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Gerrit » History » Version 109

stsp, 12/18/2018 04:59 PM
fix english grammar mistakes and some weird wording

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{{>toc}}
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h1. Contributing using Gerrit
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At [[OpenBSC:OsmoDevCon2016]] we discussed problems with our past contribution / patch submission process using mails on the mailing list as well as patchwork.  The result was that we wanted to give Gerrit a try for some time and see if it helps us to have a better process
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Gerrit is a review tool that integrates nicely with git and ssh. You can find general information about Gerrit at https://www.gerritcodereview.com/
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The advantages of Gerrit are:
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* patch submission status is automatically tracked, also with several revisions for a patch set.
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* patches are build-tested (and possibly even further tested) by jenkins before they are applied
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* patch submissions not via git send-email but direcly from git
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h2. Osmocom Subprojects using Gerrit
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The majority of Osmocom sub-projects have chosen to use Gerrit for patch review.  In order to check if a given program uses Gerrit, please check the auto-generated list at https://gerrit.osmocom.org/#/admin/projects/
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If the project is listed there, then it uses Gerrit.   If the project is not listed there, please send patches by e-mail to the respective project [[Mailing_Lists]] instead.
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h2. Configuring Gerrit/Account
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You will need to sign up at https://gerrit.osmocom.org/login/. If you have an Osmocom Redmine account you can use https://osmocom.org/openid as OpenID provider.
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* first sign in on https://osmocom.org. Do this before logging into gerrit (the redmine login process loses the gerrit login data and you'd have to do the same thing twice if not logged in on osmocom.org already).
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* go to https://gerrit.osmocom.org and click the "Sign in" link.
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* click the "Sign in with Osmocom":https://gerrit.osmocom.org/login/%23%2Fq%2Fstatus%3Aopen?id=https://osmocom.org/openid link (can be bookmarked). -- This is the same as entering https://osmocom.org/openid as OpenID provider and hitting the "Sign in" button.
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*careful:* enter 'https' to ensure that your openid credentials are passed on encrypted.
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*pitfall:* if you're logged in on 'projects.osmocom.org' (including the 'projects.' part), you should also use the openid provider: https://projects.osmocom.org/openid; the 'projects.' part may be omitted, what's important is that redmine login and OpenID URLs match. Also, decide for one of those URLs once, because when picking a different OpenID URL next time, you will create a new user instead of logging in as yourself.
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*note:* gerrit will create a distinct user for each openid URL you pass. If you logged in successfully but your user seems to have lost permissions, you may have created an evil twin user: contact us on the mailing list so we can fix it in the user database.
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If you have no Osmocom redmine account, you can simply create one online at the "Register" link in the upper right corner.
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Even without an existing or new redmine account, you should also be able to use any other OpenID provider to authenticate against gerrit (untested).
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After the initial sign-up you will need to:
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* Pick a username (cannot be changed)
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* Add your public ssh key(s)
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* Add email addresses you intend to use as author/comitter
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If you would like to push private branches to the Gerrit repository, you also need to be added to the "known users" group.
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Please send a short requesting email to openbsc@lists.osmocom.org.
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h2. Setting up Gerrit for commits and pushing
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*Note:* it is easiest to work with gerrit when gerrit is the only remote in your git clone.
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When you clone from git.osmocom.org and add the gerrit remote, git will have two remotes,
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so when you first checkout a branch you have to supply the remote explicitly (cumbersome).
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The gerrit repositories and git.osmocom.org are constantly synced, so it is sufficient
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to clone from gerrit only.
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h3. Simplest: new clone
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* Create a new clone from gerrit
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* Fetch the commit hook that adds Change-Id to each commit to uniquely identify a commit
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<pre>
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git clone ssh://$USERNAME@gerrit.osmocom.org:29418/$PROJECT.git
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scp -P 29418 $USERNAME@gerrit.osmocom.org:hooks/commit-msg $PROJECT/.git/hooks/
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</pre>
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h3. SSH config
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In '~/.ssh/config', add these lines:
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<pre>
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Host go
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Hostname gerrit.osmocom.org
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Port 29418
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User $USERNAME
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</pre>
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('go' means gerrit.osmocom, replace with your favorite shortcut name,
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replace '$USERNAME' with your user name as used on the gerrit website)
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Then you can shorten above commands to
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<pre>
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git clone ssh://go/$PROJECT.git
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cd $PROJECT
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scp go:hooks/commit-msg .git/hooks/
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</pre>
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h3. Committer must match
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Your email address on gerrit and the email address git places in your
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commits must match, or you will get rejected with an error message like
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"invalid committer". You can add email addresses on the gerrit web UI.
