> The socket layer calls lower layers and the send request hits the
> link layer. For instance we do sosend() -> udp_output() ->
> ip_output() -> ether_output().

> At the link layer, IFQ_ENQUEUE() is used to put the packet onto the
> interface queue.  If the interface is full, ENOBUFS is returned and
> sosend() fails instead of blocking.

If it really does go through udp_output, it's a UDP socket, and any
send failure really should just drop the packet rather than pushing the
error up.  (UDP is not a reliable protocol.)

I'm not sure what POSIX would have to say about this.  I find it hard
to imagine that it couldn't be finessed on the "as if" princple - make
it behave "as if" the packet were sent but dropped by the underlying
network.

> Opinions?

My opinion: if POSIX forbids silently dropping the packet in the UDP
case, it is nuts and should be ignored (in this respect).

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