[RFC PATCH qemu-server 0/4] allow VMs to start with missing CD-ROM

[RFC PATCH qemu-server 0/4] allow VMs to start with missing CD-ROM

[Daniel Herzig]

Currently VMs refuse to start if a configured CD-ROM is unavailable for
a reason.

1) This is desirable if the CD-ROM is essential for the VM.
2) It can however can be inconvenient, if the CD-ROM was just used at
for initial guest installation (and later on 'forgotten').

If the corresponding ISO e.g. resided on a network share, connectivity
issues to the network share prohibit the VM to start.

This RFC addresses case 2. It allows users to set a parameter
'dismissable' for a drive. If set, and if the drive is a
CD-ROM, the CD-ROM will be removed from the VM configuration
in the case of unavailability. As a consequence, the VM can start.

The removal of the file from the configuration will be logged through
log_warn() to have a backtrace of the process.

The RFC addresses the backend-side of #4225 on bugzilla [0] and
supersedes [1], integrating the valuable on- and offline input
on the topic.

[0] https://bugzilla.proxmox.com/show_bug.cgi?id=4225
[1] https://lore.proxmox.com/pve-devel/20250130113121.157273-1-d.herzig@proxmox.com/

*** BLURB HERE ***

qemu-server: Daniel Herzig (4):
  drive: Introduce parameter to mark CD-ROM as dissmissable
  drive: ignore 'dismissable' parameter for everything but CD-ROMs
  introduce sub 'activate_current_vm_volumes'
  integrate new sub 'activate_current_vm_volumes'

 src/PVE/QemuServer.pm       | 75 ++++++++++++++++++++++++++++++++-----
 src/PVE/QemuServer/Drive.pm | 10 +++++
 2 files changed, 75 insertions(+), 10 deletions(-)

-- 
2.47.3

[RFC PATCH qemu-server 1/4] drive: Introduce parameter to mark CD-ROM as dissmissable

[Daniel Herzig]

Signed-off-by: Daniel Herzig <d.herzig@proxmox.com>
---
 src/PVE/QemuServer/Drive.pm | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/PVE/QemuServer/Drive.pm b/src/PVE/QemuServer/Drive.pm
index 10106ebd..8539a1d3 100644
--- a/src/PVE/QemuServer/Drive.pm
+++ b/src/PVE/QemuServer/Drive.pm
@@ -254,6 +254,14 @@ my %drivedesc_base = (
         optional => 1,
         default => 0,
     },
+     dismissable => {
+         type => 'boolean',
+         description => 'Mark CD-ROM as dismissable for starting the VM.',
+         verbose_description =>
+             'If set to 1, file will be removed from config if unavailable.',
+         optional => 1,
+         default => 0,
+    },
 );
 
 my %iothread_fmt = (
-- 
2.47.3

[RFC PATCH qemu-server 2/4] drive: ignore 'dismissable' parameter for everything but CD-ROMs

[Daniel Herzig]

Signed-off-by: Daniel Herzig <d.herzig@proxmox.com>
---
 src/PVE/QemuServer/Drive.pm | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/PVE/QemuServer/Drive.pm b/src/PVE/QemuServer/Drive.pm
index 8539a1d3..43f89aae 100644
--- a/src/PVE/QemuServer/Drive.pm
+++ b/src/PVE/QemuServer/Drive.pm
@@ -854,6 +854,8 @@ sub parse_drive {
     if ($res->{media} && ($res->{media} eq 'cdrom')) {
         return if $res->{snapshot} || $res->{format};
         return if $res->{interface} eq 'virtio';
+    } else {
+	return if $res->{dismissable};
     }
 
     if (my $size = $res->{size}) {
-- 
2.47.3

[RFC PATCH qemu-server 3/4] introduce sub 'activate_current_vm_volumes'

[Daniel Herzig]

Signed-off-by: Daniel Herzig <d.herzig@proxmox.com>
---
 src/PVE/QemuServer.pm | 54 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
index 09e7a19b..a7b98e01 100644
--- a/src/PVE/QemuServer.pm
+++ b/src/PVE/QemuServer.pm
@@ -6068,6 +6068,60 @@ sub get_current_vm_volumes {
     return $volumes;
 }
 