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h3. Add gerrit to an existing clone
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* Add the remote to be able to fetch and push to gerrit
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* Fetch the commit hook that adds Change-Id to each commit to uniquely identify a commit
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<pre>
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USERNAME=gerrit_user_name
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PROJECT=$(basename $PWD)
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git remote add gerrit ssh://$USERNAME@gerrit.osmocom.org:29418/$PROJECT.git
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scp -P 29418 $USERNAME@gerrit.osmocom.org:hooks/commit-msg .git/hooks/
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</pre>
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h2. Push for review
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Prerequisites:
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* your user on gerrit has an SSH public key
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* your patch is committed in your local clone
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* the commit log message has a Change-Id (see 'commit-msg' hook above, and 'Tips and Tricks' below to add a Change-Id to a commit that lacks one.)
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<pre>
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git push $REMOTE $GITHASH:refs/for/$BRANCH/$TOPIC
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</pre>
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$REMOTE: from above instructions, that's either 'origin' (cloned from gerrit) or 'gerrit' (if you added a second remote).
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$GITHASH: the committed patch to push, typically you're on your branch and simply push 'HEAD'.
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$BRANCH: you will typically intend a patch to go to 'master'.
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$TOPIC: an optional name you may choose.
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For example, check out the revision or branch that you want to submit for review,
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i.e. the one where your patch or several patches are committed on top of the current master, then:
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If you cloned directly from gerrit:
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<pre>
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git push origin HEAD:refs/for/master
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</pre>
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If you added 'gerrit' as a second remote to an existing clone:
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<pre>
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git push gerrit HEAD:refs/for/master
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</pre>
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You can optionally add a topic name with
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<pre>
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git push origin HEAD:refs/for/master/my_topic
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</pre>
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h2. Voting Rules for merging a patch to master
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Please follow these voting rules:
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h3. Code Review ("CR")
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* Please review patches by others.
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* Do not vote for your own patches (exceptions below).
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* Before merging, each patch should receive at least two reviews that approve merging.
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When voting, please follow this social contract:
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* When you approve, vote CR +1.
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* If there already is someone else's CR +1, you may also choose to vote CR +2.
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* If the patch owner sees two or more CR +1, the patch owner may apply to self a CR +2.
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* Once there is at least one CR +2 and one CR +1 vote, a patch may be merged ("Submit" button), except:
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** If there are two -1 votes, you should not merge, instead clarify the reason and try to fix it.
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** If there is a single -1 vote, you may still merge the patch, if you are sure that the opinion of the -1 vote does not carry.
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* Give the benefit of the doubt to the -1 vote, do not lightheartedly overrule.
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* If there is a CR -2 vote, the patch will likely never pass review, it marks a fundamental flaw.
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* Merging a patch ("Submit" button) may be done by a reviewer or by the patch owner,
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  But if there is any negative vote, rather leave merging up to the patch owner.
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* If you remove a +1 vote, try to make sure that there are no other CR +2 votes left alone
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  (to prevent accidental "Submit including parents"). If needed, ping other reviewer / admin on IRC.
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  But try to vote +1 only when you're sure, hence this situation should be rare.
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* To prevent merging of your own patch before some issue is resolved, consider marking it Work In Progress.
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h3. Exceptions for Trivial / Urgent Patches
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A patch may receive a direct +2 when:
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* it is very trivial, like a typo fix in a comment or log string, so that it is not worth wasting review time on.
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* it reverts an earlier change that broke the master builds.
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In these cases, the patch submitter may decide to +2 to self, after careful consideration. This should be rare.
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h3. Verification ("V")
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* For most projects, jenkins takes care of voting V +1 automatically.
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* If you have actually tried out a patch and verified that it works, you may vote V +1.
