qemuFirmwareEnsureNVRAM: Don't try to setup non-local nvram

'qemuFirmwareEnsureNVRAM' which fills the NVRAM configuration bits which
may be missing was basing its decision to do something based on whether
the 'path' field was set. This is insufficient if remote storage is to
be considered.

Use 'virStorageSourceIsEmpty()' instead as that properly considers
remote filesystems and explain why the source is unref'd when the
function decides to rewrite the config.

The 'firmware-auto-efi-format-nvram-qcow2-network-nbd' is modified to
omit filling the 'path' field, which without this fix would result in
the nvram to be reset to a local file.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/qemu/qemu_firmware.c

@@ -1054,13 +1054,14 @@ qemuFirmwareEnsureNVRAM(virDomainDef *def,
     if (loader->nvram && !loader->nvram->format)
         loader->nvram->format = loader->format;
 
-    /* If the source already exists and is fully specified, including
+    if (loader->nvram) {
-     * the path, leave it alone */
+        /* Nothing to do if a proper NVRAM backend is already configured */
-    if (loader->nvram && loader->nvram->path)
+        if (!virStorageSourceIsEmpty(loader->nvram))
             return;
 
-    if (loader->nvram)
+        /* otherwise we want to reset and re-populate the definition */
         virObjectUnref(loader->nvram);
+    }
 
     loader->nvram = virStorageSourceNew();
     loader->nvram->type = VIR_STORAGE_TYPE_FILE;

tests/qemuxmlconfdata/firmware-auto-efi-format-nvram-qcow2-network-nbd.x86_64-latest.args

@@ -12,7 +12,7 @@ XDG_CONFIG_HOME=/var/lib/libvirt/qemu/domain--1-guest/.config \
 -object '{"qom-type":"secret","id":"masterKey0","format":"raw","file":"/var/lib/libvirt/qemu/domain--1-guest/master-key.aes"}' \
 -blockdev '{"driver":"file","filename":"/usr/share/edk2/ovmf/OVMF_CODE_4M.qcow2","node-name":"libvirt-pflash0-storage","auto-read-only":true,"discard":"unmap"}' \
 -blockdev '{"node-name":"libvirt-pflash0-format","read-only":true,"driver":"qcow2","file":"libvirt-pflash0-storage"}' \
--blockdev '{"driver":"nbd","server":{"type":"inet","host":"example.org","port":"6000"},"export":"bar","node-name":"libvirt-pflash1-storage","auto-read-only":true,"discard":"unmap"}' \
+-blockdev '{"driver":"nbd","server":{"type":"inet","host":"example.org","port":"6000"},"node-name":"libvirt-pflash1-storage","auto-read-only":true,"discard":"unmap"}' \
 -blockdev '{"node-name":"libvirt-pflash1-format","read-only":false,"driver":"qcow2","file":"libvirt-pflash1-storage"}' \
 -machine pc-i440fx-4.0,usb=off,dump-guest-core=off,memory-backend=pc.ram,pflash0=libvirt-pflash0-format,pflash1=libvirt-pflash1-format,acpi=on \
 -accel tcg \

tests/qemuxmlconfdata/firmware-auto-efi-format-nvram-qcow2-network-nbd.x86_64-latest.xml

@@ -11,7 +11,7 @@
     </firmware>
     <loader readonly='yes' type='pflash' format='qcow2'>/usr/share/edk2/ovmf/OVMF_CODE_4M.qcow2</loader>
     <nvram type='network' format='qcow2'>
-      <source protocol='nbd' name='bar'>
+      <source protocol='nbd'>
         <host name='example.org' port='6000'/>
       </source>
     </nvram>

tests/qemuxmlconfdata/firmware-auto-efi-format-nvram-qcow2-network-nbd.xml

@@ -6,7 +6,7 @@
   <os firmware='efi'>
     <type arch='x86_64' machine='pc-i440fx-4.0'>hvm</type>
     <nvram type='network' format='qcow2'>
-      <source protocol='nbd' name='bar'>
+      <source protocol='nbd'>
         <host name='example.org' port='6000'/>
       </source>
     </nvram>