The Design and Implementation of the FreeBSD Operating System, Second Edition
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sys/Documentation/applying-patches.txt

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    1 
    2         Applying Patches To The Linux Kernel
    3         ------------------------------------
    4 
    5         Original by: Jesper Juhl, August 2005
    6         Last update: 2006-01-05
    7 
    8 
    9 A frequently asked question on the Linux Kernel Mailing List is how to apply
   10 a patch to the kernel or, more specifically, what base kernel a patch for
   11 one of the many trees/branches should be applied to. Hopefully this document
   12 will explain this to you.
   13 
   14 In addition to explaining how to apply and revert patches, a brief
   15 description of the different kernel trees (and examples of how to apply
   16 their specific patches) is also provided.
   17 
   18 
   19 What is a patch?
   20 ---
   21  A patch is a small text document containing a delta of changes between two
   22 different versions of a source tree. Patches are created with the `diff'
   23 program.
   24 To correctly apply a patch you need to know what base it was generated from
   25 and what new version the patch will change the source tree into. These
   26 should both be present in the patch file metadata or be possible to deduce
   27 from the filename.
   28 
   29 
   30 How do I apply or revert a patch?
   31 ---
   32  You apply a patch with the `patch' program. The patch program reads a diff
   33 (or patch) file and makes the changes to the source tree described in it.
   34 
   35 Patches for the Linux kernel are generated relative to the parent directory
   36 holding the kernel source dir.
   37 
   38 This means that paths to files inside the patch file contain the name of the
   39 kernel source directories it was generated against (or some other directory
   40 names like "a/" and "b/").
   41 Since this is unlikely to match the name of the kernel source dir on your
   42 local machine (but is often useful info to see what version an otherwise
   43 unlabeled patch was generated against) you should change into your kernel
   44 source directory and then strip the first element of the path from filenames
   45 in the patch file when applying it (the -p1 argument to `patch' does this).
   46 
   47 To revert a previously applied patch, use the -R argument to patch.
   48 So, if you applied a patch like this:
   49         patch -p1 < ../patch-x.y.z
   50 
   51 You can revert (undo) it like this:
   52         patch -R -p1 < ../patch-x.y.z
   53 
   54 
   55 How do I feed a patch/diff file to `patch'?
   56 ---
   57  This (as usual with Linux and other UNIX like operating systems) can be
   58 done in several different ways.
   59 In all the examples below I feed the file (in uncompressed form) to patch
   60 via stdin using the following syntax:
   61         patch -p1 < path/to/patch-x.y.z
   62 
   63 If you just want to be able to follow the examples below and don't want to
   64 know of more than one way to use patch, then you can stop reading this
   65 section here.
   66 
   67 Patch can also get the name of the file to use via the -i argument, like
   68 this:
   69         patch -p1 -i path/to/patch-x.y.z
   70 
   71 If your patch file is compressed with gzip or bzip2 and you don't want to
   72 uncompress it before applying it, then you can feed it to patch like this
   73 instead:
   74         zcat path/to/patch-x.y.z.gz | patch -p1
   75         bzcat path/to/patch-x.y.z.bz2 | patch -p1
   76 
   77 If you wish to uncompress the patch file by hand first before applying it
   78 (what I assume you've done in the examples below), then you simply run
   79 gunzip or bunzip2 on the file -- like this:
   80         gunzip patch-x.y.z.gz
   81         bunzip2 patch-x.y.z.bz2
   82 
   83 Which will leave you with a plain text patch-x.y.z file that you can feed to
   84 patch via stdin or the -i argument, as you prefer.
   85 
   86 A few other nice arguments for patch are -s which causes patch to be silent
   87 except for errors which is nice to prevent errors from scrolling out of the
   88 screen too fast, and --dry-run which causes patch to just print a listing of
   89 what would happen, but doesn't actually make any changes. Finally --verbose
   90 tells patch to print more information about the work being done.
   91 
   92 
   93 Common errors when patching
   94 ---
   95  When patch applies a patch file it attempts to verify the sanity of the
   96 file in different ways.
   97 Checking that the file looks like a valid patch file & checking the code
   98 around the bits being modified matches the context provided in the patch are
   99 just two of the basic sanity checks patch does.
  100 
  101 If patch encounters something that doesn't look quite right it has two
  102 options. It can either refuse to apply the changes and abort or it can try
  103 to find a way to make the patch apply with a few minor changes.
