Add shm_key config keyword to use shared memory for BDB environment

Unmeasurable performance difference on my tests, but who knows...

servers/slapd/back-bdb/back-bdb.h

@@ -157,6 +157,7 @@ struct bdb_info {
 	u_int32_t	bi_txn_cp_kbyte;
 
 	int			bi_lock_detect;
+	long		bi_shm_key;
 
 	ID			bi_lastid;
 	ldap_pvt_thread_mutex_t	bi_lastid_mutex;

servers/slapd/back-bdb/config.c

@@ -50,7 +50,7 @@ bdb_db_config(
 	} else if ( strcasecmp( argv[0], "dirtyread" ) == 0 ) {
 		bdb->bi_db_opflags |= DB_DIRTY_READ;
 #endif
-	/* transaction checkpoint configuration */
+	/* transaction logging configuration */
 	} else if ( strcasecmp( argv[0], "dbnosync" ) == 0 ) {
 		bdb->bi_dbenv_xflags |= DB_TXN_NOSYNC;
 
@@ -125,6 +125,16 @@ bdb_db_config(
 
 		if( rc != LDAP_SUCCESS ) return 1;
 
+	/* unique key for shared memory regions */
+        } else if ( strcasecmp( argv[0], "shm_key" ) == 0 ) {
+                 if ( argc < 2 ) {
+                         fprintf( stderr,
+                 "%s: line %d: missing key in \"shm_key <key>\" line\n",
+                             fname, lineno );
+                         return( 1 );
+                 }
+                 bdb->bi_shm_key = atoi( argv[1] );
+
 	/* size of the cache in entries */
         } else if ( strcasecmp( argv[0], "cachesize" ) == 0 ) {
                  if ( argc < 2 ) {

servers/slapd/back-bdb/init.c

@@ -194,6 +194,12 @@ bdb_db_open( BackendDB *be )
 	if( !(slapMode & SLAP_TOOL_MODE) ) flags |= DB_RECOVER;
 #endif
 
+	/* If a key was set, use shared memory for the BDB environment */
+	if ( bdb->bi_shm_key ) {
+		bdb->bi_dbenv->set_shm_key( bdb->bi_dbenv, bdb->bi_shm_key );
+		flags |= DB_SYSTEM_MEM;
+	}
+
 	bdb->bi_dbenv->set_errpfx( bdb->bi_dbenv, be->be_suffix[0].bv_val );
 	bdb->bi_dbenv->set_errcall( bdb->bi_dbenv, bdb_errcall );
 	bdb->bi_dbenv->set_lk_detect( bdb->bi_dbenv, bdb->bi_lock_detect );