storage_file: Add a new flag to mark backing files that are safe to probe

Signed-off-by: NAdam Litke <agl@us.ibm.com>

src/conf/domain_conf.c

@@ -8230,6 +8230,10 @@ int virDomainDiskDefForeachPath(virDomainDiskDefPtr disk,
         if (format == VIR_STORAGE_FILE_AUTO &&
             !allowProbing)
             format = VIR_STORAGE_FILE_RAW; /* Stops further recursion */
+
+        /* Allow probing for image formats that are safe */
+        if (format == VIR_STORAGE_FILE_AUTO_SAFE)
+            format = VIR_STORAGE_FILE_AUTO;
     } while (nextpath);
 
     ret = 0;

src/util/storage_file.c

@@ -42,7 +42,7 @@
 
 VIR_ENUM_IMPL(virStorageFileFormat,
               VIR_STORAGE_FILE_LAST,
-              "raw", "dir", "bochs",
+              "raw", "probe", "dir", "bochs",
               "cloop", "cow", "dmg", "iso",
               "qcow", "qcow2", "qed", "vmdk", "vpc")
 

src/util/storage_file.h

@@ -30,6 +30,7 @@
 enum virStorageFileFormat {
     VIR_STORAGE_FILE_AUTO = -1,
     VIR_STORAGE_FILE_RAW = 0,
+    VIR_STORAGE_FILE_AUTO_SAFE,
     VIR_STORAGE_FILE_DIR,
     VIR_STORAGE_FILE_BOCHS,
     VIR_STORAGE_FILE_CLOOP,