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 13If you are submitting a driver, also read Documentation/SubmittingDrivers. 14 15 16 17-------------------------------------------- 18SECTION 1 - CREATING AND SENDING YOUR CHANGE 19-------------------------------------------- 20 21 22 231) "diff -up" 24------------ 25 26Use "diff -up" or "diff -uprN" to create patches. 27 28All changes to the Linux kernel occur in the form of patches, as 29generated by diff(1). When creating your patch, make sure to create it 30in "unified diff" format, as supplied by the '-u' argument to diff(1). 31Also, please use the '-p' argument which shows which C function each 32change is in - that makes the resultant diff a lot easier to read. 33Patches should be based in the root kernel source directory, 34not in any lower subdirectory. 35 36To create a patch for a single file, it is often sufficient to do: 37 38 SRCTREE= linux-2.6 39 MYFILE= drivers/net/mydriver.c 40 41 cd $SRCTREE 42 cp $MYFILE $MYFILE.orig 43 vi $MYFILE # make your change 44 cd .. 45 diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch 46 47To create a patch for multiple files, you should unpack a "vanilla", 48or unmodified kernel source tree, and generate a diff against your 49own source tree. For example: 50 51 MYSRC= /devel/linux-2.6 52 53 tar xvfz linux-2.6.12.tar.gz 54 mv linux-2.6.12 linux-2.6.12-vanilla 55 diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \ 56 linux-2.6.12-vanilla $MYSRC > /tmp/patch 57 58"dontdiff" is a list of files which are generated by the kernel during 59the build process, and should be ignored in any diff(1)-generated 60patch. The "dontdiff" file is included in the kernel tree in 612.6.12 and later. For earlier kernel versions, you can get it 62from <http://www.xenotime.net/linux/doc/dontdiff>. 63 64Make sure your patch does not include any extra files which do not 65belong in a patch submission. Make sure to review your patch -after- 66generated it with diff(1), to ensure accuracy. 67 68If your changes produce a lot of deltas, you may want to look into 69splitting them into individual patches which modify things in 70logical stages. This will facilitate easier reviewing by other 71kernel developers, very important if you want your patch accepted. 72There are a number of scripts which can aid in this: 73 74Quilt: 75http://savannah.nongnu.org/projects/quilt 76 77Randy Dunlap's patch scripts: 78http://www.xenotime.net/linux/scripts/patching-scripts-002.tar.gz 79 80Andrew Morton's patch scripts: 81http://www.zip.com.au/~akpm/linux/patches/patch-scripts-0.20 82 83 84 852) Describe your changes. 86 87Describe the technical detail of the change(s) your patch includes. 88 89Be as specific as possible. The WORST descriptions possible include 90things like "update driver X", "bug fix for driver X", or "this patch 91includes updates for subsystem X. Please apply." 92 93If your description starts to get long, that's a sign that you probably 94need to split up your patch. See #3, next. 95 96 97 983) Separate your changes. 99 100Separate each logical change into its own patch. 101 102For example, if your changes include both bug fixes and performance 103enhancements for a single driver, separate those changes into two 104or more patches. If your changes include an API update, and a new 105driver which uses that new API, separate those into two patches. 106 107On the other hand, if you make a single change to numerous files, 108group those changes into a single patch. Thus a single logical change 109is contained within a single patch. 110 111If one patch depends on another patch in order for a change to be 112complete, that is OK. Simply note "this patch depends on patch X" 113in your patch description. 114 115 1164) Select e-mail destination. 117 118Look through the MAINTAINERS file and the source code, and determine 119if your change applies to a specific subsystem of the kernel, with 120an assigned maintainer. If so, e-mail that person. 121 122If no maintainer is listed, or the maintainer does not respond, send 123your patch to the primary Linux kernel developer's mailing list, 124linux-kernel@vger.kernel.org. Most kernel developers monitor this 125e-mail list, and can comment on your changes. 126 127Linus Torvalds is the final arbiter of all changes accepted into the 128Linux kernel. His e-mail address is <torvalds@osdl.org>. He gets 129a lot of e-mail, so typically you should do your best to -avoid- sending 130him e-mail. 131 132Patches which are bug fixes, are "obvious" changes, or similarly 133require little discussion should be sent or CC'd to Linus. Patches 134which require discussion or do not have a clear advantage should 135usually be sent first to linux-kernel. Only after the patch is 136discussed should the patch then be submitted to Linus. 