Re: [PATCH 3/5] NET: IPV4: ARP: allow to invalidate specific ARP entries

[Eric Dumazet <eric.dumazet@gmail.com>]

Le dimanche 05 décembre 2010 à 01:15 +0200, Maxim Levitsky a écrit :
> On Mon, 2010-11-29 at 04:09 +0200, Maxim Levitsky wrote:
> > IPv4 over firewire needs to be able to remove ARP entries
> > from the ARP cache that belong to nodes that are removed, because
> > IPv4 over firewire uses ARP packets for private information
> > about nodes.
> > 
> > This information becomes invalid as soon as node drops
> > off the bus and when it reconnects, its only possible
> > to start takling to is after it responded to an ARP packet.
> > But ARP cache prevents such packets from being sent.
> > 
> > CC: netdev@vger.kernel.org
> > CC: "David S. Miller" <davem@davemloft.net>
> > CC: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
> > CC: James Morris <jmorris@namei.org>
> > CC: Patrick McHardy <kaber@trash.net>
> 
> Anybody?
> 
> Best regards,
> 	Maxim Levitsky
> > 
> > 
> > Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
> > ---
> >  include/net/arp.h |    1 +
> >  net/ipv4/arp.c    |   29 ++++++++++++++++++-----------
> >  2 files changed, 19 insertions(+), 11 deletions(-)
> > 
> > diff --git a/include/net/arp.h b/include/net/arp.h
> > index f4cf6ce..91f0568 100644
> > --- a/include/net/arp.h
> > +++ b/include/net/arp.h
> > @@ -25,5 +25,6 @@ extern struct sk_buff *arp_create(int type, int ptype, __be32 dest_ip,
> >  				  const unsigned char *src_hw,
> >  				  const unsigned char *target_hw);
> >  extern void arp_xmit(struct sk_buff *skb);
> > +int arp_invalidate(struct net_device *dev, __be32 ip);
> >  
> >  #endif	/* _ARP_H */
> > diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
> > index d8e540c..35b1272 100644
> > --- a/net/ipv4/arp.c
> > +++ b/net/ipv4/arp.c
> > @@ -1142,6 +1142,23 @@ static int arp_req_get(struct arpreq *r, struct net_device *dev)
> >  	return err;
> >  }
> >  
> > +int arp_invalidate(struct net_device *dev, __be32 ip)
> > +{
> > +	int err = -ENXIO;
> > +	struct neighbour *neigh = neigh_lookup(&arp_tbl, &ip, dev);
> > +
> > +	if (neigh) {
> > +		if (neigh->nud_state & ~NUD_NOARP)
> > +			err = neigh_update(neigh, NULL, NUD_FAILED,
> > +					   NEIGH_UPDATE_F_OVERRIDE|
> > +					   NEIGH_UPDATE_F_ADMIN);
> > +		neigh_release(neigh);
> > +	}
> > +
> > +	return err;
> > +}
> > +EXPORT_SYMBOL(arp_invalidate);
> > +
> >  static int arp_req_delete_public(struct net *net, struct arpreq *r,
> >  		struct net_device *dev)
> >  {
> > @@ -1162,7 +1179,6 @@ static int arp_req_delete(struct net *net, struct arpreq *r,
> >  {
> >  	int err;
> >  	__be32 ip;
> > -	struct neighbour *neigh;
> >  
> >  	if (r->arp_flags & ATF_PUBL)
> >  		return arp_req_delete_public(net, r, dev);
> > @@ -1180,16 +1196,7 @@ static int arp_req_delete(struct net *net, struct arpreq *r,
> >  		if (!dev)
> >  			return -EINVAL;
> >  	}
> > -	err = -ENXIO;
> > -	neigh = neigh_lookup(&arp_tbl, &ip, dev);
> > -	if (neigh) {
> > -		if (neigh->nud_state & ~NUD_NOARP)
> > -			err = neigh_update(neigh, NULL, NUD_FAILED,
> > -					   NEIGH_UPDATE_F_OVERRIDE|
> > -					   NEIGH_UPDATE_F_ADMIN);
> > -		neigh_release(neigh);
> > -	}
> > -	return err;
> > +	return arp_invalidate(dev, ip);
> >  }
> >  
> >  /*
> 

Hmm..

If somebody can explain why RTNL is held in arp_ioctl() (and therefore
in arp_req_delete()), we might first remove RTNL use in arp_ioctl() so
that your patch can be applied.

Right now it is not good, because RTNL wont be necessarly held when you
are going to call arp_invalidate() ?