From df951c01ebd89bac53d50fa62fbc6a65d3914d40 Mon Sep 17 00:00:00 2001
From: Michal Fox <me@dualfroz.com>
Date: Thu, 8 Oct 2026 09:46:50 +0000
Subject: [PATCH] partially fix #4012: migrate: mention snapshots referencing a
 local ISO image

When a VM has no local ISO image attached anymore, but one of its
snapshots still references it, migration fails with:

  can't migrate local disk 'local:iso/debian.iso': local cdrom image

which does not tell where the image is coming from, since it is not
visible in the current configuration of the VM.

Add the names of the snapshots referencing the image to the error in
that case, like it is already done for a physical CD/DVD drive. The
check for the physical drive now reuses the same hint, which also
uses the plural form if more than one snapshot references it.

Add a migration test with an ISO image on the 'local' storage that is
only referenced in a snapshot. This requires the 'iso' content type
for the 'local' storage in the test.

Signed-off-by: Michal Fox <me@dualfroz.com>
Link: https://lore.proxmox.com/20261008094650.7-3-me@dualfroz.com
[FE: note that it's a partial fix as the UI still needs to be improved]
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 src/PVE/QemuMigrate.pm             | 15 ++++-----
 src/test/run_qemu_migrate_tests.pl | 49 +++++++++++++++++++++++++++++-
 2 files changed, 56 insertions(+), 8 deletions(-)

diff --git a/src/PVE/QemuMigrate.pm b/src/PVE/QemuMigrate.pm
index 8da6f15..6605f5d 100644
--- a/src/PVE/QemuMigrate.pm
+++ b/src/PVE/QemuMigrate.pm
@@ -412,15 +412,16 @@ sub scan_local_volumes {
             }
 
             my $snaprefs = $attr->{referenced_in_snapshot};
+            my $snapshot_hint = '';
+            if (defined($snaprefs) && !$attr->{is_attached}) {
+                my $snapnames = join(', ', sort keys %$snaprefs);
+                my $plural = scalar(keys %$snaprefs) > 1 ? 's' : '';
+                $snapshot_hint = " (referenced in snapshot$plural - $snapnames)";
+            }
 
             if ($attr->{cdrom}) {
                 if ($volid eq 'cdrom') {
-                    my $msg = "can't migrate local cdrom drive";
-                    if (defined($snaprefs) && !$attr->{is_attached}) {
-                        my $snapnames = join(', ', sort keys %$snaprefs);
-                        $msg .= " (referenced in snapshot - $snapnames)";
-                    }
-                    &$log_error("$msg\n");
+                    &$log_error("can't migrate local cdrom drive$snapshot_hint\n");
                     return;
                 }
                 return if $volid eq 'none';
@@ -475,7 +476,7 @@ sub scan_local_volumes {
                     $local_volumes->{$volid}->{ref} = 'generated';
                     return;
                 }
-                die "local cdrom image\n";
+                die "local cdrom image$snapshot_hint\n";
             }
 
             my ($path, $owner) = PVE::Storage::path($storecfg, $volid);
diff --git a/src/test/run_qemu_migrate_tests.pl b/src/test/run_qemu_migrate_tests.pl
index 9f4cef6..fc2f137 100644
--- a/src/test/run_qemu_migrate_tests.pl
+++ b/src/test/run_qemu_migrate_tests.pl
@@ -37,6 +37,7 @@ my $storage_config = {
         local => {
             content => {
                 images => 1,
+                iso => 1,
             },
             path => "/var/lib/vz",
             type => "dir",
@@ -438,7 +439,18 @@ my $source_vdisks = {
 
 # Non-image volumes on the source, e.g. ISO images, with the same structure as $source_vdisks. They
 # are only used for the mocked volume_size_info(), because vdisk_list() only returns images.
-my $source_other_volumes = {};
+my $source_other_volumes = {
+    'local' => [
+        {
+            'ctime' => 1589439681,
+            'format' => 'iso',
+            'parent' => undef,
+            'size' => 663748608,
+            'used' => 663748608,
+            'volid' => 'local:iso/debian.iso',
+        },
+    ],
+};
 
 my $default_expected_calls_online = {
     move_config_to_node => 1,
@@ -1240,6 +1252,41 @@ my $tests = [
             },
         },
     },
+    {
+        name => '105_local_iso_in_snapshot',
+        target => 'pve1',
+        vmid => 105,
+        vm_status => {
+            running => 0,
+        },
+        config_patch => {
+            snapshots => {
+                ohsnap => {
+                    ide2 => 'local:iso/debian.iso,media=cdrom',
+                },
+            },
+        },
+        expected_calls => {},
+        expect_die => "can't migrate local disk 'local:iso/debian.iso': local cdrom image"
+            . " (referenced in snapshot - ohsnap)",
+        expected => {
+            source_volids => local_volids_for_vm(105),
+            target_volids => {},
+            vm_config => get_patched_config(
+                105,
+                {
+                    snapshots => {
+                        ohsnap => {
+                            ide2 => 'local:iso/debian.iso,media=cdrom',
+                        },
+                    },
+                },
+            ),
+            vm_status => {
+                running => 0,
+            },
+        },
+    },
     {
         name => '105_cdrom',
         target => 'pve1',