neigh: Allow for user space users of the neighbour table

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@aristanetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/neighbour.h b/include/linux/neighbour.h
index 8730d5dae1bc2a3c5b8a33aab453cb8382a19dcf..12c9de1384517e7097a74e5df7da825472bf1f64 100644 (file)
--- 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 417b6d739fb7b440119af9ae267f50d5a891fc78..a1cbce7fdae5851f6534f433eb0aa3be3a06e1e6 100644 (file)
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1654,7 +1654,11 @@ 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;
        }