[PATCH v7 06/33] refs: add a backend method structure with transaction functions

[David Turner <dturner@twopensource.com>]

From: Ronnie Sahlberg <sahlberg@google.com>

Add a ref structure for storage backend methods. Start by adding a
method pointer for the transaction commit function.

Add a function set_refs_backend to switch between storage
backends. The files based storage backend is the default.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: David Turner <dturner@twopensource.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Jeff King <peff@peff.net>
---
 refs.c               | 40 ++++++++++++++++++++++++++++++++++++++++
 refs.h               |  7 +++++++
 refs/files-backend.c | 10 ++++++++--
 refs/refs-internal.h | 12 ++++++++++++
 4 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/refs.c b/refs.c
index 15aabc6..2e8efa9 100644
--- a/refs.c
+++ b/refs.c
@@ -10,6 +10,38 @@
 #include "tag.h"
 
 /*
+ * We always have a files backend and it is the default.
+ */
+static struct ref_storage_be *the_refs_backend = &refs_be_files;
+/*
+ * List of all available backends
+ */
+static struct ref_storage_be *refs_backends = &refs_be_files;
+
+static struct ref_storage_be *find_ref_storage_backend(const char *name)
+{
+	struct ref_storage_be *be;
+	for (be = refs_backends; be; be = be->next)
+		if (!strcmp(be->name, name))
+			return be;
+	return NULL;
+}
+
+int set_ref_storage_backend(const char *name)
+{
+	struct ref_storage_be *be = find_ref_storage_backend(name);
+	if (!be)
+		return -1;
+	the_refs_backend = be;
+	return 0;
+}
+
+int ref_storage_backend_exists(const char *name)
+{
+	return find_ref_storage_backend(name) != NULL;
+}
+
+/*
  * How to handle various characters in refnames:
  * 0: An acceptable character for refs
  * 1: End-of-component
@@ -1161,6 +1193,7 @@ int for_each_rawref(each_ref_fn fn, void *cb_data)
 	return do_for_each_ref(NULL, "", fn, 0,
 			       DO_FOR_EACH_INCLUDE_BROKEN, cb_data);
 }
+
 /* This function needs to return a meaningful errno on failure */
 static const char *resolve_ref_1(const char *refname,
 				 int resolve_flags,
@@ -1265,3 +1298,10 @@ const char *resolve_ref_unsafe(const char *refname, int resolve_flags,
 	strbuf_release(&sb_path);
 	return ret;
 }
+
+/* backend functions */
+int ref_transaction_commit(struct ref_transaction *transaction,
+			   struct strbuf *err)
+{
+	return the_refs_backend->transaction_commit(transaction, err);
+}
diff --git a/refs.h b/refs.h
index 31a2fa6..3405842 100644
--- a/refs.h
+++ b/refs.h
@@ -509,4 +509,11 @@ extern int reflog_expire(const char *refname, const unsigned char *sha1,
 			 reflog_expiry_cleanup_fn cleanup_fn,
 			 void *policy_cb_data);
 
+/*
+ * Switch to an alternate ref storage backend.
+ */
+int set_ref_storage_backend(const char *name);
+
+int ref_storage_backend_exists(const char *name);
+
 #endif /* REFS_H */
diff --git a/refs/files-backend.c b/refs/files-backend.c
index 2fb7714..a509240 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -3003,8 +3003,8 @@ static int ref_update_reject_duplicates(struct string_list *refnames,
 	return 0;
 }
 
-int ref_transaction_commit(struct ref_transaction *transaction,
-			   struct strbuf *err)
+static int files_transaction_commit(struct ref_transaction *transaction,
+				    struct strbuf *err)
 {
 	int ret = 0, i;
 	int n = transaction->nr;
@@ -3390,3 +3390,9 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
 	unlock_ref(lock);
 	return -1;
 }
+
+struct ref_storage_be refs_be_files = {
+	NULL,
+	"files",
+	files_transaction_commit,
+};
diff --git a/refs/refs-internal.h b/refs/refs-internal.h
index 979a136..62ba0c0 100644
--- a/refs/refs-internal.h
+++ b/refs/refs-internal.h
@@ -212,4 +212,16 @@ int do_for_each_ref(const char *submodule, const char *base,
 int read_raw_ref(const char *refname, unsigned char *sha1,
 		 struct strbuf *symref, struct strbuf *sb_path,
 		 unsigned int *flags);
+
+/* refs backends */
+typedef int ref_transaction_commit_fn(struct ref_transaction *transaction,
+				      struct strbuf *err);
+
+struct ref_storage_be {
+	struct ref_storage_be *next;
+	const char *name;
+	ref_transaction_commit_fn *transaction_commit;
+};
+
+extern struct ref_storage_be refs_be_files;
 #endif /* REFS_REFS_INTERNAL_H */
-- 
2.4.2.767.g62658d5-twtrsrc