[PATCH-SERIES qemu-server 0/2] hotplug pending: only issue QMP commands related to USB hotplug if actually needed

[PATCH-SERIES qemu-server 0/2] hotplug pending: only issue QMP commands related to USB hotplug if actually needed

[Fiona Ebner]

There is a report in the enterprise support about Veeam failing to set
the 'lock' property in the VM configuration, because they are blocking
the QMP socket. The proper fix would be for them to not block the QMP
socket (at least not while interacting with our API), but there still
is an improvement to be made on the Proxmox VE side, which is to avoid
doing QMP commands related to USB hotplug if they are not actually
needed.

qemu-server:

Fiona Ebner (2):
  hotplug pending: only check if USB devices are left when one was
    unplugged
  hotplug pending: only check for USB hoptplug support when actually
    needed

 src/PVE/QemuServer.pm | 41 ++++++++++++++++++++++++++++++-----------
 1 file changed, 30 insertions(+), 11 deletions(-)


Summary over all repositories:
  1 files changed, 30 insertions(+), 11 deletions(-)

-- 
Generated by git-murpp 0.5.0

[PATCH qemu-server 1/2] hotplug pending: only check if USB devices are left when one was unplugged

[Fiona Ebner]

The call to unplug the 'xhci' controller would happen each time as
part of the vmconfig_hotplug_pending() call as long as the VM did not
have any USB devices and as long as it had a new enough version to
support USB hotplug, even if the actual changes have nothing to do
with USB.

Only check if there are any USB devices left if one was unplugged. In
particular, this avoid issuing superfluous QMP commands (via
vm_devices_list()) to check for the presence of the 'xhci' controller
for unrelated changes.

Previously, if an 'xhci' was added as part of a failing USB hotplug in
qemu_usb_hotplug(), it would be removed again implicitly by the check
at the end of vmconfig_hotplug_pending() that is now guarded. Add
explicitly error handling to remove the added 'xhci' controller again
in the error handling case in qemu_usb_hotplug() to avoid a left-over.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 src/PVE/QemuServer.pm | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
index 5acd1ac8..26560122 100644
--- a/src/PVE/QemuServer.pm
+++ b/src/PVE/QemuServer.pm
@@ -4245,15 +4245,26 @@ sub qemu_usb_hotplug {
     vm_deviceunplug($vmid, $conf, $deviceid);
 
     # check if xhci controller is necessary and available
+    my $added_xhci;
     my $devicelist = vm_devices_list($vmid);
 
     if (!$devicelist->{xhci}) {
         my $pciaddr = print_pci_addr("xhci", undef, $arch);
         qemu_deviceadd($vmid, PVE::QemuServer::USB::print_qemu_xhci_controller($pciaddr));
+        $added_xhci = 1;
     }
 
     # add the new one
-    vm_deviceplug($storecfg, $conf, $vmid, $deviceid, $device, $arch, $machine_type);
+    eval { vm_deviceplug($storecfg, $conf, $vmid, $deviceid, $device, $arch, $machine_type); };
+    if (my $err = $@) {
+        if ($added_xhci) {
+            eval { vm_deviceunplug($vmid, $conf, 'xhci'); };
+            warn "failed to unplug xhci controller - $@" if $@;
+        }
+        die $err;
+    }
+
+    return;
 }
 
 sub qemu_cpu_hotplug {
@@ -4650,6 +4661,7 @@ sub vmconfig_hotplug_pending {
     my $version = extract_version($machine_type, get_running_qemu_version($vmid));
     my $hotplug_features =
         parse_hotplug_features(defined($conf->{hotplug}) ? $conf->{hotplug} : '1');
+    my $usb_was_unplugged = 0;
     my $usb_hotplug =
         $hotplug_features->{usb}
         && min_version($version, 7, 1)
@@ -4680,6 +4692,7 @@ sub vmconfig_hotplug_pending {
                 die "skip\n" if !$usb_hotplug;
                 vm_deviceunplug($vmid, $conf, "usbredirdev$index"); # if it's a spice port
                 vm_deviceunplug($vmid, $conf, $opt);
+                $usb_was_unplugged = 1;
             } elsif ($opt eq 'vcpus') {
                 die "skip\n" if !$hotplug_features->{cpu};
                 qemu_cpu_hotplug($vmid, $conf, undef);
@@ -4852,7 +4865,7 @@ sub vmconfig_hotplug_pending {
     }
 
     # unplug xhci controller if no usb device is left
-    if ($usb_hotplug) {
+    if ($usb_was_unplugged) {
         my $has_usb = 0;
         for (my $i = 0; $i < $PVE::QemuServer::USB::MAX_USB_DEVICES; $i++) {
             next if !defined($conf->{"usb$i"});
-- 
2.47.3

[PATCH qemu-server 2/2] hotplug pending: only check for USB hoptplug support when actually needed

[Fiona Ebner]

