CONTRIBUTING.md: import "How to submit patches" from criu.org

Import "How to submit patches" article from CRIU wiki and update its
format to match GitHub markdown.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>

CONTRIBUTING.md

@@ -14,6 +14,204 @@ Here are some useful hints to get involved.
 * CRIU does need [extensive testing](https://github.com/checkpoint-restore/criu/issues?q=is%3Aissue+is%3Aopen+label%3Atesting);
 * Documentation is always hard, we have [some information](https://criu.org/Category:Empty_articles) that is to be extracted from people's heads into wiki pages as well as [some texts](https://criu.org/Category:Editor_help_needed) that all need to be converted into useful articles;
 * Feedback is expected on the github issues page and on the [mailing list](https://lists.openvz.org/mailman/listinfo/criu);
-* We accept github pull requests and this is the preferred way to contribute to CRIU. If you prefer to send patches by email, you are welcome to send them to [the devel list](http://criu.org/How_to_submit_patches);
+* We accept github pull requests and this is the preferred way to contribute to CRIU. If you prefer to send patches by email, you are welcome to send them to [CRIU development mailing list](https://lists.openvz.org/mailman/listinfo/criu).
+Below we describe in more detail recommend practices for CRIU developemnt.
 * Spread the word about CRIU in [social networks](http://criu.org/Contacts);
 * If you're giving a talk about CRIU -- let us know, we'll mention it on the [wiki main page](https://criu.org/News/events);
+
+### Seting up the developemnt environment
+
+Although criu could be run as non-root (see [Security](https://criu.org/Security), development is better to be done as root. For example, some tests require root. So, it would be a good idea to set up some recent Linux distro on a virtual machine.
+
+### Get the source code
+
+The CRIU sources are tracked by Git. Official CRIU repo is at https://github.com/checkpoint-restore/criu.
+
+The repository may contain multiple branches. Development happens in the **criu-dev** branch.
+
+To clone CRIU repo and switch to the proper branch, run:
+
+```
+        git clone https://github.com/checkpoint-restore/criu criu
+        cd criu
+        git checkout criu-dev
+```
+
+### Compile
+
+First, you need to install compile-time dependencies. Check [Installation dependencies](https://criu.org/Installation#Dependencies) for more info.
+
+To compile CRIU, run:
+
+```
+        make
+```
+
+This should create the `./criu/criu` executable.
+
+## Edit the source code
+
+If you use ctags, you can generate the ctags file by running
+
+```
+        make tags
+```
+
+When you change the source code, please keep in mind the following code conventions:
+
+* we prefer tabs and indentations to be 8 characters width
+* CRIU mostly follows [Linux kernel coding style](https://www.kernel.org/doc/Documentation/process/coding-style.rst), but we are less strict than the kernel community.
+
+Other conventions can be learned from the source code itself. In short, make sure your new code
+looks similar to what is already there.
+
+## Test your changes
+
+CRIU comes with an extensive test suite. To check whether your changes introduce any regressions, run
+
+```
+         make test
+```
+
+The command runs [ZDTM Test Suite](https://criu.org/ZDTM_Test_Suite). Check for any error messages produced by it.
+
+In case you'd rather have someone else run the tests, you can use travis-ci for your
+own github fork of CRIU. It will check the compilation for various supported platforms,
+as well as run most of the tests from the suite. See https://travis-ci.org/checkpoint-restore/criu
+for more details.
+
+## Sign your work
+
+To improve tracking of who did what, we ask you to sign off the patches
+that are to be emailed.
+
+The sign-off is a simple line at the end of the explanation for the
+patch, which certifies that you wrote it or otherwise have the right to
+pass it on as an open-source patch.  The rules are pretty simple: if you
+can certify the below:
+
+### Developer's Certificate of Origin 1.1
+    By making a contribution to this project, I certify that:
+
+    (a) The contribution was created in whole or in part by me and I
+        have the right to submit it under the open source license
+        indicated in the file; or
+
+    (b) The contribution is based upon previous work that, to the best
+        of my knowledge, is covered under an appropriate open source
+        license and I have the right under that license to submit that
+        work with modifications, whether created in whole or in part
