vhost/vsock: Refuse the connection immediately when guest isn't ready

When the host initiates an AF_VSOCK connect() to a guest that has not
yet loaded the virtio-vsock transport (i.e. still booting), the caller
blocks for VSOCK_DEFAULT_CONNECT_TIMEOUT.

A caller that wants to know if the guest is up yet instead of waiting
could theoretically tune SO_VM_SOCKETS_CONNECT_TIMEOUT, but it's tricky
to find the right timeout, if not impossible: there's no way to
distinguish "guest won't reply because it's not up yet" vs "guest is up
and tried to reply, but was too slow".

Furthermore, this delay is pointless:
- If the guest doesn't initialize within this timeout, connect()
  returns ETIMEDOUT.
- If the guest **does** initialize, it'll reply with RST immediately,
  because there won't be a listener on the port yet; connect() returns
  ECONNRESET.

That's also inconsistent with the behavior at other initialization
stages: if a connection is attempted when the guest driver is already
loaded, but nothing is listening yet, we return ECONNRESET immediately
without waiting.

Fix this by checking the RX virtqueue backend in
vhost_transport_send_pkt() before queuing. If it's NULL, return
-EHOSTUNREACH immediately.

Callers that used to get ETIMEDOUT will now usually get EHOSTUNREACH.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Co-developed-by: Polina Vishneva <polina.vishneva@virtuozzo.com>
Signed-off-by: Polina Vishneva <polina.vishneva@virtuozzo.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20260513145842.809404-1-polina.vishneva@virtuozzo.com>

0 files changed, 0 insertions, 0 deletions