From: Sven Eckelmann <sven@narfation.org>
Date: Sat, 13 Jun 2020 17:59:34 +0200
Subject: batctl: Only remove batadv interface on hardif reduction

A deletion of a hardif from a batadv meshif will also get a success reply
from the kernel when the hardif was never part of the batadv meshif. If the
batadv meshif had no attached hardifs before the removal was started, then
users are then not expecting that the batadv meshif is removed at all.

Since the delete operation is not an atomic compare-and-swap operation,
just check first the number of attached interfaces and only start the
removal of the batadv meshif when the number attached hardifs was reduced.

Fixes: 25022e0b154d ("batctl: Use rtnl to add/remove interfaces")
Reported-by: Matthias Schiffer <mschiffer@universe-factory.net>
Signed-off-by: Sven Eckelmann <sven@narfation.org>

Origin: upstream, https://git.open-mesh.org/batctl.git/commit/6d49a82cf58ee5ebd6235b6ddaca46febd42f876

diff --git a/interface.c b/interface.c
index 5951b471c6477e78ff557e97a7478ba774a0aa20..1ad36826fdb91a3e0254ed4dec758e7c383596e9 100644
--- a/interface.c
+++ b/interface.c
@@ -305,6 +305,7 @@ int interface(char *mesh_iface, int argc, char **argv)
 	int ret;
 	unsigned int ifindex;
 	unsigned int ifmaster;
+	unsigned int pre_cnt;
 	const char *long_op;
 	unsigned int cnt;
 	int rest_argc;
@@ -421,6 +422,8 @@ int interface(char *mesh_iface, int argc, char **argv)
 		goto err;
 	}
 
+	pre_cnt = count_interfaces(mesh_iface);
+
 	for (i = 1; i < rest_argc; i++) {
 		ifindex = if_nametoindex(rest_argv[i]);
 
@@ -450,7 +453,7 @@ int interface(char *mesh_iface, int argc, char **argv)
 	/* check if there is no interface left and then destroy mesh_iface */
 	if (!manual_mode && rest_argv[0][0] == 'd') {
 		cnt = count_interfaces(mesh_iface);
-		if (cnt == 0)
+		if (cnt == 0 && pre_cnt > 0)
 			destroy_interface(mesh_iface);
 	}