1 2 How to Get Your Change Into the Linux Kernel 3 or 4 Care And Operation Of Your Linus Torvalds 5 6 7 8For a person or company who wishes to submit a change to the Linux 9kernel, the process can sometimes be daunting if you're not familiar 10with "the system." This text is a collection of suggestions which 11can greatly increase the chances of your change being accepted. 12 13Read Documentation/SubmitChecklist for a list of items to check 14before submitting code. If you are submitting a driver, also read 15Documentation/SubmittingDrivers. 16 17 18 19-------------------------------------------- 20SECTION 1 - CREATING AND SENDING YOUR CHANGE 21-------------------------------------------- 22 23 24 251) "diff -up" 26------------ 27 28Use "diff -up" or "diff -uprN" to create patches. 29 30All changes to the Linux kernel occur in the form of patches, as 31generated by diff(1). When creating your patch, make sure to create it 32in "unified diff" format, as supplied by the '-u' argument to diff(1). 33Also, please use the '-p' argument which shows which C function each 34change is in - that makes the resultant diff a lot easier to read. 35Patches should be based in the root kernel source directory, 36not in any lower subdirectory. 37 38To create a patch for a single file, it is often sufficient to do: 39 40 SRCTREE= linux-2.6 41 MYFILE= drivers/net/mydriver.c 42 43 cd $SRCTREE 44 cp $MYFILE $MYFILE.orig 45 vi $MYFILE # make your change 46 cd .. 47 diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch 48 49To create a patch for multiple files, you should unpack a "vanilla", 50or unmodified kernel source tree, and generate a diff against your 51own source tree. For example: 52 53 MYSRC= /devel/linux-2.6 54 55 tar xvfz linux-2.6.12.tar.gz 56 mv linux-2.6.12 linux-2.6.12-vanilla 57 diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \ 58 linux-2.6.12-vanilla $MYSRC > /tmp/patch 59 60"dontdiff" is a list of files which are generated by the kernel during 61the build process, and should be ignored in any diff(1)-generated 62patch. The "dontdiff" file is included in the kernel tree in 632.6.12 and later. For earlier kernel versions, you can get it 64from <http://www.xenotime.net/linux/doc/dontdiff>. 65 66Make sure your patch does not include any extra files which do not 67belong in a patch submission. Make sure to review your patch -after- 68generated it with diff(1), to ensure accuracy. 69 70If your changes produce a lot of deltas, you may want to look into 71splitting them into individual patches which modify things in 72logical stages. This will facilitate easier reviewing by other 73kernel developers, very important if you want your patch accepted. 74There are a number of scripts which can aid in this: 75 76Quilt: 77http://savannah.nongnu.org/projects/quilt 78 79Andrew Morton's patch scripts: 80http://www.zip.com.au/~akpm/linux/patches/ 81Instead of these scripts, quilt is the recommended patch management 82tool (see above). 83 84 85 862) Describe your changes. 87 88Describe the technical detail of the change(s) your patch includes. 89 90Be as specific as possible. The WORST descriptions possible include 91things like "update driver X", "bug fix for driver X", or "this patch 92includes updates for subsystem X. Please apply." 93 94If your description starts to get long, that's a sign that you probably 95need to split up your patch. See #3, next. 96 97 98 993) Separate your changes. 100 101Separate _logical changes_ into a single patch file. 102 103For example, if your changes include both bug fixes and performance 104enhancements for a single driver, separate those changes into two 105or more patches. If your changes include an API update, and a new 106driver which uses that new API, separate those into two patches. 107 108On the other hand, if you make a single change to numerous files, 109group those changes into a single patch. Thus a single logical change 110is contained within a single patch. 111 112If one patch depends on another patch in order for a change to be 113complete, that is OK. Simply note "this patch depends on patch X" 114in your patch description. 115 116If you cannot condense your patch set into a smaller set of patches, 117then only post say 15 or so at a time and wait for review and integration. 118 119 120 1214) Select e-mail destination. 122 123Look through the MAINTAINERS file and the source code, and determine 124if your change applies to a specific subsystem of the kernel, with 125an assigned maintainer. If so, e-mail that person. 126 127If no maintainer is listed, or the maintainer does not respond, send 128your patch to the primary Linux kernel developer's mailing list, 129linux-kernel@vger.kernel.org. Most kernel developers monitor this 130e-mail list, and can comment on your changes. 131 132 133Do not send more than 15 patches at once to the vger mailing lists!!! 