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/libostree-experimental.sym

@@ -50,6 +50,8 @@ global:
   ostree_repo_finder_config_get_type;
   ostree_repo_finder_config_new;
   ostree_repo_finder_get_type;
+  ostree_repo_finder_mount_get_type;
+  ostree_repo_finder_mount_new;
   ostree_repo_finder_resolve_async;
   ostree_repo_finder_resolve_all_async;
   ostree_repo_finder_resolve_all_finish;

src/libostree/ostree-autocleanups.h

@@ -65,6 +65,7 @@ G_DEFINE_AUTO_CLEANUP_FREE_FUNC (OstreeCollectionRefv, ostree_collection_ref_fre
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeRemote, ostree_remote_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeRepoFinder, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeRepoFinderConfig, g_object_unref)
+G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeRepoFinderMount, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeRepoFinderResult, ostree_repo_finder_result_free)
 G_DEFINE_AUTO_CLEANUP_FREE_FUNC (OstreeRepoFinderResultv, ostree_repo_finder_result_freev, NULL)
 #endif  /* OSTREE_ENABLE_EXPERIMENTAL_API */

src/libostree/ostree-core-private.h

@@ -190,6 +190,9 @@ G_DEFINE_AUTO_CLEANUP_FREE_FUNC (OstreeRepoFinderResultv, ostree_repo_finder_res
 
 #include "ostree-repo-finder-config.h"
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeRepoFinderConfig, g_object_unref)
+
+#include "ostree-repo-finder-mount.h"
+G_DEFINE_AUTOPTR_CLEANUP_FUNC (OstreeRepoFinderMount, g_object_unref)
 #endif
 
