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-
- Applying Patches To The Linux Kernel
- ------------------------------------
-
- Original by: Jesper Juhl, August 2005
- Last update: 2006-01-05
-
-
-A frequently asked question on the Linux Kernel Mailing List is how to apply
-a patch to the kernel or, more specifically, what base kernel a patch for
-one of the many trees/branches should be applied to. Hopefully this document
-will explain this to you.
-
-In addition to explaining how to apply and revert patches, a brief
-description of the different kernel trees (and examples of how to apply
-their specific patches) is also provided.
-
-
-What is a patch?
----
- A patch is a small text document containing a delta of changes between two
-different versions of a source tree. Patches are created with the `diff'
-program.
-To correctly apply a patch you need to know what base it was generated from
-and what new version the patch will change the source tree into. These
-should both be present in the patch file metadata or be possible to deduce
-from the filename.
-
-
-How do I apply or revert a patch?
----
- You apply a patch with the `patch' program. The patch program reads a diff
-(or patch) file and makes the changes to the source tree described in it.
-
-Patches for the Linux kernel are generated relative to the parent directory
-holding the kernel source dir.
-
-This means that paths to files inside the patch file contain the name of the
-kernel source directories it was generated against (or some other directory
-names like "a/" and "b/").
-Since this is unlikely to match the name of the kernel source dir on your
-local machine (but is often useful info to see what version an otherwise
-unlabeled patch was generated against) you should change into your kernel
-source directory and then strip the first element of the path from filenames
-in the patch file when applying it (the -p1 argument to `patch' does this).
-
-To revert a previously applied patch, use the -R argument to patch.
-So, if you applied a patch like this:
- patch -p1 < ../patch-x.y.z
-
-You can revert (undo) it like this:
- patch -R -p1 < ../patch-x.y.z
-
-
-How do I feed a patch/diff file to `patch'?
----
- This (as usual with Linux and other UNIX like operating systems) can be
-done in several different ways.
-In all the examples below I feed the file (in uncompressed form) to patch
-via stdin using the following syntax:
- patch -p1 < path/to/patch-x.y.z
-
-If you just want to be able to follow the examples below and don't want to
-know of more than one way to use patch, then you can stop reading this
-section here.
-
-Patch can also get the name of the file to use via the -i argument, like
-this:
- patch -p1 -i path/to/patch-x.y.z
-
-If your patch file is compressed with gzip or bzip2 and you don't want to
-uncompress it before applying it, then you can feed it to patch like this
-instead:
- zcat path/to/patch-x.y.z.gz | patch -p1
- bzcat path/to/patch-x.y.z.bz2 | patch -p1
-
-If you wish to uncompress the patch file by hand first before applying it
-(what I assume you've done in the examples below), then you simply run
-gunzip or bunzip2 on the file -- like this:
- gunzip patch-x.y.z.gz
- bunzip2 patch-x.y.z.bz2
-
-Which will leave you with a plain text patch-x.y.z file that you can feed to
-patch via stdin or the -i argument, as you prefer.
-
-A few other nice arguments for patch are -s which causes patch to be silent
-except for errors which is nice to prevent errors from scrolling out of the
-screen too fast, and --dry-run which causes patch to just print a listing of
-what would happen, but doesn't actually make any changes. Finally --verbose
-tells patch to print more information about the work being done.
-
-
-Common errors when patching
----
- When patch applies a patch file it attempts to verify the sanity of the
-file in different ways.
-Checking that the file looks like a valid patch file & checking the code
-around the bits being modified matches the context provided in the patch are
-just two of the basic sanity checks patch does.
-
-If patch encounters something that doesn't look quite right it has two
-options. It can either refuse to apply the changes and abort or it can try
-to find a way to make the patch apply with a few minor changes.
-
-One example of something that's not 'quite right' that patch will attempt to
-fix up is if all the context matches, the lines being changed match, but the
-line numbers are different. This can happen, for example, if the patch makes
-a change in the middle of the file but for some reasons a few lines have
-been added or removed near the beginning of the file. In that case
-everything looks good it has just moved up or down a bit, and patch will
-usually adjust the line numbers and apply the patch.