134 135 136Linus Torvalds is the final arbiter of all changes accepted into the 137Linux kernel. His e-mail address is <torvalds@linux-foundation.org>. 138He gets a lot of e-mail, so typically you should do your best to -avoid- 139sending him e-mail. 140 141Patches which are bug fixes, are "obvious" changes, or similarly 142require little discussion should be sent or CC'd to Linus. Patches 143which require discussion or do not have a clear advantage should 144usually be sent first to linux-kernel. Only after the patch is 145discussed should the patch then be submitted to Linus. 146 147 148 1495) Select your CC (e-mail carbon copy) list. 150 151Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org. 152 153Other kernel developers besides Linus need to be aware of your change, 154so that they may comment on it and offer code review and suggestions. 155linux-kernel is the primary Linux kernel developer mailing list. 156Other mailing lists are available for specific subsystems, such as 157USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the 158MAINTAINERS file for a mailing list that relates specifically to 159your change. 160 161Majordomo lists of VGER.KERNEL.ORG at: 162 <http://vger.kernel.org/vger-lists.html> 163 164If changes affect userland-kernel interfaces, please send 165the MAN-PAGES maintainer (as listed in the MAINTAINERS file) 166a man-pages patch, or at least a notification of the change, 167so that some information makes its way into the manual pages. 168 169Even if the maintainer did not respond in step #4, make sure to ALWAYS 170copy the maintainer when you change their code. 171 172For small patches you may want to CC the Trivial Patch Monkey 173trivial@kernel.org managed by Adrian Bunk; which collects "trivial" 174patches. Trivial patches must qualify for one of the following rules: 175 Spelling fixes in documentation 176 Spelling fixes which could break grep(1) 177 Warning fixes (cluttering with useless warnings is bad) 178 Compilation fixes (only if they are actually correct) 179 Runtime fixes (only if they actually fix things) 180 Removing use of deprecated functions/macros (eg. check_region) 181 Contact detail and documentation fixes 182 Non-portable code replaced by portable code (even in arch-specific, 183 since people copy, as long as it's trivial) 184 Any fix by the author/maintainer of the file (ie. patch monkey 185 in re-transmission mode) 186URL: <http://www.kernel.org/pub/linux/kernel/people/bunk/trivial/> 187 188 189 190 1916) No MIME, no links, no compression, no attachments. Just plain text. 192 193Linus and other kernel developers need to be able to read and comment 194on the changes you are submitting. It is important for a kernel 195developer to be able to "quote" your changes, using standard e-mail 196tools, so that they may comment on specific portions of your code. 197 198For this reason, all patches should be submitting e-mail "inline". 199WARNING: Be wary of your editor's word-wrap corrupting your patch, 200if you choose to cut-n-paste your patch. 201 202Do not attach the patch as a MIME attachment, compressed or not. 203Many popular e-mail applications will not always transmit a MIME 204attachment as plain text, making it impossible to comment on your 205code. A MIME attachment also takes Linus a bit more time to process, 206decreasing the likelihood of your MIME-attached change being accepted. 207 208Exception: If your mailer is mangling patches then someone may ask 209you to re-send them using MIME. 210 211 212WARNING: Some mailers like Mozilla send your messages with 213---- message header ---- 214Content-Type: text/plain; charset=us-ascii; format=flowed 215---- message header ---- 216The problem is that "format=flowed" makes some of the mailers 217on receiving side to replace TABs with spaces and do similar 218changes. Thus the patches from you can look corrupted. 219 220To fix this just make your mozilla defaults/pref/mailnews.js file to look like: 221pref("mailnews.send_plaintext_flowed", false); // RFC 2646======= 222pref("mailnews.display.disable_format_flowed_support", true); 223 224 225 2267) E-mail size. 227 228When sending patches to Linus, always follow step #6. 229 230Large changes are not appropriate for mailing lists, and some 231maintainers. If your patch, uncompressed, exceeds 40 kB in size, 232it is preferred that you store your patch on an Internet-accessible 233server, and provide instead a URL (link) pointing to your patch. 234 235 236 2378) Name your kernel version. 238 239It is important to note, either in the subject line or in the patch 240description, the kernel version to which this patch applies. 241 242If the patch does not apply cleanly to the latest kernel version, 243Linus will not apply it. 244 245 246 2479) Don't get discouraged. Re-submit. 