Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
[PATCH] Add HOWTO do kernel development document to the Documentation directory
Here's a document that describes the process and procedures of how to do Linux
kernel development. It has gone through a number of rounds of review on the
linux-kernel mailing list, and contains contributions and help from Paolo
Ciarrocchi, Randy Dunlap, Gerrit Huizenga, Pat Mochel, Hanna Linder, Kay
Sievers, Vojtech Pavlik, Jan Kara, Josh Boyer, Kees Cook, Andrew Morton, Andi
Kleen, Vadim Lobanov, Jesper Juhl, Adrian Bunk, Keri Harris, Frans Pop, David
A. Wheeler, Junio Hamano, Michael Kerrisk, and Alex Shepard.
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
authored by
Greg Kroah-Hartman
and committed by
Linus Torvalds
d36cc9d0
6fb0425b
+620
+2
Documentation/00-INDEX
+2
Documentation/00-INDEX
···
24
24
- info for PCI drivers using DMA portably across all platforms.
25
25
DocBook/
26
26
- directory with DocBook templates etc. for kernel documentation.
27
+
HOWTO
28
+
- The process and procedures of how to do Linux kernel development.
27
29
IO-mapping.txt
28
30
- how to access I/O mapped memory from within device drivers.
29
31
IPMI.txt
+618
Documentation/HOWTO
+618
Documentation/HOWTO
···
1
+
HOWTO do Linux kernel development
2
+
---------------------------------
3
+
4
+
This is the be-all, end-all document on this topic. It contains
5
+
instructions on how to become a Linux kernel developer and how to learn
6
+
to work with the Linux kernel development community. It tries to not
7
+
contain anything related to the technical aspects of kernel programming,
8
+
but will help point you in the right direction for that.
9
+
10
+
If anything in this document becomes out of date, please send in patches
11
+
to the maintainer of this file, who is listed at the bottom of the
12
+
document.
13
+
14
+
15
+
Introduction
16
+
------------
17
+
18
+
So, you want to learn how to become a Linux kernel developer? Or you
19
+
have been told by your manager, "Go write a Linux driver for this
20
+
device." This document's goal is to teach you everything you need to
21
+
know to achieve this by describing the process you need to go through,
22
+
and hints on how to work with the community. It will also try to
23
+
explain some of the reasons why the community works like it does.
24
+
25
+
The kernel is written mostly in C, with some architecture-dependent
26
+
parts written in assembly. A good understanding of C is required for
27
+
kernel development. Assembly (any architecture) is not required unless
28
+
you plan to do low-level development for that architecture. Though they
29
+
are not a good substitute for a solid C education and/or years of
30
+
experience, the following books are good for, if anything, reference:
31
+
- "The C Programming Language" by Kernighan and Ritchie [Prentice Hall]
32
+
- "Practical C Programming" by Steve Oualline [O'Reilly]
33
+
34
+
The kernel is written using GNU C and the GNU toolchain. While it
35
+
adheres to the ISO C89 standard, it uses a number of extensions that are
36
+
not featured in the standard. The kernel is a freestanding C
37
+
environment, with no reliance on the standard C library, so some
38
+
portions of the C standard are not supported. Arbitrary long long
39
+
divisions and floating point are not allowed. It can sometimes be
40
+
difficult to understand the assumptions the kernel has on the toolchain
41
+
and the extensions that it uses, and unfortunately there is no
42
+
definitive reference for them. Please check the gcc info pages (`info
43
+
gcc`) for some information on them.
44
+
45
+
Please remember that you are trying to learn how to work with the
46
+
existing development community. It is a diverse group of people, with
47
+
high standards for coding, style and procedure. These standards have
48
+
been created over time based on what they have found to work best for
49
+
such a large and geographically dispersed team. Try to learn as much as
50
+
possible about these standards ahead of time, as they are well
51
+
documented; do not expect people to adapt to you or your company's way
52
+
of doing things.
53
+
54
+
55
+
Legal Issues
56
+
------------
57
+
58
+
The Linux kernel source code is released under the GPL. Please see the
59
+
file, COPYING, in the main directory of the source tree, for details on
60
+
the license. If you have further questions about the license, please
61
+
contact a lawyer, and do not ask on the Linux kernel mailing list. The
62
+
people on the mailing lists are not lawyers, and you should not rely on
63
+
their statements on legal matters.
