Re: [win-pv-devel] [PATCH 3/5] Add override for MaxRingPageOrder

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: win-pv-devel [mailto:win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On
> Behalf Of owen.smith@xxxxxxxxxx
> Sent: 26 September 2017 14:50
> To: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Owen Smith <owen.smith@xxxxxxxxxx>
> Subject: [win-pv-devel] [PATCH 3/5] Add override for MaxRingPageOrder
> 
> From: Owen Smith <owen.smith@xxxxxxxxxx>
> 
> Allow a Windows admin to limit the ring page count without
> affecting any other VMs on the host. The override can be used
> to restrict blkback's generous 16 page ring to a smaller value.
> 
> Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>

Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

> ---
>  src/xenvbd/driver.c |  3 ++-
>  src/xenvbd/driver.h |  1 +
>  src/xenvbd/ring.c   | 12 ++++++++++--
>  3 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/src/xenvbd/driver.c b/src/xenvbd/driver.c
> index e7a3d3a..59b380c 100644
> --- a/src/xenvbd/driver.c
> +++ b/src/xenvbd/driver.c
> @@ -266,7 +266,8 @@ __DriverInitializeOverrides(
>                { "discard-enable", FeatureDiscardEnable },
>                { "discard-secure", FeatureDiscardSecure },
>                { "discard-alignment", FeatureDiscardAlignment },
> -              { "discard-granularity", FeatureDiscardGranularity }
> +              { "discard-granularity", FeatureDiscardGranularity },
> +              { "max-ring-page-order", FeatureMaxRingPageOrder }
>            };
> 
>      for (Index = 0; Index < ARRAYSIZE(Mapping); Index++) {
> diff --git a/src/xenvbd/driver.h b/src/xenvbd/driver.h
> index 940968e..d99c09a 100644
> --- a/src/xenvbd/driver.h
> +++ b/src/xenvbd/driver.h
> @@ -79,6 +79,7 @@ typedef enum _XENVBD_FEATURE {
>      FeatureDiscardSecure,
>      FeatureDiscardAlignment,
>      FeatureDiscardGranularity,
> +    FeatureMaxRingPageOrder,
> 
>      // Add any new features before this enum
>      NumberOfFeatures
> diff --git a/src/xenvbd/ring.c b/src/xenvbd/ring.c
> index 77eee54..033975b 100644
> --- a/src/xenvbd/ring.c
> +++ b/src/xenvbd/ring.c
> @@ -1711,9 +1711,17 @@ RingConnect(
>                            "max-ring-page-order",
>                            &Buffer);
>      if (NT_SUCCESS(status)) {
> +        ULONG           MaxOrder;
> +
> +        if (DriverGetFeatureOverride(FeatureMaxRingPageOrder,
> +                                     &MaxOrder)) {
> +            MaxOrder = min(MaxOrder, XENVBD_MAX_RING_PAGE_ORDER);
> +        } else {
> +            MaxOrder = XENVBD_MAX_RING_PAGE_ORDER;
> +        }
> +
>          Ring->Order = strtoul(Buffer, NULL, 10);
> -        if (Ring->Order > XENVBD_MAX_RING_PAGE_ORDER)
> -            Ring->Order = XENVBD_MAX_RING_PAGE_ORDER;
> +        Ring->Order = min(Ring->Order, MaxOrder);
> 
>          XENBUS_STORE(Free,
>                       &Ring->StoreInterface,
> --
> 2.8.3
> 
> 
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