[virtio-dev] Re: [PATCH] virtio-blk: document that the capacity field can change

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

On Tue, Mar 01, 2022 at 12:00:21PM +0000, Stefan Hajnoczi wrote:
> Block devices can change size during operation. A configuration change
> notification is sent by the device and the driver detects that the field
> has changed. Document this behavior that has already been implemented in
> Linux and QEMU since 2011.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

github issue so we can track this?

> ---
>  content.tex | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/content.tex b/content.tex
> index c6f116c..96d2aa9 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -4863,6 +4863,9 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope
>  
>  \drivernormative{\subsubsection}{Device Operation}{Device Types / Block Device / Device Operation}
>  
> +The driver SHOULD check if the content of the \field{capacity} field has
> +changed upon receiving a configuration change notification.
> +
>  A driver MUST NOT submit a request which would cause a read or write
>  beyond \field{capacity}.
>  
> @@ -4909,6 +4912,10 @@ \subsection{Device Operation}\label{sec:Device Types / Block Device / Device Ope
>  
>  \devicenormative{\subsubsection}{Device Operation}{Device Types / Block Device / Device Operation}
>  
> +The device MAY change the content of the \field{capacity} field during
> +operation of the device. When this happens, the device SHOULD trigger a
> +configuration change notification.
> +
>  A device MUST set the \field{status} byte to VIRTIO_BLK_S_IOERR
>  for a write request if the VIRTIO_BLK_F_RO feature if offered, and MUST NOT
>  write any data.
> -- 
> 2.35.1


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