64
+
65
+
For common questions and answers about the GPL, please see:
66
+
http://www.gnu.org/licenses/gpl-faq.html
67
+
68
+
69
+
Documentation
70
+
------------
71
+
72
+
The Linux kernel source tree has a large range of documents that are
73
+
invaluable for learning how to interact with the kernel community. When
74
+
new features are added to the kernel, it is recommended that new
75
+
documentation files are also added which explain how to use the feature.
76
+
When a kernel change causes the interface that the kernel exposes to
77
+
userspace to change, it is recommended that you send the information or
78
+
a patch to the manual pages explaining the change to the manual pages
79
+
maintainer at mtk-manpages@gmx.net.
80
+
81
+
Here is a list of files that are in the kernel source tree that are
82
+
required reading:
83
+
README
84
+
This file gives a short background on the Linux kernel and describes
85
+
what is necessary to do to configure and build the kernel. People
86
+
who are new to the kernel should start here.
87
+
88
+
Documentation/Changes
89
+
This file gives a list of the minimum levels of various software
90
+
packages that are necessary to build and run the kernel
91
+
successfully.
92
+
93
+
Documentation/CodingStyle
94
+
This describes the Linux kernel coding style, and some of the
95
+
rationale behind it. All new code is expected to follow the
96
+
guidelines in this document. Most maintainers will only accept
97
+
patches if these rules are followed, and many people will only
98
+
review code if it is in the proper style.
99
+
100
+
Documentation/SubmittingPatches
101
+
Documentation/SubmittingDrivers
102
+
These files describe in explicit detail how to successfully create
103
+
and send a patch, including (but not limited to):
104
+
- Email contents
105
+
- Email format
106
+
- Who to send it to
107
+
Following these rules will not guarantee success (as all patches are
108
+
subject to scrutiny for content and style), but not following them
109
+
will almost always prevent it.
110
+
111
+
Other excellent descriptions of how to create patches properly are:
112
+
"The Perfect Patch"
113
+
http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt
114
+
"Linux kernel patch submission format"
115
+
http://linux.yyz.us/patch-format.html
116
+
117
+
Documentation/stable_api_nonsense.txt
118
+
This file describes the rationale behind the conscious decision to
119
+
not have a stable API within the kernel, including things like:
120
+
- Subsystem shim-layers (for compatibility?)
121
+
- Driver portability between Operating Systems.
122
+
- Mitigating rapid change within the kernel source tree (or
123
+
preventing rapid change)
124
+
This document is crucial for understanding the Linux development
125
+
philosophy and is very important for people moving to Linux from
126
+
development on other Operating Systems.
127
+
128
+
Documentation/SecurityBugs
129
+
If you feel you have found a security problem in the Linux kernel,
130
+
please follow the steps in this document to help notify the kernel
131
+
developers, and help solve the issue.
132
+
133
+
Documentation/ManagementStyle
134
+
This document describes how Linux kernel maintainers operate and the
135
+
shared ethos behind their methodologies. This is important reading
136
+
for anyone new to kernel development (or anyone simply curious about
137
+
it), as it resolves a lot of common misconceptions and confusion
138
+
about the unique behavior of kernel maintainers.
139
+
140
+
Documentation/stable_kernel_rules.txt
141
+
This file describes the rules on how the stable kernel releases
142
+
happen, and what to do if you want to get a change into one of these
143
+
releases.
144
+
145
+
Documentation/kernel-docs.txt
146
+
A list of external documentation that pertains to kernel
147
+
development. Please consult this list if you do not find what you
148
+
are looking for within the in-kernel documentation.
149
+
150
+
Documentation/applying-patches.txt
151
+
A good introduction describing exactly what a patch is and how to
152
+
apply it to the different development branches of the kernel.
153
+
154
+
The kernel also has a large number of documents that can be
155
+
automatically generated from the source code itself. This includes a
156
+
full description of the in-kernel API, and rules on how to handle
157
+
locking properly. The documents will be created in the
158
+
Documentation/DocBook/ directory and can be generated as PDF,
159
+
Postscript, HTML, and man pages by running:
160
+
make pdfdocs
161
+
make psdocs
162
+
make htmldocs
163
+
make mandocs
164
+
respectively from the main kernel source directory.