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* A patch owner may vote V +1 to self in a project that has no Jenkins verification job.
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h3. Rationale
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Gerrit allows merging a patch as soon as a CR +2 vote and a V +1 vote are in.
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For quite some time, we had CR +2 permissions for only very few gatekeeper reviewers.
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The result was that non-gatekeepers' votes seemed to not matter.
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To encourage more peer review that actually has an effect, we would like to sum up +1 votes.
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We have tried to apply a summing of votes in Gerrit with automatic enforcing
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( https://gerrit-review.googlesource.com/Documentation/prolog-cookbook.html#_example_13_1_1_2_code_review )
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but this had numerous quirks, particularly the issues summary shows wildly mismatching voting status.
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The solution is to agree on a social contract: everyone gets +2 permissions,
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but you shall only use it when it makes sense. Thanks!
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h2. Manage private branches
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Use a sub-directory with your name to group your own branches, please.
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*Note* that you must be a member of the "known users" group, see above.
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To share / backup local branches to git.osmocom.org, without starting a code review process on gerrit.osmocom.org, just push them as usual to gerrit.
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* Note that the git repository must be cloned from the gerrit SSH URL -- all pushing goes to gerrit ("pushurl" as described below also works).
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* All private branches are automatically synced to git.osmocom.org in a matter of minutes.
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* Private branches do not kick off patch sets for review, they are just branches. To kick off review for all patches on your branch, you'd use a 'refs/for/master' URL, as shown in the example below.
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The typical transcript for "Fred" developing feature "Kazoo" looks like this:
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<pre>
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# Set up ~/.ssh/config so that 'go' points at gerrit.osmocom.org
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git clone ssh://go/libosmocore
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cd libosmocore
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git checkout -b fred/kazoo   # create local branch
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$EDITOR
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git add kazoo.c
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git commit -m "implement kazoo"
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# just invoke 'git push' and git tells you how to create the branch once-off:
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git push
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|fatal: The current branch asdf has no upstream branch.
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|To push the current branch and set the remote as upstream, use
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|
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|    git push --set-upstream origin fred/kazoo
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git push --set-upstream origin fred/kazoo
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# Now the branch exists on gerrit, very soon will also exist on git.osmocom.org
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# Further tweaks
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$EDITOR
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git add kazoo.h
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git commit --amend
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# You are free to force-push private branches
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git push -f
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# origin/master has changed? Rebase onto the latest.
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git fetch
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git rebase -i origin/master
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# resolve conflicts...
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git push -f
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# Feature is ready
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git push origin HEAD:refs/for/master/kazoo
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</pre>
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h2. List changesets in gerrit
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<pre>
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git ls-remote gerrit changes/*
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</pre>
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h1. Tips and Tricks
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h2. A commit lacks a Change-Id
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once you added the commit hook as above, just re-edit the commit log message, e.g. with
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<pre>
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git commit --amend
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</pre>
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or by
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<pre>
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git rebase -i
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</pre>
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and in the upcoming editor replacing 'pick' with 'r' in front of the commit to edit.
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No need to change the commit log if you don't want to, just exit the editor and the commit hook will add a Change-Id.
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h2. Ignore WIP patches
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Using following operators in "search" field of web UI allows to ignore Work-in-progress changes:
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<pre>
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status:open AND -is:wip
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</pre>
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h2. Fetch fast from git.osmocom.org, push to gerrit
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Gerrit has moved to a faster host, so this should no longer be necessary. Anyway...
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Adding a second remote forces you to explicitly pass the remote on the command line ("origin").
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It is possible to have only one remote for convenience, with different push and pull URLs:
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<pre>
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git remote set-url origin git://git.osmocom.org/$PROJECT
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git remote set-url --push origin ssh://$USERNAME@gerrit.osmocom.org:29418/$PROJECT
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</pre>
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With above .ssh config you can also use the shorter ssh:// URL:
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<pre>
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git remote set-url --push origin ssh://go/$PROJECT
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</pre>
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The resulting .git/config in libosmocore would look something like:
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<pre>
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[remote "origin"]
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        url = git://git.osmocom.org/libosmocore
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        pushurl = ssh://go/libosmocore
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        fetch = +refs/heads/*:refs/remotes/origin/*
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</pre>
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Now you're fetching from git.osmocom.org, which is lightning fast, while pushing patches will still go to gerrit as usual.
