storage: Detect backing_store format automatically

By attempting to manage/import the passed path. This makes it
work via both virt-install and virt-manager

https://bugzilla.redhat.com/show_bug.cgi?id=1235406

tests/cli-test-xml/compare/virt-install-many-devices.xml

@@ -145,6 +145,11 @@
       <source file="/dev/default-pool/new2.img"/>
       <target dev="vdm" bus="virtio"/>
     </disk>
+    <disk type="file" device="disk">
+      <driver name="qemu" type="qcow2"/>
+      <source file="/tmp/brand-new.img"/>
+      <target dev="vdn" bus="virtio"/>
+    </disk>
     <controller type="usb" index="0" model="ich9-ehci1">
       <address type="pci" domain="0" bus="0" slot="4" function="7"/>
     </controller>

tests/clitest.py

@@ -466,6 +466,7 @@ c.add_compare(""" \
 --disk vol=gluster-pool/test-gluster.raw,startup_policy=optional \
 --disk %(DIR)s,device=floppy,address.type=ccw,address.cssid=0xfe,address.ssid=0,address.devno=01 \
 --disk %(NEWIMG2)s,size=1,backing_store=/tmp/foo.img,backing_format=vmdk \
+--disk /tmp/brand-new.img,size=1,backing_store=/dev/default-pool/iso-vol \
 \
 --network user,mac=12:34:56:78:11:22,portgroup=foo,link_state=down,rom_bar=on,rom_file=/tmp/foo \
 --network bridge=foobar,model=virtio,driver_name=qemu,driver_queues=3 \

virtinst/storage.py

@@ -230,6 +230,17 @@ class StoragePool(_StorageObject):
                 _("Couldn't create default storage pool '%s': %s") %
                 (path, str(e)))
 
+    @staticmethod
+    def manage_path(conn, path):
+        """
+        If the passed path is managed, lookup its storage objects.
+        If the passed path isn't managed, attempt to manage it if
+        we can.
+
+        :returns: (vol, parent pool) tuple
+        """
+        from . import diskbackend
+        return diskbackend.manage_path(conn, path)
 
     @staticmethod
     def get_default_dir(conn, build=False):
@@ -678,7 +689,14 @@ class StorageVolume(_StorageObject):
 
     def _get_vol_type(self):
         if self.type:
-            return self.type
+            if self.type == "file":
+                return self.TYPE_FILE
+            elif self.type == "block":
+                return self.TYPE_BLOCK
+            elif self.type == "dir":
+                return self.TYPE_DIR
+            elif self.type == "network":
+                return self.TYPE_NETWORK
         if (self._pool_xml.type == StoragePool.TYPE_DISK or
             self._pool_xml.type == StoragePool.TYPE_LOGICAL):
             return self.TYPE_BLOCK
@@ -718,6 +736,31 @@ class StorageVolume(_StorageObject):
         is_bool=True, default_cb=_lazy_refcounts_default_cb)
 
 
+    def _detect_backing_store_format(self):
+        logging.debug("Attempting to detect format for backing_store=%s",
+                self.backing_store)
+        vol, pool = StoragePool.manage_path(self.conn, self.backing_store)
+
+        if not vol:
+            logging.debug("Didn't find any volume for backing_store")
+            return None
+
+        # Only set backing format for volumes that support
+        # the 'format' parameter as we know it, like qcow2 etc.
+        volxml = StorageVolume(self.conn, vol.XMLDesc(0))
+        volxml.pool = pool
+        logging.debug("Found backing store volume XML:\n%s",
+                volxml.get_xml_config())
+
+        if volxml.supports_property("format"):
+            logging.debug("Returning format=%s", volxml.format)
+            return volxml.format
+
+        logging.debug("backing_store volume doesn't appear to have "
+            "a file format we can specify, returning None")
+        return None
+
+
     ######################
     # Public API helpers #
     ######################
@@ -729,7 +772,6 @@ class StorageVolume(_StorageObject):
             return True
         return False
 
-
     def supports_property(self, propname):
         if propname == "format":
             return self._supports_format()
@@ -761,6 +803,9 @@ class StorageVolume(_StorageObject):
         """
         Build and install storage volume from xml
         """
+        if self.backing_store and not self.backing_format:
+            self.backing_format = self._detect_backing_store_format()
+
         xml = self.get_xml_config()
         logging.debug("Creating storage volume '%s' with xml:\n%s",
                       self.name, xml)
@@ -785,7 +830,6 @@ class StorageVolume(_StorageObject):
             cloneflags |= getattr(libvirt,
                 "VIR_STORAGE_VOL_CREATE_REFLINK", 1)
 
-
         try:
             self._install_finished = False
             t.start()