-
-Whenever patch applies a patch that it had to modify a bit to make it fit
-it'll tell you about it by saying the patch applied with 'fuzz'.
-You should be wary of such changes since even though patch probably got it
-right it doesn't /always/ get it right, and the result will sometimes be
-wrong.
-
-When patch encounters a change that it can't fix up with fuzz it rejects it
-outright and leaves a file with a .rej extension (a reject file). You can
-read this file to see exactly what change couldn't be applied, so you can
-go fix it up by hand if you wish.
-
-If you don't have any third-party patches applied to your kernel source, but
-only patches from kernel.org and you apply the patches in the correct order,
-and have made no modifications yourself to the source files, then you should
-never see a fuzz or reject message from patch. If you do see such messages
-anyway, then there's a high risk that either your local source tree or the
-patch file is corrupted in some way. In that case you should probably try
-re-downloading the patch and if things are still not OK then you'd be advised
-to start with a fresh tree downloaded in full from kernel.org.
-
-Let's look a bit more at some of the messages patch can produce.
-
-If patch stops and presents a "File to patch:" prompt, then patch could not
-find a file to be patched. Most likely you forgot to specify -p1 or you are
-in the wrong directory. Less often, you'll find patches that need to be
-applied with -p0 instead of -p1 (reading the patch file should reveal if
-this is the case -- if so, then this is an error by the person who created
-the patch but is not fatal).
-
-If you get "Hunk #2 succeeded at 1887 with fuzz 2 (offset 7 lines)." or a
-message similar to that, then it means that patch had to adjust the location
-of the change (in this example it needed to move 7 lines from where it
-expected to make the change to make it fit).
-The resulting file may or may not be OK, depending on the reason the file
-was different than expected.
-This often happens if you try to apply a patch that was generated against a
-different kernel version than the one you are trying to patch.
-
-If you get a message like "Hunk #3 FAILED at 2387.", then it means that the
-patch could not be applied correctly and the patch program was unable to
-fuzz its way through. This will generate a .rej file with the change that
-caused the patch to fail and also a .orig file showing you the original
-content that couldn't be changed.
-
-If you get "Reversed (or previously applied) patch detected! Assume -R? [n]"
-then patch detected that the change contained in the patch seems to have
-already been made.
-If you actually did apply this patch previously and you just re-applied it
-in error, then just say [n]o and abort this patch. If you applied this patch
-previously and actually intended to revert it, but forgot to specify -R,
-then you can say [y]es here to make patch revert it for you.
-This can also happen if the creator of the patch reversed the source and
-destination directories when creating the patch, and in that case reverting
-the patch will in fact apply it.
-
-A message similar to "patch: **** unexpected end of file in patch" or "patch
-unexpectedly ends in middle of line" means that patch could make no sense of
-the file you fed to it. Either your download is broken, you tried to feed
-patch a compressed patch file without uncompressing it first, or the patch
-file that you are using has been mangled by a mail client or mail transfer
-agent along the way somewhere, e.g., by splitting a long line into two lines.
-Often these warnings can easily be fixed by joining (concatenating) the
-two lines that had been split.
-
-As I already mentioned above, these errors should never happen if you apply
-a patch from kernel.org to the correct version of an unmodified source tree.
-So if you get these errors with kernel.org patches then you should probably
-assume that either your patch file or your tree is broken and I'd advise you
-to start over with a fresh download of a full kernel tree and the patch you
-wish to apply.
-
-
-Are there any alternatives to `patch'?
----
- Yes there are alternatives.
-
- You can use the `interdiff' program (http://cyberelk.net/tim/patchutils/) to
-generate a patch representing the differences between two patches and then
-apply the result.
-This will let you move from something like 2.6.12.2 to 2.6.12.3 in a single
-step. The -z flag to interdiff will even let you feed it patches in gzip or
-bzip2 compressed form directly without the use of zcat or bzcat or manual
-decompression.