+        by me, under the same open source license (unless I am
+        permitted to submit under a different license), as indicated
+        in the file; or
+
+    (c) The contribution was provided directly to me by some other
+        person who certified (a), (b) or (c) and I have not modified
+        it.
+
+    (d) I understand and agree that this project and the contribution
+        are public and that a record of the contribution (including all
+        personal information I submit with it, including my sign-off) is
+        maintained indefinitely and may be redistributed consistent with
+        this project or the open source license(s) involved.
+
+then you just add a line saying
+
+```
+        Signed-off-by: Random J Developer <random at developer.example.org>
+```
+
+using your real name (please, no pseudonyms or anonymous contributions if
+it possible).
+
+Hint: you can use `git commit -s` to add Signed-off-by line to your
+commit message. To append such line to a commit you already made, use
+`git commit --amend -s`.
+
+```
+ From: Random J Developer <random at developer.example.org>
+ Subject: [PATCH] Short patch description
+
+ Long patch description (could be skipped if patch
+ is trivial enough)
+
+ Signed-off-by: Random J Developer <random at developer.example.org>
+ ---
+ Patch body here
+```
+
+## Submit your work upstream
+
+We accept github pull requests and this is the preferred way to contribute to CRIU.
+For that you should push your work to your fork of CRIU at [GitHub](https://github.com) and create a [pull request](https://help.github.com/en/github/collaborating-with-issues-and-pull-requests/about-pull-requests)
+
+Historically, CRIU worked with mailing lists and patches so if you still prefer this way continue reading till the end of this section.
+
+### Make a patch
+
+To create a patch, run
+
+```
+    git format-patch --signoff origin/criu-dev
+```
+
+You might need to read GIT documentation on how to prepare patches
+for mail submission. Take a look at http://book.git-scm.com/ and/or
+http://git-scm.com/documentation for details. It should not be hard
+at all.
+
+We recommend to post patches using `git send-email`
+
+```
+  git send-email --cover-letter --no-chain-reply-to --annotate \
+                 --confirm=always --to=criu@openvz.org criu-dev
+```
+
+Note that the `git send-email` subcommand may not be in
+the main git package and using it may require installation of a
+separate package, for example the "git-email" package in Fedora and
+Debian.
+
+If this is your first time using git send-email, you might need to
+configure it to point it to your SMTP server with something like:
+
+```
+    git config --global sendemail.smtpServer stmp.example.net
+```
+
+If you get tired of typing `--to=criu@openvz.org` all the time,
+you can configure that to be automatically handled as well:
+
+```
+    git config sendemail.to criu@openvz.org
+```
+
+If a developer is sending another version of the patch (e.g. to address
+review comments), they are advised to note differences to previous versions
+after the `---` line in the patch so that it helps reviewers but
+doesn't become part of git history. Moreover, such patch needs to be prefixed
+correctly with `--subject-prefix=PATCHv2` appended to
+`git send-email` (substitute `v2` with the correct
+version if needed though).
+
+### Mail patches
+
+The patches should be sent to CRIU development mailing list, `criu AT openvz.org`. Note that you need to be subscribed first in order to post. The list web interface is available at https://openvz.org/mailman/listinfo/criu; you can also use standard mailman aliases to work with it.
+
+Please make sure the email client you're using doesn't screw your patch (line wrapping and so on).
+
+{{Note| When sending a patch set that consists of more than one patch, please, push your changes in your local repo and provide the URL of the branch in the cover-letter}}
+
+### Wait for response
+
+Be patient. Most CRIU developers are pretty busy people so if
+there is no immediate response on your patch — don't be surprised,
+sometimes a patch may fly around a week before it gets reviewed.
+
+## Continuous integration
+
+Wiki article: [Continuous integration](https://criu.org/Continuous_integration)
+
+CRIU tests are run for each series sent to the mailing list. If you get a message from our patchwork that patches failed to pass the tests, you have to investigate what is wrong.
+
+We also recommend you to [enable Travis CI for your repo](https://criu.org/Continuous_integration#Enable_Travis_CI_for_your_repo) to check patches in your git branch, before sending them to the mailing list.