 G_END_DECLS

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

@@ -0,0 +1,547 @@
+/* -*- 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>
+ */
+
+#include "config.h"
+
+#include <gio/gio.h>
+#include <glib.h>
+#include <glib-object.h>
+#include <libglnx.h>
+#include <stdlib.h>
+
+#include "ostree-autocleanups.h"
+#include "ostree-remote-private.h"
+#include "ostree-repo-finder.h"
+#include "ostree-repo-finder-mount.h"
+
+/**
+ * SECTION:ostree-repo-finder-mount
+ * @title: OstreeRepoFinderMount
+ * @short_description: Finds remote repositories from ref names by looking at
+ *    mounted removable volumes
+ * @stability: Unstable
+ * @include: libostree/ostree-repo-finder-mount.h
+ *
+ * #OstreeRepoFinderMount is an implementation of #OstreeRepoFinder which looks
+ * refs up in well-known locations on any mounted removable volumes.
+ *
+ * For an #OstreeCollectionRef, (`C`, `R`), it checks whether `.ostree/repos/C/R`
+ * exists and is an OSTree repository on each mounted removable volume. Collection
+ * IDs and ref names are not escaped when building the path, so if either
+ * contains `/` in its name, the repository will be checked for in a
+ * subdirectory of `.ostree/repos`. Non-removable volumes are ignored.
+ *
+ * For each repository which is found, a result will be returned for the
+ * intersection of the refs being searched for, and the refs in `refs/heads` and
+ * `refs/mirrors` in the repository on the removable volume.
+ *
+ * Symlinks are followed when resolving the refs, so a volume might contain a
+ * single OSTree at some arbitrary path, with a number of refs linking to it
+ * from `.ostree/repos`. Any symlink which points outside the volume’s file
+ * system will be ignored. Repositories are deduplicated in the results.
+ *
+ * The volume monitor used to find mounted volumes can be overridden by setting
+ * #OstreeRepoFinderMount:monitor. By default, g_volume_monitor_get() is used.
+ *
+ * Since: 2017.8
+ */
+
+typedef GList/*<owned GObject>*/ ObjectList;
+
+static void
+object_list_free (ObjectList *list)
+{
+  g_list_free_full (list, g_object_unref);
+}
+
+G_DEFINE_AUTOPTR_CLEANUP_FUNC (ObjectList, object_list_free)
+
+static void ostree_repo_finder_mount_iface_init (OstreeRepoFinderInterface *iface);
+
+struct _OstreeRepoFinderMount
+{
+  GObject parent_instance;
+
+  GVolumeMonitor *monitor;  /* owned */
+};
+
+G_DEFINE_TYPE_WITH_CODE (OstreeRepoFinderMount, ostree_repo_finder_mount, G_TYPE_OBJECT,
+                         G_IMPLEMENT_INTERFACE (OSTREE_TYPE_REPO_FINDER, ostree_repo_finder_mount_iface_init))
+
+typedef struct
+{
+  gchar *uri;
+  gchar *keyring;
+} UriAndKeyring;
+
+static void
+uri_and_keyring_free (UriAndKeyring *data)
+{
+  g_free (data->uri);
+  g_free (data->keyring);
+  g_free (data);
+}
+
+G_DEFINE_AUTOPTR_CLEANUP_FUNC (UriAndKeyring, uri_and_keyring_free)
+
+static UriAndKeyring *
+uri_and_keyring_new (const gchar *uri,
+                     const gchar *keyring)
+{
+  g_autoptr(UriAndKeyring) data = NULL;
+
+  data = g_new0 (UriAndKeyring, 1);
+  data->uri = g_strdup (uri);
+  data->keyring = g_strdup (keyring);
+
+  return g_steal_pointer (&data);
+}
+
+static guint
+uri_and_keyring_hash (gconstpointer key)
+{
+  const UriAndKeyring *_key = key;
+
+  return g_str_hash (_key->uri) ^ g_str_hash (_key->keyring);
+}
+
+static gboolean
+uri_and_keyring_equal (gconstpointer a,
+                       gconstpointer b)
+{
+  const UriAndKeyring *_a = a, *_b = b;
+
+  return g_str_equal (_a->uri, _b->uri) && g_str_equal (_a->keyring, _b->keyring);
+}
+
+/* This must return a valid remote name (suitable for use in a refspec). */
+static gchar *
+uri_and_keyring_to_name (UriAndKeyring *data)
+{
+  g_autofree gchar *escaped_uri = g_uri_escape_string (data->uri, NULL, FALSE);
+  g_autofree gchar *escaped_keyring = g_uri_escape_string (data->keyring, NULL, FALSE);
+
+  /* FIXME: Need a better separator than `_`, since it’s not escaped in the input. */
+  g_autofree gchar *out = g_strdup_printf ("%s_%s", escaped_uri, escaped_keyring);
+
+  for (gsize i = 0; out[i] != '\0'; i++)
+    {
+      if (out[i] == '%')
+        out[i] = '_';
+    }
+
+  g_return_val_if_fail (ostree_validate_remote_name (out, NULL), NULL);
+
+  return g_steal_pointer (&out);
+}
+
+static gint
+results_compare_cb (gconstpointer a,
+                    gconstpointer b)
+{
+  const OstreeRepoFinderResult *result_a = *((const OstreeRepoFinderResult **) a);
+  const OstreeRepoFinderResult *result_b = *((const OstreeRepoFinderResult **) b);
+
+  return ostree_repo_finder_result_compare (result_a, result_b);
+}
+
+static void
+ostree_repo_finder_mount_resolve_async (OstreeRepoFinder                  *finder,
+                                        const OstreeCollectionRef * const *refs,
+                                        OstreeRepo                        *parent_repo,
+                                        GCancellable                      *cancellable,
+                                        GAsyncReadyCallback                callback,
+                                        gpointer                           user_data)
+{
+  OstreeRepoFinderMount *self = OSTREE_REPO_FINDER_MOUNT (finder);
+  g_autoptr(GTask) task = NULL;
+  g_autoptr(ObjectList) mounts = NULL;
