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 4.x release is a major kernel release with new features, internal
32 thus 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 2.6.40,
53 be called 2.6.40-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 4.16 development cycle went (all dates in
78 February 11 4.16-rc1, merge window closes
79 February 18 4.16-rc2
80 February 25 4.16-rc3
81 March 4 4.16-rc4
82 March 11 4.16-rc5
83 March 18 4.16-rc6
84 March 25 4.16-rc7
91 break systems which worked in the past are considered to be especially
97 release is made. In the real world, this kind of perfection is hard to
98 achieve; there are just too many variables in a project of this size.
106 "stable team," currently consisting of Greg Kroah-Hartman. The stable team
110 next development kernel. Kernels will typically receive stable updates for
112 for example, the 4.13 kernel's history looked like:
132 3.16 Ben Hutchings (very long-term stable kernel)
134 4.4 Greg Kroah-Hartman (very long-term stable kernel)
135 4.9 Greg Kroah-Hartman
136 4.14 Greg Kroah-Hartman
139 The selection of a kernel for long-term support is purely a matter of a
141 are no known plans for long-term support for any specific upcoming
146 ------------------------
149 kernel. There is, instead, a somewhat involved (if somewhat informal)
151 each patch implements a change which is desirable to have in the mainline.
152 This process can happen quickly for minor fixes, or, in the case of large
157 In the hopes of reducing that frustration, this document will describe how
158 a patch gets into the kernel. What follows below is an introduction which
159 describes the process in a somewhat idealized way. A much more detailed
160 treatment will come in later sections.
164 - Design. This is where the real requirements for the patch - and the way
165 those requirements will be met - are laid out. Design work is often
167 in the open if at all possible; it can save a lot of time redesigning
170 - Early review. Patches are posted to the relevant mailing list, and
175 - Wider review. When the patch is getting close to ready for mainline
176 inclusion, it should be accepted by a relevant subsystem maintainer -
178 all the way to the mainline. The patch will show up in the maintainer's
179 subsystem tree and into the -next trees (described below). When the
184 - Please note that most maintainers also have day jobs, so merging
190 in updating the patch to the current kernel so that it applies cleanly
193 - Merging into the mainline. Eventually, a successful patch will be
198 - Stable release. The number of users potentially affected by the patch
201 - Long-term maintenance. While it is certainly possible for a developer
203 leave a poor impression in the development community. Merging code
204 eliminates some of the maintenance burden, in that others will fix
207 in the longer term.
209 One of the largest mistakes made by kernel developers (or their employers)
214 How patches get into the Kernel
215 -------------------------------
217 There is exactly one person who can merge patches into the mainline kernel
219 into the 2.6.38 kernel, only 112 (around 1.3%) were directly chosen by Linus
220 himself. The kernel project has long since grown to a size where no single
222 way the kernel developers have addressed this growth is through the use of
225 The kernel code base is logically broken down into a set of subsystems:
229 subsystem maintainers are the gatekeepers (in a loose way) for the portion
230 of the kernel they manage; they are the ones who will (usually) accept a
231 patch for inclusion into the mainline kernel.
233 Subsystem maintainers each manage their own version of the kernel source
238 patches in his or her repository are not found in the mainline.
240 When the merge window opens, top-level maintainers will ask Linus to "pull"
243 becoming part of the mainline kernel. The amount of attention that Linus
244 pays to specific patches received in a pull operation varies. It is clear
248 Subsystem maintainers, in turn, can pull patches from other maintainers.
250 first in trees dedicated to network device drivers, wireless networking,
252 exceeds two or three links. Since each maintainer in the chain trusts
253 those managing lower-level trees, this process is known as the "chain of
256 Clearly, in a system like this, getting patches into the kernel depends on
262 ----------
264 The chain of subsystem trees guides the flow of patches into the kernel,
267 Developers will be interested in what other changes are pending to see
269 core kernel function prototype, for example, will conflict with any other
271 want access to the changes in their integrated form before all of those
272 changes land in the mainline kernel. One could pull changes from all of
273 the interesting subsystem trees, but that would be a big and error-prone
276 The answer comes in the form of -next trees, where subsystem trees are
278 Andrew Morton, is called "-mm" (for memory management, which is how it got
279 started). The -mm tree integrates patches from a long list of subsystem
282 Beyond that, -mm contains a significant collection of patches which have
284 mailing list, or they may apply to a part of the kernel for which there is
285 no designated subsystem tree. As a result, -mm operates as a sort of
287 patch into the mainline, it is likely to end up in -mm. Miscellaneous
288 patches which accumulate in -mm will eventually either be forwarded on to
289 an appropriate subsystem tree or be sent directly to Linus. In a typical
290 development cycle, approximately 5-10% of the patches going into the
291 mainline get there via -mm.
