virtinst/guest: use EFI firmware if osinfo-db shows lack of BIOS support

Windows 11 only supports EFI for installation, legacy BIOS is
discontinued as an option for new installs, unless you switch into
the console and run various regedit hacks in the installer.

This is not something we expect users to do, so osinfo-db will
report:

   <firmware arch="x86_64" type="efi"/>
   <firmware arch="x86_64" type="bios" supported="false"/>

for Windows 11.

When seeing 'bios' with supported=false, we need to prefer EFI
firmware no matter what.

For other OS we should stil prefer BIOS, because EFI blocks the usage of
internal qcow2 snapshots until some libvirt work is done to use the new
QMP snapshot commands.

Note this relies on a new API osinfo_os_get_complete_firmware_list
just added to libosinfo in version 1.10, so for most existing OS
distros this will be dormant functionality until they rebase to
latest libosinfo APIs.

The Windows 11 entry for osinfo-db will be the first that exposes
the metadata indicating lack of BIOS support.

Related: https://github.com/virt-manager/virt-manager/issues/310
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

virtinst/guest.py

@@ -522,7 +522,21 @@ class Guest(XMLBuilder):
         arm+machvirt prefers UEFI since it's required for traditional
         install methods
         """
-        return self.os.is_arm_machvirt() or self.conn.is_bhyve()
+        if self.os.is_x86() and self.conn.is_qemu():
+            # If OS has dropped support for 'bios', we have no
+            # choice but to use EFI.
+            # For other OS still prefer BIOS since it is faster
+            # and doesn't break QEMU internal snapshots
+            has_efi = self.osinfo.supports_firmware_efi(self.os.arch)
+            has_bios = self.osinfo.supports_firmware_bios(self.os.arch)
+            log.debug("Guest osinfo firmware has_efi=%d has_bios=%d",
+                      has_efi, has_bios)
+            prefer_efi = has_efi and not has_bios
+        else:
+            prefer_efi = self.os.is_arm_machvirt() or self.conn.is_bhyve()
+
+        log.debug("Prefer EFI => %s", prefer_efi)
+        return prefer_efi
 
     def is_uefi(self):
         if self.os.loader and self.os.loader_type == "pflash":

virtinst/osdict.py

@@ -439,6 +439,28 @@ class _OsVariant(object):
         devids = ["http://qemu.org/chipset/x86/q35"]
         return bool(self._device_filter(devids=devids, extra_devs=extra_devs))
 
+    def _get_firmware_list(self):
+        if hasattr(self._os, "get_complete_firmware_list"):
+            return self._os.get_complete_firmware_list().get_elements()
+        return []
+
+    def _supports_firmware_type(self, name, arch, default):
+        firmwares = self._get_firmware_list()
+
+        for firmware in firmwares:
+            if firmware.get_architecture() != arch:
+                continue
+            if firmware.get_firmware_type() == name:
+                return firmware.is_supported()
+
+        return default
+
+    def supports_firmware_efi(self, arch):
+        return self._supports_firmware_type("efi", arch, False)
+
+    def supports_firmware_bios(self, arch):
+        return self._supports_firmware_type("bios", arch, True)
+
     def get_recommended_resources(self):
         minimum = self._os.get_minimum_resources()
         recommended = self._os.get_recommended_resources()