New attempt at TDB transaction nesting allow/disallow.

Make the default be that transaction is not allowed and any attempt to create a nested transaction will fail with TDB_ERR_NESTING.

If an application can cope with transaction nesting and the implicit
semantics of tdb_transaction_commit(), it can enable transaction nesting
by using the TDB_ALLOW_NESTING flag.
(cherry picked from ctdb commit 3e49e41c21eb8c53084aa8cc7fd3557bdd8eb7b6)

Signed-off-by: Stefan Metzmacher <metze@samba.org>

diff --git a/lib/tdb/common/transaction.c b/lib/tdb/common/transaction.c
index 035b4e1d54cec932d728683967337f84d1f1adc2..501cd62b96ee367626f148f24eebbfd07a5de3b2 100644 (file)
--- a/lib/tdb/common/transaction.c
+++ b/lib/tdb/common/transaction.c
@@ -85,6 +85,13 @@
     still available, but no transaction recovery area is used and no
     fsync/msync calls are made.
 
+  - if TDB_ALLOW_NESTING is passed to flags in tdb open, or added using
+    tdb_add_flags() transaction is enabled.
+    The default is that transaction nesting is not allowed and an attempt
+    to create a nested transaction will fail with TDB_ERR_NESTING.
+
+    Beware. when transactions are nested a transaction successfully
+    completed with tdb_transaction_commit() can be silently unrolled later.
 */
 
 
@@ -427,6 +434,10 @@ int tdb_transaction_start(struct tdb_context *tdb)
 
        /* cope with nested tdb_transaction_start() calls */
        if (tdb->transaction != NULL) {
+               if (!(tdb->flags & TDB_ALLOW_NESTING)) {
+                       tdb->ecode = TDB_ERR_NESTING;
+                       return -1;
+               }
                tdb->transaction->nesting++;
                TDB_LOG((tdb, TDB_DEBUG_TRACE, "tdb_transaction_start: nesting %d\n", 
                         tdb->transaction->nesting));

diff --git a/lib/tdb/include/tdb.h b/lib/tdb/include/tdb.h
index e849f2064145cdb8d52e5c1080fe351b561f9770..5cc1eecdd114c6ff689055bc5e2cc8d2179fe3af 100644 (file)
--- a/lib/tdb/include/tdb.h
+++ b/lib/tdb/include/tdb.h
@@ -48,11 +48,13 @@ extern "C" {
 #define TDB_NOSYNC   64 /* don't use synchronous transactions */
 #define TDB_SEQNUM   128 /* maintain a sequence number */
 #define TDB_VOLATILE   256 /* Activate the per-hashchain freelist, default 5 */
+#define TDB_ALLOW_NESTING 512 /* Allow transactions to nest */
 
 /* error codes */
 enum TDB_ERROR {TDB_SUCCESS=0, TDB_ERR_CORRUPT, TDB_ERR_IO, TDB_ERR_LOCK, 
                TDB_ERR_OOM, TDB_ERR_EXISTS, TDB_ERR_NOLOCK, TDB_ERR_LOCK_TIMEOUT,
-               TDB_ERR_NOEXIST, TDB_ERR_EINVAL, TDB_ERR_RDONLY};
+               TDB_ERR_NOEXIST, TDB_ERR_EINVAL, TDB_ERR_RDONLY,
+               TDB_ERR_NESTING};
 
 /* debugging uses one of the following levels */
 enum tdb_debug_level {TDB_DEBUG_FATAL = 0, TDB_DEBUG_ERROR,