248 249After you have submitted your change, be patient and wait. If Linus 250likes your change and applies it, it will appear in the next version 251of the kernel that he releases. 252 253However, if your change doesn't appear in the next version of the 254kernel, there could be any number of reasons. It's YOUR job to 255narrow down those reasons, correct what was wrong, and submit your 256updated change. 257 258It is quite common for Linus to "drop" your patch without comment. 259That's the nature of the system. If he drops your patch, it could be 260due to 261* Your patch did not apply cleanly to the latest kernel version. 262* Your patch was not sufficiently discussed on linux-kernel. 263* A style issue (see section 2). 264* An e-mail formatting issue (re-read this section). 265* A technical problem with your change. 266* He gets tons of e-mail, and yours got lost in the shuffle. 267* You are being annoying. 268 269When in doubt, solicit comments on linux-kernel mailing list. 270 271 272 27310) Include PATCH in the subject 274 275Due to high e-mail traffic to Linus, and to linux-kernel, it is common 276convention to prefix your subject line with [PATCH]. This lets Linus 277and other kernel developers more easily distinguish patches from other 278e-mail discussions. 279 280 281 28211) Sign your work 283 284To improve tracking of who did what, especially with patches that can 285percolate to their final resting place in the kernel through several 286layers of maintainers, we've introduced a "sign-off" procedure on 287patches that are being emailed around. 288 289The sign-off is a simple line at the end of the explanation for the 290patch, which certifies that you wrote it or otherwise have the right to 291pass it on as a open-source patch. The rules are pretty simple: if you 292can certify the below: 293 294 Developer's Certificate of Origin 1.1 295 296 By making a contribution to this project, I certify that: 297 298 (a) The contribution was created in whole or in part by me and I 299 have the right to submit it under the open source license 300 indicated in the file; or 301 302 (b) The contribution is based upon previous work that, to the best 303 of my knowledge, is covered under an appropriate open source 304 license and I have the right under that license to submit that 305 work with modifications, whether created in whole or in part 306 by me, under the same open source license (unless I am 307 permitted to submit under a different license), as indicated 308 in the file; or 309 310 (c) The contribution was provided directly to me by some other 311 person who certified (a), (b) or (c) and I have not modified 312 it. 313 314 (d) I understand and agree that this project and the contribution 315 are public and that a record of the contribution (including all 316 personal information I submit with it, including my sign-off) is 317 maintained indefinitely and may be redistributed consistent with 318 this project or the open source license(s) involved. 319 320then you just add a line saying 321 322 Signed-off-by: Random J Developer <random@developer.example.org> 323 324using your real name (sorry, no pseudonyms or anonymous contributions.) 325 326Some people also put extra tags at the end. They'll just be ignored for 327now, but you can do this to mark internal company procedures or just 328point out some special detail about the sign-off. 329 330 33112) The canonical patch format 332 333The canonical patch subject line is: 334 335 Subject: [PATCH 001/123] subsystem: summary phrase 336 337The canonical patch message body contains the following: 338 339 - A "from" line specifying the patch author. 340 341 - An empty line. 342 343 - The body of the explanation, which will be copied to the 344 permanent changelog to describe this patch. 345 346 - The "Signed-off-by:" lines, described above, which will 347 also go in the changelog. 348 349 - A marker line containing simply "---". 350 351 - Any additional comments not suitable for the changelog. 352 353 - The actual patch (diff output). 354 355The Subject line format makes it very easy to sort the emails 356alphabetically by subject line - pretty much any email reader will 357support that - since because the sequence number is zero-padded, 358the numerical and alphabetic sort is the same. 359 360The "subsystem" in the email's Subject should identify which 361area or subsystem of the kernel is being patched. 362 363The "summary phrase" in the email's Subject should concisely 364describe the patch which that email contains. The "summary 365phrase" should not be a filename. Do not use the same "summary 366phrase" for every patch in a whole patch series. 367 368Bear in mind that the "summary phrase" of your email becomes 369a globally-unique identifier for that patch. It propagates 370all the way into the git changelog. The "summary phrase" may 371later be used in developer discussions which refer to the patch. 