4-rc3
81 October 20 5.4-rc4
82 October 27 5.4-rc5
83 November 3 5.4-rc6
84 November 10 5.4-rc7
85 November 17 5.4-rc8
92 break systems which worked in the past are considered to be especially
98 release is made. In the real world, this kind of perfection is hard to
99 achieve; there are just too many variables in a project of this size.
107 "stable team," currently Greg Kroah-Hartman. The stable team will release
111 kernel. Kernels will typically receive stable updates for a little more
113 5.2 kernel's history looked like this (all dates in 2019):
130 long term kernel versions and their maintainers:
132 https://www.kernel.org/category/releases.html
134 The selection of a kernel for long-term support is purely a matter of a
136 are no known plans for long-term support for any specific upcoming
141 ------------------------
144 kernel. There is, instead, a somewhat involved (if somewhat informal)
146 each patch implements a change which is desirable to have in the mainline.
147 This process can happen quickly for minor fixes, or, in the case of large
152 In the hopes of reducing that frustration, this document will describe how
153 a patch gets into the kernel. What follows below is an introduction which
154 describes the process in a somewhat idealized way. A much more detailed
155 treatment will come in later sections.
159 - Design. This is where the real requirements for the patch - and the way
160 those requirements will be met - are laid out. Design work is often
162 in the open if at all possible; it can save a lot of time redesigning
165 - Early review. Patches are posted to the relevant mailing list, and
170 - Wider review. When the patch is getting close to ready for mainline
171 inclusion, it should be accepted by a relevant subsystem maintainer -
173 all the way to the mainline. The patch will show up in the maintainer's
174 subsystem tree and into the -next trees (described below). When the
179 - Please note that most maintainers also have day jobs, so merging
185 in updating the patch to the current kernel so that it applies cleanly
188 - Merging into the mainline. Eventually, a successful patch will be
193 - Stable release. The number of users potentially affected by the patch
196 - Long-term maintenance. While it is certainly possible for a developer
198 leave a poor impression in the development community. Merging code
199 eliminates some of the maintenance burden, in that others will fix
202 in the longer term.
204 One of the largest mistakes made by kernel developers (or their employers)
209 How patches get into the Kernel
210 -------------------------------
212 There is exactly one person who can merge patches into the mainline kernel
214 which went into the 2.6.38 kernel, only 112 (around 1.3%) were directly
215 chosen by Linus himself. The kernel project has long since grown to a size
217 unassisted. The way the kernel developers have addressed this growth is
220 The kernel code base is logically broken down into a set of subsystems:
224 subsystem maintainers are the gatekeepers (in a loose way) for the portion
225 of the kernel they manage; they are the ones who will (usually) accept a
226 patch for inclusion into the mainline kernel.
228 Subsystem maintainers each manage their own version of the kernel source
233 patches in his or her repository are not found in the mainline.
235 When the merge window opens, top-level maintainers will ask Linus to "pull"
238 becoming part of the mainline kernel. The amount of attention that Linus
239 pays to specific patches received in a pull operation varies. It is clear
243 Subsystem maintainers, in turn, can pull patches from other maintainers.
245 first in trees dedicated to network device drivers, wireless networking,
247 exceeds two or three links. Since each maintainer in the chain trusts
248 those managing lower-level trees, this process is known as the "chain of
251 Clearly, in a system like this, getting patches into the kernel depends on
257 ----------
259 The chain of subsystem trees guides the flow of patches into the kernel,
262 Developers will be interested in what other changes are pending to see
264 core kernel function prototype, for example, will conflict with any other
266 want access to the changes in their integrated form before all of those
267 changes land in the mainline kernel. One could pull changes from all of
268 the interesting subsystem trees, but that would be a big and error-prone
271 The answer comes in the form of -next trees, where subsystem trees are
273 Andrew Morton, is called "-mm" (for memory management, which is how it got
274 started). The -mm tree integrates patches from a long list of subsystem
277 Beyond that, -mm contains a significant collection of patches which have
279 mailing list, or they may apply to a part of the kernel for which there is
280 no designated subsystem tree. As a result, -mm operates as a sort of
282 patch into the mainline, it is likely to end up in -mm. Miscellaneous
283 patches which accumulate in -mm will eventually either be forwarded on to
284 an appropriate subsystem tree or be sent directly to Linus. In a typical
285 development cycle, approximately 5-10% of the patches going into the
286 mainline get there via -mm.
