Introduce a new getsockopt operation to retrieve the socket cookie
for a specific socket based on the socket fd. It returns a unique
non-decreasing cookie for each socket.
Tested: https://android-review.googlesource.com/#/c/358163/
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Chenbo Feng <fengc@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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