Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. _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+   This document is obsolete.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 4.7.2 to 4.7.3 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 4.7.2 to 4.7.3 in a single step::
+
+	interdiff -z ../patch-4.7.2.gz ../patch-4.7.3.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 (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 4.x.y (-stable) and 4.x patches live at
+
+	https://www.kernel.org/pub/linux/kernel/v4.x/
+
+The -rc patches live at
+
+	https://www.kernel.org/pub/linux/kernel/v4.x/testing/
+
+
+The 4.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 4.x base
+kernel is released, a patch is made available that is a delta between the
+previous 4.x kernel and the new one.
+
+To apply a patch moving from 4.6 to 4.7, you'd do the following (note
+that such patches do **NOT** apply on top of 4.x.y kernels but on top of the
+base 4.x kernel -- if you need to move from 4.x.y to 4.x+1 you need to
+first revert the 4.x.y patch).
+
+Here are some examples::
+
+	# moving from 4.6 to 4.7
+
+	$ cd ~/linux-4.6		# change to kernel source dir
+	$ patch -p1 < ../patch-4.7	# apply the 4.7 patch
+	$ cd ..
+	$ mv linux-4.6 linux-4.7	# rename source dir
+
+	# moving from 4.6.1 to 4.7
+
+	$ cd ~/linux-4.6.1		# change to kernel source dir
+	$ patch -p1 -R < ../patch-4.6.1	# revert the 4.6.1 patch
+					# source dir is now 4.6
+	$ patch -p1 < ../patch-4.7	# apply new 4.7 patch
+	$ cd ..
+	$ mv linux-4.6.1 linux-4.7	# rename source dir
+
+
+The 4.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 4.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 4.x.y kernel is available, then the highest numbered 4.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/v4.x/incr/
+
+These patches are not incremental, meaning that for example the 4.7.3
+patch does not apply on top of the 4.7.2 kernel source, but rather on top
+of the base 4.7 kernel source.
+
+So, in order to apply the 4.7.3 patch to your existing 4.7.2 kernel
+source you have to first back out the 4.7.2 patch (so you are left with a
+base 4.7 kernel source) and then apply the new 4.7.3 patch.
+
+Here's a small example::
+
+	$ cd ~/linux-4.7.2		# change to the kernel source dir
+	$ patch -p1 -R < ../patch-4.7.2	# revert the 4.7.2 patch
+	$ patch -p1 < ../patch-4.7.3	# apply the new 4.7.3 patch
+	$ cd ..
+	$ mv linux-4.7.2 linux-4.7.3	# 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 4.x kernel, just
+like the 4.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, 4.8-rc5 means that this is the fifth release candidate for the 4.8
+kernel and the patch should be applied on top of the 4.7 kernel source.
+
+Here are 3 examples of how to apply these patches::
+
+	# first an example of moving from 4.7 to 4.8-rc3
+
+	$ cd ~/linux-4.7			# change to the 4.7 source dir
+	$ patch -p1 < ../patch-4.8-rc3		# apply the 4.8-rc3 patch
+	$ cd ..
+	$ mv linux-4.7 linux-4.8-rc3		# rename the source dir
+
+	# now let's move from 4.8-rc3 to 4.8-rc5
+
+	$ cd ~/linux-4.8-rc3			# change to the 4.8-rc3 dir
+	$ patch -p1 -R < ../patch-4.8-rc3	# revert the 4.8-rc3 patch
+	$ patch -p1 < ../patch-4.8-rc5		# apply the new 4.8-rc5 patch
+	$ cd ..
+	$ mv linux-4.8-rc3 linux-4.8-rc5	# rename the source dir
+
+	# finally let's try and move from 4.7.3 to 4.8-rc5
+
+	$ cd ~/linux-4.7.3			# change to the kernel source dir
+	$ patch -p1 -R < ../patch-4.7.3		# revert the 4.7.3 patch
+	$ patch -p1 < ../patch-4.8-rc5		# apply new 4.8-rc5 patch
+	$ cd ..
+	$ mv linux-4.7.3 linux-4.8-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.