linux/Documentation/applying-patches.txt
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   2        Applying Patches To The Linux Kernel
   3        ------------------------------------
   4
   5        Original by: Jesper Juhl, August 2005
   6        Last update: 2006-01-05
   7
   8
   9A frequently asked question on the Linux Kernel Mailing List is how to apply
  10a patch to the kernel or, more specifically, what base kernel a patch for
  11one of the many trees/branches should be applied to. Hopefully this document
  12will explain this to you.
  13
  14In addition to explaining how to apply and revert patches, a brief
  15description of the different kernel trees (and examples of how to apply
  16their specific patches) is also provided.
  17
  18
  19What is a patch?
  20---
  21 A patch is a small text document containing a delta of changes between two
  22different versions of a source tree. Patches are created with the `diff'
  23program.
  24To correctly apply a patch you need to know what base it was generated from
  25and what new version the patch will change the source tree into. These
  26should both be present in the patch file metadata or be possible to deduce
  27from the filename.
  28
  29
  30How 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
  35Patches for the Linux kernel are generated relative to the parent directory
  36holding the kernel source dir.
  37
  38This means that paths to files inside the patch file contain the name of the
  39kernel source directories it was generated against (or some other directory
  40names like "a/" and "b/").
  41Since this is unlikely to match the name of the kernel source dir on your
  42local machine (but is often useful info to see what version an otherwise
  43unlabeled patch was generated against) you should change into your kernel
  44source directory and then strip the first element of the path from filenames
  45in the patch file when applying it (the -p1 argument to `patch' does this).
  46
  47To revert a previously applied patch, use the -R argument to patch.
  48So, if you applied a patch like this:
  49        patch -p1 < ../patch-x.y.z
  50
  51You can revert (undo) it like this:
  52        patch -R -p1 < ../patch-x.y.z
  53
  54
  55How do I feed a patch/diff file to `patch'?
  56---
  57 This (as usual with Linux and other UNIX like operating systems) can be
  58done in several different ways.
  59In all the examples below I feed the file (in uncompressed form) to patch
  60via stdin using the following syntax:
  61        patch -p1 < path/to/patch-x.y.z
  62
  63If you just want to be able to follow the examples below and don't want to
  64know of more than one way to use patch, then you can stop reading this
  65section here.
  66
  67Patch can also get the name of the file to use via the -i argument, like
  68this:
  69        patch -p1 -i path/to/patch-x.y.z
  70
  71If your patch file is compressed with gzip or bzip2 and you don't want to
  72uncompress it before applying it, then you can feed it to patch like this
  73instead:
  74        zcat path/to/patch-x.y.z.gz | patch -p1
  75        bzcat path/to/patch-x.y.z.bz2 | patch -p1
  76
  77If 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
  79gunzip or bunzip2 on the file -- like this:
  80        gunzip patch-x.y.z.gz
  81        bunzip2 patch-x.y.z.bz2
  82
  83Which will leave you with a plain text patch-x.y.z file that you can feed to
  84patch via stdin or the -i argument, as you prefer.
  85
  86A few other nice arguments for patch are -s which causes patch to be silent
  87except for errors which is nice to prevent errors from scrolling out of the
  88screen too fast, and --dry-run which causes patch to just print a listing of
  89what would happen, but doesn't actually make any changes. Finally --verbose
  90tells patch to print more information about the work being done.
  91
  92
  93Common errors when patching
  94---
  95 When patch applies a patch file it attempts to verify the sanity of the
  96file in different ways.
  97Checking that the file looks like a valid patch file & checking the code
  98around the bits being modified matches the context provided in the patch are
  99just two of the basic sanity checks patch does.
 100
 101If patch encounters something that doesn't look quite right it has two
 102options. It can either refuse to apply the changes and abort or it can try
 103to find a way to make the patch apply with a few minor changes.
 104
 105One example of something that's not 'quite right' that patch will attempt to
 106fix up is if all the context matches, the lines being changed match, but the
 107line numbers are different. This can happen, for example, if the patch makes
 108a change in the middle of the file but for some reasons a few lines have
 109been added or removed near the beginning of the file. In that case
 110everything looks good it has just moved up or down a bit, and patch will
 111usually adjust the line numbers and apply the patch.
 112
 113Whenever patch applies a patch that it had to modify a bit to make it fit
 114it'll tell you about it by saying the patch applied with 'fuzz'.
 115You should be wary of such changes since even though patch probably got it
 116right it doesn't /always/ get it right, and the result will sometimes be
 117wrong.
 118
 119When patch encounters a change that it can't fix up with fuzz it rejects it
 120outright and leaves a file with a .rej extension (a reject file). You can
 121read this file to see exactly what change couldn't be applied, so you can
 122go fix it up by hand if you wish.
 123
 124If you don't have any third-party patches applied to your kernel source, but
 125only patches from kernel.org and you apply the patches in the correct order,
 126and have made no modifications yourself to the source files, then you should
 127never see a fuzz or reject message from patch. If you do see such messages
 128anyway, then there's a high risk that either your local source tree or the
 129patch file is corrupted in some way. In that case you should probably try
 130re-downloading the patch and if things are still not OK then you'd be advised
 131to start with a fresh tree downloaded in full from kernel.org.
