devguide: update backports policy for Suricata 7.0

Also remove mentions to `master` and `6.0x`.

Task OISF#7937

(cherry picked from commit 6c06ab6)

Author: jufajardini

doc/userguide/devguide/codebase/contributing/backports-guide.rst

@@ -0,0 +1,133 @@
+========================
+Suricata Backports Guide
+========================
+
+This document describes the processes used to backport content to current stable
+Suricata releases. Most often, this means security and/or bug fixes;
+however, in some cases, features may be backported to previous Suricata releases.
+
+There are multiple versions of Suricata at any given time:
+    * Main
+    * Major stable release
+    * Old stable release
+
+For example, at the moment, there are 3 releases based on these Suricata branches:
+    * main: 9.0.0-dev, current development branch
+    * main-8.0.x: major stable release
+    * main-7.0.x: old stable release
+
+For Suricata's release cadence and *end of life* policies, please check
+https://suricata.io/our-story/eol-policy/.
+
+The next sections discuss when and what to backport, and some guidelines when
+doing so.
+
+What should be backported?
+--------------------------
+
+Usually, when the team creates a ticket, we'll add the *Needs backport* related
+labels, so necessary backporting tickets will be automatically created. If you
+are working on a ticket that doesn't have such labels, nor backporting tasks
+associated, it probably doesn't need backporting. If you understand that the
+issue should be backported, please let us know in the ticket or related PR. But
+sometimes we'll miss those.
+
+The general principle used to determine what will be backported is:
+    * security fixes (please see our `Security Policy <https://github.com/OISF/suricata/blob/main/SECURITY.md>`_)
+    * bug fixes
+    * in some cases, new features are backported if there are sufficient reasons to
+      backport a new feature.
+
+.. note:: 7.0.x backports
+
+    With the release of Suricata 8.0, Suricata 7 has reached a mature stage of its
+    release cycle. Thus, as a rule, only critical issues (bugs and security),
+    should be considered for backporting.
+
+.. Note:: Exceptions
+
+    There can be cases where backports may be "missed" -- some issues may not be
+    labeled as needing backports and some PRs may be merged without an issue.
+
+    This guide may be insufficient for some situations. When in doubt, please reach
+    out to the team on the backport ticket or PR.
+
+Selection overview
+------------------
+
+All items considered for backports should be reviewed with the following:
+    * risk estimate: will the change introduce new bugs? Consider the scope and
+      items affected by the change.
+    * behavioral change: how much will the behavior of the system be changed by the
+      backport. For example, a small change to decode additional encapsulation
+      protocols may result in more traffic being presented to Suricata.
+    * default settings: if the issue alters behavior, can it be made optional, and
+      at what cost?
+
+Creating backport tickets -- new issues
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Redmine: for security and bug fixes, when creating a new Redmine issue,
+label the Redmine issue with "Needs backport to x.0", where x.0 is a supported
+Suricata release, e.g, 8.0.x.
+
+Creating backport tickets -- existing issues/PRs
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+We want to minimize the occurrence of "missed backports" -- that is, work that
+should be backported but wasn't. Sometimes this happens when there is no Redmine
+issue, or the Redmine issue wasn't labeled as needing a backport.
+
+Therefore, we will be periodically reviewing:
+    * Redmine issues without backport labels, including recently closed issues, to
+      see which require backport labels.
+    * PRs without associated Redmine issues. Those requiring backports should be
+      labeled with *needs backport*.
+
+Then, also periodically, we will create backport issues from those items
+identified in the previous steps. When doing so, we will evaluate what are the
+relevant target backport releases. Some issues reported against main or the
+current Suricata release may not apply to older releases.
+
+Git Backport Workflow
+---------------------
+
+If you are working on a task that needs to be backported, only start the
+backporting process once the PR for main has been merged. Then:
+
+    * *Identify the commit(s) needed* for the backport. Start with the PR that merged
+      the commits into main and select only the commits from the issue being
+      backported.
+    * *Bring each commit into the new branch,* one at a time -- starting with the
+      oldest commit. Use ``git cherry-pick -x commit-hash``, where ``commit-hash``
+      is the hash to the commit already in main or main-8.0x that is being
+      backported, as it maintains the linkage with said cherry-picked commit.
+    * *Resolve conflicts:* Some of the cherry-picked commits may contain merge
+      conflicts. If the conflicts are small, include the corrections in the
+      cherry-picked commit.
+    * *Add additional commits*, if any are needed (e.g., to adjust cherry-picked code
+      to old behavior).
+
+.. Note:: Commit hashes
+
+   We have a CI check that ensures the validity of the cherry-pick line.
+
+.. Note:: Exceptions
+
+   Sometimes, the fix for main will not work for the stable or old releases.
+   In such cases, the backporting process won't be through cherry-picking, but
+   through actually implementing a fix for the specific version.
+
+Create a PR:
+~~~~~~~~~~~~
+
+Please indicate in the title that this is a backport PR, with something like
+*(8.0.x-backport)*, and add the related milestone label.
+
+In the PR description, indicate the backport ticket.
+
+QA
+--
+
+Add suricata-verify PRs when needed. Some existing suricata-verify tests may require
+version specification changes.

doc/userguide/devguide/codebase/contributing/contribution-process.rst

@@ -154,11 +154,12 @@ What branch to work on
 There are 2 or 3 active branches:
 
     * main-x.x.x (e.g. main-7.0.x)
+    * main-x.x.x (e.g. main-8.0.x)
     * main
 
-The former is a stable branch. The latter is the development branch.
+The first two are stable branches. The latter is the development branch.
 
-The stable branch should only be worked on for important bug fixes. Those are
+Stable branches should only be worked on for important bug fixes. Those are
 mainly expected from more experienced contributors.
 
 Development of new features or large scale redesign is done in the development

doc/userguide/devguide/codebase/contributing/index.rst

@@ -5,5 +5,6 @@ Contributing
     :maxdepth: 2
 
     contribution-process
+    backports-guide
     code-submission-process
     github-pr-workflow