tdb: use tdb_nest_lock() for active lock.

Rather than a boutique lock and a separate nest count, use our
newly-generic nested lock tracking for the active lock.

Note that the tdb_have_extra_locks() and tdb_release_extra_locks()
functions have to skip over this lock now it is tracked.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

ccan/tdb/lock.c

@@ -675,6 +675,11 @@ bool tdb_have_extra_locks(struct tdb_context *tdb)
 		return true;
 	}
 
+	/* We always hold the active lock if CLEAR_IF_FIRST. */
+	if (find_nestlock(tdb, ACTIVE_LOCK)) {
+		extra--;
+	}
+
 	/* In a transaction, we expect to hold the transaction lock */
 	if (tdb->transaction && find_nestlock(tdb, TRANSACTION_LOCK)) {
 		extra--;
@@ -698,8 +703,11 @@ void tdb_release_extra_locks(struct tdb_context *tdb)
 	for (i=0;i<tdb->num_lockrecs;i++) {
 		struct tdb_lock_type *lck = &tdb->lockrecs[i];
 
+		/* Don't release transaction or active locks! */
 		if (tdb->transaction && lck->off == TRANSACTION_LOCK) {
 			tdb->lockrecs[extra++] = *lck;
+		} else if (lck->off == ACTIVE_LOCK) {
+			tdb->lockrecs[extra++] = *lck;
 		} else {
 			tdb_brunlock(tdb, lck->ltype, lck->off, 1);
 		}

ccan/tdb/open.c

@@ -249,7 +249,7 @@ struct 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 ((tdb_flags & TDB_CLEAR_IF_FIRST) &&
 	    (!tdb->read_only) &&
-	    (locked = (tdb->methods->brlock(tdb, F_WRLCK, ACTIVE_LOCK, 1, TDB_LOCK_NOWAIT|TDB_LOCK_PROBE) == 0))) {
+	    (locked = (tdb_nest_lock(tdb, ACTIVE_LOCK, F_WRLCK, TDB_LOCK_NOWAIT|TDB_LOCK_PROBE) == 0))) {
 		open_flags |= O_CREAT;
 		if (ftruncate(tdb->fd, 0) == -1) {
 			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_open_ex: "
@@ -312,7 +312,7 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 	tdb->inode = st.st_ino;
 	tdb_mmap(tdb);
 	if (locked) {
-		if (tdb->methods->brunlock(tdb, F_WRLCK, ACTIVE_LOCK, 1) == -1) {
+		if (tdb_nest_unlock(tdb, ACTIVE_LOCK, F_WRLCK, false) == -1) {
 			TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: "
 				 "failed to take ACTIVE_LOCK on %s: %s\n",
 				 name, strerror(errno)));
@@ -327,8 +327,9 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 
 	if (tdb_flags & TDB_CLEAR_IF_FIRST) {
 		/* leave this lock in place to indicate it's in use */
-		if (tdb->methods->brlock(tdb, F_RDLCK, ACTIVE_LOCK, 1, TDB_LOCK_WAIT) == -1)
+		if (tdb_nest_lock(tdb, ACTIVE_LOCK, F_RDLCK, TDB_LOCK_WAIT) == -1) {
 			goto fail;
+		}
 	}
 
 	/* if needed, run recovery */
@@ -382,6 +383,7 @@ struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
 	if (tdb->fd != -1)
 		if (close(tdb->fd) != 0)
 			TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: failed to close tdb->fd on error!\n"));
+	SAFE_FREE(tdb->lockrecs);
 	SAFE_FREE(tdb);
 	errno = save_errno;
 	return NULL;
@@ -493,8 +495,11 @@ static int tdb_reopen_internal(struct tdb_context *tdb, bool active_lock)
 	}
 	tdb_mmap(tdb);
 
-	if (active_lock &&
-	    (tdb->methods->brlock(tdb, F_RDLCK, ACTIVE_LOCK, 1, TDB_LOCK_WAIT) == -1)) {
+	/* We may still think we hold the active lock. */
+	tdb->num_lockrecs = 0;
+	SAFE_FREE(tdb->lockrecs);
+
+	if (active_lock && tdb_nest_lock(tdb, ACTIVE_LOCK, F_RDLCK, TDB_LOCK_WAIT) == -1) {
 		TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: failed to obtain active lock\n"));
 		goto fail;
 	}

ccan/tdb/tdb_private.h

@@ -259,6 +259,7 @@ int tdb_nest_lock(struct tdb_context *tdb, uint32_t offset, int ltype,
 		  enum tdb_lock_flags flags);
 int tdb_nest_unlock(struct tdb_context *tdb, uint32_t offset, int ltype,
 		    bool mark_lock);
+bool tdb_have_locks(struct tdb_context *tdb);
 int tdb_unlock(struct tdb_context *tdb, int list, int ltype);
 int tdb_brlock(struct tdb_context *tdb,
 	       int rw_type, tdb_off_t offset, size_t len,