lib: Add server_id_db_set_exclusive

This is used for server names where only one instance can exist.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

source3/lib/server_id_db_util.c

@@ -0,0 +1,104 @@
+/*
+ * Unix SMB/CIFS implementation.
+ * Utils around server_id_db with more dependencies
+ * Copyright (C) Volker Lendecke 2014
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "replace.h"
+#include "server_id_db_util.h"
+#include "serverid.h"
+
+static int server_id_db_check_exclusive(
+	struct server_id_db *db, const char *name,
+	unsigned num_servers, struct server_id *servers);
+
+int server_id_db_set_exclusive(struct server_id_db *db, const char *name)
+{
+	int ret;
+	unsigned num_servers;
+	struct server_id *servers;
+
+	ret = server_id_db_add(db, name);
+	if (ret != 0) {
+		return ret;
+	}
+
+	ret = server_id_db_lookup(db, name, talloc_tos(),
+				  &num_servers, &servers);
+	if (ret != 0) {
+		goto done;
+	}
+
+	/*
+	 * Remove entries from the server_id_db for processes that have died
+	 * and could not clean up. This is racy, as two processes could
+	 * simultaneously try to register a name. Both would succeed in the
+	 * server_id_db_add call, and both would see their peer active during
+	 * the check_exclusive call. Both would get an EEXIST, and nobody
+	 * would be able to register itself. But this is okay, as this is
+	 * meant to be a cleanup routine, and normally only one daemon should
+	 * start up at a time anyway. Getting this "right" would mean we would
+	 * have to add locking to server_id_db, or add a dependency on
+	 * serverids_exist to server_id_db. Both are too heavy-weight for my
+	 * taste.
+	 */
+
+	ret = server_id_db_check_exclusive(db, name, num_servers, servers);
+	TALLOC_FREE(servers);
+
+done:
+	if (ret != 0) {
+		server_id_db_remove(db, name);
+	}
+	return ret;
+}
+
+static int server_id_db_check_exclusive(
+	struct server_id_db *db, const char *name,
+	unsigned num_servers, struct server_id *servers)
+{
+	struct server_id me = server_id_db_pid(db);
+	bool exists[num_servers];
+	bool ok;
+	int i;
+
+	ok = serverids_exist(servers, num_servers, exists);
+	if (!ok) {
+		return ENOMEM;
+	}
+
+	for (i=0; i<num_servers; i++) {
+		int ret;
+
+		if (server_id_same_process(&me, &servers[i])) {
+			/*
+			 * I am always around ... :-)
+			 */
+			continue;
+		}
+
+		if (exists[i]) {
+			return EEXIST;
+		}
+
+		ret = server_id_db_prune_name(db, name, servers[i]);
+		if (ret != 0) {
+			return ret;
+		}
+	}
+
+	return 0;
+}

source3/lib/server_id_db_util.h

@@ -0,0 +1,22 @@
+/*
+ * Unix SMB/CIFS implementation.
+ * Utils around server_id_db with more dependencies
+ * Copyright (C) Volker Lendecke 2014
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "lib/util/server_id_db.h"
+
+int server_id_db_set_exclusive(struct server_id_db *db, const char *name);

source3/wscript_build

@@ -320,6 +320,7 @@ bld.SAMBA3_SUBSYSTEM('samba3core',
                    lib/id_cache.c
                    lib/talloc_dict.c
                    lib/serverid.c
+                   lib/server_id_db_util.c
                    lib/addrchange.c
                    ../lib/util/debug_s3.c
                    lib/dumpcore.c