Gerrit Code Review - Uploading Changes

Gerrit supports three methods of uploading changes:

Use repo upload, to create changes for review
Use git push, to create changes for review
Use git push, and bypass code review

All three methods rely on authentication, which must first be configured by the uploading user.

Gerrit supports two methods of authenticating the uploading user. SSH public key, and HTTP/HTTPS.

HTTP/HTTPS

On Gerrit installations that do not support SSH authentication, the user must authenticate via HTTP/HTTPS.

When gitBasicAuth is enabled, the user is authenticated using standard BasicAuth and credentials validated using the same authentication method configured for the Gerrit Web UI.

When gitBasicAuth is not configured, the user’s HTTP credentials can be accessed within Gerrit by going to Settings, and then accessing the HTTP Password tab.

For Gerrit installations where an HTTP password URL is configured, the password can be obtained by clicking on Obtain Password and then following the site-specific instructions. On sites where this URL is not configured, the password can be obtained by clicking on Generate Password.

SSH

Each user uploading changes to Gerrit must configure one or more SSH public keys. The per-user SSH key list can be accessed over the web within Gerrit by Settings, and then accessing the SSH Public Keys tab.

Configuration

To register a new SSH key for use with Gerrit, paste the contents of your id_rsa.pub or id_dsa.pub file into the text box and click the add button. Gerrit only understands SSH version 2 public keys. Keys may be supplied in either the OpenSSH format (key starts with ssh-rsa or ssh-dss) or the RFC 4716 format (file starts with ---- BEGIN SSH2 PUBLIC KEY ----).

Typically SSH keys are stored in your home directory, under ~/.ssh. If you don’t have any keys yet, you can create a new one and protect it with a passphrase:

ssh-keygen -t rsa

Then copy the content of the public key file onto your clipboard, and paste it into Gerrit’s web interface:

cat ~/.ssh/id_rsa.pub

Tip

Users who frequently upload changes will also want to consider starting an ssh-agent, and adding their private key to the list managed by the agent, to reduce the frequency of entering the key’s passphrase. Consult man ssh-agent, or your SSH client’s documentation, for more details on configuration of the agent process and how to add the private key.

Testing Connections

To verify your SSH key is working correctly, try using an SSH client to connect to Gerrit’s SSHD port. By default Gerrit runs on port 29418, using the same hostname as the web server:

  $ ssh -p 29418 sshusername@hostname

    ****    Welcome to Gerrit Code Review    ****

    Hi John Doe, you have successfully connected over SSH.

    Unfortunately, interactive shells are disabled.
    To clone a hosted Git repository, use:

    git clone ssh://sshusername@hostname:29418/REPOSITORY_NAME.git

  Connection to hostname closed.

In the command above, sshusername was configured as Username on the Profile tab of the Settings screen. If it is not set, propose a name and use Select Username to select the name.

To determine the port number Gerrit is running on, visit the special information URL http://'hostname'/ssh_info, and copy the port number from the second field:

$ curl http://hostname/ssh_info
hostname 29418

If you are developing an automated tool to perform uploads to Gerrit, let the user supply the hostname or the web address for Gerrit, and obtain the port number on the fly from the /ssh_info URL. The returned output from this URL is always 'hostname' SP 'port', or NOT_AVAILABLE if the SSHD server is not currently running.

git push

Create Changes

To create new changes for review, simply push to the project’s magical refs/for/'branch' ref using any Git client tool:

git push ssh://sshusername@hostname:29418/projectname HEAD:refs/for/branch

E.g. john.doe can use git push to upload new changes for the experimental branch of project kernel/common, hosted at the git.example.com Gerrit server:

git push ssh://john.doe@git.example.com:29418/kernel/common HEAD:refs/for/experimental

Each new commit uploaded by the git push client will be converted into a change record on the server. The remote ref refs/for/experimental is not actually created by Gerrit, even though the client’s status messages may say otherwise.

Other users (e.g. project owners) who have configured Gerrit to notify them of new changes will be automatically sent an email message when the push is completed.

