This applies to commits to Chromium OS repositories. For changes to Chromium repository branches, see the information about Drover; for Blink, see experimental branches.
This works the same on branches as on trunk: If you're merging a change to code that's built as part of a
The Gerrit UI now contains a 'Cherry Pick' button which is currently the easiest way of merging a change which does not conflict, if the change you want to merge to a branch is already on Gerrit, you need only a browser.
1. Open up the CL in question on Gerrit.
2. Click the Cherry Pick button (near the middle of the page).
3. In the pop up 'Cherry Pick to Branch' field, type in some characters from the branch you wish to merge to (e.g. R52) and Gerrit will provide a list of possible branches, pick the one you want.
4. Click Cherry Pick Change at the bottom of the pop up.
5. This should give you a new CL in Gerrit, mark the resulting CL ready just like any other so it lands.
Note this only works if the patch applies cleanly on the target branch, if there is a conflict then the merge must be done manually as Gerrit provides no way of dealing with merge conflicts in the UI.
The second easiest way to create a change from a change you already committed on ToT in Chrome OS is using
This creates Gerrit changes for R25 from CL's 32027, 32030, and 32031 in less than 10 seconds. After running, you can check Gerrit to actually commit the changes (check your open commits for R25-* branch). You can also run these changes through a try-bot (make sure to specify the branch with -b with the remote try-bot). For more advanced usage information, use --help, or ping sosa@ or vapier@.
You should run with --dry-run the first time around to not actually upload your change until you are sure about how to use the tool. Note this tool accepts gerrit change numbers or change-id's, however, since the former is guaranteed to be unique, it is advised you use those instead.
You must have different checkouts (yes, new chroots in a completely new directory) for every branch you are working on. This is to ensure all the prebuilts work automatically for you. You have to pass the -b <branch_name> option to repo during init and you will follow exactly the same workflow described in the Chromium OS Developer Guide (i.e cros_workon + repo start etc)
If you have an existing repo checkout: You can run repo init with --reference to re-use the objects of your existing checkout, to reduce sync time. Note that an absolute path is required (../../foo won't work) and that it must be the topmost directory of the existing repo checkout, i.e. the one that contains the .repo directory.
You can find the exact name of the branch by browsing the manifest repo.
NOTE: For older branches (e.g. R22 and earlier), you'll need to specify -m minilayout.xml instead of -g minilayout.
Example (See http://goto/chromeos-building if you are doing an internal build and replace the manifest.git link with the appropriate one)
Next, follow steps in the developer's guide to sync/edit/modify files i.e repo sync, cros_work start, repo start, etc. After you've cherry-picked/made the changes you want, upload the changes for review. If cherry-picking/etc..., make sure to recreate the ChangeID in the log message so that you get a new one -- simply delete the line and git will create a new one for you.
Before you commit the change, test it! Launch a tryjob to verify it actually builds properly. See Using Remote Trybots for more information.
If you don't have a full repo checked out already and want to do a quick one-off merge, you can still check out the much smaller buildtools group:
This will get you chromite and all the tools it includes -- i.e. cros_merge_to_branch. Make sure you pass the --nomirror option so it will fetch the single git repo needed to cherry-pick & upload the CL.
Finally, use cbuildbot with --remote to run remote trybots. See the section above for more info.
If you want to push up a few changes without checking out the entire tree, then you can use git to do just that.
You can re-use an existing repo checkout if you like (but make sure you clean up when you're done). Let's assume you're going to make a new checkout to keep things clean though.
Find the git url you care about. You can get it by going into your repo checkout and look at .git/config (the url field). You'll need to use the -review variant of the URL to push to the special refs/for/* refs. Let's demonstrate with the chromite git tree.
If you want to speed things up, you can use the --reference option to re-use a local tree.
If your normal user information is not your chromium.org e-mail, you'll need to set it in the new repo.
Let's assume you want to work on the R23 branch. You need the full name of the branch, and then create a new local branch to work on with that info.
That shows us the full branch name is "remotes/cros/release-R23-2913.B", so we can do:
This part is where the real work happens :). Use git's or repo's cherry-pick feature, or make the changes by hand, or apply patches, or whatever you want.
Now for the last step. If you didn't create a new clone, you might have to change "origin" to "cros", or replace it with the full git url. The "R23" is whatever you called the local branch, and the "release-R23-2913.B" is exactly what the official branch name is called -- make sure it's correct as gerrit will allow you to push to anything.