Gerrit » History » Revision 101

Revision 100 (osmith, 12/17/2018 09:08 AM) → Revision 101/130 (neels, 12/17/2018 01:55 PM)

h1. Voting Rules 


 Once you are a "Known User" on Gerrit (see below), please follow these voting rules: 

 h2. Code Review ("CR") 

 * Please review patches by others. 
 * Do not vote for your own patches (exceptions below). 
 * Before merging, each patch should receive at least two reviews that approve merging. 

 When voting, please follow this social contract: 

 * When you approve, vote CR +1. 
 * If there already is someone else's CR +1, you may also choose to vote CR +2. 
 * If the patch owner sees two or more CR +1, the patch owner may apply to self a CR +2. 
 * Once there is at least one CR +2 and one CR +1 vote, a patch may be merged ("Submit" button), except: 
 ** If there are two -1 votes, you should not merge, instead clarify the reason and try to fix it. 
 ** 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. 
 * Give the benefit of the doubt to the -1 vote, do not lightheartedly overrule. 
 * If there is a CR -2 vote, the patch will likely never pass review, it marks a fundamental flaw. 
 * Merging a patch ("Submit" button) may be done by a reviewer or by the patch owner, 
   But if there is any negative vote, rather leave merging up to the patch owner. 
 * If you remove a +1 vote, try to make sure that there are no other CR +2 votes left alone 
   (to prevent accidental "Submit including parents"). If needed, ping other reviewer / admin on IRC. 
   But try to vote +1 only when you're sure, hence this situation should be rare. 
 * To prevent merging of your own patch before some issue is resolved, consider marking it Work In Progress. 

 h3. Exceptions for Trivial / Urgent Patches 

 A patch may receive a direct +2 when: 

 * it is very trivial, like a typo fix in a comment or log string, so that it is not worth wasting review time on. 
 * it reverts an earlier change that broke the master builds. 

 In these cases, the patch submitter may decide to +2 to self, after careful consideration. This should be rare. 

 h2. Verification ("V") 

 * For most projects, jenkins takes care of voting V +1 automatically. 
 * If you have actually tried out a patch and verified that it works, you may vote V +1. 
 * A patch owner may vote V +1 to self in a project that has no Jenkins verification job. 

 h2. Rationale 

 Gerrit allows merging a patch as soon as a CR +2 vote and a V +1 vote are in. 
 For quite some time, we had CR +2 permissions for only very few gatekeeper reviewers. 
 The result was that non-gatekeepers' votes seemed to not matter. 

 To encourage more peer review that actually has an effect, we would like to sum up +1 votes. 
 We have tried to apply a summing of votes in Gerrit with automatic enforcing 
 ( ) 
 but this had numerous quirks, particularly the issues summary shows wildly mismatching voting status. 

 The solution is to agree on a social contract: everyone gets +2 permissions, 
 but you shall only use it when it makes sense. Thanks! 

 h1. Contributing using Gerrit 

 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 is that we want to give Gerrit a try for some time and see if it helps us to have a better process 

 Gerrit is a review tool that integrates nicely with git and ssh. You can find general information about Gerrit at 

 The advantages of Gerrit are: 
 * patch submission status is automatically tracked, also with several revisions for a patch set. 
 * patches are build-tested (and possibly even further tested) by jenkins before they are applied 
 * developers + maintainers can formally vote on a patch (developer: -1/0/+1, maintainer: -2/0/+2) 
 * once a patch has +2 score, it can be (automatically) merged into master 
 * patch sumissions not via git send-email but direcly from git 

 h2. Osmocom Subprojects using Gerrit 

 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 

 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. 

 h2. Configuring Gerrit/Account 

 You will need to sign-up at If you have an Osmocom Redmine account you can use as OpenID provider. 

 * first sign in on Do this before logging in on 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 already). 
 * go to and click the "Sign in" link. 
 * click the "Sign in with Osmocom": link (can be bookmarked). -- This is the same as entering as OpenID provider and hitting the "Sign in" button. 

 *careful:* enter 'https' to ensure that your openid credentials are passed on encryptedly. 
 *pitfall:* if you're logged in on '' (including the 'projects.' part), you should also use the openid provider:; 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. 
 *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. 

 If you have no Osmocom redmine account, you can simply create one online at the "Register" link in the upper right corner. 
 Even without an existing or new redmine account, you should also be able to use any other OpenID provider to authenticate against gerrit (untested). 