-
-Here's how you'd go from 2.6.12.2 to 2.6.12.3 in a single step:
- interdiff -z ../patch-2.6.12.2.bz2 ../patch-2.6.12.3.gz | patch -p1
-
-Although interdiff may save you a step or two you are generally advised to
-do the additional steps since interdiff can get things wrong in some cases.
-
- Another alternative is `ketchup', which is a python script for automatic
-downloading and applying of patches (http://www.selenic.com/ketchup/).
-
- Other nice tools are diffstat, which shows a summary of changes made by a
-patch; lsdiff, which displays a short listing of affected files in a patch
-file, along with (optionally) the line numbers of the start of each patch;
-and grepdiff, which displays a list of the files modified by a patch where
-the patch contains a given regular expression.
-
-
-Where can I download the patches?
----
- The patches are available at http://kernel.org/
-Most recent patches are linked from the front page, but they also have
-specific homes.
-
-The 2.6.x.y (-stable) and 2.6.x patches live at
- ftp://ftp.kernel.org/pub/linux/kernel/v2.6/
-
-The -rc patches live at
- ftp://ftp.kernel.org/pub/linux/kernel/v2.6/testing/
-
-The -git patches live at
- ftp://ftp.kernel.org/pub/linux/kernel/v2.6/snapshots/
-
-The -mm kernels live at
- ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/
-
-In place of ftp.kernel.org you can use ftp.cc.kernel.org, where cc is a
-country code. This way you'll be downloading from a mirror site that's most
-likely geographically closer to you, resulting in faster downloads for you,
-less bandwidth used globally and less load on the main kernel.org servers --
-these are good things, so do use mirrors when possible.
-
-
-The 2.6.x kernels
----
- These are the base stable releases released by Linus. The highest numbered
-release is the most recent.
-
-If regressions or other serious flaws are found, then a -stable fix patch
-will be released (see below) on top of this base. Once a new 2.6.x base
-kernel is released, a patch is made available that is a delta between the
-previous 2.6.x kernel and the new one.
-
-To apply a patch moving from 2.6.11 to 2.6.12, you'd do the following (note
-that such patches do *NOT* apply on top of 2.6.x.y kernels but on top of the
-base 2.6.x kernel -- if you need to move from 2.6.x.y to 2.6.x+1 you need to
-first revert the 2.6.x.y patch).
-
-Here are some examples:
-
-# moving from 2.6.11 to 2.6.12
-$ cd ~/linux-2.6.11 # change to kernel source dir
-$ patch -p1 < ../patch-2.6.12 # apply the 2.6.12 patch
-$ cd ..
-$ mv linux-2.6.11 linux-2.6.12 # rename source dir
-
-# moving from 2.6.11.1 to 2.6.12
-$ cd ~/linux-2.6.11.1 # change to kernel source dir
-$ patch -p1 -R < ../patch-2.6.11.1 # revert the 2.6.11.1 patch
- # source dir is now 2.6.11
-$ patch -p1 < ../patch-2.6.12 # apply new 2.6.12 patch
-$ cd ..
-$ mv linux-2.6.11.1 linux-2.6.12 # rename source dir
-
-
-The 2.6.x.y kernels
----
- Kernels with 4-digit versions are -stable kernels. They contain small(ish)
-critical fixes for security problems or significant regressions discovered
-in a given 2.6.x kernel.
-
-This is the recommended branch for users who want the most recent stable
-kernel and are not interested in helping test development/experimental
-versions.
-
-If no 2.6.x.y kernel is available, then the highest numbered 2.6.x kernel is
-the current stable kernel.
-
- note: the -stable team usually do make incremental patches available as well
- as patches against the latest mainline release, but I only cover the
- non-incremental ones below. The incremental ones can be found at
- ftp://ftp.kernel.org/pub/linux/kernel/v2.6/incr/
-
-These patches are not incremental, meaning that for example the 2.6.12.3
-patch does not apply on top of the 2.6.12.2 kernel source, but rather on top
-of the base 2.6.12 kernel source .
