ntdb: fix database corruption when transaction doesn't change anything.

ntdb's transaction code has an optimization which tdb's doesnt: it
only writes the parts of blocks whose contents have changed.  This
means we can actually have a transaction which turns out to need no
recovery region.

This breaks the recovery setup logic, which sets the current recovery
size to 0 if there's no recovery area, and assumes that we'll always
create a new recovery area since the recovery will always need > 0
bytes.

In fact, if we really haven't changed anything, we can skip the
transaction commit altogether: since this happens at least once with
Samba, it's worth doing.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

1 files changed, 58 insertions, 0 deletions

diff --git a/lib/ntdb/test/api-60-noop-transaction.c b/lib/ntdb/test/api-60-noop-transaction.c
new file mode 100644
index 0000000000..a429e67907
--- /dev/null
+++ b/lib/ntdb/test/api-60-noop-transaction.c
@@ -0,0 +1,58 @@
+#include "private.h" // struct ntdb_context
+#include "ntdb.h"
+#include "tap-interface.h"
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include "logging.h"
+
+int main(int argc, char *argv[])
+{
+	unsigned int i;
+	struct ntdb_context *ntdb;
+	int flags[] = { NTDB_DEFAULT, NTDB_NOMMAP,
+			NTDB_CONVERT, NTDB_NOMMAP|NTDB_CONVERT };
+	NTDB_DATA key = ntdb_mkdata("key", 3);
+	NTDB_DATA data = ntdb_mkdata("data", 4), d;
+
+	plan_tests(sizeof(flags) / sizeof(flags[0]) * 12 + 1);
+
+	for (i = 0; i < sizeof(flags) / sizeof(flags[0]); i++) {
+		ntdb = ntdb_open("api-60-transaction.ntdb",
+				 flags[i]|MAYBE_NOSYNC,
+				 O_RDWR|O_CREAT|O_TRUNC, 0600, &tap_log_attr);
+		ok1(ntdb);
+		if (!ntdb)
+			continue;
+
+		ok1(ntdb_store(ntdb, key, data, NTDB_INSERT) == 0);
+
+		ok1(ntdb_transaction_start(ntdb) == 0);
+		/* Do an identical replace. */
+		ok1(ntdb_store(ntdb, key, data, NTDB_REPLACE) == 0);
+		ok1(ntdb_transaction_commit(ntdb) == 0);
+
+		ok1(ntdb_check(ntdb, NULL, NULL) == 0);
+		ok1(ntdb_fetch(ntdb, key, &d) == NTDB_SUCCESS);
+		ok1(ntdb_deq(data, d));
+		free(d.dptr);
+		ntdb_close(ntdb);
+
+		/* Reopen, fetch. */
+		ntdb = ntdb_open("api-60-transaction.ntdb",
+				 flags[i]|MAYBE_NOSYNC,
+				 O_RDWR, 0600, &tap_log_attr);
+		ok1(ntdb);
+		if (!ntdb)
+			continue;
+		ok1(ntdb_check(ntdb, NULL, NULL) == 0);
+		ok1(ntdb_fetch(ntdb, key, &d) == NTDB_SUCCESS);
+		ok1(ntdb_deq(data, d));
+		free(d.dptr);
+		ntdb_close(ntdb);
+	}
+
+	ok1(tap_log_messages == 0);
+	return exit_status();
+}