Re: [PATCH net 1/2] ipv6: add ipv6_dev_find()

On Fri, Aug 7, 2020 at 5:26 PM Hideaki Yoshifuji
[off-list ref] wrote:

Hi,

2020年8月6日(木) 23:03 David Ahern [off-list ref]:

quoted

On 8/6/20 2:55 AM, Xin Long wrote:

quoted

On Thu, Aug 6, 2020 at 10:50 AM Hideaki Yoshifuji
[off-list ref] wrote:

quoted

Hi,

2020年8月4日(火) 0:35 Xin Long [off-list ref]:

quoted

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@gmail.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.

User supplied scope id which should be set for link-local addresses
in TIPC_NLA_UDP_LOCAL attribute must be honored when we
check the address.

Hi, Hideaki san,

Sorry for not understanding your comment earlier.

The bad thing is tipc in iproute2 doesn't seem able to set scope_id.
I saw many places in kernel doing this check:

                         if (__ipv6_addr_needs_scope_id(atype) &&
                             !ip6->sin6_scope_id) { return -EINVAL; }

Can I ask why scope id is needed for link-local addresses?
and is that for link-local addresses only?

ipv6_chk_addr() can check if the address and supplied ifindex is a valid
local address.  Or introduce an extra ifindex argument to ipv6_dev_find().

Yeah, but if scope id means ifindex for  link-local addresses, ipv6_dev_find()
would be more like a function to validate the address with right scope id.

Thanks for your reviewing.