Simple test program to check the behaviour we need for bind() address
conflicts between listening sockets and repair mode sockets.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

To simplify lifetime management of "listening" UDP sockets, UDP flow
support needs to duplicate existing bound sockets.  Those duplicates will
be close()d when their corresponding flow expires, but we expect the
original to still receive datagrams as always.  That is, we expect the
close() on the duplicate to remove the duplicated fd, but not to close the
underlying UDP socket.

Add a test program to doc/platform-requirements to verify this requirement.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Add a test program verifying that we're able to discard datagrams from a
socket without needing a big discard buffer, by using a zero length recv().

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

For the approach we intend to use for handling UDP flows, we have some
pretty specific requirements about how SO_REUSEADDR works with UDP sockets.
Specifically SO_REUSEADDR allows multiple sockets with overlapping bind()s,
and therefore there can be multiple sockets which are eligible to receive
the same datagram.  Which one will actually receive it is important to us.

Add a test program which verifies things work the way we expect, which
documents what those expectations are in the process.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>