[PATCH pve-network 08/10] debian: handle user modifications to FRR templates via ucf

[Gabriel Goller <g.goller@proxmox.com>]

This ensures that user customizations to frr jinja templates in
/etc/proxmox-frr/templates/ are preserved across package updates through
ucf's three-way merge, preventing silent overwrites of local changes.
When a user has customized a template and updates this package which
ships a new template version, ucf shows a three-way merge dialog
(ncurses) allowing them to view the differences and choose between the
maintainer's version, their version, or manually edit the merge result.

Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
---
 debian/control                      |  1 +
 debian/libpve-network-perl.postinst | 34 ++++++++++++++++++++++++++++-
 debian/libpve-network-perl.postrm   | 33 ++++++++++++++++++++++++++++
 3 files changed, 67 insertions(+), 1 deletion(-)
 create mode 100644 debian/libpve-network-perl.postrm

diff --git a/debian/control b/debian/control
index 6fe98822e64c..83ddfc053048 100644
--- a/debian/control
+++ b/debian/control
@@ -29,6 +29,7 @@ Depends: libpve-common-perl (>= 9.1.1),
          libnetaddr-ip-perl,
          libpve-rs-perl (>= 0.11.1),
          libuuid-perl,
+         ucf,
          ${misc:Depends},
          ${perl:Depends},
 Recommends: frr-pythontools (>= 10.3.1-1+pve2~),
diff --git a/debian/libpve-network-perl.postinst b/debian/libpve-network-perl.postinst
index 99faedf48f56..629c5bdc9e18 100644
--- a/debian/libpve-network-perl.postinst
+++ b/debian/libpve-network-perl.postinst
@@ -2,6 +2,36 @@
 
 set -e
 
+TEMPLATE_OVERRIDE_DIR="/etc/proxmox-frr/templates"
+
+update_override_frr_templates() {
+  for override_file in "$TEMPLATE_OVERRIDE_DIR"/*; do
+    # only consider files ending in .jinja. we often have .ucf-old files as
+    # well storing the previous ucf decision.
+    case "$override_file" in
+      *.jinja)
+        ;;
+      *)
+        continue
+        ;;
+    esac
+
+    filename=$(basename "$override_file")
+
+    temp_packaged_file=$(mktemp)
+
+    # we want to embed the variable now, not when the trap is executed
+    # shellcheck disable=SC2064
+    trap "rm -f -- '$temp_packaged_file'" EXIT
+
+    if pvesdn template show "$filename" > "$temp_packaged_file"; then
+      ucf --three-way --debconf-ok "$temp_packaged_file" "$override_file"
+    fi
+
+    ucfr libpve-network-perl "$override_file"
+  done
+}
+
 migrate_ipam_db() {
   LEGACY_IPAM_DB_FILE="/etc/pve/priv/ipam.db"
   IPAM_DB_FILE="/etc/pve/sdn/pve-ipam-state.json"
@@ -29,7 +59,9 @@ case "$1" in
       migrate_ipam_db
       migrate_mac_cache
     fi
-  ;;
+
+    update_override_frr_templates
+    ;;
 esac
 
 exit 0
diff --git a/debian/libpve-network-perl.postrm b/debian/libpve-network-perl.postrm
new file mode 100644
index 000000000000..5a1c6834111b
--- /dev/null
+++ b/debian/libpve-network-perl.postrm
@@ -0,0 +1,33 @@
+#!/bin/bash
+set -e
+
+TEMPLATE_OVERRIDE_DIR="/etc/proxmox-frr/templates"
+
+case "$1" in
+    purge)
+        # Remove ucf registrations on purge
+        if [ -d "$TEMPLATE_OVERRIDE_DIR" ]; then
+            for package_file in "$TEMPLATE_OVERRIDE_DIR"/*; do
+                [ -e "$package_file" ] || continue
+
+                filename=$(basename "$package_file")
+                target_file="$TEMPLATE_OVERRIDE_DIR/$filename"
+
+                ucf --purge "$target_file" 2>/dev/null || true
+                ucfr --purge libpve-network-perl "$target_file" 2>/dev/null || true
+            done
+        fi
+        ;;
+
+    remove|upgrade|failed-upgrade|abort-install|abort-upgrade|disappear)
+        ;;
+
+    *)
+        echo "postrm called with unknown argument \`$1'" >&2
+        exit 1
+        ;;
+esac
+
+#DEBHELPER#
+
+exit 0
-- 
2.47.3