From: Christian Borntraeger <borntrae...@de.ibm.com>
when I tried qemu with -virtio-console pty the guest hangs and attaching on
/dev/pts/<x> does
not return anything if the attachement is too late.
Turns out that the console is already throttled and the guest is heavily
spinning but get_buf
never returns the buffer. There seems to be no way for the console to
unthrottle the port.
For the virtio-serial use case we dont want to loose data but for the console
case we better
drop data instead of "killing" the guest console. If we get chardev->frontend
notification
and a better behaving virtio-console we can revert this fix.
Signed-off-by: Christian Borntraeger <borntrae...@de.ibm.com>
---
hw/virtio-serial-bus.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
Index: b/hw/virtio-serial-bus.c
===================================================================
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -163,7 +163,19 @@ static void do_flush_queued_data(VirtIOS
abort();
}
if (ret == -EAGAIN || (ret >= 0 && ret < buf_size)) {
- virtio_serial_throttle_port(port, true);
+ /*
+ * this is a temporary check until chardevs can signal to
+ * frontends that they are writable again. This prevents
+ * the console from going into throttled mode (forever)
+ * if virtio-console is connected to a pty without a
+ * listener. Otherwise the guest spins forever.
+ * We can revert this if
+ * 1: chardevs can notify frondends
+ * 2: the guest driver does not spin in these cases
+ */
+ if (!info->is_console) {
+ virtio_serial_throttle_port(port, true);
+ }
port->iov_idx = i;
if (ret > 0) {
port->iov_offset += ret;
