Re: [Qemu-devel] [PATCH v5 13/13] serial: chardev hotswap support

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jul 05, 2017 at 05:02:04PM +0300, Anton Nefedov wrote:
> for a backend change, a number of ioctls has to be replayed to sync
> the current setup of a frontend to a backend tty. This is hopefully
> enough so we don't have to track, store and replay the whole original
> control byte sequence.
> 
> Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>


Could you please add a description of the feature here?
How does one use it e.g. for windbg?

> ---
>  hw/char/serial.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/char/serial.c b/hw/char/serial.c
> index e47f0b6..9aec6c6 100644
> --- a/hw/char/serial.c
> +++ b/hw/char/serial.c
> @@ -891,9 +891,37 @@ static void serial_reset(void *opaque)
>      s->msr &= ~UART_MSR_ANY_DELTA;
>  }
>  
> +static int serial_be_change(void *opaque)
> +{
> +    SerialState *s = opaque;
> +
> +    qemu_chr_fe_set_handlers(&s->chr, serial_can_receive1, serial_receive1,
> +                             serial_event, serial_be_change, s, NULL, true);
> +
> +    serial_update_parameters(s);
> +
> +    qemu_chr_fe_ioctl(&s->chr, CHR_IOCTL_SERIAL_SET_BREAK,
> +                      &s->last_break_enable);
> +
> +    s->poll_msl = (s->ier & UART_IER_MSI) ? 1 : 0;
> +    serial_update_msl(s);
> +
> +    if (s->poll_msl >= 0 && !(s->mcr & UART_MCR_LOOP)) {
> +        serial_update_tiocm(s);
> +    }
> +
> +    if (s->watch_tag > 0) {
> +        g_source_remove(s->watch_tag);
> +        s->watch_tag = qemu_chr_fe_add_watch(&s->chr, G_IO_OUT | G_IO_HUP,
> +                                             serial_watch_cb, s);
> +    }
> +
> +    return 0;
> +}
> +
>  void serial_realize_core(SerialState *s, Error **errp)
>  {
> -    if (!qemu_chr_fe_get_driver(&s->chr)) {
> +    if (!qemu_chr_fe_backend_connected(&s->chr)) {
>          error_setg(errp, "Can't create serial device, empty char device");
>          return;
>      }
> @@ -904,7 +932,7 @@ void serial_realize_core(SerialState *s, Error **errp)
>      qemu_register_reset(serial_reset, s);
>  
>      qemu_chr_fe_set_handlers(&s->chr, serial_can_receive1, serial_receive1,
> -                             serial_event, NULL, s, NULL, true);
> +                             serial_event, serial_be_change, s, NULL, true);
>      fifo8_create(&s->recv_fifo, UART_FIFO_LENGTH);
>      fifo8_create(&s->xmit_fifo, UART_FIFO_LENGTH);
>      serial_reset(s);
> -- 
> 2.7.4