sockopt: Make SO_BINDTODEVICE readable

The SO_BINDTODEVICE option is the only SOL_SOCKET one that can be set, but
cannot be get via sockopt API. The only way we can find the device id a
socket is bound to is via sock-diag interface. But the diag works only on
hashed sockets, while the opt in question can be set for yet unhashed one.

That said, in order to know what device a socket is bound to (we do want
to know this in checkpoint-restore project) I propose to make this option
getsockopt-able and report the respective device index.

Another solution to the problem might be to teach the sock-diag reporting
info on unhashed sockets. Should I go this way instead?

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/sock.c b/net/core/sock.c
index 8a146cfcc366fbead42d31d882893a74ec8dcf4e..c49412cdd12c867ffda0afefe1d2146d25e002bc 100644 (file)
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1074,6 +1074,9 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
        case SO_NOFCS:
                v.val = sock_flag(sk, SOCK_NOFCS);
                break;
+       case SO_BINDTODEVICE:
+               v.val = sk->sk_bound_dev_if;
+               break;
        default:
                return -ENOPROTOOPT;
        }