293 The current -mm patch is available in the "mmotm" (-mm of the moment)
301 The primary tree for next-cycle patch merging is linux-next, maintained by
302 Stephen Rothwell. The linux-next tree is, by design, a snapshot of what
304 Linux-next trees are announced on the linux-kernel and linux-next mailing
307 http://www.kernel.org/pub/linux/kernel/next/
309 Linux-next has become an integral part of the kernel development process;
311 their way into linux-next some time before the merge window opens.
315 -------------
317 The kernel source tree contains the drivers/staging/ directory, where
318 many sub-directories for drivers or filesystems that are on their way to
319 being added to the kernel tree live. They remain in drivers/staging while
321 kernel proper. This is a way to keep track of drivers that aren't
322 up to Linux kernel coding or quality standards, but people may want to use
325 Greg Kroah-Hartman currently maintains the staging tree. Drivers that
327 subdirectory in drivers/staging/. Along with the driver source files, a
328 TODO file should be present in the directory as well. The TODO file lists
329 the pending work that the driver needs for acceptance into the kernel
337 code in staging which is not seeing regular progress will eventually be
344 -----
346 As can be seen from the above text, the kernel development process depends
347 heavily on the ability to herd collections of patches in various
353 By far the dominant source code management system used by the kernel
355 systems being developed in the free software community. It is well tuned
356 for kernel development, in that it performs quite well when dealing with
359 time. Some sort of familiarity with git is almost a requirement for kernel
366 http://git-scm.com/
370 Among the kernel developers who do not use git, the most popular choice is
386 upstream. For the management of certain kinds of trees (-mm, for example),
391 -------------
393 A great deal of Linux kernel development work is done by way of mailing
394 lists. It is hard to be a fully-functioning member of the community
400 Most kernel mailing lists are run on vger.kernel.org; the master list can
403 http://vger.kernel.org/vger-lists.html
408 The core mailing list for kernel development is, of course, linux-kernel.
412 degree of politeness. But there is no other place where the kernel
416 There are a few hints which can help with linux-kernel survival:
418 - Have the list delivered to a separate folder, rather than your main
422 - Do not try to follow every conversation - nobody else does. It is
424 long-running conversations can drift away from the original subject
428 - Do not feed the trolls. If somebody is trying to stir up an angry
431 - When responding to linux-kernel email (or that on other lists) preserve
432 the Cc: header for all involved. In the absence of a strong reason (such
434 sure that the person you are responding to is in the Cc: list. This
438 - Search the list archives (and the net as a whole) before asking
442 - Avoid top-posting (the practice of putting your answer above the quoted
446 - Ask on the correct mailing list. Linux-kernel may be the general meeting
450 The last point - finding the correct mailing list - is a common place for
451 beginning developers to go wrong. Somebody who asks a networking-related
452 question on linux-kernel will almost certainly receive a polite suggestion
456 in the MAINTAINERS file packaged with the kernel source.
459 Getting started with Kernel development
460 ---------------------------------------
462 Questions about how to get started with the kernel development process are
463 common - from both individuals and companies. Equally common are missteps
466 Companies often look to hire well-known developers to get a development
467 group started. This can, in fact, be an effective technique. But it also
469 kernel developers. It is possible to bring in-house developers up to speed
470 on Linux kernel development, given the investment of a bit of time. Taking
472 the kernel and the company both, and who can help to train others as well.
485 Andrew Morton gives this advice for aspiring kernel developers
489 The #1 project for all kernel beginners should surely be "make sure
490 that the kernel runs perfectly at all times on all machines which
493 persistence!) but that's fine - it's a part of kernel development.
497 In the absence of obvious problems to fix, developers are advised to look
498 at the current lists of regressions and open bugs in general. There is
499 never any shortage of issues in need of fixing; by addressing these issues,