From a2847d0068a5812a06ffd4bc4a8dea30eb9bb7e9 Mon Sep 17 00:00:00 2001
From: Quanah Gibson-Mount <quanah@openldap.org>
Date: Wed, 23 Jul 2014 15:55:36 -0500
Subject: [PATCH] ITS#7904 writewait patch     Add sc_writewait callback

    Invoked before a blocked writer waits for socket to be writable.
    Use in back-mdb to release reader txn while waiting.
---
 servers/slapd/back-mdb/search.c | 50 +++++++++++++++++++++++++++++++++
 servers/slapd/result.c          | 17 +++++++++++
 servers/slapd/slap.h            |  4 +++
 3 files changed, 71 insertions(+)

diff --git a/servers/slapd/back-mdb/search.c b/servers/slapd/back-mdb/search.c
index 9872c52205..c63db9c164 100644
--- a/servers/slapd/back-mdb/search.c
+++ b/servers/slapd/back-mdb/search.c
@@ -316,6 +316,21 @@ static void scope_chunk_ret( Operation *op, ID2 *scopes )
 
 static void *search_stack( Operation *op );
 
+typedef struct ww_ctx {
+	MDB_txn *txn;
+	int flag;
+} ww_ctx;
+
+static void
+mdb_writewait( Operation *op, slap_callback *sc )
+{
+	ww_ctx *ww = sc->sc_private;
+	if ( !ww->flag ) {
+		mdb_txn_reset( ww->txn );
+		ww->flag = 1;
+	}
+}
+
 int
 mdb_search( Operation *op, SlapReply *rs )
 {
@@ -335,6 +350,8 @@ mdb_search( Operation *op, SlapReply *rs )
 	int		tentries = 0;
 	IdScopes	isc;
 	MDB_cursor	*mci, *mcd;
+	ww_ctx wwctx;
+	slap_callback cb = { 0 };
 
 	mdb_op_info	opinfo = {{{0}}}, *moi = &opinfo;
 	MDB_txn			*ltid = NULL;
@@ -673,6 +690,16 @@ dn2entry_retry:
 		id = mdb_idl_first( candidates, &cursor );
 	}
 
+	wwctx.flag = 0;
+	/* If we're running in our own read txn */
+	if (  moi == &opinfo ) {
+		cb.sc_writewait = mdb_writewait;
+		cb.sc_private = &wwctx;
+		wwctx.txn = ltid;
+		cb.sc_next = op->o_callback;
+		op->o_callback = &cb;
+	}
+
 	while (id != NOID)
 	{
 		int scopeok;
@@ -935,6 +962,12 @@ notfound:
 			rs->sr_flags = 0;
 
 			send_search_reference( op, rs );
+			if ( wwctx.flag ) {
+				wwctx.flag = 0;
+				mdb_txn_renew( ltid );
+				mdb_cursor_renew( ltid, mci );
+				mdb_cursor_renew( ltid, mcd );
+			}
 
 			mdb_entry_return( op, e );
 			rs->sr_entry = NULL;
@@ -972,6 +1005,12 @@ notfound:
 				rs->sr_flags = 0;
 				rs->sr_err = LDAP_SUCCESS;
 				rs->sr_err = send_search_entry( op, rs );
+				if ( wwctx.flag ) {
+					wwctx.flag = 0;
+					mdb_txn_renew( ltid );
+					mdb_cursor_renew( ltid, mci );
+					mdb_cursor_renew( ltid, mcd );
+				}
 				rs->sr_attrs = NULL;
 				rs->sr_entry = NULL;
 				if (e != base)
@@ -1062,6 +1101,17 @@ nochange:
 	rs->sr_err = LDAP_SUCCESS;
 
 done:
+	if ( cb.sc_private ) {
+		/* remove our writewait callback */
+		slap_callback **scp = &op->o_callback;
+		while ( *scp ) {
+			if ( *scp == &cb ) {
+				*scp = cb.sc_next;
+				cb.sc_private = NULL;
+				break;
+			}
+		}
+	}
 	mdb_cursor_close( mcd );
 	mdb_cursor_close( mci );
 	if ( moi == &opinfo ) {
diff --git a/servers/slapd/result.c b/servers/slapd/result.c
index 0f1336a17f..35cddc70d6 100644
--- a/servers/slapd/result.c
+++ b/servers/slapd/result.c
@@ -279,6 +279,22 @@ rs_entry2modifiable( Operation *op, SlapReply *rs, slap_overinst *on )
 	return 1;
 }
 
+/* Check for any callbacks that want to be informed about being blocked
+ * on output. These callbacks are expected to leave the callback list
+ * unmodified. Their result is ignored.
+ */
+static void
+slap_writewait_play(
+	Operation *op )
+{
+	slap_callback	*sc = op->o_callback;
+
+	for ( ; sc; sc = sc->sc_next ) {
+		if ( sc->sc_writewait )
+			sc->sc_writewait( op, sc );
+	}
+}
+
 static long send_ldap_ber(
 	Operation *op,
 	BerElement *ber )
@@ -348,6 +364,7 @@ static long send_ldap_ber(
 		}
 
 		/* wait for socket to be write-ready */
+		slap_writewait_play( op );
 		ldap_pvt_thread_mutex_lock( &conn->c_write2_mutex );
 		conn->c_writewaiter = 1;
 		slapd_set_write( conn->c_sd, 2 );
diff --git a/servers/slapd/slap.h b/servers/slapd/slap.h
index 99100dd9f8..baf8bc3f6b 100644
--- a/servers/slapd/slap.h
+++ b/servers/slapd/slap.h
@@ -2367,10 +2367,14 @@ struct BackendInfo {
 
 typedef int (slap_response)( Operation *, SlapReply * );
 
+struct slap_callback;
+typedef void (slap_writewait)( Operation *, struct slap_callback * );
+
 typedef struct slap_callback {
 	struct slap_callback *sc_next;
 	slap_response *sc_response;
 	slap_response *sc_cleanup;
+	slap_writewait *sc_writewait;
 	void *sc_private;
 } slap_callback;
 
-- 
2.39.5