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h2. Throw-away branch
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If you need to adjust and re-submit patches, it may be handy to create a throw-away branch ("R D" in magit-gerrit in emacs for example),
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make your changes/amendments and then send patch(es) back to gerrit while removing temporary branch automatically with "git review -f".
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h2. Fetch a patch from gerrit
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This script (I called it @P@) makes fetching a patch set from gerrit a breeze:
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<pre>
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#!/bin/sh
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# fetch gerrit patch into new branch named like the patch number.
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#
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# Usage: go to a git clone and pass a patch number:
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#
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#   cd openbsc
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#   P 973
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# or
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#   P 973/2
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#
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# Will create new local branches '973_4' (if 4 is the latest patch set)
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# or '973_2', respectively.
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patch="$1"
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if [ -z "$patch" ]; then
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  echo "Usage: P 1234[/5]"
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  exit 1
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fi
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if [ -z "$(echo "$patch" | grep '/')" ]; then
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  patch="/$patch/"
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fi
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if [ -z "$(echo "$patch" | grep '^/')" ]; then
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  patch="/$patch"
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fi
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last_set="$(git ls-remote origin "changes/*" | grep "$patch" | sed 's#.*/\([^/]*\)$#\1 &#' | sort -n | tail -n 1)"
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if [ -z "$last_set" ]; then
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  echo "Not found: $patch"
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  exit 1
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fi
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change_name="$(echo "$last_set" | sed 's/.*\(refs.*\)/\1/')"
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branch_name="$(echo "$change_name" | sed 's#refs/changes/../\([0-9]*\)/\([0-9]*\)#\1_\2#')"
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set -x
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git fetch origin "$change_name"
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git co -b "$branch_name" FETCH_HEAD
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</pre>
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h2. Re-submit a Branch with Amended Commits
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On a feature branch, one typically has numerous commits that depend on their preceding commits.
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Often, some of the branch commits need to be amended for fixes. You can re-submit changes to
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patches on your branch by pushing in the same way that you first submitted the branch.
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Note: if you modify the Change-Ids in the commit logs, your push would open entirely new
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review entries and you would have to abandon your previous submission. Comments on the first
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submission are "lost" and you cannot diff between patch sets.
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h2. Re-submit Previously Abandoned Changes
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You have to edit the Change-Ids, on a branch that would be every single commit log message.
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<pre>
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cd openbsc
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git co my-branch
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git rebase -i master
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# replace all 'pick' with 'r' (or 'reword'), exit your editor
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# git presents each commit log message for editing
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</pre>
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h2. 502 Bad Gateway
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When getting a "Bad Gateway" error message upon trying to login on gerrit, you probably just need to restart your web browser. The reason is not clear.
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h2. Commit hook: Always put Change-Id at the bottom of the log message
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The commit-msg hook places a Change-Id tag in the footer, often above other tags like 'Depends:' or 'Related:'. Since the Change-Id is an implementation detail for Gerrit, I personally prefer it always placed right at the bottom. This simple edit changes the commit-msg hook to add Change-Id at the bottom unconditionally:
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<pre>
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cd $PROJECT
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sed -i 's/if (unprinted /if (0 \&\& unprinted /' .git/hooks/commit-msg
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</pre>
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The goal is to disable the condition in line 163 with an 'if (0...':
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<pre>
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                        if (0 && unprinted && match(tolower(footer[line]), changeIdAfter) != 1) {
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                                unprinted = 0
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                                print "Change-Id: I'"$id"'"
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                        }
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</pre>
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Then the Change-Id will be placed by line 170 instead.
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h1. Reasons for Particular Configuration
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h2. Rebase if necessary
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There are different merge strategies that Gerrit performs to accept patches.
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Each project can be configured to a specific merge strategy, but unfortunately you can't
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decide on a strategy per patch submission.
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It seems that the "Merge if Necessary" strategy is best supported, but it creates non-linear
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history with numerous merge commits that are usually not at all necessary.
