odb: make creation of on-disk structures pluggable

When creating a new "files" object database source we have to create a
couple of directories. These directories are of course specific to this
particular backend, and a different backend may require a setup that is
completely different.

Make the creation of on-disk structures pluggable to accommodate for
this.

Note that there is one exception though: the "objects" directory must
exist in a repository regardless of which backend is in use. If it
doesn't exist then the repository is not treated as a Git repository at
all. Consequently, we create this directory regardless of the backend.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

odb/source-files.c

@@ -9,6 +9,7 @@
 #include "odb/source-files.h"
 #include "odb/source-loose.h"
 #include "packfile.h"
+#include "path.h"
 #include "strbuf.h"
 #include "write-or-die.h"
 
@@ -41,6 +42,23 @@ static void odb_source_files_close(struct odb_source *source)
 	odb_source_close(&files->packed->base);
 }
 
+static int odb_source_files_create_on_disk(struct odb_source *source)
+{
+	struct strbuf path = STRBUF_INIT;
+
+	safe_create_dir(source->odb->repo, source->path, 1);
+
+	strbuf_addf(&path, "%s/pack", source->path);
+	safe_create_dir(source->odb->repo, path.buf, 1);
+
+	strbuf_reset(&path);
+	strbuf_addf(&path, "%s/info", source->path);
+	safe_create_dir(source->odb->repo, path.buf, 1);
+
+	strbuf_release(&path);
+	return 0;
+}
+
 static void odb_source_files_prepare(struct odb_source *source,
 				     enum odb_prepare_flags flags)
 {
@@ -271,6 +289,7 @@ struct odb_source_files *odb_source_files_new(struct object_database *odb,
 
 	files->base.free = odb_source_files_free;
 	files->base.close = odb_source_files_close;
+	files->base.create_on_disk = odb_source_files_create_on_disk;
 	files->base.prepare = odb_source_files_prepare;
 	files->base.read_object_info = odb_source_files_read_object_info;
 	files->base.read_object_stream = odb_source_files_read_object_stream;

odb/source.h

@@ -89,6 +89,18 @@ struct odb_source {
 	 */
 	void (*close)(struct odb_source *source);
 
+	/*
+	 * This callback is expected to create on-disk data structures that are
+	 * required for this source to operate.
+	 *
+	 * The callback is expected to return 0 on success, a negative error
+	 * code otherwise.
+	 *
+	 * This callback may be NULL in case the source does not need any
+	 * on-disk setup.
+	 */
+	int (*create_on_disk)(struct odb_source *source);
+
 	/*
 	 * This callback is expected to prepare the source so that it becomes
 	 * ready for use. It optionally clears underlying caches of the object
@@ -316,6 +328,17 @@ static inline void odb_source_close(struct odb_source *source)
 	source->close(source);
 }
 
+/*
+ * Create on-disk data structures that are required for this source to operate
+ * correctly. Returns 0 on success, a negative error code otherwise.
+ */
+static inline int odb_source_create_on_disk(struct odb_source *source)
+{
+	if (!source->create_on_disk)
+		return 0;
+	return source->create_on_disk(source);
+}
+
 /*
  * Prepare the object database source and clear any caches. Depending on the
  * backend used this may have the effect that concurrently-written objects

setup.c

@@ -2666,29 +2666,34 @@ static int create_default_files(struct repository *repo,
 static void create_object_database(struct repository *repo)
 {
 	char *object_directory, *alternate_object_directories;
-	struct strbuf path = STRBUF_INIT;
-	size_t baselen;
 
 	get_object_directories(&object_directory, &alternate_object_directories);
-	repo->objects = odb_new(repo, object_directory,
-				alternate_object_directories);
 
-	strbuf_addstr(&path, repo_get_object_directory(repo));
-	baselen = path.len;
-
-	safe_create_dir(repo, path.buf, 1);
+	/*
+	 * Create the "objects" directory in the common directory. This is done
+	 * so that the repository can be discovered regardless of the backend
+	 * used.
+	 *
+	 * Note that we only do this in case the object directory wasn't
+	 * overwritten via an environment variable. If it _is_ being overridden
+	 * then we skip this step, as the repository won't be discoverable
+	 * anyway without the environment variable.
+	 */
+	if (!object_directory) {
+		struct strbuf objects_dir = STRBUF_INIT;
+		repo_common_path_append(repo, &objects_dir, "objects");
+		safe_create_dir(repo, objects_dir.buf, 1);
+		strbuf_release(&objects_dir);
+	}
 
-	strbuf_setlen(&path, baselen);
-	strbuf_addstr(&path, "/pack");
-	safe_create_dir(repo, path.buf, 1);
+	repo->objects = odb_new(repo, object_directory,
+				alternate_object_directories);
 
-	strbuf_setlen(&path, baselen);
-	strbuf_addstr(&path, "/info");
-	safe_create_dir(repo, path.buf, 1);
+	if (odb_source_create_on_disk(repo->objects->sources) < 0)
+		die("failed creating object database");
 
 	free(alternate_object_directories);
 	free(object_directory);
-	strbuf_release(&path);
 }
 
 static void separate_git_dir(const char *git_dir, const char *git_link)