288 The current -mm patch is available in the "mmotm" (-mm of the moment)
296 The primary tree for next-cycle patch merging is linux-next, maintained by
297 Stephen Rothwell. The linux-next tree is, by design, a snapshot of what
299 Linux-next trees are announced on the linux-kernel and linux-next mailing
302 https://www.kernel.org/pub/linux/kernel/next/
304 Linux-next has become an integral part of the kernel development process;
306 their way into linux-next some time before the merge window opens.
310 -------------
312 The kernel source tree contains the drivers/staging/ directory, where
313 many sub-directories for drivers or filesystems that are on their way to
314 being added to the kernel tree live. They remain in drivers/staging while
316 kernel proper. This is a way to keep track of drivers that aren't
317 up to Linux kernel coding or quality standards, but people may want to use
320 Greg Kroah-Hartman currently maintains the staging tree. Drivers that
322 subdirectory in drivers/staging/. Along with the driver source files, a
323 TODO file should be present in the directory as well. The TODO file lists
324 the pending work that the driver needs for acceptance into the kernel
332 code in staging which is not seeing regular progress will eventually be
339 -----
341 As can be seen from the above text, the kernel development process depends
342 heavily on the ability to herd collections of patches in various
348 By far the dominant source code management system used by the kernel
350 systems being developed in the free software community. It is well tuned
351 for kernel development, in that it performs quite well when dealing with
354 time. Some sort of familiarity with git is almost a requirement for kernel
361 https://git-scm.com/
365 Among the kernel developers who do not use git, the most popular choice is
381 upstream. For the management of certain kinds of trees (-mm, for example),
386 -------------
388 A great deal of Linux kernel development work is done by way of mailing
389 lists. It is hard to be a fully-functioning member of the community
395 Most kernel mailing lists are run on vger.kernel.org; the master list can
398 http://vger.kernel.org/vger-lists.html
403 The core mailing list for kernel development is, of course, linux-kernel.
407 degree of politeness. But there is no other place where the kernel
411 There are a few hints which can help with linux-kernel survival:
413 - Have the list delivered to a separate folder, rather than your main
417 - Do not try to follow every conversation - nobody else does. It is
419 long-running conversations can drift away from the original subject
423 - Do not feed the trolls. If somebody is trying to stir up an angry
426 - When responding to linux-kernel email (or that on other lists) preserve
427 the Cc: header for all involved. In the absence of a strong reason (such
429 sure that the person you are responding to is in the Cc: list. This
433 - Search the list archives (and the net as a whole) before asking
437 - Avoid top-posting (the practice of putting your answer above the quoted
441 - Ask on the correct mailing list. Linux-kernel may be the general meeting
445 The last point - finding the correct mailing list - is a common place for
446 beginning developers to go wrong. Somebody who asks a networking-related
447 question on linux-kernel will almost certainly receive a polite suggestion
451 in the MAINTAINERS file packaged with the kernel source.
454 Getting started with Kernel development
455 ---------------------------------------
457 Questions about how to get started with the kernel development process are
458 common - from both individuals and companies. Equally common are missteps
461 Companies often look to hire well-known developers to get a development
462 group started. This can, in fact, be an effective technique. But it also
464 kernel developers. It is possible to bring in-house developers up to speed
465 on Linux kernel development, given the investment of a bit of time. Taking
467 the kernel and the company both, and who can help to train others as well.
480 Andrew Morton gives this advice for aspiring kernel developers
484 The #1 project for all kernel beginners should surely be "make sure
485 that the kernel runs perfectly at all times on all machines which
488 persistence!) but that's fine - it's a part of kernel development.
492 In the absence of obvious problems to fix, developers are advised to look
493 at the current lists of regressions and open bugs in general. There is
494 never any shortage of issues in need of fixing; by addressing these issues,