 After the initial sign-up you will need to: 

 * Pick a username (can not be changed) 
 * Add your public ssh key(s) 
 * Add email addresses you intend to use as author/comitter 

 If you would like to push private branches to the Gerrit repository, you also need to be added to the "known users" group. 
 Please send a short requesting email to 

 h2. Setting up Gerrit for commits and pushing 

 *Note:* it is easiest to work with gerrit when gerrit is the only remote in your git clone. 
 When you clone from and add the gerrit remote, git will have two remotes, 
 so when you first checkout a branch you have to supply the remote explicitly (cumbersome). 
 The gerrit repositories and are constantly synced, so it is sufficient 
 to clone from gerrit only. 

 h3. Simplest: new clone 

 * Create a new clone from gerrit 
 * Fetch the commit hook that adds Change-Id to each commit to uniquely identify a commit 

 git clone ssh://$$PROJECT.git 
 scp -P 29418 $ $PROJECT/.git/hooks/ 

 h3. SSH config 

 In '~/.ssh/config', add these lines: 
 Host go 
 Port 29418 
 ('go' means gerrit.osmocom, replace with your favorite shortcut name, 
 replace '$USERNAME' with your user name as used on the gerrit website) 

 Then you can shorten above commands to 
 git clone ssh://go/$PROJECT.git 
 scp go:hooks/commit-msg .git/hooks/ 

 h3. Committer must match 

 Your email address on gerrit and the email address git places in your 
 commits must match, or you will get rejected with an error message like 
 "invalid commiter". You can add email addresses on the gerrit web UI. 

 h3. Add gerrit to an existing clone 

 * Add the remote to be able to fetch and push to gerrit 
 * Fetch the commit hook that adds Change-Id to each commit to uniquely identify a commit 

 PROJECT=$(basename $PWD) 
 git remote add gerrit ssh://$$PROJECT.git 
 scp -P 29418 $ .git/hooks/ 

 h2. Push for review 


 * your user on gerrit has an SSH public key 
 * your patch is committed in your local clone 
 * 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.) 

 git push $REMOTE $GITHASH:refs/for/$BRANCH/$TOPIC 

 $REMOTE: from above instructions, that's either 'origin' (cloned from gerrit) or 'gerrit' (if you added a second remote). 
 $GITHASH: the committed patch to push, typically you're on your branch and simply push 'HEAD'. 
 $BRANCH: you will typically intend a patch to go to 'master'. 
 $TOPIC: an optional name you may choose. 

 For example, checkout the revision or branch that you want to submit for review, 
 i.e. the one where your patch or several patches are committed on top of the current master, then: 

 If you cloned directly from gerrit: 

 git push origin HEAD:refs/for/master 

 If you added 'gerrit' as a second remote to an existing clone: 

 git push gerrit HEAD:refs/for/master 

 You can optionally add a topic name with 

 git push origin HEAD:refs/for/master/my_topic 

 h2. Merge patch to master 

 A patch can be merged when it has CR+2 and V+1 votes, and if, in case of a 
 series of patches pushed from a branch, when its ancestor patches can also be 

 Sometimes the reviewer that gives CR+2 also hits the "Submit" button right away  
 to merge the patch to master. Sometimes it is left up to the owner of the patch 
 to decide when to hit "Submit" (who needs to be in the "Known Users" group). 

 The V+1 vote means "build is verified" and is usually given by our jenkins 
 gerrit builds: 

 The CR+2 vote means "code reviewed and ready for merge to master branch". 
 Accounts with the "Reviewer" role for a given project are allowed to give CR+2 
 votes. Others are allowed to give CR+1 (and CR-1). CR votes _don't_ add up. 

 _Fixed by gerrit 2.12.6, see 
 -Sometimes hitting the "Submit" button results in an error message saying 
 "Change is New", which is a bug related to a private branch with the same 
 patches being present. Can be fixed e.g. by an admin's manual push to master.- 

 h2. Manage private branches 

 Use a sub-directory with your name to group your own branches, please. 
 *Note* that you must be a member of the "known users" group, see above. 

 To share / backup local branches to, without starting a code review process on, just push them as usual to gerrit. 

 * Note that the git repository must be cloned from the gerrit SSH URL -- all pushing goes to gerrit ("pushurl" as described below also works). 
 * All private branches are automatically synced to in a matter of minutes. 
 * 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. 