-So, in order to apply the 2.6.12.3 patch to your existing 2.6.12.2 kernel
-source you have to first back out the 2.6.12.2 patch (so you are left with a
-base 2.6.12 kernel source) and then apply the new 2.6.12.3 patch.
-
-Here's a small example:
-
-$ cd ~/linux-2.6.12.2 # change into the kernel source dir
-$ patch -p1 -R < ../patch-2.6.12.2 # revert the 2.6.12.2 patch
-$ patch -p1 < ../patch-2.6.12.3 # apply the new 2.6.12.3 patch
-$ cd ..
-$ mv linux-2.6.12.2 linux-2.6.12.3 # rename the kernel source dir
-
-
-The -rc kernels
----
- These are release-candidate kernels. These are development kernels released
-by Linus whenever he deems the current git (the kernel's source management
-tool) tree to be in a reasonably sane state adequate for testing.
-
-These kernels are not stable and you should expect occasional breakage if
-you intend to run them. This is however the most stable of the main
-development branches and is also what will eventually turn into the next
-stable kernel, so it is important that it be tested by as many people as
-possible.
-
-This is a good branch to run for people who want to help out testing
-development kernels but do not want to run some of the really experimental
-stuff (such people should see the sections about -git and -mm kernels below).
-
-The -rc patches are not incremental, they apply to a base 2.6.x kernel, just
-like the 2.6.x.y patches described above. The kernel version before the -rcN
-suffix denotes the version of the kernel that this -rc kernel will eventually
-turn into.
-So, 2.6.13-rc5 means that this is the fifth release candidate for the 2.6.13
-kernel and the patch should be applied on top of the 2.6.12 kernel source.
-
-Here are 3 examples of how to apply these patches:
-
-# first an example of moving from 2.6.12 to 2.6.13-rc3
-$ cd ~/linux-2.6.12 # change into the 2.6.12 source dir
-$ patch -p1 < ../patch-2.6.13-rc3 # apply the 2.6.13-rc3 patch
-$ cd ..
-$ mv linux-2.6.12 linux-2.6.13-rc3 # rename the source dir
-
-# now let's move from 2.6.13-rc3 to 2.6.13-rc5
-$ cd ~/linux-2.6.13-rc3 # change into the 2.6.13-rc3 dir
-$ patch -p1 -R < ../patch-2.6.13-rc3 # revert the 2.6.13-rc3 patch
-$ patch -p1 < ../patch-2.6.13-rc5 # apply the new 2.6.13-rc5 patch
-$ cd ..
-$ mv linux-2.6.13-rc3 linux-2.6.13-rc5 # rename the source dir
-
-# finally let's try and move from 2.6.12.3 to 2.6.13-rc5
-$ cd ~/linux-2.6.12.3 # change to the kernel source dir
-$ patch -p1 -R < ../patch-2.6.12.3 # revert the 2.6.12.3 patch
-$ patch -p1 < ../patch-2.6.13-rc5 # apply new 2.6.13-rc5 patch
-$ cd ..
-$ mv linux-2.6.12.3 linux-2.6.13-rc5 # rename the kernel source dir
-
-
-The -git kernels
----
- These are daily snapshots of Linus' kernel tree (managed in a git
-repository, hence the name).
-
-These patches are usually released daily and represent the current state of
-Linus's tree. They are more experimental than -rc kernels since they are
-generated automatically without even a cursory glance to see if they are
-sane.
-
--git patches are not incremental and apply either to a base 2.6.x kernel or
-a base 2.6.x-rc kernel -- you can see which from their name.
-A patch named 2.6.12-git1 applies to the 2.6.12 kernel source and a patch
-named 2.6.13-rc3-git2 applies to the source of the 2.6.13-rc3 kernel.
-
-Here are some examples of how to apply these patches:
-
-# moving from 2.6.12 to 2.6.12-git1
-$ cd ~/linux-2.6.12 # change to the kernel source dir
-$ patch -p1 < ../patch-2.6.12-git1 # apply the 2.6.12-git1 patch
-$ cd ..
