netdev - Re: [RFC PATCH net-next 03/22] nexthop: Only emit a notification when nexthop is actually deleted

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Message-ID: <20200908143959.GP2997@nanopsycho.orion>
Date:   Tue, 8 Sep 2020 16:39:59 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        dsahern@...il.com, roopa@...dia.com, mlxsw@...dia.com,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [RFC PATCH net-next 03/22] nexthop: Only emit a notification
 when nexthop is actually deleted

Tue, Sep 08, 2020 at 11:10:18AM CEST, idosch@...sch.org wrote:
>From: Ido Schimmel <idosch@...dia.com>
>
>Currently, the delete notification is emitted from the error path of
>nexthop_add() and replace_nexthop(), which can be confusing to listeners
>as they are not familiar with the nexthop.
>
>Instead, only emit the notification when the nexthop is actually
>deleted. The following sub-cases are covered:

Well, in theory, this might break some very odd app that is adding a
route and checking the errors using this notification. My opinion is to
allow this breakage to happen, but I'm usually too benevolent :)


>
>1. User space deletes the nexthop
>2. The nexthop is deleted by the kernel due to a netdev event (e.g.,
>   nexthop device going down)
>3. A group is deleted because its last nexthop is being deleted
>4. The network namespace of the nexthop device is deleted
>
>Signed-off-by: Ido Schimmel <idosch@...dia.com>
>---
> net/ipv4/nexthop.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
>index 13d9219a9aa1..8c0f17c6863c 100644
>--- a/net/ipv4/nexthop.c
>+++ b/net/ipv4/nexthop.c
>@@ -870,8 +870,6 @@ static void __remove_nexthop_fib(struct net *net, struct nexthop *nh)
> 	bool do_flush = false;
> 	struct fib_info *fi;
> 
>-	call_nexthop_notifiers(net, NEXTHOP_EVENT_DEL, nh);
>-
> 	list_for_each_entry(fi, &nh->fi_list, nh_list) {
> 		fi->fib_flags |= RTNH_F_DEAD;
> 		do_flush = true;
>@@ -909,6 +907,8 @@ static void __remove_nexthop(struct net *net, struct nexthop *nh,
> static void remove_nexthop(struct net *net, struct nexthop *nh,
> 			   struct nl_info *nlinfo)
> {
>+	call_nexthop_notifiers(net, NEXTHOP_EVENT_DEL, nh);
>+
> 	/* remove from the tree */
> 	rb_erase(&nh->rb_node, &net->nexthop.rb_root);
> 
>-- 
>2.26.2
>