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diff --git a/Documentation/applying-patches.txt b/Documentation/applying-patches.txt new file mode 100644 index 0000000..681e426 --- /dev/null +++ b/Documentation/applying-patches.txt @@ -0,0 +1,439 @@ + + Applying Patches To The Linux Kernel + ------------------------------------ + + (Written by Jesper Juhl, August 2005) + + + +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 exactely 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 +redownloading 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 or you tried to feed +patch a compressed patch file without uncompressing it first. + +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 advice 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, 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 inux-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. + +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' 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 and I +hope you are now crystal clear on how to apply the various patches and help +testing the kernel. + |