 The typical transcript for "Fred" developing feature "Kazoo" looks like this: 

 # Set up ~/.ssh/config so that 'go' points at 
 git clone ssh://go/libosmocore 

 cd libosmocore 
 git checkout -b fred/kazoo     # create local branch 

 git add kazoo.c 
 git commit -m "implement kazoo" 

 # just invoke 'git push' and git tells you how to create the branch once-off: 
 git push 
 |fatal: The current branch asdf has no upstream branch. 
 |To push the current branch and set the remote as upstream, use 
 |      git push --set-upstream origin fred/kazoo 

 git push --set-upstream origin fred/kazoo 
 # Now the branch exists on gerrit, very soon will also exist on 

 # Further tweaks 
 git add kazoo.h 
 git commit --amend 

 # You are free to force-push private branches 
 git push -f 

 # origin/master has changed? Rebase onto the latest. 
 git fetch 
 git rebase -i origin/master 
 # resolve conflicts... 
 git push -f 

 # Feature is ready 
 git push origin HEAD:refs/for/master/kazoo 

 h2. List changesets in gerrit 

 git ls-remote gerrit changes/* 

 h1. Tips and Tricks 

 h2. A commit lacks a Change-Id 

 once you added the commit hook as above, just re-edit the commit log message, e.g. with 

 git commit --amend 

 or by 

 git rebase -i 

 and in the upcoming editor replacing 'pick' with 'r' in front of the commit to edit. 

 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. 

 h2. Ignore WIP patches 

 Using following operators in "search" field of web UI allows to ignore Work-in-progress changes: 
 status:open AND -is:wip 

 h2. Fetch fast from, push to gerrit 

 Gerrit has moved to a faster host, so this should no longer be necessary. Anyway... 

 Adding a second remote forces you to often pass the remote on the command line ("origin"). 
 It is possible to have only one remote for cmdline convenience, with differing push and pull URLs: 

 git remote set-url origin git://$PROJECT 
 git remote set-url --push origin ssh://$$PROJECT 

 With above .ssh config you can also use the shorter ssh:// URL: 
 git remote set-url --push origin ssh://go/$PROJECT 

 The resulting .git/config in libosmocore would look something like: 
 [remote "origin"] 
         url = git:// 
         pushurl = ssh://go/libosmocore 
         fetch = +refs/heads/*:refs/remotes/origin/* 

 Now you're fetching from, which is lightning fast, while pushing patches will still go to gerrit as usual. 

 h2. Throw-away branch 

 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), 
 make your changes/amendments and then send patch(es) back to gerrit while removing temporary branch automatically with "git review -f". 

 h2. Fetch a patch from gerrit 

 This script (I called it @P@) makes fetching a patch set from gerrit a breeze: 
 # fetch gerrit patch into new branch named like the patch number. 
 # Usage: go to a git clone and pass a patch number: 
 #     cd openbsc 
 #     P 973 
 # or 
 #     P 973/2 
 # Will create new local branches '973_4' (if 4 is the latest patch set) 
 # or '973_2', respectively. 


 if [ -z "$patch" ]; then 
   echo "Usage: P 1234[/5]" 
   exit 1 

 if [ -z "$(echo "$patch" | grep '/')" ]; then 

 if [ -z "$(echo "$patch" | grep '^/')" ]; then 

 last_set="$(git ls-remote origin "changes/*" | grep "$patch" | sed 's#.*/\([^/]*\)$#\1 &#' | sort -n | tail -n 1)" 
 if [ -z "$last_set" ]; then 
   echo "Not found: $patch" 
   exit 1 

 change_name="$(echo "$last_set" | sed 's/.*\(refs.*\)/\1/')" 
 branch_name="$(echo "$change_name" | sed 's#refs/changes/../\([0-9]*\)/\([0-9]*\)#\1_\2#')" 

 set -x 
 git fetch origin "$change_name" 
 git co -b "$branch_name" FETCH_HEAD 

 h2. Re-submit a Branch with Amended Commits 

 On a feature branch, one typically has numerous commits that depend on their preceding commits. 
 Often, some of the branch commits need to be amended for fixes. You can re-submit changes to 
 patches on your branch by pushing in the same way that you first submitted the branch. 

 Note: if you modify the Change-Ids in the commit logs, your push would open entirely new 
 review entries and you would have to abandon your previous submission. Comments on the first 
 submission are "lost" and you cannot diff between patch sets. 

 (There used to be a bug in gerrit that required editing the first patch to be able to 
 re-submit a branch, but that's fixed.) 

 h2. Re-submit Previously Abandoned Changes 

 You have to edit the Change-Ids, on a branch that would be every single commit log message. 

 cd openbsc 
 git co my-branch 
 git rebase -i master 
 # replace all 'pick' with 'r' (or 'reword'), exit your editor 
 # git presents each commit log message for editing 

 h2. 502 Bad Gateway 

 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. 

 h2. Commit hook: Always put Change-Id at the bottom of the log message 

 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: 

 sed -i 's/if (unprinted /if (0 \&\& unprinted /' .git/hooks/commit-msg 

 The goal is to disable the condition in line 163 with an 'if (0...': 

                         if (0 && unprinted && match(tolower(footer[line]), changeIdAfter) != 1) { 
                                 unprinted = 0 
                                 print "Change-Id: I'"$id"'" 

 Then the Change-Id will be placed by line 170 instead. 

 h1. Reasons for Particular Configuration 

 h2. Rebase if necessary 

 There are different merge strategies that Gerrit performs to accept patches. 
 Each project can be configured to a specific merge strategy, but unfortunately you can't 
 decide on a strategy per patch submission. 

