[PATCH qemu-server] fix #4012: migrate: mention snapshots referencing a local ISO image

[Michal Fox <me@dualfroz.com>]

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.

Signed-off-by: Michal Fox <me@dualfroz.com>
---
Tested with a new migration test for an ISO image on local storage
that is only referenced in a snapshot. Without the fix, the error does
not contain the snapshot name. The whole qemu-server test suite passes.

The test needed the ISO in the mocked volume list and 'iso' content on
the mocked 'local' storage.

The GUI still only shows 'Cannot migrate VM with local CD/DVD' in that
case, which could be done as a follow-up in pve-manager.

 src/PVE/QemuMigrate.pm             | 14 ++++-----
 src/test/run_qemu_migrate_tests.pl | 47 ++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 7 deletions(-)

diff --git a/src/PVE/QemuMigrate.pm b/src/PVE/QemuMigrate.pm
index 8da6f15d..a9b69898 100644
--- a/src/PVE/QemuMigrate.pm
+++ b/src/PVE/QemuMigrate.pm
@@ -412,15 +412,15 @@ 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);
+                $snapshot_hint = " (referenced in snapshot - $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 +475,7 @@ 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 05eed1d9..49248ed9 100755
--- 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",
@@ -346,6 +347,17 @@ my $source_vdisks = {
             'volid' => 'local-dir:4567/vm-4567-state-snap2.raw',
         },
     ],
+    'local' => [
+        {
+            'ctime' => 1589439681,
+            'format' => 'iso',
+            'parent' => undef,
+            'size' => 663748608,
+            'used' => 663748608,
+            'vmid' => '0',
+            'volid' => 'local:iso/debian.iso',
+        },
+    ],
     'local-lvm' => [
         {
             'ctime' => '1589277334',
@@ -1236,6 +1248,41 @@ 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',
-- 
2.43.0