tools: add script and CI workflow to sync stable-rc branches

Add sync_stable_branches.py which fetches kernel.org/releases.json
and updates config/trees/stable-rc.yaml with current stable and
longterm branches, removing any that have reached EOL.

Add GitHub Actions workflow that runs weekly to check for updates
and automatically creates a PR when changes are needed.

Signed-off-by: Ben Copeland <ben.copeland@linaro.org>

Author: bhcopeland

.github/workflows/sync-stable-branches.yml

@@ -0,0 +1,50 @@
+name: Sync stable-rc branches
+
+on:
+  schedule:
+    # Run weekly on Monday at 08:00 UTC
+    - cron: '0 8 * * 1'
+  workflow_dispatch:
+
+jobs:
+  sync:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+
+    steps:
+      - name: Check out source code
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Check for updates
+        id: check
+        run: |
+          python tools/sync_stable_branches.py --dry-run 2>&1 | tee output.txt
+          if grep -q "Config is already up to date" output.txt; then
+            echo "needs_update=false" >> $GITHUB_OUTPUT
+          else
+            echo "needs_update=true" >> $GITHUB_OUTPUT
+          fi
+
+      - name: Apply updates
+        if: steps.check.outputs.needs_update == 'true'
+        run: python tools/sync_stable_branches.py
+
+      - name: Create Pull Request
+        if: steps.check.outputs.needs_update == 'true'
+        uses: peter-evans/create-pull-request@v7
+        with:
+          commit-message: "config/trees: sync stable-rc with kernel.org"
+          title: "config/trees: sync stable-rc with kernel.org"
+          body: |
+            Automated sync of stable-rc.yaml with current kernel.org releases.
+
+            This PR was created automatically by the sync-stable-branches workflow.
+          branch: sync-stable-branches
+          delete-branch: true

tools/sync_stable_branches.py

@@ -0,0 +1,155 @@
+#!/usr/bin/env python3
+#
+# SPDX-License-Identifier: LGPL-2.1-or-later
+#
+# Copyright (C) 2026 Linaro Limited
+# Author: Ben Copeland <ben.copeland@linaro.org>
+#
+# Sync stable-rc.yaml with current kernel.org stable/longterm branches
+
+"""
+Fetch current stable and longterm kernel versions from kernel.org
+and update config/trees/stable-rc.yaml accordingly.
+"""
+
+import argparse
+import json
+import re
+import sys
+import urllib.request
+from pathlib import Path
+
+RELEASES_URL = "https://www.kernel.org/releases.json"
+CONFIG_PATH = Path(__file__).parent.parent / "config" / "trees" / "stable-rc.yaml"
+
+
+def fetch_releases():
+    """Fetch releases.json from kernel.org"""
+    with urllib.request.urlopen(RELEASES_URL, timeout=30) as response:
+        return json.loads(response.read().decode())
+
+
+def get_active_branches(releases_data):
+    """
+    Extract active (non-EOL) stable and longterm branch versions.
+    Returns sorted list of (major, minor) tuples.
+    """
+    branches = set()
+
+    for release in releases_data.get("releases", []):
+        moniker = release.get("moniker", "")
+        if moniker not in ("stable", "longterm"):
+            continue
+
+        if release.get("iseol", False):
+            continue
+
+        version = release.get("version", "")
+        match = re.match(r"^(\d+)\.(\d+)\.", version)
+        if match:
+            major, minor = int(match.group(1)), int(match.group(2))
+            branches.add((major, minor))
+
+    return sorted(branches)
+
+
+def generate_yaml(branches):
+    """Generate the stable-rc.yaml content"""
+    lines = ["build_configs:"]
+
+    for i, (major, minor) in enumerate(branches):
+        version_str = f"{major}.{minor}"
+        config_name = f"stable-rc_{version_str}"
+        branch_name = f"linux-{version_str}.y"
+
+        if i == 0:
+            # First entry defines the anchor
+            lines.append(f"  {config_name}: &stable-rc")
+            lines.append("    tree: stable-rc")
+            lines.append(f"    branch: '{branch_name}'")
+        else:
+            lines.append("")
+            lines.append(f"  {config_name}:")
+            lines.append("    <<: *stable-rc")
+            lines.append(f"    branch: '{branch_name}'")
+
+    lines.append("")
+    return "\n".join(lines)
+
+
+def parse_current_branches(config_path):
+    """Parse current branches from existing config file"""
+    if not config_path.exists():
+        return set()
+
+    branches = set()
+    content = config_path.read_text()
+
+    for match in re.finditer(r"branch:\s*'linux-(\d+)\.(\d+)\.y'", content):
+        major, minor = int(match.group(1)), int(match.group(2))
+        branches.add((major, minor))
+
+    return branches
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Sync stable-rc.yaml with kernel.org releases"
+    )
+    parser.add_argument(
+        "--dry-run", "-n",
+        action="store_true",
+        help="Show what would change without modifying the file"
+    )
+    parser.add_argument(
+        "--config",
+        type=Path,
+        default=CONFIG_PATH,
+        help=f"Path to stable-rc.yaml (default: {CONFIG_PATH})"
+    )
+    args = parser.parse_args()
+
+    print(f"Fetching releases from {RELEASES_URL}...")
+    try:
+        releases_data = fetch_releases()
+    except Exception as e:
+        print(f"Error fetching releases: {e}", file=sys.stderr)
+        return 1
+
+    active_branches = get_active_branches(releases_data)
+    if not active_branches:
+        print("Error: No active branches found", file=sys.stderr)
+        return 1
+
+    print(f"Active kernel.org branches: {', '.join(f'{m}.{n}' for m, n in active_branches)}")
+
+    current_branches = parse_current_branches(args.config)
+    print(f"Current config branches: {', '.join(f'{m}.{n}' for m, n in sorted(current_branches))}")
+
+    # Calculate differences
+    to_add = set(active_branches) - current_branches
+    to_remove = current_branches - set(active_branches)
+
+    if not to_add and not to_remove:
+        print("Config is already up to date.")
+        return 0
+
+    if to_add:
+        print(f"Branches to add: {', '.join(f'{m}.{n}' for m, n in sorted(to_add))}")
+    if to_remove:
+        print(f"Branches to remove (EOL): {', '.join(f'{m}.{n}' for m, n in sorted(to_remove))}")
+
+    new_content = generate_yaml(active_branches)
+
+    if args.dry_run:
+        print("\n--- New config (dry-run) ---")
+        print(new_content)
+        return 0
+
+    args.config.write_text(new_content)
+    print(f"Updated {args.config}")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())