-$ mv linux-2.6.12 linux-2.6.12-git1 # rename the kernel source dir
-
-# moving from 2.6.12-git1 to 2.6.13-rc2-git3
-$ cd ~/linux-2.6.12-git1 # change to the kernel source dir
-$ patch -p1 -R < ../patch-2.6.12-git1 # revert the 2.6.12-git1 patch
- # we now have a 2.6.12 kernel
-$ patch -p1 < ../patch-2.6.13-rc2 # apply the 2.6.13-rc2 patch
- # the kernel is now 2.6.13-rc2
-$ patch -p1 < ../patch-2.6.13-rc2-git3 # apply the 2.6.13-rc2-git3 patch
- # the kernel is now 2.6.13-rc2-git3
-$ cd ..
-$ mv linux-2.6.12-git1 linux-2.6.13-rc2-git3 # rename source dir
-
-
-The -mm kernels
----
- These are experimental kernels released by Andrew Morton.
-
-The -mm tree serves as a sort of proving ground for new features and other
-experimental patches.
-Once a patch has proved its worth in -mm for a while Andrew pushes it on to
-Linus for inclusion in mainline.
-
-Although it's encouraged that patches flow to Linus via the -mm tree, this
-is not always enforced.
-Subsystem maintainers (or individuals) sometimes push their patches directly
-to Linus, even though (or after) they have been merged and tested in -mm (or
-sometimes even without prior testing in -mm).
-
-You should generally strive to get your patches into mainline via -mm to
-ensure maximum testing.
-
-This branch is in constant flux and contains many experimental features, a
-lot of debugging patches not appropriate for mainline etc., and is the most
-experimental of the branches described in this document.
-
-These kernels are not appropriate for use on systems that are supposed to be
-stable and they are more risky to run than any of the other branches (make
-sure you have up-to-date backups -- that goes for any experimental kernel but
-even more so for -mm kernels).
-
-These kernels in addition to all the other experimental patches they contain
-usually also contain any changes in the mainline -git kernels available at
-the time of release.
-
-Testing of -mm kernels is greatly appreciated since the whole point of the
-tree is to weed out regressions, crashes, data corruption bugs, build
-breakage (and any other bug in general) before changes are merged into the
-more stable mainline Linus tree.
-But testers of -mm should be aware that breakage in this tree is more common
-than in any other tree.
-
-The -mm kernels are not released on a fixed schedule, but usually a few -mm
-kernels are released in between each -rc kernel (1 to 3 is common).
-The -mm kernels apply to either a base 2.6.x kernel (when no -rc kernels
-have been released yet) or to a Linus -rc kernel.
-
-Here are some examples of applying the -mm patches:
-
-# moving from 2.6.12 to 2.6.12-mm1
-$ cd ~/linux-2.6.12 # change to the 2.6.12 source dir
-$ patch -p1 < ../2.6.12-mm1 # apply the 2.6.12-mm1 patch
-$ cd ..
-$ mv linux-2.6.12 linux-2.6.12-mm1 # rename the source appropriately
-
-# moving from 2.6.12-mm1 to 2.6.13-rc3-mm3
-$ cd ~/linux-2.6.12-mm1
-$ patch -p1 -R < ../2.6.12-mm1 # revert the 2.6.12-mm1 patch
- # we now have a 2.6.12 source
-$ patch -p1 < ../patch-2.6.13-rc3 # apply the 2.6.13-rc3 patch
- # we now have a 2.6.13-rc3 source
-$ patch -p1 < ../2.6.13-rc3-mm3 # apply the 2.6.13-rc3-mm3 patch
-$ cd ..
-$ mv linux-2.6.12-mm1 linux-2.6.13-rc3-mm3 # rename the source dir
-
-
-This concludes this list of explanations of the various kernel trees.
-I hope you are now clear on how to apply the various patches and help testing
-the kernel.
-
-Thank you's to Randy Dunlap, Rolf Eike Beer, Linus Torvalds, Bodo Eggert,
-Johannes Stezenbach, Grant Coady, Pavel Machek and others that I may have
-forgotten for their reviews and contributions to this document.
-