1 files changed, 12 insertions, 2 deletions

diff --git a/ot_socket.h b/ot_socket.h
index aa4e2d2..f73a5c9 100644
--- a/ot_socket.h
+++ b/ot_socket.h
@@ -16,8 +16,18 @@
    as the v4 mapped address */
 
 /* How an address may be shared with other sockets. Which socket option says
-   so differs between kernels, which is socket_set_sharing's business */
-typedef enum { SOCKET_EXCLUSIVE, SOCKET_SHARED } socket_sharing;
+   so differs between kernels, which is socket_set_sharing's business.
+
+   SHARED lets another socket bind the same address. BALANCED asks the kernel
+   to spread arriving datagrams over the sockets that did, which is a
+   different thing and not everywhere available: ask socket_can_balance
+   before binding a group that depends on it. */
+typedef enum { SOCKET_EXCLUSIVE, SOCKET_SHARED, SOCKET_BALANCED } socket_sharing;
+
+/* Whether this kernel spreads datagrams over a group of sockets bound to one
+   address. Where it does not, binding a group is worse than one socket with
+   several readers, so the caller wants to know first. */
+int     socket_can_balance(void);
 
 /* Create, bind and, for TCP, listen. The returned socket is non blocking
    Returns -1 on failure with errno set */