When we establish a new UDP flow we create connect()ed sockets that will
only handle datagrams for this flow.  However, there is a race between
bind() and connect() where they might get some packets queued for a
different flow.  Currently we handle this by simply discarding any
queued datagrams after the connect.  UDP protocols should be able to handle
such packet loss, but it's not ideal.

We now have the tools we need to handle this better, by redirecting any
datagrams received during that race to the appropriate flow.  We need to
use a deferred handler for this to avoid unexpectedly re-ordering datagrams
in some edge cases.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
[sbrivio: Update comment to udp_flow_defer()]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Recent changes mean that this define is no longer used anywhere except in
udp.c.  Move it back into udp.c from udp_internal.h.

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

udp_buf_listen_sock_data() and udp_vu_listen_sock_data() now have
effectively identical structure.  The forwarding functions used for flow
specific sockets (udp_buf_sock_to_tap(), udp_vu_sock_to_tap() and
udp_sock_to_sock()) also now take a number of datagrams.  This means we
can re-use them for the listening socket path, just passing '1' so they
handle a single datagram at a time.

This allows us to merge both the vhost-user and flow specific paths into
a single, simpler udp_listen_sock_data().

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

udp_vu_sock_info() uses MSG_PEEK to look ahead at the next datagram to be
received and gets its source address.  Currently we only use it in the
vhost-user path, but there's nothing inherently vhost-user specific about
it.  We have upcoming uses for it elsewhere so rename and move to udp.c.

While we're there, polish its error reporting a litle.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
[sbrivio: Drop excess newline before udp_sock_recv()]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

The vhost-user and non-vhost-user paths for both udp_listen_sock_handler()
and udp_reply_sock_handler() are more or less completely separate.  Both,
however, start with essentially the same invocation of udp_sock_errs(), so
that can be made common.

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

When a local peer sends a UDP message to a non-existing port on an
existing remote host, that host will return an ICMP message containing
the error code ICMP_PORT_UNREACH, plus the header and the first eight
bytes of the original message. If the sender socket has been connected,
it uses this message to issue a "Connection Refused" event to the user.

Until now, we have only read such events from the externally facing
socket, but we don't forward them back to the local sender because
we cannot read the ICMP message directly to user space. Because of
this, the local peer will hang and wait for a response that never
arrives.

We now fix this for IPv4 by recreating and forwarding a correct ICMP
message back to the internal sender. We synthesize the message based
on the information in the extended error structure, plus the returned
part of the original message body.

Note that for the sake of completeness, we even produce ICMP messages
for other error codes. We have noticed that at least ICMP_PROT_UNREACH
is propagated as an error event back to the user.

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Jon Maloy <jmaloy@redhat.com>
[sbrivio: fix cppcheck warning: udp_send_conn_fail_icmp4() doesn't
 modify 'in', it can be declared as const]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Export udp_payload_t, udp_update_hdr4(), udp_update_hdr6() and
udp_sock_errs().

Rename udp_listen_sock_handler() to udp_buf_listen_sock_handler() and
udp_reply_sock_handler to udp_buf_reply_sock_handler().

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