+  g_autoptr(GPtrArray) results = NULL;  /* (element-type OstreeRepoFinderResult) */
+  GList *l;
+  const gint priority = 50;  /* arbitrarily chosen */
+
+  task = g_task_new (finder, cancellable, callback, user_data);
+  g_task_set_source_tag (task, ostree_repo_finder_mount_resolve_async);
+
+  mounts = g_volume_monitor_get_mounts (self->monitor);
+  results = g_ptr_array_new_with_free_func ((GDestroyNotify) ostree_repo_finder_result_free);
+
+  g_debug ("%s: Found %u mounts", G_STRFUNC, g_list_length (mounts));
+
+  for (l = mounts; l != NULL; l = l->next)
+    {
+      GMount *mount = G_MOUNT (l->data);
+      g_autofree gchar *mount_name = NULL;
+      g_autoptr(GFile) mount_root = NULL;
+      g_autofree gchar *mount_root_path = NULL;
+      glnx_fd_close int mount_root_dfd = -1;
+      struct stat mount_root_stbuf;
+      glnx_fd_close int repos_dfd = -1;
+      gsize i;
+      g_autoptr(GHashTable) repo_to_refs = NULL;  /* (element-type UriAndKeyring GHashTable) */
+      GHashTable *supported_ref_to_checksum;  /* (element-type OstreeCollectionRef utf8) */
+      GHashTableIter iter;
+      UriAndKeyring *repo;
+      g_autoptr(GError) local_error = NULL;
+
+      mount_name = g_mount_get_name (mount);
+
+      /* Check the mount’s general properties. */
+      if (g_mount_is_shadowed (mount))
+        {
+          g_debug ("Ignoring mount ‘%s’ as it’s shadowed.", mount_name);
+          continue;
+        }
+
+      /* Check if it contains a .ostree/repos directory. */
+      mount_root = g_mount_get_root (mount);
+      mount_root_path = g_file_get_path (mount_root);
+
+      if (!glnx_opendirat (AT_FDCWD, mount_root_path, TRUE, &mount_root_dfd, &local_error))
+        {
+          g_debug ("Ignoring mount ‘%s’ as ‘%s’ directory can’t be opened: %s",
+                   mount_name, mount_root_path, local_error->message);
+          continue;
+        }
+
+      if (!glnx_opendirat (mount_root_dfd, ".ostree/repos", TRUE, &repos_dfd, &local_error))
+        {
+          if (g_error_matches (local_error, G_IO_ERROR, G_IO_ERROR_NOT_FOUND))
+            g_debug ("Ignoring mount ‘%s’ as ‘%s/.ostree/repos’ directory doesn’t exist.",
+                     mount_name, mount_root_path);
+          else
+            g_debug ("Ignoring mount ‘%s’ as ‘%s/.ostree/repos’ directory can’t be opened: %s",
+                     mount_name, mount_root_path, local_error->message);
+
+          continue;
+        }
+
+      /* stat() the mount root so we can later check whether the resolved
+       * repositories for individual refs are on the same device (to avoid the
+       * symlinks for them pointing outside the mount root). */
+      if (!glnx_fstat (mount_root_dfd, &mount_root_stbuf, &local_error))
+        {
+          g_debug ("Ignoring mount ‘%s’ as querying info of ‘%s’ failed: %s",
+                   mount_name, mount_root_path, local_error->message);
+          continue;
+        }
+
+      /* Check whether a subdirectory exists for any of the @refs we’re looking
+       * for. If so, and it’s a symbolic link, dereference it so multiple links
+       * to the same repository (containing multiple refs) are coalesced.
+       * Otherwise, include it as a result by itself. */
+      repo_to_refs = g_hash_table_new_full (uri_and_keyring_hash, uri_and_keyring_equal,
+                                            (GDestroyNotify) uri_and_keyring_free, (GDestroyNotify) g_hash_table_unref);
+
+      for (i = 0; refs[i] != NULL; i++)
+        {
+          struct stat stbuf;
+          g_autofree gchar *collection_and_ref = NULL;
+          g_autofree gchar *repo_dir_path = NULL;
+          g_autofree gchar *resolved_repo_uri = NULL;
+          g_autofree gchar *keyring = NULL;
+          g_autoptr(UriAndKeyring) resolved_repo = NULL;
+
+          collection_and_ref = g_build_filename (refs[i]->collection_id, refs[i]->ref_name, NULL);
+          repo_dir_path = g_build_filename (mount_root_path, ".ostree", "repos",
+                                            collection_and_ref, NULL);
+
+          if (!glnx_fstatat (repos_dfd, collection_and_ref, &stbuf, AT_NO_AUTOMOUNT, &local_error))
+            {
+              g_debug ("Ignoring ref (%s, %s) on mount ‘%s’ as querying info of ‘%s’ failed: %s",
+                       refs[i]->collection_id, refs[i]->ref_name, mount_name, repo_dir_path, local_error->message);
+              g_clear_error (&local_error);
+              continue;
+            }
+
+          if ((stbuf.st_mode & S_IFMT) != S_IFDIR)
+            {
+              g_debug ("Ignoring ref (%s, %s) on mount ‘%s’ as ‘%s’ is of type %u, not a directory.",
+                       refs[i]->collection_id, refs[i]->ref_name, mount_name, repo_dir_path, (stbuf.st_mode & S_IFMT));
+              g_clear_error (&local_error);
+              continue;
+            }
+
+          /* Check the resolved repository path is below the mount point. Do not
+           * allow ref symlinks to point somewhere outside of the mounted
+           * volume. */
+          if (stbuf.st_dev != mount_root_stbuf.st_dev)
+            {
+              g_debug ("Ignoring ref (%s, %s) on mount ‘%s’ as it’s on a different file system from the mount.",
+                       refs[i]->collection_id, refs[i]->ref_name, mount_name);
