sysroot: Drop an fsync for origin file when writing deployments

More fsync pruning.  Since we have a public API for writing the origin
file and it did a fsync before, let's preserve that.  But when writing
deployments as part of a full transaction, we rely on the global
`syncfs()`, so add an internal function for origin file writing that
doesn't.

Closes: #509
Approved by: giuseppe

src/libostree/ostree-sysroot-deploy.c

@@ -894,22 +894,11 @@ merge_configuration (OstreeSysroot         *sysroot,
   return ret;
 }
 
-/**
- * ostree_sysroot_write_origin_file:
- * @sysroot: System root
- * @deployment: Deployment
- * @new_origin: (allow-none): Origin content
- * @cancellable: Cancellable
- * @error: Error
- *
- * Immediately replace the origin file of the referenced @deployment
- * with the contents of @new_origin.  If @new_origin is %NULL,
- * this function will write the current origin of @deployment.
- */
-gboolean
-ostree_sysroot_write_origin_file (OstreeSysroot         *sysroot,
+static gboolean
+write_origin_file_internal (OstreeSysroot         *sysroot,
                             OstreeDeployment      *deployment,
                             GKeyFile              *new_origin,
+                            GLnxFileReplaceFlags   flags,
                             GCancellable          *cancellable,
                             GError               **error)
 {
@@ -933,7 +922,7 @@ ostree_sysroot_write_origin_file (OstreeSysroot         *sysroot,
 
       if (!glnx_file_replace_contents_at (sysroot->sysroot_fd,
                                           origin_path, (guint8*)contents, len,
-                                          GLNX_FILE_REPLACE_DATASYNC_NEW,
+                                          flags,
                                           cancellable, error))
         return FALSE;
     }
@@ -941,6 +930,30 @@ ostree_sysroot_write_origin_file (OstreeSysroot         *sysroot,
   return TRUE;
 }
 
+/**
+ * ostree_sysroot_write_origin_file:
+ * @sysroot: System root
+ * @deployment: Deployment
+ * @new_origin: (allow-none): Origin content
+ * @cancellable: Cancellable
+ * @error: Error
+ *
+ * Immediately replace the origin file of the referenced @deployment
+ * with the contents of @new_origin.  If @new_origin is %NULL,
+ * this function will write the current origin of @deployment.
+ */
+gboolean
+ostree_sysroot_write_origin_file (OstreeSysroot         *sysroot,
+                                  OstreeDeployment      *deployment,
+                                  GKeyFile              *new_origin,
+                                  GCancellable          *cancellable,
+                                  GError               **error)
+{
+  return write_origin_file_internal (sysroot, deployment, new_origin,
+                                     GLNX_FILE_REPLACE_DATASYNC_NEW,
+                                     cancellable, error);
+}
+
 static gboolean
 get_kernel_from_tree (int             deployment_dfd,
                       int            *out_boot_dfd,
@@ -2152,7 +2165,11 @@ ostree_sysroot_deploy_tree (OstreeSysroot     *self,
           goto out;
       }
 
-    if (!ostree_sysroot_write_origin_file (self, new_deployment, NULL,
+    /* Don't fsync here, as we assume that's all done in
+     * ostree_sysroot_write_deployments().
+     */
+    if (!write_origin_file_internal (self, new_deployment, NULL,
+                                     GLNX_FILE_REPLACE_NODATASYNC,
                                      cancellable, error))
       {
         g_prefix_error (error, "Writing out origin file: ");