[PATCH] don't load and decompress objects twice with parse_object()

It turns out that parse_object() is loading and decompressing given
object to free it just before calling the specific object parsing
function which does mmap and decompress the same object again. This
patch introduces the ability to parse specific objects directly from a
memory buffer.

Without this patch, running git-fsck-cache on the kernel repositorytake:

	real    0m13.006s
	user    0m11.421s
	sys     0m1.218s

With this patch applied:

	real    0m8.060s
	user    0m7.071s
	sys     0m0.710s

The performance increase is significant, and this is kind of a
prerequisite for sane delta object support with fsck.

Signed-off-by: Nicolas Pitre <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

blob.c

@@ -22,21 +22,29 @@ struct blob *lookup_blob(unsigned char *sha1)
 	return (struct blob *) obj;
 }
 
+int parse_blob_buffer(struct blob *item, void *buffer, unsigned long size)
+{
+	item->object.parsed = 1;
+	return 0;
+}
+
 int parse_blob(struct blob *item)
 {
         char type[20];
         void *buffer;
         unsigned long size;
+	int ret;
+
         if (item->object.parsed)
                 return 0;
-        item->object.parsed = 1;
         buffer = read_sha1_file(item->object.sha1, type, &size);
         if (!buffer)
                 return error("Could not read %s",
                              sha1_to_hex(item->object.sha1));
-	free(buffer);
         if (strcmp(type, blob_type))
                 return error("Object %s not a blob",
                              sha1_to_hex(item->object.sha1));
-	return 0;
+	ret = parse_blob_buffer(item, buffer, size);
+	free(buffer);
+	return ret;
 }

blob.h

@@ -11,6 +11,8 @@ struct blob {
 
 struct blob *lookup_blob(unsigned char *sha1);
 
+int parse_blob_buffer(struct blob *item, void *buffer, unsigned long size);
+
 int parse_blob(struct blob *item);
 
 #endif /* BLOB_H */

commit.c

@@ -41,24 +41,14 @@ static unsigned long parse_commit_date(const char *buf)
 	return date;
 }
 
-int parse_commit(struct commit *item)
+int parse_commit_buffer(struct commit *item, void *buffer, unsigned long size)
 {
-	char type[20];
-	void * buffer, *bufptr;
-	unsigned long size;
+	void *bufptr = buffer;
 	unsigned char parent[20];
+
 	if (item->object.parsed)
 		return 0;
 	item->object.parsed = 1;
-	buffer = bufptr = read_sha1_file(item->object.sha1, type, &size);
-	if (!buffer)
-		return error("Could not read %s",
-			     sha1_to_hex(item->object.sha1));
-	if (strcmp(type, commit_type)) {
-		free(buffer);
-		return error("Object %s not a commit",
-			     sha1_to_hex(item->object.sha1));
-	}
 	get_sha1_hex(bufptr + 5, parent);
 	item->tree = lookup_tree(parent);
 	if (item->tree)
@@ -74,10 +64,32 @@ int parse_commit(struct commit *item)
 		bufptr += 48;
 	}
 	item->date = parse_commit_date(bufptr);
-	free(buffer);
 	return 0;
 }
 
+int parse_commit(struct commit *item)
+{
+	char type[20];
+	void *buffer;
+	unsigned long size;
+	int ret;
+
+	if (item->object.parsed)
+		return 0;
+	buffer = read_sha1_file(item->object.sha1, type, &size);
+	if (!buffer)
+		return error("Could not read %s",
+			     sha1_to_hex(item->object.sha1));
+	if (strcmp(type, commit_type)) {
+		free(buffer);
+		return error("Object %s not a commit",
+			     sha1_to_hex(item->object.sha1));
+	}
+	ret = parse_commit_buffer(item, buffer, size);
+	free(buffer);
+	return ret;
+}
+
 void commit_list_insert(struct commit *item, struct commit_list **list_p)
 {
 	struct commit_list *new_list = xmalloc(sizeof(struct commit_list));

commit.h

@@ -20,6 +20,8 @@ extern const char *commit_type;
 
 struct commit *lookup_commit(unsigned char *sha1);
 