137 138 139 1405) Select your CC (e-mail carbon copy) list. 141 142Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org. 143 144Other kernel developers besides Linus need to be aware of your change, 145so that they may comment on it and offer code review and suggestions. 146linux-kernel is the primary Linux kernel developer mailing list. 147Other mailing lists are available for specific subsystems, such as 148USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the 149MAINTAINERS file for a mailing list that relates specifically to 150your change. 151 152If changes affect userland-kernel interfaces, please send 153the MAN-PAGES maintainer (as listed in the MAINTAINERS file) 154a man-pages patch, or at least a notification of the change, 155so that some information makes its way into the manual pages. 156 157Even if the maintainer did not respond in step #4, make sure to ALWAYS 158copy the maintainer when you change their code. 159 160For small patches you may want to CC the Trivial Patch Monkey 161trivial@rustcorp.com.au set up by Rusty Russell; which collects "trivial" 162patches. Trivial patches must qualify for one of the following rules: 163 Spelling fixes in documentation 164 Spelling fixes which could break grep(1). 165 Warning fixes (cluttering with useless warnings is bad) 166 Compilation fixes (only if they are actually correct) 167 Runtime fixes (only if they actually fix things) 168 Removing use of deprecated functions/macros (eg. check_region). 169 Contact detail and documentation fixes 170 Non-portable code replaced by portable code (even in arch-specific, 171 since people copy, as long as it's trivial) 172 Any fix by the author/maintainer of the file. (ie. patch monkey 173 in re-transmission mode) 174URL: <http://www.kernel.org/pub/linux/kernel/people/rusty/trivial/> 175 176 177 178 1796) No MIME, no links, no compression, no attachments. Just plain text. 180 181Linus and other kernel developers need to be able to read and comment 182on the changes you are submitting. It is important for a kernel 183developer to be able to "quote" your changes, using standard e-mail 184tools, so that they may comment on specific portions of your code. 185 186For this reason, all patches should be submitting e-mail "inline". 187WARNING: Be wary of your editor's word-wrap corrupting your patch, 188if you choose to cut-n-paste your patch. 189 190Do not attach the patch as a MIME attachment, compressed or not. 191Many popular e-mail applications will not always transmit a MIME 192attachment as plain text, making it impossible to comment on your 193code. A MIME attachment also takes Linus a bit more time to process, 194decreasing the likelihood of your MIME-attached change being accepted. 195 196Exception: If your mailer is mangling patches then someone may ask 197you to re-send them using MIME. 198 199 200 2017) E-mail size. 202 203When sending patches to Linus, always follow step #6. 204 205Large changes are not appropriate for mailing lists, and some 206maintainers. If your patch, uncompressed, exceeds 40 kB in size, 207it is preferred that you store your patch on an Internet-accessible 208server, and provide instead a URL (link) pointing to your patch. 209 210 211 2128) Name your kernel version. 213 214It is important to note, either in the subject line or in the patch 215description, the kernel version to which this patch applies. 216 217If the patch does not apply cleanly to the latest kernel version, 218Linus will not apply it. 219 220 221 2229) Don't get discouraged. Re-submit. 223 224After you have submitted your change, be patient and wait. If Linus 225likes your change and applies it, it will appear in the next version 226of the kernel that he releases. 227 228However, if your change doesn't appear in the next version of the 229kernel, there could be any number of reasons. It's YOUR job to 230narrow down those reasons, correct what was wrong, and submit your 231updated change. 232 233It is quite common for Linus to "drop" your patch without comment. 234That's the nature of the system. If he drops your patch, it could be 235due to 236* Your patch did not apply cleanly to the latest kernel version 237* Your patch was not sufficiently discussed on linux-kernel. 238* A style issue (see section 2), 239* An e-mail formatting issue (re-read this section) 240* A technical problem with your change 241* He gets tons of e-mail, and yours got lost in the shuffle 242* You are being annoying (See Figure 1) 243 244When in doubt, solicit comments on linux-kernel mailing list. 245 246 247 24810) Include PATCH in the subject 249 250Due to high e-mail traffic to Linus, and to linux-kernel, it is common 251convention to prefix your subject line with [PATCH]. This lets Linus 252and other kernel developers more easily distinguish patches from other 253e-mail discussions. 