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diff --git a/Documentation/process/applying-patches.rst b/Documentation/process/applying-patches.rst new file mode 100644 index 000000000..2e7017bef --- /dev/null +++ b/Documentation/process/applying-patches.rst @@ -0,0 +1,426 @@ +.. _applying_patches: + +Applying Patches To The Linux Kernel +++++++++++++++++++++++++++++++++++++ + +Original by: + Jesper Juhl, August 2005 + +.. note:: + + This document is obsolete. In most cases, rather than using ``patch`` + manually, you'll almost certainly want to look at using Git instead. + +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 xz and you don't want to +uncompress it before applying it, then you can feed it to patch like this +instead:: + + xzcat path/to/patch-x.y.z.xz | patch -p1 + bzcat path/to/patch-x.y.z.gz | 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 xz on the file -- like this:: + + gunzip patch-x.y.z.gz + xz -d patch-x.y.z.xz + +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 and 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 5.7.2 to 5.7.3 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 5.7.2 to 5.7.3 in a single step:: + + interdiff -z ../patch-5.7.2.gz ../patch-5.7.3.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 (https://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 https://kernel.org/ +Most recent patches are linked from the front page, but they also have +specific homes. + +The 5.x.y (-stable) and 5.x patches live at + + https://www.kernel.org/pub/linux/kernel/v5.x/ + +The -rc patches are not stored on the webserver but are generated on +demand from git tags such as + + https://git.kernel.org/torvalds/p/v5.1-rc1/v5.0 + +The stable -rc patches live at + + https://www.kernel.org/pub/linux/kernel/v5.x/stable-review/ + + +The 5.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 5.x base +kernel is released, a patch is made available that is a delta between the +previous 5.x kernel and the new one. + +To apply a patch moving from 5.6 to 5.7, you'd do the following (note +that such patches do **NOT** apply on top of 5.x.y kernels but on top of the +base 5.x kernel -- if you need to move from 5.x.y to 5.x+1 you need to +first revert the 5.x.y patch). + +Here are some examples:: + + # moving from 5.6 to 5.7 + + $ cd ~/linux-5.6 # change to kernel source dir + $ patch -p1 < ../patch-5.7 # apply the 5.7 patch + $ cd .. + $ mv linux-5.6 linux-5.7 # rename source dir + + # moving from 5.6.1 to 5.7 + + $ cd ~/linux-5.6.1 # change to kernel source dir + $ patch -p1 -R < ../patch-5.6.1 # revert the 5.6.1 patch + # source dir is now 5.6 + $ patch -p1 < ../patch-5.7 # apply new 5.7 patch + $ cd .. + $ mv linux-5.6.1 linux-5.7 # rename source dir + + +The 5.x.y kernels +================= + +Kernels with 3-digit versions are -stable kernels. They contain small(ish) +critical fixes for security problems or significant regressions discovered +in a given 5.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 5.x.y kernel is available, then the highest numbered 5.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 + https://www.kernel.org/pub/linux/kernel/v5.x/incr/ + +These patches are not incremental, meaning that for example the 5.7.3 +patch does not apply on top of the 5.7.2 kernel source, but rather on top +of the base 5.7 kernel source. + +So, in order to apply the 5.7.3 patch to your existing 5.7.2 kernel +source you have to first back out the 5.7.2 patch (so you are left with a +base 5.7 kernel source) and then apply the new 5.7.3 patch. + +Here's a small example:: + + $ cd ~/linux-5.7.2 # change to the kernel source dir + $ patch -p1 -R < ../patch-5.7.2 # revert the 5.7.2 patch + $ patch -p1 < ../patch-5.7.3 # apply the new 5.7.3 patch + $ cd .. + $ mv linux-5.7.2 linux-5.7.3 # 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 -next and -mm kernels below). + +The -rc patches are not incremental, they apply to a base 5.x kernel, just +like the 5.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, 5.8-rc5 means that this is the fifth release candidate for the 5.8 +kernel and the patch should be applied on top of the 5.7 kernel source. + +Here are 3 examples of how to apply these patches:: + + # first an example of moving from 5.7 to 5.8-rc3 + + $ cd ~/linux-5.7 # change to the 5.7 source dir + $ patch -p1 < ../patch-5.8-rc3 # apply the 5.8-rc3 patch + $ cd .. + $ mv linux-5.7 linux-5.8-rc3 # rename the source dir + + # now let's move from 5.8-rc3 to 5.8-rc5 + + $ cd ~/linux-5.8-rc3 # change to the 5.8-rc3 dir + $ patch -p1 -R < ../patch-5.8-rc3 # revert the 5.8-rc3 patch + $ patch -p1 < ../patch-5.8-rc5 # apply the new 5.8-rc5 patch + $ cd .. + $ mv linux-5.8-rc3 linux-5.8-rc5 # rename the source dir + + # finally let's try and move from 5.7.3 to 5.8-rc5 + + $ cd ~/linux-5.7.3 # change to the kernel source dir + $ patch -p1 -R < ../patch-5.7.3 # revert the 5.7.3 patch + $ patch -p1 < ../patch-5.8-rc5 # apply new 5.8-rc5 patch + $ cd .. + $ mv linux-5.7.3 linux-5.8-rc5 # rename the kernel source dir + + +The -mm patches and the linux-next tree +======================================= + +The -mm patches are experimental patches released by Andrew Morton. + +In the past, -mm tree were used to also test subsystem patches, but this +function is now done via the +`linux-next <https://www.kernel.org/doc/man-pages/linux-next.html>` +tree. The Subsystem maintainers push their patches first to linux-next, +and, during the merge window, sends them directly to Linus. + +The -mm patches serve as a sort of proving ground for new features and other +experimental patches that aren't merged via a subsystem tree. +Once such patches has proved its worth in -mm for a while Andrew pushes +it on to Linus for inclusion in mainline. + +The linux-next tree is daily updated, and includes the -mm patches. +Both are 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 patches 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 patches or using a Kernel from the linux-next tree). + +Testing of -mm patches and linux-next is greatly appreciated since the whole +point of those are 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 and linux-next should be aware that breakages are +more common than in any other tree. + + +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. |