[PATCH 05/12] git repository reading: start reading the actual file contents

[Linus Torvalds]

From: Linus Torvalds <torvalds at linux-foundation.org>
Date: Sat, 8 Mar 2014 13:11:50 -0800
Subject: [PATCH 05/12] git repository reading: start reading the actual file contents

If we want to scale to thousands of dives, we'll eventually want to read
the dive computer files lazily when actually needed, but for now we do
everything synchronously.  Even if that may actually be slower than
parsing one big XML file.

The git object store is pretty efficient, but especially with some
history, the compression and delta application will certainly not be
free.

This does all the git object unpacking, but none of the actual data
parsing yet.  But as part of looking up the file objects, we do get the
dive number (which is in the name of the dive file).

Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
---
 load-git.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 64 insertions(+), 5 deletions(-)

diff --git a/load-git.c b/load-git.c
index 60159381f5c6..79c17ef2261d 100644
--- a/load-git.c
+++ b/load-git.c
@@ -244,25 +244,84 @@ static int walk_tree_directory(const char *root, const git_tree_entry *entry)
 	return dive_trip_directory(root, name);
 }
 
-static int walk_tree_file(const char *root, const git_tree_entry *entry)
+git_blob *git_tree_entry_blob(git_repository *repo, const git_tree_entry *entry)
 {
-	/* Parse actual dive/trip data here */
-	return GIT_WALK_OK;
+	const git_oid *id = git_tree_entry_id(entry);
+	git_blob *blob;
+
+	if (git_blob_lookup(&blob, repo, id))
+		return NULL;
+	return blob;
+}
+
+/*
+ * We should *really* try to delay the dive computer data parsing
+ * until necessary, in order to reduce load-time. The parsing is
+ * cheap, but the loading of the git blob into memory can be pretty
+ * costly.
+ */
+static int parse_divecomputer_entry(git_repository *repo, const git_tree_entry *entry, const char *suffix)
+{
+	git_blob *blob = git_tree_entry_blob(repo, entry);
+	if (!blob)
+		return report_error("Unable to read divecomputer file");
+	git_blob_free(blob);
+	return 0;
+}
+
+static int parse_dive_entry(git_repository *repo, const git_tree_entry *entry, const char *suffix)
+{
+	struct dive *dive = active_dive;
+	git_blob *blob = git_tree_entry_blob(repo, entry);
+	if (!blob)
+		return report_error("Unable to read dive file");
+	if (*suffix)
+		dive->number = atoi(suffix+1);
+	git_blob_free(blob);
+	return 0;
+}
+
+static int parse_trip_entry(git_repository *repo, const git_tree_entry *entry)
+{
+	git_blob *blob = git_tree_entry_blob(repo, entry);
+	if (!blob)
+		return report_error("Unable to read trip file");
+	git_blob_free(blob);
+	return 0;
+}
+
+static int walk_tree_file(const char *root, const git_tree_entry *entry, git_repository *repo)
+{
+	struct dive *dive = active_dive;
+	dive_trip_t *trip = active_trip;
+	const char *name = git_tree_entry_name(entry);
+
+	if (dive && !strncmp(name, "Divecomputer", 12))
+		return parse_divecomputer_entry(repo, entry, name+12);
+	if (dive && !strncmp(name, "Dive", 4))
+		return parse_dive_entry(repo, entry, name+4);
+	if (trip && !strcmp(name, "00-Trip"))
+		return parse_trip_entry(repo, entry);
+	report_error("Unknown file %s%s (%p %p)", root, name, dive, trip);
+	return GIT_WALK_SKIP;
 }
 
 static int walk_tree_cb(const char *root, const git_tree_entry *entry, void *payload)
 {
+	git_repository *repo = payload;
 	git_filemode_t mode = git_tree_entry_filemode(entry);
 
 	if (mode == GIT_FILEMODE_TREE)
 		return walk_tree_directory(root, entry);
 
-	return walk_tree_file(root, entry);
+	walk_tree_file(root, entry, repo);
+	/* Ignore failed blob loads */
+	return GIT_WALK_OK;
 }
 
 static int load_dives_from_tree(git_repository *repo, git_tree *tree)
 {
-	git_tree_walk(tree, GIT_TREEWALK_PRE, walk_tree_cb, NULL);
+	git_tree_walk(tree, GIT_TREEWALK_PRE, walk_tree_cb, repo);
 	return 0;
 }
 
-- 
1.8.5.3