165
+
166
+
167
+
Becoming A Kernel Developer
168
+
---------------------------
169
+
170
+
If you do not know anything about Linux kernel development, you should
171
+
look at the Linux KernelNewbies project:
172
+
http://kernelnewbies.org
173
+
It consists of a helpful mailing list where you can ask almost any type
174
+
of basic kernel development question (make sure to search the archives
175
+
first, before asking something that has already been answered in the
176
+
past.) It also has an IRC channel that you can use to ask questions in
177
+
real-time, and a lot of helpful documentation that is useful for
178
+
learning about Linux kernel development.
179
+
180
+
The website has basic information about code organization, subsystems,
181
+
and current projects (both in-tree and out-of-tree). It also describes
182
+
some basic logistical information, like how to compile a kernel and
183
+
apply a patch.
184
+
185
+
If you do not know where you want to start, but you want to look for
186
+
some task to start doing to join into the kernel development community,
187
+
go to the Linux Kernel Janitor's project:
188
+
http://janitor.kernelnewbies.org/
189
+
It is a great place to start. It describes a list of relatively simple
190
+
problems that need to be cleaned up and fixed within the Linux kernel
191
+
source tree. Working with the developers in charge of this project, you
192
+
will learn the basics of getting your patch into the Linux kernel tree,
193
+
and possibly be pointed in the direction of what to go work on next, if
194
+
you do not already have an idea.
195
+
196
+
If you already have a chunk of code that you want to put into the kernel
197
+
tree, but need some help getting it in the proper form, the
198
+
kernel-mentors project was created to help you out with this. It is a
199
+
mailing list, and can be found at:
200
+
http://selenic.com/mailman/listinfo/kernel-mentors
201
+
202
+
Before making any actual modifications to the Linux kernel code, it is
203
+
imperative to understand how the code in question works. For this
204
+
purpose, nothing is better than reading through it directly (most tricky
205
+
bits are commented well), perhaps even with the help of specialized
206
+
tools. One such tool that is particularly recommended is the Linux
207
+
Cross-Reference project, which is able to present source code in a
208
+
self-referential, indexed webpage format. An excellent up-to-date
209
+
repository of the kernel code may be found at:
210
+
http://sosdg.org/~coywolf/lxr/
211
+
212
+
213
+
The development process
214
+
-----------------------
215
+
216
+
Linux kernel development process currently consists of a few different
217
+
main kernel "branches" and lots of different subsystem-specific kernel
218
+
branches. These different branches are:
219
+
- main 2.6.x kernel tree
220
+
- 2.6.x.y -stable kernel tree
221
+
- 2.6.x -git kernel patches
222
+
- 2.6.x -mm kernel patches
223
+
- subsystem specific kernel trees and patches
224
+
225
+
2.6.x kernel tree
226
+
-----------------
227
+
2.6.x kernels are maintained by Linus Torvalds, and can be found on
228
+
kernel.org in the pub/linux/kernel/v2.6/ directory. Its development
229
+
process is as follows:
230
+
- As soon as a new kernel is released a two weeks window is open,
231
+
during this period of time maintainers can submit big diffs to
232
+
Linus, usually the patches that have already been included in the
233
+
-mm kernel for a few weeks. The preferred way to submit big changes
234
+
is using git (the kernel's source management tool, more information
235
+
can be found at http://git.or.cz/) but plain patches are also just
236
+
fine.
237
+
- After two weeks a -rc1 kernel is released it is now possible to push
238
+
only patches that do not include new features that could affect the
239
+
stability of the whole kernel. Please note that a whole new driver
240
+
(or filesystem) might be accepted after -rc1 because there is no
241
+
risk of causing regressions with such a change as long as the change
242
+
is self-contained and does not affect areas outside of the code that
243
+
is being added. git can be used to send patches to Linus after -rc1
244
+
is released, but the patches need to also be sent to a public
245
+
mailing list for review.
246
+
- A new -rc is released whenever Linus deems the current git tree to
247
+
be in a reasonably sane state adequate for testing. The goal is to
248
+
release a new -rc kernel every week.
