applying-patches.txt 19 KB

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  1. Applying Patches To The Linux Kernel
  2. ------------------------------------
  3. Original by: Jesper Juhl, August 2005
  4. Last update: 2006-01-05
  5. A frequently asked question on the Linux Kernel Mailing List is how to apply
  6. a patch to the kernel or, more specifically, what base kernel a patch for
  7. one of the many trees/branches should be applied to. Hopefully this document
  8. will explain this to you.
  9. In addition to explaining how to apply and revert patches, a brief
  10. description of the different kernel trees (and examples of how to apply
  11. their specific patches) is also provided.
  12. What is a patch?
  13. ---
  14. A patch is a small text document containing a delta of changes between two
  15. different versions of a source tree. Patches are created with the `diff'
  16. program.
  17. To correctly apply a patch you need to know what base it was generated from
  18. and what new version the patch will change the source tree into. These
  19. should both be present in the patch file metadata or be possible to deduce
  20. from the filename.
  21. How do I apply or revert a patch?
  22. ---
  23. You apply a patch with the `patch' program. The patch program reads a diff
  24. (or patch) file and makes the changes to the source tree described in it.
  25. Patches for the Linux kernel are generated relative to the parent directory
  26. holding the kernel source dir.
  27. This means that paths to files inside the patch file contain the name of the
  28. kernel source directories it was generated against (or some other directory
  29. names like "a/" and "b/").
  30. Since this is unlikely to match the name of the kernel source dir on your
  31. local machine (but is often useful info to see what version an otherwise
  32. unlabeled patch was generated against) you should change into your kernel
  33. source directory and then strip the first element of the path from filenames
  34. in the patch file when applying it (the -p1 argument to `patch' does this).
  35. To revert a previously applied patch, use the -R argument to patch.
  36. So, if you applied a patch like this:
  37. patch -p1 < ../patch-x.y.z
  38. You can revert (undo) it like this:
  39. patch -R -p1 < ../patch-x.y.z
  40. How do I feed a patch/diff file to `patch'?
  41. ---
  42. This (as usual with Linux and other UNIX like operating systems) can be
  43. done in several different ways.
  44. In all the examples below I feed the file (in uncompressed form) to patch
  45. via stdin using the following syntax:
  46. patch -p1 < path/to/patch-x.y.z
  47. If you just want to be able to follow the examples below and don't want to
  48. know of more than one way to use patch, then you can stop reading this
  49. section here.
  50. Patch can also get the name of the file to use via the -i argument, like
  51. this:
  52. patch -p1 -i path/to/patch-x.y.z
  53. If your patch file is compressed with gzip or bzip2 and you don't want to
  54. uncompress it before applying it, then you can feed it to patch like this
  55. instead:
  56. zcat path/to/patch-x.y.z.gz | patch -p1
  57. bzcat path/to/patch-x.y.z.bz2 | patch -p1
  58. If you wish to uncompress the patch file by hand first before applying it
  59. (what I assume you've done in the examples below), then you simply run
  60. gunzip or bunzip2 on the file -- like this:
  61. gunzip patch-x.y.z.gz
  62. bunzip2 patch-x.y.z.bz2
  63. Which will leave you with a plain text patch-x.y.z file that you can feed to
  64. patch via stdin or the -i argument, as you prefer.
  65. A few other nice arguments for patch are -s which causes patch to be silent
  66. except for errors which is nice to prevent errors from scrolling out of the
  67. screen too fast, and --dry-run which causes patch to just print a listing of
  68. what would happen, but doesn't actually make any changes. Finally --verbose
  69. tells patch to print more information about the work being done.
  70. Common errors when patching
  71. ---
  72. When patch applies a patch file it attempts to verify the sanity of the
  73. file in different ways.
  74. Checking that the file looks like a valid patch file & checking the code
  75. around the bits being modified matches the context provided in the patch are
  76. just two of the basic sanity checks patch does.
  77. If patch encounters something that doesn't look quite right it has two
  78. options. It can either refuse to apply the changes and abort or it can try
  79. to find a way to make the patch apply with a few minor changes.
  80. One example of something that's not 'quite right' that patch will attempt to
  81. fix up is if all the context matches, the lines being changed match, but the
  82. line numbers are different. This can happen, for example, if the patch makes
  83. a change in the middle of the file but for some reasons a few lines have
  84. been added or removed near the beginning of the file. In that case
  85. everything looks good it has just moved up or down a bit, and patch will
  86. usually adjust the line numbers and apply the patch.
