Add --disable-fsync option to pull-local, and API to repo

This will be used by guestmount - it's WAY faster.  We only take disks
as a unit, so it's safe.  If the process fails halfway through, we
just start over from scratch the next time anyways.

src/libostree/ostree-repo-commit.c

@@ -157,10 +157,13 @@ commit_loose_object_trusted (OstreeRepo        *self,
       /* Ensure that in case of a power cut, these files have the data we
        * want.   See http://lwn.net/Articles/322823/
        */
-      if (fsync (fd) == -1)
+      if (!self->disable_fsync)
         {
-          ot_util_set_error_from_errno (error, errno);
-          goto out;
+          if (fsync (fd) == -1)
+            {
+              ot_util_set_error_from_errno (error, errno);
+              goto out;
+            }
         }
           
       if (!g_output_stream_close (temp_out, cancellable, error))

src/libostree/ostree-repo-private.h

@@ -57,6 +57,7 @@ struct OstreeRepo {
 
   gboolean inited;
   gboolean in_transaction;
+  gboolean disable_fsync;
   GHashTable *loose_object_devino_hash;
   GHashTable *updated_uncompressed_dirs;
   GHashTable *object_sizes;

src/libostree/ostree-repo.c

@@ -552,6 +552,24 @@ ostree_repo_open (OstreeRepo    *self,
   return ret;
 }
 
+/**
+ * ostree_repo_set_disable_fsync:
+ * @self: An #OstreeRepo
+ * @disable_fsync: If %TRUE, do not fsync
+ *
+ * Disable requests to fsync() to stable storage during commits.  This
+ * option should only be used by build system tools which are creating
+ * disposable virtual machines, or have higher level mechanisms for
+ * ensuring data consistency.
+ */
+void
+ostree_repo_set_disable_fsync (OstreeRepo    *self,
+                               gboolean       disable_fsync)
+{
+  self->disable_fsync = disable_fsync;
+}
+
+
 /**
  * ostree_repo_get_path:
  * @self:

src/libostree/ostree-repo.h

@@ -48,6 +48,9 @@ gboolean      ostree_repo_open   (OstreeRepo     *self,
                                   GCancellable   *cancellable,
                                   GError        **error);
 
+void          ostree_repo_set_disable_fsync (OstreeRepo    *self,
+                                             gboolean       disable_fsync);
+
 gboolean      ostree_repo_create (OstreeRepo     *self,
                                   OstreeRepoMode  mode,
                                   GCancellable   *cancellable,