improve libguestfs exception handling

* nova/virt/disk/vfs/guestfs.py (teardown): Handle specific
exceptions when tearing down so that (future) nova bugs
aren't masked.  Also handle AttributeError so that the
relatively new handle() and close() don't cause erroneous
debug logs on older versions of libguestfs.
(has_file): remove the last use of generic exception
catching and use the more specific RuntimeError.

Change-Id: Ia7345675d75c1c6727e9254791d44475c0ed9295

nova/tests/fakeguestfs.py

@@ -96,13 +96,13 @@ class GuestFS(object):
 
     def stat(self, path):
         if not path in self.files:
-            raise Exception("No such file: " + path)
+            raise RuntimeError("No such file: " + path)
 
         return self.files[path]["mode"]
 
     def chown(self, uid, gid, path):
         if not path in self.files:
-            raise Exception("No such file: " + path)
+            raise RuntimeError("No such file: " + path)
 
         if uid != -1:
             self.files[path]["uid"] = uid
@@ -111,7 +111,7 @@ class GuestFS(object):
 
     def chmod(self, mode, path):
         if not path in self.files:
-            raise Exception("No such file: " + path)
+            raise RuntimeError("No such file: " + path)
 
         self.files[path]["mode"] = mode
 
@@ -123,7 +123,7 @@ class GuestFS(object):
 
     def aug_get(self, cfgpath):
         if not self.auginit:
-            raise Exception("Augeus not initialized")
+            raise RuntimeError("Augeus not initialized")
 
         if cfgpath == "/files/etc/passwd/root/uid":
             return 0
@@ -137,4 +137,4 @@ class GuestFS(object):
             return 500
         elif cfgpath == "/files/etc/group/admins/gid":
             return 600
-        raise Exception("Unknown path %s", cfgpath)
+        raise RuntimeError("Unknown path %s", cfgpath)

nova/virt/disk/vfs/guestfs.py

@@ -101,6 +101,7 @@ class VFSGuestFS(vfs.VFS):
 
             self.handle.aug_init("/", 0)
         except RuntimeError, e:
+            # dereference object and implicitly close()
             self.handle = None
             raise exception.NovaException(
                 _("Error mounting %(imgfile)s with libguestfs (%(e)s)") %
@@ -111,19 +112,31 @@ class VFSGuestFS(vfs.VFS):
 
     def teardown(self):
         LOG.debug(_("Tearing down appliance"))
+
         try:
-            self.handle.aug_close()
-        except Exception, e:
-            LOG.debug(_("Failed to close augeas %s"), e)
-        try:
-            self.handle.shutdown()
-        except Exception, e:
-            LOG.debug(_("Failed to shutdown appliance %s"), e)
-        try:
-            self.handle.close()
-        except Exception, e:
-            LOG.debug(_("Failed to close guest handle %s"), e)
-        self.handle = None
+            try:
+                self.handle.aug_close()
+            except RuntimeError, e:
+                LOG.warn(_("Failed to close augeas %s"), e)
+
+            try:
+                self.handle.shutdown()
+            except AttributeError:
+                # Older libguestfs versions haven't an explicit shutdown
+                pass
+            except RuntimeError, e:
+                LOG.warn(_("Failed to shutdown appliance %s"), e)
+
+            try:
+                self.handle.close()
+            except AttributeError:
+                # Older libguestfs versions haven't an explicit close
+                pass
+            except RuntimeError, e:
+                LOG.warn(_("Failed to close guest handle %s"), e)
+        finally:
+            # dereference object and implicitly close()
+            self.handle = None
 
     @staticmethod
     def _canonicalize_path(path):
@@ -157,7 +170,7 @@ class VFSGuestFS(vfs.VFS):
         try:
             self.handle.stat(path)
             return True
-        except Exception, e:
+        except RuntimeError:
             return False
 
     def set_permissions(self, path, mode):