  87. Whenever patch applies a patch that it had to modify a bit to make it fit
  88. it'll tell you about it by saying the patch applied with 'fuzz'.
  89. You should be wary of such changes since even though patch probably got it
  90. right it doesn't /always/ get it right, and the result will sometimes be
  91. wrong.
  92. When patch encounters a change that it can't fix up with fuzz it rejects it
  93. outright and leaves a file with a .rej extension (a reject file). You can
  94. read this file to see exactly what change couldn't be applied, so you can
  95. go fix it up by hand if you wish.
  96. If you don't have any third-party patches applied to your kernel source, but
  97. only patches from kernel.org and you apply the patches in the correct order,
  98. and have made no modifications yourself to the source files, then you should
  99. never see a fuzz or reject message from patch. If you do see such messages
  100. anyway, then there's a high risk that either your local source tree or the
  101. patch file is corrupted in some way. In that case you should probably try
  102. re-downloading the patch and if things are still not OK then you'd be advised
  103. to start with a fresh tree downloaded in full from kernel.org.
  104. Let's look a bit more at some of the messages patch can produce.
  105. If patch stops and presents a "File to patch:" prompt, then patch could not
  106. find a file to be patched. Most likely you forgot to specify -p1 or you are
  107. in the wrong directory. Less often, you'll find patches that need to be
  108. applied with -p0 instead of -p1 (reading the patch file should reveal if
  109. this is the case -- if so, then this is an error by the person who created
  110. the patch but is not fatal).
  111. If you get "Hunk #2 succeeded at 1887 with fuzz 2 (offset 7 lines)." or a
  112. message similar to that, then it means that patch had to adjust the location
  113. of the change (in this example it needed to move 7 lines from where it
  114. expected to make the change to make it fit).
  115. The resulting file may or may not be OK, depending on the reason the file
  116. was different than expected.
  117. This often happens if you try to apply a patch that was generated against a
  118. different kernel version than the one you are trying to patch.
  119. If you get a message like "Hunk #3 FAILED at 2387.", then it means that the
  120. patch could not be applied correctly and the patch program was unable to
  121. fuzz its way through. This will generate a .rej file with the change that
  122. caused the patch to fail and also a .orig file showing you the original
  123. content that couldn't be changed.
  124. If you get "Reversed (or previously applied) patch detected! Assume -R? [n]"
  125. then patch detected that the change contained in the patch seems to have
  126. already been made.
  127. If you actually did apply this patch previously and you just re-applied it
  128. in error, then just say [n]o and abort this patch. If you applied this patch
  129. previously and actually intended to revert it, but forgot to specify -R,
  130. then you can say [y]es here to make patch revert it for you.
  131. This can also happen if the creator of the patch reversed the source and
  132. destination directories when creating the patch, and in that case reverting
  133. the patch will in fact apply it.
  134. A message similar to "patch: **** unexpected end of file in patch" or "patch
  135. unexpectedly ends in middle of line" means that patch could make no sense of
  136. the file you fed to it. Either your download is broken, you tried to feed
  137. patch a compressed patch file without uncompressing it first, or the patch
  138. file that you are using has been mangled by a mail client or mail transfer
  139. agent along the way somewhere, e.g., by splitting a long line into two lines.
  140. Often these warnings can easily be fixed by joining (concatenating) the
  141. two lines that had been split.
  142. As I already mentioned above, these errors should never happen if you apply
  143. a patch from kernel.org to the correct version of an unmodified source tree.
  144. So if you get these errors with kernel.org patches then you should probably
  145. assume that either your patch file or your tree is broken and I'd advise you
  146. to start over with a fresh download of a full kernel tree and the patch you
  147. wish to apply.
  148. Are there any alternatives to `patch'?
  149. ---
  150. Yes there are alternatives.
  151. You can use the `interdiff' program (http://cyberelk.net/tim/patchutils/) to
  152. generate a patch representing the differences between two patches and then
  153. apply the result.
  154. This will let you move from something like 2.6.12.2 to 2.6.12.3 in a single
  155. step. The -z flag to interdiff will even let you feed it patches in gzip or
  156. bzip2 compressed form directly without the use of zcat or bzcat or manual
  157. decompression.
