RFR: Section on backporting [v6]

[Severin Gehwolf]

On Thu, 25 Nov 2021 18:17:46 GMT, Jesper Wilhelmsson <jwilhelm at openjdk.org> wrote:

>> Guidance on backporting.
>> Also moved "Backing out a change" to the testing section where I believe it fits better. This section is unchanged.
>
> Jesper Wilhelmsson has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update src/index.md
>   
>   Co-authored-by: Andrew Haley <aph-open at littlepinkcloud.com>

src/index.md line 1478:

> 1476: The guideline for what to backport into a specific update release will vary over the lifetime of that release. Initially more fixes are expected to be backported as new features and large changes introduced in a mainline release stabilize. Over time the focus will shift from stabilization to keeping it stable - the release will go into maintenance mode. This means that bug fixes that require larger disruptive changes are more likely to be made in mainline and backported to more recent release trains only, and not to older release trains.
> 1477: 
> 1478: Over time it's likely that the code base will diverge between mainline and any given update release, and the cost of backporting will increase. The cost in this case is not only the effort needed to perform the actual backport, but also the cost inferred by bugs introduced by the backport. This should be taken into consideration when deciding if a change should be backported or not. For more details on how to reson around what to backport, [this email from JDK 8 Updates Project lead Andrew Haley](https://mail.openjdk.java.net/pipermail/jdk8u-dev/2020-June/012002.html) has some guidelines for JDK 8u. The reasoning in this mail is specific to JDK 8u, but will in general apply to any JDK release in maintenance mode.

`s/reson/reason/`?

src/index.md line 1504:

> 1502: ## Using the Skara tooling to help with backports
> 1503: 
> 1504: The Skara tooling includes support for backports. [The official Skara documentation](https://wiki.openjdk.java.net/display/SKARA/Backports) describes in detail how to work with the tooling to create backport PRs on GitHub or using the CLI tools. As described in the documentation, the [`/backport`](https://wiki.openjdk.java.net/display/SKARA/Commit+Commands#CommitCommands-/backport) command can be used on a commit (not a PR!) to create the backport PR. If a backport PR is manually created, set the title to `Backport <original commit hash>`.

Suggestion: "... set the PR title to `Backport <original commit hash>`. This ensures that the the bots will recognize it as a backport as opposed to a fix specifically targetting an older release only. One can tell whether or not the bots recognized a PR as a backport by the `backport` label being added if it is being recognized."

-------------

PR: https://git.openjdk.java.net/guide/pull/66