Project

General

Profile

Gerrit » History » Version 30

neels, 07/05/2016 10:48 AM

1 1 zecke
h1. Contributing using Gerrit
2 1 zecke
3 11 laforge
{{>toc}}
4 11 laforge
5 10 laforge
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
6 1 zecke
7 10 laforge
Gerrit is a review tool that integrates nicely with git and ssh. You can find general information about Gerrit at https://www.gerritcodereview.com/
8 1 zecke
9 10 laforge
The advantages of Gerrit are:
10 10 laforge
* patch submission status is automatically tracked, also with several revisions for a patch set.
11 10 laforge
* patches are build-tested (and possibly even further tested) by jenkins before they are applied
12 10 laforge
* developers + maintainers can formally vote on a patch (developer: -1/0/+1, maintainer: -2/0/+2)
13 10 laforge
* once a patch has +2 score, it can be (automatically) merged into master
14 10 laforge
* patch sumissions not via git send-email but direcly from git
15 10 laforge
16 10 laforge
h2. Osmocom Subprojects using Gerrit
17 10 laforge
18 1 zecke
The following projects use Gerrit to contribute changes:
19 1 zecke
20 1 zecke
* libosmocore.git
21 1 zecke
* libosmo-abis.git
22 1 zecke
* libosmo-netif.git
23 1 zecke
* libosmo-sccp.git
24 1 zecke
* libsmpp34.git
25 1 zecke
* openbsc.git
26 1 zecke
* osmo-bts.git
27 1 zecke
* osmo-iuh.git
28 1 zecke
* osmo-pcu.git
29 5 zecke
* cellmgr-ng.git
30 1 zecke
* osmo-sip-connector.git
31 30 neels
32 1 zecke
h2. Configuring Gerrit/Account
33 1 zecke
34 10 laforge
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. If you have no Osmocom redmine account, you can simply create one online at the "Register" link in the upper right corner.
35 10 laforge
36 10 laforge
Even without an existing or new redmine account, you should also be able to use any other OpenID provider to authenticate against gerrit (untested).
37 10 laforge
38 10 laforge
After the initial sign-up you will need to:
39 1 zecke
40 1 zecke
* Pick a username (can not be changed)
41 1 zecke
* Add your public ssh key(s)
42 1 zecke
* Add email addresses you intend to use as author/comitter
43 30 neels
44 30 neels
If you would like to push private branches to the Gerrit repository, you also need to be added to the "known users" group.
45 30 neels
Please send a short requesting email to openbsc@lists.osmocom.org.
46 1 zecke
47 1 zecke
h2. Setting up Gerrit for commits and pushing
48 1 zecke
49 2 zecke
* Add the remote to be able to fetch and push to gerrit
50 2 zecke
* Fetch the commit hook that adds Change-Id to each commit to uniquely identify a commit
51 2 zecke
52 2 zecke
<pre>
53 7 neels
USERNAME=gerrit_user_name
54 7 neels
PROJECT=$(basename $PWD)
55 7 neels
git remote add gerrit ssh://$USERNAME@gerrit.osmocom.org:29418/$PROJECT.git
56 7 neels
scp -P 29418 $USERNAME@gerrit.osmocom.org:hooks/commit-msg .git/hooks/
57 7 neels
</pre>
58 7 neels
59 7 neels
* In case your local username matches the gerrit username, the setup shortens to
60 7 neels
61 7 neels
<pre>
62 7 neels
PROJECT=$(basename $PWD)
63 7 neels
git remote add gerrit ssh://gerrit.osmocom.org:29418/$PROJECT.git
64 7 neels
scp -P 29418 gerrit.osmocom.org:hooks/commit-msg .git/hooks/
65 7 neels
</pre>
66 7 neels
67 7 neels
Then
68 7 neels
69 7 neels
* Push for review
70 7 neels
<pre>
71 7 neels
git push gerrit HEAD:refs/for/master
72 7 neels
</pre>
73 7 neels
74 7 neels
* Push a user branch
75 7 neels
<pre>
76 9 neels
git push gerrit HEAD:refs/heads/users/$USERNAME/topic
77 7 neels
</pre>
78 7 neels
79 7 neels
* Directly push to master if you are allowed to
80 7 neels
<pre>
81 7 neels
git push gerrit HEAD:refs/heads/master
82 7 neels
</pre>
83 7 neels
84 7 neels
* List changesets in gerrit
85 7 neels
<pre>
86 7 neels
git ls-remote gerrit changes/*
87 2 zecke
</pre>
88 12 msuraev
89 17 neels
h1. Tips and Tricks
90 1 zecke
91 17 neels
h2. Throw-away branch
92 17 neels
93 17 neels
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),
94 17 neels
make your changes/amendments and than send patch(es) back to gerrit while removing temporary branch automatically with "git review -f".
95 13 neels
96 25 neels
h2. Re-submit a Branch with Amended Commits
97 13 neels
98 1 zecke
On a feature branch, one typically has numerous commits that depend on their preceding commits.
99 29 neels
Often, some of the branch commits need to be amended for fixes. But, Gerrit will refuse your branch
100 29 neels
re-submission if the first branch commit is unchanged.
101 1 zecke
102 16 neels
To re-submit a branch, make sure to cosmetically tweak the branch's first commit log message
103 22 neels
before each re-submission (keep the Change-Id, really make just a cosmetic change).
104 13 neels
105 16 neels
<pre>
106 16 neels
git rebase -i master
107 16 neels
# replace the first line's 'pick' with 'r' (or 'reword'), exit editor
108 16 neels
# git presents you with commit log message, make any tiny modification.
109 1 zecke
</pre>
110 1 zecke
111 29 neels
The cause: Gerrit refuses to accept a commit with a Change-Id that it already knows and
112 29 neels
where the commit hash is identical.
113 1 zecke
114 29 neels
If you just cosmetically tweak the first commit's log message, the commit hash
115 29 neels
is changed. Since the following commits contain their predecessor's commit hash, now
116 29 neels