  158. Here's how you'd go from 2.6.12.2 to 2.6.12.3 in a single step:
  159. interdiff -z ../patch-2.6.12.2.bz2 ../patch-2.6.12.3.gz | patch -p1
  160. Although interdiff may save you a step or two you are generally advised to
  161. do the additional steps since interdiff can get things wrong in some cases.
  162. Another alternative is `ketchup', which is a python script for automatic
  163. downloading and applying of patches (http://www.selenic.com/ketchup/).
  164. Other nice tools are diffstat, which shows a summary of changes made by a
  165. patch; lsdiff, which displays a short listing of affected files in a patch
  166. file, along with (optionally) the line numbers of the start of each patch;
  167. and grepdiff, which displays a list of the files modified by a patch where
  168. the patch contains a given regular expression.
  169. Where can I download the patches?
  170. ---
  171. The patches are available at http://kernel.org/
  172. Most recent patches are linked from the front page, but they also have
  173. specific homes.
  174. The 2.6.x.y (-stable) and 2.6.x patches live at
  175. ftp://ftp.kernel.org/pub/linux/kernel/v2.6/
  176. The -rc patches live at
  177. ftp://ftp.kernel.org/pub/linux/kernel/v2.6/testing/
  178. The -git patches live at
  179. ftp://ftp.kernel.org/pub/linux/kernel/v2.6/snapshots/
  180. The -mm kernels live at
  181. ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/
  182. In place of ftp.kernel.org you can use ftp.cc.kernel.org, where cc is a
  183. country code. This way you'll be downloading from a mirror site that's most
  184. likely geographically closer to you, resulting in faster downloads for you,
  185. less bandwidth used globally and less load on the main kernel.org servers --
  186. these are good things, so do use mirrors when possible.
  187. The 2.6.x kernels
  188. ---
  189. These are the base stable releases released by Linus. The highest numbered
  190. release is the most recent.
  191. If regressions or other serious flaws are found, then a -stable fix patch
  192. will be released (see below) on top of this base. Once a new 2.6.x base
  193. kernel is released, a patch is made available that is a delta between the
  194. previous 2.6.x kernel and the new one.
  195. To apply a patch moving from 2.6.11 to 2.6.12, you'd do the following (note
  196. that such patches do *NOT* apply on top of 2.6.x.y kernels but on top of the
  197. base 2.6.x kernel -- if you need to move from 2.6.x.y to 2.6.x+1 you need to
  198. first revert the 2.6.x.y patch).
  199. Here are some examples:
  200. # moving from 2.6.11 to 2.6.12
  201. $ cd ~/linux-2.6.11 # change to kernel source dir
  202. $ patch -p1 < ../patch-2.6.12 # apply the 2.6.12 patch
  203. $ cd ..
  204. $ mv linux-2.6.11 linux-2.6.12 # rename source dir
  205. # moving from 2.6.11.1 to 2.6.12
  206. $ cd ~/linux-2.6.11.1 # change to kernel source dir
  207. $ patch -p1 -R < ../patch-2.6.11.1 # revert the 2.6.11.1 patch
  208. # source dir is now 2.6.11
  209. $ patch -p1 < ../patch-2.6.12 # apply new 2.6.12 patch
  210. $ cd ..
  211. $ mv linux-2.6.11.1 linux-2.6.12 # rename source dir
  212. The 2.6.x.y kernels
  213. ---
  214. Kernels with 4-digit versions are -stable kernels. They contain small(ish)
  215. critical fixes for security problems or significant regressions discovered
  216. in a given 2.6.x kernel.
  217. This is the recommended branch for users who want the most recent stable
  218. kernel and are not interested in helping test development/experimental
  219. versions.
  220. If no 2.6.x.y kernel is available, then the highest numbered 2.6.x kernel is
  221. the current stable kernel.
  222. note: the -stable team usually do make incremental patches available as well
  223. as patches against the latest mainline release, but I only cover the
  224. non-incremental ones below. The incremental ones can be found at
  225. ftp://ftp.kernel.org/pub/linux/kernel/v2.6/incr/
  226. These patches are not incremental, meaning that for example the 2.6.12.3
  227. patch does not apply on top of the 2.6.12.2 kernel source, but rather on top
  228. of the base 2.6.12 kernel source .