+int parse_commit_buffer(struct commit *item, void *buffer, unsigned long size);
+
 int parse_commit(struct commit *item);
 
 void commit_list_insert(struct commit *item, struct commit_list **list_p);

object.c

@@ -104,6 +104,7 @@ struct object *parse_object(unsigned char *sha1)
 	unsigned long mapsize;
 	void *map = map_sha1_file(sha1, &mapsize);
 	if (map) {
+		struct object *obj;
 		char type[100];
 		unsigned long size;
 		void *buffer = unpack_sha1_file(map, mapsize, type, &size);
@@ -112,26 +113,27 @@ struct object *parse_object(unsigned char *sha1)
 			return NULL;
 		if (check_sha1_signature(sha1, buffer, size, type) < 0)
 			printf("sha1 mismatch %s\n", sha1_to_hex(sha1));
-		free(buffer);
 		if (!strcmp(type, "blob")) {
-			struct blob *ret = lookup_blob(sha1);
-			parse_blob(ret);
-			return &ret->object;
+			struct blob *blob = lookup_blob(sha1);
+			parse_blob_buffer(blob, buffer, size);
+			obj = &blob->object;
 		} else if (!strcmp(type, "tree")) {
-			struct tree *ret = lookup_tree(sha1);
-			parse_tree(ret);
-			return &ret->object;
+			struct tree *tree = lookup_tree(sha1);
+			parse_tree_buffer(tree, buffer, size);
+			obj = &tree->object;
 		} else if (!strcmp(type, "commit")) {
-			struct commit *ret = lookup_commit(sha1);
-			parse_commit(ret);
-			return &ret->object;
+			struct commit *commit = lookup_commit(sha1);
+			parse_commit_buffer(commit, buffer, size);
+			obj = &commit->object;
 		} else if (!strcmp(type, "tag")) {
-			struct tag *ret = lookup_tag(sha1);
-			parse_tag(ret);
-			return &ret->object;
+			struct tag *tag = lookup_tag(sha1);
+			parse_tag_buffer(tag, buffer, size);
+			obj = &tag->object;
 		} else {
-			return NULL;
+			obj = NULL;
 		}
+		free(buffer);
+		return obj;
 	}
 	return NULL;
 }

tag.c

@@ -21,62 +21,68 @@ struct tag *lookup_tag(unsigned char *sha1)
         return (struct tag *) obj;
 }
 
-int parse_tag(struct tag *item)
+int parse_tag_buffer(struct tag *item, void *data, unsigned long size)
 {
-        char type[20];
-        void *data, *bufptr;
-        unsigned long size;
 	int typelen, taglen;
 	unsigned char object[20];
 	const char *type_line, *tag_line, *sig_line;
 
         if (item->object.parsed)
                 return 0;
         item->object.parsed = 1;
-        data = bufptr = read_sha1_file(item->object.sha1, type, &size);
-        if (!data)
-                return error("Could not read %s",
-                             sha1_to_hex(item->object.sha1));
-        if (strcmp(type, tag_type)) {
-		free(data);
-                return error("Object %s not a tag",
-                             sha1_to_hex(item->object.sha1));
-	}
 
 	if (size < 64)
-		goto err;
+		return -1;
 	if (memcmp("object ", data, 7) || get_sha1_hex(data + 7, object))
-		goto err;
+		return -1;
 
 	item->tagged = parse_object(object);
 	if (item->tagged)
 		add_ref(&item->object, item->tagged);
 
 	type_line = data + 48;
 	if (memcmp("\ntype ", type_line-1, 6))
-		goto err;
+		return -1;
 
 	tag_line = strchr(type_line, '\n');
 	if (!tag_line || memcmp("tag ", ++tag_line, 4))
-		goto err;
+		return -1;
 
 	sig_line = strchr(tag_line, '\n');
 	if (!sig_line)
-		goto err;
+		return -1;
 	sig_line++;
 
 	typelen = tag_line - type_line - strlen("type \n");
 	if (typelen >= 20)
-		goto err;
+		return -1;
 	taglen = sig_line - tag_line - strlen("tag \n");
 	item->tag = xmalloc(taglen + 1);
 	memcpy(item->tag, tag_line + 4, taglen);
 	item->tag[taglen] = '\0';
 