all of the branch's commit hashes are modified, and gerrit happily accepts them as a 
117 29 neels
new patch set. It will still pick up the Change-Ids (which you shouldn't edit) and 
118 29 neels
notice if commits have remained identical (keeping the votes). But with the minor
119 29 neels
commit log tweak, it will no longer thwart your re-submission with an error message.
120 29 neels
121 29 neels
Note: you could modify all the Change-Ids, but now your branch submission would
122 29 neels
open entirely new review entries and you would have to abandon your previous submission.
123 29 neels
Comments on the first submission are lost and you cannot diff between patch sets.
124 29 neels
125 29 neels
126 26 neels
h2. Re-submit Previously Abandoned Changes
127 16 neels
128 16 neels
You have to edit the Change-Ids, on a branch that would be every single commit log message.
129 16 neels
130 13 neels
<pre>
131 1 zecke
cd openbsc
132 1 zecke
git co my-branch
133 1 zecke
git rebase -i master
134 1 zecke
# replace all 'pick' with 'r' (or 'reword'), exit your editor
135 13 neels
# git presents each commit log message for editing
136 13 neels
</pre>
137 13 neels
138 27 neels
h2. Submit a "private" branch for master
139 21 neels
140 21 neels
If you've pushed a branch to refs/heads/* somewhere, gerrit will already know the Change-Ids on it.
141 24 neels
Make sure the option [[Gerrit#Private-Branches-Create-a-new-change-for-every-commit|Create a new change for every commit not in the target branch]] is _TRUE_ for your project,
142 21 neels
or gerrit will refuse to accept your submission.
143 21 neels
144 16 neels
h1. Reasons for Particular Configuration
145 13 neels
146 16 neels
h2. Rebase if necessary
147 16 neels
148 16 neels
There are different merge strategies that Gerrit performs to accept patches.
149 13 neels
Each project can be configured to a specific merge strategy, but unfortunately you can't
150 13 neels
decide on a strategy per patch submission.
151 13 neels
152 13 neels
It seems that the "Merge if Necessary" strategy is best supported, but it creates non-linear
153 13 neels
history with numerous merge commits that are usually not at all necessary.
154 13 neels
155 13 neels
Instead, the "Cherry Pick" strategy puts each patch onto current master's HEAD to create
156 13 neels
linear history. However, this will cause merge failures as soon as one patch depends on
157 13 neels
another submitted patch, as typical for a feature branch submission.
158 13 neels
159 1 zecke
So we prefer the "Rebase if Necessary" strategy, which always tries to apply your patches to
160 13 neels
the current master HEAD, in sequence with the previous patches on the same branch.
161 13 neels
However, some problems still remain, including some bugs in "Rebase if Necessary".
162 1 zecke
163 13 neels
There's a problem with "Rebase if Necessary": If your branch sits at master's HEAD, Gerrit
164 13 neels
refuses to accept the submission, because it thinks that no new changes are submitted.
165 13 neels
This is a bug in Gerrit, which holger has fixed manually in our Gerrit installation:
166 1 zecke
167 1 zecke
https://bugs.chromium.org/p/gerrit/issues/detail?id=4158
168 1 zecke
169 1 zecke
170 16 neels
h2. Private Branches: Create a new change for every commit...
171 1 zecke
172 13 neels
Say you have an extensive feature in development, and you want to keep it on the
173 13 neels
upstream git repository to a) keep it safe and b) collaborate with other devs on it.
174 16 neels
So, of course, you have regularly pushed to refs/heads/yoyodyne/feature.
175 13 neels
176 13 neels
Since you have the gerrit commit hook installed, your feature branch already has
177 13 neels
Change-Id tags in all commit log messages.
178 13 neels
179 13 neels
Now your feature is complete and you would like to submit it to master.
180 13 neels
Alas, Gerrit refuses to accept your patch submission for master, because it
181 13 neels
knows the Change-Ids are also on a different branch.
182 13 neels
183 16 neels
Gerrit by default enforces that a Change-Id must be unique across all branches,
184 16 neels
so that each submission for review is separate for each branch. Instead, we
185 16 neels
want to handle Change-Ids per-branch, so that you can have the same change
186 16 neels
submitted to different branches, as separate patch submissions, without having
187 16 neels
to cosmetically adjust the Change-Id.
188 13 neels
189 16 neels
Solution: set the option 
190 16 neels
_Create a new change for every commit not in the target branch_ to _TRUE_
191 13 neels
192 20 neels
h2. Allow content merges
193 14 neels
194 14 neels
By default, gerrit compares patches only by the files' paths. If two paths are the same,
195 14 neels
it immediately shows them as conflicts (path conflicts).
196 14 neels
197 14 neels
In software development, a conflict usually means an actual content conflict, so if the
198 14 neels
edits are in two entirely separate places in the file, we don't consider this a conflict.
199 14 neels
200 23 neels
By setting _Allow content merges_ to _TRUE_ in the git project config, we tell Gerrit to
201 14 neels
perform text merges of the submitted patches and only complain about actual content
202 14 neels
conflicts, in the usual software engineering sense.
Add picture from clipboard (Maximum size: 48.8 MB)