+              g_clear_error (&local_error);
+              continue;
+            }
+
+          /* Exclude repositories which resolve to @parent_repo. */
+          g_autofree char *canonical_repo_dir_path = realpath (repo_dir_path, NULL);
+          g_autofree gchar *parent_repo_path = g_file_get_path (ostree_repo_get_path (parent_repo));
+          g_autofree char *canonical_parent_repo_path = realpath (parent_repo_path, NULL);
+
+          if (g_strcmp0 (canonical_repo_dir_path, canonical_parent_repo_path) == 0)
+            {
+              g_debug ("Ignoring ref (%s, %s) on mount ‘%s’ as its repository was the one we are resolving for: %s",
+                       refs[i]->collection_id, refs[i]->ref_name, mount_name, canonical_parent_repo_path);
+              g_clear_error (&local_error);
+              continue;
+            }
+
+          /* Grab the given ref and a checksum for it from the repo.
+           * FIXME: Ideally, there would be some ostree_repo_open_at() which we
+           * could use to keep the openat() chain going. See
+           * https://github.com/ostreedev/ostree/pull/820. */
+          g_autoptr(OstreeRepo) repo = NULL;
+          g_autoptr(GFile) repo_dir_file = g_file_new_for_path (repo_dir_path);
+          repo = ostree_repo_new (repo_dir_file);
+
+          if (!ostree_repo_open (repo, cancellable, &local_error))
+            {
+              g_debug ("Ignoring ref (%s, %s) on mount ‘%s’ as its repository could not be opened: %s",
+                       refs[i]->collection_id, refs[i]->ref_name, mount_name, local_error->message);
+              g_clear_error (&local_error);
+              continue;
+            }
+
+          g_autoptr(GHashTable) repo_refs = NULL;  /* (element-type OstreeCollectionRef utf8) */
+
+          if (!ostree_repo_list_collection_refs (repo, refs[i]->collection_id, &repo_refs, cancellable, &local_error))
+            {
+              g_debug ("Ignoring ref (%s, %s) on mount ‘%s’ as its refs could not be listed: %s",
+                       refs[i]->collection_id, refs[i]->ref_name, mount_name, local_error->message);
+              g_clear_error (&local_error);
+              continue;
+            }
+
+          const gchar *checksum = g_hash_table_lookup (repo_refs, refs[i]);
+
+          if (checksum == NULL)
+            {
+              g_debug ("Ignoring ref (%s, %s) on mount ‘%s’ as its repository doesn’t contain the ref.",
+                       refs[i]->collection_id, refs[i]->ref_name, mount_name);
+              g_clear_error (&local_error);
+              continue;
+            }
+
+          /* Finally, look up the GPG keyring for this ref. */
+          keyring = ostree_repo_resolve_keyring_for_collection (parent_repo, refs[i]->collection_id,
+                                                                cancellable, &local_error);
+
+          if (keyring == NULL)
+            {
+              g_debug ("Ignoring ref (%s, %s) on mount ‘%s’ due to missing keyring: %s",
+                       refs[i]->collection_id, refs[i]->ref_name, mount_name, local_error->message);
+              g_clear_error (&local_error);
+              continue;
+            }
+
+          /* There is a valid repo at (or pointed to by)
+           * $mount_root/.ostree/repos/$refs[i]->collection_id/$refs[i]->ref_name.
+           * Add it to the results, keyed by the canonicalised repository URI
+           * to deduplicate the results. */
+          resolved_repo_uri = g_strconcat ("file://", canonical_repo_dir_path, NULL);
+          g_debug ("Resolved ref (%s, %s) on mount ‘%s’ to repo URI ‘%s’ with keyring ‘%s’.",
+                   refs[i]->collection_id, refs[i]->ref_name, mount_name, resolved_repo_uri, keyring);
+
+          resolved_repo = uri_and_keyring_new (resolved_repo_uri, keyring);
+
+          supported_ref_to_checksum = g_hash_table_lookup (repo_to_refs, resolved_repo);
+
+          if (supported_ref_to_checksum == NULL)
+            {
+              supported_ref_to_checksum = g_hash_table_new_full (ostree_collection_ref_hash,
+                                                                 ostree_collection_ref_equal,
+                                                                 NULL, g_free);
+              g_hash_table_insert (repo_to_refs, g_steal_pointer (&resolved_repo), supported_ref_to_checksum  /* transfer */);
+            }
+
+          g_hash_table_insert (supported_ref_to_checksum, (gpointer) refs[i], g_strdup (checksum));
+        }
+
+      /* Aggregate the results. */
+      g_hash_table_iter_init (&iter, repo_to_refs);
+
+      while (g_hash_table_iter_next (&iter, (gpointer *) &repo, (gpointer *) &supported_ref_to_checksum))
+        {
+          g_autoptr(OstreeRemote) remote = NULL;
+
+          /* Build an #OstreeRemote. Use the escaped URI, since remote->name
+           * is used in file paths, so needs to not contain special characters. */
+          g_autofree gchar *name = uri_and_keyring_to_name (repo);
+          remote = ostree_remote_new (name);
+
+          g_clear_pointer (&remote->keyring, g_free);
+          remote->keyring = g_strdup (repo->keyring);
+
+          g_key_file_set_string (remote->options, remote->group, "url", repo->uri);
