Centralize epoll_add() and epoll_del() helper functions into new
epoll_ctl.c/h files.

This also moves the union epoll_ref definition from passt.h to
epoll_ctl.h where it's more logically placed.

The new epoll_add() helper simplifies adding file descriptors to epoll
by taking an epoll_ref and events, handling error reporting
consistently across all call sites.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
[sbrivio: Include epoll_ctl.h from netlink.c as it's now needed there]
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

If the target doesn't have a connected passt-repair helper,
repair_wait() sets a timeout and forcibly calls accept4(), but if the
timeout expires, we don't report any error and proceed as if we had a
connected helper.

Later, in repair_flush(), sendmsg() will fail for each flow we try to
migrate with EBADF, and we'll handle that gracefully, but it makes no
sense to even try, and it also leads to noise in the logs.

Similarly to how we handle a missing repair helper in
flow_migrate_repair_all(), propagate timeout and other errors through
repair_wait(), and don't attempt to migrate flows if repair_wait()
failed.

Fixes: c8b520c0625b ("flow, repair: Wait for a short while for passt-repair to connect")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

...and time out after that. This will be needed because of an upcoming
change to passt-repair enabling it to start before passt is started,
on both source and target, by means of an inotify watch.

Once the inotify watch triggers, passt-repair will connect right away,
but we have no guarantees that the connection completes before we
start the migration process, so wait for it (for a reasonable amount
of time).

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

This implements flow preparation on the source, transfer of data with
a format roughly inspired by struct tcp_tap_conn, plus a specific
structure for parameters that don't fit in the flow table, and flow
insertion on the target, with all the appropriate window options,
window scaling, MSS, etc.

Contents of pending queues are transferred as well.

The target side is rather convoluted because we first need to create
sockets and switch them to repair mode, before we can apply options
that are *not* stored in the flow table. This also means that, if
we're testing this on the same machine, in the same namespace, we need
to close the listening socket on the source before we can start moving
data.

Further, we need to connect() the socket on the target before we can
restore data queues, but we can't do that (again, on the same machine)
as long as the matching source socket is open, which implies an
arbitrary limit on queue sizes we can transfer, because we can only
dump pending queues on the source as long as the socket is open, of
course.

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

Checked against musl 1.2.5.

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

In vhost-user mode, by default, create a second UNIX domain socket
accepting connections from passt-repair, with the usual listener
socket.

When we need to set or clear TCP_REPAIR on sockets, we'll send them
via SCM_RIGHTS to passt-repair, who sets the socket option values we
ask for.

To that end, introduce batched functions to request TCP_REPAIR
settings on sockets, so that we don't have to send a single message
for each socket, on migration. When needed, repair_flush() will
send the message and check for the reply.

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