249
+
- Process continues until the kernel is considered "ready", the
250
+
process should last around 6 weeks.
251
+
252
+
It is worth mentioning what Andrew Morton wrote on the linux-kernel
253
+
mailing list about kernel releases:
254
+
"Nobody knows when a kernel will be released, because it's
255
+
released according to perceived bug status, not according to a
256
+
preconceived timeline."
257
+
258
+
2.6.x.y -stable kernel tree
259
+
---------------------------
260
+
Kernels with 4 digit versions are -stable kernels. They contain
261
+
relatively small and critical fixes for security problems or significant
262
+
regressions discovered in a given 2.6.x kernel.
263
+
264
+
This is the recommended branch for users who want the most recent stable
265
+
kernel and are not interested in helping test development/experimental
266
+
versions.
267
+
268
+
If no 2.6.x.y kernel is available, then the highest numbered 2.6.x
269
+
kernel is the current stable kernel.
270
+
271
+
2.6.x.y are maintained by the "stable" team <stable@kernel.org>, and are
272
+
released almost every other week.
273
+
274
+
The file Documentation/stable_kernel_rules.txt in the kernel tree
275
+
documents what kinds of changes are acceptable for the -stable tree, and
276
+
how the release process works.
277
+
278
+
2.6.x -git patches
279
+
------------------
280
+
These are daily snapshots of Linus' kernel tree which are managed in a
281
+
git repository (hence the name.) These patches are usually released
282
+
daily and represent the current state of Linus' tree. They are more
283
+
experimental than -rc kernels since they are generated automatically
284
+
without even a cursory glance to see if they are sane.
285
+
286
+
2.6.x -mm kernel patches
287
+
------------------------
288
+
These are experimental kernel patches released by Andrew Morton. Andrew
289
+
takes all of the different subsystem kernel trees and patches and mushes
290
+
them together, along with a lot of patches that have been plucked from
291
+
the linux-kernel mailing list. This tree serves as a proving ground for
292
+
new features and patches. Once a patch has proved its worth in -mm for
293
+
a while Andrew or the subsystem maintainer pushes it on to Linus for
294
+
inclusion in mainline.
295
+
296
+
It is heavily encouraged that all new patches get tested in the -mm tree
297
+
before they are sent to Linus for inclusion in the main kernel tree.
298
+
299
+
These kernels are not appropriate for use on systems that are supposed
300
+
to be stable and they are more risky to run than any of the other
301
+
branches.
302
+
303
+
If you wish to help out with the kernel development process, please test
304
+
and use these kernel releases and provide feedback to the linux-kernel
305
+
mailing list if you have any problems, and if everything works properly.
306
+
307
+
In addition to all the other experimental patches, these kernels usually
308
+
also contain any changes in the mainline -git kernels available at the
309
+
time of release.
310
+
311
+
The -mm kernels are not released on a fixed schedule, but usually a few
312
+
-mm kernels are released in between each -rc kernel (1 to 3 is common).
313
+
314
+
Subsystem Specific kernel trees and patches
315
+
-------------------------------------------
316
+
A number of the different kernel subsystem developers expose their
317
+
development trees so that others can see what is happening in the
318
+
different areas of the kernel. These trees are pulled into the -mm
319
+
kernel releases as described above.