+          g_key_file_set_boolean (remote->options, remote->group, "gpg-verify", TRUE);
+          g_key_file_set_boolean (remote->options, remote->group, "gpg-verify-summary", TRUE);
+
+          /* Set the timestamp in the #OstreeRepoFinderResult to 0 because
+           * the code in ostree_repo_pull_from_remotes_async() will be able to
+           * check it just as quickly as we can here; so don’t duplicate the
+           * code. */
+          g_ptr_array_add (results, ostree_repo_finder_result_new (remote, finder, priority, supported_ref_to_checksum, 0));
+        }
+    }
+
+  g_ptr_array_sort (results, results_compare_cb);
+
+  g_task_return_pointer (task, g_steal_pointer (&results), (GDestroyNotify) g_ptr_array_unref);
+}
+
+static GPtrArray *
+ostree_repo_finder_mount_resolve_finish (OstreeRepoFinder  *self,
+                                         GAsyncResult      *result,
+                                         GError           **error)
+{
+  g_return_val_if_fail (g_task_is_valid (result, self), NULL);
+  return g_task_propagate_pointer (G_TASK (result), error);
+}
+
+static void
+ostree_repo_finder_mount_init (OstreeRepoFinderMount *self)
+{
+  /* Nothing to see here. */
+}
+
+static void
+ostree_repo_finder_mount_constructed (GObject *object)
+{
+  OstreeRepoFinderMount *self = OSTREE_REPO_FINDER_MOUNT (object);
+
+  G_OBJECT_CLASS (ostree_repo_finder_mount_parent_class)->constructed (object);
+
+  if (self->monitor == NULL)
+    self->monitor = g_volume_monitor_get ();
+}
+
+typedef enum
+{
+  PROP_MONITOR = 1,
+} OstreeRepoFinderMountProperty;
+
+static void
+ostree_repo_finder_mount_get_property (GObject    *object,
+                                       guint       property_id,
+                                       GValue     *value,
+                                       GParamSpec *pspec)
+{
+  OstreeRepoFinderMount *self = OSTREE_REPO_FINDER_MOUNT (object);
+
+  switch ((OstreeRepoFinderMountProperty) property_id)
+    {
+    case PROP_MONITOR:
+      g_value_set_object (value, self->monitor);
+      break;
+    default:
+      g_assert_not_reached ();
+    }
+}
+
+static void
+ostree_repo_finder_mount_set_property (GObject      *object,
+                                       guint         property_id,
+                                       const GValue *value,
+                                       GParamSpec   *pspec)
+{
+  OstreeRepoFinderMount *self = OSTREE_REPO_FINDER_MOUNT (object);
+
+  switch ((OstreeRepoFinderMountProperty) property_id)
+    {
+    case PROP_MONITOR:
+      /* Construct-only. */
+      g_assert (self->monitor == NULL);
+      self->monitor = g_value_dup_object (value);
+      break;
+    default:
+      g_assert_not_reached ();
+    }
+}
+
+static void
+ostree_repo_finder_mount_dispose (GObject *object)
+{
+  OstreeRepoFinderMount *self = OSTREE_REPO_FINDER_MOUNT (object);
+
+  g_clear_object (&self->monitor);
+
+  G_OBJECT_CLASS (ostree_repo_finder_mount_parent_class)->dispose (object);
+}
+
+static void
+ostree_repo_finder_mount_class_init (OstreeRepoFinderMountClass *klass)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+  object_class->get_property = ostree_repo_finder_mount_get_property;
+  object_class->set_property = ostree_repo_finder_mount_set_property;
+  object_class->constructed = ostree_repo_finder_mount_constructed;
+  object_class->dispose = ostree_repo_finder_mount_dispose;
+
+  /**
+   * OstreeRepoFinderMount:monitor:
+   *
+   * Volume monitor to use to look up mounted volumes when queried.
+   *
+   * Since: 2017.8
+   */
+  g_object_class_install_property (object_class, PROP_MONITOR,
+                                   g_param_spec_object ("monitor",
+                                                        "Volume Monitor",
+                                                        "Volume monitor to use "
+                                                        "to look up mounted "
+                                                        "volumes when queried.",
+                                                        G_TYPE_VOLUME_MONITOR,
+                                                        G_PARAM_CONSTRUCT_ONLY |
+                                                        G_PARAM_READWRITE |
+                                                        G_PARAM_STATIC_STRINGS));
+}
+
+static void
+ostree_repo_finder_mount_iface_init (OstreeRepoFinderInterface *iface)
+{
+  iface->resolve_async = ostree_repo_finder_mount_resolve_async;
+  iface->resolve_finish = ostree_repo_finder_mount_resolve_finish;
+}
+
+/**
+ * ostree_repo_finder_mount_new:
+ * @monitor: (nullable) (transfer none): volume monitor to use, or %NULL to use
+ *    the system default
+ *
+ * Create a new #OstreeRepoFinderMount, using the given @monitor to look up
+ * volumes. If @monitor is %NULL, the monitor from g_volume_monitor_get() will
+ * be used.
+ *
+ * Returns: (transfer full): a new #OstreeRepoFinderMount
+ * Since: 2017.8
+ */
+OstreeRepoFinderMount *
+ostree_repo_finder_mount_new (GVolumeMonitor *monitor)
+{
+  g_return_val_if_fail (monitor == NULL || G_IS_VOLUME_MONITOR (monitor), NULL);
+
+  return g_object_new (OSTREE_TYPE_REPO_FINDER_MOUNT,
+                       "monitor", monitor,
+                       NULL);
+}

