[pve-devel] [PATCH qemu-server 1/1] fix #5779: vm start: pass storage hints when activating guest volumes

[Friedrich Weber]

Currently supported hints are

- 'guest-is-windows' to denote a Windows guest,
- 'plugin-may-deactivate-volume' which denotes that the plugin may
  deactivate and re-activate a volume to apply a hint.

Currently the only consumer of hints is the RBD plugin. In case a
Windows VM guest volume is mapped using KRBD, certain VM workloads may
cause degraded performance and e.g. "libceph: [...] bad crc/signature"
messages in the host journal. A workaround is to pass the rxbounce
option when mapping the volume [1]. If 'guest-is-windows' is set to 1,
the RBD plugin will map the guest volume with the rxbounce option.

[1] https://docs.ceph.com/en/squid/man/8/rbd/#kernel-rbd-krbd-options

Signed-off-by: Friedrich Weber <f.weber at proxmox.com>
---
 src/PVE/QemuServer.pm | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
index cf195ccc..17ddd39b 100644
--- a/src/PVE/QemuServer.pm
+++ b/src/PVE/QemuServer.pm
@@ -5363,6 +5363,21 @@ my sub remove_left_over_vmstate_opts {
     PVE::QemuConfig->write_config($vmid, $conf) if $found;
 }
 
+sub generate_storage_hints {
+    my ($conf, $plugin_may_deactivate_volume) = @_;
+
+    my $hints = {};
+
+    if (PVE::Storage::Plugin::is_hint_supported('guest-is-windows')) {
+        $hints->{'guest-is-windows'} = int(!!windows_version($conf->{ostype}));
+    }
+    if (PVE::Storage::Plugin::is_hint_supported('plugin-may-deactivate-volume')) {
+        $hints->{'plugin-may-deactivate-volume'} = $plugin_may_deactivate_volume || 0;
+    }
+
+    return $hints;
+}
+
 # see vm_start_nolock for parameters, additionally:
 # migrate_opts:
 #   storagemap = parsed storage map for allocating NBD disks
@@ -5530,7 +5545,9 @@ sub vm_start_nolock {
     my $pci_reserve_list = [];
     eval {
         # With -blockdev, it is necessary to activate the volumes before generating the command line
-        PVE::Storage::activate_volumes($storecfg, $vollist);
+        # 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);
 
         # Note that for certain cases like templates, the configuration is minimized, so need to ensure
         # the rest of the function here uses the same configuration that was used to build the command
-- 
2.47.3