In particular, this makes the variables $ostype and $version more
local and, for VMs without and explicit machine version, avoids a
'query-version' QMP call when not actually needed.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 src/PVE/QemuServer.pm | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
index 26560122..da2379e0 100644
--- a/src/PVE/QemuServer.pm
+++ b/src/PVE/QemuServer.pm
@@ -4657,16 +4657,22 @@ sub vmconfig_hotplug_pending {
         PVE::QemuConfig->write_config($vmid, $conf);
     }
 
-    my $ostype = $conf->{ostype};
-    my $version = extract_version($machine_type, get_running_qemu_version($vmid));
     my $hotplug_features =
         parse_hotplug_features(defined($conf->{hotplug}) ? $conf->{hotplug} : '1');
+
+    my $usb_hotplug;
     my $usb_was_unplugged = 0;
-    my $usb_hotplug =
-        $hotplug_features->{usb}
-        && min_version($version, 7, 1)
-        && defined($ostype)
-        && ($ostype eq 'l26' || windows_version($ostype) > 7);
+    my $is_usb_hotplug_supported = sub {
+        return $usb_hotplug if defined($usb_hotplug);
+        my $ostype = $conf->{ostype};
+        my $version = extract_version($machine_type, get_running_qemu_version($vmid));
+        $usb_hotplug =
+            $hotplug_features->{usb}
+            && min_version($version, 7, 1)
+            && defined($ostype)
+            && ($ostype eq 'l26' || windows_version($ostype) > 7) ? 1 : 0;
+        return $usb_hotplug;
+    };
 
     my $cgroup = PVE::QemuServer::CGroup->new($vmid);
     my $pending_delete_hash = PVE::QemuConfig->parse_pending_delete($conf->{pending}->{delete});
@@ -4689,7 +4695,7 @@ sub vmconfig_hotplug_pending {
                 }
             } elsif ($opt =~ m/^usb(\d+)$/) {
                 my $index = $1;
-                die "skip\n" if !$usb_hotplug;
+                die "skip\n" if !$is_usb_hotplug_supported->();
                 vm_deviceunplug($vmid, $conf, "usbredirdev$index"); # if it's a spice port
                 vm_deviceunplug($vmid, $conf, $opt);
                 $usb_was_unplugged = 1;
@@ -4760,7 +4766,7 @@ sub vmconfig_hotplug_pending {
                 }
             } elsif ($opt =~ m/^usb(\d+)$/) {
                 my $index = $1;
-                die "skip\n" if !$usb_hotplug;
+                die "skip\n" if !$is_usb_hotplug_supported->();
                 my $d = eval { parse_property_string('pve-qm-usb', $value) };
                 my $id = $opt;
                 if ($d->{host} =~ m/^spice$/i) {
-- 
2.47.3

Re: [PATCH-SERIES qemu-server 0/2] hotplug pending: only issue QMP commands related to USB hotplug if actually needed

[Manuel Federanko]

On 2026-03-30 1:09 PM, Fiona Ebner wrote:
> There is a report in the enterprise support about Veeam failing to set
> the 'lock' property in the VM configuration, because they are blocking
> the QMP socket. The proper fix would be for them to not block the QMP
> socket (at least not while interacting with our API), but there still
> is an improvement to be made on the Proxmox VE side, which is to avoid
> doing QMP commands related to USB hotplug if they are not actually
> needed.
> 
> qemu-server:
> 
> Fiona Ebner (2):
>   hotplug pending: only check if USB devices are left when one was
>     unplugged
>   hotplug pending: only check for USB hoptplug support when actually
>     needed
> 
>  src/PVE/QemuServer.pm | 41 ++++++++++++++++++++++++++++++-----------
>  1 file changed, 30 insertions(+), 11 deletions(-)
> 
> 
> Summary over all repositories:
>   1 files changed, 30 insertions(+), 11 deletions(-)
> 

Thanks!

Tested this by blocking the QMP socket and acquiring a lock on the
guest afterwards, also tried to add a USB device while blocking the
socket, which times out as expected.

Tested-by: Manuel Federanko <m.federanko@proxmox.com>

applied: [PATCH-SERIES qemu-server 0/2] hotplug pending: only issue QMP commands related to USB hotplug if actually needed

[Thomas Lamprecht]

On Mon, 30 Mar 2026 13:09:42 +0200, Fiona Ebner wrote:
> There is a report in the enterprise support about Veeam failing to set
> the 'lock' property in the VM configuration, because they are blocking
> the QMP socket. The proper fix would be for them to not block the QMP
> socket (at least not while interacting with our API), but there still
> is an improvement to be made on the Proxmox VE side, which is to avoid
> doing QMP commands related to USB hotplug if they are not actually
> needed.
> 
> [...]

Applied, thanks!

[1/2] hotplug pending: only check if USB devices are left when one was unplugged
      commit: a23bab5178ecbe2df7d6d425bbd5e0a7005b8c7e
[2/2] hotplug pending: only check for USB hoptplug support when actually needed
      commit: ebe5f14c50d938a654eebf72a1bfb006caeceaff