 132
 133Let's look a bit more at some of the messages patch can produce.
 134
 135If patch stops and presents a "File to patch:" prompt, then patch could not
 136find a file to be patched. Most likely you forgot to specify -p1 or you are
 137in the wrong directory. Less often, you'll find patches that need to be
 138applied with -p0 instead of -p1 (reading the patch file should reveal if
 139this is the case -- if so, then this is an error by the person who created
 140the patch but is not fatal).
 141
 142If you get "Hunk #2 succeeded at 1887 with fuzz 2 (offset 7 lines)." or a
 143message similar to that, then it means that patch had to adjust the location
 144of the change (in this example it needed to move 7 lines from where it
 145expected to make the change to make it fit).
 146The resulting file may or may not be OK, depending on the reason the file
 147was different than expected.
 148This often happens if you try to apply a patch that was generated against a
 149different kernel version than the one you are trying to patch.
 150
 151If you get a message like "Hunk #3 FAILED at 2387.", then it means that the
 152patch could not be applied correctly and the patch program was unable to
 153fuzz its way through. This will generate a .rej file with the change that
 154caused the patch to fail and also a .orig file showing you the original
 155content that couldn't be changed.
 156
 157If you get "Reversed (or previously applied) patch detected!  Assume -R? [n]"
 158then patch detected that the change contained in the patch seems to have
 159already been made.
 160If you actually did apply this patch previously and you just re-applied it
 161in error, then just say [n]o and abort this patch. If you applied this patch
 162previously and actually intended to revert it, but forgot to specify -R,
 163then you can say [y]es here to make patch revert it for you.
 164This can also happen if the creator of the patch reversed the source and
 165destination directories when creating the patch, and in that case reverting
 166the patch will in fact apply it.
 167
 168A message similar to "patch: **** unexpected end of file in patch" or "patch
 169unexpectedly ends in middle of line" means that patch could make no sense of
 170the file you fed to it. Either your download is broken, you tried to feed
 171patch a compressed patch file without uncompressing it first, or the patch
 172file that you are using has been mangled by a mail client or mail transfer
 173agent along the way somewhere, e.g., by splitting a long line into two lines.
 174Often these warnings can easily be fixed by joining (concatenating) the
 175two lines that had been split.
 176
 177As I already mentioned above, these errors should never happen if you apply
 178a patch from kernel.org to the correct version of an unmodified source tree.
 179So if you get these errors with kernel.org patches then you should probably
 180assume that either your patch file or your tree is broken and I'd advise you
 181to start over with a fresh download of a full kernel tree and the patch you
 182wish to apply.
 183
 184
 185Are 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
 190generate a patch representing the differences between two patches and then
 191apply the result.
 192This will let you move from something like 2.6.12.2 to 2.6.12.3 in a single
 193step. The -z flag to interdiff will even let you feed it patches in gzip or
 194bzip2 compressed form directly without the use of zcat or bzcat or manual
 195decompression.
 196
 197Here'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
 200Although interdiff may save you a step or two you are generally advised to
 201do 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
 204downloading 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
 207patch; lsdiff, which displays a short listing of affected files in a patch
 208file, along with (optionally) the line numbers of the start of each patch;
 209and grepdiff, which displays a list of the files modified by a patch where
 210the patch contains a given regular expression.
 211
 212
 213Where can I download the patches?
 214---
 215 The patches are available at http://kernel.org/
 216Most recent patches are linked from the front page, but they also have
 217specific homes.
 218
 219The 2.6.x.y (-stable) and 2.6.x patches live at
 220 ftp://ftp.kernel.org/pub/linux/kernel/v2.6/
 221
 222The -rc patches live at
 223 ftp://ftp.kernel.org/pub/linux/kernel/v2.6/testing/
 224
 225The -git patches live at
 226 ftp://ftp.kernel.org/pub/linux/kernel/v2.6/snapshots/
 227
 228The -mm kernels live at
 229 ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/
 230
 231In place of ftp.kernel.org you can use ftp.cc.kernel.org, where cc is a
 232country code. This way you'll be downloading from a mirror site that's most
 233likely geographically closer to you, resulting in faster downloads for you,
 234less bandwidth used globally and less load on the main kernel.org servers --
 235these are good things, so do use mirrors when possible.
 236
 237
 238The 2.6.x kernels
 239---
 240 These are the base stable releases released by Linus. The highest numbered
 241release is the most recent.
 242
 243If regressions or other serious flaws are found, then a -stable fix patch
 244will be released (see below) on top of this base. Once a new 2.6.x base
 245kernel is released, a patch is made available that is a delta between the
 246previous 2.6.x kernel and the new one.
 247
 248To apply a patch moving from 2.6.11 to 2.6.12, you'd do the following (note
 249that such patches do *NOT* apply on top of 2.6.x.y kernels but on top of the
 250base 2.6.x kernel -- if you need to move from 2.6.x.y to 2.6.x+1 you need to
 251first revert the 2.6.x.y patch).
