MAINTAINERS: define the inactive CODEOWNERS policy

The policy defines inactivity (1 year without review activity), outlines
the removal process with notification periods, and provides templates
for issue notifications and removal PRs.
Also document the `check_inactive_codeowners.py` script usage for
identifying inactive members.

See #187 for more details.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Author: stefano-garzarella

MAINTAINERS.md

@@ -59,6 +59,161 @@ that are published to crates.io the release process includes publishing a new
 version. Ask one of the maintainers to give you permissions for the crate
 on crates.io.
 
+## Inactive CODEOWNERS Policy
+
+To maintain an accurate view of repository health and ensure an efficient PR
+review process, we have implemented a policy for managing inactive CODEOWNERS
+(see [issue #187](https://github.com/rust-vmm/community/issues/187) for
+details).
+
+### Inactivity Definition
+
+A CODEOWNER is considered inactive after **1 year** without any review activity
+(comments, approvals, etc.) in a repository.
+
+### Removal Process
+
+1. Regular checks (e.g. monthly) will identify CODEOWNERS who haven't been
+   active in a year
+2. An issue will be opened in the community repository tagging all inactive
+   CODEOWNERS
+3. After a 1-month notification period, inactive members will be gracefully
+   removed from the `CODEOWNERS` file
+4. The required number of approvals per PR should be adjusted to align with
+   the current number of active maintainers
+
+### Re-adding Removed CODEOWNERS
+
+Being removed from CODEOWNERS doesn't mean someone isn't wanted as a maintainer
+anymore. It's simply to keep track of how many active maintainers we have and
+monitor project health. Anyone removed can easily be re-added as a maintainer
+whenever they wish to become active again by:
+- Pinging the current maintainers, or
+- Opening a PR against the `CODEOWNERS` file to re-add themselves
+
+**Note:** The gatekeeper inactivity policy has been deferred until the monorepo
+migration is complete, at which point gatekeepers will be "codeowners for the
+repo root" and can be handled by this policy automatically.
+
+### Checking for Inactive CODEOWNERS
+
+The [rust-vmm-ci](https://github.com/rust-vmm/rust-vmm-ci/) repository contains
+the `codeowners/check_inactive_codeowners.py` script. It can help with the
+process of identifying inactive CODEOWNERS by checking their activity
+(PR reviews, PR/issue comments, and optionally commits) in one or more repositories.
+
+**Requirements:**
+- Python 3 with dependencies from `codeowners/requirements.txt` (install with `pip install -r codeowners/requirements.txt`)
+- GitHub personal access token (optional but recommended, set as `GITHUB_TOKEN` environment variable)
+
+**Basic usage:**
+```bash
+export GITHUB_TOKEN=your_token_here
+python codeowners/check_inactive_codeowners.py
+```
+
+**Common options:**
+- `--repos`: Comma-separated repository name(s) to check (if not specified, checks all repos in the organization)
+- `--org`: GitHub organization (default: rust-vmm)
+- `--days`: Number of days to check for activity (default: 365)
+- `--until`: End date for activity check in YYYY-MM-DD format (default: today)
+- `--verbose` or `-v`: Enable detailed debug output including API queries and individual activity found
+- `--include-commits`: Include commit count in activity check (default: only reviews and comments)
+
+The script will:
+1. Fetch all repositories from the organization (if `--repos` is not specified)
+2. Skip archived repositories
+3. Fetch the CODEOWNERS file from each repository (trying common locations)
+4. Skip repositories with no CODEOWNERS file or empty CODEOWNERS
+5. Extract individual GitHub usernames (team references are not supported)
+6. Check if users exist on GitHub
+7. Check each user's activity over the specified period (PR reviews, PR/issue comments, and optionally commits)
+8. Report inactive and non-existent users with a summary
+
+**Exit codes:**
+- `0`: All CODEOWNERS are active
+- `1`: There are inactive CODEOWNERS
+- `2`: Errors occurred while querying GitHub
+
+**Notes:**
+- The script uses PyGithub to efficiently batch GitHub API queries for checking activity.
+- Without a GitHub token, the script will work but slower due to lower
+  [rate limits](https://docs.github.com/en/rest/using-the-rest-api/rate-limits-for-the-rest-api)
+  (60 requests/hour vs 5000 requests/hour with authentication).
+- You can generate a token at https://github.com/settings/tokens
+
+### Notification Issue Template
+
+When inactive CODEOWNERS are identified, an issue should be created in the
+community repository using this template:
+
+```markdown
+Title: Inactive CODEOWNERS Notification - [Month Year]
+
+# Inactive CODEOWNERS Notification
+
+During our regular audit, we identified CODEOWNERS who haven't had any review
+activity (comments, approvals, etc.) in their respective repositories for over
+1 year.
+
+The following users are affected:
+
+@username1 @username2 @username3 ...
+
+## Next Steps
+
+According to our [Inactive CODEOWNERS Policy](https://github.com/rust-vmm/community/blob/main/MAINTAINERS.md#inactive-codeowners-policy):
+
+1. We will wait **1 month** from the date of this issue before proceeding with
+   any removals
+2. If you are still interested in maintaining your repository, please comment on
+   this issue or resume review activity
+3. If you are no longer able to maintain the repository, no action is needed -
+   we will proceed with the removal after the notification period
+4. You can be re-added as a CODEOWNER at any time in the future by pinging
+   current maintainers or opening a PR
+
+Being removed from CODEOWNERS doesn't mean you aren't wanted as a maintainer.
+It's simply to help us track active maintainers and adjust approval rules
+accordingly.
+
+If you have any questions or concerns, please comment below.
+
+**Removal Date:** [Date 1 month from issue creation]
+```
+
+### Removal PR Template
+
+After the notification period expires, a PR should be created to remove
+inactive CODEOWNERS using this template:
+
+```markdown
+Title: Remove inactive CODEOWNERS - [Month Year]
+
+# Remove Inactive CODEOWNERS
+
+This PR removes CODEOWNERS who have been inactive for over 1 year and were
+notified in https://github.com/rust-vmm/community/issues/[issue-number].
+
+## Changes
+
+- Removed inactive CODEOWNERS: @username1 @username2 @username3 ...
+- Adjusted PR approval requirements where needed to match the new number of
+  active maintainers
+
+## Notification
+
+All affected CODEOWNERS were notified on [date] via https://github.com/rust-vmm/community/issues/[issue-number]
+and given a 1-month period to respond.
+
+## Policy Reference
+
+This removal follows our [Inactive CODEOWNERS Policy](https://github.com/rust-vmm/community/blob/main/MAINTAINERS.md#inactive-codeowners-policy).
+
+Removed maintainers can be re-added at any time by opening a PR or pinging
+current maintainers.
+```
+
 ## The Gatekeeper Role
 
 The wider organization is managed by a team