Re: [win-pv-devel] [PATCH] Add registry overrides for features

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: win-pv-devel [mailto:win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On
> Behalf Of owen.smith@xxxxxxxxxx
> Sent: 02 February 2017 14:08
> To: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Owen Smith <owen.smith@xxxxxxxxxx>
> Subject: [win-pv-devel] [PATCH] Add registry overrides for features
> 
> From: Owen Smith <owen.smith@xxxxxxxxxx>
> 
> * Add a REG_DWORD to XenVbd's Parameters key, with names based
>   on the features, as per xenstore value, and set to 0 to
>   override use of that feature.
> 
> For example,
>  "HKLM\System\CCS\Services\XenVbd\Parameters" "feature-barrier" 0
>   will prevent the frontend issuing BLKIF_OP_WRITE_BARRIERs
>  "HKLM\System\CCS\Services\XenVbd\Parameters" "feature-discard" 0
>   will prevent the frontend issuing BLKIF_OP_DISCARDs
> 
> Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>
> ---
>  src/xenvbd/driver.c   | 16 ++++++++++++++++
>  src/xenvbd/driver.h   |  5 +++++
>  src/xenvbd/frontend.c | 37 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 58 insertions(+)
> 
> diff --git a/src/xenvbd/driver.c b/src/xenvbd/driver.c
> index 114c740..1f713c4 100644
> --- a/src/xenvbd/driver.c
> +++ b/src/xenvbd/driver.c
> @@ -82,6 +82,22 @@ __DriverParseOption(
>      RegistryFreeSzValue(Option);
>  }
> 
> +static FORCEINLINE HANDLE
> +__DriverGetParametersKey(
> +    VOID
> +    )
> +{
> +    return Driver.ParametersKey;
> +}
> +
> +HANDLE
> +DriverGetParametersKey(
> +    VOID
> +    )
> +{
> +    return __DriverGetParametersKey();
> +}
> +
>  NTSTATUS
>  DriverDispatchPnp(
>      IN  PDEVICE_OBJECT  DeviceObject,
> diff --git a/src/xenvbd/driver.h b/src/xenvbd/driver.h
> index cf55330..e7730a9 100644
> --- a/src/xenvbd/driver.h
> +++ b/src/xenvbd/driver.h
> @@ -57,6 +57,11 @@ typedef struct _XENVBD_PARAMETERS {
> 
>  extern XENVBD_PARAMETERS    DriverParameters;
> 
> +extern HANDLE
> +DriverGetParametersKey(
> +    VOID
> +    );
> +
>  extern NTSTATUS
>  DriverDispatchPnp(
>      IN  PDEVICE_OBJECT  DeviceObject,
> diff --git a/src/xenvbd/frontend.c b/src/xenvbd/frontend.c
> index 11e9121..e141f92 100644
> --- a/src/xenvbd/frontend.c
> +++ b/src/xenvbd/frontend.c
> @@ -30,6 +30,7 @@
>   */
> 
>  #include "frontend.h"
> +#include "registry.h"
>  #include "driver.h"
>  #include "fdo.h"
>  #include "pdoinquiry.h"
> @@ -621,6 +622,8 @@ FrontendReadFeature(
>  {
>      NTSTATUS        status;
>      PCHAR           Buffer;
> +    ULONG           Override;
> +    HANDLE          Key;
>      BOOLEAN         Old = *Value;
> 
>      status = XENBUS_STORE(Read,
> @@ -637,6 +640,18 @@ FrontendReadFeature(
>                      Frontend->Store,
>                      Buffer);
> 
> +    // check registry for disable-override
> +    Key = DriverGetParametersKey();
> +    if (Key != NULL) {

I don't think Key can be NULL here can it? IIRC DriverEntry() will fail if 
there's no parameters key.

  Paul

> +        status = RegistryQueryDwordValue(Key,
> +                                        Name,
> +                                        &Override);
> +        if (NT_SUCCESS(status)) {
> +            if (Override == 0)
> +                *Value = FALSE;
> +        }
> +    }
> +
>      return Old != *Value;
>  }
> 
> @@ -644,11 +659,14 @@ static FORCEINLINE BOOLEAN
>  FrontendReadValue32(
>      IN  PXENVBD_FRONTEND            Frontend,
>      IN  PCHAR                       Name,
> +    IN  BOOLEAN                     AllowOverride,
>      IN  PULONG                      Value
>      )
>  {
>      NTSTATUS        status;
>      PCHAR           Buffer;
> +    HANDLE          Key;
> +    ULONG           Override;
>      ULONG           Old = *Value;
> 
>      status = XENBUS_STORE(Read,
> @@ -665,6 +683,19 @@ FrontendReadValue32(
>                      Frontend->Store,
>                      Buffer);
> 
> +    // check registry for disable-override
> +    if (AllowOverride) {
> +        Key = DriverGetParametersKey();
> +        if (Key != NULL) {
> +            status = RegistryQueryDwordValue(Key,
> +                                            Name,
> +                                            &Override);
> +            if (NT_SUCCESS(status)) {
> +                *Value = Override;
> +            }
> +        }
> +    }
> +
>      return Old != *Value;
>  }
> 
> @@ -727,12 +758,15 @@ __ReadDiskInfo(
> 
>      Changed |= FrontendReadValue32(Frontend,
>                                    "info",
> +                                  FALSE,
>                                    &Frontend->DiskInfo.DiskInfo);
>      Changed |= FrontendReadValue32(Frontend,
>                                    "sector-size",
> +                                  FALSE,
>                                    &Frontend->DiskInfo.SectorSize);
>      Changed |= FrontendReadValue32(Frontend,
>                                    "physical-sector-size",
> +                                  FALSE,
>                                    &Frontend->DiskInfo.PhysSectorSize);
>      Changed |= FrontendReadValue64(Frontend,
>                                    "sectors",
> @@ -780,6 +814,7 @@ FrontendReadFeatures(
>                                     &Frontend->Caps.Removable);
>      Changed |= FrontendReadValue32(Frontend,
>                                     "feature-max-indirect-segments",
> +                                   TRUE,
>                                     &Frontend->Features.Indirect);
>      Changed |= FrontendReadFeature(Frontend,
>                                     "feature-persistent",
> @@ -821,9 +856,11 @@ FrontendReadDiskInfo(
>                                     &Frontend->DiskInfo.DiscardSecure);
>      Changed |= FrontendReadValue32(Frontend,
>                                     "discard-alignment",
> +                                   TRUE,
>                                     &Frontend->DiskInfo.DiscardAlignment);
>      Changed |= FrontendReadValue32(Frontend,
>                                     "discard-granularity",
> +                                   TRUE,
>                                     &Frontend->DiskInfo.DiscardGranularity);
> 
>      if (!Changed)
> --
> 2.8.3
> 
> 
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