 252
 253Here 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
 270The 2.6.x.y kernels
 271---
 272 Kernels with 4-digit versions are -stable kernels. They contain small(ish)
 273critical fixes for security problems or significant regressions discovered
 274in a given 2.6.x kernel.
 275
 276This is the recommended branch for users who want the most recent stable
 277kernel and are not interested in helping test development/experimental
 278versions.
 279
 280If no 2.6.x.y kernel is available, then the highest numbered 2.6.x kernel is
 281the 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
 288These patches are not incremental, meaning that for example the 2.6.12.3
 289patch does not apply on top of the 2.6.12.2 kernel source, but rather on top
 290of the base 2.6.12 kernel source .
 291So, in order to apply the 2.6.12.3 patch to your existing 2.6.12.2 kernel
 292source you have to first back out the 2.6.12.2 patch (so you are left with a
 293base 2.6.12 kernel source) and then apply the new 2.6.12.3 patch.
 294
 295Here'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
 304The -rc kernels
 305---
 306 These are release-candidate kernels. These are development kernels released
 307by Linus whenever he deems the current git (the kernel's source management
 308tool) tree to be in a reasonably sane state adequate for testing.
 309
 310These kernels are not stable and you should expect occasional breakage if
 311you intend to run them. This is however the most stable of the main
 312development branches and is also what will eventually turn into the next
 313stable kernel, so it is important that it be tested by as many people as
 314possible.
 315
 316This is a good branch to run for people who want to help out testing
 317development kernels but do not want to run some of the really experimental
 318stuff (such people should see the sections about -git and -mm kernels below).
 319
 320The -rc patches are not incremental, they apply to a base 2.6.x kernel, just
 321like the 2.6.x.y patches described above. The kernel version before the -rcN
 322suffix denotes the version of the kernel that this -rc kernel will eventually
 323turn into.
 324So, 2.6.13-rc5 means that this is the fifth release candidate for the 2.6.13
 325kernel and the patch should be applied on top of the 2.6.12 kernel source.
 326
 327Here 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
 350The -git kernels
 351---
 352 These are daily snapshots of Linus' kernel tree (managed in a git
 353repository, hence the name).
 354
 355These patches are usually released daily and represent the current state of
 356Linus's tree. They are more experimental than -rc kernels since they are
 357generated automatically without even a cursory glance to see if they are
 358sane.
 359
 360-git patches are not incremental and apply either to a base 2.6.x kernel or
 361a base 2.6.x-rc kernel -- you can see which from their name.
 362A patch named 2.6.12-git1 applies to the 2.6.12 kernel source and a patch
 363named 2.6.13-rc3-git2 applies to the source of the 2.6.13-rc3 kernel.
 364
 365Here 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
 385The -mm kernels
 386---
 387 These are experimental kernels released by Andrew Morton.
 388
 389The -mm tree serves as a sort of proving ground for new features and other
 390experimental patches.
 391Once a patch has proved its worth in -mm for a while Andrew pushes it on to
 392Linus for inclusion in mainline.
 393
 394Although it's encouraged that patches flow to Linus via the -mm tree, this
 395is not always enforced.
 396Subsystem maintainers (or individuals) sometimes push their patches directly
 397to Linus, even though (or after) they have been merged and tested in -mm (or
 398sometimes even without prior testing in -mm).
 399
 400You should generally strive to get your patches into mainline via -mm to
 401ensure maximum testing.
 402
 403This branch is in constant flux and contains many experimental features, a
 404lot of debugging patches not appropriate for mainline etc., and is the most
 405experimental of the branches described in this document.
 406
 407These kernels are not appropriate for use on systems that are supposed to be
 408stable and they are more risky to run than any of the other branches (make
 409sure you have up-to-date backups -- that goes for any experimental kernel but
 410even more so for -mm kernels).
 411
 412These kernels in addition to all the other experimental patches they contain
 413usually also contain any changes in the mainline -git kernels available at
 414the time of release.
 415
 416Testing of -mm kernels is greatly appreciated since the whole point of the
 417tree is to weed out regressions, crashes, data corruption bugs, build
 418breakage (and any other bug in general) before changes are merged into the
 419more stable mainline Linus tree.
 420But testers of -mm should be aware that breakage in this tree is more common
 421than in any other tree.
 422
 423The -mm kernels are not released on a fixed schedule, but usually a few -mm
 424kernels are released in between each -rc kernel (1 to 3 is common).
 425The -mm kernels apply to either a base 2.6.x kernel (when no -rc kernels
 426have been released yet) or to a Linus -rc kernel.
 427
 428Here 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
 447This concludes this list of explanations of the various kernel trees.
 448I hope you are now clear on how to apply the various patches and help testing
 449the kernel.
 450
 451Thank you's to Randy Dunlap, Rolf Eike Beer, Linus Torvalds, Bodo Eggert,
 452Johannes Stezenbach, Grant Coady, Pavel Machek and others that I may have
 453forgotten for their reviews and contributions to this document.
 454
 455
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