372People will want to google for the "summary phrase" to read 373discussion regarding that patch. 374 375A couple of example Subjects: 376 377 Subject: [patch 2/5] ext2: improve scalability of bitmap searching 378 Subject: [PATCHv2 001/207] x86: fix eflags tracking 379 380The "from" line must be the very first line in the message body, 381and has the form: 382 383 From: Original Author <author@example.com> 384 385The "from" line specifies who will be credited as the author of the 386patch in the permanent changelog. If the "from" line is missing, 387then the "From:" line from the email header will be used to determine 388the patch author in the changelog. 389 390The explanation body will be committed to the permanent source 391changelog, so should make sense to a competent reader who has long 392since forgotten the immediate details of the discussion that might 393have led to this patch. 394 395The "---" marker line serves the essential purpose of marking for patch 396handling tools where the changelog message ends. 397 398One good use for the additional comments after the "---" marker is for 399a diffstat, to show what files have changed, and the number of inserted 400and deleted lines per file. A diffstat is especially useful on bigger 401patches. Other comments relevant only to the moment or the maintainer, 402not suitable for the permanent changelog, should also go here. 403Use diffstat options "-p 1 -w 70" so that filenames are listed from the 404top of the kernel source tree and don't use too much horizontal space 405(easily fit in 80 columns, maybe with some indentation). 406 407See more details on the proper patch format in the following 408references. 409 410 411 412 413----------------------------------- 414SECTION 2 - HINTS, TIPS, AND TRICKS 415----------------------------------- 416 417This section lists many of the common "rules" associated with code 418submitted to the kernel. There are always exceptions... but you must 419have a really good reason for doing so. You could probably call this 420section Linus Computer Science 101. 421 422 423 4241) Read Documentation/CodingStyle 425 426Nuff said. If your code deviates too much from this, it is likely 427to be rejected without further review, and without comment. 428 429 430 4312) #ifdefs are ugly 432 433Code cluttered with ifdefs is difficult to read and maintain. Don't do 434it. Instead, put your ifdefs in a header, and conditionally define 435'static inline' functions, or macros, which are used in the code. 436Let the compiler optimize away the "no-op" case. 437 438Simple example, of poor code: 439 440 dev = alloc_etherdev (sizeof(struct funky_private)); 441 if (!dev) 442 return -ENODEV; 443 #ifdef CONFIG_NET_FUNKINESS 444 init_funky_net(dev); 445 #endif 446 447Cleaned-up example: 448 449(in header) 450 #ifndef CONFIG_NET_FUNKINESS 451 static inline void init_funky_net (struct net_device *d) {} 452 #endif 453 454(in the code itself) 455 dev = alloc_etherdev (sizeof(struct funky_private)); 456 if (!dev) 457 return -ENODEV; 458 init_funky_net(dev); 459 460 461 4623) 'static inline' is better than a macro 463 464Static inline functions are greatly preferred over macros. 465They provide type safety, have no length limitations, no formatting 466limitations, and under gcc they are as cheap as macros. 467 468Macros should only be used for cases where a static inline is clearly 469suboptimal [there a few, isolated cases of this in fast paths], 470or where it is impossible to use a static inline function [such as 471string-izing]. 472 473'static inline' is preferred over 'static __inline__', 'extern inline', 474and 'extern __inline__'. 475 476 477 4784) Don't over-design. 479 480Don't try to anticipate nebulous future cases which may or may not 481be useful: "Make it as simple as you can, and no simpler." 482 483 484 485---------------------- 486SECTION 3 - REFERENCES 487---------------------- 488 489Andrew Morton, "The perfect patch" (tpp). 490 <http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt> 491 492Jeff Garzik, "Linux kernel patch submission format". 493 <http://linux.yyz.us/patch-format.html> 494 495Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer". 496 <http://www.kroah.com/log/2005/03/31/> 497 <http://www.kroah.com/log/2005/07/08/> 498 <http://www.kroah.com/log/2005/10/19/> 499 <http://www.kroah.com/log/2006/01/11/> 500 501NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people! 502 <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2> 503 504Kernel Documentation/CodingStyle: 505 <http://sosdg.org/~coywolf/lxr/source/Documentation/CodingStyle> 506 507Linus Torvalds's mail on the canonical patch format: 508 <http://lkml.org/lkml/2005/4/7/183> 509-- 510