[ostree] Add ostree_ensure_repo_writable()

[Colin Walters <walters src gnome org>]

commit 7941189dfde3795fb649aba41e207f0072dfcd86
Author: Matthew Barnes <mbarnes redhat com>
Date:   Fri Jan 16 10:04:18 2015 -0500

    Add ostree_ensure_repo_writable()
    
    Commands that need to write files within the repo directory can call
    this early to ensure the directory is writable for the current user.
    If not, it fails with a helpful "You need to be root to perform this
    command" message.

 src/ostree/ot-main.c |   14 ++++++++++++++
 src/ostree/ot-main.h |    2 ++
 2 files changed, 16 insertions(+), 0 deletions(-)
---
diff --git a/src/ostree/ot-main.c b/src/ostree/ot-main.c
index c48a03c..94d29ca 100644
--- a/src/ostree/ot-main.c
+++ b/src/ostree/ot-main.c
@@ -360,3 +360,17 @@ ostree_admin_option_context_parse (GOptionContext *context,
 out:
   return success;
 }
+
+gboolean
+ostree_ensure_repo_writable (OstreeRepo *repo,
+                             GError **error)
+{
+  gboolean ret;
+
+  ret = ostree_repo_is_writable (repo, error);
+
+  g_prefix_error (error, "Cannot write to repository: ");
+
+  return ret;
+}
+
diff --git a/src/ostree/ot-main.h b/src/ostree/ot-main.h
index 5f31b24..659727f 100644
--- a/src/ostree/ot-main.h
+++ b/src/ostree/ot-main.h
@@ -51,3 +51,5 @@ gboolean ostree_admin_option_context_parse (GOptionContext *context,
                                             int *argc, char ***argv,
                                             OstreeSysroot **out_sysroot,
                                             GCancellable *cancellable, GError **error);
+
+gboolean ostree_ensure_repo_writable (OstreeRepo *repo, GError **error);