Patching Ubuntu Kernel

Obtain ther kernel source

Which distro? Which version?

git clone git://kernel.ubuntu.com/ubuntu/ubuntu-artful.git

After cloning or updating its folder already cloned.

cd ubuntu-artful
git clone fetch --all --tags

Choice a bug number to identify the job you are working, for example bug12345, and so create a branch to track it. A tip, use a github interface to archive and work. After alreay created a repository in the github, you can add a remote branch from your computer to send them to github.

git remote add github https://github.com/walbon/ubuntu-xenial.git
git checkout -b bug12345 origin/master-next
git push -u github bug12345

Why master-next? Well, to align with the latest updates from the kernel team then to suggest your updates.

Identify which patches are needed

Width the main patches on hands already tracked on the Linus tree, next steps are using cherry-pick or format-patch. Order them since the oldest to youngest to apply them. </ul>

Git Cherry-pick [1]

When you use the this the command will bring the modifies and the needed files from other commits to complete it. Look the sample above.

Sample

#     (G)+stuff1.c
#      |
#     (F)<-----(E)+Modified stuff1.c
#      |        |
#     (D)      (C)+Created stuff1.c and stuff2.c
#      \       /
# Master\     / Feature
# Branch  (B)   Branch
#          |
#         (A)

# I'm in the HASH_F
git cherry-pick HASH_E
# Resolving some possible conflicts(using git merge tool), because the brach master does
# not have the stuff1.c file and the cherry-pick will bring it alone instead of all HASH_C.
git cherry-pick --continue
# Finish
ls
...
stuff1.c
...

Git Format-patch [2]

My format-patch way is more hands-on, because via git format-patch I extracted the the patch in that especific patch and just test it on the current branch to apply them.

git format-patch -k -1 --stdout HASH_E | git am -k
Applying: Modified stuff1.c
error: stuff1.c1: does not exist in index
Patch failed at 0001 Modified stuff1.c
The copy of the patch that failed is found in: .git/rebase-apply/patch
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

#Conflicts ^o^
#So, you should add by hand the stuff1.c(opt 1) or to bring the HASH_C then HASH_E(opt 2)
##Option 1
###pushing the stuff1.c one step before the HASH_E
git checkout HASH_C stuff1.c
###retry the patching
git am --continue
Applying: Modified stuff1.c

ls
...
stuff1.c
...
#FINISH

##Option 2
###cancel the am and so add the patch that add the stuff1.c file.
git am --abort # to cancel the current status of git am
git format-patch -k -1 --stdout HASH_C | git am -k
Applying: Created stuff1.c and stuff2.c

git format-patch -k -1 --stdout HASH_E | git am -k
Applying: Modified stuff1.c

ls
...
stuff1.c
stuff2.c
...
#FINISH

Sending patches to the Kernel Team Maillist

First, adopt some tips which they are related to send-email from Git Tips [3]. Now, you must create a bug tracking in the Launchpad [4] and add its link in each patch of your backport, I suggest git rebase to re-edit the commits, look:

git rebase -i HEAD~N # N= number of commits to be edited
  1 pick 39943c4 +A
  2 pick febba76 +B
  3 pick 2410879 Modified stuff1.c
  4 ¬
  5 # Rebase 19b82d4..2410879 onto 19b82d4 (3 commands)¬
  6 #¬
  7 # Commands:¬
  8 # p, pick = use commit¬
  9 # r, reword = use commit, but edit the commit message¬
 10 # e, edit = use commit, but stop for amending¬
 11 # s, squash = use commit, but meld into previous commit¬
 12 # f, fixup = like "squash", but discard this commit's log message¬
 13 # x, exec = run command (the rest of the line) using shell¬
 14 # d, drop = remove commit¬
 15 #¬
 16 # These lines can be re-ordered; they are executed from top to bottom.¬
 17 #¬
 18 # If you remove a line here THAT COMMIT WILL BE LOST.¬
 19 #¬
 20 # However, if you remove everything, the rebase will be aborted.¬
 21 #¬
 22 # Note that empty commits are commented out¬
:wq
#Stopped at 2410879...  Modified stuff1.c
#You can amend the commit now, with
git commit --amend
#Added its http://bugs.launchpad.net/bugs/<bug-id> in the third line of
#commit, it must be the first line of describe message.
...
#Once you are satisfied with your changes, run
git rebase --continue
...
#Then generate the patche files.
git format-patch origin/master-next.. --cover-letter --subject-prefix="Artful][PATCH"
...
# Edit and describe the cover-letter and do not forget to add the Buglink there.
vim 0000-cover-letter.patch
...

#Sent them to kernel mail list.
git send-email --to kernel-team@lists.ubuntu.com 00*patch

Example : https://lists.ubuntu.com/archives/kernel-team/2017-May/084443.html

References

• [1]https://git-scm.com/docs/git-cherry-pick
• [2]https://git-scm.com/docs/git-format-patch
• [3]https://walbon.github.io//git
• [4]https://wiki.ubuntu.com/Kernel/Dev/StablePatchFormat

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