[RFC][PATCH] neigh: Allow for user space users of the neighbour table

[ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman)]

Currently it is possible to do just about everything with the arp table
from user space except treat an entry like you are using it.  To that end
implement and a flag NTF_USE that when set in a netwlink update request
treats the neighbour table entry like the kernel does on the output path.

This allows user space applications to share the kernel's arp cache.

Signed-off-by: Eric Biederman <ebiederm-BGArkANP9klv6pq1l3V1OdBPR1lH4CV8@public.gmane.org>
---
 include/linux/neighbour.h |    1 +
 net/core/neighbour.c      |    6 +++++-
 2 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/include/linux/neighbour.h b/include/linux/neighbour.h
index 8730d5d..12c9de1 100644
--- a/include/linux/neighbour.h
+++ b/include/linux/neighbour.h
@@ -31,6 +31,7 @@ enum
  *	Neighbor Cache Entry Flags
  */
 
+#define NTF_USE		0x01
 #define NTF_PROXY	0x08	/* == ATF_PUBL */
 #define NTF_ROUTER	0x80
 
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 278a142..0fc92ed 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1656,7 +1656,11 @@ static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 				flags &= ~NEIGH_UPDATE_F_OVERRIDE;
 		}
 
-		err = neigh_update(neigh, lladdr, ndm->ndm_state, flags);
+		if (ndm->ndm_flags & NTF_USE) {
+			neigh_event_send(neigh, NULL);
+			err = 0;
+		} else
+			err = neigh_update(neigh, lladdr, ndm->ndm_state, flags);
 		neigh_release(neigh);
 		goto out_dev_put;
 	}
-- 
1.6.1.2.350.g88cc

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