Fix the "too many fcntl locks" scalability problem raised by tridge.

I've now tested this in daemon mode and also on xinetd and I'm pretty
sure it's working.
Jeremy.
(This used to be commit 14dee038019b11300466b148c53515fc76e5e870)

2 files changed, 23 insertions, 11 deletions

diff --git a/source3/tdb/tdb.c b/source3/tdb/tdb.c
index 7ad39175ac..7b10cfb377 100644
--- a/source3/tdb/tdb.c
+++ b/source3/tdb/tdb.c
@@ -1705,7 +1705,7 @@ TDB_CONTEXT *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 {
 	TDB_CONTEXT *tdb;
 	struct stat st;
-	int rev = 0, locked;
+	int rev = 0, locked = 0;
 	unsigned char *vp;
 	u32 vertest;
 
@@ -1763,8 +1763,8 @@ TDB_CONTEXT *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 	}
 
 	/* we need to zero database if we are the only one with it open */
-	if ((locked = (tdb_brlock(tdb, ACTIVE_LOCK, F_WRLCK, F_SETLK, 0) == 0))
-	    && (tdb_flags & TDB_CLEAR_IF_FIRST)) {
+	if ((tdb_flags & TDB_CLEAR_IF_FIRST) &&
+		(locked = (tdb_brlock(tdb, ACTIVE_LOCK, F_WRLCK, F_SETLK, 0) == 0))) {
 		open_flags |= O_CREAT;
 		if (ftruncate(tdb->fd, 0) == -1) {
 			TDB_LOG((tdb, 0, "tdb_open_ex: "
@@ -1837,10 +1837,19 @@ TDB_CONTEXT *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 				 name, strerror(errno)));
 			goto fail;
 		}
+
 	}
-	/* leave this lock in place to indicate it's in use */
-	if (tdb_brlock(tdb, ACTIVE_LOCK, F_RDLCK, F_SETLKW, 0) == -1)
-		goto fail;
+
+	/* We always need to do this if the CLEAR_IF_FIRST flag is set, even if
+	   we didn't get the initial exclusive lock as we need to let all other
+	   users know we're using it. */
+
+	if (tdb_flags & TDB_CLEAR_IF_FIRST) {
+		/* leave this lock in place to indicate it's in use */
+		if (tdb_brlock(tdb, ACTIVE_LOCK, F_RDLCK, F_SETLKW, 0) == -1)
+			goto fail;
+	}
+
 
  internal:
 	/* Internal (memory-only) databases skip all the code above to
@@ -2018,12 +2027,14 @@ void tdb_logging_function(TDB_CONTEXT *tdb, void (*fn)(TDB_CONTEXT *, int , cons
 }
 
 
-/* reopen a tdb - this is used after a fork to ensure that we have an independent
+/* reopen a tdb - this can be used after a fork to ensure that we have an independent
    seek pointer from our parent and to re-establish locks */
 int tdb_reopen(TDB_CONTEXT *tdb)
 {
 	struct stat st;
 
+	if (tdb->flags & TDB_INTERNAL)
+		return 0; /* Nothing to do. */
 	if (tdb_munmap(tdb) != 0) {
 		TDB_LOG((tdb, 0, "tdb_reopen: munmap failed (%s)\n", strerror(errno)));
 		goto fail;
@@ -2044,7 +2055,7 @@ int tdb_reopen(TDB_CONTEXT *tdb)
 		goto fail;
 	}
 	tdb_mmap(tdb);
-	if (tdb_brlock(tdb, ACTIVE_LOCK, F_RDLCK, F_SETLKW, 0) == -1) {
+	if ((tdb->flags & TDB_CLEAR_IF_FIRST) && (tdb_brlock(tdb, ACTIVE_LOCK, F_RDLCK, F_SETLKW, 0) == -1)) {
 		TDB_LOG((tdb, 0, "tdb_reopen: failed to obtain active lock\n"));
 		goto fail;
 	}
@@ -2062,7 +2073,10 @@ int tdb_reopen_all(void)
 	TDB_CONTEXT *tdb;
 
 	for (tdb=tdbs; tdb; tdb = tdb->next) {
-		if (tdb_reopen(tdb) != 0) return -1;
+		/* Ensure no clear-if-first. */
+		tdb->flags &= ~TDB_CLEAR_IF_FIRST;
+		if (tdb_reopen(tdb) != 0)
+			return -1;
 	}
 
 	return 0;
diff --git a/source3/tdb/tdbutil.c b/source3/tdb/tdbutil.c
index bae9a8b9d4..304bf9c816 100644
--- a/source3/tdb/tdbutil.c
+++ b/source3/tdb/tdbutil.c
@@ -826,5 +826,3 @@ void tdb_search_list_free(TDB_LIST_NODE* node)
 		node = next_node;
 	};
 }
-
-