Re: [win-pv-devel] [PATCH 2/3] Advertise "feature-flush-cache" to backend.

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: win-pv-devel [mailto:win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On
> Behalf Of owen.smith@xxxxxxxxxx
> Sent: 21 November 2016 15:28
> To: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Owen Smith <owen.smith@xxxxxxxxxx>
> Subject: [win-pv-devel] [PATCH 2/3] Advertise "feature-flush-cache" to
> backend.
> 
> From: Owen Smith <owen.smith@xxxxxxxxxx>
> 
> Suggestion to the backend to enable caching on the storage. If the
> backend supports flush, then it will write "feature-flush-cache"
> (to the backend area) before going Connected. If the backend does
> not support flush, this flag should be ignored and the backend
> should not write "feature-flush-cache" (to the backend area), or
> set it to 0.
> If the frontend reads "feature-flush-cache" from the backend,
> the frontend will issue BLKIF_OP_FLUSH_DISKCACHE and report the
> cache capability to the guest OS.
> 
> Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>

This is not part of the blkif protocol, although it should be. So let's defer 
this until the canonical blkif header has actually been updated.

  Paul

> ---
>  src/xenvbd/frontend.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/src/xenvbd/frontend.c b/src/xenvbd/frontend.c
> index b1fa1a9..c993c25 100644
> --- a/src/xenvbd/frontend.c
> +++ b/src/xenvbd/frontend.c
> @@ -1078,6 +1078,16 @@ FrontendConnect(
>                                Frontend->Store,
>                                Transaction,
>                                Frontend->FrontendPath,
> +                              "feature-flush-cache",
> +                              "%u",
> +                              1);
> +        if (!NT_SUCCESS(Status))
> +            goto abort;
> +
> +        Status = XENBUS_STORE(Printf,
> +                              Frontend->Store,
> +                              Transaction,
> +                              Frontend->FrontendPath,
>                                "feature-online-resize",
>                                "%u",
>                                1);
> --
> 2.8.3
> 
> 
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