[virtio-dev] Re: [PATCH v1] content: support SR-IOV

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, May 21, 2018 at 06:52:06PM +0800, Tiwei Bie wrote:
> Reserve a feature bit for virtio devices which support SR-IOV.

s/Reserve/Allocate/ in that you define the behaviour here.

> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>

Pls go ahead and add a github issue, you can then
include a Fixes: tag with a link to it,
which comes it handy down the road for voting.

> ---
> More details can be found from this thread:
> 
> https://patchwork.kernel.org/patch/10285541/
> 
> RFC -> v1:
> - Mention PCI in the description (Cornelia);
> 
>  content.tex | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/content.tex b/content.tex
> index 7a92cb1..9f981fb 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -95,10 +95,10 @@ Feature bits are allocated as follows:
>  \begin{description}
>  \item[0 to 23] Feature bits for the specific device type
>  
> -\item[24 to 33] Feature bits reserved for extensions to the queue and
> +\item[24 to 36] Feature bits reserved for extensions to the queue and
>    feature negotiation mechanisms
>  
> -\item[34 and above] Feature bits reserved for future extensions.
> +\item[37 and above] Feature bits reserved for future extensions.
>  \end{description}
>  
>  \begin{note}
> @@ -5348,6 +5348,9 @@ Descriptors} and \ref{sec:Packed Virtqueues / Indirect Flag: Scatter-Gather Supp
>    \item[VIRTIO_F_IN_ORDER(35)] This feature indicates
>    that all buffers are used by the device in the same
>    order in which they have been made available.
> +  \item[VIRTIO_F_SR_IOV(36)] This feature indicates that
> +  the device supports Single Root I/O Virtualization.
> +  Currently only virtio PCI devices support this feature.
>  \end{description}
>  
>  \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
> @@ -5363,6 +5366,10 @@ addresses to the device.
>  
>  A driver SHOULD accept VIRTIO_F_RING_PACKED if it is offered.
>  
> +A driver SHOULD accept VIRTIO_F_SR_IOV if it is offered.
> +If VIRTIO_F_SR_IOV has been negotiated, a driver can
> +access device's PCI SR-IOV capability structure.

Does "access" here really mean "enable virtual functions"
through the PCI SR-IOV capability?

> +
>  \devicenormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
>  
>  A device MUST offer VIRTIO_F_VERSION_1.  A device MAY fail to operate further
> @@ -5376,6 +5383,10 @@ accepted.
>  If VIRTIO_F_IN_ORDER has been negotiated, a device MUST use
>  buffers in the same order in which they have been available.
>  
> +A device SHOULD offer VIRTIO_F_SR_IOV if it presents a PCI
> +SR-IOV capability structure.  A device MAY fail to operate
> +further if VIRTIO_F_SR_IOV is not accepted.

Why is the last sentence here? What are you trying to accomplish?  It
seems that if we allow drivers not to accept the bit, we should require
the devices to function without it or at least not go out of our way to
say they do not have to.


> +
>  \section{Legacy Interface: Reserved Feature Bits}\label{sec:Reserved Feature Bits / Legacy Interface: Reserved Feature Bits}
>  
>  Transitional devices MAY offer the following:
> -- 
> 2.17.0

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