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

src/libostree/ostree-repo-pull.c

@@ -42,6 +42,7 @@
 #ifdef OSTREE_ENABLE_EXPERIMENTAL_API
 #include "ostree-repo-finder.h"
 #include "ostree-repo-finder-config.h"
+#include "ostree-repo-finder-mount.h"
 #endif /* OSTREE_ENABLE_EXPERIMENTAL_API */
 
 #include <gio/gunixinputstream.h>
@@ -4087,6 +4088,7 @@ ostree_repo_find_remotes_async (OstreeRepo                     *self,
   GMainContext *context;
   OstreeRepoFinder *default_finders[4] = { NULL, };
   g_autoptr(OstreeRepoFinder) finder_config = NULL;
+  g_autoptr(OstreeRepoFinder) finder_mount = NULL;
 
   g_return_if_fail (OSTREE_IS_REPO (self));
   g_return_if_fail (is_valid_collection_ref_array (refs));
@@ -4106,8 +4108,10 @@ ostree_repo_find_remotes_async (OstreeRepo                     *self,
   if (finders == NULL)
     {
       finder_config = OSTREE_REPO_FINDER (ostree_repo_finder_config_new ());
+      finder_mount = OSTREE_REPO_FINDER (ostree_repo_finder_mount_new (NULL));
 
       default_finders[0] = finder_config;
+      default_finders[1] = finder_mount;
 
       finders = default_finders;
     }

src/libostree/ostree.h

@@ -39,6 +39,7 @@
 #include <ostree-ref.h>
 #include <ostree-repo-finder.h>
 #include <ostree-repo-finder-config.h>
+#include <ostree-repo-finder-mount.h>
 #endif /* OSTREE_ENABLE_EXPERIMENTAL_API */
 
 #include <ostree-autocleanups.h>