There's a problem with how rdma cm events are reported to userspace
that can lead to application crashes.

When a new connection request arrives, a context for the connection is
allocated in the kernel.  The connection event is then reported to
userspace.  The userspace library retrieves the event and allocates
its own context for the connection.  The userspace context is
associated with the kernel's context when accepting.  This allows the
kernel to give userspace context with other events.

A problem occurs if a second event for the same connection occurs
before the user has had a chance to call accept.  The userspace
context has not yet been set, which causes the librdmacm to crash.
(This has been seen when the app takes too long to call accept,
resulting in the remote side timing out and rejecting the connection)

Fix this by ignoring events for new connections until userspace has
set their context.  This can only happen if an error occurs on a new
connection before the user accepts it.  This is okay, since the accept
will just fail later.
Signed-off-by: NSean Hefty <sean.hefty@intel.com>
Signed-off-by: NRoland Dreier <rolandd@cisco.com>

We discard new connection requests while the listen backlog is full,
but leak a struct ucma_event in the process.  Free the structure in
this case.
Signed-off-by: NSean Hefty <sean.hefty@intel.com>
Signed-off-by: NRoland Dreier <rolandd@cisco.com>

Export the rdma cm interfaces to userspace via a misc device.
Signed-off-by: NSean Hefty <sean.hefty@intel.com>
Signed-off-by: NRoland Dreier <rolandd@cisco.com>