  229. So, in order to apply the 2.6.12.3 patch to your existing 2.6.12.2 kernel
  230. source you have to first back out the 2.6.12.2 patch (so you are left with a
  231. base 2.6.12 kernel source) and then apply the new 2.6.12.3 patch.
  232. Here's a small example:
  233. $ cd ~/linux-2.6.12.2 # change into the kernel source dir
  234. $ patch -p1 -R < ../patch-2.6.12.2 # revert the 2.6.12.2 patch
  235. $ patch -p1 < ../patch-2.6.12.3 # apply the new 2.6.12.3 patch
  236. $ cd ..
  237. $ mv linux-2.6.12.2 linux-2.6.12.3 # rename the kernel source dir
  238. The -rc kernels
  239. ---
  240. These are release-candidate kernels. These are development kernels released
  241. by Linus whenever he deems the current git (the kernel's source management
  242. tool) tree to be in a reasonably sane state adequate for testing.
  243. These kernels are not stable and you should expect occasional breakage if
  244. you intend to run them. This is however the most stable of the main
  245. development branches and is also what will eventually turn into the next
  246. stable kernel, so it is important that it be tested by as many people as
  247. possible.
  248. This is a good branch to run for people who want to help out testing
  249. development kernels but do not want to run some of the really experimental
  250. stuff (such people should see the sections about -git and -mm kernels below).
  251. The -rc patches are not incremental, they apply to a base 2.6.x kernel, just
  252. like the 2.6.x.y patches described above. The kernel version before the -rcN
  253. suffix denotes the version of the kernel that this -rc kernel will eventually
  254. turn into.
  255. So, 2.6.13-rc5 means that this is the fifth release candidate for the 2.6.13
  256. kernel and the patch should be applied on top of the 2.6.12 kernel source.
  257. Here are 3 examples of how to apply these patches:
  258. # first an example of moving from 2.6.12 to 2.6.13-rc3
  259. $ cd ~/linux-2.6.12 # change into the 2.6.12 source dir
  260. $ patch -p1 < ../patch-2.6.13-rc3 # apply the 2.6.13-rc3 patch
  261. $ cd ..
  262. $ mv linux-2.6.12 linux-2.6.13-rc3 # rename the source dir
  263. # now let's move from 2.6.13-rc3 to 2.6.13-rc5
  264. $ cd ~/linux-2.6.13-rc3 # change into the 2.6.13-rc3 dir
  265. $ patch -p1 -R < ../patch-2.6.13-rc3 # revert the 2.6.13-rc3 patch
  266. $ patch -p1 < ../patch-2.6.13-rc5 # apply the new 2.6.13-rc5 patch
  267. $ cd ..
  268. $ mv linux-2.6.13-rc3 linux-2.6.13-rc5 # rename the source dir
  269. # finally let's try and move from 2.6.12.3 to 2.6.13-rc5
  270. $ cd ~/linux-2.6.12.3 # change to the kernel source dir
  271. $ patch -p1 -R < ../patch-2.6.12.3 # revert the 2.6.12.3 patch
  272. $ patch -p1 < ../patch-2.6.13-rc5 # apply new 2.6.13-rc5 patch
  273. $ cd ..
  274. $ mv linux-2.6.12.3 linux-2.6.13-rc5 # rename the kernel source dir
  275. The -git kernels
  276. ---
  277. These are daily snapshots of Linus' kernel tree (managed in a git
  278. repository, hence the name).
  279. These patches are usually released daily and represent the current state of
  280. Linus's tree. They are more experimental than -rc kernels since they are
  281. generated automatically without even a cursory glance to see if they are
  282. sane.
  283. -git patches are not incremental and apply either to a base 2.6.x kernel or
  284. a base 2.6.x-rc kernel -- you can see which from their name.
  285. A patch named 2.6.12-git1 applies to the 2.6.12 kernel source and a patch
  286. named 2.6.13-rc3-git2 applies to the source of the 2.6.13-rc3 kernel.
  287. Here are some examples of how to apply these patches:
  288. # moving from 2.6.12 to 2.6.12-git1
  289. $ cd ~/linux-2.6.12 # change to the kernel source dir
  290. $ patch -p1 < ../patch-2.6.12-git1 # apply the 2.6.12-git1 patch
  291. $ cd ..
