Rename HACKING -> CONTRIBUTING, add info about git + PRs

`CONTRIBUTING.md` is a friendlier and more common name.
Explain the DCO bits in particular.

Closes: #574

Signed-off-by: Colin Walters <[email protected]>

CONTRIBUTING.md

@@ -1,20 +1,193 @@
-# Required dependencies
+# Contributing to bootc
 
-In order to build `bootc` you will need the following dependencies.
+Thanks for your interest in contributing!  At the current time,
+bootc is implemented in Rust, and calls out to important components
+which are written in Go (e.g. https://github.com/containers/image)
+as well as C (e.g. https://github.com/ostreedev/ostree/).  Depending
+on what area you want to work on, you'll need to be familiar with
+the relevant language.
 
-Fedora:
+There isn't a single approach to working on bootc; however
+the primary developers tend to use Linux host systems,
+and test in Linux VMs.  One specifically recommended
+approach is to use [toolbox](https://github.com/containers/toolbox/)
+to create a containerized development environment
+(it's possible, though not necessary to create the toolbox
+ dev environment using a bootc image as well).
+
+At the current time most upstream developers use a Fedora derivative
+as a base, and the [hack/Containerfile](hack/Containerfile) defaults
+to Fedora.  However, bootc itself is not intended to strongly tie to a particular
+OS or distribution, and patches to handle others are gratefully
+accepted!
+
+## Key recommended ingredients:
+
+- A development environment (toolbox or a host) with a Rust and C compiler, etc.
+  While this isn't specific to bootc, you will find the experience of working on Rust
+  is greatly aided with use of e.g. [rust-analyzer](https://github.com/rust-lang/rust-analyzer/).
+- An installation of [podman-bootc](https://github.com/containers/podman-bootc-cli)
+  which note on Linux requires that you set up "podman machine". This document
+  assumes you have the environment variable `CONTAINER_CONNECTION` set to your
+  podman machine's name.
+
+## Ensure you're familiar with a bootc system
+
+Worth stating: before you start diving into the code you should understand using
+the system as a user and how it works.  See the user documentation for that.
+
+## Creating your edit-compile-debug cycle
+
+Edit the source code; a simple thing to do is add e.g.
+`eprintln!("hello world);` into `run_from_opt` in [lib/src/cli.rs](lib/src/cli.rs).
+You can run `make` or `cargo build` to build that locally.  However, a key
+next step is to get that binary into a bootc container image.
+
+Use e.g. `podman build -t localhost/bootc -f hack/Containerfile .`.
+
+From there, you can create and spawn a VM from that container image
+with your modified bootc code in exactly the same way as a systems operator
+would test their own bootc images:
+
+```
+$ podman-bootc run localhost/bootc
+```
+
+### Faster iteration cycles
+
+You don't need to create a whole new VM for each change, of course.
+<https://github.com/containers/podman-bootc/pull/36> is an outstanding
+PR to add virtiofsd support, which would allow easily accessing the locally-built
+binaries.  Another avenue we'll likely investigate is supporting podman-bootc
+accessing the container images which currently live in the podman-machine VM,
+or having a local registry which frontends the built container images.
+
+A simple hack though (assuming your development environment is compatible
+with the target container host) is to just run a webserver on the host, e.g.
+`python3 -m http.server` or whatever, and then from the podman-bootc guest
+run `bootc usroverlay` once, and 
+`curl -L -o /usr/bin/bootc http://10.0.1.2:8080/target/release/bootc && restorecon /usr/bin/bootc`.
+
+### Debugging via lldb
+
+The `hack/lldb` directory contains an example of how to use lldb to debug bootc code.
+`hack/lldb/deploy.sh` can be used to build and deploy a bootc VM in libvirt with an lldb-server
+running as a systemd service. Depending on your editor, you can then connect to the lldb server
+to use an interactive debugger, and set up the editor to build and push the new binary to the VM.
+`hack/lldb/dap-example-vim.lua` is an example for neovim.
+
+The VM can be connected to via `ssh test@bootc-lldb` if you have [nss](https://libvirt.org/nss.html)
+enabled.
+
+For some bootc install commands, it's simpler to run the lldb-server in a container, e.g.
 
 ```bash
-sudo dnf install clippy openssl-devel ostree-devel ostree-libs rustfmt
+sudo podman run --pid=host --network=host --privileged --security-opt label=type:unconfined_t -v /var/lib/containers:/var/lib/containers -v /dev:/dev -v .:/output localhost/bootc-lldb lldb-server platform --listen "*:1234" --server
+```
+
+## Running the tests
+
+First, you can run many unit tests with `cargo test`.
+
+### container tests
+
+There's a small set of tests which are designed to run inside a bootc container
+and are built into the default container image:
+
+```
+$ podman run --rm -ti localhost/bootc bootc-integration-tests container
 ```
 
-# Pre flight checks
+## Submitting a patch
 
-Make sure you commented your code additions, then run
+The podman project has some [generic useful guidance](https://github.com/containers/podman/blob/main/CONTRIBUTING.md#submitting-pull-requests);
+like that project, a "Developer Certificate of Origin" is required.
+
+### Sign your PRs
+
+The sign-off is a line at the end of the explanation for the patch. Your
+signature certifies that you wrote the patch or otherwise have the right to pass
+it on as an open-source patch. The rules are simple: if you can certify
+the below (from [developercertificate.org](https://developercertificate.org/)):
+
+```
+Developer Certificate of Origin
+Version 1.1
+
+Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
+660 York Street, Suite 102,
+San Francisco, CA 94110 USA
+
+Everyone is permitted to copy and distribute verbatim copies of this
+license document, but changing it is not allowed.
+
+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 to every git commit message:
+
+    Signed-off-by: Joe Smith <[email protected]>
+
+Use your real name (sorry, no pseudonyms or anonymous contributions.)
+
+If you set your `user.name` and `user.email` git configs, you can sign your
+commit automatically with `git commit -s`.
+
+### Git commit style
+
+Please look at `git log` and match the commit log style, which is very
+similar to the
+[Linux kernel](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git).
+
+You may use `Signed-off-by`, but we're not requiring it.
+
+**General Commit Message Guidelines**:
+
+1. Title
+    - Specify the context or category of the changes e.g. `lib` for library changes, `docs` for document changes, `bin/<command-name>` for command changes, etc.
+    - Begin the title with the first letter of the first word capitalized.
+    - Aim for less than 50 characters, otherwise 72 characters max.
+    - Do not end the title with a period.
+    - Use an [imperative tone](https://en.wikipedia.org/wiki/Imperative_mood).
+2. Body
+    - Separate the body with a blank line after the title.
+    - Begin a paragraph with the first letter of the first word capitalized.
+    - Each paragraph should be formatted within 72 characters.
+    - Content should be about what was changed and why this change was made.
+    - If your commit fixes an issue, the commit message should end with `Closes: #<number>`.
+
+Commit Message example:
 
 ```bash
-cargo fmt
-cargo clippy
+<context>: Less than 50 characters for subject title
+
+A paragraph of the body should be within 72 characters.
+
+This paragraph is also less than 72 characters.
 ```
 
-Make sure to apply any relevant suggestions.
+For more information see [How to Write a Git Commit Message](https://chris.beams.io/posts/git-commit/)

README.md

@@ -31,5 +31,5 @@ are also operating systems and distributions using bootc; here are some examples
 
 ## Developing bootc
 
-Are you interested in working on bootc?  Great!  See our [HACKING.md](HACKING.md) guide.
+Are you interested in working on bootc?  Great!  See our [CONTRIBUTING.md](CONTRIBUTING.md) guide.