  104 
  105 One example of something that's not 'quite right' that patch will attempt to
  106 fix up is if all the context matches, the lines being changed match, but the
  107 line numbers are different. This can happen, for example, if the patch makes
  108 a change in the middle of the file but for some reasons a few lines have
  109 been added or removed near the beginning of the file. In that case
  110 everything looks good it has just moved up or down a bit, and patch will
  111 usually adjust the line numbers and apply the patch.
  112 
  113 Whenever patch applies a patch that it had to modify a bit to make it fit
  114 it'll tell you about it by saying the patch applied with 'fuzz'.
  115 You should be wary of such changes since even though patch probably got it
  116 right it doesn't /always/ get it right, and the result will sometimes be
  117 wrong.
  118 
  119 When patch encounters a change that it can't fix up with fuzz it rejects it
  120 outright and leaves a file with a .rej extension (a reject file). You can
  121 read this file to see exactly what change couldn't be applied, so you can
  122 go fix it up by hand if you wish.
  123 
  124 If you don't have any third-party patches applied to your kernel source, but
  125 only patches from kernel.org and you apply the patches in the correct order,
  126 and have made no modifications yourself to the source files, then you should
  127 never see a fuzz or reject message from patch. If you do see such messages
  128 anyway, then there's a high risk that either your local source tree or the
  129 patch file is corrupted in some way. In that case you should probably try
  130 re-downloading the patch and if things are still not OK then you'd be advised
  131 to start with a fresh tree downloaded in full from kernel.org.
  132 
  133 Let's look a bit more at some of the messages patch can produce.
  134 
  135 If patch stops and presents a "File to patch:" prompt, then patch could not
  136 find a file to be patched. Most likely you forgot to specify -p1 or you are
  137 in the wrong directory. Less often, you'll find patches that need to be
  138 applied with -p0 instead of -p1 (reading the patch file should reveal if
  139 this is the case -- if so, then this is an error by the person who created
  140 the patch but is not fatal).
  141 
  142 If you get "Hunk #2 succeeded at 1887 with fuzz 2 (offset 7 lines)." or a
  143 message similar to that, then it means that patch had to adjust the location
  144 of the change (in this example it needed to move 7 lines from where it
  145 expected to make the change to make it fit).
  146 The resulting file may or may not be OK, depending on the reason the file
  147 was different than expected.
  148 This often happens if you try to apply a patch that was generated against a
  149 different kernel version than the one you are trying to patch.
  150 
  151 If you get a message like "Hunk #3 FAILED at 2387.", then it means that the
  152 patch could not be applied correctly and the patch program was unable to
  153 fuzz its way through. This will generate a .rej file with the change that
  154 caused the patch to fail and also a .orig file showing you the original
  155 content that couldn't be changed.
  156 
  157 If you get "Reversed (or previously applied) patch detected!  Assume -R? [n]"
  158 then patch detected that the change contained in the patch seems to have
  159 already been made.
  160 If you actually did apply this patch previously and you just re-applied it
  161 in error, then just say [n]o and abort this patch. If you applied this patch
  162 previously and actually intended to revert it, but forgot to specify -R,
  163 then you can say [y]es here to make patch revert it for you.
  164 This can also happen if the creator of the patch reversed the source and
  165 destination directories when creating the patch, and in that case reverting
  166 the patch will in fact apply it.
  167 
  168 A message similar to "patch: **** unexpected end of file in patch" or "patch
  169 unexpectedly ends in middle of line" means that patch could make no sense of
  170 the file you fed to it. Either your download is broken, you tried to feed
  171 patch a compressed patch file without uncompressing it first, or the patch
  172 file that you are using has been mangled by a mail client or mail transfer
  173 agent along the way somewhere, e.g., by splitting a long line into two lines.
  174 Often these warnings can easily be fixed by joining (concatenating) the
  175 two lines that had been split.
  176 
  177 As I already mentioned above, these errors should never happen if you apply
  178 a patch from kernel.org to the correct version of an unmodified source tree.
  179 So if you get these errors with kernel.org patches then you should probably
  180 assume that either your patch file or your tree is broken and I'd advise you
  181 to start over with a fresh download of a full kernel tree and the patch you
  182 wish to apply.
  183 
  184 
  185 Are there any alternatives to `patch'?
  186 ---
  187  Yes there are alternatives.
  188 
  189  You can use the `interdiff' program (http://cyberelk.net/tim/patchutils/) to
  190 generate a patch representing the differences between two patches and then
  191 apply the result.
  192 This will let you move from something like 2.6.12.2 to 2.6.12.3 in a single
  193 step. The -z flag to interdiff will even let you feed it patches in gzip or
  194 bzip2 compressed form directly without the use of zcat or bzcat or manual
  195 decompression.
