[PATCH qemu-server 1/2] drive device: use configured serial as SCSI device ID

["Michael Köppl" <m.koeppl@proxmox.com>]

Since the switch to '-blockdev', the device ID of SCSI disks is
explicitly set to the drive name, even if serial is configured. So with
machine version 10.0 or newer, a SCSI disk with a serial reports the
drive name (e.g. 'drive-scsi1') and the /dev/disk/by-id paths that udev
derives from it no longer contain the serial. In a guest running Proxmox
VE, the disk list API endpoint (/nodes/<node>/disks/list) therefore does
not report the configured serial either.

Set the device ID explicitly to the serial if one is configured, like
libvirt does since its switch to '-blockdev' [0]. For serials of up to
20 bytes, this is the same device ID that QEMU used by default with
'-drive'.

Relying on QEMU's default instead would not work for all serials. QEMU
accepts serials of up to 36 bytes [1], but only uses serials of up to
20 bytes as the default device ID and refuses to start the device for
longer ones instead of truncating them [2][3].

As this changes what the guest sees, only do so starting with machine
version 11.1+pve1. Check it with the version guard, so that only VMs
with a SCSI disk with a serial require the new revision.

[0]: https://gitlab.com/libvirt/libvirt/-/commit/a1dce96236f6d35167924fa7e6a70f58f394b23c
[1]: https://lists.gnu.org/archive/html/qemu-stable/2016-09/msg00117.html
[2]: https://lists.gnu.org/archive/html/qemu-block/2024-06/msg00027.html
[3]: https://github.com/systemd/systemd/issues/39262

Fixes: 46d1225e ("drive device: fix regression with missing '/dev/disk/by-id' paths")

Signed-off-by: Michael Köppl <m.koeppl@proxmox.com>
---
Added a machine version 11.1+pve1 specifically for this. If it makes
more sense to wait for 11.2, considering this is not an urgent issue,
I'll of course send a v2. Should be a bit simpler to implement anyway.

 src/PVE/QemuServer.pm             |  7 ++++---
 src/PVE/QemuServer/DriveDevice.pm | 22 +++++++++++++++++++---
 src/PVE/QemuServer/Machine.pm     |  6 ++++++
 3 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
index 1efeeb66..36471bdf 100644
--- a/src/PVE/QemuServer.pm
+++ b/src/PVE/QemuServer.pm
@@ -3686,9 +3686,10 @@ sub config_to_command {
                 push @$devices, '-drive', $drive_cmd;
             }

-            push @$devices, '-device', print_drivedevice_full(
-                $storecfg, $conf, $vmid, $drive, $arch, $machine_type,
-            );
+            push @$devices, '-device',
+                print_drivedevice_full(
+                    $storecfg, $conf, $vmid, $drive, $arch, $machine_type, $version_guard,
+                );
         },
     );

diff --git a/src/PVE/QemuServer/DriveDevice.pm b/src/PVE/QemuServer/DriveDevice.pm
index 621fcc2b..980a217a 100644
--- a/src/PVE/QemuServer/DriveDevice.pm
+++ b/src/PVE/QemuServer/DriveDevice.pm
@@ -69,13 +69,23 @@ sub get_max_scsihw_index {
 }

 sub print_drivedevice_full {
-    my ($storecfg, $conf, $vmid, $drive, $arch, $machine_type) = @_;
+    my (
+        $storecfg,
+        $conf,
+        $vmid,
+        $drive,
+        $arch,
+        $machine_type,
+        $version_guard, # checks the machine version and records the required +pveX revision
+    ) = @_;

     my $device = '';
     my $maxdev = 0;

     my $machine_version =
         PVE::QemuServer::Machine::extract_version($machine_type, kvm_user_version());
+    # when hotplugging, the machine is already running, so there is no required version to record
+    $version_guard //= sub { return min_version($machine_version, @_); };
     my $has_write_cache = 1; # whether the device has a 'write-cache' option

     my $use_blockdev = min_version($machine_version, 10, 0);
@@ -112,9 +122,15 @@ sub print_drivedevice_full {
         $device .= ",id=$drive_id";

         # For the switch to -blockdev, the SCSI device ID needs to be explicitly specified. Note
-        # that only ide-cd and ide-hd have a 'device_id' option.
+        # that only ide-cd and ide-hd have a 'device_id' option. Since machine version 11.1+pve1,
+        # a configured serial is used as the device ID, like QEMU's default with -drive.
         if ($use_blockdev && ($device_type eq 'cd' || $device_type eq 'hd')) {
-            $device .= ",device_id=drive-${drive_id}";
+            if ($drive->{serial} && $version_guard->(11, 1, 1)) {
+                my $serial = _escape_qemu_arg_value(URI::Escape::uri_unescape($drive->{serial}));
+                $device .= ",device_id=$serial";
+            } else {
+                $device .= ",device_id=drive-${drive_id}";
+            }
         }

         if ($drive->{ssd} && ($device_type eq 'block' || $device_type eq 'hd')) {
diff --git a/src/PVE/QemuServer/Machine.pm b/src/PVE/QemuServer/Machine.pm
index 35161d1f..68cc5daf 100644
--- a/src/PVE/QemuServer/Machine.pm
+++ b/src/PVE/QemuServer/Machine.pm
@@ -50,6 +50,12 @@ our $PVE_MACHINE_VERSION = {
             '+pve2' => 'Enable hv_emcs for Windows 11/2022/2025 to mitigate issues with VBS.',
         },
     },
+    '11.1' => {
+        highest => 1,
+        revisions => {
+            '+pve1' => 'Use the configured serial as device ID for SCSI disks.',
+        },
+    },
 };

 my $machine_fmt = {
--
2.47.3