netdev - Re: [PATCH net 1/2] ipv6: add ipv6_dev

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Date:   Fri, 7 Aug 2020 15:30:58 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     David Ahern <dsahern@...il.com>, Ying Xue <ying.xue@...driver.com>
Cc:     Hideaki Yoshifuji <hideaki.yoshifuji@...aclelinux.com>,
        network dev <netdev@...r.kernel.org>,
        davem <davem@...emloft.net>, Jon Maloy <jon.maloy@...csson.com>,
        tipc-discussion@...ts.sourceforge.net,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH net 1/2] ipv6: add ipv6_dev_find()

On Thu, Aug 6, 2020 at 10:03 PM David Ahern <dsahern@...il.com> wrote:
>
> On 8/6/20 2:55 AM, Xin Long wrote:
> > On Thu, Aug 6, 2020 at 10:50 AM Hideaki Yoshifuji
> > <hideaki.yoshifuji@...aclelinux.com> wrote:
> >>
> >> Hi,
> >>
> >> 2020年8月4日(火) 0:35 Xin Long <lucien.xin@...il.com>:
> >>>
> >>> This is to add an ip_dev_find like function for ipv6, used to find
> >>> the dev by saddr.
> >>>
> >>> It will be used by TIPC protocol. So also export it.
> >>>
> >>> Signed-off-by: Xin Long <lucien.xin@...il.com>
> >>> ---
> >>>  include/net/addrconf.h |  2 ++
> >>>  net/ipv6/addrconf.c    | 39 +++++++++++++++++++++++++++++++++++++++
> >>>  2 files changed, 41 insertions(+)
> >>>
> >>> diff --git a/include/net/addrconf.h b/include/net/addrconf.h
> >>> index 8418b7d..ba3f6c15 100644
> >>> --- a/include/net/addrconf.h
> >>> +++ b/include/net/addrconf.h
> >>> @@ -97,6 +97,8 @@ bool ipv6_chk_custom_prefix(const struct in6_addr *addr,
> >>>
> >>>  int ipv6_chk_prefix(const struct in6_addr *addr, struct net_device *dev);
> >>>
> >>> +struct net_device *ipv6_dev_find(struct net *net, const struct in6_addr *addr);
> >>> +
> >>
> >> How do we handle link-local addresses?
> > This is what "if (!result)" branch meant to do:
> >
> > +       if (!result) {
> > +               struct rt6_info *rt;
> > +
> > +               rt = rt6_lookup(net, addr, NULL, 0, NULL, 0);
> > +               if (rt) {
> > +                       dev = rt->dst.dev;
> > +                       ip6_rt_put(rt);
> > +               }
> > +       } else {
> > +               dev = result->idev->dev;
> > +       }
> >
>
> the stated purpose of this function is to find the netdevice to which an
> address is attached. A route lookup should not be needed. Walking the
> address hash list finds the address and hence the netdev or it does not.
Hi, David,
Sorry. it does. I misunderstood the code in __ip_dev_find().
I will delete the rt6_lookup() part from ipv6_dev_find().

Also for the compatibility, tipc part should change to:
@@ -741,10 +741,8 @@ static int tipc_udp_enable(struct net *net,
struct tipc_bearer *b,
                struct net_device *dev;

               dev = ipv6_dev_find(net, &local.ipv6);
               if (!dev)
                      ub->ifindex = dev->ifindex;

as when dev is not found from the hash list, it should fall back to
the old tipc code.

Ying, what do you think?