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

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Date:   Fri, 11 Sep 2020 17:40:48 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     Jiri Pirko <jiri@...nulli.us>
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

On Tue, Sep 08, 2020 at 04:39:59PM +0200, Jiri Pirko wrote:
> 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 :)

There is no uAPI breakage since the patch is only changing the in-kernel
notification. After this patch the in-kernel and RTM_DELNEXTHOP netlink
notifications are both emitted from the same function (i.e.,
remove_nexthop()).

I'll reword the commit message to make it clear.

> 
> 
> >
> >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
> >