From 707cad6188313bc289ced5eaac44f10a9e056d13 Mon Sep 17 00:00:00 2001
From: Maria Matejka <mq@ucw.cz>
Date: Tue, 3 Dec 2024 10:57:10 +0100
Subject: [PATCH] CLI: Dumping forces new file creation instead of truncating.

---
 doc/bird.sgml    | 11 ++++++-----
 sysdep/unix/io.c |  2 +-
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/doc/bird.sgml b/doc/bird.sgml
index 5393edb2e..5bed6df3c 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -1455,11 +1455,12 @@ This argument can be omitted if there exists only a single instance.
 	Control protocol debugging.
 
 	<tag><label id="cli-dump">dump resources|sockets|interfaces|neighbors|attributes|routes|protocols "<m/file/"</tag>
-	Truncates the given file and dumps contents of internal data structures
-	there. By sending SIGUSR1, you get all of these concatenated to
-	<cf/bird.dump/ in the current directory. The file is only readable for
-	the user running the daemon. The format of dump files is internal and
-	could change in the future.
+        Creates the given file (it must not exist) and dumps contents of
+        internal data structures there. By sending SIGUSR1, you get all of
+	these concatenated to <cf/bird.dump/ in the current directory.
+	The file is only readable for the user running the daemon.
+	The format of dump files is internal and could change in the future
+	without any notice.
 
 	<tag><label id="cli-echo">echo all|off|{ <m/list of log classes/ } [ <m/buffer-size/ ]</tag>
 	Control echoing of log messages to the command-line output.
diff --git a/sysdep/unix/io.c b/sysdep/unix/io.c
index b06324860..54768d47f 100644
--- a/sysdep/unix/io.c
+++ b/sysdep/unix/io.c
@@ -217,7 +217,7 @@ void
 dump_to_file_run(struct dump_request *dr, const char *file, const char *what, void (*dump)(struct dump_request *))
 {
   struct dump_request_file *req = SKIP_BACK(struct dump_request_file, dr, dr);
-  req->fd = open(file, O_CREAT | O_WRONLY | O_TRUNC, S_IRUSR);
+  req->fd = open(file, O_CREAT | O_WRONLY | O_EXCL, S_IRUSR);
 
   if (req->fd < 0)
   {
-- 
2.47.2