How to make a patch that might get accepted into Ubuntu, using bzr (Shallow Thoughts)

Akkana's Musings on Open Source Computing, Science, and Nature.

Mon, 16 May 2011

How to make a patch that might get accepted into Ubuntu, using bzr

Update and warning: My bzr diff was not accepted. It turns out this particular package doesn't accept that format. Apparently different packages within Ubuntu require different types of patches, and there's no good way to find out besides submitting one type of patch and seeing if it's rejected or ignored. In the end, I did get a patch accepted, and will write up separately how that patch was generated.

The process of submitting bugs and patches to Ubuntu can be deeply frustrating. Even if you figure out how to fix a bug and attach a patch, the patch can sit in Launchpad for years with no attention, as this ubuntu-devel-discuss thread attests.

The problem is that there are a lot of bugs and not enough people qualified to review patches and check them in. To make things easier for the packagers, sometimes people are told to "make a debdiff" or "make a ppa". But it's tough to find good instructions on how to do these things. There are partial instructions at Contributing and on the Packaging Guide -- but both pages are aimed at people who want to become regular packagers of new apps, not someone who just has one patch for a specific bug, and they're both missing crucial steps. Apparently there's a new and better packaging guide being written, but it's not publically available yet.

These days, Bazaar (bzr), not debdiff, is considered the best way to make a patch easy for Ubuntu developers to review. With a lot of help from #ubuntu-women, and particularly Maco (THANKS!), I worked through the steps to submit a patch I'd posted to bug 370735 two years ago for gmemusage. Here's what I needed to do.

Set up the tools

First, install some build tools you'll need, if you don't already have them:

sudo apt-get install bzr bzr-builddeb pbuilder

You will also need a Launchpad account:

and connect bzr to your Launchpad account:
bzr whoami "Firstname Lastname <yourname@example.com>"
bzr launchpad-login your-acct

Check out the code

Create a directory where you'll do the work:

mkdir pkgname
cd pkgname

Check out the source from bzr:

bzr branch lp:ubuntu/pkgname pkgname

Make a bzr branch for your fixes. It's probably a good idea to include the bug number or other specifics in the branch name:

bzr branch pkgname pkgname-fix-bugnum
cd pkgname-fix-bugnum

Now you can apply the patch, e.g. patch <../mypatch.diff, or edit source files directly.

Make a package you can test

Making a package from a bzr directory requires several steps.

Making a source package is easy:

bzr bd -S -- -uc -us
This will show up as ../pkgname_version.dsc.

But if you want something you can install and test, you need a binary package. That's quite a bit more trouble to generate. You'll be using pbuilder to create a minimal install of Ubuntu in a chroot environment, so the build isn't polluted by any local changes you have on your own machine.

First create the chroot: this takes a while, maybe 10 minutes or so, or a lot longer if you have a slow network connection. You'll also need some disk space: on my machine it used 168M in /var/cache (plus more for the next step). Since it uses /var/cache, it needs sudo to write there:

sudo pbuilder --create natty

Now build a .deb binary package from your .dsc source package:

sudo pbuilder --build ../pkgname_version.dsc
pbuilder will install a bunch of additional packages, like X and other libraries that are needed to build your package but weren't included in the minimal pbuilder setup.

And then once it's done with the build, it removes them all again. Apparently there's a way to make it cache them so you'll have them if you need to build again, but I'm not sure how.

pbuilder --build gives lots of output, but none of that output tells you where it's actually creating the .deb. Look in /var/cache/pbuilder/result for it.

And now you can finally try installing it:

sudo  dpkg -i /var/cache/pbuilder/result/pkgname_blahblah.deb

You can now test your fix, and make sure you fixed the problem and didn't break anything else.

Check in your bzr branch

Once you're confident your fix is good. it's time to check it in.

Make a new changelog entry:

dch -i
This will open your editor of choice, where you should explain briefly what you changed and why. If it's a fix for a Launchpad bug, list the bug number like this: (LP: #370735).

If you're proposing a fix for an Ubuntu that's already released, you also need to add -proposed to the release name in the top line in the changelog, e.g.:

pkgname (0.2-11ubuntu1) natty-proposed; urgency=low

Also, pay attention to that ubuntu1 part of the version string if the entry prior to yours doesn't include "ubuntu" in the version. If you're proposing a change to a stable release, change that to ubuntu0.1; if it's for the current development release, it's okay to leave it at ubuntu1 (more details on this Packaging page).

Finally, you can check it in to your local repository:

debcommit
and push it to Launchpad:
bzr push lp:~yourname/ubuntu/natty/pkgname/pkgname-fix-bugnum

Notify possible sponsors

You'll want to make sure your patch gets on the sponsorship queue, so someone can review it and check in the fix.

bzr lp-open
(For me, this opened chromium even though firefox is my preferred browser. To use Firefox, I had to: sudo update-alternatives --config x-www-browser first. Boo chromium for making itself default without asking me.)

You should now have a launchpad page open in your browser. Click on "Propose for merging into another branch" and include a description of your change and why it should be merged. This, I'm told, notifies potential sponsors who can review your patch and approve it for check-in.

Whew! That's a lot of steps. You could argue that it's harder to prepare a patch for Ubuntu than it was to fix the bug in the first place. Stay tuned ... I'll let you know when and if my patch actually gets approved.

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[ 14:38 May 16, 2011    More linux | permalink to this entry | comments ]
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