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 152Even if the maintainer did not respond in step #4, make sure to ALWAYS 153copy the maintainer when you change their code. 154 155For small patches you may want to CC the Trivial Patch Monkey 156trivial@rustcorp.com.au set up by Rusty Russell; which collects "trivial" 157patches. Trivial patches must qualify for one of the following rules: 158 Spelling fixes in documentation 159 Spelling fixes which could break grep(1). 160 Warning fixes (cluttering with useless warnings is bad) 161 Compilation fixes (only if they are actually correct) 162 Runtime fixes (only if they actually fix things) 163 Removing use of deprecated functions/macros (eg. check_region). 164 Contact detail and documentation fixes 165 Non-portable code replaced by portable code (even in arch-specific, 166 since people copy, as long as it's trivial) 167 Any fix by the author/maintainer of the file. (ie. patch monkey 168 in re-transmission mode) 169URL: <http://www.kernel.org/pub/linux/kernel/people/rusty/trivial/> 170 171 172 173 1746) No MIME, no links, no compression, no attachments. Just plain text. 175 176Linus and other kernel developers need to be able to read and comment 177on the changes you are submitting. It is important for a kernel 178developer to be able to "quote" your changes, using standard e-mail 179tools, so that they may comment on specific portions of your code. 180 181For this reason, all patches should be submitting e-mail "inline". 182WARNING: Be wary of your editor's word-wrap corrupting your patch, 183if you choose to cut-n-paste your patch. 184 185Do not attach the patch as a MIME attachment, compressed or not. 186Many popular e-mail applications will not always transmit a MIME 187attachment as plain text, making it impossible to comment on your 188code. A MIME attachment also takes Linus a bit more time to process, 189decreasing the likelihood of your MIME-attached change being accepted. 190 191Exception: If your mailer is mangling patches then someone may ask 192you to re-send them using MIME. 193 194 195 1967) E-mail size. 197 198When sending patches to Linus, always follow step #6. 199 200Large changes are not appropriate for mailing lists, and some 201maintainers. If your patch, uncompressed, exceeds 40 kB in size, 202it is preferred that you store your patch on an Internet-accessible 203server, and provide instead a URL (link) pointing to your patch. 204 205 206 2078) Name your kernel version. 208 209It is important to note, either in the subject line or in the patch 210description, the kernel version to which this patch applies. 211 212If the patch does not apply cleanly to the latest kernel version, 213Linus will not apply it. 214 215 216 2179) Don't get discouraged. Re-submit. 218 219After you have submitted your change, be patient and wait. If Linus 220likes your change and applies it, it will appear in the next version 221of the kernel that he releases. 222 223However, if your change doesn't appear in the next version of the 224kernel, there could be any number of reasons. It's YOUR job to 225narrow down those reasons, correct what was wrong, and submit your 226updated change. 227 228It is quite common for Linus to "drop" your patch without comment. 229That's the nature of the system. If he drops your patch, it could be 230due to 231* Your patch did not apply cleanly to the latest kernel version 232* Your patch was not sufficiently discussed on linux-kernel. 233* A style issue (see section 2), 234* An e-mail formatting issue (re-read this section) 235* A technical problem with your change 236* He gets tons of e-mail, and yours got lost in the shuffle 237* You are being annoying (See Figure 1) 238 239When in doubt, solicit comments on linux-kernel mailing list. 240 241 242 24310) Include PATCH in the subject 244 245Due to high e-mail traffic to Linus, and to linux-kernel, it is common 246convention to prefix your subject line with [PATCH]. This lets Linus 247and other kernel developers more easily distinguish patches from other 248e-mail discussions. 249 250 251 25211) Sign your work 253 254To improve tracking of who did what, especially with patches that can 255percolate to their final resting place in the kernel through several 256layers of maintainers, we've introduced a "sign-off" procedure on 257patches that are being emailed around. 258 259The sign-off is a simple line at the end of the explanation for the 260patch, which certifies that you wrote it or otherwise have the right to 261pass it on as a open-source patch. The rules are pretty simple: if you 262can certify the below: 263 264 Developer's Certificate of Origin 1.1 265 266 By making a contribution to this project, I certify that: 267 268 (a) The contribution was created in whole or in part by me and I 269 have the right to submit it under the open source license 270 indicated in the file; or 271 272 (b) The contribution is based upon previous work that, to the best 273 of my knowledge, is covered under an appropriate open source 274 license and I have the right under that license to submit that 275 work with modifications, whether created in whole or in part 276 by me, under the same open source license (unless I am 277 permitted to submit under a different license), as indicated 278 in the file; or 279 280 (c) The contribution was provided directly to me by some other 281 person who certified (a), (b) or (c) and I have not modified 282 it. 283 284 (d) I understand and agree that this project and the contribution 285 are public and that a record of the contribution (including all 286 personal information I submit with it, including my sign-off) is 287 maintained indefinitely and may be redistributed consistent with 288 this project or the open source license(s) involved. 289 290then you just add a line saying 291 292 Signed-off-by: Random J Developer <random@developer.example.org> 293 294Some people also put extra tags at the end. They'll just be ignored for 295now, but you can do this to mark internal company procedures or just 296point out some special detail about the sign-off. 297 298 299 30012) More references for submitting patches 301 302Andrew Morton, "The perfect patch" (tpp). 303 <http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt> 304 305Jeff Garzik, "Linux kernel patch submission format." 306 <http://linux.yyz.us/patch-format.html> 307 308 309 310----------------------------------- 311SECTION 2 - HINTS, TIPS, AND TRICKS 312----------------------------------- 313 314This section lists many of the common "rules" associated with code 315submitted to the kernel. There are always exceptions... but you must 316have a really good reason for doing so. You could probably call this 317section Linus Computer Science 101. 318 319 320 3211) Read Documentation/CodingStyle 322 323Nuff said. If your code deviates too much from this, it is likely 324to be rejected without further review, and without comment. 325 326 327 3282) #ifdefs are ugly 329 330Code cluttered with ifdefs is difficult to read and maintain. Don't do 331it. Instead, put your ifdefs in a header, and conditionally define 332'static inline' functions, or macros, which are used in the code. 333Let the compiler optimize away the "no-op" case. 334 335Simple example, of poor code: 336 337 dev = alloc_etherdev (sizeof(struct funky_private)); 338 if (!dev) 339 return -ENODEV; 340 #ifdef CONFIG_NET_FUNKINESS 341 init_funky_net(dev); 342 #endif 343 344Cleaned-up example: 345 346(in header) 347 #ifndef CONFIG_NET_FUNKINESS 348 static inline void init_funky_net (struct net_device *d) {} 349 #endif 350 351(in the code itself) 352 dev = alloc_etherdev (sizeof(struct funky_private)); 353 if (!dev) 354 return -ENODEV; 355 init_funky_net(dev); 356 357 358 3593) 'static inline' is better than a macro 360 361Static inline functions are greatly preferred over macros. 362They provide type safety, have no length limitations, no formatting 363limitations, and under gcc they are as cheap as macros. 364 365Macros should only be used for cases where a static inline is clearly 366suboptimal [there a few, isolated cases of this in fast paths], 367or where it is impossible to use a static inline function [such as 368string-izing]. 369 370'static inline' is preferred over 'static __inline__', 'extern inline', 371and 'extern __inline__'. 372 373 374 3754) Don't over-design. 376 377Don't try to anticipate nebulous future cases which may or may not 378be useful: "Make it as simple as you can, and no simpler." 379 380