qemu/qemu-virtio-console-unconnected-pty.patch

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commit ed8e5a85a1741147ce06932b478a509ce3407061
Author: Christian Borntraeger <borntraeger@de.ibm.com>
Date: Thu Dec 29 13:47:43 2011 +0100
virtio-console: Fix failure on unconnected pty
when I tried qemu with -virtio-console pty the guest hangs and attaching
on /dev/pts/<x> does not return anything if the attachment is too late.
This results in pty_chr_write() returning 0, which causes the port to
get throttled. This results in the guest getting frozen as the
guest->host virtio_console writes don't return until the host releases
the vq element back to the guest.
For the virtio-serial use case we don't want to lose 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 <borntraeger@de.ibm.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
index fe0233f..3a9004a 100644
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -163,7 +163,19 @@ static void do_flush_queued_data(VirtIOSerialPort *port, VirtQueue *vq,
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;