To include a short tag associated with all of the changes in the same group, such as the local topic branch name, append it after the destination branch name. In this example the short topic tag driver/i42 will be saved on each change this push creates or updates:

git push ssh://john.doe@git.example.com:29418/kernel/common HEAD:refs/for/experimental%topic=driver/i42

If you are frequently uploading changes to the same Gerrit server, consider adding an SSH host block in ~/.ssh/config to remember your username, hostname and port number. This permits the use of shorter URLs on the command line, such as:

$ cat ~/.ssh/config
...
Host tr
  Hostname git.example.com
  Port 29418
  User john.doe

$ git push tr:kernel/common HEAD:refs/for/experimental

Specific reviewers can be requested and/or additional carbon copies of the notification message may be sent by including these as options in the reference

git push tr:kernel/common HEAD:refs/for/experimental%r=a@a.com,cc=b@o.com

The r='email' and cc='email' options may be specified as many times as necessary to cover all interested parties. Gerrit will automatically avoid sending duplicate email notifications, such as if one of the specified reviewers or CC addresses had also requested to receive all new change notifications.

If you are frequently sending changes to the same parties and/or branches, consider adding a custom remote block to your project’s .git/config file:

$ cat .git/config
...
[remote "exp"]
  url = tr:kernel/common
  push = HEAD:refs/for/experimental%r=a@a.com,cc=b@o.com

$ git push exp

Replace Changes

To add an additional patch set to a change, ensure Change-Id lines were created in the original commit messages, and just use git push URL HEAD:refs/for/... as described above. Gerrit Code Review will automatically match the commits back to their original changes by taking advantage of the Change-Id lines.

If Change-Id lines are not present in the commit messages, consider amending the message and copying the line from the change’s page on the web, and then using git push as described above.

If Change-Id lines are not available, then the user must use the manual mapping technique described below.

For more about Change-Ids, see Change-Id Lines.

Manual Replacement Mapping

Deprecation Warning

The remainder of this section describes a manual method of replacing changes by matching each commit name to an existing change number. End-users should instead prefer to use Change-Id lines in their commit messages, as the process is then fully automated by Gerrit during normal uploads.

See above for the preferred technique of replacing changes. See above for the preferred technique of replacing changes.

To add an additional patch set to a change, replacing it with an updated version of the same logical modification, send the new commit to the change’s ref. For example, to add the commit whose SHA-1 starts with c0ffee as a new patch set for change number 1979, use the push refspec c0ffee:refs/changes/1979 as below:

git push ssh://sshusername@hostname:29418/projectname c0ffee:refs/changes/1979

This form can be combined together with refs/for/'branchname' (above) to simultaneously create new changes and replace changes during one network transaction.

For example, consider the following sequence of events:

$ git commit -m A                    ; # create 3 commits
$ git commit -m B
$ git commit -m C

$ git push ... HEAD:refs/for/master  ; # upload for review
... A is 1500 ...
... B is 1501 ...
... C is 1502 ...

$ git rebase -i HEAD~3               ; # edit "A", insert D before B
                                     ; # now series is A'-D-B'-C'
$ git push ...
    HEAD:refs/for/master
    HEAD~3:refs/changes/1500
    HEAD~1:refs/changes/1501
    HEAD~0:refs/changes/1502         ; # upload replacements

At the final step during the push Gerrit will attach A' as a new patch set on change 1500; B' as a new patch set on change 1501; C' as a new patch set on 1502; and D will be created as a new change.

Ensuring D is created as a new change requires passing the refspec HEAD:refs/for/branchname, otherwise Gerrit will ignore D and won’t do anything with it. For this reason it is a good idea to always include the create change refspec when uploading replacements.

Bypass Review

Changes (and annotated tags) can be pushed directly into a repository, bypassing the review process. This is primarily useful for a project owner to create new branches, create annotated tags for releases, or to force-update a branch whose history needed to be rewritten.

Gerrit restricts direct pushes that bypass review to:

refs/heads/*: any branch can be updated, created, deleted, or rewritten by the pusher.
refs/tags/*: annotated tag objects pointing to any other type of Git object can be created.