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Instead, the "Cherry Pick" strategy puts each patch onto current master's HEAD to create
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linear history. However, this will cause merge failures as soon as one patch depends on
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another submitted patch, as typical for a feature branch submission.
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So we prefer the "Rebase if Necessary" strategy, which always tries to apply your patches to
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the current master HEAD, in sequence with the previous patches on the same branch.
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h2. Private Branches: Create a new change for every commit...
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Say you have an extensive feature in development, and you want to keep it on the
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upstream git repository to a) keep it safe and b) collaborate with other devs on it.
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So, of course, you have regularly pushed to refs/heads/yoyodyne/feature.
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Since you have the gerrit commit hook installed, your feature branch already has
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Change-Id tags in all commit log messages.
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Now your feature is complete and you would like to submit it to master.
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Alas, Gerrit refuses to accept your patch submission for master, because it
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knows the Change-Ids are also on a different branch.
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Gerrit by default enforces that a Change-Id must be unique across all branches,
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so that each submission for review is separate for each branch. Instead, we
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want to handle Change-Ids per-branch, so that you can have the same change
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submitted to different branches, as separate patch submissions, without having
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to cosmetically adjust the Change-Id.
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Solution: set the option 
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_Create a new change for every commit not in the target branch_ to _TRUE_
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h2. Allow content merges
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By default, gerrit compares patches only by the files' paths. If two paths are the same,
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it immediately shows them as conflicts (path conflicts).
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In software development, a conflict usually means an actual content conflict, so if the
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edits are in two entirely separate places in the file, we don't consider this a conflict.
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By setting _Allow content merges_ to _TRUE_ in the git project config, we tell Gerrit to
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perform text merges of the submitted patches and only complain about actual content
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conflicts, in the usual software engineering sense.
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h1. Admin
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h2. Adding a new repository
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* create the repository in the Gerrit Ui, inherit from "All-Projects"
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* create an empty git repository using gitosis on git.osmcoom.org
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* configure a jenkins build testing job for this project (see gerrit-verifications.yml in osmo-ci.git/jobs)
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git replication to gerrit.osmocom.org is enabled automatically, nothing to be done here.  In case of doubt, try
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@ssh -p 29418 gerrit.osmocom.org replication start --all --wait@
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h2. Adding users to groups
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Normally, the gerrit UI auto-completes a user name in the edit field. It has happened
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though that an existing user is not auto-completed, as if it didn't exist. In that case,
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find out the user ID (seven digit number like 1000123) and just enter that.
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The user ID can be found on the user's "Settings" page, or in the database (s.b.).
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h2. Querying the database directly
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If your user has permission to access the database, you can place SQL queries using the
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'gerrit gsql' commands over ssh:
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<pre>
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ssh go "gerrit gsql -c \"show tables\""
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ssh go "gerrit gsql -c \"select full_name,account_id from accounts\""
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</pre>
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(see ~/.ssh/config above for the 'go' shortcut)
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This seems to be the MySQL dialect.
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The "...\"...\"" quoting allows including single-quotes in the SQL statements.
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h2. Fix evil twin users
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If differing openid URLs have lead to evil twin users shadowing the same email address just without the permissions, you can fix it like this:
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<pre>
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ssh go "gerrit gsql -c \"select * from account_external_ids where email_address like '%foo%'\""
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# ACCOUNT_ID | EMAIL_ADDRESS   | PASSWORD | EXTERNAL_ID
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# -----------+-----------------+----------+----------------------------------
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# 100004     | foo@example.com | NULL     | https://osmocom.org/openid/user/777
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# 100021     | foo@example.com | NULL     | https://projects.osmocom.org/openid/user/777
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ssh go "gerrit gsql -c \"update account_external_ids set account_id = 100004 where email_address like '%foo%'\""
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ssh go "gerrit gsql -c \"select * from account_external_ids where email_address like '%foo%'\""
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# ACCOUNT_ID | EMAIL_ADDRESS   | PASSWORD | EXTERNAL_ID
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# -----------+-----------------+----------+----------------------------------
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# 100004     | foo@example.com | NULL     | https://osmocom.org/openid/user/777
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# 100004     | foo@example.com | NULL     | https://projects.osmocom.org/openid/user/777
512
</pre>
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