Re: [RFC v3 04/29] vhost: Add x-vhost-enable-shadow-vq qmp

[Markus Armbruster <armbru@redhat.com>]

Eugenio Pérez <eperezma@redhat.com> writes:

> Command to enable shadow virtqueue looks like:
>
> { "execute": "x-vhost-enable-shadow-vq",
>   "arguments": { "name": "dev0", "enable": true } }
>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>  qapi/net.json     | 22 ++++++++++++++++++++++
>  hw/virtio/vhost.c |  6 ++++++
>  2 files changed, 28 insertions(+)
>
> diff --git a/qapi/net.json b/qapi/net.json
> index c31748c87f..660feafdd2 100644
> --- a/qapi/net.json
> +++ b/qapi/net.json
> @@ -77,6 +77,28 @@
>  ##
>  { 'command': 'netdev_del', 'data': {'id': 'str'} }
>  
> +##
> +# @x-vhost-enable-shadow-vq:
> +#
> +# Use vhost shadow virtqueue.
> +#
> +# @name: the device name of the VirtIO device
> +#
> +# @enable: true to use he alternate shadow VQ notification path

Typo "he".

What's a "notification path", and why should I care?

Maybe

   # @enable: Enable alternate shadow VQ notification

> +#
> +# Returns: Error if failure, or 'no error' for success. Not found if vhost is not enabled.

This is confusing.  What do you mean by "Not found"?

If you mean DeviceNotFound:

1. Not actually true: qmp_x_vhost_enable_shadow_vq() always fails with
GenericError.  Perhaps later patches will change that.

2. Do you really need to distinguish "vhost is not enabled" from other
errors?

> +#
> +# Since: 6.1
> +#
> +# Example:
> +#
> +# -> { "execute": "x-vhost-enable-shadow-vq", "arguments": { "name": "virtio-net", "enable": false } }

Please break the long line, e.g. like this:

   # -> { "execute": "x-vhost-enable-shadow-vq",
   #      "arguments": { "name": "virtio-net", "enable": false } }

We normally show output in examples, too.

> +#
> +##
> +{ 'command': 'x-vhost-enable-shadow-vq',
> +  'data': {'name': 'str', 'enable': 'bool'},
> +  'if': 'defined(CONFIG_VHOST_KERNEL)' }
> +
>  ##
>  # @NetLegacyNicOptions:
>  #
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 40f9f64ebd..c4c1f80661 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -15,6 +15,7 @@
>  
>  #include "qemu/osdep.h"
>  #include "qapi/error.h"
> +#include "qapi/qapi-commands-net.h"
>  #include "hw/virtio/vhost.h"
>  #include "qemu/atomic.h"
>  #include "qemu/range.h"
> @@ -1831,3 +1832,8 @@ int vhost_net_set_backend(struct vhost_dev *hdev,
>  
>      return -1;
>  }
> +
> +void qmp_x_vhost_enable_shadow_vq(const char *name, bool enable, Error **errp)
> +{
> +    error_setg(errp, "Shadow virtqueue still not implemented");
> +}