  196 
  197 Here's how you'd go from 2.6.12.2 to 2.6.12.3 in a single step:
  198         interdiff -z ../patch-2.6.12.2.bz2 ../patch-2.6.12.3.gz | patch -p1
  199 
  200 Although interdiff may save you a step or two you are generally advised to
  201 do the additional steps since interdiff can get things wrong in some cases.
  202 
  203  Another alternative is `ketchup', which is a python script for automatic
  204 downloading and applying of patches (http://www.selenic.com/ketchup/).
  205 
  206  Other nice tools are diffstat, which shows a summary of changes made by a
  207 patch; lsdiff, which displays a short listing of affected files in a patch
  208 file, along with (optionally) the line numbers of the start of each patch;
  209 and grepdiff, which displays a list of the files modified by a patch where
  210 the patch contains a given regular expression.
  211 
  212 
  213 Where can I download the patches?
  214 ---
  215  The patches are available at http://kernel.org/
  216 Most recent patches are linked from the front page, but they also have
  217 specific homes.
  218 
  219 The 2.6.x.y (-stable) and 2.6.x patches live at
  220  ftp://ftp.kernel.org/pub/linux/kernel/v2.6/
  221 
  222 The -rc patches live at
  223  ftp://ftp.kernel.org/pub/linux/kernel/v2.6/testing/
  224 
  225 The -git patches live at
  226  ftp://ftp.kernel.org/pub/linux/kernel/v2.6/snapshots/
  227 
  228 The -mm kernels live at
  229  ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/
  230 
  231 In place of ftp.kernel.org you can use ftp.cc.kernel.org, where cc is a
  232 country code. This way you'll be downloading from a mirror site that's most
  233 likely geographically closer to you, resulting in faster downloads for you,
  234 less bandwidth used globally and less load on the main kernel.org servers --
  235 these are good things, so do use mirrors when possible.
  236 
  237 
  238 The 2.6.x kernels
  239 ---
  240  These are the base stable releases released by Linus. The highest numbered
  241 release is the most recent.
  242 
  243 If regressions or other serious flaws are found, then a -stable fix patch
  244 will be released (see below) on top of this base. Once a new 2.6.x base
  245 kernel is released, a patch is made available that is a delta between the
  246 previous 2.6.x kernel and the new one.
  247 
  248 To apply a patch moving from 2.6.11 to 2.6.12, you'd do the following (note
  249 that such patches do *NOT* apply on top of 2.6.x.y kernels but on top of the
  250 base 2.6.x kernel -- if you need to move from 2.6.x.y to 2.6.x+1 you need to
  251 first revert the 2.6.x.y patch).
  252 
  253 Here are some examples:
  254 
  255 # moving from 2.6.11 to 2.6.12
  256 $ cd ~/linux-2.6.11                     # change to kernel source dir
  257 $ patch -p1 < ../patch-2.6.12           # apply the 2.6.12 patch
  258 $ cd ..
  259 $ mv linux-2.6.11 linux-2.6.12          # rename source dir
  260 
  261 # moving from 2.6.11.1 to 2.6.12
  262 $ cd ~/linux-2.6.11.1                   # change to kernel source dir
  263 $ patch -p1 -R < ../patch-2.6.11.1      # revert the 2.6.11.1 patch
  264                                         # source dir is now 2.6.11
  265 $ patch -p1 < ../patch-2.6.12           # apply new 2.6.12 patch
  266 $ cd ..
  267 $ mv linux-2.6.11.1 linux-2.6.12                # rename source dir
  268 
  269 
  270 The 2.6.x.y kernels
  271 ---
  272  Kernels with 4-digit versions are -stable kernels. They contain small(ish)
  273 critical fixes for security problems or significant regressions discovered
  274 in a given 2.6.x kernel.
  275 
  276 This is the recommended branch for users who want the most recent stable
  277 kernel and are not interested in helping test development/experimental
  278 versions.
  279 
  280 If no 2.6.x.y kernel is available, then the highest numbered 2.6.x kernel is
  281 the current stable kernel.
  282 
  283  note: the -stable team usually do make incremental patches available as well
  284  as patches against the latest mainline release, but I only cover the
  285  non-incremental ones below. The incremental ones can be found at
  286  ftp://ftp.kernel.org/pub/linux/kernel/v2.6/incr/
  287 
  288 These patches are not incremental, meaning that for example the 2.6.12.3
  289 patch does not apply on top of the 2.6.12.2 kernel source, but rather on top
  290 of the base 2.6.12 kernel source .
