Fix traverse nesting unlock bug.

ccan/tdb/test/run-nested-traverse.c

+#define _XOPEN_SOURCE 500
+#include "tdb/tdb.h"
+#include "tdb/io.c"
+#include "tdb/tdb.c"
+#include "tdb/lock.c"
+#include "tdb/freelist.c"
+#include "tdb/traverse.c"
+#include "tdb/transaction.c"
+#include "tdb/error.c"
+#include "tdb/open.c"
+#include "tap/tap.h"
+#include <stdlib.h>
+#include <stdbool.h>
+#include <err.h>
+
+static bool correct_key(TDB_DATA key)
+{
+	return key.dsize == strlen("hi")
+		&& memcmp(key.dptr, "hi", key.dsize) == 0;
+}
+
+static bool correct_data(TDB_DATA data)
+{
+	return data.dsize == strlen("world")
+		&& memcmp(data.dptr, "world", data.dsize) == 0;
+}
+
+static int traverse2(struct tdb_context *tdb, TDB_DATA key, TDB_DATA data,
+		     void *p)
+{
+	ok1(correct_key(key));
+	ok1(correct_data(data));
+	return 0;
+}
+
+static int traverse1(struct tdb_context *tdb, TDB_DATA key, TDB_DATA data,
+		     void *p)
+{
+	ok1(correct_key(key));
+	ok1(correct_data(data));
+	ok1(tdb->have_transaction_lock);
+	tdb_traverse(tdb, traverse2, NULL);
+
+	/* That should *not* release the transaction lock! */
+	ok1(tdb->have_transaction_lock);
+	return 0;
+}
+
+int main(int argc, char *argv[])
+{
+	struct tdb_context *tdb;
+	TDB_DATA key, data;
+
+	plan_tests(14);
+	tdb = tdb_open("/tmp/test.tdb", 1024, TDB_CLEAR_IF_FIRST,
+		       O_CREAT|O_TRUNC|O_RDWR, 0600);
+	ok1(tdb);
+
+	/* Tickle bug on appending zero length buffer to zero length buffer. */
+	key.dsize = strlen("hi");
+	key.dptr = (void *)"hi";
+	data.dptr = (void *)"world";
+	data.dsize = strlen("world");
+
+	ok1(tdb_store(tdb, key, data, TDB_INSERT) == 0);
+	tdb_traverse(tdb, traverse1, NULL);
+	tdb_traverse_read(tdb, traverse1, NULL);
+	tdb_close(tdb);
+
+	return exit_status();
+}

ccan/tdb/traverse.c

@@ -182,6 +182,7 @@ static int tdb_traverse_internal(struct tdb_context *tdb,
 		}
 		if (fn && fn(tdb, key, dbuf, private_data)) {
 			/* They want us to terminate traversal */
+			tdb_trace(tdb, "tdb_traverse_end = %i\n", count);
 			ret = count;
 			if (tdb_unlock_record(tdb, tl->off) != 0) {
 				TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_traverse: unlock_record failed!\n"));;
@@ -192,6 +193,7 @@ static int tdb_traverse_internal(struct tdb_context *tdb,
 		}
 		SAFE_FREE(key.dptr);
 	}
+	tdb_trace(tdb, "tdb_traverse_end\n");
 out:
 	tdb->travlocks.next = tl->next;
 	if (ret < 0)
@@ -212,17 +214,18 @@ int tdb_traverse_read(struct tdb_context *tdb,
 
 	/* we need to get a read lock on the transaction lock here to
 	   cope with the lock ordering semantics of solaris10 */
-	if (tdb_transaction_lock(tdb, F_RDLCK)) {
+	if (tdb->traverse_read == 0 && tdb_transaction_lock(tdb, F_RDLCK)) {
 		return -1;
 	}
 
 	tdb->traverse_read++;
 	tdb_trace(tdb, "tdb_traverse_read_start\n");
 	ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
-	tdb_trace(tdb, "tdb_traverse_end = %i\n", ret);
 	tdb->traverse_read--;
 
-	tdb_transaction_unlock(tdb);
+	if (tdb->traverse_read == 0) {
+		tdb_transaction_unlock(tdb);
+	}
 
 	return ret;
 }
@@ -243,18 +246,20 @@ int tdb_traverse(struct tdb_context *tdb,
 	if (tdb->read_only || tdb->traverse_read) {
 		return tdb_traverse_read(tdb, fn, private_data);
 	}
-	
-	if (tdb_transaction_lock(tdb, F_WRLCK)) {
+
+	/* Nested traversals: transaction lock doesn't nest. */
+	if (tdb->traverse_write == 0 && tdb_transaction_lock(tdb, F_WRLCK)) {
 		return -1;
 	}
 
 	tdb->traverse_write++;
 	tdb_trace(tdb, "tdb_traverse_start\n");
 	ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
-	tdb_trace(tdb, "tdb_traverse_end = %i\n", ret);
 	tdb->traverse_write--;
 
-	tdb_transaction_unlock(tdb);
+	if (tdb->traverse_write == 0) {
+		tdb_transaction_unlock(tdb);
+	}
 
 	return ret;
 }