+=head3 activate_current_vm_volumes($storecfg, $conf, $vmid [, $statefile_volume])
+Activates VM volumes (With -blockdev, it is necessary to activate the volumes
+before generating the command line).
+
+NOTE: If $drive->{dismissable} is specified for a CD-ROM, C<$conf> may change.
+If $drive->{file} is unavailable, $drive->{file} will be set to 'none', and
+the entries $drive->{size} and $drive->{format} will be deleted.
+This will be written out to C<$conf>.
+
+=cut
+sub activate_current_vm_volumes {
+    my ($storecfg, $conf, $vmid, $statefile_volume, $storage_hints) = @_;
+    my $volumes_to_be_activated = [];
+    my $activated_volumes = [];
+
+    if ($statefile_volume) {
+	push $volumes_to_be_activated->@*, $statefile_volume;
+    }
+    PVE::QemuConfig->foreach_volume_full(
+        $conf,
+        { extra_keys => ['vmstate'] },
+        sub {
+            my ($ds, $drive) = @_;
+	    my $volid = $drive->{file};
+	    if (PVE::Storage::parse_volume_id($volid, 1)) {
+		check_volume_storage_type($storecfg, $volid);
+		if ($drive->{dismissable}) {
+		    eval { PVE::Storage::activate_volumes($storecfg, [$volid]) };
+		    if ($@) {
+			log_warn($@);
+			log_warn("removing dismissable CD-ROM from VM configuration: ". $volid);
+			$drive->{file} = "none";
+			delete $drive->{size};
+			delete $drive->{format};
+			$conf->{$ds} = print_drive($drive);
+			PVE::QemuConfig->write_config($vmid, $conf);
+		    } else {
+			push $activated_volumes->@*, $volid;
+		    }
+		} else {
+		    push $volumes_to_be_activated->@*, $volid;
+		}
+	    }
+	}
+    );
+    eval { PVE::Storage::activate_volumes($storecfg, $volumes_to_be_activated, undef, $storage_hints) };
+    if ($@) {
+	die $@;
+    } else {
+	push $activated_volumes->@*, $volumes_to_be_activated;
+    }
+    return $activated_volumes;
+}
+
 sub cleanup_pci_devices {
     my ($vmid, $conf) = @_;
 
-- 
2.47.3

[RFC PATCH qemu-server 4/4] integrate new sub 'activate_current_vm_volumes'

[Daniel Herzig]

Signed-off-by: Daniel Herzig <d.herzig@proxmox.com>
---
 src/PVE/QemuServer.pm | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
index a7b98e01..8b4510d6 100644
--- a/src/PVE/QemuServer.pm
+++ b/src/PVE/QemuServer.pm
@@ -5598,16 +5598,18 @@ sub vm_start_nolock {
         $state_cmdline = ['-S'];
     }
 
-    my $vollist = get_current_vm_volumes($storecfg, $conf);
-    push $vollist->@*, $statefile if $statefile_is_a_volume;
+    my $storage_hints = generate_storage_hints($conf, 1);
+    my $activated_vollist;
+    if ($statefile_is_a_volume) {
+	$activated_vollist = activate_current_vm_volumes($storecfg, $conf, $vmid, $statefile, $storage_hints);
+    } else {
+	$activated_vollist = activate_current_vm_volumes($storecfg, $conf, $vmid, undef, $storage_hints);
+    }
 
     my ($cmd, $spice_port, $start_timeout);
     my $pci_reserve_list = [];
     eval {
-        # With -blockdev, it is necessary to activate the volumes before generating the command line
         # Plugins can safely deactivate already-active volumes here if needed
-        my $storage_hints = generate_storage_hints($conf, 1);
-        PVE::Storage::activate_volumes($storecfg, $vollist, undef, $storage_hints);
 
         check_efi_vars($storecfg, $vmid, $conf) if $conf->{bios} && $conf->{bios} eq 'ovmf';
 
@@ -5673,7 +5675,7 @@ sub vm_start_nolock {
         push @$cmd, '-uuid', $uuid if defined($uuid);
     };
     if (my $err = $@) {
-        eval { PVE::Storage::deactivate_volumes($storecfg, $vollist); };
+        eval { PVE::Storage::deactivate_volumes($storecfg, $activated_vollist); };
         warn $@ if $@;
         eval { cleanup_pci_devices($vmid, $conf) };
         warn $@ if $@;
@@ -5804,7 +5806,7 @@ sub vm_start_nolock {
 
     if (my $err = $@) {
         # deactivate volumes if start fails
-        eval { PVE::Storage::deactivate_volumes($storecfg, $vollist); };
+        eval { PVE::Storage::deactivate_volumes($storecfg, $activated_vollist); };
         warn $@ if $@;
         eval { cleanup_pci_devices($vmid, $conf) };
         warn $@ if $@;
@@ -5994,12 +5996,11 @@ sub vm_commandline {
     my $defaults = load_defaults();
 
     my $running = PVE::QemuServer::Helpers::vm_running_locally($vmid);
-    my $volumes = [];
+    my $activated_volumes = [];
 
     # With -blockdev, it is necessary to activate the volumes before generating the command line
     if (!$running) {
-        $volumes = get_current_vm_volumes($storecfg, $conf);
-        PVE::Storage::activate_volumes($storecfg, $volumes);
+        $activated_volumes = activate_current_vm_volumes($storecfg, $conf);
     }
 
     # There might be concurrent operations on the volumes, so do not deactivate.
-- 
2.47.3