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commit ed8e5a85a1741147ce06932b478a509ce3407061
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Author: Christian Borntraeger <borntraeger@de.ibm.com>
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Date: Thu Dec 29 13:47:43 2011 +0100
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virtio-console: Fix failure on unconnected pty
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when I tried qemu with -virtio-console pty the guest hangs and attaching
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on /dev/pts/<x> does not return anything if the attachment is too late.
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This results in pty_chr_write() returning 0, which causes the port to
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get throttled. This results in the guest getting frozen as the
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guest->host virtio_console writes don't return until the host releases
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the vq element back to the guest.
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For the virtio-serial use case we don't want to lose data but for the
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console case we better drop data instead of "killing" the guest
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console. If we get chardev->frontend notification and a better behaving
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virtio-console we can revert this fix.
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Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
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Signed-off-by: Amit Shah <amit.shah@redhat.com>
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diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
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index fe0233f..3a9004a 100644
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--- a/hw/virtio-serial-bus.c
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+++ b/hw/virtio-serial-bus.c
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@@ -163,7 +163,19 @@ static void do_flush_queued_data(VirtIOSerialPort *port, VirtQueue *vq,
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abort();
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}
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if (ret == -EAGAIN || (ret >= 0 && ret < buf_size)) {
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- virtio_serial_throttle_port(port, true);
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+ /*
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+ * this is a temporary check until chardevs can signal to
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+ * frontends that they are writable again. This prevents
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+ * the console from going into throttled mode (forever)
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+ * if virtio-console is connected to a pty without a
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+ * listener. Otherwise the guest spins forever.
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+ * We can revert this if
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+ * 1: chardevs can notify frondends
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+ * 2: the guest driver does not spin in these cases
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+ */
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+ if (!info->is_console) {
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+ virtio_serial_throttle_port(port, true);
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+ }
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port->iov_idx = i;
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if (ret > 0) {
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port->iov_offset += ret;
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