To push branches, the proper access rights must be configured first. Here follows a few examples of how to configure this in Gerrit:

Update: Any existing branch can be fast-forwarded to a new commit. This is the safest mode as commits cannot be discarded. Creation of new branches is rejected. Can be configured with Push access.
Create: Allows creation of a new branch if the name does not already designate an existing branch name. Needs Create Reference configured. Please note that once created, this permission doesn’t grant the right to update the branch with further commits (see above for update details).
Delete: Implies Update, but also allows an existing branch to be deleted. Since a force push is effectively a delete followed by a create, but performed atomically on the server and logged, this also permits forced push updates to branches. To grant this access, configure Push with the Force option ticked.

To push annotated tags, the Push Annotated Tag project right must be granted to one (or more) of the user’s groups. There is only one level of access in this category.

Project owners may wish to grant themselves Push Annotated Tag only at times when a new release is being prepared, and otherwise grant nothing at all. This ensures that accidental pushes don’t make undesired changes to the public repository.

Auto-Merge during Push

Changes can be directly submitted on push. This is primarily useful for teams that don’t want to do code review but want to use Gerrit’s submit strategies to handle contention on busy branches. Using %submit creates a change and submits it immediately, if the caller has Submit permission on refs/for/<ref> (e.g. on refs/for/refs/heads/master).

git push ssh://john.doe@git.example.com:29418/kernel/common HEAD:refs/for/master%submit

On auto-merge of a change neither labels nor submit rules are checked. If the merge fails the change stays open, but when pushing a new patch set the merge can be reattempted by using %submit again.

Selecting Merge Base

By default new changes are opened only for new unique commits that have never before been seen by the Gerrit server. Clients may override that behavior and force new changes to be created by setting the merge base SHA-1 using the %base argument:

git push ssh://john.doe@git.example.com:29418/kernel/common HEAD:refs/for/master%base=$(git rev-parse origin/master)

It is also possible to specify more than one %base argument. This may be useful when pushing a merge commit. Note that the % character has only to be provided once, for the first %base argument:

git push ssh://john.doe@git.example.com:29418/kernel/common HEAD:refs/for/master%base=commit-id1,base=commit-id2

repo upload

repo is a multiple repository management tool, most commonly used by the Android Open Source Project. For more details, see using repo.

Create Changes

To upload changes to a project using repo, ensure the manifest’s review field has been configured to point to the Gerrit server. Only the hostname or the web address needs to be given in the manifest file. During upload repo will automatically determine the correct port number by reading http://'reviewhostname'/ssh_info when its invoked.

Each new commit uploaded by repo upload will be converted into a change record on the server. Other users (e.g. project owners) who have configured Gerrit to notify them of new changes will be automatically sent an email message. Additional notifications can be sent through command line options.

For more details on using repo upload, see repo help upload.

Replace Changes

To replace changes, ensure Change-Id lines were created in the commit messages, and just use repo upload. Gerrit Code Review will automatically match the commits back to their original changes by taking advantage of their Change-Id lines.

If Change-Id lines are not present in the commit messages, consider amending the message and copying the line from the change’s page on the web.

If Change-Id lines are not available, then the user must use the much more manual mapping technique offered by using git push to a specific refs/changes/change# reference.

For more about Change-Ids, see Change-Id Lines.

Gritty Details

As Gerrit implements the entire SSH and Git server stack within its own process space, Gerrit maintains complete control over how the repository is updated, and what responses are sent to the git push client invoked by the end-user, or by repo upload. This allows Gerrit to provide magical refs, such as refs/for/* for new change submission and refs/changes/* for change replacement. When a push request is received to create a ref in one of these namespaces Gerrit performs its own logic to update the database, and then lies to the client about the result of the operation. A successful result causes the client to believe that Gerrit has created the ref, but in reality Gerrit hasn’t created the ref at all.

By implementing the entire server stack, Gerrit is also able to perform project level access control checks (to verify the end-user is permitted to access a project) prior to advertising the available refs, and potentially leaking information to a snooping client. Clients cannot tell the difference between project not found and project exists, but access is denied.

Gerrit can also ensure users have completed a valid Contributor Agreement prior to accepting any transferred objects, and if an agreement is required, but not completed, it aborts the network connection before data is sent. This ensures that project owners can be certain any object available in their repository has been supplied under at least one valid agreement.

Part of Gerrit Code Review