76b004d10d
On a real serial device, the open can block if the handshake lines are in a particular state. If a QEMU is passing the serial device to the guest, the QEMU startup is blocked opening the device (with a symptom seen as a timeout from libvirt). Open the serial port with O_NONBLOCK. Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>