From c9dbcd73b9c999b6939b86acaa36ce3bb25a6b55 Mon Sep 17 00:00:00 2001
From: MickLesk <47820557+MickLesk@users.noreply.github.com>
Date: Thu, 8 Oct 2026 09:57:20 +0200
Subject: [PATCH] Remember a kept cached image until the upstream changes

Keep cached was asked on every run once the mirror had rebuilt an image. The answer is now stored in <file>.keep with the upstream checksum, and the question returns only when that checksum changes; a download removes the marker.
---
 pve/vm-core.func    | 16 ++++++++++++++--
 tests/vm-helpers.sh | 17 +++++++++++++++++
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/pve/vm-core.func b/pve/vm-core.func
index 85381b2..330c7df 100644
--- a/pve/vm-core.func
+++ b/pve/vm-core.func
@@ -1678,7 +1678,9 @@ vm_image_cache_path() {
 
 # A cached image that no longer matches usually means the upstream was rebuilt,
 # not that anything is wrong. Offer the choice instead of silently re-downloading
-# several hundred MB. Unattended or without a terminal, take the new one.
+# several hundred MB. Unattended or without a terminal, take the new one. A
+# "Keep cached" answer is remembered in <file>.keep with the upstream checksum
+# it was given against, so the question returns only when the upstream changes.
 _vm_cache_choice() {
   local file="$1" url="$2" local_size local_date remote_size remote_date head
 
@@ -1742,13 +1744,23 @@ vm_fetch_image() {
   fi
 
   if [[ "$cache" == yes && -e "$target" ]]; then
+    local keep="${target}.keep"
     if _vm_image_ok "$target" "$exact_bytes" "$min_bytes" "$sha_tool" "$sha_want" "$xz"; then
+      rm -f "$keep"
       msg_ok "Using cached ${CL}${BL}$(basename "$target")${CL}"
       return 0
     fi
+    if [[ -n "$sha_want" && -f "$keep" && "$(<"$keep")" == "${sha_tool}:${sha_want}" ]]; then
+      msg_ok "Using cached ${CL}${BL}$(basename "$target")${CL} (kept; the upstream has not changed)"
+      return 0
+    fi
     if _vm_cache_choice "$target" "$url"; then
       msg_warn "Replacing the cached $(basename "$target")"
-      rm -f "$target"
+      rm -f "$target" "$keep"
+    elif [[ -n "$sha_want" ]]; then
+      printf '%s' "${sha_tool}:${sha_want}" >"$keep"
+      msg_ok "Using cached ${CL}${BL}$(basename "$target")${CL} (kept until the upstream changes)"
+      return 0
     else
       msg_ok "Using cached ${CL}${BL}$(basename "$target")${CL}"
       return 0
diff --git a/tests/vm-helpers.sh b/tests/vm-helpers.sh
index c6fa09f..7205b71 100644
--- a/tests/vm-helpers.sh
+++ b/tests/vm-helpers.sh
@@ -182,6 +182,23 @@ vm_fetch_image "https://dl.test/openwrt.img.gz" "$TEST_DIR/cache/nosums.img" --c
 assert_contains "$WARNINGS" "checking the size only"
 ok "digest case is ignored; missing checksum list warns and continues"
 
+CHOICE_CALLS="$TEST_DIR/choice-calls"
+: >"$CHOICE_CALLS"
+_vm_cache_choice() { echo keep >>"$CHOICE_CALLS"; return 1; }
+KEPT="$TEST_DIR/cache/kept.img"
+mkdir -p "$TEST_DIR/cache" && printf 'old build\n' >"$KEPT"
+vm_fetch_image "https://dl.test/openwrt.img.gz" "$KEPT" --cache --sha256 "$IMAGE_SHA256" || fail "keep cached"
+[[ -f "$KEPT.keep" ]] || fail "a kept cache gets a marker"
+vm_fetch_image "https://dl.test/openwrt.img.gz" "$KEPT" --cache --sha256 "$IMAGE_SHA256" || fail "kept cache reused"
+assert_eq "$(grep -c keep "$CHOICE_CALLS")" 1 "asked once while the upstream is unchanged"
+vm_fetch_image "https://dl.test/openwrt.img.gz" "$KEPT" --cache --sha256 "$(printf '%064d' 1)" || fail "keep again after a change"
+assert_eq "$(grep -c keep "$CHOICE_CALLS")" 2 "asked again once the upstream changed"
+_vm_cache_choice() { return 0; }
+vm_fetch_image "https://dl.test/openwrt.img.gz" "$KEPT" --cache --sha256 "$IMAGE_SHA256" || fail "replace cached"
+[[ ! -f "$KEPT.keep" ]] || fail "the marker goes with the replaced file"
+assert_eq "$(sha256sum "$KEPT" | cut -d' ' -f1)" "$IMAGE_SHA256" "fresh download in place"
+ok "a kept cache is reused until the upstream checksum changes"
+
 # ── vm_import_disk ──────────────────────────────────────────────────────────
 VMID=100
 QM_MODERN=yes