320
+
321
+
Here is a list of some of the different kernel trees available:
322
+
git trees:
323
+
- Kbuild development tree, Sam Ravnborg <sam@ravnborg.org>
324
+
kernel.org:/pub/scm/linux/kernel/git/sam/kbuild.git
325
+
326
+
- ACPI development tree, Len Brown <len.brown@intel.com>
327
+
kernel.org:/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6.git
328
+
329
+
- Block development tree, Jens Axboe <axboe@suse.de>
330
+
kernel.org:/pub/scm/linux/kernel/git/axboe/linux-2.6-block.git
331
+
332
+
- DRM development tree, Dave Airlie <airlied@linux.ie>
333
+
kernel.org:/pub/scm/linux/kernel/git/airlied/drm-2.6.git
334
+
335
+
- ia64 development tree, Tony Luck <tony.luck@intel.com>
336
+
kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
337
+
338
+
- ieee1394 development tree, Jody McIntyre <scjody@modernduck.com>
339
+
kernel.org:/pub/scm/linux/kernel/git/scjody/ieee1394.git
340
+
341
+
- infiniband, Roland Dreier <rolandd@cisco.com>
342
+
kernel.org:/pub/scm/linux/kernel/git/roland/infiniband.git
343
+
344
+
- libata, Jeff Garzik <jgarzik@pobox.com>
345
+
kernel.org:/pub/scm/linux/kernel/git/jgarzik/libata-dev.git
346
+
347
+
- network drivers, Jeff Garzik <jgarzik@pobox.com>
348
+
kernel.org:/pub/scm/linux/kernel/git/jgarzik/netdev-2.6.git
349
+
350
+
- pcmcia, Dominik Brodowski <linux@dominikbrodowski.net>
351
+
kernel.org:/pub/scm/linux/kernel/git/brodo/pcmcia-2.6.git
352
+
353
+
- SCSI, James Bottomley <James.Bottomley@SteelEye.com>
354
+
kernel.org:/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6.git
355
+
356
+
Other git kernel trees can be found listed at http://kernel.org/git
357
+
358
+
quilt trees:
359
+
- USB, PCI, Driver Core, and I2C, Greg Kroah-Hartman <gregkh@suse.de>
360
+
kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/
361
+
362
+
363
+
Bug Reporting
364
+
-------------
365
+
366
+
bugzilla.kernel.org is where the Linux kernel developers track kernel
367
+
bugs. Users are encouraged to report all bugs that they find in this
368
+
tool. For details on how to use the kernel bugzilla, please see:
369
+
http://test.kernel.org/bugzilla/faq.html
370
+
371
+
The file REPORTING-BUGS in the main kernel source directory has a good
372
+
template for how to report a possible kernel bug, and details what kind
373
+
of information is needed by the kernel developers to help track down the
374
+
problem.
375
+
376
+
377
+
Mailing lists
378
+
-------------
379
+
380
+
As some of the above documents describe, the majority of the core kernel
381
+
developers participate on the Linux Kernel Mailing list. Details on how
382
+
to subscribe and unsubscribe from the list can be found at:
383
+
http://vger.kernel.org/vger-lists.html#linux-kernel
384
+
There are archives of the mailing list on the web in many different
385
+
places. Use a search engine to find these archives. For example:
386
+
http://dir.gmane.org/gmane.linux.kernel
387
+
It is highly recommended that you search the archives about the topic
388
+
you want to bring up, before you post it to the list. A lot of things
389
+
already discussed in detail are only recorded at the mailing list
390
+
archives.
391
+
392
+
Most of the individual kernel subsystems also have their own separate
393
+
mailing list where they do their development efforts. See the
394
+
MAINTAINERS file for a list of what these lists are for the different
395
+
groups.
396
+
397
+
Many of the lists are hosted on kernel.org. Information on them can be
398
+
found at:
399
+
http://vger.kernel.org/vger-lists.html
400
+
401
+
Please remember to follow good behavioral habits when using the lists.
402
+
Though a bit cheesy, the following URL has some simple guidelines for
403
+
interacting with the list (or any list):
404
+
http://www.albion.com/netiquette/
405
+
406
+
If multiple people respond to your mail, the CC: list of recipients may
407
+
get pretty large. Don't remove anybody from the CC: list without a good
408
+
reason, or don't reply only to the list address. Get used to receiving the
409
+
mail twice, one from the sender and the one from the list, and don't try
410
+
to tune that by adding fancy mail-headers, people will not like it.
411
+
412
+
Remember to keep the context and the attribution of your replies intact,
413
+
keep the "John Kernelhacker wrote ...:" lines at the top of your reply, and
414
+
add your statements between the individual quoted sections instead of
415
+
writing at the top of the mail.
416
+
417
+
If you add patches to your mail, make sure they are plain readable text
418
+
as stated in Documentation/SubmittingPatches. Kernel developers don't
419
+
want to deal with attachments or compressed patches; they may want
420
+
to comment on individual lines of your patch, which works only that way.
421
+
Make sure you use a mail program that does not mangle spaces and tab
422
+
characters. A good first test is to send the mail to yourself and try
423
+
to apply your own patch by yourself. If that doesn't work, get your
424
+
mail program fixed or change it until it works.
