netdev - Re: [RFC PATCH net-next 15/22] nexthop: Emit a notification when a nexthop group is reduced

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Date:   Fri, 11 Sep 2020 19:29:05 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     David Ahern <dsahern@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        roopa@...dia.com, mlxsw@...dia.com,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [RFC PATCH net-next 15/22] nexthop: Emit a notification when a
 nexthop group is reduced

On Tue, Sep 08, 2020 at 09:33:42AM -0600, David Ahern wrote:
> On 9/8/20 3:10 AM, Ido Schimmel wrote:
> > From: Ido Schimmel <idosch@...dia.com>
> > 
> > When a single nexthop is deleted, the configuration of all the groups
> > using the nexthop is effectively modified. In this case, emit a
> > notification in the nexthop notification chain for each modified group
> > so that listeners would not need to keep track of which nexthops are
> > member in which groups.
> > 
> > In the rare cases where the notification fails, emit an error to the
> > kernel log.
> > 
> > Signed-off-by: Ido Schimmel <idosch@...dia.com>
> > ---
> >  net/ipv4/nexthop.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/ipv4/nexthop.c b/net/ipv4/nexthop.c
> > index 0edc3e73d416..33f611bbce1f 100644
> > --- a/net/ipv4/nexthop.c
> > +++ b/net/ipv4/nexthop.c
> > @@ -893,7 +893,7 @@ static void remove_nh_grp_entry(struct net *net, struct nh_grp_entry *nhge,
> >  	struct nexthop *nhp = nhge->nh_parent;
> >  	struct nexthop *nh = nhge->nh;
> >  	struct nh_group *nhg, *newg;
> > -	int i, j;
> > +	int i, j, err;
> >  
> >  	WARN_ON(!nh);
> >  
> > @@ -941,6 +941,10 @@ static void remove_nh_grp_entry(struct net *net, struct nh_grp_entry *nhge,
> >  	list_del(&nhge->nh_list);
> >  	nexthop_put(nhge->nh);
> >  
> > +	err = call_nexthop_notifiers(net, NEXTHOP_EVENT_REPLACE, nhp, NULL);
> > +	if (err)
> > +		pr_err("Failed to replace nexthop group after nexthop deletion\n");
> 
> This should refer to the notifier failing since wrt nexthop code the
> structs are ok. extack on the stack and logging that message would be
> useful too (or have the users of the notifier log why it fails).

'extack on the stack' idea is cool! I will do that

> 
> > +
> >  	if (nlinfo)
> >  		nexthop_notify(RTM_NEWNEXTHOP, nhp, nlinfo);
> >  }
> > 
>