[ostree] commit: Clarify reasoning for "commit-update-summary" default

[Matthew Barnes <mbarnes src gnome org>]

commit 2233d443e76ba0557b6c57a76e0668b991003fb9
Author: Matthew Barnes <mbarnes redhat com>
Date:   Fri Sep 11 13:15:58 2015 -0400

    commit: Clarify reasoning for "commit-update-summary" default
    
    In case anyone else gets the idea of changing the default for archive-z2
    repos.  Should have the rationale captured in the source code somewhere.

 src/ostree/ot-builtin-commit.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/src/ostree/ot-builtin-commit.c b/src/ostree/ot-builtin-commit.c
index db3700b..3176ae9 100644
--- a/src/ostree/ot-builtin-commit.c
+++ b/src/ostree/ot-builtin-commit.c
@@ -524,6 +524,11 @@ ostree_builtin_commit (int argc, char **argv, GCancellable *cancellable, GError
       if (!ostree_repo_commit_transaction (repo, &stats, cancellable, error))
         goto out;
 
+      /* The default for this option is FALSE, even for archive-z2 repos,
+       * because ostree supports multiple processes committing to the same
+       * repo (but different refs) concurrently, and in fact gnome-continuous
+       * actually does this.  In that context it's best to update the summary
+       * explicitly instead of automatically here. */
       if (!ot_keyfile_get_boolean_with_default (ostree_repo_get_config (repo), "core",
                                                 "commit-update-summary", FALSE,
                                                 &update_summary, error))