425
+
426
+
Above all, please remember to show respect to other subscribers.
427
+
428
+
429
+
Working with the community
430
+
--------------------------
431
+
432
+
The goal of the kernel community is to provide the best possible kernel
433
+
there is. When you submit a patch for acceptance, it will be reviewed
434
+
on its technical merits and those alone. So, what should you be
435
+
expecting?
436
+
- criticism
437
+
- comments
438
+
- requests for change
439
+
- requests for justification
440
+
- silence
441
+
442
+
Remember, this is part of getting your patch into the kernel. You have
443
+
to be able to take criticism and comments about your patches, evaluate
444
+
them at a technical level and either rework your patches or provide
445
+
clear and concise reasoning as to why those changes should not be made.
446
+
If there are no responses to your posting, wait a few days and try
447
+
again, sometimes things get lost in the huge volume.
448
+
449
+
What should you not do?
450
+
- expect your patch to be accepted without question
451
+
- become defensive
452
+
- ignore comments
453
+
- resubmit the patch without making any of the requested changes
454
+
455
+
In a community that is looking for the best technical solution possible,
456
+
there will always be differing opinions on how beneficial a patch is.
457
+
You have to be cooperative, and willing to adapt your idea to fit within
458
+
the kernel. Or at least be willing to prove your idea is worth it.
459
+
Remember, being wrong is acceptable as long as you are willing to work
460
+
toward a solution that is right.
461
+
462
+
It is normal that the answers to your first patch might simply be a list
463
+
of a dozen things you should correct. This does _not_ imply that your
464
+
patch will not be accepted, and it is _not_ meant against you
465
+
personally. Simply correct all issues raised against your patch and
466
+
resend it.
467
+
468
+
469
+
Differences between the kernel community and corporate structures
470
+
-----------------------------------------------------------------
471
+
472
+
The kernel community works differently than most traditional corporate
473
+
development environments. Here are a list of things that you can try to
474
+
do to try to avoid problems:
475
+
Good things to say regarding your proposed changes:
476
+
- "This solves multiple problems."
477
+
- "This deletes 2000 lines of code."
478
+
- "Here is a patch that explains what I am trying to describe."
479
+
- "I tested it on 5 different architectures..."
480
+
- "Here is a series of small patches that..."
481
+
- "This increases performance on typical machines..."
482
+
483
+
Bad things you should avoid saying:
484
+
- "We did it this way in AIX/ptx/Solaris, so therefore it must be
485
+
good..."
486
+
- "I've being doing this for 20 years, so..."
487
+
- "This is required for my company to make money"
488
+
- "This is for our Enterprise product line."
489
+
- "Here is my 1000 page design document that describes my idea"
490
+
- "I've been working on this for 6 months..."
491
+
- "Here's a 5000 line patch that..."
492
+
- "I rewrote all of the current mess, and here it is..."
493
+
- "I have a deadline, and this patch needs to be applied now."
494
+
495
+
Another way the kernel community is different than most traditional
496
+
software engineering work environments is the faceless nature of
497
+
interaction. One benefit of using email and irc as the primary forms of
498
+
communication is the lack of discrimination based on gender or race.
499
+
The Linux kernel work environment is accepting of women and minorities
500
+
because all you are is an email address. The international aspect also
501
+
helps to level the playing field because you can't guess gender based on
502
+
a person's name. A man may be named Andrea and a woman may be named Pat.
503
+
Most women who have worked in the Linux kernel and have expressed an
504
+
opinion have had positive experiences.
505
+
506
+
The language barrier can cause problems for some people who are not
507
+
comfortable with English. A good grasp of the language can be needed in
508
+
order to get ideas across properly on mailing lists, so it is
509
+
recommended that you check your emails to make sure they make sense in
510
+
English before sending them.