254 255 256 25711) Sign your work 258 259To improve tracking of who did what, especially with patches that can 260percolate to their final resting place in the kernel through several 261layers of maintainers, we've introduced a "sign-off" procedure on 262patches that are being emailed around. 263 264The sign-off is a simple line at the end of the explanation for the 265patch, which certifies that you wrote it or otherwise have the right to 266pass it on as a open-source patch. The rules are pretty simple: if you 267can certify the below: 268 269 Developer's Certificate of Origin 1.1 270 271 By making a contribution to this project, I certify that: 272 273 (a) The contribution was created in whole or in part by me and I 274 have the right to submit it under the open source license 275 indicated in the file; or 276 277 (b) The contribution is based upon previous work that, to the best 278 of my knowledge, is covered under an appropriate open source 279 license and I have the right under that license to submit that 280 work with modifications, whether created in whole or in part 281 by me, under the same open source license (unless I am 282 permitted to submit under a different license), as indicated 283 in the file; or 284 285 (c) The contribution was provided directly to me by some other 286 person who certified (a), (b) or (c) and I have not modified 287 it. 288 289 (d) I understand and agree that this project and the contribution 290 are public and that a record of the contribution (including all 291 personal information I submit with it, including my sign-off) is 292 maintained indefinitely and may be redistributed consistent with 293 this project or the open source license(s) involved. 294 295then you just add a line saying 296 297 Signed-off-by: Random J Developer <random@developer.example.org> 298 299Some people also put extra tags at the end. They'll just be ignored for 300now, but you can do this to mark internal company procedures or just 301point out some special detail about the sign-off. 302 303 304 30512) More references for submitting patches 306 307Andrew Morton, "The perfect patch" (tpp). 308 <http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt> 309 310Jeff Garzik, "Linux kernel patch submission format." 311 <http://linux.yyz.us/patch-format.html> 312 313 314 315----------------------------------- 316SECTION 2 - HINTS, TIPS, AND TRICKS 317----------------------------------- 318 319This section lists many of the common "rules" associated with code 320submitted to the kernel. There are always exceptions... but you must 321have a really good reason for doing so. You could probably call this 322section Linus Computer Science 101. 323 324 325 3261) Read Documentation/CodingStyle 327 328Nuff said. If your code deviates too much from this, it is likely 329to be rejected without further review, and without comment. 330 331 332 3332) #ifdefs are ugly 334 335Code cluttered with ifdefs is difficult to read and maintain. Don't do 336it. Instead, put your ifdefs in a header, and conditionally define 337'static inline' functions, or macros, which are used in the code. 338Let the compiler optimize away the "no-op" case. 339 340Simple example, of poor code: 341 342 dev = alloc_etherdev (sizeof(struct funky_private)); 343 if (!dev) 344 return -ENODEV; 345 #ifdef CONFIG_NET_FUNKINESS 346 init_funky_net(dev); 347 #endif 348 349Cleaned-up example: 350 351(in header) 352 #ifndef CONFIG_NET_FUNKINESS 353 static inline void init_funky_net (struct net_device *d) {} 354 #endif 355 356(in the code itself) 357 dev = alloc_etherdev (sizeof(struct funky_private)); 358 if (!dev) 359 return -ENODEV; 360 init_funky_net(dev); 361 362 363 3643) 'static inline' is better than a macro 365 366Static inline functions are greatly preferred over macros. 367They provide type safety, have no length limitations, no formatting 368limitations, and under gcc they are as cheap as macros. 369 370Macros should only be used for cases where a static inline is clearly 371suboptimal [there a few, isolated cases of this in fast paths], 372or where it is impossible to use a static inline function [such as 373string-izing]. 374 375'static inline' is preferred over 'static __inline__', 'extern inline', 376and 'extern __inline__'. 377 378 379 3804) Don't over-design. 381 382Don't try to anticipate nebulous future cases which may or may not 383be useful: "Make it as simple as you can, and no simpler." 384 385