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+Interface differences between TDB1 and TDB2.
+
+- tdb2 uses 'struct tdb_data', tdb1 uses 'struct TDB_DATA'.  Use the
+  TDB_DATA typedef if you want portability between the two.
+
+- tdb2 functions return 0 on success, and a negative error on failure,
+  whereas tdb1 functions returned 0 on success, and -1 on failure.
+  tdb1 then used tdb_error() to determine the error; this is also
+  supported in tdb2 to ease backwards compatibility, though the other
+  form is preferred.
+
+- tdb2's tdb_fetch() returns an error, tdb1's returned the data directly
+  (or tdb_null, and you were supposed to check tdb_error() to find out why).
+
+- tdb2's tdb_nextkey() frees the old key's dptr, in tdb2 you needed to do
+  this manually.
+
+- tdb1's tdb_open/tdb_open_ex took an explicit hash size.  tdb2's hash table
+  resizes as required.
+
+- tdb2 uses a linked list of attribute structures to implement logging and
+  alternate hashes.  tdb1 used tdb_open_ex, which was not extensible.
+
+- tdb2 does locking on read-only databases (ie. O_RDONLY passed to tdb_open).
+  tdb1 did not: use the TDB_NOLOCK flag if you want to suppress locking.
+
+- tdb2's log function is simpler than tdb1's log function.  The string is
+  already formatted, and it takes an enum tdb_log_level not a tdb_debug_level,
+  and which has only three values: TDB_LOG_ERROR, TDB_LOG_USE_ERROR and
+  TDB_LOG_WARNING.
+
+- tdb2 provides tdb_deq() for comparing two struct tdb_data.
+
+- tdb2's tdb_name() returns a copy of the name even for TDB_INTERNAL dbs.
+
+- tdb2 does not need tdb_reopen() or tdb_reopen_all().  If you call
+  fork() after during certain operations the child should close the
+  tdb, or complete the operations before continuing to use the tdb:
+
+	tdb_transaction_start(): child must tdb_transaction_cancel()
+	tdb_lockall(): child must call tdb_unlockall()
+	tdb_lockall_read(): child must call tdb_unlockall_read()
+	tdb_chainlock(): child must call tdb_chainunlock()
+	tdb_parse() callback: child must return from tdb_parse()