  291 So, in order to apply the 2.6.12.3 patch to your existing 2.6.12.2 kernel
  292 source you have to first back out the 2.6.12.2 patch (so you are left with a
  293 base 2.6.12 kernel source) and then apply the new 2.6.12.3 patch.
  294 
  295 Here's a small example:
  296 
  297 $ cd ~/linux-2.6.12.2                   # change into the kernel source dir
  298 $ patch -p1 -R < ../patch-2.6.12.2      # revert the 2.6.12.2 patch
  299 $ patch -p1 < ../patch-2.6.12.3         # apply the new 2.6.12.3 patch
  300 $ cd ..
  301 $ mv linux-2.6.12.2 linux-2.6.12.3      # rename the kernel source dir
  302 
  303 
  304 The -rc kernels
  305 ---
  306  These are release-candidate kernels. These are development kernels released
  307 by Linus whenever he deems the current git (the kernel's source management
  308 tool) tree to be in a reasonably sane state adequate for testing.
  309 
  310 These kernels are not stable and you should expect occasional breakage if
  311 you intend to run them. This is however the most stable of the main
  312 development branches and is also what will eventually turn into the next
  313 stable kernel, so it is important that it be tested by as many people as
  314 possible.
  315 
  316 This is a good branch to run for people who want to help out testing
  317 development kernels but do not want to run some of the really experimental
  318 stuff (such people should see the sections about -git and -mm kernels below).
  319 
  320 The -rc patches are not incremental, they apply to a base 2.6.x kernel, just
  321 like the 2.6.x.y patches described above. The kernel version before the -rcN
  322 suffix denotes the version of the kernel that this -rc kernel will eventually
  323 turn into.
  324 So, 2.6.13-rc5 means that this is the fifth release candidate for the 2.6.13
  325 kernel and the patch should be applied on top of the 2.6.12 kernel source.
  326 
  327 Here are 3 examples of how to apply these patches:
  328 
  329 # first an example of moving from 2.6.12 to 2.6.13-rc3
  330 $ cd ~/linux-2.6.12                     # change into the 2.6.12 source dir
  331 $ patch -p1 < ../patch-2.6.13-rc3       # apply the 2.6.13-rc3 patch
  332 $ cd ..
  333 $ mv linux-2.6.12 linux-2.6.13-rc3      # rename the source dir
  334 
  335 # now let's move from 2.6.13-rc3 to 2.6.13-rc5
  336 $ cd ~/linux-2.6.13-rc3                 # change into the 2.6.13-rc3 dir
  337 $ patch -p1 -R < ../patch-2.6.13-rc3    # revert the 2.6.13-rc3 patch
  338 $ patch -p1 < ../patch-2.6.13-rc5       # apply the new 2.6.13-rc5 patch
  339 $ cd ..
  340 $ mv linux-2.6.13-rc3 linux-2.6.13-rc5  # rename the source dir
  341 
  342 # finally let's try and move from 2.6.12.3 to 2.6.13-rc5
  343 $ cd ~/linux-2.6.12.3                   # change to the kernel source dir
  344 $ patch -p1 -R < ../patch-2.6.12.3      # revert the 2.6.12.3 patch
  345 $ patch -p1 < ../patch-2.6.13-rc5       # apply new 2.6.13-rc5 patch
  346 $ cd ..
  347 $ mv linux-2.6.12.3 linux-2.6.13-rc5    # rename the kernel source dir
  348 
  349 
  350 The -git kernels
  351 ---
  352  These are daily snapshots of Linus' kernel tree (managed in a git
  353 repository, hence the name).
  354 
  355 These patches are usually released daily and represent the current state of
  356 Linus's tree. They are more experimental than -rc kernels since they are
  357 generated automatically without even a cursory glance to see if they are
  358 sane.
  359 
  360 -git patches are not incremental and apply either to a base 2.6.x kernel or
  361 a base 2.6.x-rc kernel -- you can see which from their name.
  362 A patch named 2.6.12-git1 applies to the 2.6.12 kernel source and a patch
  363 named 2.6.13-rc3-git2 applies to the source of the 2.6.13-rc3 kernel.
  364 
  365 Here are some examples of how to apply these patches:
  366 
  367 # moving from 2.6.12 to 2.6.12-git1
  368 $ cd ~/linux-2.6.12                     # change to the kernel source dir
  369 $ patch -p1 < ../patch-2.6.12-git1      # apply the 2.6.12-git1 patch
  370 $ cd ..
