lib/repo-finder: Add mount based OstreeRepoFinder implementation

This is a basic implementation of OstreeRepoFinder which resolves ref
names to remote URIs by looking for them on any currently mounted
removable storage volumes. The idea is to support OS and app updates via
USB stick.

Unit tests are included.

This bumps libostree’s maximum GLib dependency from 2.44 to 2.50 for
g_drive_is_removable(). If GLib 2.50 is not available, the call which
needs it will be omitted and the OstreeRepoFinderMount implementation
will scan all volumes (not just removable ones); this is a performance
hit, but not a functionality hit.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #924
Approved by: cgwalters

src/libostree/ostree-repo-finder-mount.h

@@ -0,0 +1,55 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
+ *
+ * Copyright © 2017 Endless Mobile, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ *
+ * Authors:
+ *  - Philip Withnall <withnall@endlessm.com>
+ */
+
+#pragma once
+
+#include <gio/gio.h>
+#include <glib.h>
+#include <glib-object.h>
+
+#include "ostree-repo-finder.h"
+#include "ostree-types.h"
+
+G_BEGIN_DECLS
+
+#define OSTREE_TYPE_REPO_FINDER_MOUNT (ostree_repo_finder_mount_get_type ())
+
+/* Manually expanded version of the following, omitting autoptr support (for GLib < 2.44):
+_OSTREE_PUBLIC
+G_DECLARE_FINAL_TYPE (OstreeRepoFinderMount, ostree_repo_finder_mount, OSTREE, REPO_FINDER_MOUNT, GObject) */
+
+_OSTREE_PUBLIC
+GType ostree_repo_finder_mount_get_type (void);
+
+G_GNUC_BEGIN_IGNORE_DEPRECATIONS
+typedef struct _OstreeRepoFinderMount OstreeRepoFinderMount;
+typedef struct { GObjectClass parent_class; } OstreeRepoFinderMountClass;
+
+static inline OstreeRepoFinderMount *OSTREE_REPO_FINDER_MOUNT (gpointer ptr) { return G_TYPE_CHECK_INSTANCE_CAST (ptr, ostree_repo_finder_mount_get_type (), OstreeRepoFinderMount); }
+static inline gboolean OSTREE_IS_REPO_FINDER_MOUNT (gpointer ptr) { return G_TYPE_CHECK_INSTANCE_TYPE (ptr, ostree_repo_finder_mount_get_type ()); }
+G_GNUC_END_IGNORE_DEPRECATIONS
+
+_OSTREE_PUBLIC
+OstreeRepoFinderMount *ostree_repo_finder_mount_new (GVolumeMonitor *monitor);
+
+G_END_DECLS