  292. $ mv linux-2.6.12 linux-2.6.12-git1 # rename the kernel source dir
  293. # moving from 2.6.12-git1 to 2.6.13-rc2-git3
  294. $ cd ~/linux-2.6.12-git1 # change to the kernel source dir
  295. $ patch -p1 -R < ../patch-2.6.12-git1 # revert the 2.6.12-git1 patch
  296. # we now have a 2.6.12 kernel
  297. $ patch -p1 < ../patch-2.6.13-rc2 # apply the 2.6.13-rc2 patch
  298. # the kernel is now 2.6.13-rc2
  299. $ patch -p1 < ../patch-2.6.13-rc2-git3 # apply the 2.6.13-rc2-git3 patch
  300. # the kernel is now 2.6.13-rc2-git3
  301. $ cd ..
  302. $ mv linux-2.6.12-git1 linux-2.6.13-rc2-git3 # rename source dir
  303. The -mm kernels
  304. ---
  305. These are experimental kernels released by Andrew Morton.
  306. The -mm tree serves as a sort of proving ground for new features and other
  307. experimental patches.
  308. Once a patch has proved its worth in -mm for a while Andrew pushes it on to
  309. Linus for inclusion in mainline.
  310. Although it's encouraged that patches flow to Linus via the -mm tree, this
  311. is not always enforced.
  312. Subsystem maintainers (or individuals) sometimes push their patches directly
  313. to Linus, even though (or after) they have been merged and tested in -mm (or
  314. sometimes even without prior testing in -mm).
  315. You should generally strive to get your patches into mainline via -mm to
  316. ensure maximum testing.
  317. This branch is in constant flux and contains many experimental features, a
  318. lot of debugging patches not appropriate for mainline etc., and is the most
  319. experimental of the branches described in this document.
  320. These kernels are not appropriate for use on systems that are supposed to be
  321. stable and they are more risky to run than any of the other branches (make
  322. sure you have up-to-date backups -- that goes for any experimental kernel but
  323. even more so for -mm kernels).
  324. These kernels in addition to all the other experimental patches they contain
  325. usually also contain any changes in the mainline -git kernels available at
  326. the time of release.
  327. Testing of -mm kernels is greatly appreciated since the whole point of the
  328. tree is to weed out regressions, crashes, data corruption bugs, build
  329. breakage (and any other bug in general) before changes are merged into the
  330. more stable mainline Linus tree.
  331. But testers of -mm should be aware that breakage in this tree is more common
  332. than in any other tree.
  333. The -mm kernels are not released on a fixed schedule, but usually a few -mm
  334. kernels are released in between each -rc kernel (1 to 3 is common).
  335. The -mm kernels apply to either a base 2.6.x kernel (when no -rc kernels
  336. have been released yet) or to a Linus -rc kernel.
  337. Here are some examples of applying the -mm patches:
  338. # moving from 2.6.12 to 2.6.12-mm1
  339. $ cd ~/linux-2.6.12 # change to the 2.6.12 source dir
  340. $ patch -p1 < ../2.6.12-mm1 # apply the 2.6.12-mm1 patch
  341. $ cd ..
  342. $ mv linux-2.6.12 linux-2.6.12-mm1 # rename the source appropriately
  343. # moving from 2.6.12-mm1 to 2.6.13-rc3-mm3
  344. $ cd ~/linux-2.6.12-mm1
  345. $ patch -p1 -R < ../2.6.12-mm1 # revert the 2.6.12-mm1 patch
  346. # we now have a 2.6.12 source
  347. $ patch -p1 < ../patch-2.6.13-rc3 # apply the 2.6.13-rc3 patch
  348. # we now have a 2.6.13-rc3 source
  349. $ patch -p1 < ../2.6.13-rc3-mm3 # apply the 2.6.13-rc3-mm3 patch
  350. $ cd ..
  351. $ mv linux-2.6.12-mm1 linux-2.6.13-rc3-mm3 # rename the source dir
  352. This concludes this list of explanations of the various kernel trees.
  353. I hope you are now clear on how to apply the various patches and help testing
  354. the kernel.
  355. Thank you's to Randy Dunlap, Rolf Eike Beer, Linus Torvalds, Bodo Eggert,
  356. Johannes Stezenbach, Grant Coady, Pavel Machek and others that I may have
  357. forgotten for their reviews and contributions to this document.