From 0efbeddfb4ab1a9c0f1d18d73141b5fa3b5e23b1 Mon Sep 17 00:00:00 2001
From: Tiago Sousa <joao.sousa@eurotux.com>
Date: Fri, 10 Oct 2025 18:11:29 +0100
Subject: [PATCH] blockdev: add underlay resize

---
 src/PVE/QemuServer/Blockdev.pm | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/src/PVE/QemuServer/Blockdev.pm b/src/PVE/QemuServer/Blockdev.pm
index 55344784..3d78dcde 100644
--- a/src/PVE/QemuServer/Blockdev.pm
+++ b/src/PVE/QemuServer/Blockdev.pm
@@ -715,6 +715,24 @@ sub resize {
     );
 }
 
+sub underlay_resize {
+    my ($storecfg, $vmid, $drive_id, $volid) = @_;
+
+    my $running = PVE::QemuServer::Helpers::vm_running_locally($vmid);
+
+    # get backing_snap
+    my $snapshots = PVE::Storage::volume_snapshot_info($storecfg, $volid);
+    my $backing_snap = $snapshots->{current}->{parent};
+    my $size = PVE::Storage::volume_underlay_resize($storecfg, $volid, $backing_snap);
+
+    return if !$running;
+    my $block_info = get_block_info($vmid);
+    my $inserted = $block_info->{$drive_id}->{inserted}
+        or die "no block node inserted for drive '$drive_id'\n";
+
+    set_write_threshold($storecfg, $vmid, $drive_id, $volid);
+}
+
 my sub blockdev_change_medium {
     my ($storecfg, $vmid, $qdev_id, $drive) = @_;
 
@@ -851,7 +869,7 @@ sub block_set_write_threshold {
 sub compute_write_threshold {
     my ($storecfg, $scfg, $volid) = @_;
 
-    my $lv_size = PVE::Storage::volume_size_info($storecfg, $volid, 5);
+    my $lv_size = PVE::Storage::volume_underlay_size_info($storecfg, $volid, 5);
 
     my $write_threshold = $lv_size - $scfg->{chunksize} * (1 - $scfg->{'chunk-percentage'});