[ostree] repo: Move the scanning hardlinks optimization out of prepare_transaction

[Jasper St. Pierre <jstpierre src gnome org>]

commit bd2948e9641b4179d53ee5763bd3effb1617ca5a
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Fri Sep 6 18:51:54 2013 -0400

    repo: Move the scanning hardlinks optimization out of prepare_transaction
    
    This is just a terrible API to have. Make the scanning a separate method,
    and document it as an optimization.

 doc/ostree-sections.txt            |    1 +
 src/libostree/ostree-repo-commit.c |   48 +++++++++++++++++++++++++++--------
 src/libostree/ostree-repo-pull.c   |    2 +-
 src/libostree/ostree-repo.h        |    5 +++-
 src/ostree/ot-builtin-commit.c     |    5 +++-
 src/ostree/ot-builtin-pull-local.c |    2 +-
 6 files changed, 48 insertions(+), 15 deletions(-)
---
diff --git a/doc/ostree-sections.txt b/doc/ostree-sections.txt
index f5abbd5..1e4a6f5 100644
--- a/doc/ostree-sections.txt
+++ b/doc/ostree-sections.txt
@@ -64,6 +64,7 @@ ostree_repo_copy_config
 ostree_repo_get_parent
 ostree_repo_write_config
 OstreeRepoTransactionStats
+ostree_repo_scan_hardlinks
 ostree_repo_prepare_transaction
 ostree_repo_commit_transaction
 ostree_repo_abort_transaction
diff --git a/src/libostree/ostree-repo-commit.c b/src/libostree/ostree-repo-commit.c
index 8b69e48..32b0e2e 100644
--- a/src/libostree/ostree-repo-commit.c
+++ b/src/libostree/ostree-repo-commit.c
@@ -525,9 +525,45 @@ devino_cache_lookup (OstreeRepo           *self,
 }
 
 /**
+ * ostree_repo_scan_hardlinks:
+ * @self: An #OstreeRepo
+ * @cancellable: Cancellable
+ * @error: Error
+ *
+ * When ostree builds a mutable tree from directory like in
+ * ostree_repo_write_directory_to_mtree(), it has to scan all files that you
+ * pass in and compute their checksums. If your commit contains hardlinks from
+ * ostree's existing repo, ostree can build a mapping of device numbers and
+ * inodes to their checksum.
+ *
+ * There is an upfront cost to creating this mapping, as this will scan the
+ * entire objects directory. If your commit is composed of mostly hardlinks to
+ * existing ostree objects, then this will speed up considerably, so call it
+ * before you call ostree_write_directory_to_mtree() or similar.
+ */
+gboolean
+ostree_repo_scan_hardlinks (OstreeRepo    *self,
+                            GCancellable  *cancellable,
+                            GError       **error)
+{
+  gboolean ret = FALSE;
+
+  g_return_val_if_fail (self->in_transaction == TRUE, FALSE);
+
+  if (!self->loose_object_devino_hash)
+    self->loose_object_devino_hash = g_hash_table_new_full (devino_hash, devino_equal, g_free, g_free);
+  g_hash_table_remove_all (self->loose_object_devino_hash);
+  if (!scan_loose_devino (self, self->loose_object_devino_hash, cancellable, error))
+    goto out;
+
+  ret = TRUE;
+ out:
+  return ret;
+}
+
+/**
  * ostree_repo_prepare_transaction:
  * @self: An #OstreeRepo
- * @enable_commit_hardlink_scan:
  * @out_transaction_resume: (allow-none) (out): Whether this transaction
  * is resuming from a previous one.
  * @cancellable: Cancellable
@@ -543,7 +579,6 @@ devino_cache_lookup (OstreeRepo           *self,
  */
 gboolean
 ostree_repo_prepare_transaction (OstreeRepo     *self,
-                                 gboolean        enable_commit_hardlink_scan,
                                  gboolean       *out_transaction_resume,
                                  GCancellable   *cancellable,
                                  GError        **error)
@@ -575,15 +610,6 @@ ostree_repo_prepare_transaction (OstreeRepo     *self,
                                   cancellable, error))
     goto out;
 
-  if (enable_commit_hardlink_scan)
-    {
-      if (!self->loose_object_devino_hash)
-        self->loose_object_devino_hash = g_hash_table_new_full (devino_hash, devino_equal, g_free, g_free);
-      g_hash_table_remove_all (self->loose_object_devino_hash);
-      if (!scan_loose_devino (self, self->loose_object_devino_hash, cancellable, error))
-        goto out;
-    }
-
   ret = TRUE;
   if (out_transaction_resume)
     *out_transaction_resume = ret_transaction_resume;
diff --git a/src/libostree/ostree-repo-pull.c b/src/libostree/ostree-repo-pull.c
index 0a42e3f..d557e42 100644
--- a/src/libostree/ostree-repo-pull.c
+++ b/src/libostree/ostree-repo-pull.c
@@ -1286,7 +1286,7 @@ ostree_repo_pull (OstreeRepo               *self,
         }
     }
 
-  if (!ostree_repo_prepare_transaction (pull_data->repo, FALSE, &pull_data->transaction_resuming,
+  if (!ostree_repo_prepare_transaction (pull_data->repo, &pull_data->transaction_resuming,
                                         cancellable, error))
     goto out;
 
diff --git a/src/libostree/ostree-repo.h b/src/libostree/ostree-repo.h
index 882e306..8a4c75d 100644
--- a/src/libostree/ostree-repo.h
+++ b/src/libostree/ostree-repo.h
@@ -112,8 +112,11 @@ struct _OstreeRepoTransactionStats {
 
 GType ostree_repo_transaction_stats_get_type (void);
 
+gboolean      ostree_repo_scan_hardlinks      (OstreeRepo     *self,
+                                               GCancellable   *cancellable,
+                                               GError        **error);
+
 gboolean      ostree_repo_prepare_transaction (OstreeRepo     *self,
-                                               gboolean        enable_commit_hardlink_scan,
                                                gboolean       *out_transaction_resume,
                                                GCancellable   *cancellable,
                                                GError        **error);
diff --git a/src/ostree/ot-builtin-commit.c b/src/ostree/ot-builtin-commit.c
index 80d0e50..d9ed29d 100644
--- a/src/ostree/ot-builtin-commit.c
+++ b/src/ostree/ot-builtin-commit.c
@@ -290,7 +290,10 @@ ostree_builtin_commit (int argc, char **argv, OstreeRepo *repo, GCancellable *ca
       goto out;
     }
 
-  if (!ostree_repo_prepare_transaction (repo, opt_link_checkout_speedup, NULL, cancellable, error))
+  if (!ostree_repo_prepare_transaction (repo, NULL, cancellable, error))
+    goto out;
+
+  if (opt_link_checkout_speedup && !ostree_repo_scan_hardlinks (repo, cancellable, error))
     goto out;
 
   mtree = ostree_mutable_tree_new ();
diff --git a/src/ostree/ot-builtin-pull-local.c b/src/ostree/ot-builtin-pull-local.c
index 98ba6cd..e435457 100644
--- a/src/ostree/ot-builtin-pull-local.c
+++ b/src/ostree/ot-builtin-pull-local.c
@@ -230,7 +230,7 @@ ostree_builtin_pull_local (int argc, char **argv, OstreeRepo *repo, GCancellable
         }
     }
 
-  if (!ostree_repo_prepare_transaction (data->dest_repo, FALSE, &transaction_resuming,
+  if (!ostree_repo_prepare_transaction (data->dest_repo, &transaction_resuming,
                                         cancellable, error))
     goto out;