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Date: Thu, 11 Oct 2012 08:53:53 +0200
From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] hw/qxl: warn on sync io usage
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To: Alon Levy <alevy@redhat.com>
Cc: qemu-devel@nongnu.org

  Hi,

> +static void sync_io_warning(PCIQXLDevice *qxl, uint32_t io_port)
> +{
> +    fprintf(stderr, "qxl-%d: WARNING: sync io used, see (RHBZ 747011)",
> +            qxl->id);
> +    fprintf(stderr, "qxl-%d: WARNING: virt-viewer/remote-viewer can hang\n",
> +            qxl->id);
> +    if (qxl->revision < 3) {
> +        fprintf(stderr, "qxl-%d: WARNING: revision >= 3 should be used\n",
> +                qxl->id);
> +    }
> +}

The message should also include hints how to fix that.

For the revision this probably means to update the machine type from
pc-0.12 (which sets rev=2 via compat properties) to something newer.
Telling the user what to do about it is tricky though as there seems to
be no simple GUI way to do that, at least not in virt-manager.  In the
other hand if the user manages to find the message in
/var/log/libvirt/qemu/${guest}.log he might be experienced enough to
just "virsh edit ${guest}".

For the sync I/O it's easy, just say something like "Update qxl drivers
in the guest."

BTW: You can print multi-line messages this way ...

	fprintf(stderr,
                "long line one\n"
		"long line two\n",
                args, here);

... which I find more readable in the source code.

Do we wanna have a "suggest to update guest drivers for device $foo" qmp
message for management?  Or has ovirt/rhev better ways (guest agent?) to
deal with that?

cheers,
  Gerd