511
+
512
+
513
+
Break up your changes
514
+
---------------------
515
+
516
+
The Linux kernel community does not gladly accept large chunks of code
517
+
dropped on it all at once. The changes need to be properly introduced,
518
+
discussed, and broken up into tiny, individual portions. This is almost
519
+
the exact opposite of what companies are used to doing. Your proposal
520
+
should also be introduced very early in the development process, so that
521
+
you can receive feedback on what you are doing. It also lets the
522
+
community feel that you are working with them, and not simply using them
523
+
as a dumping ground for your feature. However, don't send 50 emails at
524
+
one time to a mailing list, your patch series should be smaller than
525
+
that almost all of the time.
526
+
527
+
The reasons for breaking things up are the following:
528
+
529
+
1) Small patches increase the likelihood that your patches will be
530
+
applied, since they don't take much time or effort to verify for
531
+
correctness. A 5 line patch can be applied by a maintainer with
532
+
barely a second glance. However, a 500 line patch may take hours to
533
+
review for correctness (the time it takes is exponentially
534
+
proportional to the size of the patch, or something).
535
+
536
+
Small patches also make it very easy to debug when something goes
537
+
wrong. It's much easier to back out patches one by one than it is
538
+
to dissect a very large patch after it's been applied (and broken
539
+
something).
540
+
541
+
2) It's important not only to send small patches, but also to rewrite
542
+
and simplify (or simply re-order) patches before submitting them.
543
+
544
+
Here is an analogy from kernel developer Al Viro:
545
+
"Think of a teacher grading homework from a math student. The
546
+
teacher does not want to see the student's trials and errors
547
+
before they came up with the solution. They want to see the
548
+
cleanest, most elegant answer. A good student knows this, and
549
+
would never submit her intermediate work before the final
550
+
solution."
551
+
552
+
The same is true of kernel development. The maintainers and
553
+
reviewers do not want to see the thought process behind the
554
+
solution to the problem one is solving. They want to see a
555
+
simple and elegant solution."
556
+
557
+
It may be challenging to keep the balance between presenting an elegant
558
+
solution and working together with the community and discussing your
559
+
unfinished work. Therefore it is good to get early in the process to
560
+
get feedback to improve your work, but also keep your changes in small
561
+
chunks that they may get already accepted, even when your whole task is
562
+
not ready for inclusion now.
563
+
564
+
Also realize that it is not acceptable to send patches for inclusion
565
+
that are unfinished and will be "fixed up later."
566
+
567
+
568
+
Justify your change
569
+
-------------------
570
+
571
+
Along with breaking up your patches, it is very important for you to let
572
+
the Linux community know why they should add this change. New features
573
+
must be justified as being needed and useful.
574
+
575
+
576
+
Document your change
577
+
--------------------
578
+
579
+
When sending in your patches, pay special attention to what you say in
580
+
the text in your email. This information will become the ChangeLog
581
+
information for the patch, and will be preserved for everyone to see for
582
+
all time. It should describe the patch completely, containing:
583
+
- why the change is necessary
584
+
- the overall design approach in the patch
585
+
- implementation details
586
+
- testing results
587
+
588
+
For more details on what this should all look like, please see the
589
+
ChangeLog section of the document:
590
+
"The Perfect Patch"
591
+
http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt
592
+
593
+
594
+
595
+
596
+
All of these things are sometimes very hard to do. It can take years to
597
+
perfect these practices (if at all). It's a continuous process of
598
+
improvement that requires a lot of patience and determination. But
599
+
don't give up, it's possible. Many have done it before, and each had to
600
+
start exactly where you are now.
601
+
602
+
603
+
604
+
605
+
----------
606
+
Thanks to Paolo Ciarrocchi who allowed the "Development Process" section
607
+
to be based on text he had written, and to Randy Dunlap and Gerrit
608
+
Huizenga for some of the list of things you should and should not say.
609
+
Also thanks to Pat Mochel, Hanna Linder, Randy Dunlap, Kay Sievers,
610
+
Vojtech Pavlik, Jan Kara, Josh Boyer, Kees Cook, Andrew Morton, Andi
611
+
Kleen, Vadim Lobanov, Jesper Juhl, Adrian Bunk, Keri Harris, Frans Pop,
612
+
David A. Wheeler, Junio Hamano, Michael Kerrisk, and Alex Shepard for
613
+
their review, comments, and contributions. Without their help, this
614
+
document would not have been possible.
615
+
616
+
617
+
618
+
Maintainer: Greg Kroah-Hartman <greg@kroah.com>