[PATCH qemu-server 2/2] cpu flags: introduce get_cpu_model_expansions() helper

[Fiona Ebner <f.ebner@proxmox.com>]

Make the static list of CPU model expansions, which is newly shipped
by pve-qemu-kvm, accessible in qemu-server.

Note that some CPU flags in the expansions are gated behind others and
thus cannot be queried via the static expansions. Most prominently,
this is the case for the flags for nested virtualization. For example,
'Skylake-Server' will not support any vmx-* flags, but
'Skylake-Server,+vmx' would.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 src/PVE/QemuServer/CPUFlags.pm | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/src/PVE/QemuServer/CPUFlags.pm b/src/PVE/QemuServer/CPUFlags.pm
index 0d3206b2..60683486 100644
--- a/src/PVE/QemuServer/CPUFlags.pm
+++ b/src/PVE/QemuServer/CPUFlags.pm
@@ -3,6 +3,7 @@ package PVE::QemuServer::CPUFlags;
 use v5.36;
 
 use Exporter qw(import);
+use JSON qw();
 
 use PVE::Cluster;
 use PVE::File;
@@ -129,6 +130,32 @@ my $qemu_cpu_flag_alias_map = {
     lbr_fmt => 'lbr-fmt',
 };
 
+my $cpu_model_expansions;
+
+=head3 get_cpu_model_expansions($arch)
+
+Get the CPU model expansions for the given architecture C<$arch>. Will return C<undef> for QEMU
+package versions that don't yet ship the static model expansions. Note that some CPU flags in the
+expansions are gated behind others and thus cannot be queried via the static expansions. Most
+prominently, this is the case for the flags for nested virtualization. For example,
+C<Skylake-Server> will not support any C<vmx-*> flags, but C<Skylake-Server,+vmx> would. The latter
+cannot be queried here.
+
+=cut
+
+my sub get_cpu_model_expansions($arch) {
+    if (!defined($cpu_model_expansions->{$arch})) {
+        my $cpu_models_file = "/usr/share/kvm/cpu-model-expansions-${arch}.json";
+        return if !PVE::File::file_exists($cpu_models_file);
+
+        my $data = PVE::File::file_get_contents($cpu_models_file, 10 * 1024 * 1024);
+
+        $cpu_model_expansions->{$arch} = JSON::decode_json($data);
+    }
+
+    return $cpu_model_expansions->{$arch};
+}
+
 =head3 normalize_cpu_flag($flag)
 
 Normalize a CPU flag to its QEMU form.
-- 
2.47.3