qemuDomainDiskChangeSupported: Deny changing reservations

Couple of reasons for that:

a) there's no monitor command to change path where the pr-helper
connects to, or
b) there's no monitor command to introduce a new pr-helper for a
disk that already exists.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>

src/libvirt_private.syms

@@ -2803,6 +2803,7 @@ virStorageNetHostTransportTypeToString;
 virStorageNetProtocolTypeToString;
 virStoragePRDefFormat;
 virStoragePRDefFree;
+virStoragePRDefIsEqual;
 virStoragePRDefParseXML;
 virStorageSourceBackingStoreClear;
 virStorageSourceClear;

src/qemu/qemu_domain.c

@@ -7842,6 +7842,14 @@ qemuDomainDiskChangeSupported(virDomainDiskDefPtr disk,
     CHECK_EQ(src->readonly, "readonly", true);
     CHECK_EQ(src->shared, "shared", true);
 
+    if (!virStoragePRDefIsEqual(disk->src->pr,
+                                orig_disk->src->pr)) {
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
+                       _("cannot modify field '%s' of the disk"),
+                       "reservations");
+        return false;
+    }
+
 #undef CHECK_EQ
 
     return true;

src/util/virstoragefile.c

@@ -2022,6 +2022,25 @@ virStoragePRDefFormat(virBufferPtr buf,
 }
 
 
+bool
+virStoragePRDefIsEqual(virStoragePRDefPtr a,
+                       virStoragePRDefPtr b)
+{
+    if (!a && !b)
+        return true;
+
+    if (!a || !b)
+        return false;
+
+    if (a->enabled != b->enabled ||
+        a->managed != b->managed ||
+        STRNEQ_NULLABLE(a->path, b->path))
+        return false;
+
+    return true;
+}
+
+
 virSecurityDeviceLabelDefPtr
 virStorageSourceGetSecurityLabelDef(virStorageSourcePtr src,
                                     const char *model)

src/util/virstoragefile.h

@@ -395,6 +395,8 @@ void virStoragePRDefFree(virStoragePRDefPtr prd);
 virStoragePRDefPtr virStoragePRDefParseXML(xmlXPathContextPtr ctxt);
 void virStoragePRDefFormat(virBufferPtr buf,
                            virStoragePRDefPtr prd);
+bool virStoragePRDefIsEqual(virStoragePRDefPtr a,
+                            virStoragePRDefPtr b);
 
 virSecurityDeviceLabelDefPtr
 virStorageSourceGetSecurityLabelDef(virStorageSourcePtr src,