Re: [PATCH v2 4/4] Add CCW configuration field "indirect_num" to vq_info_block

[Stefan Hajnoczi <stefanha@redhat.com>]

On Mon, Feb 21, 2022 at 06:01:41PM +0100, Christian Schoenebeck wrote:
> This new CCW configuration field allows to negotiate a more fine
> graded maximum lenght of indirect descriptor chains.
> 
> Fixes: https://github.com/oasis-tcs/virtio-spec/issues/122
> Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com
> Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
> ---
>  content.tex | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/content.tex b/content.tex
> index a3baf4d..d400ea7 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -2599,6 +2599,7 @@ \subsubsection{Configuring a Virtqueue}\label{sec:Virtio Transport Options / Vir
>          be16 num;
>          be64 driver;
>          be64 device;
> +        be32 indirect_num;
>  };
>  \end{lstlisting}
>  
> @@ -2607,6 +2608,10 @@ \subsubsection{Configuring a Virtqueue}\label{sec:Virtio Transport Options / Vir
>  available area and used area for queue \field{index}, respectively. The actual
>  virtqueue size (number of allocated buffers) is transmitted in \field{num}.
>  
> +If VIRTIO_RING_F_INDIRECT_SIZE has been negotiated then \field{indirect_num}
> +reflects the maximum length of indirect descriptor tables for queue
> +\field{index}.

I think the transfer direction of CCW_CMD_SET_VQ struct vq_info_block is
driver-to-device. So it allows the driver to set the Queue Indirect
Size, but how does the driver query the device's maximum Queue Indirect
Size value?

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