-	free(data);
 	return 0;
+}
 
-err:
+int parse_tag(struct tag *item)
+{
+	char type[20];
+	void *data;
+	unsigned long size;
+	int ret;
+
+	if (item->object.parsed)
+		return 0;
+	data = read_sha1_file(item->object.sha1, type, &size);
+	if (!data)
+		return error("Could not read %s",
+			     sha1_to_hex(item->object.sha1));
+	if (strcmp(type, tag_type)) {
+		free(data);
+		return error("Object %s not a tag",
+			     sha1_to_hex(item->object.sha1));
+	}
+	ret = parse_tag_buffer(item, data, size);
 	free(data);
-	return -1;
+	return ret;
 }

tag.h

@@ -13,6 +13,7 @@ struct tag {
 };
 
 extern struct tag *lookup_tag(unsigned char *sha1);
+extern int parse_tag_buffer(struct tag *item, void *data, unsigned long size);
 extern int parse_tag(struct tag *item);
 
 #endif /* TAG_H */

tree.c

@@ -88,24 +88,14 @@ struct tree *lookup_tree(unsigned char *sha1)
 	return (struct tree *) obj;
 }
 
-int parse_tree(struct tree *item)
+int parse_tree_buffer(struct tree *item, void *buffer, unsigned long size)
 {
-	char type[20];
-	void *buffer, *bufptr;
-	unsigned long size;
+	void *bufptr = buffer;
 	struct tree_entry_list **list_p;
+
 	if (item->object.parsed)
 		return 0;
 	item->object.parsed = 1;
-	buffer = bufptr = read_sha1_file(item->object.sha1, type, &size);
-	if (!buffer)
-		return error("Could not read %s",
-			     sha1_to_hex(item->object.sha1));
-	if (strcmp(type, tree_type)) {
-		free(buffer);
-		return error("Object %s not a tree",
-			     sha1_to_hex(item->object.sha1));
-	}
 	list_p = &item->entries;
 	while (size) {
 		struct object *obj;
@@ -115,10 +105,8 @@ int parse_tree(struct tree *item)
 		char *path = strchr(bufptr, ' ');
 		unsigned int mode;
 		if (size < len + 20 || !path || 
-		    sscanf(bufptr, "%o", &mode) != 1) {
-			free(buffer);
+		    sscanf(bufptr, "%o", &mode) != 1)
 			return -1;
-		}
 
 		entry = xmalloc(sizeof(struct tree_entry_list));
 		entry->name = strdup(path + 1);
@@ -144,6 +132,28 @@ int parse_tree(struct tree *item)
 		*list_p = entry;
 		list_p = &entry->next;
 	}
-	free(buffer);
 	return 0;
 }
+
+int parse_tree(struct tree *item)
+{
+	 char type[20];
+	 void *buffer;
+	 unsigned long size;
+	 int ret;
+
+	if (item->object.parsed)
+		return 0;
+	buffer = read_sha1_file(item->object.sha1, type, &size);
+	if (!buffer)
+		return error("Could not read %s",
+			     sha1_to_hex(item->object.sha1));
+	if (strcmp(type, tree_type)) {
+		free(buffer);
+		return error("Object %s not a tree",
+			     sha1_to_hex(item->object.sha1));
+	}
+	ret = parse_tree_buffer(item, buffer, size);
+	free(buffer);
+	return ret;
+}

tree.h

@@ -25,6 +25,8 @@ struct tree {
 
 struct tree *lookup_tree(unsigned char *sha1);
 
+int parse_tree_buffer(struct tree *item, void *buffer, unsigned long size);
+
 int parse_tree(struct tree *tree);
 
 #endif /* TREE_H */