 It seems that the "Merge if Necessary" strategy is best supported, but it creates non-linear 
 history with numerous merge commits that are usually not at all necessary. 

 Instead, the "Cherry Pick" strategy puts each patch onto current master's HEAD to create 
 linear history. However, this will cause merge failures as soon as one patch depends on 
 another submitted patch, as typical for a feature branch submission. 

 So we prefer the "Rebase if Necessary" strategy, which always tries to apply your patches to 
 the current master HEAD, in sequence with the previous patches on the same branch. 
 However, some problems still remain, including some bugs in "Rebase if Necessary". 

 There's a problem with "Rebase if Necessary": If your branch sits at master's HEAD, Gerrit 
 refuses to accept the submission, because it thinks that no new changes are submitted. 
 This is a bug in Gerrit, which holger has fixed manually in our Gerrit installation: 

 h2. Private Branches: Create a new change for every commit... 

 Say you have an extensive feature in development, and you want to keep it on the 
 upstream git repository to a) keep it safe and b) collaborate with other devs on it. 
 So, of course, you have regularly pushed to refs/heads/yoyodyne/feature. 

 Since you have the gerrit commit hook installed, your feature branch already has 
 Change-Id tags in all commit log messages. 

 Now your feature is complete and you would like to submit it to master. 
 Alas, Gerrit refuses to accept your patch submission for master, because it 
 knows the Change-Ids are also on a different branch. 

 Gerrit by default enforces that a Change-Id must be unique across all branches, 
 so that each submission for review is separate for each branch. Instead, we 
 want to handle Change-Ids per-branch, so that you can have the same change 
 submitted to different branches, as separate patch submissions, without having 
 to cosmetically adjust the Change-Id. 

 Solution: set the option  
 _Create a new change for every commit not in the target branch_ to _TRUE_ 

 h2. Allow content merges 

 By default, gerrit compares patches only by the files' paths. If two paths are the same, 
 it immediately shows them as conflicts (path conflicts). 

 In software development, a conflict usually means an actual content conflict, so if the 
 edits are in two entirely separate places in the file, we don't consider this a conflict. 

 By setting _Allow content merges_ to _TRUE_ in the git project config, we tell Gerrit to 
 perform text merges of the submitted patches and only complain about actual content 
 conflicts, in the usual software engineering sense. 

 h1. Admin 

 h2. Adding a new repository 

 * create the repository in the Gerrit Ui, inherit from "All-Projects" 
 * create an empty git repository using gitosis on 
 * configure a jenkins build testing job for this project (see gerrit-verifications.yml in osmo-ci.git/jobs) 

 git replication to is enabled automatically, nothing to be done here.    In case of doubt, try 
 @ssh -p 29418 replication start --all --wait@ 

 h2. Adding users to groups 

 Normally, the gerrit UI auto-completes a user name in the edit field. It has happened 
 though that an existing user is not auto-completed, as if it didn't exist. In that case, 
 find out the user ID (seven digit number like 1000123) and just enter that. 

 The user ID can be found on the user's "Settings" page, or in the database (s.b.). 

 h2. Querying the database directly 

 If your user has permission to access the database, you can place SQL queries using the 
 'gerrit gsql' commands over ssh: 

 ssh go "gerrit gsql -c \"show tables\"" 
 ssh go "gerrit gsql -c \"select full_name,account_id from accounts\"" 

 (see ~/.ssh/config above for the 'go' shortcut) 

 This seems to be the MySQL dialect. 

 The "...\"...\"" quoting allows including single-quotes in the SQL statements. 

 h2. Fix evil twin users 

 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: 

 ssh go "gerrit gsql -c \"select * from account_external_ids where email_address like '%foo%'\"" 
 # -----------+-----------------+----------+---------------------------------- 
 # 100004       | | NULL       | 
 # 100021       | | NULL       | 

 ssh go "gerrit gsql -c \"update account_external_ids set account_id = 100004 where email_address like '%foo%'\"" 

 ssh go "gerrit gsql -c \"select * from account_external_ids where email_address like '%foo%'\"" 
 # -----------+-----------------+----------+---------------------------------- 
 # 100004       | | NULL       | 
 # 100004       | | NULL       | 
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