netdev - Re: [PATCH] Netlink messages for multicast HW addr programming

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Date:	Wed, 3 Feb 2016 14:14:41 +0000
From:	Patrick Ruddy <pruddy@...cade.com>
To:	"jiri@...nulli.us" <jiri@...nulli.us>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	David Stapleton <dstaplet@...cade.com>,
	Olufemi Komolafe <okomolaf@...cade.com>,
	"Stephen Hemminger" <shemming@...cade.com>
Subject: Re: [PATCH] Netlink messages for multicast HW addr programming

On Sat, 2016-01-23 at 08:53 +0100, Jiri Pirko wrote:
> Fri, Jan 22, 2016 at 04:49:36PM CET, pruddy@...cade.com wrote:
> >On Fri, 2016-01-22 at 16:05 +0100, Jiri Pirko wrote:
> >> Fri, Jan 22, 2016 at 03:51:55PM CET, pruddy@...cade.com wrote:
> >> >On Thu, 2016-01-21 at 21:04 +0100, Jiri Pirko wrote:
> >> >> Thu, Jan 21, 2016 at 12:47:54PM CET, pruddy@...cade.com wrote:
> >> >> >Add RTM_NEWADDR and RTM_DELADDR netlink messages to indicate
> >> >> >interest in specific multicast hardware addresses. These messages
> >> >> >are sent when addressed are added or deleted from the appropriate
> >> >> >interface driver.
> >> >> >
> >> >> >Signed-off-by: Patrick Ruddy <pruddy@...cade.com>
> >> >> >
> >> >> >diff --git a/net/core/dev_addr_lists.c b/net/core/dev_addr_lists.c
> >> >> >index c0548d2..a0ebadd 100644
> >> >> >--- a/net/core/dev_addr_lists.c
> >> >> >+++ b/net/core/dev_addr_lists.c
> >> >> >@@ -12,6 +12,7 @@
> >> >> >  */
> >> >> > 
> >> >> > #include <linux/netdevice.h>
> >> >> >+#include <net/netlink.h>
> >> >> > #include <linux/rtnetlink.h>
> >> >> > #include <linux/export.h>
> >> >> > #include <linux/list.h>
> >> >> >@@ -661,6 +662,62 @@ out:
> >> >> > }
> >> >> > EXPORT_SYMBOL(dev_mc_add_excl);
> >> >> > 
> >> >> >+static int fill_addr(struct sk_buff *skb, struct net_device *dev,
> >> >> >+		     const unsigned char *addr, int type)
> >> >> >+{
> >> >> >+	struct nlmsghdr *nlh;
> >> >> >+	struct ifaddrmsg *ifm;
> >> >> >+
> >> >> >+	nlh = nlmsg_put(skb, 0, 0, type, sizeof(*ifm), 0);
> >> >> >+	if (nlh == NULL)
> >> >> >+		return -EMSGSIZE;
> >> >> >+
> >> >> >+	ifm = nlmsg_data(nlh);
> >> >> >+	ifm->ifa_family = AF_UNSPEC;
> >> >> >+	ifm->ifa_prefixlen = 0;
> >> >> >+	ifm->ifa_flags = IFA_F_PERMANENT;
> >> >> >+	ifm->ifa_scope = RT_SCOPE_LINK;
> >> >> >+	ifm->ifa_index = dev->ifindex;
> >> >> >+	if (nla_put(skb, IFA_ADDRESS, dev->addr_len, addr))
> >> >> >+		goto nla_put_failure;
> >> >> >+	nlmsg_end(skb, nlh);
> >> >> 
> >> >> How can userspace tell if this is a multicast addr? Also, why not add
> >> >> notifications for unicast addrs so we handle both the same?
> >> >
> >> >I am only using this RTM_NEW/DELADDR AF_UNSPEC message for multicast
> >> >addresses. I understand that the unicast addresses are notified in the
> >> >RTM_NEW/DELLINK.
> >> 
> >> dev->dev_addr is notified by that. UC addresses do not have any
> >> notification now.
> >It is the multicast MAC address (ie the multicast equivalent of the
> >dev_addr) that we are notifying here right? Not L3 addresses.
> 
> I know :)
> 
> For example if kernel code calls dev_uc_add or dev_uc_del, thise
> addresses are not notified to the userspace. All I'm saying is, if you
> add notification for dev_mc_add and dev_mc_del, add it for uc variants
> as well. Then you have to distinguish mc and uc in the netlink message.

One more Q on this. I can use IFA_ADDRESS for unicast addresses and
IFA_MULTICAST for multicast addresses but are these distinctions
actually required since the multicast nature of an address is clear from
the address itself - at least it is for ethernet and ifininet?

-pr