  371 $ mv linux-2.6.12 linux-2.6.12-git1     # rename the kernel source dir
  372 
  373 # moving from 2.6.12-git1 to 2.6.13-rc2-git3
  374 $ cd ~/linux-2.6.12-git1                # change to the kernel source dir
  375 $ patch -p1 -R < ../patch-2.6.12-git1   # revert the 2.6.12-git1 patch
  376                                         # we now have a 2.6.12 kernel
  377 $ patch -p1 < ../patch-2.6.13-rc2       # apply the 2.6.13-rc2 patch
  378                                         # the kernel is now 2.6.13-rc2
  379 $ patch -p1 < ../patch-2.6.13-rc2-git3  # apply the 2.6.13-rc2-git3 patch
  380                                         # the kernel is now 2.6.13-rc2-git3
  381 $ cd ..
  382 $ mv linux-2.6.12-git1 linux-2.6.13-rc2-git3    # rename source dir
  383 
  384 
  385 The -mm kernels
  386 ---
  387  These are experimental kernels released by Andrew Morton.
  388 
  389 The -mm tree serves as a sort of proving ground for new features and other
  390 experimental patches.
  391 Once a patch has proved its worth in -mm for a while Andrew pushes it on to
  392 Linus for inclusion in mainline.
  393 
  394 Although it's encouraged that patches flow to Linus via the -mm tree, this
  395 is not always enforced.
  396 Subsystem maintainers (or individuals) sometimes push their patches directly
  397 to Linus, even though (or after) they have been merged and tested in -mm (or
  398 sometimes even without prior testing in -mm).
  399 
  400 You should generally strive to get your patches into mainline via -mm to
  401 ensure maximum testing.
  402 
  403 This branch is in constant flux and contains many experimental features, a
  404 lot of debugging patches not appropriate for mainline etc., and is the most
  405 experimental of the branches described in this document.
  406 
  407 These kernels are not appropriate for use on systems that are supposed to be
  408 stable and they are more risky to run than any of the other branches (make
  409 sure you have up-to-date backups -- that goes for any experimental kernel but
  410 even more so for -mm kernels).
  411 
  412 These kernels in addition to all the other experimental patches they contain
  413 usually also contain any changes in the mainline -git kernels available at
  414 the time of release.
  415 
  416 Testing of -mm kernels is greatly appreciated since the whole point of the
  417 tree is to weed out regressions, crashes, data corruption bugs, build
  418 breakage (and any other bug in general) before changes are merged into the
  419 more stable mainline Linus tree.
  420 But testers of -mm should be aware that breakage in this tree is more common
  421 than in any other tree.
  422 
  423 The -mm kernels are not released on a fixed schedule, but usually a few -mm
  424 kernels are released in between each -rc kernel (1 to 3 is common).
  425 The -mm kernels apply to either a base 2.6.x kernel (when no -rc kernels
  426 have been released yet) or to a Linus -rc kernel.
  427 
  428 Here are some examples of applying the -mm patches:
  429 
  430 # moving from 2.6.12 to 2.6.12-mm1
  431 $ cd ~/linux-2.6.12                     # change to the 2.6.12 source dir
  432 $ patch -p1 < ../2.6.12-mm1             # apply the 2.6.12-mm1 patch
  433 $ cd ..
  434 $ mv linux-2.6.12 linux-2.6.12-mm1      # rename the source appropriately
  435 
  436 # moving from 2.6.12-mm1 to 2.6.13-rc3-mm3
  437 $ cd ~/linux-2.6.12-mm1
  438 $ patch -p1 -R < ../2.6.12-mm1          # revert the 2.6.12-mm1 patch
  439                                         # we now have a 2.6.12 source
  440 $ patch -p1 < ../patch-2.6.13-rc3       # apply the 2.6.13-rc3 patch
  441                                         # we now have a 2.6.13-rc3 source
  442 $ patch -p1 < ../2.6.13-rc3-mm3         # apply the 2.6.13-rc3-mm3 patch
  443 $ cd ..
  444 $ mv linux-2.6.12-mm1 linux-2.6.13-rc3-mm3      # rename the source dir
  445 
  446 
  447 This concludes this list of explanations of the various kernel trees.
  448 I hope you are now clear on how to apply the various patches and help testing
  449 the kernel.
  450 
  451 Thank you's to Randy Dunlap, Rolf Eike Beer, Linus Torvalds, Bodo Eggert,
  452 Johannes Stezenbach, Grant Coady, Pavel Machek and others that I may have
  453 forgotten for their reviews and contributions to this document.
  454 

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